Stable high temperature sensor system with tungsten on AlN
A sensor system has an AlN substrate, a W layer on the substrate, a signal source adapted to apply an electrical actuating signal to the W layer, and a sensor adapted to sense the response of the W layer. The W layer can comprise a thin film, with various types of optional protective layers over the film. Applications include sensing temperature, fluid flow rates, fluid levels, pressure and chemical environments. For a planar heater, the W layer comprises a plurality of conductive strands distributed on the substrate, with the strands generally parallel and serpentine shaped for a rectangular substrate, and extending along respective lines of longitude that merge at opposite poles of the substrate for a circular substrate.
1. A sensor system, comprising:
an AlN substrate,
a W layer on said substrate,
an oxidation resistant gold, Au—Pt alloy, Pt or B 2 O 3 —SiO 2 protective layer on said W layer,
a signal source connected to apply a current or voltage actuating signal to said W layer, and
a sensor connected to sense the voltage across said W layer in the case of a current actuating signal, or the current through said W layer in the case of a voltage actuating signal.
2. The system of claim 1 , said W layer comprising a thin film.
3. The system of claim 1 , said protective layer comprising an Au—Pt alloy with W on said Au—Pt alloy.
4. The system of claim 1 , said protective layer comprising an Au—Pt alloy with B 2 O 3 —SiO 2 on said Au—Pt alloy.
5. The system of claim 1 , said protective layer further comprising Pt with B 2 O 3 —SiO 2 on said Pt.
6. The system of claim 1 , further comprising an AlN cap on said protective layer.
7. The system of claim 1 , said W layer comprising a plurality of conductive strands distributed on said substrate.
8. The system of claim 7 , wherein said strands are generally parallel and serpentine shaped.
9. The system of claim 8 , wherein said substrate is rectangular.
10. The system of claim 1 , further comprising an additional AlN substrate with an additional W layer thereon, said signal source connected to apply a substantially non-heating current or voltage signal to said additional W layer, and a sensor connected to sense the voltage across said additional W layer in the case of a non-heating current signal, or the current through said additional W layer in the case of a non-heating voltage signal, as an indication of its temperature,
said additional substrate and additional W layer disposed downstream of said substrate and W layer in a fluid flow path, with the difference in temperature between said W and additional W layers corresponding to the fluid flow rate.
11. The system of claim 1 , said substrate and W layer disposed in a fluid flow path, said response sensed by said sensor corresponding to a fluid flow rate along said path.