DE19822677A1 - Planar electrochemical sensor element, e.g. for studying cell growth in biological systems or in small caliber flow-through systems - Google Patents

Abstract

The electrochemical sensor element has planar half-cells comprising precious metal functional layers (2) chemically deposited on nickel-phosphorus coatings (5) on a dielectric substrate (1). The sensor element for electrochemical measurements has one or more planar half-cells which are located on a dielectric (preferably oxide-ceramic or glass) substrate (1) and which comprise metallic functional layers (2) and optionally overlying metallic or nonmetallic layers (3), each half-cell being connected to a conductor line (4) of the same metal as the lowermost metal layer. The metal layers comprise 1-10 mu m thick precious metal (alloy) layers chemically deposited on nickel-phosphorus coatings (5), whereby various chemically deposited metal layers can be provided on a substrate. An Independent claim is also included for the production of the above sensor element in which a dielectric substrate is cleaned and then subjected to a lithographic process for forming a negative image of the sensor element structure.

Description

Field of application of the invention

The invention relates to planar sensor elements for electrochemical measurements and Process for their production

State of the art

In addition to electrochemical sensors in conventional design, e.g. B. with cylinder shaped shafts and z. B. spherical or dome-shaped membranes are also Known sensors in planar design, which for different applications, for. B. for studying cell growth in biological systems or in narrow calibri flow systems are needed. For the sensor structure are generally me metallic functional elements necessary. So are for conductometric sensors mostly the metals gold or platinum used, with several surfaces of these metals form the measuring cell in a defined geometry. For potentiometric determination of the redox potential are preferably indicator electrodes made of platinum or gold applied. Other electrochemical sensors work together effect of metallic electrodes with layers of salt and / or other materials, e.g. B. glazes, or electrodes made of a precious metal.

Planar electrochemical sensors have so far been available in a thick film version on di electrical substrates [see e.g. B. A.A. Shul'ga, B. Ahlers, K. Camman: Ions selective conductometric microsensors: theory and practice. 2. Dresden Sen sor symposium (short versions), Dresden 1995; G. Steiner, K. Camman, B. Ross: Thick-film nitrate sensor with integrated miniaturized reference electrode. Euroses sors 1994. Toluose, April, 25-28 1994 (proc. P. 64); H. Kaden, M. Hösel, M. Brille, W. Oelßner: pH sensor in thick-film technology and process for its production.  

DE 195 06 883 (1995); W. Oelßner, H. Kaden, G. Köhler, B. Hegewald: Iridium oxides Electrode for measuring the pH value and process for its production. DE 4 40 662 (1994); W. Vonau, H. Kaden, C. Kretzschmar, P. Otschik, I. Krabbes, W. Woithe, M. Große (1997): Electrochemical sensor and method for its production. P 197 14 474.8] and in thin film technology [M. Lamprechts, W. Sansen: Biosensors: Micromechanical devices. Institute of Physics Publishing. Bristol, Philadelphia, New York. 1992; W. Oelßner: ISFET - advantages and problems. Achema magazine (Frank furt / Main) (1991) 48-54].

Criticism of the state of the art

The economy of thin film products is general Experience is only given for quantities <100,000 per year, due to high Investment costs for the acquisition of equipment for implementation of thin film technology. By contrast, products manufactured using thick-film technology can produce profitably from a requirement of a few hundred pieces per year be decorated. However, electrochemical sensors are not used for the users profitable production figures.

The thickness of the precious metal layers that can be produced using thin-film technology is ≦ 1 µm. In the cases in which a partial chemical conversion is required for sensor production these layers (for example by forming AgBr from silver according to: Ag + Br → AgBr + e⁻) is necessary, there is a risk with thin layers of metal, that all the metal is implemented. There would then be no electron conductor Derivation of the sensor signal are available. Furthermore, the layer is on construction on the silicon substrates up to the external metallic use layer very complex and can therefore only be realized with great effort. In the case of egg ner Pt thin film electrode is e.g. B. the layer sequence silicon-silicon dioxide Silicon nitride titanium platinum usual, with appropriate gold electrodes Zwi layer layers of Ni and nickel / chrome can be produced. When separating the Electrodes produced on a wafer become conductive at the edges of the substrate  full silicon exposed by subsequent steps, such as anodic oxidation or capping with resins, must be isolated.

The use of thick-film technology has the disadvantage that Addition of additives to the thick-film pastes, e.g. B. organic or inorganic binders, foreign substances introduced into the layers to be produced become. This proves to be unfavorable if these foreign substances interfere de Interactions between the functional layer of the sensor and constituent len of the measuring media occur. For example, an organic binder can Contact of the thick-film structure with organic solvents at higher temperatures instruments are at least partially attacked. In addition, it can be too chemi reactions between the fine-grained metal in the thick layer and the as Binder acting substance come. Furthermore, the electrical properties give way through the application of metal layers produced in thick-film technology Foreign substances undesirably from those of pure metals. The result is that the higher internal resistance of the thick film sensors Similar sensors with functional elements made of compact metal bodies, such as Wires and sheets, can lead to measurement problems. In case that in the manufacturing process of the sensor metal layers by subsequent chemical Reactions that need to be modified are also reduced conductivity disadvantageous. The high temperatures necessary for baking the pastes can adversely affect in a variety of ways, e.g. B. on the dimensional stability of Glass substrates.

task

The invention has for its object a sensor element for electrochemical Measurements to create one or more metal arranged side by side ical surfaces on a planar substrate that ge adherent and resistant compared to electrolyte solutions. It is another object of the invention to provide a technical scale rationally feasible manufacturing process for such a to show the sensor element.  

solution

According to the invention the object is achieved in that a coating of nickel phosphorus (unstoichiometric connection of both elements, hereinafter referred to as NiP) with a phosphorus content between 8 and 11 percent by mass or several coatings 5 of NiP on oxide-ceramic or glass substrates 1 without current brought up and these are covered with one or more electroless or electrodeposited precious metal or precious metal alloy layers 2 . To form a defined sensor surface, an insulating protective layer 6 , possibly with windows, is applied over the metal structure (s). In addition, additional metals can be electroplated onto the metallic layer system. Further structural elements can be present on the substrate, which are either identical or different in structure with regard to their geometric shape and composition. Several structural elements located on the substrate can be interconnected to form a sensor, e.g. B. as a three-electrode measuring cell, consisting of spatially separated working electrode with the layer structure NiP / Au, reference electrode with the layer structure: NiP / Au / Ag / AgCl and counter electrode with the layer structure: NiP / Au. Several individual sensors can be used as a multi-sensor module, for example as an amperometric two-electrode measuring cell with the layer structure NiP / Au / Ag / AgCl as anode and NiP / Au as cathode, redox electrode with the layer structure NiP / Au and reference electrode with the layer structure NiP / Au / Ag / AgCl work together.

The structures are electrically contacted via the electrical interconnects 4, which are also produced by chemical metal deposition, by means of a plug or bond connection 8 with a discharge cable 7 .

Embodiment

The following steps for producing a sensor for the potentiometric determination of the redox potential are carried out on an aluminum oxide ceramic substrate (purity <99.9%) 1 :

• 1. Clean the substrate surface from dust, dirt, grease and adhering Contamination by treatment with an alkaline hot degreaser 60 ° C and then with acetone, subsequent pickling with 20% NaOH solution at 60 ° C
• 2. Complete coating of the substrate surface with photoresist
• 3. Exposing the photoresist with structure negative using UV radiation. According to Figure 2, the structure consists of two rectangular areas and the electrical conductor tracks.
• 4. Open the windows to be metallized in the photoresist
• 5. Sensitize the substrate surface with tin (II) ions at room temperature
• 6. Reduction of Pd (II) ions on the substrate surface to form palla germinating
• 7. Deposition of a phosphorus-rich NiP coating 5 in the electrolyte, the layer thickness not exceeding 1 .mu.m, since otherwise the Entlac ken is no longer possible
• 8. Remove the lacquer structure with acetone in an ultrasonic bath
• 9. electroplated gold layer (gold content <99.9 mass percent) 2 on NiP structures 5 based on a potassium gold cyanide electrolyte with a gold concentration of 12 g / l Au at pH = 7 and a temperature of 50 ° C. with a deposition rate of 0 , Deposit 15 µm / min
• 10.Bonding two cables 7 to the interconnects 4
• 11. Application of an insulating cover layer with window (s) 6 over metal structures. The insulation material consists of epoxy resin, which is applied using the casting process. The resin is trough-shaped around at least one of the two gold structures, ie there is a resin overhang of at least 1 mm.
• 12. Generation of additional layers 3 in one or both of the windows
  The gold layer is chemically silver-plated and the resulting silver is electrochemically converted to AgCl. Subsequently, a polymer gel filled with potassium chloride based on polyvinyl alcohol is introduced into the tub formed by the insulating material and a thin membrane is deposited over it by applying a mixture of 10% cellulose acetate in acetone or 7.5% cellulose triacetate in methylene chloride.

Advantages of the invention

The advantage of the invention is that a planar sensor element for electro chemical measurements with both mechanical and under the influence of elec trolytic solutions of adherent structured structured functional layers What is available is by demolition tests and polarization tests in electrolytic Solutions was proven, these metallic layers with an inexpensive Technology can be generated. Structure widths of at least 50 µm can be achieved achieved and both similar and different metallic layers are applied to a substrate using identical methods.  

Reference list

1

Substrate

2nd

metallic functional layer

3rd

further functional layer (s)

4th

electrical interconnect

5

Ni-P coating

6

Sheathing material

7

electric wire

8th

Solder or bond point

Illustrations

Fig. 1
Cross section through the sensor element according to the invention for electrochemical measurement solutions

Fig. 2
Top view of an embodiment of the sensor element according to the invention for redox potential measurement.

Claims (14)

1. Sensor element for electrochemical measurements with one or more plan, on a dielectric substrate ( 1 ), preferably oxide-ceramic or glass, located half-cells, either only from metallic functional layers ( 2 ) or in addition to these from other overlying metallic or not metallic layers ( 3 ), each half cell being connected to an electrical interconnect ( 4 ) made of the metal of the lowest metal layer, characterized in that the metal layer is in each case made of nickel-phosphorus coatings ( 5 ) by chemical means applied noble metal or noble metal alloy layers with thicknesses of 1 to 10 microns, wherein different layers of chemically applied metal layers may be present on a substrate. 2. Sensor element according to claim 2, characterized in that the nickel-phosphor coating ( 5 ) has a thickness of 3 microns. 3. Sensor element according to claims 1 and 2, characterized in that the Nickel-phosphorus coating contains 8 to 11 percent by mass of phosphorus. 4. Sensor element according to claims 1 to 3, characterized in that the on the nickel-phosphor coatings ( 5 ) applied precious metal or Edelme tall alloy layers are structured. 5. Sensor element according to one or more of the preceding claims, characterized in that the noble metal or noble metal alloy layers ( 2 ) produced by chemical means by chemical or electrochemical reactions, for. B. chlorination of silver, partially on the side facing the substrate ( 1 ) implemented or electrolessly or electrolytically coated with other metals ( 3 ). 6. Sensor element according to one or more of the preceding claims, characterized in that over the noble metal or noble metal alloy layers ( 2 ) or over the additional layers produced by chemical or electrochemical implementation of these layers or by galvanic or electrolytic metal deposition other methods, e.g. B. layers produced by screen printing of chemically active pastes are present. 7. Sensor element according to one or more of the preceding claims, characterized in that the coated substrates ( 1 ) are assembled, ie provided with electrical conductors ( 7 ) or plug connectors on the interconnects ( 4 ) via soldering or bonding points ( 8 ) and are coated with insulating capping materials ( 6 ) in such a way that defined areas of the respective outer layers for signal generation with measuring media are exposed. 8. Process for the production of sensor elements for electrochemical measurements according to the preceding claims, characterized in that according to the Cleaning a dielectric substrate in a photolithographic process the negative image of the structure provided for the sensor element is generated. 9. The method according to claim 8, characterized in that the substrate surface, which is structured in the presence of at least two insulated lying lying areas, generated by photolithography, is sensitized, activated and electrolessly metallized with a NiP coating ( 5 ), the NiP layer must not exceed a thickness of 0.1 µm. 10. The method according to claims 8 and 9, characterized in that the ge entire sample is stripped and thereby the metal structure is determined. 11. The method according to claims 8 to 10, characterized in that the NiP Coating is electrolessly or galvanically reinforced. 12. The method according to claims 8 to 11, characterized in that the reinforced NiP stop layer ( 5 ) is chemically coated with a noble metal, preferably gold, palladium or silver, whereby any number of flat, linear or point-shaped structural elements who can. 13. The method according to claims 8 to 12, characterized in that all or only some of the noble metal layers produced by chemical means (2) are covered by additional, overlying these layers (3) by partial electrochemical mix or chemical reaction of the noble metal layers, . 14. The method according to claims 8 to 13, characterized in that the substrate carrying all the structural elements ( 1 ), including the deflection paths ( 4 ) produced according to the method specifications of claims 8 to 12 and possibly additional layers ( 3 ) is assembled, that is, it is contacted on the interconnects ( 4 ) and by extrusion coating or encapsulation with non-conductive sheathing materials ( 6 ), such as polypropene or epoxy resins, to protect them from attack by measuring media.