Piezoelectric MEMS switches and methods of making
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.
1. A method of making a piezoelectric MEMS switch comprising:
forming a sacrificial layer on a substrate;
forming a first electrode layer over the substrate and the sacrificial layer;
forming an annealed piezoelectric dielectric layer over the first electrode layer;
forming a second electrode layer over the annealed piezoelectric layer, the second electrode layer cooperating with the first electrode layer and the annealed piezoelectric dielectric layer to form a piezoelectric actuator;
patterning the piezoelectric actuator to create a through-hole through which the sacrificial layer is exposed;
after forming the annealed piezoelectric dielectric layer, forming radio frequency signal lines adjacent the first and second electrode layers;
removing the sacrificial layer through the through-hole to create a void underlying the piezoelectric actuator;
forming a polymer coat over the piezoelectric actuator, the polymer coat extending through the through-hole and into the void to contact the substrate and define a polymeric finger supporting the piezoelectric actuator;
forming a contact in the polymer coat;
forming a boom mechanically coupling the piezoelectric actuator to the contact; and
removing the polymer coat including the polymeric finger.
2. The method of claim 1 , wherein the forming of the first electrode layer comprises depositing a metallic composition and patterning deposited metal.
3. The method of claim 1 , wherein the forming the annealed piezoelectric dielectric layer comprises depositing, at high temperatures, a piezoelectric dielectric material in a layer.
4. The method of claim 1 , wherein the forming the annealed piezoelectric dielectric layer comprises depositing a piezoelectric dielectric material layer and annealing the piezoelectric dielectric material layer at high temperatures.
5. The method of claim 1 , wherein the forming of the second electrode layer comprises depositing a metallic composition and patterning the second electrode layer.
6. The method of claim 1 , wherein the sacrificial layer comprises any of silicon dioxide, polysilicon and silicon oxynitride.
7. The method of claim 1 , wherein the polymer coat comprises any of polyimide and BCB.
8. A method of making a piezoelectric MEMS switch comprising:
forming a sacrificial layer on a substrate;
forming a first electrode layer over the substrate and the sacrificial layer;
forming an annealed piezoelectric dielectric layer over the first electrode layer;
forming a second electrode layer over the annealed piezoelectric layer;
patterning the annealed piezoelectric to create a through-hole exposing the sacrificial layer;
forming radio frequency signal lines adjacent the first and second electrode layers after the forming of the annealed piezoelectric dielectric material layer;
forming a first polymer coat over the first electrode layer and the radio frequency signal lines;
removing the sacrificial layer through the through-hole;
forming a second polymer coat over the first polymer coat, the second polymer coat extending through the through-hole and contacting an upper surface of the substrate to support the annealed piezoelectric layer;
forming a contact in the second polymer coat after the forming of the annealed piezoelectric dielectric material layer;
patterning the second polymer coat to expose a portion of the second electrode layer;
depositing an upper dielectric layer over the exposed portion of second electrode layer and the contact so as to form a boom mechanically coupling the second electrode layer to the contact; and
removing the first and second polymer coatings.
9. The method of claim 8 , wherein the forming of an annealed piezoelectric layer comprises depositing, at high temperatures, a piezoelectric dielectric material in a layer.
10. The method of claim 8 , wherein the forming of an annealed piezoelectric layer comprises depositing a piezoelectric dielectric material layer and annealing the layer at high temperatures.
11. The method of claim 8 , further comprising applying heat and voltage across the piezoelectric layer to polarize the annealed piezoelectric layer.
12. The method of claim 8 , 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.
13. The method of claim 8 , wherein the sacrificial layer comprises silicon oxide, silicon oxynitride or polysilicon.
14. The method of claim 8 , wherein the first and second polymer coats each comprises any one of polyimide, or BCB.
15. A method of fabricating a piezoelectric MEMS switch, comprising:
providing a base substrate;
forming a sacrificial layer on the substrate;
forming an annealed piezoelectric actuator on the base substrate and over the sacrificial layer;
patterning the annealed piezoelectric actuator to create a through-hole exposing the sacrificial layer;
after forming the annealed piezoelectric actuator, forming first and second radio frequency (RF) signal lines on the base substrate proximate the annealed piezoelectric actuator;
depositing a first polymeric coating over the first and second RF signal lines and over the annealed piezoelectric actuator;
removing the sacrificial layer through the through-hole to create a void underlying the piezoelectric actuator;
depositing a second polymeric coating over the piezoelectric actuator, the second polymeric coating extending through the through-hole and into the void to contact a surface of the substrate and define a supportive polymeric finger;
forming a contact on the second polymeric coating above the first and second RF signal lines;
forming a boom mechanically coupling the contact to the annealed piezoelectric actuator; and
removing the first and second polymeric coatings including the supportive polymeric finger.
16. The method of claim 15 wherein the step of forming a boom comprises:
patterning the first and second polymeric coatings to expose the annealed piezoelectric actuator therethrough; and
depositing an upper dielectric layer over the exposed portion of the piezoelectric actuator and the contact.
17. The method of claim 16 wherein the step of depositing an upper dielectric layer is performed such that the upper dielectric layer is disposed around but not over the through-hole.
18. The method of claim 15 wherein the step of depositing a first polymeric coating is performed such that the first polymeric coating at least partially fills the through-hole and contacts an upper surface of the sacrificial layer.