Wafer level processed microbolometer focal plane array

Patent metadata

Field	Value
Publication number	US-10976202-B2
Application number	US-201916373460-A
Country	US
Kind code	B2
Filing date	Apr 2, 2019
Priority date	Apr 3, 2018
Publication date	Apr 13, 2021
Grant date	Apr 13, 2021

Abstract

Focal Plane Arrays (FPAs) or methods to produce FPAs may be provided for a microbolometer based thermal imaging sensor utilizing wafer level processing (WLP) techniques for manufacture. Batch processing techniques for sealing a cap wafer to an FPA wafer to produce vacuum sealed FPAs may be accomplished with suitable FPA design features in conjunction with a glass frit seal methodology utilizing appropriate frit glass compositions.

First claim

What is claimed is:

1. A thermal imaging focal plane array (FPA), comprising:
an array of microbolometer thermal photodetectors integrated with readout electronics, microfabricated as an array of dies on a first silicon wafer;
a second silicon wafer parallel to and spaced from the first silicon wafer such that the array of dies is disposed between the first silicon wafer and the second silicon wafer; and
a glass frit seal disposed between the first silicon wafer and the second silicon wafer, the glass frit seal sealing the second silicon wafer to the first silicon wafer,
wherein the glass frit seal material is disposed between the first silicon wafer and the second silicon wafer in a seal structure surrounding a corresponding location of each die of the array of dies, and
wherein the glass frit seal comprises a glass frit material having a melting temperature lower than 350 degrees C.

2. The method of claim 1 , wherein at least the second silicon wafer comprises a material that is at least partially transparent to thermal radiation.

3. The thermal imaging FPA of claim 1 , wherein the melting temperature of the glass frit material is less than 300 degrees C.

4. The thermal imaging FPA of claim 1 , wherein the glass frit seal is deposited on the second silicon wafer as a paste and is conditioned at at least two temperatures including a first conditioning temperature lower than the melting temperature and a second conditioning temperature higher than the melting temperature to convert the paste into a glass bond line.

5. The thermal imaging FPA of claim 1 , wherein a separation distance between a bottom surface of the second silicon wafer and top surfaces of the microbolometer photodetectors is set by a height of the glass frit seal.

6. The thermal imaging FPA of claim 1 , wherein the second silicon wafer comprises one or more raised structures underlying at least a portion of the glass frit seal.

7. The thermal imaging FPA of claim 6 , wherein the one or more raised structures improve alignment of the glass frit material and reduce spreading of the glass frit material during deposition of the glass frit material.

8. The thermal imaging FPA of claim 1 , wherein a getter is fabricated on a bottom surface of the second silicon wafer for each die.

9. The thermal imaging FPA of claim 8 , wherein the getter is positioned to optically occlude at least one reference bolometer when the first silicon wafer and the second silicon wafer are sealed together.

10. The thermal imaging FPA of claim 1 , wherein a bond area surrounding each FPA die is configured to have dimensions compatible with glass frit seal printing tolerances.

11. A method of producing a thermal imaging Focal Plane Array (FPA), the method comprising:
microfabricating an array of microbolometer thermal photodetectors integrated with readout electronics, as an array of dies on a first silicon wafer;
depositing a glass frit material on a bottom surface of a second silicon wafer in a seal structure surrounding one or more areas corresponding to locations of the dies on the first silicon wafer, the glass frit material having a melting temperature lower than 350 degrees C.; and
sealing the second silicon wafer to the first silicon wafer by forming a glass frit seal from the glass frit material such that the array of dies is disposed between the first silicon wafer and the second silicon wafer,
wherein the second silicon wafer is sealed to the first silicon wafer under vacuum at a sealing temperature of less than 350 degrees C.

12. The method of claim 11 , wherein at least the second silicon wafer comprises a material that is at least partially transparent to thermal radiation.

13. The method of claim 11 , wherein the melting temperature of the glass frit material is less than 300 degrees C., and wherein the sealing temperature is less than 300 degrees C.

14. The method of claim 11 , wherein the glass frit material is deposited on the second silicon wafer as a paste, and wherein the glass frit material is conditioned at at least two temperatures including a first conditioning temperature lower than the melting temperature and a second conditioning temperature higher than the melting temperature to convert the glass paste into a glass bond line.

15. The method of claim 11 , wherein, after the second silicon wafer is sealed to the first silicon wafer, a separation distance between the bottom surface of the second silicon wafer and top surfaces of the microbolometer photodetectors is set by a height of the glass frit seal.

16. The method of claim 11 , further comprising, prior to depositing the glass frit material, fabricating the second silicon wafer with one or more raised structures underlying a location of the seal structure.

17. The method of claim 16 , wherein the one or more raised structures improve alignment of the glass frit material and reduce spreading of the glass frit material during deposition of the glass frit material.

18. The method of claim 11 , further comprising fabricating a getter on the bottom surface of the second silicon wafer for each die.

19. The method of claim 18 , wherein the getter is positioned to optically occlude at least one reference bolometer when the first silicon wafer and the second silicon wafer are sealed together.

20. The method of claim 11 , wherein a bond area surrounding each FPA die is configured to have dimensions compatible with glass frit seal printing tolerances.

Assignees

• Seek Thermal Inc

Inventors

• Parrish William J

Classifications

• G01J5/045 Primary

  Sealings; Vacuum enclosures; Encapsulated packages; Wafer bonding structures; Getter arrangements (getter arrangements per se H10W76/48, H10P36/03) · CPC title

• G01J2005/204

  prepared by semiconductor processing, e.g. VLSI · CPC title

• G01J5/20

  using resistors, thermistors or semiconductors sensitive to radiation, e.g. photoconductive devices · CPC title

• G01J2005/065

  by shielding · CPC title

• G01J2005/0077

  Imaging · CPC title