Micro-mechanical inertial sensors

• US 6,308,569 B1
• Filed: 07/30/1999
• Issued: 10/30/2001
• Est. Priority Date: 07/30/1999
• Status: Expired due to Term

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: Litton Systems Incorporated
• Inventors: Stewart, Robert E.
• Primary Examiner(s): KWOK, HELEN C
• Application Number:
  US09/365,336
• Time in Patent Office: 823 Days
• Field of Search: 735/041.2, 735/041.4, 735/040.4, 735/140.2, 735/143.2, 735/141.8, 735/142.1, 735/142.3, 735/143.6, 361/280, 361/283.1, 361/283.3
• US Class Current: 73/514.32
• CPC Class Codes: B81B 7/0064 for protecting against electromagnetic or electrostatic interferences
• CPC Class Codes: G01C 19/56 Turn-sensitive devices using vibrating masses, e.g. vibratory angular rate sensors based on Coriolis forces
• CPC Class Codes: G01P 1/023 for acceleration measuring devices
• CPC Class Codes: G01P 15/0802 Details
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 15/131 with electrostatic counterbalancing means
• CPC Class Codes: G01P 2015/0828 the mass being of the paddle type being suspended at one of its longitudinal ends
• CPC Class Codes: G01P 2015/0831 the mass being of the paddle type having the pivot axis between the longitudinal ends of the mass, e.g. see-saw configuration

Abstract

Micromechanical inertial sensors are formed of a plurality of substantially-planar semiconductor wafers interspersed with oxide layers. The sensitive element is located within an internal aperture of a wafer of the device and is separate therefrom. It is connected to an overlying oxide layer at pedestals that minimize contact area to thereby reduce stray capacitance. Portions of side edges of the various wafers are successively recessed to create topside-exposed wafer sections that permit the grounding of all exposed portions of the device as operational potentials are applied to internal electrodes and sensitive elements.

Claims

1. A micromechanical silicon accelerometer comprising, in combination:

(a) top cover, top electrode, pendulum, bottom electrode, and bottom cover wafers, each of said wafers being generally-planar;

(b) said wafers being arranged so that said top cover wafer is adjacent said top electrode wafer, said top electrode wafer is adjacent said pendulum wafer, said pendulum wafer is adjacent said bottom electrode wafer, and said bottom electrode wafer is adjacent said bottom cover wafer;

(c) a first generally-planar oxide layer located between said top cover and said top electrode wafers, a second generally-planar oxide layer located between said top electrode and said pendulum wafers, a third generally-planar oxide layer located between said pendulum and said bottom electrode wafers and a fourth generally-planar oxide layer located between said bottom electrode and said bottom cover wafers;

(d) said pendulum wafer defining a substantially-planar pendulum member and a surrounding frame member having an internal aperture; and

(e) said pendulum member being located within said internal aperture and separate from said frame member.

2. A micro-mechanical silicon accelerometer as defined in claim 1 further characterized in that each of said second and third oxide layers comprises a composite of two substantially-planar oxide layers bonded to one another at facing surfaces.

3. A micro-mechanical silicon accelerometer as defined in claim 1 wherein each of said second and third oxide layers has an internal aperture to accommodate said pendulum member.

4. A micromechanical silicon accelerometer as defined in claim 3 further including:

(a) said pendulum member comprises a paddle and a pair of opposed legs extending therefrom;

(b) each of said legs terminates in a pedestal; and

(c) each of said pedestals is fixed to the bottom surface of said second generally-planar oxide layer.

5. A micromechanical silicon accelerometer as defined in claim 3 wherein each of said top and bottom electrode wafers further includes:

(a) a substantially-planar electrode and a surrounding guard ring having an internal aperture; and

(b) said electrode being located within said internal aperture of said guard ring and separate from said guard ring.

6. A micromechanical silicon accelerometer as defined in claim 1 further characterized in that at least one edge of each wafer is at least partially recessed with respect to the edges of all underlying wafers.

7. A micromechanical silicon accelerometer as defined in claim 6 wherein peripheral edges of said top and bottom electrode wafers are recessed with respect to the peripheral edges of adjacent oxide layers.

8. A micromechanical silicon sensor element for an angular rate of rotation sensor comprising, in combination:

(a) top cover, top electrode, sensing element, bottom electrode, and bottom cover wafers, each of said wafers being generally-planar;

(b) said wafers being arranged so that said top cover wafer is adjacent said top electrode wafer, said top electrode wafer is adjacent to said sensing element wafer, said sensing element wafer is adjacent said bottom electrode wafer, and said bottom electrode wafer is adjacent said bottom cover wafer;

(c) a first generally-planar oxide layer located between said top cover and said top electrode wafers, a second generally-planar oxide layer located between said top electrode and said sensing element wafers, a third generally-planar oxide layer located between said sensing element and said bottom electrode wafers and a fourth generally-planar oxide layer located between said bottom electrode and said bottom cover wafers;

(d) said sensing element wafer defining a substantially-planar sensing member and a surrounding frame having an internal aperture; and

(e) said sensing member being located within said internal aperture and separate from said frame.

9. A micromechanical silicon sensor element as defined in claim 8 further characterized in that each of said second and third oxide layers comprises a composite of two substantially-planar oxide layers bonded to one another at facing surfaces.

10. A micromechanical silicon sensor element as defined in claim 8 wherein each of said second and third oxide layers has an internal aperture to accommodate said sensing member.

11. A micromechanical silicon sensor element as defined in claim 10 further including:

(a) said sensing member comprises a paddle in an aligned pair of transverse members defining an axis of rotation;

(b) each of said transverse members terminates in a pedestal; and

(c) each of said pedestals is fixed to the bottom surface of said second generally-planar oxide layer.

12. A micromechanical silicon sensor element as defined in claim 10 wherein top and bottom electrode layers each further includes:

(a) two substantially-planar electrodes and a surrounding guard ring having an internal aperture; and

(b) said electrodes being located within said internal aperture and separate from said guard ring.

13. A micromechanical sensor element as defined in claim 10 further characterized in that at least one edge of each wafer is a least partially recessed with respect to the edges of all underlying wafers.

14. A micromechanical sensor element as defined in claim 13 wherein peripheral edges of said top and bottom electrode wafers are recessed with respect to the peripheral edges of adjacent oxide layers.

15. A micromechanical silicon accelerometer comprising, in combination:

(a) top cover, top electrode, pendulum, bottom electrode, and bottom cover wafers, each of said wafers being generally-planar;

(b) said wafers being arranged so that said top cover wafer is adjacent said top electrode wafer, said top electrode wafer is adjacent said pendulum wafer, said pendulum wafer is adjacent said bottom electrode wafer, and said bottom electrode wafer is adjacent said bottom cover wafer;

(c) a first generally-planar oxide layer located between said top cover and said top electrode wafers, a second generally-planar oxide layer located between said top electrode and said pendulum wafers, a third generally-planar oxide layer located between said pendulum and said bottom electrode wafers and a fourth generally-planar oxide layer located between said bottom electrode and said bottom cover wafers;

(d) said pendulum wafer defining a substantially-planar pendulum member and a surrounding frame member having an internal aperture;

(e) said pendulum member being located within said internal aperture and separate from said frame member;

(f) each of said second and third oxide layers has an internal aperture to accommodate said pendulum member;

(g) each of said top and bottom electrode wafers further includes (i) a substantially-planar electrode and a surrounding guard ring having an internal aperture; and

(ii) said electrode being located within said internal aperture of said guard ring and separate from said guard ring;

(h) one side of said top cover wafer being recessed with respect to an underlying top electrode wafer so that the top surface of a section of said guard ring is exposed;

(i) an ohmic contact being located within said top surface of said section of said guard ring;

(j) an ohmic contact being located within a top surface of said electrode of said top electrode wafer;

(k) an aperture passing through said top cover wafer overlying and aligned with said ohmic contact located within said top surface of said electrode of said top electrode wafer;

(l) one side of said exposed section of said guard ring being recessed to expose the top surface of an underlying portion of said frame member;

(m) an ohmic contact being located within the top surface of said exposed portion of said frame member;

(n) an ohmic contact being located within the top surface of said pendulum member;

(o) an aperture passing through said top electrode wafer overlying and aligned with said ohmic contact located within the top surface of said electrode of said bottom electrode wafer;

(p) one side of said exposed portion of said frame member being recessed to expose the top surface of an underlying portion of the guard ring of said bottom electrode wafer;

(q) an ohmic contact being located within the top surface of said exposed portion of said guard ring of bottom electrode wafer;

(r) an ohmic contact being located within the top surface of said electrode of said bottom electrode wafer;

(s) the opposed sides of said top cover and top electrode wafers being recessed to expose the top surface of a second underlying portion of said frame member of said pendulum wafer;

(t) an aperture passing through said exposed second underlying portion of said frame member of said pendulum wafer, said aperture overlying and being aligned with said ohmic contact located within the top surface of said electrode of said bottom electrode wafer;

(u) one side of said bottom electrode wafer being recessed to expose the top surface of a portion of said bottom cover wafer; and

(v) an ohmic contact being located within said top surface of said exposed portion of said bottom cover wafer.

16. A micromechanical silicon sensor element for an angular rate of rotation sensor comprising, in combination:

(a) top cover, top electrode, sensing element, bottom electrode, and bottom cover wafers, each of said wafers being generally-planar;

(b) said wafers being arranged so that said top cover wafer is adjacent said top electrode wafer, said top electrode wafer is adjacent to said sensing element wafer, said sensing element wafer is adjacent said bottom electrode wafer, and said bottom electrode wafer is adjacent said bottom cover wafer;

(c) a first generally-planar oxide layer located between said top cover and said top electrode wafers, a second generally-planar oxide layer located between said top electrode and said sensing element wafers, a third generally-planar oxide layer located between said sensing element and said bottom electrode wafers and a fourth generally-planar oxide layer located between said bottom electrode and said bottom cover wafers;

(d) said sensing element wafer defining a substantially-planar sensing member and a surrounding frame having an internal aperture;

(e) said sensing member being located within said internal aperture and separate from said frame;

(f) each of said second and third oxide layers has an internal aperture to accommodate said sensing member;

(g) said top and bottom electrode wafers each further includes (i) two substantially-planar electrodes and a surrounding guard ring having an internal aperture; and

(ii) said electrodes being located within said internal aperture and separate from said guard ring;

(h) one side of said top cover wafer being recessed with respect to an underlying top electrode wafer so that the top surfaces of a first section of said guard ring and a first section of said frame are exposed;

(i) an ohmic contact being located within said top surfaces of said section of said guard ring;

(j) ohmic contacts being located within a top surface of each of said electrodes of said top electrode wafer;

(k) apertures passing through said top cover wafer overlying and aligned with said ohmic contacts located within a top surface of each of said electrodes of said top electrode wafer;

(l) a second side of said top cover wafer being recessed to expose a second section of said guard ring;

(m) an ohmic contact being located within the top surface of a pedestal of said sensing member;

(n) an aperture passing through said second section of said guard ring overlying and aligned with said ohmic contact located within the top surface of a pedestal of said sensing member;

(o) an ohmic contact being located within said first section of said frame;

(p) an ohmic contact located within the top surface of each electrode of said bottom electrode wafer;

(q) a third side of said top cover wafer, a second side of said top electrode wafer and a side of said sensing element wafer being recessed so that sections of said bottom electrode wafer are successively exposed;

(r) an ohmic contact being located within the top surfaces of each of said electrodes of said bottom electrode wafer and said exposed section of said bottom electrode wafer;

(s) apertures passing through said exposed sections of said sensing element wafer overlying and aligned with said ohmic contact located within the top surfaces of said electrodes of said bottom electrode wafer;

(t) one side of said bottom electrode wafer being recessed to expose the top surface of a portion of said bottom cover wafer; and

(u) an ohmic contact being located within said top surface of said exposed portion of said bottom cover wafer.