Method for making micromechanical structures having at least one lateral, small gap therebetween and micromechanical device produced thereby

• US 20040150057A1
• Filed: 07/24/2003
• Published: 08/05/2004
• Est. Priority Date: 08/24/2000
• Status: Active Grant

• Current Assignee: Board of Regents of the University of Michigan (University of Michigan)
• Original Assignee: Board of Regents of the University of Michigan (University of Michigan)
• Inventors: Nguyen, Clark T.C., Hsu, Wan-Thai, Clark, John R.
• Granted Patent: US 6,846,691 B2
• Time in Patent Office: Days
• US Class Current: 257/414
• CPC Class Codes: B81B 2201/0235 Accelerometers
• CPC Class Codes: B81B 2201/0242 Gyroscopes
• CPC Class Codes: B81B 2201/0271 Resonators; ultrasonic resonators
• CPC Class Codes: B81B 2203/0307 Anchors
• CPC Class Codes: B81C 1/0019 Flexible or deformable structures not provided for in groups B81C1/00142 - B81C1/00182
• CPC Class Codes: B81C 1/00626 Processes for achieving a desired geometry not provided for in groups B81C1/00563 - B81C1/00619
• CPC Class Codes: B81C 2201/0109 Sacrificial layers not provided for in B81C2201/0107 - B81C2201/0108
• CPC Class Codes: H03H 2009/02496 Horizontal, i.e. parallel to the substrate plane
• CPC Class Codes: H03H 3/007 for the manufacture of electromechanical resonators or networks
• CPC Class Codes: H03H 3/0072 of microelectro-mechanical resonators or networks micromembranes or microbeams B81B2203/01; manufacture of microstructural devices in general B81C
• CPC Class Codes: H03H 3/013 for obtaining desired frequency or temperature coefficient H03H3/0076 H03H3/04, H03H3/10 take precedence
• CPC Class Codes: H03H 9/02362 Folded-flexure
• CPC Class Codes: H03H 9/2436 Disk resonators
• CPC Class Codes: H03H 9/46 Filters multiple-port electromechanical filters H03H9/70
• CPC Class Codes: H03H 9/462 Microelectro-mechanical filters
• CPC Class Codes: H03H 9/505 for microelectro-mechanical filters

Abstract

A method and resulting formed device are disclosed wherein the method combines polysilicon surface-micromachining with metal electroplating technology to achieve a capacitively-driven, lateral micromechanical resonator with submicron electrode-to-resonator capacitor gaps. Briefly, surface-micromachining is used to achieve the structural material for a resonator, while conformal metal-plating is used to implement capacitive transducer electrodes. This technology makes possible a variety of new resonator configurations, including disk resonators and lateral clamped-clamped and free-free flexural resonators, all with significant frequency and Q advantages over vertical resonators. In addition, this technology introduces metal electrodes, which greatly reduces the series resistance in electrode interconnects, thus, minimizing Q-loading effects while increasing the power handling ability of micromechanical resonators.

Claims

1. A method for making micromechanical structures having at least one lateral gap therebetween, the method comprising:

providing a substrate;

surface micromachining the substrate to form a first micromechanical structure having a first vertical sidewall and a sacrificial spacer layer on the first vertical sidewall;

forming a second micromechanical structure on the substrate, the second micromechanical structure including a second vertical sidewall separated from the first vertical sidewall by the spacer layer; and

removing the spacer layer to form a first lateral gap between the first and second micromechanical structures.

2. The method as claimed in claim 1 wherein the step of surface micromachining further forms a third vertical sidewall on the first micromechanical structure with the sacrificial spacer layer thereon and wherein the method further comprises forming a third micromechanical structure including a fourth vertical sidewall separated from the third vertical sidewall by the spacer layer and wherein the step of removing further forms a second lateral gap between the first and third micromechanical structures.

3. The method as claimed in claim 1 wherein the second micromechanical structure includes an electrode.

4. The method as claimed in claim 3 wherein the first micromechanical structure includes a resonator and wherein the first lateral gap is an electrode-to-resonator capacitive gap.

5. The method as claimed in claim 1 wherein the step of forming includes the step of plating metal on the substrate and wherein the second micromechanical structure is a plated metal electrode.

6. The method as claimed in claim 5 further comprising preventing metal from being plated on the first micromechanical structure.

7. The method as claimed in claim 1 wherein the first lateral gap is a submicron gap.

23. The method as claimed in claim 3 wherein the step of forming includes the step of growing the electrode via selective epoxy growth.

24. The method as claimed in claim 3 wherein the step of forming includes the steps of depositing polysilicon and etching the polysilicon to form the electrode.

8. A micromechanical device comprising:

a substrate;

a first micromechanical structure supported on the substrate and having a first vertical sidewall;

a second micromechanical structure supported on the substrate and having a second vertical sidewall; and

a first submicron lateral gap between the first and second vertical sidewalls to increase electromechanical coupling of the first and second micromechanical structures.

9. The device as claimed in claim 8 wherein the second micromechanical structure comprises an electrode.

10. The device as claimed in claim 9 wherein the electrode is a metal electrode.

11. The device as claimed in claim 10 wherein the metal electrode is a plated metal electrode.

12. The device as claimed in claim 8 wherein the first micromechanical structure is a lateral resonator.

13. The device as claimed in claim 8 wherein the first micromechanical structure has a third vertical sidewall and wherein the device further comprises a third micromechanical structure supported on the substrate and having a fourth vertical sidewall and a second submicron lateral gap between the third and fourth vertical sidewalls to increase electromechanical coupling of the first and third micromechanical structures.

14. The device as claimed in claim 12 wherein the lateral resonator is a polysilicon resonator.

15. The device as claimed in claim 12 wherein the lateral resonator is a flexural-mode resonator beam.

16. The device as claimed in claim 8 wherein the substrate is a semiconductor substrate.

17. The device as claimed in claim 16 wherein the semiconductor substrate is a silicon substrate.

18. The device as claimed in claim 8 wherein the first submicron lateral gap is a capacitive gap.

19. The device as claimed in claim 13 wherein the second and third micromechanical structures are electrodes.

20. The device as claimed in claim 19 wherein the electrodes are metal electrodes.

21. The device as claimed in claim 20 wherein the metal electrodes are plated metal electrodes.

22. The device as claimed in claim 13 wherein the first and second submicron lateral gaps are capacitive gaps.

25. The device as claimed in claim 9 wherein the electrode is a polysilicon electrode.

26. The device as claimed in claim 9 wherein the electrode is an SEG-grown electrode.