Thermoelastic self-actuation in piezoresistive resonators
Systems and methods for thermally actuating piezoresistive cantilevers are described. One embodiment includes a nanoelectromechanical resonator connected in at least one location to a substrate, an electrically conductive path formed on the resonator and a signal source connected to the electrically conductive path and configured to provide an oscillating actuation signal capable of exciting a resonant mode in the resonator.
1. A piezoresistive sensor, comprising:
a substrate;
a nanoelectromechanical cantilever connected to the substrate in at least one location;
a current path defined proximate the cantilever;
a signal source connected via circuitry to the current path; and
wherein the signal source is configured to provide a signal to thermally actuate a resonant mode in the cantilever.
2. The piezoresistive sensor of claim 1 , wherein the nanoelectromechanical cantilever is a bi-layer cantilever.
3. The piezoresistive sensor of claim 2 , wherein the bi-layer cantilever comprises:
a base layer; and
a piezoresistive layer formed on the surface of the base layer.
4. The piezoresistive sensor of claim 3 , wherein one end of the bi-layer cantilever is connected to the substrate via a first cantilever leg and a second cantilever leg.
5. The piezoresistive sensor of claim 4 , wherein the base layer is silicon and the piezoresistive layer is p-doped silicon.
6. The piezoresistive sensor of claim 2 , wherein the bi-layer cantilever comprises:
a base layer; and
a metallic circuit trace formed on the base layer, which forms part of the current path.
7. The piezoresistive sensor of claim 6 , further comprising detection circuitry configured to detect variations in the resistance of the metallic circuit trace.
8. The piezoresistive sensor of claim 6 , wherein the base layer includes silicon carbide and the circuit trace includes metallic gold.
9. The piezoresistive sensor of claim 3 , wherein the current path includes the piezoresistive layer of the bi-layer cantilever.
10. The piezoresistive sensor of claim 9 , wherein:
each of the first and second cantilever legs comprises:
a base layer; and
a piezoresistive layer formed on the surface of the base layer; and
the circuitry includes a pair of symmetric bias resistors that are connected between the signal source and the piezoresistive layer of the first and second cantilever legs.
11. The piezoresistive sensor of claim 9 , further comprising detection circuitry configured to detect variations in the resistance of the piezoresistive layer of the bi-layer cantilever.
12. A piezoresistive sensor, comprising:
a doubly-clamped nanoelectromechanical beam;
a first current path formed on one end of the doubly-clamped beam; and
a signal source connected to the first current path via circuitry and configured to provide a signal to thermally actuate a resonant mode in the doubly-clamped beam.
13. The piezoresistive sensor of claim 12 , wherein the doubly clamed beam comprises:
a base layer;
a first metallic circuit trace formed on the surface of the base layer at one end of the doubly-clamped beam, which forms part of the first current path; and
a second metallic circuit trace formed on the surface of the base layer at the other end of the doubly-clamped beam, which forms part of a second current path.
14. The piezoresistive sensor of claim 13 , further comprising detection circuitry connected to the second current path and configured to detect actuation of the beam using downmixing detection.
15. The piezoresistive sensor of claim 13 , wherein the base layer includes silicon carbide and the metallic circuit traces include metallic gold.
16. A piezoresistive sensor, comprising
a substrate;
a beam that includes a channel, where the beam is connected to the substrate by at least two springs;
a current path passing through the beam; and
a signal source connected to the current path via circuitry and configured to provide a signal to thermally actuate a resonant mode in the beam.
17. The piezoresistive sensor of claim 16 , wherein the beam is constructed from a base layer and a metallic surface layer.
18. The piezoresistive sensor of claim 17 , wherein the base layer includes silicon nitride and the metallic surface layer includes metallic gold.
19. The piezoresistive sensor of claim 16 , wherein the beam is formed from a thin layer of metal.
20. A piezoresistive sensor, comprising:
a nanoelectromechanical resonator connected in at least one location to a substrate;
an electrically conductive path formed on the resonator; and
a signal source connected to the electrically conductive path and configured to provide a signal to thermally actuate a resonant mode in the resonator.
21. The piezoresistive sensor of claim 20 , wherein the nanoelectromechanical resonator is a bi-layer cantilever.
22. The piezoresistive sensor of claim 20 , wherein the nanoelectromechanical resonator is a doubly-clamped beam.
23. The piezoresistive sensor of claim 20 , wherein the nanoelectromechanical resonator is a beam including a channel connected to the substrate in two locations.