Methods related to gradient raised frames in film bulk acoustic resonators
Methods related to gradient raised frames in film bulk acoustic resonators. According to certain aspects, a method for fabricating a film bulk acoustic resonator device can include: forming a first metal layer over a substrate; forming a piezoelectric layer; forming a second metal layer, the piezoelectric layer positioned between the first and second metal layers; and forming a gradient raised frame implemented relative to one of the first and second metal layers and configured to improve reflection of lateral mode waves and to reduce conversion of main mode waves into lateral mode waves.
1. A method for fabricating a film bulk acoustic resonator device, the method comprising:
forming a first metal layer over a substrate;
forming a piezoelectric layer;
forming a second metal layer, the piezoelectric layer positioned between the first and second metal layers, the first metal layer, the second metal layer, and the piezoelectric layer forming an active region; and
forming a gradient raised frame implemented relative to one of the first and second metal layers and configured to improve reflection of lateral mode waves and to reduce conversion of main mode waves into lateral mode waves, the gradient raised frame including a gradient portion that interfaces with one or more of the first metal layer, the second metal layer, or the piezoelectric layer without passing through the active region.
2. The method of claim 1 wherein the second metal layer is above the piezoelectric layer and the first metal layer is below the piezoelectric layer.
3. The method of claim 2 wherein the gradient raised frame is implemented above the second metal layer.
4. The method of claim 2 wherein the gradient raised frame is implemented below the second metal layer.
5. The method of claim 2 wherein the gradient raised frame has an angle relative to a direction parallel to the first and second metal layers and the piezoelectric layer.
6. The method of claim 5 wherein the angle is less than 90°.
7. The method of claim 6 wherein the angle is less than 45°.
8. The method of claim 7 wherein the angle is less than 30°.
9. The method of claim 2 wherein the gradient raised frame is made of one or more of a heavy material or a low acoustic impedance material.
10. The method of claim 2 further comprising forming a second gradient raised frame implemented relative to one of the first and second metal layers and configured to improve reflection of lateral mode waves and to reduce conversion of main mode waves into lateral mode waves.
11. The method of claim 10 wherein the gradient raised frame is implemented above the second metal layer and the second gradient raised frame is implemented below the second metal layer.
12. The method of claim 10 wherein the gradient raised frame is implemented above the second metal layer and the second gradient raised frame is implemented above the first metal layer.
13. The method of claim 10 wherein the gradient raised frame is implemented below the second metal layer and the second gradient raised frame is implemented below the first metal layer.
14. The method of claim 10 wherein the gradient raised frame and the second gradient raised frame have respective angles relative to a direction parallel to the first and second metal layers and the piezoelectric layer.
15. The method of claim 14 wherein each of the respective angles is less than 90°.
16. The method of claim 15 wherein each of the respective angles is less than 45°.
17. The method of claim 10 wherein the gradient raised frame and the second gradient raised frame are made of one or more of a heavy material or a low acoustic impedance material.
18. The method of claim 17 wherein the gradient raised frame is made of a heavy material and the second gradient raised frame is made of a low acoustic impedance material.
19. The method of claim 2 wherein a passivation layer is implemented above the gradient raised frame.
20. The method of claim 19 wherein the passivation layer includes a recessed frame adjacent to an active region.