WO2001089986A1

WO2001089986A1 - A stiction-free electrostatically driven microstructure device

Info

Publication number: WO2001089986A1
Application number: PCT/DK2001/000361
Authority: WO
Inventors: Chaker Khalfaoui
Original assignee: Chaker Khalfaoui
Priority date: 2000-05-26
Filing date: 2001-05-23
Publication date: 2001-11-29
Also published as: AU2001262065A1

Abstract

An electrostatically driven microstructure device comprises a substrate having a principal surface and at least one main beam suspended over the principal surface. Each end of the main beam is connected to an addressing connection beam. The addressing connection beam is anchored to the substrate. A connection beam electrode is coupled to the addressing connection beam, and a corresponding static electrode is provided, whereby the electrodes are adapted to apply electrostatic forces to the connection beam and/or act as a mechanical stopper for at least one connection beam. The electrostatic forces applied to the connection beam may be controlled, so that the main beam may move between a stretched position and an end buckling position. In order to prevent 'stiction' problems, the electrodes are positioned so that no mechanical contact is provided between the addressing connection beam electrode and the corresponding static electrode during operation. A method for addressing a matrix structure of devices is provided.

Description

A STICTION-FREE ELECTROSTATICALLY DRIVEN MICROSTRUCTURE DEVICE

FIELD OF THE INVENTION

The present invention relates generally to micromechanical structures and more particularly to an electrostatically driven microstructure device, and addressing methods for addressing the electrostatically driven device.

BACKGROUND OF THE INVENTION

A wide variety of Micro Electro Mechanical Systems (MEMS) are fabricated using microfabrication technology. The fabrication technology is also widely described and an overview of the fabrication processes may be found in the following publications: J.H. Smith, et al.: 'Micromachining and microfabrication Process Technology V, and M.E. Motamedi, et al.: 'Miniaturized Systems with Micro-Optics and MEMS' both form

Proceedings of SPIE, Sept. 1999, and Marc Madou: 'Fundamentals of Microfabrication'.

A large number of microstructure devices have been designed and fabricated with microfabrication techniques, primarily in silicon. Many of these devices comprise moving parts and static parts which inherently will contact each other during use of the devices. It is realised that when static parts and moving parts contact each other in the presence of water condensation or other wetting liquids, the problem known as 'stiction' will occur. It is necessary to induce an initiation force to overcome the stiction forces and the operation of the microstructure device become difficult and unpredictable and further leads to a short lifetime of the devices. The stiction problem is not very well understood but is believed to mainly occur due to excessive van der Waals or capillary forces. Examination of the problem is rendered difficult because of the small sizes of the structures.

A number of different approaches have been proposed to solve the stiction problem. For example by coating the surfaces where stiction might occur. Different organic coatings which avoid wetting of the surfaces in question have been proposed. These coatings are adapted to avoid wetting of the surfaces by changing the wetting angle of liquids on the surfaces whereby the stiction phenomenon will also be reduced. However, introduction of a coating layer creates other problems, such as adhesion problems, problems related to mechanical wear of the coatings, etc.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an electrostatically driven microstructure device wherein the stiction problem is avoided.

According to a first aspect of the invention, the above-mentioned and other objects are fulfilled by an electrostatically driven microstructure device comprising

a substrate having a principal surface

at least one main beam suspended over the principal surface, each end of the at least one main beam being connected to a connection beam, at least one connection beam being an addressing connection beam, each connection beam being suspended over the principal surface and the at least one addressing connection beam being anchored in at least one anchoring position to the substrate,

at least one connection beam electrode coupled to the at least one addressing connection beam, and at least one corresponding static electrode, the electrodes being adapted to apply electrostatic force to the connection beam(s), and/or act as a mechanical stopper for at least one connection beam,

a control circuit for controlling the electrostatic forces applied to the connection beam(s),

the at least one main beam being adapted to move between a stretched position and at least one end buckling position according to the electrostatic force(s) applied to the connection beam(s),

the electrodes being positioned so that no mechanical contact is provided between the at least one addressing connection beam electrode and the at least one corresponding static electrode during operation. Hence, electrostatic force applied to the addressing connection beam to initiate a change in the main beam position does not need to overcome stiction between the static electrode and the addressing connection beam electrode.

It is an advantage of the present invention that contact between the relevant moving parts and static parts are avoided so that stiction will not occur.

It is a further advantage of the device that a large mechanical amplification of movement (and force) is obtained. A relatively small movement at the connection beam positions results in a relatively large deflection or displacement in the middle of the main beam.

It is a still further advantage that the device in some configurations makes use of the buckling beam bistability, whereby no electrostatic force is necessary to maintain the buckled shape.

The substrate is preferably a silicon substrate so as to facilitate the use of standard silicon process technology. However, other substrates may be used, such as glass, such as quartz, Bk7, etc. Hereby, advantage is taken on the large range of standard processes developed in the silicon IC technology, and this further facilitates the integration of microelectronics and micromechanics.

The shape of the electrodes may be chosen so as to optimise the electrostatic driving voltage. The electrodes may, thus, be rectangular, triangular, curved, or the electrodes may have a comb shape.

The main beam(s) suspended over the substrate may preferably be hinged or clamped to the connection beams, or the main beam may be hinged to a connection beam in one end and clamped to an other connection beam in the other end. Also, other connection modes, such as pinned joint mode, a propped mode, etc., could be used. Still further, the main beam may be a cantilever structure being connected in one end and free, i.e. not connected, in the other end.

The background theory for the buckling and/or deflection of the buckling beams according to the present invention is the Euler column theory or the Euler buckling beam theory. The principles of the Euler buckling theory is that if a compression force is applied to one or both ends of a beam, the beam will begin to deflect when the compression force is larger than the critical load. If the main beam is, for example, designed as a slender beam so that the length of the main beam is much larger than the cross section of the main beam, the displacement at the centre of the main beam due to the deflection of the main beam will be larger than the displacement of the connection beams due to the compression forces applied to the connection beams. Hereby, an amplification is achieved so that for example a large displacement is achieved even when the device is operated at relatively low power. Likewise, low forces applied to the main beam(s) may be amplified so that large forces may be achieved from the connection beam(s). Furthermore, by acting on the main beam to obtain a displacement or deflection of the main beam, it is possible to obtain a very precise displacement or deflection at the connection beam.

For a detailed description of the Euler theory, see for example S. P. Timoshenko and J.M. Gere: 'The theory of elastic stability' and 'Mechanics of Materials' by the same authors. In this reference also a relation between the displacement of the connection beams and the deflection at the centre of the main beam can be found, the relation being mainly dependent on the connection mode between the main beam(s) and the connection beams and the length of the main beam. In the present context, mainly the first order buckling mode of the main beam is considered.

The main beam may comprise one or more sub-beams arranged in series between the connection beams. For example, two sub-beams may be connected by a thinner beam in the middle, whereby the main beam, when subjected to compressive forces, will deflect to a triangular shape. It is seen that the amplification in this example is more efficient than by having a uniform main beam.

Likewise, the one or more connection beams may comprise one or more sub-beam(s) arranged in series, so that for example the displacement of the connection beam(s) is amplified before being applied to the main beam.

Furthermore, the main beam may comprise one or more sub-beams arranged in parallel, the sub-beams being connected to the same connection beams so as to facilitate parallel processing of the sub-beams.

The connection beams may comprise the connection beam electrodes, whereby attachment of the connection beam electrodes to the connection beams is avoided. For example, the connection beams may be fabricated of a semiconductor material, such as silicon, so that the connection beam inherently may serve as connection beam electrode. Alternatively, the connection beam may comprise a multilayer structure, one layer being adapted to serve as the connection beam electrode.

The electrodes of the initiation connection beam and the corresponding static electrode may be coated with an insulation layer to avoid short circuit. However, in a preferred embodiment, micro-welding of the initiation connection beam and the corresponding static electrode is provided to obtain a locking of the initiation beam and in this case the electrodes are not necessarily coated with an insulation layer.

The control circuit is adapted to apply an initiation voltage to the at least one connection beam electrode and the corresponding static electrode so that an initiation electrostatic force is applied to at least one connection beam, the initiation connection beam being displaced or deflected so that an initial buckling of the at least one main beam is provided.

Preferably, the initial buckling of the at least one main beam is locked mechanically, for example by fabricating a lock mechanism, during processing of the device so that the connection beam is locked the first time the main beam is buckled to a predetermined buckling position. Instead of a lock mechanism the connection beam initiating the buckling may be permanently locked when the main beam is buckled to a predetermined position by for example micro-welding the initiation connection beam to an anchor.

Alternatively, the initial buckling of the at least one main beam may be maintained by applying a maintaining electrostatic force to the at least one connection beam during operation of the device.

Another alternative is to perform the initial buckling of the at least one main beam during manufacturing and post manufacturing, such as during post-annealing of the structure. The buckling may, for example, be performed by designing the fabrication masks for the structure so that the main beam will always be buckled, for example by having a curved structure forming the initial buckling of the main beam. Alternatively, stress, such as thermal stress, or mechanical stress, may be introduced in the main beam, whereby the main beam will be buckled. The at least one main beam may, for example, have a predetermined buckling, the buckling being provided by a multilayer main beam comprising at least a first layer having a first property and a second layer having a second property, the combination of at least the first and the second layer inducing a controlled stress in the structure. In a preferred example, the main beam is manufactured in a two-layer structure, wherein the first layer is a silicon layer and the second layer is silicon oxide layer, the thickness of the layers being designed so that the main beam will initially be buckled or have a preferential buckling side.

For example, the first property of the first layer may be a first thermal coefficient of expansion and the second property of the second layer may have a second thermal coefficient of expansion, the first and the second thermal coefficient of expansion being distinct, whereby a thermal stress is induced in the at least one main beam, for example during post-annealing of the structure. The first and second layer may for example be silicon in combination with silicon oxide, silicon nitride, etc.

Furthermore, the first and the second layer of the main beam may be of the same material, wherein stress is induced, for example, by ion implantation of a top surface layer or by ion implantation of a middle part of the main beam, whereby the stress in the material is changed. Other combinations of materials may be used so as to obtain properties of the materials inducing a controlled stress in the main beam structure.

Preferably, the main beam is designed so that the main beam is preferably deflected to either one side or an opposite side of the stretched position when a force is applied to the connection beam(s), the two sides being termed 'A' and 'B', respectively.

When the initial bending or buckling is performed by applying an initial force to the main beam the main beam may be deflected towards A or towards B depending on initial bending conditions. To obtain a predetermined behaviour and a predetermined end buckling position an asymmetry may be introduced. A predetermined buckling may for example be done by a slight rotation of one of the connection beam ends, clockwise or counter-clockwise whereby the beam will have a preferred bending towards A or B according to the rotation of the connection beam. For example, when the main beam is suspended between two connection beams and each connection beam is addressed by two static connection beam electrodes, the static electrodes being positioned at either side of the main beam in the buckling plane (side A and side B) addressing the addressing connection beam, and when the initial buckling of the beam is performed, addressing of the main beam from its actual position, for example A, to the opposite position, B, may be performed in three steps. First, the main beam is stretched to an unbuckled or stretched position by pulling both sides of the addressing beam, secondly, releasing the side corresponding to the last position of the main beam, side A, whereby the main beam will initiate a buckling to the opposite side, thirdly, releasing the other side of the addressing beam, side B, to bring the buckling beam to a fully buckled position. Hereby, the main beam is addressed to a predetermined side (from A to B).

In a preferred embodiment, the initiation electrodes may not influence the device operation even if stiction occurs and contact between the addressing connection beam electrode and the corresponding static electrode may be avoided by a mechanical fuse function. The principle of the mechanical fuse, is to provide a gap between the addressing connection beam electrode and the corresponding static electrode being slightly bigger than the gap between the initiation connection beam electrode and the corresponding static electrode and a distance between the addressing and the connection beam electrodes corresponding to the length of the main beam. Hereby, contact between the electrodes at the addressing side is avoided, even when excess voltage is accidentally applied.

In the out-of-plane configuration, the buckling of the main beam to a preferred side A or B may be performed by external means, such as an air or gas flow out of openings performed in the substrate or by bumpers at the bottom side of the buckling beam or on the substrate at specific selected positions.

When the beam is buckled initially according to one of the above-mentioned procedures, the control circuit may be adapted to address the position of the at least one main beam by varying the electrostatic force(s) applied to the at least one addressing connection beam by varying the voltage applied to the at least one addressing connection beam electrode and the corresponding static electrode. The voltage applied to the addressing connection beam electrode and the corresponding static electrode may be varied continuously, whereby the main beam is deflected continuously. Alternatively, the at least one main beam may be adapted to assume a selected number of stable buckling positions between the stretched position and the at least one end buckling position in response to a corresponding set of selected address voltages applied to the addressing connection beam electrode(s) and the corresponding static electrode(s).

The main beam may in a preferred embodiment be adapted to be deflected so that the buckling of the main beam is substantially parallel to the principal surface of the substrate, which is also referred to as in plane buckling. Alternatively, in an other preferred embodiment the main beam may be adapted to be deflected so that the buckling of the beam is substantially orthogonal to the principal surface of the substrate, which is also referred to as out of plane buckling. The buckling of the main beam is determined by the ratio of the beam width over the beam thickness. If the ratio is less than one a preferred buckling in the plane of the principal surface is obtained, and if the ratio is larger than one a preferred buckling out of plane is obtained.

The device may further comprise a shutter plate, which is preferably a flat plate, the shutter plate being positioned at a shutter attachment position on the main beam so that the shutter plate is moved according to the buckling of the main beam.

The shutter plate may be attached to the main beam by anchoring or by a shutter plate connection beam having any shape, such as an L-shape, S-shape, l-shape, etc., or, alternatively, the shutter plate may be fabricated as an integral part of the main beam.

The shutter plate may be positioned so that an angle is formed between the principal surface and the plane defined by the shutter plate. In a preferred embodiment the shutter plate is positioned so that the plane defined by the shutter plate is substantially parallel to the principal surface when the main beam is in the stretched position. In another preferred embodiment the shutter plate is positioned so that the plane defined by the shutter plate is substantially perpendicular to the principal surface when the main beam is in the stretched position.

Furthermore, the substrate may comprise a transparent opening positioned so that the shutter plate in at least one buckling position covers the transparent opening. The opening and also the shutter plate may have any form, such as polygonal, rectangular, triangular, elliptical, circular, etc.

Also, more than one shutter plate may be positioned at the at least one main beam and furthermore, the substrate may comprise more than one transparent opening.

The device may further comprise at least one electromagnetic radiation source for emission of electromagnetic radiation beam adapted to be transmitted through the transparent opening when the shutter plate is not covering the transparent opening, whereby the shutter plate functions as a shutter for the electromagnetic radiation beam.

The electromagnetic radiation source(s) may be any electromagnetic radiation sources, such as lasers, light emitting diodes, Arc-lamps, Halogen-bulbs, black body radiation sources, x-ray sources, etc. The electromagnetic radiation may be transmitted to the transparent opening directly from the radiation source, or the electromagnetic radiation may be transmitted through fibre optic cables, waveguides, light pipes, etc. The electromagnetic radiation sources may be shaped with optics, such as focussing elements, diverging optical elements, beamsplitters, and may further be filtered with colour filters, wavelength filters, such as RGB, infrared or ultraviolet filters. Furthermore, a polarisation element may be inserted.

The shutter plate may have a first surface having a reflective coating so that incident electromagnetic radiation on the first shutter plate surface will be reflected when the shutter plate covers the transparent opening. Alternatively, the first surface may be coated so that incident light is absorbed when the shutter plate covers the transparent opening.

Furthermore, the first surface may be coated by a coating which selectively absorbs or reflects electromagnetic radiation. The selection may be made by selection of specific wavelengths or specific wavelength ranges, or by the angle of the incident electromagnetic radiation beam.

The opening in the substrate is adapted to be transparent for the specific electromagnetic radiation used with different applications of the device. Preferably, the shutter plate is positioned on the main beam at a shutter attachment position substantially half way between the connection beams so as to obtain maximum displacement of the shutter plate. In another preferred embodiment, the shutter plate is positioned at a shutter attachment position on the main beam substantially one fourth the length of the main beam from one of the at least one connection beams corresponding to a maximum deflection of the shutter plate, corresponding to the second angle being as large as possible. However, the shutter plate may be positioned at any position along the main beam.

In another embodiment of the device, the shutter plate may be attached to the main beam at a shutter attachment position so that the angle between the shutter plate and the principal surface is shifted by an angle lager than zero degrees as the main beam is buckled from a stretched position to an end buckling position. Hereby, the shutter plate may when the main beam is in the stretched position cover the transparent opening in the substrate, and when the main beam is in an end buckling position allow maximum electromagnetic radiation to be transmitted through the transparent opening without being obstructed by the shutter plate or vice-versa.

The shutter plate is preferably manufactured so that the shutter plate forms a part of the main beam. Hereby, the attachment between the shutter plate and the main beam is avoided which reduces the complexity of the device which inherently reduces the manufacturing costs of the device.

In a still further embodiment of the device, the device may comprise a reflective device having a reflective surface and being attached to the main beam at a first attachment position, the reflective surface forming a first angle with a tangent to the main beam first attachment position, the first angle being maintained irrespective of the main beam buckling position. Furthermore, the tangent to the main beam first attachment position may form a second angle with the principal surface, so that the second angle is changed according to the deflection of the main beam. The reflective surface may have any form, such as polygonal, rectangular, triangular, elliptical, circular, etc

The reflective device may be attached to the main beam by anchoring or by a reflective device connection beam having any shape, such as an L-shape, S-shape, l-shape, etc., or, alternatively, the reflective device may be fabricated as an integral part of the main beam.

Also, more than one reflective device comprising one or more reflective surfaces may be positioned at the at least one main beam.

The device may further comprise an electromagnetic radiation source for emission of a first electromagnetic radiation beam towards the reflective surface whereby a corresponding second electromagnetic radiation beam is reflected from the reflective surface, so that the second electromagnetic radiation beam is deflected or displaced according to the buckling position of the main beam.

The first attachment position wherein the reflective device is attached to the main beam may preferably be a position substantially one fourth the length of the main beam from one of the at least one connection beams so as to obtain a maximum deflection of the second electromagnetic radiation beam. Another preferred first attachment position is substantially half way between the connection beams so that the second electromagnetic radiation beam is displaced according to a centre deflection of the main beam so that there is substantially no deflection of the reflecting device. However, the reflective device may be positioned at any position along the main beam.

When the main beam is addressed to assume a selected number of stable positions, the reflective device, and, accordingly, the reflective surface of the reflective device and, thus, the second electromagnetic radiation beam is deflected or displaced according to the selected number of stable positions. The second electromagnetic radiation beam is thus deflected according to the stable buckling positions of the main beam. By changing the deflection of the main beam continuously the second electromagnetic radiation beam will accordingly be deflected continuously.

In a still other preferred embodiment, the reflection device is attached to the main beam at a first attachment position so that the second angle is shifted to an angle equal to or larger than 0 (zero) degrees as the main beam is buckled from a stretched position to an end buckling position. Hereby, the reflective device may when the main beam is in the stretched position reflect at least the part of electromagnetic radiation incident on the reflective surface, and when the main beam is in an end buckling position allow electromagnetic radiation coming from a direction parallel to the plane defined by the reflecting device to be transmitted without reflecting the electromagnetic radiation, or vice- versa.

It is envisaged that certain design rules are observed when designing a device according to the above-mentioned. It is for example preferred that the elastic return force of the addressing connection beam is larger than the force required to buckle the main beam to a buckled position. Furthermore, the force applied to the structure has to be larger than the critical buckling load of the structure in order to obtain a buckling of the beam. Still further, the buckling, in-plane or out-of-plane, of the main beam is determined by the ratio of the beam width over the beam thickness. If the ratio is less than one a preferred buckling in a plane parallel to the principal surface is obtained, and if the ratio is larger than one a preferred buckling out of plane is obtained. In the microfabrication technique and for in-plane buckling, it is preferred that the beam thickness of all the beams in the structure is the same so that the beams widths are varied. Still further, it is preferred that the force required to stretch the beam is larger than the difference between the addressing beam elastic return force and the buckling beam load, the buckling beam load and the addressing force acting in the same direction. The voltages required for initiation and addressing of the main beam are dependent on the geometry of the structure, the materials used and dielectric between the electrodes (air, vacuum, etc.). Furthermore, as mentioned above, the electrodes may be designed so as to minimise the voltages required for initiation and addressing of the main beam. Hereby, the required voltages may be in the range from 0 - 125 V, preferably in the range from 0 V - 60 V, but also higher voltages may be applied, such as few hundred volts, provided that the structures and electronics are designed for high voltages.

Still further, the maximum frequency of operation for the structure is dependent on numerous parameters, such as the structure geometry, the material used, and internal as well as external damping effects.

In a still further preferred embodiment the actuation forces, such as the forces for initiation of the buckling of the main beam, may comprise other actuation forces than electrostatic forces. For example, thermal or piezoelectric forces may be used. Furthermore, a system for motion or scanning having three degrees of freedom is provided. The system comprises a first and a second device according to the above- mentioned devices, wherein the buckling of the main beams is in-plane, and a third device, wherein the buckling of the main beam is out-of-plane. The first device comprises a first bearing plate, the first bearing plate being connected to first and second parallel main beams of the first device, the first bearing plate comprises the second device, the second device comprises a second bearing plate connected to third and fourth parallel main beams of the second device, the third and fourth main beams being orthogonal to the first and second main beams, the second bearing plate comprises the third device, and the third device comprises a fifth main beam, whereby the first device is adapted to move the first bearing plate in a first direction in the plane of the principal surface, the x- direction, the second device being adapted to move the second bearing plate in a second direction in the plane of the principal surface, the y-direction, and the third device being adapted to buckle the fifth main beam in a third direction orthogonal to the principal surface, the z-direction, so that a three dimensional movement of substantially any position on the fifth main beam is obtained.

Attached to the fifth main beam may be any shutter plate, reflective device, etc. which may then be moved in three dimensions.

According to a further embodiment of the invention, wherein at least one transparent opening in the substrate is provided, the device may comprise at least one sensing element positioned so as to receive electromagnetic radiation transmitted through the at least one transparent opening in the substrate, the at least one sensing element being adapted to sense the amount of electromagnetic radiation transmitted through the at least one transparent opening, the shutter plate being adapted to cover a variable part of the transparent opening according to the buckling of the main beam. The sensing element may be any sensing element adapted to detect the electromagnetic radiation transmitted through the transparent opening of the substrate, such as any optical sensing elements, such as light detectors, CCD arrays, etc. External readout of the sensing elements may be provided.

According to a still further embodiment of the invention, the device may further comprise a sensing element for sensing any force applied to the sensing element, the sensing element being positioned so that any force applied to the sensing element is transferred to the addressing beam,

a read out element for reading the force applied to the sensing element, the read out element being adapted to read any change in the main beam buckling position,

The sensing element may be any sensing element adapted to sense a forced applied to the sensing element, such as an acoustic force element, such as a microphone plate, such as a pressure sensing element, such as a seismic mass element, etc.

The readout element may be an electrostatic readout element, such as a capacitive readout element, or a piezoresistive readout element.

In the sensing device, the addressing connection beam may act only as a sensing connection beam, since the main beam may not need to be addressed in the sensing configuration.

Furthermore, the addressing connection beams and corresponding connection electrodes may be used for performing an active sensor, whereby a voltage applied to the connection electrodes will induce, for example, a change in the mechanical performance or the readout range of the sensing device.

When manufacturing a device according to the invention, an isotropic etching may be used. In a preferred embodiment, the suspended beams and the connection beams are manufactured in polysilicon and the standard applied etching process is a KOH diluted in Alcohol at 160-180 degrees Celsius, being an isotropic etching process.

However, it may be difficult to control such an isotropic etching process whereby overetching or underetching of the structure may occur. The width and length of the beams may, thus, vary according to predetermined values of the widths and/or lengths of the beams resulting from over- or underetching of the structure. The width may vary by 10-20 %. When the width of the beam is changed, the distance between the static electrodes and the moving electrodes is also changed whereby the voltages required for initiation and/or addressing of the beams may vary accordingly. However, since the beams are also thinned/thickened according to the predetermined values, the voltages required for initiation and/or addressing of the beams may be altered because of the reduced/increased widths/lengths of the beams. There will, because of the variations in lengths and/or widths be a variation in the return elastic force and the critical buckling force. This variation is mainly due to the addressing beam and buckling beam length ratio, which is not linear with the addressing voltage. It is, thus, difficult to predict the required voltages according to the overetched/underetched beams, and it is therefore desired to either obtain an improved control of the etching process or amend the structure so that it is less sensitive to overetching/underetching of the beams.

It is often difficult to obtain a better control of the etching process itself and since an overetching of 10 -15 % may result in a variation of the required addressing voltage of up to 50 % or more, an alternative or amended structure may be preferred. Furthermore, the etching may vary from fabrication batch to fabrication batch which render an amended less sensitive structure even more preferred.

It is therefore preferred to add a process variation compensation feature. The idea of such a feature being to perform a non-linear etching ratio between main beam and addressing connection beams. The compensation feature may for example be a triangular shape added to the addressing beam at the anchoring locations or a triangular shape added to the main beam at an interconnection between the main beam and the connection beam. The optimum angle of the triangle is mainly defined by the process variation tolerance and the beams lengths, but the angle may in a preferred embodiment be between 2 and 5 degrees. When an over/under etching occurs, the compensation feature acts in a way so that the length of the addressing and initiation beams is not linear with the over/under etching. The cross section of all beams is substantially affected in the same way by the over- and underetching and the voltage variation resulting from these variations has no major effect on the addressing voltages compared to the length variations. It is, hereby, possible to reduce the variation in addressing voltage to 10-15 % of the predetermined addressing voltage even when having an overetching of 10-15 %.

One substrate may comprise one or more electrostatically driven devices according to the above-mentioned description. Each device may be driven individually or the devices may be set up in a matrix structure, regular or irregular, so that the devices may be driven by dedicated driving electronics. The devices may be of any type, shape and functionality according to the above-mentioned description of the devices.

In an m x n matrix structure, as mentioned above, the addressing of the devices may be performed by using one of the following methods:

If the devices of the m x n matrix structure contain only one single addressing electrode, the addressing of the matrix structure, which in this case is referred to as single electrode addressing, may, when an initiation voltage, Vinit, is applied to all the initation electrodes of the devices, be performed by:

- holding all the devices by applying default voltages to all rows and columns, respectively, i.e. applying a voltage being substantially equal to half the negative holding voltage to all rows, i.e. VRi « -Vh/2 for i = 1 , 2, ..., m, and a voltage being substantially equal to half the holding voltage to all columns, i.e. VCj « Vh/2 for j = 1, 2, ..., n, the holding voltage being large enough to hold the state of any device,

- addressing the device by

- releasing the devices to be released by

- selecting a row, Ri, containing one or more devices to be released,

- applying a voltage being substantially equal to half the negative release voltage to the selected row, i.e. VRi « -Vr/2 for the selected rownumber i, the release voltage, Vr, being less than the holding voltage, Vh, - selecting all columns containing one or more devices(s) to be released in the selected row Ri,

- applying a voltage being substantially equal to half the release voltage to the selected column(s), i.e. VCj « Vr/2 for the selected value(s) of j,

- whereby the total voltage applied to the devices to be released is substantially equal to or less than the release voltage, Vr, so that the devices to be released will be released, and applying the default voltages to all rows and columns, respectively, so as to maintain the actual position of all devices, and/or

- capturing the devices to be captured, i.e. stretching and holding the devices in the stretched position, by - selecting a row, Ri, containing one or more devices to be captured,

- applying a voltage being substantially equal to half the negative capture voltage to the selected row, i.e. VRi « -Va/2 for the selected value of i, the capture voltage being larger than the holding voltage - selecting all columns containing one or more devices to be captured in the selected row Ri,

- applying a voltage being substantially equal to half the capture voltage to the selected column(s), i.e. VCj * Va/2 for the selected value(s) of j,

- whereby the total voltage applied to the devices to be captured is substantially equal to or above the capture voltage, Va, so that the devices to be captured will be captured, and applying the default voltages to all rows and columns, respectively, so as to maintain the actual position of all devices,

- repeating the addressing step until all the rows are scanned for devices to be released and captured,

If the devices of the m x n matrix structure comprise two separate addressing electrodes and an initiation voltage, Vinit, is applied to all the initation electrodes of the devices of the structure, the addressing, which in this case is referred to as bistable addressing, may be performed by:

- holding all the devices by applying default voltages to all rows and columns, respectively, i.e. applying a voltage being substantially equal to half the negative holding voltage to all rows, i.e. VRi « -Vh/2 for i = 1 , 2, ..., m, and a voltage being substantially equal to half the holding voltage to all columns, i.e. VCj1 » -Vh/2 and

VCj2 « -Vh/2 for j = 1, 2, ..., n, the holding voltage being large enough to hold the state of any device (the holding voltage in this configuration is in most cases 0V),

addressing the device by

- selecting a row, Ri, containing one or more devices to be addressed,

- applying a voltage being substantially equal to half the negative capture voltage to the selected row, i.e. VRi « -Va/2 for the selected value of i,

- selecting all columns containing one or more devices to be addressed in the selected row Ri, - applying a voltage being substantially equal to half the capture voltage to both electrodes of the selected column(s), i.e. VCJ1 « Va/2 and VCj2 « Va/2 for the selected value(s) of j,

- whereby the total voltage applied to the devices to be addressed is substantially equal to or above the capture voltage, Va, so that the devices to be addressed are now captured,

- for each column among the selected columns that should be addressed towards the side of the second electrode, the voltage of the first electrode is returned to the default value before the voltage of the second electrode is returned to the default value,

- for each column among the selected columns that should be addressed towards the side of the first electrode, the voltage of the second electrode is returned to the default value before the voltage of the first electrode is returned to the default value,

repeating the above until all rows have been scanned for devices to be addressed,

Finally, a third possibility is to provide each device of the matrix structure with an addressing device and performing the addressing of all the devices simultaneously, this method of addressing being referred to as individual device addressing.

In the two first mentioned methods of addressing it is clear that it could just as well be the columns that are chosen one at a time, and then the relevant rows. The sign of the voltages can also be reverted. All of the above methods for addressing an m x n matrix structure can be repeated periodically at high frequencies, as long as the frequency is kept below the eigenfrequency of the structure.

In the above-mentioned description, buckling of a beam has mainly been described in relation to the main beam. It is, though, envisaged that the buckling properties described in relation to the main beam encompass the buckling properties of any buckling beam in the structure.

BRIEF DESCRIPTION OF THE DRAWINGS. In the following, preferred embodiments of an electrostatically driven microstructure device will be described with reference to the drawings, wherein

Fig. 1a shows a buckling beam and Fig. 1b shows an alternative buckling beam structure.

Figs. 2a-c show a beam and the initiation of a buckling and stretching of the beam,

Figs. 3a-e show the addressing steps for a structure according to an embodiment of the invention

Figs. 4a-b show a device according to an embodiment of the device, and a device with initiation and addressing electronics.

Figs. 5 a-d show a device according to an embodiment of the invention comprising a shutter plate,

Fig. 6 shows a three dimensional view of an embodiment according to Fig. 5b,

Fig. 7 shows a main beam having a shutter plate attached and being connected to two cantilever connection beams,

Figs. 8a-c show a main beam buckled out of the plane, the main beam having a reflective device attached,

Figs. 9a-c show a reflective device attached to the main beam, positioned in different positions and orientations,

Figs. 10a-b show a device comprising two main beams and a plate attached to the two main beams,

Figs. 11a-b, show a main beam comprising two layers of material,

Figs. 12 shows a shutter plate connected to two main beams, Figs. 13 shows a gripping device having two grippers each being connected to a main beam,

Fig. 14 shows a device comprising a mechanical fuse,

Fig. 15 shows a device, wherein the initiation beam is a buckling beam,

Fig. 16 shows a device with curved and triangular shaped electrodes and different connection modes,

Fig. 17 shows a device with a comb shaped electrode and an initiation beam lock mechanism,

Fig. 18 shows an m x n matrix comprising m x n devices,

Fig. 19 shows the electrical signals applied to the matrix structure of Fig. 18,

Fig. 20 shows an m x n matrix with electronic circuitry,

Fig. 21 shows a capacitive microphone device,

Fig. 22 shows a microphone device with piezoresistive readout,

Fig. 23 shows an accelerometer comprising a seismic mass and having capacitive readout,

Fig. 24 shows an accelerometer comprising a seismic mass and having a piezoresistive readout,

Fig. 25 shows a flat panel screen,

Fig. 26 shows an exposure device,

Fig. 27 shows a device with n x n fibres, Fig. 28 shows a device with 1 x n fibres,

Fig. 29 shows a projection device, and

Fig. 30 shows a three dimensional scanner,

Fig. 31a-b show a three dimensional view of a device according to Figs 8a-b.

Fig. 32 a-c show a method for addressing an m x n matrix structure

Fig. 33 a-b show examples of the etching process variation compensation feature.

DETAILED DESCRIPTION OF THE DRAWINGS.

In Fig. 1a the buckling beam principle is shown. A main beam 1 is suspended between two connection beams 3 and 5. A compressive force (not shown) is applied to one connection beam 3 whereby the connection beam is displaced to a displaced connection beam 7 and the main beam 1 is buckled to a main beam buckling position 1A or 1B. A large displacement at the centre of the main beam is thus obtained by a small displacement of the connection beam 3,7, i.e. of the free end of the main beam. Fig. 1b shows a device according to Fig. 1a, wherein the main beam comprises two sub-beams 9 attached by a thinner beam 10 in the middle. When applying a force at the connection beam 3, the main beam will tend to a triangular shape resulting in a larger displacement in the centre than for the structure of Fig. 1 a for the same applied force, and the same geometrical structure of the devices.

In Figs. 2a-c an initiation operation to bring the beam in a buckled position is shown. In Fig. 2a the structure is shown having a main beam 1 suspended between an initiation connection beam 11 and an addressing connection beam 13. The connection beams 11 , 13 are both anchored to the substrate 2 in both ends by an anchor 19. The connection beams comprise the connection beam electrodes and only the static initiation connection beam electrodes 15A, 15B and the static addressing connection beam electrodes, 17A, 17B are shown. In Fig. 2b the structure is initiated by applying an initiation voltage to the initiation electrodes 15A, 15B, and the initiation connection beam 11 is locked in the initiation position. In Fig. 2c, the structure is stretched and it is seen that the addressing connection beam and the addressing connection beam electrodes do not come into contact, this so called mechanical fuse is, thus, performed by the main beam itself. An alternative mechanical fuse is shown in Fig. 14.

Figs. 3a-e show the addressing steps when addressing the main beam 1 from side A to side B for a structure as shown in Figs. 2a-c. Fig. 3a shows the start position and then in Fig. 3b the structure is initiated so that the main beam 1 is buckled towards A. Addressing of the main beam 1 from its actual position A to the opposite position B may be performed in three steps, shown in Figs. 3c-e. First, the main beam 1 is stretched to an unbuckled or stretched position by pulling both addressing connection beam electrodes 17A, 17B, secondly as shown in Fig. 3d, releasing the electrode 17A corresponding to the last position of the main beam 1 , initiate a main beam buckling to the opposite side B, thirdly, the other side B of the addressing connection beam 13 is released to bring the buckling beam to a fully buckled position. Hereby, the main beam 1 is addressed to a predetermined side.

In Fig. 4a a device according to Figs 1-3 is shown, wherein lengths and distances are shown. A numerical example for a device designed according to the design rules mentioned above is given in the following table for a structure fabricated in polysilicon and having air as dielectric in the gap between the electrodes. The structure is approximately 3 μm thick. The voltage applied, Vel is approximately 65 V.

In Fig. 4b, a device having a structure basically similar to the structure in Fig. 4a is shown. Furthermore, addressing and initiation electronics is shown. It is seen that the addressing beam comprises two sub-beams 13 and 13' each being addressed by static electrodes 17A, 17B and 17A2 and 17B2, respectively. The addressing electrodes 17A4, 17A3 and 17B3, 17B4, these addressing electrodes acting as assistance addressing electrodes to ensure that the main beam is addressed to the predetermined addressing position. When the addressing beam is released at the side A electrodes an asymmetry is introduced in the main beam by the electrostatic force generated by the assistance addressing electrodes 17B4, 17B3.The assistance addressing electrodes are positioned in way so that there is no contact between the main beam and the assistance addressing electrodes when the main beam is buckled.

Figs. 5 a-d show a device according to an embodiment of the invention comprising a shutter plate 21. In Fig 5a, the shutter plate 21 forms part of the main beam 1. The shutter plate covers a transparent opening 23 in the substrate 2 when the beam is in the buckled position A, and does not cover the opening 23 when in the buckling position B. Fig. 5b shows a shutter plate 21 attached to the main beam 1 by an anchor 25. The shutter plate attachment position 24 is in the centre of the main beam 1 , so that a displacement of the shutter plate is obtained. In Fig. 5c, the shutter plate 21 is connected to the main beam 1 in a position 26 different from the centre position 24 so that a displacement and a deflection or rotation of the shutter plate 21 is obtained. In Fig. 5d a different anchoring design 27 is shown.

Fig. 6 shows a three dimensional view of an embodiment according to Fig. 5b.

In Fig. 7 a main beam 1 having a shutter plate 21 attached by an anchor 25 at the centre of said main beam 1 , and being connected to two cantilever connection beams 11, 13 each connection beam being anchored in one point 19 to the substrate 2.

Figs. 8a-c show a main beam buckled out of the plane, the main beam having a reflective device 31 attached. In Fig. 8a a side view of the structure is shown having the reflective device 31 attached by anchor 33 at main beam 1. In Fig. 8b a top view of the device is shown, and it is seen that the thickness 32 of the main beam 1 is smaller than the width 34 of the main beam 1 so that a buckling out of the plane is obtained. For clarity, the reflective device is shown as transparent. In Fig. 8c a side view of the structure is shown and it is seen that for different buckling angles α of the buckling beam corresponding to different applied electrostatic forces, the angle between a tangent to the attachment position 36 and the reflective device β is constant.

Figs. 9a-c show a reflective device attached to the main beam, positioned in different positions and orientations. In Fig. 9a, the reflective device 31 is positioned orthogonal to the principal surface 42 of the substrate 2 and having the width of the reflective device 31 out of the plane. In Fig. 9b, the reflective device 31 is positioned having the width of the device 44 oriented along the main beam 1 length. In Fig. 9c, the reflective device 31 is attached directly on the main beam without an anchor 33.

Figs. 10a-b show side view and a top view of a device comprising two main beams 1 and a plate 41 attached to the two main beams by anchors 43, respectively. The substrate 2 is transparent whereby the device may either be a shutter as in Fig. 10b or allow incident light (not shown) to be transmitted.

Figs. 11a-b, show a main beam comprising two layers of material 51, 53, again it is seen that the width 34 of the beam is larger than the thickness 32 so that a buckling out of plane is obtained. The material 51 is silicon and the material 53 is siliconoxide, whereby initial stress is present in the main beam 1 so that a preferred buckling side for the main beam is given. Also, addressing electronics and initiation electronics are shown.

Figs. 12 shows a shutter plate 21 connected to two main beams 1 by anchors 25, the main beams are connected to connection beams 11' and 13', each being connected to the initiation and addressing connection beams 11 , 13, respectively.

Figs. 13 shows a gripping device having two grippers 61 , each being connected to a main beam 1, 1' and each main beam 1 , 1' being connected to a cantilever initiation 11 , 11' and addressing connection beam 13, 13'. The gripping device may be used in connection with a sorter mechanism so that the gripping device selects the elements 63 having a thickness 64 larger than a predetermined distance 62 between the two grippers 61 when the main beams 1 , 1' are in the stretched position.

Fig. 14 shows a device comprising a mechanical fuse, the mechanical fuse 76 being an example of another mechanical fuse than the main beam itself as it is shown in Fig. 2c. The addressing of the main beam must in this embodiment be maintained by a maintaining electrostatic force since it will not otherwise maintain the buckled shape.

In Fig. 15, a device, wherein the initiation connection beam 81 in itself is a buckling beam, having a static connection beam 87, and an initiation connection beam 83. This is a so called cascade of buckling beams.

Fig. 16 shows a device with curve shaped addressing electrodes 17 and triangular shaped initiation electrodes 15. The main beam 1 is connected to the initiation beam 11 via a flex joint 97 and connected to the addressing beam 13 with a ball-and-socket joint 98, 99.

In Fig. 17, a comb shape 92 of the static addressing connection electrodes 17 is shown. The initiation connection beam 11 is locked mechanically via a lock mechanism 91 , 93 when the initiation connection beam is initially deflected so that stoppers 91 are gripped by the hook 93.

An m x n matrix comprising m x n devices is shown in Fig. 18 and the electrical signals during switching operation are shown in Fig. 19. The relevant devices of the row m and the column n (Rm, Cn1 and Cn2) are selected. All the Rm electrodes for row m are connected to the same voltage VRm = - Vel/2 where Vel is the necessary stretching voltage (refer to Fig. 4). All the initiation electrodes of all the devices are connected to the same voltage Vinit which is the initiation voltage. The initiation voltage is kept constant during operation for holding the initiation. After the first addressing sequence for the whole array, the buckling beams positions are perfectly determined. The other columns and rows than the selected column and row are grounded (not shown) during this addressing period T.

Fig. 20 shows an m x n matrix with external electronic circuitry, with incoming clock signals 105 and incoming data signals 103. The hold devices 101 of each device reads the data corresponding to the device, i.e. the number n+2 device reads the data signal for every n+2 clock signals. The information is sent to the electrodes and the status is kept until the next data signal is read, etc. The initiation electronics is provided to keep the devices initiated during operation and to apply a constant voltage to the initiation connection beams and the static initiation electrodes at the same time. The constant voltage is equal to the initiation voltage.

Fig. 21 shows a capacitive microphone device, comprising a microphone sensing plate 5 110 attached to the addressing connection beam 13, and positioned parallel to each other, so that a force applied to the microphone sensing plate 110 is transferred to the addressing connection beam 13 so that the main beam is deflected. In Fig. 21 , the addressing connection beam does only serve as a force transferring sensing connection beam and is not used for addressing the main beam. The readout is done by a capacitor,0 partly represented by electrode plates 114 attached to the main beam and partly by electrodes 112 on the substrate. The electrodes 112 have a triangular shape. When the sensing plate 110 is vibrating because of the change in pressure between the sensing plate 110 and the addressing beam 13 caused by acoustic pressure, it will force the main beam 1 to buckle whereby the vibration is amplified. The electrode 114 attached to the5 main beam 1 will follow the movement of the main beam 1 and will induce a change in the capacitance. The readout electronics read the change in capacitance. The read out electrodes 114 is performed on both sides of the main beam, so that the microphone is not sensitive to which side the main beam 1 is initiated. If an offset voltage is applied to the addressing beam, an active microphone is obtainable. The structure must be covered0 and sealed at the sides forming a microphone chamber (not shown) so there is only an opening to the sensing plate. The general performance of the microphone structure is limited by the size of the structure, the size of the chamber and the materials used to fabricate the structure. Furthermore, the design of the capacitive readout electrodes 112, 114 may be optimised so that a linear output is obtained, and further the electrodes may5 be fabricated in several parts at one or both sides of the main beam 1.

Fig. 22 shows a microphone sensing device with piezoresistive readout, the main beam 1 being in a piezoresistive material, the readout electronics being adapted to read the change in piezoresistivity when the beam is buckled due to a force applied via 0 microphone plate 110 and addressing connection beam 13.

Fig. 23 shows an accelerometer comprising a seismic mass and having capacitive readout. The design is similar to the design of the microphone device, the sensing plate 110 being replaced by a seismic mass 119. The acceleration of the seismic mass is5 transformed to mechanical force acting on the addressing connection beam 13 whereby the acceleration is amplified by the buckling of the main beam 1. The acceleration is evaluated by measuring a change in the capacitance between a main beam electrode (not shown) and an electrode 117 positioned on the principal surface of the substrate 2 below the main beam. A voltage may be applied to the addressing electrode 13 whereby the sensitivity of the sensor may be changed or the measuring interval may be changed.

Fig. 24 shows an accelerometer comprising a seismic mass and having a piezoresistive readout. As in Fig. 22, the main beam 1 comprises a piezoresistive material whereby readout electronics reads a change in the main beam buckling position by reading the change of the piezoresistive response from the main beam.

Furthermore, a temperature sensor may be obtained by choosing a substrate material and a buckling beam material with different expansion coefficients. If the main beam has a coefficient of variation larger than the substrate, the beam will expand more than the substrate when the temperature rises. The expansion will be traduced by a buckling of the main beam 1 and the temperature change may be read by a capacitive or piezoresistive readout.

The sensor described may be performed by a main beam buckling in-plane or a main beam buckling out of plane.

Fig. 25 shows a flat panel screen. Parallel light 121 is transmitted through a colour filter 125 and through a glass plate comprising micro lenses for focusing the light to focused light beams 129. The light is focused to shutter plates 21 attached to buckling devices 18 as shown in Fig. 5a-d. The devices are mounted on a transparent substrate 126 and the defocused light emitted from the transparent surface is viewed on the image plane 131. The image may be projected on a projection screen (not shown). Spacers 123 are provided between the different elements to control spacing and for mounting means.

Fig. 26 shows an exposure device, where parallel light 121 form a light source (not shown) is incident on a glass plate 127 comprising microlenses for focusing of the light to focused light beams 129 incident on shutter plates 21 attached to buckling devices 18 as shown in Fig. 5a-d. Again the substrate 126 is transparent and the light is transmitted from the substrate 126 to a glass plate 133 comprising focusing optics for focusing the light to an image plane 135. The image plane may be in liquid or solid phase and is a light sensitive medium, such as a light sensitive film or an offset printing plate. Instead of having a transparent substrate 126, the substrate may comprise transparent openings for allowing the light to be transmitted through the openings. A relative movement between the exposure device and the light sensitive media can be provided as to cover a larger area or to perform a better resolution of the exposure.

Fig. 27 shows a device with n x n fibres, the input fibres 141 transmitting light to a number, n , of devices according to the devices shown in Fig. 9a-b. The light is then either transmitted or not to the output fibres 143. The fibres are hold in place by fibre holding devices 145 and the holders are kept in place relative to each other by spacers 123. Power and control electronics are applied so that addressing of the number of devices is possible. Preferably, the input fibres 141 1..n are selectively addressed to be connected to corresponding output fibres 143 1..n.

Fig. 28 shows a device with 1 x n fibres, wherein the light form input light fibre 141 is directed to a device according to the devices shown in Figs. 8a-c. The light incident at the device according to Figs. 8a-c is then scanned or deflected so that the reflected light is directed to any of the n fibres 143. Again, control and power electronics is applied so that selectively addressing of the device deflection angle is possible.

Fig. 29 shows a projection device, comprising a light source 161, collimating optics 163 and a colour filter, an RGB filter, 165. The light is directed to substrate 173 comprising a number of devices according to Figs. 8a-c. The light is then deflected to either projection optics 167 projecting the light to a projection screen or a photosensitive media 171 or to an absorber 169. By a configuration according to Fig. 29, for example, a projection to be used in digital projection televisions may be obtained. In the case of exposure of light sensitive media, a relative movement between the exposure device and the light sensitive media can be provided as to cover a larger area or to perform a better resolution of the exposure.

Fig. 30 shows a motion or scanning device having three degrees of freedom. The system comprises a first and a second device according to for example the device of Fig. 12, wherein the buckling of the main beams is in-plane, and a third device, wherein the buckling of the main beam is out-of-plane, for example such as shown in Figs. 8a-c or 9a- c. The first device comprises a first bearing plate 181x, the first bearing plate 181x being connected to first and second parallel main beams 1x of the first device, the first bearing plate 181x comprises the second device, the second device comprises a second bearing plate 181y connected to third and fourth parallel main beams 1y of the second device, the third and fourth main beams 1y being orthogonal to the first and second main beams 1x, the second bearing plate 181y comprises the third device, and the third device comprises a fifth main beam 1z, whereby the first device is adapted to move the first bearing plate 181x in a first direction parallel to the plane of the principal surface, the x-direction, the second device being adapted to move the second bearing plate 181y in a second direction parallel to the plane of the principal surface, the y-direction, and the third device being adapted to buckle the fifth main beam 1z in a third direction orthogonal to the principal surface, the z-direction, so that a three dimensional movement of substantially any position on the fifth main beam is obtained.

Any shutter plate, reflective device, etc. (not shown) may be attached to the fifth main beam 1z at anchor position 185 and may then be moved in three dimensions.

The electrical interconnections are performed on the top of the structure, so that wire bonding is avoided, which is desirable as the wire bonding would influence the operation of the device, by for example causing extra mechanical stiffness and vibration. Furthermore, the wire bonding on the thin structures is avoided.

It is envisaged that the system only comprises two devices, such as the x- and y- motion devices, or the z- and y- motion devices, etc. so that a motion having two degrees of freedom is obtained.

Fig. 31a-b show three dimensional views of the device shown in Figs 10a-b.

Fig. 32a shows an m x n matrix comprising m x n devices. The electrical signals during switching operation are shown in Fig. 32b-c, where Vh denotes a voltage high enough to hold any device in its current position, Vr denotes a voltage (lower than Vh) low enough to release the device and, finally, Va denotes a voltage (larger than Vh) high enough to capture the device, i.e. stretch the main beam. T1 denotes the time-period for releasing the devices and T2 denotes the time-period for capturing the devices. Fig. 33a-b show a preferred implementation of the etching process variation compensation feature, that is to add a triangular shape to the ends of one or more connection beams. In Fig. 33a a triangular shape is added to the ends of the initiation connection beam 11 and also to the ends of the addressing connection beam 13. In Fig. 33b a triangular shape is only added to the ends of the addressing connection beam 13.

Claims

1. An electrostatically driven microstructure device comprising

a substrate having a principal surface

the electrodes being positioned so that no mechanical contact is provided between the at least one addressing connection beam electrode and the at least one corresponding static electrode during operation.

2. A device according to claim 1 , wherein the connection beam(s) comprises the connection beam electrode(s).

3. A device according to claim 1 or 2, wherein the control circuit is adapted to apply an initiation voltage to the at least one connection beam electrode and the corresponding static electrode so that an initiation electrostatic force is applied to at least one connection beam, the initiation connection beam being displaced or deflected so that an initial buckling of the at least one main beam is provided.

4. A device according to claim 3, wherein the initial buckling of the at least one main beam is locked mechanically.

5 5. A device according to claim 3, wherein the initial buckling of the at least one main beam is maintained by applying a maintaining electrostatic force to the connection beam.

6. A device according to claim 1 or 2, wherein the initial buckling of the at least one main beam is performed during manufacturing of the microstructure device.

10

7. A device according to claim 6, wherein the at least one main beam is manufactured having a curved structure forming the initial buckling of the main beam.

8. A device according to claim 1 or 2, wherein the at least one main beam has a 15 predetermined buckling, the buckling being provided by a multilayer main beam comprising at least a first layer having a first property and a second layer having a second property, the connection of at least the first and the second layer introducing a controlled stress in the structure.

20 9. A device according to claim 8, wherein the first layer has a first thermal coefficient of expansion and the second layer has a second thermal coefficient of expansion, the first and the second thermal coefficient of expansion being distinct, whereby a thermal stress is induced in the at least one main beam.

25 10. A device according to any of the preceding claims, wherein the control circuit is adapted to address the position of the at least one main beam by varying the electrostatic force applied to the at least one addressing connection beam by varying the voltage applied to the at least one addressing connection beam electrode and the corresponding static electrode.

30

11. A device according to claim 10, wherein the voltage applied to the addressing connection beam electrode and the corresponding static electrode is varied continuously.

12. A device according to claim 10, wherein the at least one main beam can assume a 35 selected number of stable buckling positions between the stretched position and the at least one end buckling position in response to a corresponding set of selected address voltages applied to the addressing connection beam electrode(s) and the corresponding static electrode(s).

5 13. A device according to any of the preceding claims, wherein the main beam comprises one or more sub-beams arranged in series between the connection beams.

14. A device according to any of the preceding claims, wherein the main beam comprises one or more sub-beams arranged in parallel, the sub-beams being connected to the same

10 connection beams.

15. A device according to any of the preceding claims, wherein one or more connection beam(s) comprise(s) one or more sub-beams arranged in series.

15 16. A device according to any of the preceding claims, wherein the buckling of the main beam is substantially parallel to the principal surface of the substrate.

17. A device according to any of claims 1-15, wherein the buckling of the beam is substantially orthogonal to the principal surface of the substrate.

20

18. A device according to any of claims 1-15, wherein at least one beam comprises at least one process variation compensation feature.

19. A device according to claim 18, wherein the at least one process variation 25 compensation feature is a triangular shape.

20. A device according to any of the preceding claims further comprising at least one shutter plate, the at least one shutter plate being positioned at at least one shutter attachment position on the main beam so that the at least one shutter plate is moved

30 according to the buckling of the main beam.

21. A device according to claim 20, wherein the at least one shutter plate is positioned so that the at least one shutter plate is substantially parallel to the principal surface when the main beam is in the stretched position.

35

22. A device according to claim 21 , wherein the substrate comprises at least one transparent opening positioned so that the at least one shutter plate positioned in at least one buckling position covers the at least one transparent opening.

23. A device according to claim 21 , further comprising at least one electromagnetic radiation source for emission of at least one electromagnetic radiation beam adapted to be transmitted through the at least one transparent opening when the at least one shutter plate is not covering the at least one transparent opening, whereby the at least one shutter plate functions as a shutter for the at least one electromagnetic radiation beam.

24. A device according to claim 23, further comprising at least one optical sensing element positioned so as to receive electromagnetic radiation transmitted through the at least one transparent opening, the at least one optical sensing element being adapted to sense the amount of electromagnetic radiation transmitted through the at least one transparent opening, the shutter plate being adapted to cover a variable part of the transparent opening according to the buckling of the main beam.

25. A device according to claims 23 or 24, wherein the at least one shutter plate has a first surface having a coating so that electromagnetic radiation incident on the first shutter plate surface is selectively absorbed or selectively reflected when the shutter plate covers the at least one transparent opening.

26. A device according to claim 20, wherein the at least one shutter plate is positioned so that the at least one shutter plate is substantially orthogonal to the principal surface when the main beam is in the stretched position.

27. A device according to any of claims 20-26, wherein the at least one shutter plate is positioned on the main beam at at least one shutter attachment position substantially half the length of the main beam from the at least one connection beam so as to obtain maximum displacement of the at least one shutter plate.

28. A device according to any of claims 1-19, further comprising at least one reflective device having at least one reflective surface and being attached to the main beam at at least one first attachment position, the at least one reflective surface forming at least one first angle with a tangent to the at least one main beam first attachment position, the at least one first angle being maintained irrespective of the main beam buckling position and the tangent to the at least one main beam first attachment position forming at least one second angle with the principal surface, so that the at least one second angle is changed according to the deflection of the main beam.

29. A device according to claim 28, further comprising at least one electromagnetic radiation source for emission of at least one first electromagnetic radiation beam towards the at least one reflective surface, whereby at least one corresponding second electromagnetic radiation beam is reflected from the at least one reflective surface, so that the at least one second electromagnetic radiation beam is deflected or displaced according to the buckling position of the main beam.

30. A device according to claim 29, wherein the at least one first attachment position is a position substantially one quarter the length of the main beam from one end of the main beam so as to obtain a maximum deflection of the at least second electromagnetic radiation beam.

31. A device according to claims 29 or 30, wherein addressing of the main beam to assume a selected number of stable positions provides a deflection or a displacement of the second electromagnetic radiation beam according to the selected number of stable positions.

32. A system for two dimensional movement, the system comprising at least a first device according to any of claims 1-19, and a second device according to any of claims 1-19, the first device comprising a first bearing plate, the first bearing plate being connected to first and second parallel main beams of the first device, the first bearing plate comprising the second device, the second device comprising a second bearing plate connected to third and fourth parallel main beams of the second device, the third and fourth main beams being orthogonal to the first and second main beams, whereby the first device is adapted to move or deflect the first bearing plate in a first direction, the second device being adapted to move or deflect the second bearing plate in a second direction so that a two dimensional movement of substantially any position on the second bearing plate is obtained.

33. A system for multi dimensional movement, the system comprising a first device according to any of claims 1-15 and 16, a second device according to any of claims 1-17, and a third device according to any of claims 1-15 and 17, the first device comprising a first bearing plate, the first bearing plate being connected to first and second parallel main 5 beams of the first device, the first bearing plate comprising the second device, the second device comprising a second bearing plate connected to third and fourth parallel main beams of the second device, the third and fourth main beams being orthogonal to the first and second main beams, the second bearing plate comprising the third device, the third device comprising a fifth main beam, whereby the first device is adapted to move 10 the first bearing plate in a first direction in the plane of the principal surface, the second device being adapted to move or deflect the second bearing plate in a second direction, and the third device being adapted to deflect the fifth main beam in a third direction orthogonal to the principal surface so that a multi dimensional movement of substantially any position on the fifth main beam is obtained.

15

34. A device according to any of the preceeding claims, further comprising

a sensing element for sensing any force applied to the sensing element, the sensing element being positioned so that any force applied to the sensing element is transferred to 20 the addressing beam,

25 35. A device according to claim 34, wherein the sensing element is a microphone plate.

36. A device according to claim 34, wherein the sensing element is a seismic mass.

37. A device according to claim 34, wherein the read out element is a capacitive readout 30 element.

38. A device according to claim 34, wherein the read out element is a piezoresistive readout element.

39. A device according to any of the preceding claims, comprising a number of devices, the number of devices being arranged in an m x n matrix configuration.

40. A device according to claim 39, wherein the number of devices are positioned on the 5 same substrate.

41. A device according to any of the preceding claims, wherein actuation forces further comprises thermal and/or piezoelectric actuation.

10 42. A method for repeatedly addressing a device according to claim 39, wherein each device of the matrix configuration comprises one single addressing electrode and all the devices are initiated by applying an initiation voltage, Vinit, to the initiation electrodes of the devices, the method comprising the steps of

15 - holding all the devices by applying default voltages to all rows and columns, respectively, the default voltage being large enough to hold the state of any device,

- addressing the device by

20 - releasing the devices to be released by

- selecting a row containing one or more devices to be released,

- applying a voltage being substantially equal to half the negative release voltage to the selected row, the release voltage being less than the default voltage,

25 - selecting all columns containing one or more devices(s) to be released in the selected row,

- applying a voltage being substantially equal to half the release voltage to the selected column(s),

- whereby the total voltage applied to the devices to be released is substantially 30 equal to or less than the release voltage so that the devices to be released will be released, and applying the default voltages to all rows and columns, respectively, so as to maintain the actual position of all devices, and/or

capturing the devices to be captured by

35 - selecting a row containing one or more devices to be captured,

- applying a voltage being substantially equal to half the negative capture voltage to the selected row,

- selecting all columns containing one or more devices to be captured in the selected row,

- applying a voltage being substantially equal to half the capture voltage to the selected column(s),

- whereby the total voltage applied to the devices to be captured is substantially equal to or above the capture voltage so that the devices to be captured will be captured, and applying the default voltages to all rows and columns, respectively, so as to maintain the actual position of all devices,

- repeating all of the above periodically.

43. A method for repeatedly addressing a device according to claim 39, wherein each device of the matrix configuration comprises two addressing electrodes and all the devices are initiated by applying an initiation voltage, Vinit, to the initiation electrodes of the devices, the method comprising the steps of

- holding all the devices by applying default voltages to all rows and columns, respectively, the default voltage being large enough to hold the state of any device,

addressing the device by

- selecting a row containing one or more devices to be addressed,

- selecting all columns containing one or more devices to be addressed in the selected row,

- applying a voltage being substantially equal to half the capture voltage to both electrodes of the selected column(s), - whereby the total voltage applied to the devices to be addressed is substantially equal to or above the capture voltage so that the devices to be addressed are now captured,

- for each column among the selected columns that should be addressed towards the side of the second electrode, the voltage of the first electrode is returned to the default voltage value before the voltage of the second electrode is returned to the default voltage value,

- for each column among the selected columns that should be addressed towards the side of the first electrode, the voltage of the second electrode is returned to the default voltage value before the voltage of the first electrode is returned to the default voltage value,

- repeating the above until all rows have been scanned for devices to be addressed,

- repeating all of the above periodically.