MOTION DETECTION USING CAPACITOR HAVING DIFFERENT WORK FUNCTION MATERIALS

• US 20110219876A1
• Filed: 03/10/2010
• Published: 09/15/2011
• Est. Priority Date: 03/10/2010
• Status: Active Grant

• Current Assignee: Taiwan Semiconductor Manufacturing Company Limited
• Original Assignee: Taiwan Semiconductor Manufacturing Company Limited
• Inventors: KALNITSKY, Alexander, HSUEH, Fu-Lung
• Granted Patent: US 8,549,922 B2
• Time in Patent Office: Days
• US Class Current: 73/514.32
• CPC Class Codes: A63F 13/211 using inertial sensors, e.g. accelerometers or gyroscopes
• CPC Class Codes: A63F 13/24 Constructional details thereof, e.g. game controllers with detachable joystick handles
• CPC Class Codes: A63F 2300/1043 being characterized by constructional details
• CPC Class Codes: A63F 2300/105 using inertial sensors, e.g. accelerometers, gyroscopes
• CPC Class Codes: G01B 7/003 for measuring position, not involving coordinate determination coordinate measuring G01B7/004
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 15/16 by evaluating the time-derivative of a measured speed signal
• CPC Class Codes: G01P 3/52 by measuring amplitude of generated current or voltage

Abstract

An apparatus for detecting mechanical displacement in a micro-electromechanical system includes a capacitor having first and second plates spaced from one another, the first and second plates having different work functions and being electrically connected with each other. The capacitor plates are movable with respect to one another such that a spacing between the plates changes in response to a force. A current through the capacitor represents a rate of change in the spacing between the plates at a given time.

Claims

1. A micro-electromechanical apparatus for detecting mechanical displacement comprising a capacitor having first and second capacitor plates spaced from one another, the first and second plates having different work functions and being electrically connected with each other, wherein the plates are movable with respect to one another such that a spacing between the plates changes in response to a force, a current through the capacitor being representative of a rate of change in the spacing between the plates at a given time.

2. The apparatus of claim 1, wherein the first and second capacitor plates comprise first and second metal materials having different work functions.

3. The apparatus of claim 1, wherein the first and second capacitor plates comprise first and second semiconductor materials having different work functions.

4. The apparatus of claim 3, wherein the first and second capacitor plates further comprise a conductive contact layer to which the first and second semiconductor materials are coupled.

5. The apparatus of claim 1, wherein the apparatus includes a plurality of the capacitors oriented to detect motion along a plurality of different axes.

6. The apparatus of claim 5, wherein the plurality of capacitors comprises three capacitors oriented to detect motion along a vertical axis, a lateral axis and a longitudinal axis.

7. The apparatus of claim 1, wherein the apparatus includes a plurality of the capacitors arranged in an interdigitated assembly.

8. The apparatus of claim 7, wherein the apparatus includes:

a first comb electrode having a plurality of first capacitor plate arms having a first work function, and

a second comb electrode having a plurality of second capacitor plate arms interdigitated with the plurality of first capacitor plate arms, each second capacitor plate arm having a material having the first work function on a first side thereof facing a first capacitor plate arm and a material having a second work function different from the first work function on a second side thereof facing a different first capacitor plate arm.

9. The apparatus of claim 1, further comprising:

a second capacitor having third and fourth capacitor plates spaced from one another, the third and fourth capacitor plates having different work functions, wherein the third and fourth capacitor plates are fixed with respect to one another such that a spacing between the plates is maintained in response to the force to provide a reference current through the second capacitor.

10. The apparatus of claim 9, wherein the capacitors are connected in parallel with one another between two power supply nodes, each capacitor being coupled in series with a resistive element, the apparatus further comprising a comparator having a first input coupled to a first node intermediate the capacitor and the respective resistive element in series therewith and having a second input coupled to a first node intermediate the second capacitor and the respective resistive element in series therewith, the comparator having an output for providing a differential output signal.

11. A micro-electromechanical system (MEMS) comprising:

a fixed support member;

a deflection member attached to the support member so as to deflect relative to the support member;

a first capacitor plate connected to the fixed support member; and

a second capacitor plate connected to the deflection member, the second capacitor plate being parallel to and spaced from the first capacitor plate, the first capacitor plate and the second capacitor plate forming a capacitor, the first and second capacitor plates having different work functions and being electrically connected with each other to provide a current through the capacitor, the current through the capacitor being based on the deflection of the deflection member.

12. The MEMS of claim 11, wherein the fixed support member and the deflection member are attached through an elastic member.

13. The MEMS of claim 11, wherein the MEMS comprises three capacitors oriented to detect motion along a vertical axis, a lateral axis and a longitudinal axis, each capacitor having two spaced capacitor plates of different work functions.

14. The MEMS of claim 11, wherein the fixed support member comprises a plurality of the first capacitor plates and the deflection member has a plurality of the second capacitor plates, wherein the plurality of first and second capacitor plates are arranged in an interdigitated relationship to form a plurality of capacitors.

15. The MEMS of claim 14, wherein the plurality of first capacitor plates have a material having a first work function on both a first side and a second side thereof, and the plurality of second capacitor plates have a material having the first work function on a first side thereof and a material having a second work function different than the first work function on a second side thereof

16. The MEMS of claim 11, further comprising:

a second capacitor having third and fourth capacitor plates spaced from one another, the third and fourth capacitor plates having different work functions, wherein the third and fourth capacitor plates are fixed with respect to one another such that a spacing between the plates is maintained for providing a reference current through the second capacitor.

17. The MEMS of claim 16, further comprising a comparator having a first input coupled to the capacitor and a second input coupled to the second capacitor and an output for providing a differential output signal.

18. A method for detecting motion through a micro-electromechanical sensor (MEMS) comprising the steps of:

providing a capacitor having first and second capacitor plates spaced from one another, the first and second capacitor plates having different work functions and being electrically connected with each other, wherein the plates are movable with respect to one another such that a spacing between the plates changes in response to a force; and

monitoring current through the capacitor, the current being representative of a rate of change in the spacing between the plates at a given time.

19. The method of claim 18, further comprising the step of providing a second capacitor having third and fourth capacitor plates spaced from one another, the third and fourth capacitor plates having different work functions, wherein the third and fourth capacitor plates are fixed with respect to one another such that a spacing between the plates is maintained for providing a reference current through the second capacitor,

wherein the monitoring step comprises generating a first voltage with the current through the capacitor, generating a second voltage with the reference current, and comparing the first and second voltages.

20. The method of claim 18,

wherein the providing step comprises providing a plurality of the first capacitor plates and a plurality of the second capacitor plates, the plurality of first and second capacitor plates being arranged in an interdigitated relationship to form a plurality of capacitors, the plurality of first capacitor plates having a material having a first work function on both a first side and a second side thereof, and the plurality of second capacitor plates have a material having the first work function on a first side thereof and a material having a second work function different than the first work function on a second side thereof

wherein the monitoring step comprises monitoring a sum of the current through the plurality of capacitors.