Detection and Mitigation of Particle Contaminants in MEMS Devices

• US 20110115498A1
• Filed: 10/19/2010
• Published: 05/19/2011
• Est. Priority Date: 10/20/2009
• Status: Active Grant

• Current Assignee: Analog Devices, Inc.
• Original Assignee: Analog Devices, Inc.
• Inventors: Sherman, Steven, Wolfe, Edward, Kumar, Vineet, Clark, William A., Geen, John A.
• Granted Patent: US 8,421,481 B2
• Time in Patent Office: Days
• US Class Current: 324/649
• CPC Class Codes: B81B 7/0029 Protection against environmental influences not provided for in groups B81B7/0012 - B81B7/0025
• CPC Class Codes: B81C 1/00333 Aspects relating to packaging of MEMS devices, not covered by groups B81C1/00269 - B81C1/00325
• CPC Class Codes: B81C 99/0045 End test of the packaged device
• CPC Class Codes: G01C 19/5776 Signal processing not specific to any of the devices covered by groups G01C19/5607 - G01C19/5719
• CPC Class Codes: H01L 22/14 for electrical parameters, e.g. resistance, deep-levels, CV, diffusions by electrical means

Abstract

Detecting and/or mitigating the presence of particle contaminants in a MEMS device involves including MEMS structures that in normal operation are robust against the presence of particles but which can be made sensitive to that presence during a test mode prior to use, e.g., by switching the impedance of sensitive structures between an exceptionally sensitive condition during test and a normal sensitivity during operation; surrounding sensitive nodes with guard elements that are at the same potential as those nodes during operation, thereby offering protection against bridging particles, but are at a very different potential during test and reveal the particles by their resulting leakage currents; extending the sensitive nodes to interdigitate with or otherwise extend adjacent to the guard structures, which neither contribute to nor detract from the device operation but cover otherwise open areas with detection means during test; and/or converting benign areas in which particles might become trapped undetectably by electric fields during test to field-free regions by extending otherwise non-functional conductive layers so that the particles can then be moved into detection locations by providing some mechanical disturbance.

Claims

1. A method for detecting particle contaminants in integrated circuit device having a device structure and a sense node adjacent to the device structure, the method comprising:

during a test mode;

setting impedance of the sense node to a predetermined test mode impedance higher than a predetermined operational mode impedance for the sense node;

placing a test signal on the device structure; and

monitoring the sense node for leakage current from the device structure; and

during an operational mode;

setting impedance of the sense node to the predetermined operational mode impedance.

2. A method according to claim 1, wherein setting impedance of the sense node to the predetermined test impedance comprises:

setting the bias of a direct current amplifier feedback circuit of a low-noise charge amplifier having an input coupled to the sense node to a predetermined test mode bias.

3. A method according to claim 1, wherein the predetermined test mode impedance is around 2 TOhms and wherein the predetermined operational mode impedance is around 2 GOhms.

4. A method according to claim 1, wherein the sense node is a fixed electrode and wherein the device structure is one of a movable electrode and a fixed electrode.

5. A method according to claim 1, wherein the device structure is a guard structure that is used during the test mode for detecting particle contaminants and is placed at the same potential as the sense node during the operational mode.

6. A method according to claim 5, wherein the guard structure includes a set of elongated fingers and wherein the sense node is an elongated sense node having a proximal portion that interdigitates with the set of elongated fingers and a distal portion that interdigitates with corresponding fingers of a movable mass.

7. A method according to claim 5, wherein the guard capacitance is configured as part of the amplifier feedback capacitance to avoid noise degradation.

8. A method according to claim 1, wherein the sense node is part of or connected to a MEMS structure.

9. An integrated circuit device comprising:

a device structure;

a sense node adjacent to the device structure; and

a particle detecting controller coupled to the device structure and the sense node, the particle detecting controller comprising;

a test mode in which the controller sets impedance of the sense node to a predetermined test mode impedance higher than a predetermined operational mode impedance for the sense node, places a test signal on the device structure, and monitors the sense node for leakage current from the device structure; and

an operational mode in which the controller sets impedance of the sense node to the predetermined operational mode impedance.

10. A device according to claim 9, wherein the controller comprises a low-noise charge amplifier having an input coupled to the sense node, the low-noise charge amplifier including a direct current amplifier feedback circuit, and wherein the controller sets impedance of the sense node to the predetermined test impedance by setting the bias of the direct current amplifier feedback circuit to a predetermined test mode bias.

11. A device according to claim 9, wherein the predetermined test mode impedance is around 2 TOhms and wherein the predetermined operational mode impedance is around 2 GOhms.

12. A device according to claim 9, wherein the sense node is a fixed electrode and wherein the device structure is one of a movable electrode and a fixed electrode.

13. A device according to claim 9, wherein the device structure is a guard structure that is used during the test mode for detecting particle contaminants and is placed at the same potential as the sense node during the operational mode by the controller.

14. A device according to claim 13, wherein the guard structure includes a set of elongated fingers and wherein the sense node is an elongated sense electrode having a proximal portion that interdigitates with the set of elongated fingers and a distal portion that interdigitates with corresponding fingers of a movable mass.

15. A device according to claim 13, wherein the guard capacitance is configured as part of the amplifier feedback capacitance to avoid noise degradation.

16. A device according to claim 9, wherein the sense node is part of or connected to a MEMS structure.

17. A MEMS device comprising:

a fixed sense electrode;

a guard structure adjacent to the fixed sense electrode; and

a controller coupled to the fixed sense electrode and the guard structure, the controller comprising;

a test mode in which the controller places the guard structure at a different electrical potential than the fixed sense electrode and monitors the fixed sense electrode for leakage current from the guard structure; and

an operational mode in which the controller places the guard structure at the same electrical potential as the fixed sense electrode.

18. A MEMS device according to claim 17, wherein the guard structure includes a set of finger structures and wherein the fixed sense electrode includes a proximal portion that interdigitates with the set of finger structures of the guard structure.

19. A MEMS device according to claim 18, further comprising a movable mass having a set of finger structures, wherein the fixed sense electrode includes a distal portion that interdigitates with the finger structures of the movable mass.

20. A MEMS device according to claim 17, wherein the controller sets impedance of the sense electrode to a predetermined test mode impedance higher than a predetermined operational mode impedance during the test mode and sets impedance of the sense electrode to the predetermined operational mode impedance during the operational mode.

21. A MEMS device according to claim 20, wherein the controller comprises a low-noise charge amplifier having an input coupled to the sense electrode, the low-noise charge amplifier including a direct current amplifier feedback circuit, and wherein the controller sets impedance of the sense electrode to the predetermined test impedance by setting the bias of the direct current amplifier feedback circuit to a predetermined test mode bias.

22. A MEMS device according to claim 21, wherein the predetermined test mode impedance is around 2 TOhms and wherein the predetermined operational mode impedance is around 2 GOhms.

23. A MEMS device comprising:

a substrate supporting a set of device structures;

a conductive shield layer partially covering a surface of the substrate and leaving an uncovered potential trap region;

a conductive gate layer embedded within the substrate, the conductive gate layer having a first extended portion underlying the potential trap region; and

a controller coupled to the conductive shield layer and the conductive gate layer and configured to place the same electrical potential on both the conductive shield layer and the conductive gate layer.

24. A MEMS device according to claim 23, further comprising a device cap bonded to the substrate and covering the device structures, wherein the conductive gate layer includes a second extended portion that extends beyond an outer perimeter of the device cap, and wherein the controller connects to the second extended portion.