High temperature microelectromechanical (MEM) devices and fabrication method

• US 20070054433A1
• Filed: 09/08/2005
• Published: 03/08/2007
• Est. Priority Date: 09/08/2005
• Status: Active Grant

• Current Assignee: Teledyne Scientific & Imaging, LLC (Teledyne Technologies Incorporated)
• Original Assignee: Rockwell Scientific Licensing LLC
• Inventors: DeNatale, Jeffrey, Borwick, Robert, Stupar, Philip
• Granted Patent: US 7,303,935 B2
• Time in Patent Office: Days
• US Class Current: 438/48
• CPC Class Codes: B81C 1/0069 Thermal properties, e.g. improve thermal insulation
• CPC Class Codes: B81C 2203/032 Gluing

Abstract

A microelectromechanical (MEM) device per the present invention comprises a semiconductor wafer—typically an SOI wafer, a substrate, and a high temperature bond which bonds the wafer to the substrate to form a composite structure. Portions of the composite structure are patterned and etched to define stationary and movable MEM elements, with the movable elements being mechanically coupled to the stationary elements. The high temperature bond is preferably a mechanical bond, with the wafer and substrate having respective bonding pads which are aligned and mechanically connected to form a thermocompression bond to effect the bonding. A metallization layer is typically deposited on the composite structure and patterned to provide electrical interconnections for the device. The metallization layer preferably comprises a conductive refractory material such as platinum to withstand high temperature environments.

Claims

1. A microelectromechanical (MEM) device having a stationary element and a movable element displaceable relative to the stationary element, comprising:

a semiconductor wafer;

a substrate; and

a high temperature bond which bonds said wafer to said substrate to form a composite structure;

portions of said composite structure patterned and etched to define the stationary and movable MEM elements such that said movable element is mechanically coupled to said stationary element.

2. The device of claim 1, wherein said high temperature bond is a mechanical bond.

3. The device of claim 2, wherein said wafer and substrate have respective bonding pads which are aligned and mechanically connected such that a thermocompression bond is formed to effect the bonding of said wafer to said substrate.

4. The device of claim 3, wherein said bonding pads are gold (Au) such that said bond is an Au—

Au thermocompression bond.

5. The device of claim 1, further comprising one or more metallization layers deposited on said composite structure and patterned and etched to provide electrical interconnections for said MEM device, said metallization layers comprising a conductive refractory material.

6. The device of claim 5, wherein said conductive refractory material is selected from a group consisting of platinum, iridium, gold or titanium nitride.

7. The device of claim 1, wherein said MEM device is arranged to sense the viscosity of a fluid in which the device is immersed.

8. The device of claim 7, wherein said movable element and said stationary element are conductive and at least partially overlap so as to produce a capacitance which varies with the amount of overlap, said device further comprising a drive means for displacing said movable element relative to said stationary element.

9. The device of claim 8, further comprising a sensing means for sensing said amount of overlap.

10. The device of claim 9, wherein said sensing means is arranged to sense the capacitance between said movable and stationary elements.

11. The device of claim 9, wherein said sensing means is arranged to optically sense the amount of overlap between said movable and stationary elements.

12. The device of claim 8, wherein said drive means is selected from a group consisting of an electrostatic actuator, thermal actuator, Lorentz force actuator, or piezoelectric actuator, said actuator coupled to said movable element.

13. The device of claim 8, wherein said movable element is arranged to be displaced laterally relative to said stationary element.

14. The device of claim 8, wherein said movable element is arranged to be displaced vertically relative to said stationary element.

15. The device of claim 1, wherein said wafer is a silicon-on-insulator (SOI) wafer.

16. The device of claim 1, wherein said substrate is an insulating substrate.

17. The device of claim 1, wherein-said substrate is a conducting substrate.

18. The device of claim 1, wherein said substrate is a semiconductor wafer containing pre-processed circuitry.

19. A microelectromechanical (MEM) viscosity sensor arranged to sense the viscosity of a fluid in which the device is immersed, comprising:

a semiconductor wafer having at least one bonding pad;

a substrate having at least one bonding pad, the bonding pads of said wafer and substrate aligned and mechanically connected to form a high temperature thermocompression bond between said wafers and thereby form a composite structure, portions of said composite structure patterned and etched to define a stationary element and a movable element such that said movable element is mechanically coupled to said stationary element, said movable element and said stationary element conductive and at least partially overlapping so as to produce a capacitance which varies with the amount of overlap; and

a drive means for displacing said movable element relative to said stationary element.

20. The viscosity sensor of claim 19, further comprising a sensing means arranged to sense the capacitance between said movable and stationary elements.

21. The viscosity sensor of claim 19, further comprising one or more metallization layers deposited on said composite structure and patterned and etched to provide electrical interconnections for said MEM device, said metallization layers comprising a conductive refractory material.

22. The viscosity sensor of claim 19, wherein said composite structure is patterned and etched to form first and second set of conductive plates spaced apart from each other and having respective parallel surface areas, said first set of plates arranged to interleave with said second set of plates such that their surface areas at least partially overlap to produce said capacitance, one of said sets of plates being said movable element.

23. A method of measuring the viscosity of a fluid, comprising:

providing a microelectromechanical (MEM) viscosity sensor, comprising;

a semiconductor wafer having at least one bonding pad;

a substrate having at least one bonding pad, the bonding pads of said wafer and substrate aligned and mechanically connected to form a high temperature thermocompression bond between said wafers and thereby form a composite structure, portions of said composite structure patterned and etched to define a stationary element and a movable element such that said movable element is mechanically coupled to said stationary element, said movable element and said stationary element conductive and at least partially overlapping so as to produce a capacitance which varies with the amount of overlap;

a drive means for displacing said movable element relative to said stationary element; and

a sensing means for sensing said amount of overlap;

immersing said sensor is said fluid;

operating said drive means to displace said movable element relative to said stationary element; and

operating said sensing means to sense said amount of overlap.

24. The method of claim 23, wherein said drive means are operated such that said movable element is displaced laterally relative to said stationary means.

25. The method of claim 23, wherein said drive means are operated such that said movable element is displaced vertically relative to said stationary means.

26. The method of claim 23, wherein said sensing means is arranged to sense the capacitance between said movable and stationary elements.

27. A method of fabricating a microelectromechanical (MEM) device having a stationary element and a movable element displaceable relative to the stationary element, comprising:

providing a semiconductor wafer;

patterning one or more bonding pads on said wafer;

providing a substrate;

patterning one or more bonding pads on said substrate such that said substrate'"'"'s bonding pads can be aligned with said wafer'"'"'s bonding pads;

aligning said wafer'"'"'s bonding pads with said substrate'"'"'s bonding pads;

mechanically connecting the bonding pads of said wafer and substrate to produce a mechanical bond which bonds said wafer and substrate together to form a composite structure; and

patterning and etching portions of said composite structure to define said stationary and movable elements such that said movable element is mechanically coupled to said stationary element.

28. The method of claim 27, wherein said wafer and substrate have respective bonding pads which are aligned and mechanically connected such that a thermocompression bond is formed to effect the bonding of said wafer to said substrate.

29. The method of claim 28, wherein said bonding pads are gold bonding pads and said thermocompression bond is an Au—

Au thermocompression bond.

30. The method of claim 27, further comprising depositing, patterning and etching one or more metallization layers on said composite structure to provide electrical interconnections for said MEM device, said metallization layers comprising a conductive refractory material.

31. The method of claim 27, wherein said semiconductor wafer is a silicon-on-insulator (SOI) wafer.

32. A method of fabricating a microelectromechanical (MEM) device having a stationary element and a movable element displaceable relative to the stationary element, comprising:

providing a silicon-on-insulator (SOI) wafer which includes a silicon handle layer and a silicon device layer;

patterning one or more bonding pads on said wafer;

providing a substrate;

patterning one or more bonding pads on said substrate such that said substrate'"'"'s bonding pads can be aligned with said wafer'"'"'s bonding pads;

etching a recessed area into said substrate;

aligning said wafer'"'"'s bonding pads with said substrate'"'"'s bonding pads;

mechanically connecting the bonding pads of said wafer and substrate to produce a thermocompression bond which bonds said wafer and substrate together to form a composite structure;

underfilling gaps in said composite structure with a curable organic sacrificial material to provide mechanical support;

removing said silicon handle layer from the SOI wafer to expose said silicon device layer;

patterning and etching portions of said composite structure to define said stationary and movable elements such that said movable element is mechanically coupled to said stationary element;

depositing, patterning and etching one or more metallization layers on said composite structure to provide electrical interconnections for said MEM device, said metallization layers comprising a conductive refractory material; and

etching away said organic sacrificial layer to release said movable element.

33. The method of claim 32, wherein said bonding pads are gold bonding pads and said thermocompression bond is an Au—

Au thermocompression bond.

34. The method of claim 32, wherein said organic underfill material is selected from a group consisting of thermally-cured epoxy, UV-cured epoxy, polymide, or BCB.

35. The method of claim 32, wherein said device layer is etched using a deep-reactive ion etch (DRIE).