Fabrication of broadband surface-micromachined micro-electro-mechanical switches for microwave and millimeter-wave applications

• US 6,331,257 B1
• Filed: 11/30/1999
• Issued: 12/18/2001
• Est. Priority Date: 05/15/1998
• Status: Expired due to Term

• Current Assignee: Hughes Electronics Corporation (AT&T, Inc.)
• Original Assignee: Hughes Electronics Corporation (AT&T, Inc.)
• Inventors: Brown, Julia, Hyman, Daniel J., Foschaar, James, Schmitz, Adele, Hsu, Tsung-Yuan, Loo, Robert Y.
• Primary Examiner(s): Gulakowski, Randy
• Assistant Examiner(s): Ahmed, Shamim
• Application Number:
  US09/452,052
• Time in Patent Office: 749 Days
• Field of Search: 216/2, 216/13, 216/99, 216/83, 333/262
• US Class Current: 216/13
• CPC Class Codes: B81B 2201/014 having a cantilever fixed on one side connected to one or more dimples
• CPC Class Codes: B81B 2203/0118 Cantilevers
• CPC Class Codes: B81B 3/0072 For controlling internal stress or strain in moving or flexible elements, e.g. stress compensating layers
• CPC Class Codes: H01G 5/18 due to change in inclination, e.g. by flexing, by spiral wrapping
• CPC Class Codes: H01G 5/38 Multiple capacitors, e.g. ganged
• CPC Class Codes: H01G 5/40 Structural combinations of variable capacitors with other electric elements not covered by this subclass, the structure mainly consisting of a capacitor, e.g. RC combinations
• CPC Class Codes: H01H 1/50 Means for increasing contact pressure, preventing vibration of contacts, holding contacts together after engagement, or biasing contacts to the open position
• CPC Class Codes: H01H 59/0009 making use of micromechanics
• CPC Class Codes: H01P 1/12 by mechanical chopper

Abstract

Methods for the design and fabrication of micro-electro-mechanical switches are disclosed. Two different switch designs with three different switch fabrication techniques are presented for a total of six switch structures. Each switch has a multiple-layer armature with a suspended biasing electrode and a conducting transmission line affixed to the structural layer of the armature. A conducting dimple is connected to the conducting line to provide a reliable region of contact for the switch. The switch is fabricated using silicon nitride as the armature structural layer and silicon dioxide as the sacrificial layer supporting the armature during fabrication. Hydrofluoric acid is used to remove the silicon dioxide layer with post-processing in a critical point dryer to increase yield.

Claims

1. A process for making a micro-electro-mechanical switch on a substrate, comprising the steps of

a) depositing a first metal layer on a substrate to form an input line, an output line, a substrate bias electrode, a substrate bias pad, and an armature bias pad;

b) depositing a sacrificial layer on top of a first metal layer and the substrate;

c) defining and delineating dimple molds in regions of the conducting line above the input line and output line.

d) depositing a beam structural layer on top of a sacrificial layer to form a structure of an armature, wherein an end of the beam structural layer is affixed to the substrate near the output line;

e) depositing a second metal layer on top of the structural layer to form a conducting transmission line and a suspended armature bias electrode; and

f) removing the sacrificial layer to release the armature.

2. The process of claim 1, wherein the substrate comprises a semiconductor, dielectric, or semi-insulating material.

3. The process of claim 2, wherein the substrate comprises GaAs, InP, silicon, quartz, or ceramic.

4. The process of claim 1, wherein the step of depositing the first metal layer comprises the steps of

a) depositing a first layer of titanium;

b) depositing a layer of platinum onto the titanium; and

c) depositing a layer of gold onto the platinum.

5. The process of claim 4, wherein

a) the layer of titanium is about 200 angstroms thick;

and

b) the layer of platinum is about 1000 angstroms thick.

6. The process of claim 1, wherein the substrate bias electrode is electrically connected with the substrate bias pad.

7. The process of claim 1, wherein the sacrificial layer comprises silicon dioxide.

8. The process of claim 1, wherein the beam structural layer is comprised of silicon nitride.

9. The process of claim 1, further comprising the step of removing a portion of the structural layer and a portion of the sacrificial layer to create a dimple mold before the second metal layer is deposited.

10. The process of claim 9, wherein the step of depositing the second metal layer further comprises the step of creating a conducting dimple in the dimple receptacle that protrudes through the structural layer.

11. The process of claim 1, wherein the step of depositing a second metal layer comprises the steps of

a) depositing a layer of titanium;

b) depositing an optional layer of platinum onto the titanium; and

c) depositing a layer of gold on to the platinum.

12. The process of claim 11, wherein

a) the layer of titanium is about 250 angstroms thick;

and

b) the layer of platinum can be 1000 angstroms thick.

13. The process of claim 1, further comprising the step of creating a suspended armature bias electrode on the structural layer when the second metal layer is deposited.

14. The process of claim 13, wherein the suspended armature bias electrode is electrically connected to the armature bias pad, wherein a voltage difference can be established between the suspended armature bias electrode and the substrate bias electrode by establishing such a voltage difference between the armature bias pad and the substrate bias pad.

15. The process of claim 1, further comprising the step of depositing a second structural layer on top of the conducting line so that the two structural layers surround the conducting line.

16. The process of claim 1, wherein the step of removing the sacrificial layer comprises the step of etching the silicon dioxide with hydrofluoric acid.

17. The process of claim 16, wherein the etching is performed with post-processing in a critical point dryer to prevent the armature from sticking to the substrate.

18. The process of claim 1, wherein the first metal layer, the support layer, the beam structural layer, and the second metal layer are deposited using integrated circuit fabrication processes.

19. A process for making a micro-electro-mechanical switch on a substrate, comprising the steps of

a) depositing a first metal layer on the substrate to form an input line, an output line, a substrate bias electrode, a substrate bias pad, and an armature bias pad;

b) depositing an insulating layer on top of the first metal layer in the region of the substrate bias electrode;

c) depositing a sacrificial layer on top of the first metal layer and the substrate;

d) defining and delineating a dimple mold into the sacrificial layer at regions of the conducting transmission line above the input and output lines

e) depositing a second metal layer on top of the sacrificial layer to form a conducting line; and

f) depositing a beam structural layer on top of the conducting line and the sacrificial layer to form a structure of an armature, wherein an end of the beam structural layer is affixed to the substrate near the output line;

g) removing the sacrificial layer to free the armature.

20. The process of claim 19, further comprising the step of depositing an insulating layer on top of the electrode after the first metal layer is deposited and before the sacrificial layer is deposited.

21. The process of claim 20, wherein the insulating layer comprises a dielectric.

22. The process of claim 19, wherein the sacrificial layer comprises silicon dioxide.

23. The process of claim 22, wherein the step of removing the sacrificial layer comprises the step of etching the silicon dioxide with hydrofluoric acid.

24. The process of claim 23, wherein the etching is performed with post-processing in a critical point dryer to prevent the armature from sticking to the substrate.

25. The process of claim 19, wherein the step of depositing the first metal layer comprises the steps of

a) depositing a first layer of titanium;

b) depositing a layer of platinum onto the titanium; and

c) depositing a layer of gold onto the platinum.

26. The process of claim 19, wherein the step of depositing a second metal layer comprises the steps of

a) depositing a layer of titanium;

b) depositing an optional layer of platinum onto the titanium; and

c) depositing a layer of gold onto the platinum.

27. The process of claim 19, wherein the first metal layer, the support layer, the beam structural layer, and the second metal layer are deposited using integrated circuit fabrication processes.

28. The process of claim 19, further comprising the step of creating a suspended armature bias electrode on the sacrifical layer when the second metal layer is deposited.

29. The process of claim 28, further comprising the steps of depositing the suspended armature bias electrode, wherein the armature bias pad is electrically connected to the suspended armature bias electrode, wherein a voltage difference can be established between the suspended armature bias electrode and the substrate bias electrode by establishing such a voltage difference between the armature bias pad and the substrate bias pad.

30. The process of claim 19, wherein the substrate comprises a semiconductor, dielectric, or insulating material.