DE10129986C2 - Sensor for measuring the presence and concentration of components in a liquid - Google Patents

Description

The invention relates to a chemical sensor for measuring the presence and the Concentration of components in a liquid. According to the preamble of Claim 1 is intended for a solid-state sensor based on semiconductors, the swellability suitable polymer networks against single or multi-component liquids be used.

It is known that polymers can change their properties through absorption of chemical species: in bimorph moisture and gas sensors there are polymer layers on thin silicon membranes (DE 41 05 440 A1) or bending structures (US 5 563 341). By absorption of certain gas components, e.g. Swelling is then caused (K. Sager, A. Schroth, A. Nakladal, G. Gerlach: Humidity-dependent mechanical properties of polyimide films and their use for IC-compatible humidity sensors. Sensors and Actuators A, 53 ( 1996 ), 330), which lead to the deflection of the membrane or bending structure via the bimorph effect (G. Gerlach, K. Sager: A piezoresistive humidity sensor. Sensors and Actuators A, 43 ( 1994 ), 181). This deflection can then be done with known electromechanical transducer mechanisms, e.g. B. by means of piezoresistive resistors in the membrane or bending structure or by a capacitive arrangement of deflected membrane and counterelectrode, in an electrical output signal.

While polyimide or polyethersulfone for moisture and gas sensors as polymer Layer can be used advantageously, they are for sensors that the application or the concentration of certain chemical components in liquids should detect, mostly unsuitable, since water is always used as a solution component Saturation concentration in the polymer leads.

However, it is known that certain polymer networks in liquids have a volume phase transition with a large volume change depending on the concentration and type of certain components (SH Gehrke: Synthesis, equibrillium swelling kinetics, permeability and application of environmental responsive gels. Adv. Polym. Sci. 110 ( 1993 ), 80-144).

It is only this property of the so-called smart polymer networks that makes them suitable for Liquid sensors can be used. The fact that for each state of the liquid exactly one Degree of swelling of the polymer network exists and this effect is reversible assignable measurement signal available. Polymer networks without that Volume phase transition behavior can and only escape to a limited extent due to the significantly reduced effect reversibility unsuitable for the Application as a measuring transducer.

Sensitive polymer networks as transducers for liquid sensors or suitable transducer principles are known from the following documents:

• - The particle absorption in the polymer layer changes the mass of the layer and thus the resonance frequency of a vibrating structure if the layer is part of the vibrating structure (DE 198 48 878 A1; A. Schroth, K. Sager, G. Gerlach, H. Häberli, T. Boltshauser, H. Baltes: A resonant polyimide-based humidity sensor. Sensors and Actuators B, 34 ( 1996 ), 301). The change in the resonance frequency then forms the electrical output signal.
• - The change in mass of a polymer layer due to particle absorption can can also be converted into an electrical output signal when the Po polymer layer is part of a delay line or resonance body, where in particular a wave propagation on the surface of a solid or the Frequency change due to the variable mass of the layer on it Layer is influenced (DE 198 48 878 A1). This measuring principle has as The main disadvantage is the limited miniaturization of the sensor. Commonly used AT quartz crystals have e.g. B. diameter from 10 to 20 mm.

Polymer networks with a volume phase transition, that is, smart polymer networks, are known from the following documents:

• - Hydrogels made of polyvinyl alcohol / polyacrylic acid show a pH-sensitive volume phase transition (K.-F. Arndt, A. Richter, S. Ludwig, J. Zimmermann, J. Kressler, D. Kuckling. H.-J. Adler: Poly (vinyl alcohol) / poly (acrylic acid) hydrogels: FT-IR spectroscopic characterization and work at transition point. Acta Polymerica 50 ( 1999 ), 383-390).
• - Copolymers of N-isopropylacrylamide with comonomers which contain acidic or basic groups show a temperature-dependent volume phase transition, the temperature of the volume phase transition being adjustable by the pH of the swelling agent (D. Kuckling, H.-J. Adler, K. Arndt, L. Ling, W.-D. Habicher: Temperature and pH-depending on solubility of novel PNIPAAm-copolymers. Makromol. Chem. Phys. 201 ( 2000 ), 273-280).
• - In aqueous solvent mixtures, the phase transition temperature changes in polyacrylamide depending on the concentration and the type of component added (HG Schild, M. Muthukumar, DA Tirrell: Cononsolvency in mixed aqueous solutions of poly (N-isopropylacrylamide). Macromolecules 24 ( 1991 ) , 948-952). The polymer networks therefore show a swelling depending on the concentration and the type of organic solvent component at constant temperature.
• - Polymers (organogels) that swell in organic solvents can also have volume phase transitions, as demonstrated using the example of a polydimethylsiloxane network in mixed solvents (L. Rogovina, V. Vasiliev, G. Slonimsky: Influence of the thermodynamical quality of the solvent on the properties of polydimethylsiloxane networks in swollen and dry state. Progr. Colloid & Polymer Sci. 90 ( 1992 ), 151-155).

DE 198 28 093 now proposes sensitive polymer networks as a measurement to use size sensors to measure pH values, ion and substance concentrations or Contents of dissolved, undissolved or dispersed organic or inorganic Measure materials.  

In one of the proposed forms of the measurement transducer, the sensori sher effect evaluated the swelling behavior, wherein in the embodiments Polymer network as a free-standing, large volume working against a spring Material or as a flat carrier material carrying a strain gauge is. Both solutions have decisive disadvantages: they are not in this form can be miniaturized and the liquid works with the components to be measured directly on the electrical sensor components.

In DD 236 173, DE 43 12 788 C2, DE 198 42 514 C1 and US 5 563 341 are for Bimorph moisture and gas sensors presented solutions in which such sensors are miniaturized by the swellable polymers used there on the Surface of a thin membrane or bending structure inside a silicon chip is applied, below the polymer in the silicon piezoresistors as me chanoelectric transducer elements are introduced. Such a solution is again not for chemical sensors for liquids based on polymer networks usable because the liquid, unlike moist air and gases in all of them so far known cases, the piezoresistors in the long term also through the usual used passivation layer between polymer and silicon impaired and especially with the required contact points, which follow the resistors Connect electrically on the outside, causing corrosion. Furthermore, in the above-mentioned. polymeric networks the modulus of elasticity is considerably smaller than that for the polymers observed with the bimorph gas and moisture sensors, so that the through Swelling in the polymer network caused stress only as out-of-plane Component acts and therefore too small for practical applications Deflection of the membrane or the bending structure leads.

The object of the invention is therefore a sensor for measuring the presence and the concentration of components in a liquid based on the To indicate swelling / de-swelling of polymer networks, which is based on semiconductors a mechano-electric converter is feasible and a sufficiently large one Deformation of the mechanoelectric converter and thus a practically usable one electrical output signal generated.  

According to the invention, the object is achieved by a sensor having the features mentioned in the preamble of claim 1 in that

• The swellable polymer is a polymer network with volume phase transition,
• - The polymer network introduced into the thinned area and the mechanoelastic transducers on the undiluted side of the semiconductor chip is upset
• - The thinned area with the polymer network introduced by one Cover is closed, whereby
• - Via openings in the cover the polymer network from one to the Sensing chemical component contained liquid can be rinsed.

Advantageous further developments and refinements are the subject of Dependent claims.

According to the invention, the front and back of a semiconductor chip mechanoelastic transducer and action side of the liquid to be measured on the sensitive polymer network separated by the mechanoelastic transducer the undiluted front or top of the semiconductor chip, while in diluted volume the polymer network is introduced. So despite the low modulus of elasticity and the unfavorable transverse contraction number the polymer Network when exposed to the correspondingly sensitive components of the liquid a target of practically well evaluable deformation of the thinning in Semiconductor chip can be achieved, is the open back of the invention diluted volume closed by a cover with openings. This Openings are used to introduce a defined amount of the polymer network and are either so small that the polymer network does not swell out is possible or will be direct (cover) or indirect (e.g. stronger networking of Network surface closed in the area of the opening). At least one more each The opening remains intact and serves to supply and remove the liquid to be measured. The amount of polymer network introduced is such that the thinned area is not completely filled even when swollen and through the diagonally opposite openings on the volume edge to Feeding and removing the liquid to be measured, rinsing the polymer Network is given at all times.  

Through this arrangement according to the invention, on the one hand, the strict separation of electromechanical transducer and liquid and thus a long-term stable sensor without influencing the electrical components of the electromechanical converter reached. On the other hand, the flow principle means that the response time is short Minimization of diffusion obstacles.

The sensor according to the invention can have a number of further developments and modifications have events.

The thinned area of the semiconductor chip, which is a deformable membrane, can itself be the mechano-electric converter, in that it contains piezoresistors, which the deformation of the membrane into a change in resistance of the piezoresistor and thus performs in an electrical signal. The deformable thinned area the semiconductor chip can also be coated with an electrode, which is a part of a variable capacitor. More mechanoelectric Conversion mechanisms, such as B. mechano-optical, magneto-optical and others are also possible with the sensor according to the invention.

The covering of the filler openings for the polymer network can be covered by the polymer network itself be formed by an increased surface Stiffness that can be achieved by locally variable networking gradients. This is, for example, treatment by means of UV radiation, plasma treatment, Laser radiation or ion implantation possible.

The network can be designed in the form of one or more spherical particles. Due to the resulting greatly enlarged surface of the sensitive Polymer network and the distance between the particles in connection with the Flow principle allows the liquid to flow faster into or out of the polymer network diffuse so that the sensor has shorter response times.

The invention is explained in more detail below on the basis of exemplary embodiments. In the drawings show:

FIG. 1a is a first embodiment of a sensor embodying the present invention with piezoresistive mechanoelektrischer conversion, wherein the poly mernetzwerk in the unswollen state,

FIG. 1b, the sensor of Fig. 1a, wherein the polymeric network is by a flow of the sensitive components in the liquid in the swollen state,

Fig. 2 shows a second embodiment of a sensor embodying the present invention with a mechanoelectric transducer on a capacitive basis,

Fig. 1a and Fig. 1b show an embodiment of a sensor according to the invention for measuring the presence and concentration of chemical components, such as. B. alcohol, in liquids 1 , wherein the chemical component in the liquid 1 causes swelling or de-swelling of the polymer network, for example the neutral hydrogel poly-N-isopropylacrylamide, 2.

The polymer network 2 is located in a semiconductor chip 3 in a thinned area 4 , but also only partially fills it in the swollen state ( FIG. 1b). The surface of the semiconductor chip 5 lying opposite the thinned region 4 forms or contains, in whole or in part, the mechanoelectric converter, here piezoresistors 8 . Piezo resistors 8 and liquid 1 to be measured are therefore on opposite sides of the semiconductor chip 3 and are therefore strictly separated from one another. The sensor also contains a cover 6 on the side of the liquid 1 , which is perforated here with at least one opening 7 a in order to be able to introduce the polymer network 2 . However, the openings 7 a of the cover 6 are so small and the cover 6 mechanically so stiff that when the polymer network 2 swells, the semiconductor chip 3 is deflected in the thinned area 4 ( FIG. 1 b) and thus a change in resistance of the piezoresistor 8 is generated. The liquid 1 is passed through further openings, of which at least one 7b serves for the inflow and at least one further 7c serves for the outflow of the liquid 1 , which flows directly around the polymer network 2 in the cavity between the thinned area 4 and the cover 6 .

Fig. 2 shows an embodiment in which, in contrast to Fig. 1a and 1b of me chanoelektrische converter by electrodes 11a and 11 is formed b, one of the electrodes 11 b on a plate 9 via spacers 10 serves as a fixed reference element of the capacitive evaluation and a change in capacity takes place due to the deformation of the thinned region 4 with the electrode 11 a resulting from the swollen polymer network 2 . When using the polyelectrolytic hydrogel polyvinyl alcohol / polyacrylate acid, a volume phase transition z. B. triggered by the presence of ions, in particular by the pH.

LIST OF REFERENCE NUMBERS

1

liquid

2

polymer network

3

Semiconductor chip

4

thinned area

5

Surface of the semiconductor chip

6

cover

7

opening

8th

piezoresistive

9

chip

10

spacer

11

electrode

Claims (9)

1. Sensor for measuring the presence and concentration of components in a liquid, consisting of a semiconductor chip ( 3 ) with a surface which forms or contains a mechanoelectric transducer in whole or in part, with a thinned area ( 4 ) and surrounded by an edge with a swellable polymer sensitive to the components to be measured, characterized in that
the swellable polymer is a polymer network ( 2 ) with volume phase transition,
introduced the polymeric network (2) in the thinned-down region (4) and the mechanoelectrical transducer is applied to the side of the nichtabgedünnten region (4) of the semiconductor chip (3),
the thinned area ( 4 ) with the introduced polymeric network ( 2 ) is closed by a cover ( 6 ), wherein
Via openings ( 7 b, 7 c) in the cover ( 6 ) the polymer network ( 2 ) can be flushed by the liquid containing the components to be measured. 2. Sensor according to claim 1, characterized in that the cover ( 6 ) is a perforated plate. 3. Sensor according to claim 1 or 2, characterized in that in the cover at least one closable opening ( 7 a) for introducing the polymer network ( 2 ) is provided in the thinned area ( 4 ). 4. Sensor according to one of claims 1 to 3, characterized in that the volume between the thinned area ( 4 ) and cover ( 6 ) in the swollen state of the polymer network ( 2 ) with the liquid ( 1 ) can be rinsed. 5. Sensor according to one of claims 1 to 4, characterized in that the cover ( 6 ) contains additional openings which, as diagonally opposite inlet and outlet openings, allow the flow of the liquid ( 1 ) containing the components to be sensed and not due to the change in volume be closed. 6. Sensor according to one of claims 1 to 5, characterized in that the cover ( 6 ) consists of silicon or a glass. 7. Sensor according to any one of claims 1 to 6, characterized in that the opening ( 7 a) for introducing the polymer network ( 2 ) can be closed by changed properties of the polymer network ( 2 ). 8. Sensor according to one of claims 1 to 7, characterized in that the polymer network ( 2 ) with volume phase transition is a hydrogel. 9. Sensor according to one of claims 1 to 8, characterized in that the mechanoelectric converter is a piezoresistor ( 8 ).