NANOSTRUCTURED TITANIUM MULTILAYER ELECTRODE

Abstract

A multilayer electrode on a substrate (10) comprising titanium (20) and titanium-rich titanium nitride (30) and titanium-poor titanium nitride (40), particularly suitable for the application to thermoplastic substrates, in particular for the purpose of the impedance measurement in aqueous biological media, and method for the production thereof.

Claims

1. A titanium electrode (50) for impedance measurement in aqueous biological media, comprising on a substrate (10): a Ti carrier layer (20), consisting of comprising elemental titanium (Ti), one or more titanium-rich titanium nitride (TiN.sub.x) intermediate layer (30, 32) comprising TiN.sub.x, with x smaller than 1 or x equal to 1, disposed on the Ti carrier layer, and a titanium-poor titanium nitride (TiN.sub.y) cover layer (40), comprising TiN.sub.y with y greater than 1, disposed on the titanium-rich TiN.sub.x intermediate layer.

2. The titanium electrode (50) according to claim 1, wherein the thickness of the TiN.sub.y cover layer (40) is 0.5 to 10 times, the thickness of the TiN.sub.x intermediate layer (30).

3. The titanium electrode (50) according to claim 2, wherein the three electrode layers (20, 30, 40) have a thickness ratio of 1-5/1/0.5-10, based on Ti carrier layer (20)/TiN.sub.x intermediate layer (30)/TiN.sub.y cover layer (40).

4. The titanium electrode (50) according to claim 1, wherein each TiN.sub.x intermediate layer (30, 32) has a thickness from 100 to 500 nm.

5. The titanium electrode (50) according to claim 1, wherein the TiN.sub.x intermediate layer (30, 32) consists of TiN.sub.x, with x from 0.3 to 1.0.

6. The titanium electrode (50) according to claim 1, wherein the TiN.sub.y cover layer (40) consists of TiN.sub.y, with y from 1.1 to 1.5.

7. A measuring module (150, 160, 180) for impedance measurement in aqueous biological media, comprising: a polymeric substrate (10) for guiding liquid medium, and a titanium electrode (50) according to claim 1, which is deposited immediately on the substrate.

8. The measuring module according to claim 7, wherein the polymeric substrate (10) is selected from the group consisting of polystyrene (PS), polyamide (PA), acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), polycarbonate (PC), polyethylene terephthalate (PET), polyethylene (PE), polycaprolactone (PCT), polypropylene (PP), polyetheretherketone (PEEK), polyimide (PI), polyurethane (PU), polyvinylchloride (PVC), and combinations, mixtures, and co-polymers thereof.

9. The measuring module according to claim 7, which is provided as a cell culture vessel, a multi-well plate, a membrane reactor, a hollow fiber module, or a hose connecting piece.

10. A method for preparing a titanium electrode (50) for impedance measurement by means of reactive cathode sputtering in a process gas containing argon (Ar) and nitrogen (N.sub.2), comprising the steps: b) sputtering titanium onto a titanium-covered substrate of the electrode at increased generator power, in order to deposit at least a first titanium nitride intermediate layer (30), comprising titanium-rich TiNx with x smaller than 1 or x equal to 1, on a titanium layer (20), c) reducing the generator power, and d) sputtering titanium onto the substrate at the reduced generator power in order to deposit a titanium nitride cover layer (40), comprising titanium-poor TiNy with y greater than 1 on the titanium nitride intermediate layer (30, 32) formed in step b).

11. The method according to claim 10, wherein the steps b) and c) are passed through several times, in order to deposit at least one further titanium nitride intermediate layer (32), comprising the titanium-rich TiNx, on a first titanium nitride intermediate layer (30), wherein in steps c) for each pass-through the generator power is in each case reduced as compared to the previous pass-through, in order to form a titanium-poorer further titanium nitride intermediate layer (32) on one of the respective titanium-richer titanium nitride intermediate layer (30), which had in each case been deposited beforehand.

12. The method according to claim 10, wherein the increased generator power in step b) is 1.2 to 2.4 times the generator power in step d).

13. The method according to claim 10, wherein the composition of the process gas (Ar/N.sub.2), based on the N.sub.2 partial pressure, is held constant while performing steps b) to d).

14. The method according to claim 10, further comprising a step preceding step b): a) depositing a titanium layer (20) on an electrode substrate (10).

15. A method for producing a measuring module for the impedance measurement in aqueous biological media, comprising the steps: providing the media-guiding module as substrate of the electrode, and depositing the titanium electrode on this substrate by means of the method according to claim 13.

Description

[0043] The invention will be described by means of the following figures and examples, which should not be understood as being limiting.

[0044] FIGS. 1A and 1B show a schematic view of a measuring module according to the invention in the form of a connecting piece (150). The illustration is not scaled. A multilayer titanium electrode (50) according to the invention is formed on a carrier, which is tubular on principle, of polymer as substrate (10), at least on a portion. As shown in the sectional view in FIG. 1A (sectional plane A as in FIG. 1B), said titanium electrode in each case has a three-layer setup: a titanium layer (20) is deposited directly on the substrate (10), on it a titanium-rich TiN intermediate layer (30), on it a titanium-poor TiN cover layer (40). The diagonal view in FIG. 1B shows the connecting piece (150) for guiding liquid medium (arrow) with the titanium electrode (50), which extends into the media-guiding interior (lumen) of the tubular carrier (10) and, for the purpose of the electrical contacting, also towards the outer side, in the illustrated preferred variation.

[0045] FIG. 2 shows a schematic cross-section through a measuring arrangement according to the invention comprising cell culture plate (multi-well plate) comprising several depressions (wells) (130) arranged next to one another on a common carrier (120). A multilayer titanium electrode (50) according to the invention is formed directly on the bottom of each depression (130). In the illustrated embodiment, an electrical conductor track (134) leads from the electrode (50) at least to the upper edge of the depression (130) and provides for the electrical contacting. FIG. 2 additionally shows a cover or stamp (110), which can preferably be used. The latter has electrode carriers (112), which, when in use, can each be lowered into the depressions (130) of the multi-well plate. A multilayer titanium electrode (50) according to the invention is in each case formed on the electrode carriers (112). When in use, it forms the electrical counter electrode to the electrode on the bottom of the depression (130) of the multi-well plate.

[0046] FIG. 3 shows a schematic cross-section through another measuring arrangement according to the invention for use with a conventional cell culture plate (multi-well plate) comprising several depressions (wells) (130) arranged next to one another on a common carrier (120). The measuring arrangement according to the invention is formed as cover or stamp (110). The latter has upper electrode carriers (112) and lower electrode carriers (114), which, when in use, can each be lowered into the depressions (130) of the multi-well plate. A multilayer titanium electrode (50) according to the invention is in each case formed on the electrode carriers (112, 114). When in use, upper electrode carrier (112) and lower electrode carrier (114) serve as electrode and counter electrode in the respective depression (130).

[0047] FIG. 4 shows a schematic perspective partially cut view of a measuring module according to the invention in the form of a connecting piece (160) for guiding liquid medium (arrows). The illustration is not scaled. A carrier of polymer, which is in principle net-shaped or grid-shaped, which serves as substrate for the multilayer titanium electrode (50) according to the invention, is used in the media-guiding lumen (162) of the connecting piece (160). A contacting element (164) serves for the electrical connection. The contacting element (164) can be formed by the coated carrier itself.

[0048] FIG. 5A shows a schematic cross-section through a typical layer sequence of a three-layer titanium electrode (50) according to the invention, which, deposited on a substrate (10), forms the basic configuration of a measuring module according to the invention: A Ti layer (20) is deposited directly on the substrate (10), on it a titanium-rich TiNx intermediate layer (30), on it a titanium-poor TiNy cover layer (40).

[0049] FIG. 5B shows a schematic cross-section through a typical layer sequence of a multilayer titanium electrode (50) according to the invention comprising more than one TiNx intermediate layer: A Ti layer (20) is deposited directly on the substrate (10), on it a first titanium-rich TiNx.sub.n intermediate layer (30), on it at least one further titanium-rich TiNx.sub.n+1 intermediate layer (32), but which is titanium-poorer than the TiNx.sub.n intermediate layer, on which it is deposited, finally on it a titanium-poor TiNy cover layer (40).

[0050] FIG. 6 shows a SEM image of a cross-section through a three-layer titanium electrode (50) according to the invention: a layer of elemental titanium is deposited directly on the substrate, on it a titanium-rich TiNx intermediate layer with a dense structure, on it a titanium-poor TiNy cover layer with open structure.

[0051] FIGS. 7A and 7B show Bode diagrams of the impedance curve of actual thin titanium electrodes: A=three-layer titanium electrode according to the invention, B=simple Ti/TiN electrode. FIG. 7A shows the amplitude curve (ohmic portion), FIG. 7B shows the phase curve.

[0052] FIG. 8 shows a schematic cross-section through another measuring arrangement according to the invention in the form of a conventional membrane reactor or dialyzer comprising a housing (182) and semi-permeable hollow membranes (184) arranged therein. The interior of the hollow membranes (184) can be perfused via inlets and outlets (186). Separated therefrom, the space surrounding the hollow membranes (184) can be perfused via dialysate inlets and outlets (188). According to the invention, a three-layer titanium electrode (50) is in each case formed at least on an inlet or outlet (186) and at least one dialysate inlet or outlet of the (188), in order to provide for an electrical measurement of the impedance via the hollow membranes (184). A colonization or blockage of the membrane can thus be detected and quantified externally by means of continuous electrical measurements.

EXAMPLE 1

PVD Process for Producing TiTiN Electrode Layers

[0053] The thermoplastic substrate, on which the titanium electrode is to be created, is placed into a PVD coating chamber, and a vacuum with a pressure of 110.sup.6 mbar or lower is attained in the chamber via vacuum pumps (booster pump and turbo pump) after approximately 14 to 18 hours.

[0054] Coating preparation 1: The chamber is flooded 5 min prior to the beginning of the coating with a flow of 274 sccm of argon, wherein the gas flow is controlled and regulated by means of mass flow controllers.

[0055] Coating 1: titanium carrier layer: Coating is started with 500 W RF generator power at 274 sccm of argon flow. When plasma ignites, argon flow is directly regulated down to 100 sccm. The setting of the pure argon flow takes place within a few seconds after the ignition. A 274 sccm flow is only required to facilitate the plasma ignition. The coating duration is 5 to 30 minutes, depending on the thermal capacity of the substrate material. Here, benchmarks are 5 min in the case of polystyrene, 15 min in the case of polyamide, 30 min in the case of stainless steel substrates.

[0056] Between the Ti coating and subsequent TiNx coating, the substrates, which are now coated with titanium, are left in the evacuated coating chamber at an argon-gas flow of 100 sccm. They cool down for 1 to 2 hours under these conditions.

[0057] Coating preparation 2: 5 min prior to the beginning of the coating, argon flow is increased from 100 sccm to 274 sccm. In addition, a nitrogen flow of 2 sccm is additionally admixed, in order to create the process gas

[0058] Coating 2: TiNx intermediate layer: The coating is started with 800 W RF generator power at 274 sccm of argon and 2 sccm of N2 flow. When plasma ignites, argon flow is directly regulated down to 180 sccm, in order to create the actual process gas. (The setting of the pure argon flow takes place within a few seconds after the ignition. The 274 sccm flow is only required to facilitate the plasma ignition.)

[0059] The coating duration for the titanium-rich TiNx layer is approximately 2 minutes and, in the case of thermally stable substrates (e.g. stainless steel), can be increased to 3 minutes in individual cases.

[0060] If a titanium electrode comprising several titanium-rich intermediate layers is to be created, the generator power can be lowered in smaller stages, depending on the desired titanium content for depositing purposes. In the case of each lowering of the generator power, an intermediate layer comprising a lower titanium content than the previous layer is deposited. It may be required to increase the increased argon flow at the beginning of the deposition or to maintain the argon flow increase for the entire duration of the deposition of at least the TiNx intermediate layer.

[0061] Coating 3: TiNy cover layer: After 2 or 3 minutes of coating, respectively, with the titanium-rich TiNx layer at 800 W, the generator power is regulated down to 500 W. The process gas mixture remains unchanged (180 sccm of argon and 2 sccm of N2 flow). The sputtering process is not stopped. The deposited titanium-rich TiNx layer can now be coated with a titanium-poorer TiNy layer. The coating duration depends on the desired electrical properties of the electrode (necessary layer thickness) and on the thermal stability of the substrate. Here, guide values are: polystyrene: 5 to 15 min, polyamide: 30 min, stainless steel: 90 min to 150 min. After this time, the generator is turned off in order to stop the coating.

[0062] Conclusion of the coating process: After the generator is turned off, the coated substrates remain in the process gas atmosphere, depending on the previous coating time, while the pumps are running The cool-down time corresponds to half the coating time. After this first cool-down phase in the process gas mixture, the nitrogen flow is interrupted, and the argon flow is regulated to 100 sccm. This state, again, is maintained for half the coating time. Following this second cool-down phase, the argon flow is interrupted, the remaining argon is pumped off, and the vacuum pumps are subsequently stopped. After the turbo pump stops, another 5 to 10 min are allowed to pass, before the chamber is opened and the coated substrates are removed.

[0063] Results: The SEM picture in FIG. 5 shows the setup of the titanium electrode on the substrate. Depending on the type and temperature compatibility of the substrate, the thickness of the coating can preferably be between 200 and 450 nm. For more temperature-sensitive substrates, a thinner titanium-rich intermediate layer (TiNx) can be deposited, in order to reserve a higher heat budget for the following titanium-poorer cover layer (TiNy). For metallic substrates, the titanium-rich intermediate layer (TiNx) can also be designed to be thicker, in particular up to 450 nm.

[0064] The TiNx intermediate layer has a higher density than the titanium-poorer TiNy cover layer. This substantiates a good conductivity of the intermediate layer. The more open structure of the titanium-poorer TiNy cover layer substantiates the improved impedance behavior thereof.

EXAMPLE 2

Impedance Behavior of the Titanium Electrode

[0065] Very thin titanium electrodes are deposited on polymeric, thermally sensitive carriers (polystyrene). On the one hand, Ti/TiN electrodes with conventional two-layer setup are produced, on the other hand, three-layer titanium electrodes according to the invention of Ti/TiNx/TiNy according to Example 1 are produced. In both cases, the coating parameters are selected such that only very thin layers are created, so as not to damage the thermally sensitive carriers.

[0066] In the case of the three-layer titanium electrodes according to the invention, the impedance behavior in resistance (ohmic component) and phase angle (Bode diagram) is significantly improved primarily in the frequency range relevant for the impedance-spectroscopic TEER measurements of biological tissue: the series resistance of the electrode (A) according to the invention is smaller and shows a lower frequency dependence (FIG. 7A), the phase curve is flatter, the phase shift is smaller (FIG. 7B).