Vertical thermal gradient compensation in a z-axis MEMS accelerometer

Patent metadata

Field	Value
Publication number	US-11073531-B2
Application number	US-201916547268-A
Country	US
Kind code	B2
Filing date	Aug 21, 2019
Priority date	Aug 21, 2019
Publication date	Jul 27, 2021
Grant date	Jul 27, 2021

Abstract

A microelectromechanical (MEMS) accelerometer has a proof mass and a fixed electrode. The fixed electrode is located relative to the proof mass such that a capacitance formed by the fixed electrode and the proof mass changes in response to a linear acceleration along a sense axis of the accelerometer. The MEMS accelerometer is exposed to heat sources that produce a z-axis thermal gradient in MEMS accelerometer and an in-plane thermal gradient in the X-Y plane of the MEMS accelerometer. The z-axis thermal gradient is sensed with a plurality of thermistors located relative to anchoring regions of a CMOS layer of the MEMS accelerometer. The configuration of the thermistors within the CMOS layer measures the z-axis thermal gradient while rejecting other lateral thermal gradients. Compensation is performed at the accelerometer based on the z-axis thermal gradient.

First claim

What is claimed is:

1. A microelectromechanical (MEMS) accelerometer for measuring linear acceleration along a measurement axis, comprising:
a MEMS layer having a bottom planar surface;
a CMOS layer having an upper planar surface parallel to the bottom planar surface of the MEMS layer, wherein a gap is defined between the upper planar surface of the CMOS layer and the bottom planar surface of the MEMS layer;
a first anchor located within the gap and attached to each of the MEMS layer and the CMOS layer, wherein the attachment of the first anchor to the CMOS layer defines a first anchoring region;
a second anchor located within the gap and attached to each of the MEMS layer and the CMOS layer, wherein the attachment of the second layer to the CMOS layer defines a second anchoring profile;
four temperature sensors located within a first plane within the CMOS layer, comprising:
a first temperature sensor located below the first anchoring region, wherein the first plane is perpendicular to the measurement axis;
a second temperature sensor located below the second anchoring region, wherein the first temperature sensor and the second temperature sensor are located along a first axis and are equidistant from a center point along the first axis;
a third temperature sensor located at a location that is not under either the first anchoring region or the second anchoring region;
a fourth temperature sensor located at a location that is not under either the first anchoring region or the second anchoring region, wherein the third temperature sensor and the fourth temperature sensor are located along a second axis that is orthogonal to the first axis and are equidistant from the center point; and
processing circuitry configured to:
generate a first signal in response to a thermal gradient perpendicular to the first plane by combining outputs of the first temperature sensor, second temperature sensor, third temperature sensor, and fourth temperature sensor;
generate a second signal including a first component corresponding to movement of a portion of the MEMS layer along the measurement axis relative to the CMOS layer in response to the thermal gradient and a second component corresponding to movement of the portion of the MEMS layer along the measurement axis relative to the CMOS layer in response to linear acceleration along the measurement axis; and
generate a linear acceleration output signal based on the first signal and the second signal, wherein the first signal compensates for the first component of the second signal such that the linear acceleration corresponds to the second component of the second signal.

2. The MEMS accelerometer of claim 1 , wherein the linear acceleration output signal is not responsive to a thermal gradient parallel to the first plane.

3. The MEMS accelerometer of claim 1 , wherein the linear acceleration output signal is not responsive to strain effects on the first, second, third, and fourth temperature sensors within the first plane.

4. The MEMS accelerometer of claim 1 , wherein the first, second, third, and fourth temperature sensors are configured in a Wheatstone bridge, and wherein the processing circuitry is coupled to the first, second, third, and fourth temperature sensors via the Wheatstone bridge.

5. The MEMS accelerometer of claim 4 , wherein the Wheatstone bridge comprises two input nodes and two output nodes, wherein the first temperature sensor and the third temperature sensor are coupled to a first input node of the two input nodes and wherein the second temperature sensor and the fourth temperature sensor are coupled to a second input node of the two input nodes.

6. The MEMS accelerometer of claim 5 , wherein the first temperature sensor and the fourth temperature sensor are coupled to a first output node of the two output nodes and wherein the second temperature sensor and the third temperature sensor are coupled to a second output node of the two output nodes.

7. The MEMS accelerometer of claim 6 , wherein a first response of the first temperature sensor to a change in temperature and a second response of the second temperature sensor to the change in temperature are substantially identical.

8. The MEMS accelerometer of claim 7 , wherein a third response of the third temperature sensor to the change in temperature and a fourth response of the fourth temperature sensor to the change in temperature are substantially identical.

9. The MEMS accelerometer of claim 8 , wherein the first response, second response, third response, and fourth response are substantially identical.

10. The MEMS accelerometer of claim 1 , wherein each of the plurality of temperature sensors comprises a thermistor.

11. The method of measuring linear acceleration along a measurement axis for a microelectromechanical (MEMS) device, comprising:
receiving, from a first temperature sensor located in a CMOS layer below a first anchoring region, a first temperature signal, wherein a first anchor defines the first anchoring region and is coupled between the CMOS layer and a MEMS layer within a gap between the CMOS layer and the MEMS layer;
receiving, from a second temperature sensor located in the CMOS layer below a second anchoring region, a second temperature signal, wherein a second anchor defines the second anchoring region is coupled between the CMOS layer and the MEMS layer within the gap between the CMOS layer and the MEMS layer;
receiving, from a third temperature sensor located at a first location that is not under either the first anchoring region or the second anchoring region, a third temperature signal;
receiving, from a fourth temperature sensor located at a second location that is not under either the first anchoring region or the second anchoring region, a fourth temperature signal;
generating a first output signal in response to a thermal gradient perpendicular to a first plane by combining outputs of the first temperature sensor, second temperature sensor, third temperature sensor, and fourth temperature sensor, wherein the first temperature sensor, second temperature sensor, third temperature sensor, and fourth temperature sensor are located within a first plane within the CMOS layer;
generating a second output signal corresponding to movement of a portion of the MEMS layer along the measurement axis relative to the CMOS layer in response to the thermal gradient and a second component corresponding to movement of the portion of the MEMS layer along the measurement axis relative to the CMOS layer in response to linear acceleration along the measurement axis; and
generating a linear acceleration output signal based on the first signal and the second signal, wherein the first signal compensates for the first component of the second signal such that the linear acceleration corresponds to the second component of the second signal.

12. The method of claim 11 , wherein the linear acceleration output signal is not responsive to a thermal gradient parallel to the first plane.

13. The method of claim 11 , wherein the linear acceleration output signal is not responsive to strain effects on the first, second, third and fourth temperature sensors within the first plane.

14. The method of claim 11 , wherein the first, second, third and fourth temperature sensors are configured in a Wheatstone bridge, and wherein the processing circuitry is coupled to the first, second, third and fourth temperature sensors via the Wheatstone bridge.

15. The method of claim 14 , wherein the Wheatstone bridge comprises two input nodes and two output nodes, wherein the first temperature sensor and the third temperature sen

Assignees

• Invensense Inc

Inventors

• Dekoninck David
• Kumar Varun Subramaniam
• Thompson Matthew Julian
• Tsinker Vadim
• Jayaraman Logeeswaran Veerayah
• Nitzan Sarah
• Johari-Galle Houri
• Shin Jongwoo
• Jin Le

Classifications

• G01P1/006 Primary

  used for thermal compensation · CPC title

• G01P15/125

  by capacitive pick-up · CPC title

• G01P2015/0831

  the mass being of the paddle type having the pivot axis between the longitudinal ends of the mass, e.g. see-saw configuration · CPC title