Quantum tunnelling sensor device and method
A sensor device, method of fabricating the same, and a method of sensing a physical quantity. The sensor device comprises a substrate; a flexure member, one end of the flexure member being attached to the substrate, and a free end of the flexure member having an edge surface; a counter surface formed on the substrate such that the counter surface faces the edge surface of the flexure member and such that a separation distance between the counter surface and the edge surface remains substantially constant for movement of the edge surface as a result of flexure of the flexure member, each of the edge surface and the counter surface including one or more conductor layers disposed in a plane substantially perpendicular to a flexure direction of the flexure member; and means for applying an electrical potential difference between the conductors of the edge surface and the conductors of the counter surface for detecting a quantum tunnelling current therebetween.
1. A sensor device comprising:
a substrate;
a flexure member, wherein a first end of the flexure member is attached to the substrate, and wherein a second end of the flexure member includes an edge surface;
a counter surface formed on the substrate such that the counter surface faces the edge surface of the flexure member, wherein a separation distance between the counter surface and the edge surface is configured to remain substantially constant for movement of the edge surface as a result of flexure of the flexure member;
a potential source configured to apply an electrical potential difference between the edge surface and the counter surface; and
a signal processing device configured to detect a quantum tunnelling current between the edge surface and the counter surface.
2. The device of claim 1 , wherein a flexure direction of the flexure member is substantially perpendicular to the substrate.
3. The device of claim 1 , wherein a flexure direction of the flexure member is substantially parallel to the substrate.
4. The device of claim 1 , wherein the flexure member is formed across a recess formed in the substrate, and wherein the counter surface is formed as part of a wall structure of the recess.
5. The device of claim 4 , wherein the recess comprises an exposed longitudinal edge along at least one side of the substrate.
6. The device of claim 5 , wherein one side of the flexure member is aligned with the exposed longitudinal edge of the recess.
7. The device of claim 4 , wherein the recess is laterally enclosed along all sides of the recess.
8. The device of claim 1 , further comprising a tip formed on a surface of the flexure member.
9. The device of claim 1 , wherein the flexure member and the counter surface are built up on a surface of the substrate, and wherein a frame portion of the substrate extends around at least one longitudinal side of the flexure member.
10. The device of claim 1 , wherein the counter surface extends below, above, or both below and above a quiescent level of the flexure member along a flexure direction of the flexure member.
11. A method comprising:
applying an electrical potential difference to a sensor device, wherein the sensor device includes a flexure member, wherein a first end of the flexure member is attached to a substrate and a second end of the flexure member comprises an edge surface, wherein the sensor device further includes a counter surface formed on the substrate such that the counter surface faces the edge surface of the flexure member, wherein each of the edge surface and the counter surface comprise one or more conductor layers, and wherein the electrical potential difference is applied between the one or more conductor layers of the edge surface and the one or more conductor layers of the counter surface;
flexing the flexure member such that a separation distance between the counter surface and the edge surface remains substantially constant for movement of the edge surface as a result of flexure of the flexure member; and
detecting a tunnelling current for sensing a physical quantity, wherein movement of the flexure member or vibratory properties of the flexure member are coupled to the physical quantity.
12. A method comprising:
forming a flexure member having a first end and a second end, wherein the first end is attached to a substrate and the second end includes an edge surface;
forming a counter surface on the substrate such that the counter surface faces the edge surface of the flexure member, wherein each of the edge surface and the counter surface include one or more conductor layers, and wherein a separation distance between the counter surface and the edge surface is configured to remain substantially constant for movement of the edge surface as a result of flexure of the flexure member; and
forming a potential source that is configured to apply an electrical potential difference between the one or more conductor layers of the edge surface and the one or more conductors of the counter surface for detecting a quantum tunnelling current between the edge surface and the counter surface.
13. The device of claim 1 , wherein the edge surface comprises one or more conductor layers disposed in a plane that is substantially perpendicular to a flexure direction of the flexure member.
14. The device of claim 13 , wherein the one or more conductor layers of the edge surface extend through to respective edge portions of the substrate.
15. The device of claim 13 , further comprising one or more insulating layers between the one or more conductor layers of the edge surface.
16. The device of claim 1 , wherein the counter surface comprises one or more conductor layers disposed in a plane that is substantially perpendicular to a flexure direction of the flexure member.
17. The device of claim 16 , wherein the one or more conductor layers of the counter surface extend through to respective edge portions of the substrate.
18. The device of claim 16 , further comprising one or more insulating layers between the one or more conductor layers of the counter surface.
19. The device of claim 1 , wherein the sensor device comprises a cantilever in an atomic force microscope.
20. The device of claim 1 , wherein the sensor device comprises an acceleration sensor or a high frequency vibration sensor.
21. The device of claim 1 , further comprising a bimetallic strip formed on the flexure member.
22. The device of claim 1 , wherein the flexure member is reactive to or absorbent of a molecular species such that a mass of the flexure member changes in the presence of the molecular species.
23. The device of claim 22 , wherein the change in the mass of the flexure member results in a variation of a position of the edge surface or in vibratory properties of the flexure member.
24. The method of claim 11 , wherein the one or more conductor layers of the edge surface and the one or more conductors of the counter surface are disposed in a plane that is substantially perpendicular to a flexure direction of the flexure member.
25. The method of claim 12 , wherein the one or more conductor layers of the edge surface and the one or more conductor layers of the counter surface are disposed in a plane that is substantially perpendicular to a flexure direction of the flexure member.