Micromachined ultrasonic transducers with a slotted membrane structure

1. A piezoelectric micromachined ultrasonic transducer (PMUT) device, comprising:

a substrate having an open cavity; and

a membrane attached to the substrate over the opening, a portion of the membrane that overlies the open cavity being divided into a plurality of cantilevers wherein the cantilevers are mechanically coupled by one or more interruptions in gaps between adjacent cantilevers so that the cantilevers resonate at a common frequency, wherein the one or more interruptions are located between a perimeter of the open cavity and a center of the open cavity.

2. The device of claim 1 , wherein the open cavity is fully open through the substrate from a side of the substrate to which the membrane is attached to a side of the substrate opposite the side of the substrate to which the membrane is attached.

3. The device of claim 1 , wherein the cavity is partially open from a side of the substrate to which the membrane is attached but not through to a side of the substrate opposite the side of the substrate to which the membrane is attached.

4. The device of claim 1 , wherein a shape of the membrane is a circular shape.

5. The device of claim 1 , wherein a shape of the membrane is a squared shape.

6. The device of claim 1 , wherein a shape of the membrane is a triangular shape.

7. The device of claim 1 , wherein the plurality of cantilevers includes two or more cantilevers.

8. The device of claim 1 , wherein the plurality of cantilevers includes three or more cantilevers.

9. The device of claim 1 , wherein the plurality of cantilevers includes four or more cantilevers.

10. The device of claim 1 , wherein the plurality of cantilevers includes six or more cantilevers.

11. The device of claim 1 , wherein the plurality of cantilevers includes eight or more cantilevers.

12. The device of claim 1 , wherein the plurality of cantilevers includes two or more identically-shaped cantilevers.

13. The device of claim 1 , wherein the plurality of cantilevers includes two or more tapered cantilevers.

14. The device of claim 1 , wherein the plurality of cantilevers includes two or more identically-shaped tapered cantilevers.

15. The device of claim 1 , wherein a thickness of the substrate is such that an acoustic resonance frequency of the opening is approximately equal to the common frequency.

16. The device of claim 1 , wherein the membrane includes multiple layers of material.

17. The device of claim 16 , wherein the multiple layers include a passive layer formed on the substrate.

18. The device of claim 17 , wherein the multiple layers further include a conductive bottom electrode layer formed on the passive layer.

19. The device of claim 18 , wherein the multiple layers further include a piezoelectric layer formed on the conductive bottom electrode layer.

20. The device of claim 19 , wherein the multiple layers further include a conductive top electrode layer formed on the piezoelectric layer.

21. The device of claim 1 , wherein the cantilevers are mechanically coupled by one or more concentric rings.

22. The device of claim 1 , wherein the cantilevers are mechanically coupled by two or more concentric rings.

23. The device of claim 1 , wherein the cantilevers are mechanically coupled by three or more concentric rings.

24. The device of claim 1 , wherein a gap between adjacent cantilevers of the plurality is smaller than (1 μm)/f o , where f o is an operational frequency of the device in MHz.

25. The device of claim 24 , wherein the gap is smaller than (0.6 μm)/f o .

26. A method for fabricating a piezoelectric micromachined ultrasonic transducer (PMUT) device, comprising:

forming a membrane attached to a substrate;

dividing a portion of the membrane into a plurality of cantilevers that are mechanically coupled; and

forming an opening through a portion of the substrate underling the plurality of cantilevers to release the cantilevers, wherein the cantilevers are mechanically coupled by one or more interruptions in gaps between adjacent cantilevers so that the cantilevers resonate at a common frequency, wherein the one or more interruptions are located between a perimeter of the open cavity and a center of the open cavity.

27. The method of claim 26 , wherein a shape of the membrane is a circular shape.

28. The method of claim 26 , wherein a shape of the membrane is a squared shape.

29. The method of claim 26 , wherein a shape of the membrane is a triangular shape.

30. The method of claim 26 , wherein the plurality of identically-shaped tapered cantilevers includes two or more cantilevers.

31. The method of claim 26 , wherein the plurality of cantilevers includes three or more cantilevers.

32. The method of claim 26 , wherein the plurality of cantilevers includes four or more cantilevers.

33. The method of claim 26 , wherein the plurality of cantilevers includes six or more cantilevers.

34. The method of claim 26 , wherein the plurality of cantilevers includes eight or more cantilevers.

35. The method of claim 26 , wherein the plurality of cantilevers includes two or more identically-shaped cantilevers.

36. The method of claim 26 , wherein the plurality of cantilevers includes two or more tapered cantilevers.

37. The method of claim 26 , wherein the plurality of cantilevers includes two or more identically-shaped tapered cantilevers.

38. The method of claim 26 , wherein a thickness of the substrate is such that an acoustic resonance frequency of the opening is approximately equal to the common frequency.

39. The method of claim 26 , wherein forming the membrane includes forming multiple layers of material.

40. The method of claim 39 , wherein forming the multiple layers includes forming a passive layer on the substrate.

41. The method of claim 40 , wherein forming the multiple layers further includes forming a conductive bottom electrode layer on the passive layer.

42. The method of claim 41 , wherein forming the multiple layers further includes forming a piezoelectric layer on the conductive bottom electrode layer.

43. The method of claim 42 , wherein forming the multiple layers further includes forming a conductive top electrode layer on the piezoelectric layer.

44. The method of claim 26 , wherein dividing a portion of the membrane into a plurality of identically-shaped tapered cantilevers that are mechanically coupled includes forming one or more concentric rings that couple the identically-shaped tapered cantilevers.

45. The device of claim 44 , wherein forming the one or more concentric rings includes forming two or more concentric rings.

46. The device of claim 44 , wherein forming the one or more concentric rings includes forming three or more concentric rings.

47. The method of claim 26 , wherein dividing a portion of the membrane into a plurality of identically-shaped tapered cantilevers that are mechanically coupled includes forming a gap between adjacent cantilevers of the plurality, wherein the gap is smaller than (1 μm)/f o , where f o is an operational frequency of the device in MHz.

48. The method of claim 47 , wherein the gap is smaller than (0.6 μm)/f o .