Method and apparatus for micro-machined sensors using enhanced modulated integrative differential optical sensing

• US 7,091,715 B2
• Filed: 11/14/2001
• Issued: 08/15/2006
• Est. Priority Date: 11/15/2000
• Status: Expired due to Fees

• Current Assignee: Rafael - Armament Development Authority Ltd., UAB Research Foundation (University of Alabama System)
• Original Assignee: Rafael - Armament Development Authority Ltd., TECHNION RESEARCH AND DEVELOPMENT FOUNDATION, LTD.
• Inventors: Degani, Ofir, Nemirovsky, Yael, Seter, Dan, Socher, Eran
• Primary Examiner(s): TANG, MINH NHUT
• Application Number:
  US10/416,736
• Publication Number:
  US 20040060355A1
• Time in Patent Office: 1,735 Days
• Field of Search: None
• US Class Current: 73/514.26
• CPC Class Codes: G01P 15/093 by photoelectric pick-up
• CPC Class Codes: G01P 15/18 in two or more dimensions
• CPC Class Codes: G01P 2015/0814 for translational movement of the mass, e.g. shuttle type

Abstract

Method and apparatus for sensing the displacements of micromachined devices and sensors. The method is referred to as the enhanced modulated integrative differential optical sensing (EMIDOS). The target micromachined proof-mass, for which displacements are measured, includes a grid of slits. The micromachined device is bonded to a CMOS chip containing a matching photodiodes array and their readout electronics. The grid is aligned with the photociiodes. An illumination source, such as an LED, is then mounted above the micromachined device. A model for the noise equivalent displacement (NED), including mechanical, electrical and optical domains, as well as all noise sources is derived. The model predicts that displacements below 10⁻³ [√{square root over ( )}Hz] can be measured. The design comprises innovative inertial sensors, an accelerometer and a rategyroscope employing the EMIDOS. Performance models for the noise equivalent acceleration (NEA) and noise equivalent rate (NER) are also derived. The models show that an accelerometer with a very low NEA can be realized.

Claims

1. A micro-opto-electro-mechanical system for measuring the acceleration of a platform along a fixed axis, using partially integrated mode enhanced modulated integrative differential optical sensing, said system comprising:

a CMOS chip comprising at least two integrated arrays of photodiode illumination detectors and analog readout electronics;

a frame affixed to said CMOS chip;

an LED mounted above said frame, providing illumination for said photodiode detectors;

a sensing proof-mass, elastically suspended by a set of beams fixed to said frame;

a grid of slits integrally formed with said sensing proof-mass, and being orthogonal to said fixed acceleration axis,

such that when said system is at rest, said grid evenly and partially covers each of said arrays of photodiode detectors, so that equal amounts of light illuminate each of said arrays and equal photocurrents are measured at each of said arrays,

and when said platform accelerates, said sensing proof-mass is displaced along said fixed acceleration axis, thereby increasing the exposed area of one of said arrays of photodiode detectors to illumination, while decreasing the exposed area of another one of said arrays of photodiode detectors,

and increasing a resulting differential photocurrent from said arrays of photodiode detectors, said differential photocurrent being proportional to the displacement of said sensing proof-mass and therefore to the acceleration,

thus providing a measurement of the acceleration of said platform.

2. A system according to claim 1, wherein said micro-opto-electro-mechanical system is mass-produced.

3. A system according to claim 1, further comprising a second grid of slits and at least two additional arrays of photodiodes, wherein said at least two additional arrays of photodiodes and said second grid of slits are orthogonal to each other for measuring acceleration along multiple axes.

4. A system according to claim 1, wherein said analog readout electronics comprises:

an amplification stage for each of said arrays of photodiode detectors; and

a subtraction stage.

5. A micro-opto-electro-mechanical system for measuring the acceleration of a platform along a fixed axis using fully integrated mode enhanced modulated integrative differential optical sensing, said system comprising:

a CMOS chip comprising at least two integrated arrays of photodiode illumination detectors and analog readout electronics;

a frame affixed to said CMOS chip;

an LED mounted above said frame, providing illumination for said photodiode detectors;

a sensing proof-mass, elastically suspended by a set of beams fixed to said frame;

a first grid of slits integrally formed with said sensing proof-mass, and being orthogonal to said acceleration axis;

a second grid of slits fixed to said frame, and centered with said first grid of slits,

such that when said system is at rest, said first and second grid of slits are evenly and fully exposed to each of said arrays and photocurrents are measured at each of said arrays,

and when said platform accelerates, said sensing proof-mass is displaced along said fixed acceleration axis, and said first grid is displaced with respect to said second grid, thereby increasing the gap on one side between said first and second grid of slits and therefore increasing the exposed area of one of said arrays of photodiode detectors to illumination, while decreasing the gap on the other side between said first and second grid of slits and therefore decreasing the exposed area of another one of said arrays of photodiode detectors, and increasing a resulting differential photocurrent from said arrays of photodiode detectors, said differential photocurrent being proportional to the displacement of said sensing proof-mass and therefore to the acceleration,

thus providing a measurement of the acceleration of said platform.

6. A system according to claim 5, wherein said micro-opto-electro-mechanical system is mass-produced.

7. A system according to claim 5, further comprising at least two additional arrays of photodiodes, wherein said at least two additional arrays of photodiodes and said second grid of slits are orthogonal to each other for measuring acceleration along multiple axes.

8. A system according to claim 5, wherein said analog readout electronics comprises:

an amplification stage for each of said arrays of photodiode detectors; and

a subtraction stage.

9. A micro-opto-electro-mechanical system for measuring the rate of rotation of a platform about a fixed axis thereof using partially integrated mode enhanced modulated integrative differential optical sensing, said system comprising:

a CMOS chip comprising at least two integrated arrays of photodiode illumination detectors and analog readout electronics;

a frame attached to said CMOS chip;

an LED mounted above said frame, providing illumination for said photodiode detectors;

a excitation mass, elastically suspended by a set of beams fixed to said frame,

such that said excitation mass is allowed to move along excitation axis,

and said excitation axis is orthogonal to said rate of rotation axis;

a sensing proof-mass, elastically suspended to said excitation mass by a second set of beams,

such that sensing proof-mass is allowed to move along sensing axis,

and said sensing axis is orthogonal to said excitation axis and said rate of rotation axis;

a grid of slits integrally formed with said sensing proof-mass, and being orthogonal to said sensing axis,

such that when said system is at rest, said grid evenly and partially covers each of said arrays of photodiode detectors, so that equal amounts of light illuminate each of said arrays and equal photocurrents are measured at each of said arrays,

and when mechanical vibration is applied along said excitation axis and said platform rotates about said rate of rotation axis, said sensing proof-mass is displaced along said sensing axis due to Coriolis forces, thereby increasing the exposed area of one of said arrays of photodiode detectors to illumination while decreasing the exposed area of another one of said arrays of photodiode detectors to illumination, and increasing a resulting differential photocurrent from said arrays of photodiode detectors, said differential photocurrent being proportional to the displacement of said sensing proof-mass and therefore to the rate of rotation,

thus providing a measurement of the rate of rotation of said platform.

10. A system according to claim 9, wherein said micro-opto-electro-mechanical system is mass-produced.

11. A system according to claim 9, further comprising a second grid of slits and at least two additional arrays of photodiodes, wherein said at least two additional arrays of photodiodes and said second grid of slits comprise multiple arrays and grids orthogonal to each other for measuring the rate of rotation about multiple axes.

12. A system according to claim 9, wherein said analog readout electronics comprises:

an amplification stage for each of said arrays of photodiode detectors; and

a subtraction stage.

13. A system according to claim 9, wherein said mechanical vibration results from electrostatic actuation.

14. A system according to claim 9, wherein said mechanical vibration results from magnetostatic actuation.

15. A system according to claim 9, wherein said mechanical vibration results from piezoelectric actuation.

16. A system according to claim 9, wherein said mechanical vibration results from thermal actuation.

17. A micro-opto-electro-mechanical system for measuring the rate of rotation of a platform about a fixed axis thereof using fully integrated mode enhanced modulated integrative differential optical sensing, said system comprising:

a CMOS chip comprising at least two integrated arrays of photodiode illumination detectors and analog readout electronics;

a frame attached to said CMOS chip;

an LED mounted above said frame, providing illumination for said photodiode detectors;

an excitation mass, elastically suspended by a set of beams fixed to said frame,

such that said excitation mass is allowed to move along an excitation axis,

and said excitation axis is orthogonal to said rate of rotation axis;

a sensing proof-mass, elastically suspended to said excitation mass by a second set of beams,

such that sensing proof-mass is allowed to move along a sensing axis,

and said sensing axis is orthogonal to said excitation axis and said rate of rotation axis;

a first grid of slits integrally formed with said sensing proof-mass, and being orthogonal to said sensing axis;

a second grid of slits fixed to said frame, and centered with said first grid of slits,

such that when said system is at rest, said first and second grid of slits are evenly and fully exposed to each of said arrays of photodiode detectors, so an even amount of light illuminating each of said arrays and a photocurrent is measured at each of said arrays,

and when mechanical vibration is applied along said excitation axis and said platform rotates about said rate of rotation axis, said sensing proof-mass is displaced along said sensing axis due to Coriolis forces and said first grid is displaced with respect to said second fixed grid, thereby increasing the gap on one side between said first and second grid of slits and therefore increasing the exposed area of one of said arrays of photodiode detectors to illumination and decreasing the gap on the other side between said first and second grid of slits and therefore decreasing the exposed area of another one of said arrays of photodiode detectors, and increasing a resulting differential photocurrent from said arrays of photodiode detectors, said differential photocurrent being proportional to the displacement of said sensing proof-mass and therefore to the rate of rotation,

thus providing a measurement of the rate of rotation of said platform.

18. A system according to claim 17, wherein said micro-opto-electro-mechanical system is mass-produced.

19. A system according to claim 17, further comprising at least two additional arrays of photodiodes, wherein said at least two additional arrays of photodiodes and said second grid of slits comprise multiple arrays and grids orthogonal to each other for measuring the rate of rotation about multiple axes.

20. A system according to claim 17, wherein said analog readout electronics comprises:

an amplification stage for each of said arrays of photodiode detectors; and

a subtraction stage.

21. A system according to claim 17, wherein said mechanical vibration results from electrostatic actuation.

22. A system according to claim 17, wherein said mechanical vibration results from magnetostatic actuation.

23. A system according to claim 17, wherein said mechanical vibration results from piezoelectric actuation.

24. A system according to claim 17, wherein said mechanical vibration results from thermal actuation.

25. A partially integrated mode enhanced-modulated-integrative-differential-optical-sensing apparatus for measuring displacement along a given axis, said apparatus comprising:

a CMOS chip comprising at least two integrated arrays of photodiode illumination detectors and analog readout electronics;

a frame affixed to said CMOS chip;

an LED mounted above said frame, providing illumination for said photodiode detectors;

a sensing proof-mass, elastically suspended by a set of beams fixed to said frame;

a grid of slits integrally formed with said sensing proof-mass, and being orthogonal to said given displacement axis,

such that when said system is at rest, said grid evenly and partially covers each said arrays of photodiode detectors, so that equal amounts of light illuminate each of said arrays and equal photocurrents are measured at each of said arrays,

and when said sensing proof-mass is displaced along said given displacement axis,

the exposed area to illumination of one of said arrays of photodiode detectors is increased and the exposed area of another one of said arrays of photodiode detectors is decreased,

such that a resulting differential photocurrent from said arrays of photodiodes is increased, said differential photocurrent being proportional to the displacement of said sensing proof-mass,

thus measuring the displacement of said apparatus.

26. A fully integrated mode enhanced-modulated-integrative differential-optical-sensing apparatus for measuring displacement along a given axis, said apparatus comprising:

a CMOS chip comprising at least two integrated arrays of photodiode illumination detectors and analog readout electronics;

a frame affixed to said CMOS chip;

an LED mounted above said frame, providing illumination for said photodiode detectors;

a sensing proof-mass, elastically suspended by a set of beams fixed to said frame;

a first grid of slits integrally formed with said sensing proof-mass, and being orthogonal to said given displacement axis;

a second grid of slits fixed to said frame, and centered with said first grid of slits,

such that when said system is at rest, said first and second grid of slits are evenly and fully exposed to each of said arrays of photodiode detectors, so that equal amounts of light illuminate each of said arrays and equal photocurrents are measured at each of said arrays,

and when said sensing proof-mass is displaced along said given displacement axis, and said first grid is displaced with respect to said second fixed grid,

thereby increasing the gap on one side between said first and second grid of slits and therefore increasing the exposed area of one of said arrays of photodiode detectors to illumination and decreasing the gap on the other side between said first and second grid of slits and therefore decreasing the exposed area of another one of said arrays of photodiode detectors,

such that a resulting differential photocurrent from said arrays of photodiode detectors is increased, said differential photocurrent being proportional to the displacement of said sensing proof-mass;

thus measuring the displacement of said apparatus.