Integrated sensor and circuitry and process therefor

• US 7,562,573 B2
• Filed: 07/20/2006
• Issued: 07/21/2009
• Est. Priority Date: 07/21/2005
• Status: Active Grant

• Current Assignee: Micro Inertial LLC
• Original Assignee: Evigia Systems, Inc.
• Inventors: Yazdi, Navid
• Primary Examiner(s): CHAPMAN JR, JOHN E
• Application Number:
  US11/458,729
• Publication Number:
  US 20070029629A1
• Time in Patent Office: 1,097 Days
• Field of Search: 735/141.8, 735/143.2, 361/280
• US Class Current: 73/514.32
• CPC Class Codes: B81B 2201/0235 Accelerometers
• CPC Class Codes: B81C 1/00253 Processes for integrating an electronic processing unit with a micromechanical structure not provided for in B81C1/0023 - B81C1/00246
• CPC Class Codes: B81C 2201/019 Bonding or gluing multiple substrate layers
• CPC Class Codes: G01C 19/5719 using planar vibrating masses driven in a translation vibration along an axis
• 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 15/18 in two or more dimensions
• CPC Class Codes: H01L 2224/48091 Arched
• CPC Class Codes: H01L 2224/73265 Layer and wire connectors
• CPC Class Codes: H01L 2924/00014 the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details
• CPC Class Codes: H01L 2924/16195 Flat cap [not enclosing an internal cavity]
• CPC Class Codes: H01L 2924/16235 Connecting to a semiconductor or solid-state bodies, i.e. cap-to-chip

Abstract

A micromachined sensor and a process for fabrication and vertical integration of a sensor and circuitry at wafer-level. The process entails processing a first wafer to incompletely define a sensing structure in a first surface thereof, processing a second wafer to define circuitry on a surface thereof, bonding the first and second wafers together, and then etching the first wafer to complete the sensing structure, including the release of a member relative to the second wafer. The first wafer is preferably a silicon-on-insulator (SOI) wafer, and the sensing structure preferably includes a member containing conductive and insulator layers of the SOI wafer. Sets of capacitively coupled elements are preferably formed from a first of the conductive layers to define a symmetric capacitive full-bridge structure.

Claims

1. A micromachined sensor having a capacitive sensing structure comprising:

a first substrate comprising first and second conductive layers and a buried insulator layer separating the first and second conductive layers;

a member defined by the first and second conductive layers and the buried insulator layer of the first substrate;

a first set of elements defined with the first conductive layer of the first substrate and connected to the member, the first set of elements comprising at least first, second, third and fourth elements that are electrically isolated from each other by the buried insulator layer within the member;

a second set of elements defined with the first conductive layer, the set of elements comprising at least first, second, third, and fourth elements that are and capacitively coupled with the first, second, third, and fourth elements, respectively, of the first set of elements with gaps therebetween, the capacitive couples generating capacitive outputs that vary with changes in the gaps, the first, second, third, and fourth elements of the first and second sets of elements define a symmetric capacitive full-bridge structure; and

a second substrate bonded to the first substrate so that the member and the first set of elements are movably supported above the second substrate, the second set of elements are anchored to the second substrate, and the first and second sets of elements are physically interconnected only through the second substrate;

wherein the member is movable in a first direction to cause the gaps of the capacitive couples of the first and third elements of the first and second sets of elements to increase and the gaps of the capacitive couples of the second and fourth elements of the first and second sets of elements to decrease.

2. The micromachined sensor according to claim 1, further comprising electrical connections associated with the first and second sets of elements.

3. The micromachined sensor according to claim 2, wherein the second substrate comprises circuitry electrically connected to the first and second sets of elements through the electrical connections.

4. The micromachined sensor according to claim 3, wherein the circuitry is CMOS interface circuitry.

5. The micromachined sensor according to claim 4, wherein the CMOS interface circuitry comprises means for performing multiple correlated double sampling of input thereto and output thereof.

6. The micromachined sensor according to claim 5, wherein the CMOS interface circuitry further comprises means for performing chopper stabilization that reduces dc and low-frequency noise and drift.

7. The micromachined sensor according to claim 4, wherein the CMOS interface circuitry operates in a closed-loop mode.

8. The micromachined sensor according to claim 4, wherein the CMOS interface circuitry operates in an open-loop mode.

9. The micromachined sensor according to claim 1, wherein the first, second, third and fourth elements of the first set of elements are part of first, second, third and fourth groups, respectively, of the first set of elements, the first, second, third and fourth elements of the second set of elements are part of first, second, third, and fourth groups of elements that are interdigitated and capacitively coupled with the first, second, third, and fourth groups of elements, respectively, of the first set of elements, and the first, second, third, and fourth groups of elements of the first and second sets of elements define the symmetric capacitive full-bridge structure.

10. The micromachined sensor according to claim 9, wherein the elements within each group of the first set of elements are electrically connected to each other, and the elements within each group of the second set of elements are electrically connected to each other.

11. The micromachined sensor according to claim 9, further comprising at least one trench defined in the first conductive layer so that the buried insulator layer electrically isolates the first, second, third, and fourth groups of the first set of elements.

12. The micromachined sensor according to claim 9, wherein the first and second groups of the first set of elements extend from a first edge of the member and the third and fourth groups of the first set of elements extend from an oppositely-disposed second edge of the member.

13. The micromachined sensor according to claim 1, further comprising means for supporting the member and the first set of elements above a surface of the second substrate so as to permit bidirectional motion of the member in a plane parallel to the surface of the second substrate.

14. The micromachined sensor according to claim 13, wherein the supporting means comprises a plurality of beams at opposite ends of the member.

15. The micromachined sensor according to claim 14, further comprising circuitry on the second substrate and electrically connected to the first set of elements through the plurality of beams.

16. The micromachined sensor according to claim 1, wherein the symmetric capacitive full-bridge structure directly interfaces with a fully-differential readout front-end circuit without reference capacitors for the capacitive outputs of the capacitive couples.

17. The micromachined sensor according to claim 1, wherein the micromachined sensor is a motion sensor and the member is a proof mass of the motion sensor.

18. The micromachined sensor according to claim 1, wherein the micromachined sensor comprises at least a second sensing structure supported on the second substrate.

19. The micromachined sensor according to claim 1, wherein the first, second, third, and fourth elements of the first set of elements are electrically isolated from each other within four symmetrical quadrants on the first substrate by the buried insulator layer.

20. A micromachined sensor having a capacitive sensing structure comprising:

a member comprising first and second conductive layers and a buried insulator layer separating the first and second conductive layers;

a first set of elements defined with the first conductive layer, the first set of elements comprising at least first, second, third and fourth elements that are electrically isolated from each other on the member by the buried insulator layer; and

a second set of elements comprising at least first, second, third, and fourth elements that are capacitively coupled with the first, second, third, and fourth elements, respectively, of the first set of elements through gaps therebetween so that the capacitive couples generate capacitive outputs that vary with changes in the gaps, the first, second, third, and fourth elements of the first and second sets of elements defining a symmetric capacitive full-bridge structure;

wherein the member is movable in a first direction to cause the gaps of the capacitive couples of the first and third elements of the first and second sets of elements to increase and the gaps of the capacitive couples of the second and fourth elements of the first and second sets of elements to decrease.

21. The micromachined sensor according to claim 20, further comprising electrical connections associated with the first and second sets of elements.

22. The micromachined sensor according to claim 21, further comprising a substrate on which the sensing structure is supported and to which the second set of elements is anchored, the substrate comprising circuitry electrically connected to the first and second sets of elements through the electrical connections.

23. The micromachined sensor according to claim 22, wherein the circuitry is CMOS interface circuitry.

24. The micromachined sensor according to claim 23, wherein the CMOS interface circuitry comprises means for performing multiple correlated double sampling of input thereto and output thereof.

25. The micromachined sensor according to claim 24, wherein the CMOS interface circuitry further comprises means for performing chopper stabilization that reduces dc and low-frequency noise and drift.

26. The micromachined sensor according to claim 23, wherein the CMOS interface circuitry operates in a closed-loop mode.

27. The micromachined sensor according to claim 23, wherein the CMOS interface circuitry operates in an open-loop mode.