Micro-electro-mechanical system device and piezoelectric composite stack thereof

Patent metadata

Field	Value
Publication number	US-2024136994-A1
Application number	US-202217968812-A
Country	US
Kind code	A1
Filing date	Oct 19, 2022
Priority date	Oct 19, 2022
Publication date	Apr 25, 2024
Grant date	—

Abstract

A micro-electro-mechanical system (MEMS) device includes a substrate having a cavity and a MEMS structure disposed over the cavity and attached to the substrate. The MEMS structure includes at least one first piezoelectric layer having a first piezoelectric coefficient and two second piezoelectric layers respectively disposed under and above the first piezoelectric layer, where each second piezoelectric layer has a second piezoelectric coefficient higher than the first piezoelectric coefficient. The MEMS structure further includes a first electrode layer and a second electrode layer sandwiching the two second piezoelectric layers.

First claim

What is claimed is:

1 . A micro-electro-mechanical system (MEMS) device, comprising:
a substrate having a cavity; and a MEMS structure disposed over the cavity and attached to the substrate, wherein the MEMS structure comprises:
at least one first piezoelectric layer having a first piezoelectric coefficient;
two second piezoelectric layers respectively disposed under and above the first piezoelectric layer, each of the second piezoelectric layers having a second piezoelectric coefficient higher than the first piezoelectric coefficient; and
a first electrode layer and a second electrode layer sandwiching the two second piezoelectric layers.

2 . The MEMS device of claim 1 , wherein the MEMS structure is symmetric with respect to a horizontal plane in the middle of the at least one first piezoelectric layer.

3 . The MEMS device of claim 1 , wherein a thickness of the at least one first piezoelectric layer is greater than the thickness of each of the second piezoelectric layers.

4 . The MEMS device of claim 1 , wherein the at least one first piezoelectric layer comprises two first piezoelectric layers disposed between the two second piezoelectric layers, and having an average piezoelectric coefficient lower than the second piezoelectric coefficient, and the MEMS structure further comprises a third electrode layer disposed between the two first piezoelectric layers.

5 . The MEMS device of claim 4 , wherein the MEMS structure is symmetric with respect to the third electrode layer.

6 . The MEMS device of claim 1 , wherein the MEMS structure further comprises:
two third piezoelectric layers respectively disposed under and above the at least one first piezoelectric layer, and disposed between the two second piezoelectric layers, wherein an average piezoelectric coefficient of the two third piezoelectric layers is lower than the second piezoelectric coefficient; two fourth piezoelectric layers sandwiching the at least one first piezoelectric layer and having an average piezoelectric coefficient higher than the first piezoelectric coefficient; and a third electrode layer and a fourth electrode layer sandwiching the two fourth piezoelectric layers.

7 . The MEMS device of claim 6 , wherein the composition of the at least one first piezoelectric layer and the two third piezoelectric layers comprises aluminum nitride (AlN), zinc oxide (ZnO), or gallium nitride (GaN), and the composition of the two second piezoelectric layers and the two fourth piezoelectric layers comprises lead zirconate titanate (PZT), or AlN, ZnO or GaN doped with a dopant, and wherein the dopant comprises scandium (Sc), yttrium (Y), titanium (Ti), chromium (Cr), magnesium (Mg) or hafnium (Hf).

8 . The MEMS device of claim 1 , wherein the MEMS structure further comprises:
a seed layer disposed on a bottom surface of the first electrode layer; and a passivation layer disposed on a top surface of the second electrode layer.

9 . The MEMS device of claim 1 , wherein the MEMS structure has an interrupted portion penetrating the MEMS structure and disposed above the cavity, and the MEMS structure comprises a cantilevered beam or a cantilevered diaphragm above the cavity.

10 . The MEMS device of claim 9 , further comprising a sacrificial layer disposed between the substrate and the MEMS structure, wherein the sacrificial layer has an opening connected to the interrupted portion and the cavity.

11 . A piezoelectric composite stack of a micro-electro-mechanical system (MEMS) device, comprising:
at least one piezoelectric film, wherein the number of the at least one piezoelectric film is an integer (n); and a plurality of electrode layers, wherein the number of the plurality of electrode layers is n+1, and two of the plurality of electrode layers sandwich one of the at least one piezoelectric film, and wherein each the piezoelectric film comprises:
a lower piezoelectric coefficient layer having a first piezoelectric coefficient; and
at least one higher piezoelectric coefficient layer stacked with the lower piezoelectric coefficient layer and having a second piezoelectric coefficient higher than the first piezoelectric coefficient.

12 . The piezoelectric composite stack of claim 11 , wherein the number of n is equal to 2a, and a is an integer greater than zero, the number of the lower piezoelectric coefficient layer of the piezoelectric composite stack is an integer (i) that is equal to n, and the number of the at least one higher piezoelectric coefficient layer of the piezoelectric composite stack is an integer (j) that is equal to n.

13 . The piezoelectric composite stack of claim 11 , wherein the number of n is equal to 2a-1, and a is an integer greater than zero, the number of the lower piezoelectric coefficient layer of the piezoelectric composite stack is an integer (i) that is equal to n, and the number of the at least one higher piezoelectric coefficient layer of the piezoelectric composite stack is an integer (j) that is equal to n+1.

14 . The piezoelectric composite stack of claim 11 , wherein the number of n is 1, and the piezoelectric film comprises two higher piezoelectric coefficient layers respectively stacked above and under the lower piezoelectric coefficient layer.

15 . The piezoelectric composite stack of claim 11 , wherein the number of n is 2, and the piezoelectric composite stack comprises an upper piezoelectric film and a lower piezoelectric film, wherein the upper piezoelectric film comprises a (2-2)-th higher piezoelectric coefficient layer stacked above a (2-1)-th lower piezoelectric coefficient layer, the lower piezoelectric film comprises a (1-2)-th higher piezoelectric coefficient layer stacked under a (1-1)-th lower piezoelectric coefficient layer, and one of the plurality of electrode layers is disposed between the upper piezoelectric film and the lower piezoelectric film, the (2-2)-th and the (1-2)-th higher piezoelectric coefficient layers have the second piezoelectric coefficient, and the (2-1)-th and the (1-1)-th lower piezoelectric coefficient layers have the first piezoelectric coefficient.

16 . The piezoelectric composite stack of claim 11 , wherein the number of n is 3, and the piezoelectric composite stack comprises an upper piezoelectric film, a middle piezoelectric film and a lower piezoelectric film, wherein the upper piezoelectric film comprises a (2-2)-th higher piezoelectric coefficient layer stacked above a (2-1)-th lower piezoelectric coefficient layer, the middle piezoelectric film comprises two (3-2)-th higher piezoelectric coefficient layers sandwiching a (3-1)-th lower piezoelectric coefficient layer, the lower piezoelectric film comprises a (1-2)-th higher piezoelectric coefficient layer stacked under a (1-1)-th lower piezoelectric coefficient layer, two of the plurality of electrode layers sandwich the middle piezoelectric film, the (3-2)-th, the (2-2)-th and the (1-2)-th higher piezoelectric coefficient layers have the second piezoelectric coefficient, and the (3-1)-th, the (2-1)-th and the (1-1)-th lower piezoelectric coefficient layers have the first piezoelectric coefficient.

17 . The piezoelectric composite stack of claim 16 , wherein the middle piezoelectric film has a thickness different from both the thickness of the upper piezoelectric film and the thickness of the lower piezoelectric film.

18 . The piezoelectric composite stack of claim 11 , wherein a total thickness of the at least one higher piezoelectric coefficient layer in each the piezoelectric film is less than 50% of a total thickness of each the pie

Assignees

• Vanguard Int Semiconduct Corp

Inventors

• Xia jia jie
• Kallupalathinkal Chandran Bevita
• Nagarajan Ranganathan
• Yelehanka Ramachandramurthy Pradeep

Classifications

• B81B2201/025

  Inertial sensors not provided for in B81B2201/0235 - B81B2201/0242 · CPC title

• B81B3/0086

  Electrical characteristics, e.g. reducing driving voltage, improving resistance to peak voltage · CPC title

• H04R19/005

  using semiconductor materials · CPC title

• H04R2201/003

  Mems transducers or their use · CPC title

• H03H9/178

  of a laminated structure of multiple piezoelectric layers with inner electrodes · CPC title