Piezoelectric MEMS switches and methods of making

• US 20070202626A1
• Filed: 02/28/2006
• Published: 08/30/2007
• Est. Priority Date: 02/28/2006
• Status: Active Grant

• Current Assignee: North Star Innovations Inc. (Wi-LAN Inc.)
• Original Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Inventors: Liu, Lianjun
• Granted Patent: US 7,556,978 B2
• Time in Patent Office: Days
• US Class Current: 438/48
• CPC Class Codes: H01H 2057/006 Micromechanical piezoelectric relay
• CPC Class Codes: H01H 57/00 Electrostrictive relays; Piezoelectric relays

Abstract

MEMS piezoelectric switches 100 that provide advantages of compact structure ease of fabrication in a single unit, and that are free of high temperature-induced morphological changes of the contact materials and resultant adverse effects on properties. High temperature-induced morphological changes refer to changes that occur during fabrication when metallic contacts such as radio frequency lines 125, 130 and shorting bars 150 are exposed to temperatures required to anneal a piezoelectric layer or those temperatures encountered during high temperature deposition of the piezoelectric layer, if such process is used instead.

Claims

1. A method of making a piezoelectric MEMS switch comprising:

forming a sacrificial layer on a substrate;

forming a first electrode layer;

forming an annealed piezoelectric dielectric layer;

forming a second electrode layer;

forming radio frequency signal lines adjacent the first and second electrode layers without subjecting the lines to high temperatures in processes after forming the lines;

forming a first polymer coat;

removing the sacrificial layer;

forming a second polymer coat;

forming a contact in the second polymer coat;

patterning the second polymer coat;

forming a patterned dielectric layer to link a cantilever to the contact, the cantilever comprising the first electrode layer, the second electrode layer and the piezoelectric dielectric layer; and

removing the second polymer coat.

2. The method of claim 1, wherein the forming of the first electrode comprises depositing a metallic composition and patterning deposited metal.

3. The method of claim 1, wherein the forming and subjecting to high temperatures comprises depositing, at high temperatures, a piezoelectric dielectric material in a layer.

4. The method of claim 1, wherein the forming and subjecting to high temperatures comprises depositing a piezoelectric dielectric material layer and annealing the layer at high temperatures.

5. The method of claim 1, wherein the forming of a second electrode layer comprises depositing a metallic composition and patterning the second electrode layer.

6. The method of claim 1, further comprising applying heat and voltage across the piezoelectric layer to polarize the layer.

7. The method of claim 1, wherein removing of the sacrificial layer comprises patterning and etching the first polymer layer to form a through-hole therein and removal of the sacrificial layer via the through-hole.

8. The method of claim 1, wherein the forming of a second polymer coat comprises providing a structural support of polymer in space from which the sacrificial layer was removed.

9. The method of claim 1, wherein the sacrificial layer comprises any of silicon dioxide, polysilicon and silicon oxynitride.

10. The method of claim 1, wherein the first polymer coat comprises any of polyimide and BCB.

11. The method of claim 1, wherein the second polymer coat comprises any of polyimide and BCB.

12. A method of making a piezoelectric MEMS switch comprising:

forming sacrificial layer on a substrate;

forming a first electrode layer;

forming an annealed piezoelectric dielectric material layer;

forming a second electrode layer;

forming radio frequency signal lines adjacent the first and second electrodes after the forming and after subjecting to high temperatures of the piezoelectric material;

forming a first polymer coat;

removing the sacrificial layer;

forming a second polymer coat;

forming a contact in the second polymer coat after the forming and subjecting to high temperatures of a piezoelectric material;

patterning the second polymer coat;

forming a patterned dielectric layer so that a portion of the formed dielectric layer connects an underlying cantilever to the contact; and

removing the patterned second polymer coat.

13. The method of claim 12, wherein the forming of an annealed piezoelectric layer comprises depositing, at high temperatures, a piezoelectric dielectric material in a layer.

14. The method of claim 12, wherein the forming of an annealed piezoelectric layer comprises depositing a piezoelectric dielectric material layer and annealing the layer at high temperatures.

15. The method of claim 12, further comprising applying heat and voltage across the piezoelectric layer to polarize the layer.

16. The method of claim 12, wherein removing of the sacrificial layer comprises patterning and etching the first polymer coat to provide access to the sacrificial layer via a through-hole in the first polymer coat;

and wet etching removal of sacrificial layer material through the through-hole.

17. The method of claim 12, wherein the sacrificial layer comprises silicon oxide, silicon oxynitride or polysilicon.

18. The method of claim 12, wherein the first and second polymer coats each comprises any one of polyimide, or BCB.

19. A piezoelectric MEMS switch comprising:

a first metallic contact;

a second metallic contact at a first end portion of a boom, the second contact spaced from the first contact;

a cantilever in mechanical communication with the boom, the cantilever extending above a space created by removal of a sacrificial material, the cantilever having a through-hole through which sacrificial material was removed from the space, the cantilever having a layered structure comprising an actuator, the actuator comprising a piezoelectric layer disposed between a pair of electrode layers, the cantilever flexing when actuated so that the second contact reciprocates into electrical communication with the first contact.

20. The switch of claim 19, wherein the first and second metallic contacts are free of morphological change caused by exposure to such temperatures as required for annealing the piezoelectric layer of the cantilever or for high temperature deposition of the piezoelectric layer.