Fabricating MEMS composite transducer including compliant membrane
A method of fabricating a MEMS composite transducer includes providing a substrate having a first surface and a second surface opposite the first surface. A transducing material is deposited over the first surface of the substrate. The transducing material is patterned by retaining transducing material in a first region and removing transducing material in a second region. A polymer layer is deposited over the first region and the second region. The polymer layer is patterned by retaining polymer in a third region and removing polymer in a fourth region. A first portion of the third region is coincident with a portion of the first region and a second portion of the third region is coincident with a portion of the second region. A cavity is etched from the second surface to the first surface of the substrate. An outer boundary of the cavity at the first surface of the substrate intersects the first region where transducing material is retained, so that a first portion of the transducing material is anchored to the first surface of the substrate and a second portion of the transducing material extends over at least a portion of the cavity.
1. A method of fabricating a MEMS composite transducer, the method comprising:
providing a substrate having a first surface and a second surface opposite the first surface;
depositing a transducing material over the first surface of the substrate;
patterning the transducing material by retaining transducing material in a first region and removing transducing material in a second region;
depositing a polymer layer over the first and second regions;
patterning the polymer layer by retaining polymer in a third region and removing polymer in a fourth region, a first portion of the third region being coincident with a portion of the first region, and a second portion of the third region being coincident with a portion of the second region; and
etching a cavity from the second surface to the first surface of the substrate, wherein an outer boundary of the cavity at the first surface of the substrate intersects the first region where transducing material is retained, so that a first portion of the transducing material is anchored to the first surface of the substrate and a second portion of the transducing material extends over at least a portion of the cavity.
2. The method according to claim 1 , wherein the substrate is silicon.
3. The method according to claim 1 , further comprising depositing at least one insulating layer on the first surface of the substrate before the step of depositing the transducing material.
4. The method according to claim 3 , the transducing material being deposited in a first thickness t 1 and the at least one insulating layer being deposited in a second thickness t 2 , wherein t 2 >0.5 t 1 and t 2 <2t 1 .
5. The method according to claim 3 , the transducing material being deposited in a first thickness t 1 and the at least one insulating layer being deposited in a second thickness t 2 , wherein and t 2 <0.2t 1 .
6. The method according to claim 3 further comprising patterning the at least one insulating layer, wherein patterning the at least one insulating layer includes retaining insulating material in the first region where transducer material is retained.
7. The method according to claim 6 , wherein patterning the at least one insulating layer comprises plasma etching the at least one insulating layer with a fluorine based process gas.
8. The method according to claim 3 further comprising depositing a first metal electrode layer after the at least one insulating layer is deposited and before the transducing material is deposited.
9. The method according to claim 8 further comprising depositing a second metal electrode layer after the transducing material is deposited.
10. The method according to claim 9 , wherein patterning the transducing material further comprises etching the transducing material, the first metal electrode layer and the second metal electrode layer in a single step.
11. The method according to claim 10 , wherein the single step etching comprises plasma etching using a chlorine based process gas.
12. The method according to claim 10 , wherein the single step etching comprises wet etching.
13. The method according to claim 1 , wherein depositing the transducing material comprises sputtering the transducing material.
14. The method according to claim 1 further comprising depositing a seed layer before the step of depositing the transducing material.
15. The method according to claim 1 , wherein depositing the transducing material comprises a sol-gel process.
16. The method according to claim 15 , wherein the sol-gel process comprises applying a precursor material over the first surface of the substrate.
17. The method according to claim 16 , wherein the applying the precursor material comprises spinning the substrate.
18. The method according to claim 16 , wherein the sol-gel process comprises heat-treating the deposited precursor material.
19. The method according to claim 18 , wherein heat-treating the deposited precursor material comprises:
drying the precursor material at a first temperature;
pyrolyzing the precursor material at a second temperature higher than the first temperature to decompose organic components; and
crystallizing remaining components of the precursor material at a third temperature higher than the second temperature.
20. The method according to claim 16 , wherein the applying of precursor material comprises applying a plurality of thin layers of precursor material.
21. The method according to claim 1 , wherein depositing the transducing material comprises depositing a piezoelectric material.
22. The method according to claim 21 , wherein depositing the piezoelectric material further comprises depositing lead zirconate titanate.
23. The method according to claim 1 , wherein depositing the transducing material comprises depositing a shape memory alloy material.
24. The method according to claim 23 , wherein depositing the shape memory alloy material further comprises depositing a nickel titanium alloy.
25. The method according to claim 1 , wherein depositing the transducing material comprises:
depositing a first material having a first coefficient of thermal expansion; and
depositing a second material in contact with the first material, the second material having a second coefficient of thermal expansion, the second coefficient of thermal expansion being greater that first coefficient of thermal expansion.
26. The method according to claim 25 , wherein the first material comprises silicon oxide and the second material comprises titanium aluminide.
27. The method according to claim 1 , wherein depositing the polymer layer comprises laminating a film.
28. The method according to claim 1 , wherein depositing the polymer layer comprises spinning the wafer.
29. The method according to claim 1 , wherein the polymer layer is photopatternable.
30. The method according to claim 1 , wherein the polymer layer comprises an epoxy material.
31. The method according to claim 1 further comprising applying a masking layer to the second surface of the substrate, the masking layer exposing the second surface of the substrate in a first location where the cavity is to be etched.
32. The method according to claim 31 , wherein the masking layer exposes the substrate in a second location where a through hole is to be etched from the second surface to the first surface.
33. The method according to claim 1 , wherein etching the cavity further comprises deep reactive ion etching from the second surface of the substrate.
34. The method according to claim 33 , wherein etching the cavity further comprises using SF 6 as a process gas.