Method and Apparatus To Reduce The Leakage Rate of a Hermetic Cavity

• US 20180159547A1
• Filed: 12/01/2016
• Published: 06/07/2018
• Est. Priority Date: 12/01/2016
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Herbsommer, Juan, Cook, Benjamin, Jacobs, S. Josh
• Granted Patent: US 10,374,621 B2
• Time in Patent Office: Days
• CPC Class Codes: B81B 7/0041 maintaining a controlled atmosphere with techniques not provided for in B81B7/0038
• CPC Class Codes: H01L 2224/11 Manufacturing methods
• CPC Class Codes: H01L 2224/48091 Arched
• CPC Class Codes: H01L 24/06 of a plurality of bonding areas
• CPC Class Codes: H01L 24/46 of a plurality of wire connectors
• CPC Class Codes: H01L 24/83 using a layer connector
• CPC Class Codes: H01L 29/0649 Dielectric regions, e.g. SiO2 regions, air gaps
• CPC Class Codes: H01L 2924/00014 the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details
• CPC Class Codes: H03L 7/26 using energy levels of molecules, atoms, or subatomic particles as a frequency reference

Abstract

A chip scale vapor cell and millimeter wave atomic clock apparatus are disclosed. The chip scale vapor cell includes a first substrate and a second substrate bonded to the first substrate with a bonding material. A primary hermetic cavity includes a first bottom wall and first sidewalls formed in the first substrate and a first top wall formed by the lower surface of the second substrate. A secondary hermetic cavity includes a second bottom wall and second sidewalls formed in the first substrate and a second top wall formed by the lower surface of the second substrate. The secondary hermetic cavity is separate from the primary hermetic cavity and surrounds the perimeter of the primary hermetic cavity. A gas, which can be a dipolar molecular gas, is sealed in the primary hermetic cavity and the secondary hermetic cavity at a given initial pressure.

Claims

1. A chip scale vapor cell comprising:

a first substrate;

a second substrate bonded to the first substrate with a bonding material, the second substrate comprising an upper surface and a lower surface;

a primary hermetic cavity comprising a first bottom wall and first sidewalls formed in the first substrate and a first top wall formed by the lower surface of the second substrate;

a secondary hermetic cavity comprising a second bottom wall and second sidewalls formed in the first substrate, a second top wall formed by the lower surface of the second substrate, the secondary hermetic cavity being separate from the primary hermetic cavity and surrounding a perimeter of the primary hermetic cavity; and

a gas sealed in the primary hermetic cavity and the secondary hermetic cavity at a given initial pressure.

2. The chip scale vapor cell as recited in claim 1 wherein the given initial pressure is less than 1.0 mbar.

3. The chip scale vapor cell as recited in claim 1 wherein the given initial pressure is approximately 0.1 mBar or less.

4. The chip scale vapor cell as recited in claim 1 wherein the gas comprises a dipolar molecule.

5. The chip scale vapor cell as recited in claim 1 wherein the gas comprises water vapor.

6. The chip scale vapor cell as recited in claim 4 wherein a volume of the secondary hermetic cavity is equal to or greater than one tenth the volume of the primary hermetic cavity.

7. The chip scale vapor cell as recited in claim 4 wherein a volume of the secondary hermetic cavity is equal to or greater than a volume of the primary hermetic cavity.

8. The chip scale vapor cell as recited in claim 4 wherein the secondary hermetic cavity comprises a first region that surrounds the perimeter of the primary hermetic cavity and a second region that lies under the primary hermetic cavity, the first and second regions being conjoined.

9. The chip scale vapor cell as recited in claim 4 wherein the secondary hermetic cavity comprises a plurality of secondary hermetic cavities, a first secondary hermetic cavity of the plurality of secondary hermetic cavities surrounding the perimeter of the primary hermetic cavity and each successive secondary hermetic cavity of the plurality of secondary hermetic cavities surrounding an outside perimeter of a previous secondary hermetic cavity.

10. The chip scale vapor cell as recited in claim 4 wherein the secondary hermetic cavity comprises a gettering agent that absorbs the dipolar molecule.

11. The chip scale vapor cell as recited in claim 4 wherein the first bottom wall, first sidewalls and first top wall comprise a conductive surface and the first top wall comprises a first non-conductive aperture on the lower surface of the second substrate that provides an electromagnetic field entrance to the primary hermetic cavity and a second non-conductive aperture on the lower surface of the second substrate and spaced from the first non-conductive aperture that provides the electromagnetic field exit from the primary hermetic cavity.

12. The chip scale vapor cell as recited in claim 11 further comprising a first conductive coupling structure formed on the upper surface of the second substrate proximate the first non-conductive aperture and a second conductive coupling structure formed on the upper surface of the second substrate proximate the second non-conductive aperture.

13. A millimeter wave atomic clock apparatus comprising:

a vapor cell, comprising;

a first substrate,

a second substrate bonded to the first substrate with a bonding material, the second substrate comprising an upper surface and a lower surface,

a primary hermetic cavity comprising a first bottom wall and first sidewalls formed in the first substrate and a first top wall formed by the lower surface of the second substrate,

a secondary hermetic cavity comprising a second bottom wall and second sidewalls formed in the first substrate, a second top wall formed by the lower surface of the second substrate, the secondary hermetic cavity being separate from the primary hermetic cavity, the secondary hermetic cavity surrounding a perimeter of the primary hermetic cavity and

a dipolar molecular gas sealed in the primary hermetic cavity and the secondary hermetic cavity at a given initial pressure; and

a transceiver circuit mounted to the second substrate and electrically coupled to provide an alternating electrical output signal at a first end of the primary hermetic cavity and to receive an alternating electrical input signal at a second end of the primary hermetic cavity, the transceiver circuit coupled to selectively adjust a frequency of the alternating electrical output signal and to provide a reference clock signal.

14. The millimeter wave atomic clock apparatus as recited in claim 13 wherein the first bottom wall, the first sidewalls and the first top wall comprise a conductive surface and the first top wall further comprises a first non-conductive aperture for providing an electromagnetic field entrance to the primary hermetic cavity and a second non-conductive aperture spaced from the first non-conductive aperture for providing the electromagnetic field exit from the primary hermetic cavity.

15. The millimeter wave atomic clock apparatus as recited in claim 14 wherein the vapor cell further comprises:

a first conductive coupling structure formed on the upper surface of the second substrate proximate the first non-conductive aperture and coupled to receive the alternating electrical output signal from the transceiver circuit,

a second conductive coupling structure formed on the upper surface of the second substrate proximate the second non-conductive aperture and coupled to provide the alternating electrical input signal to the transceiver circuit.

16. The millimeter wave atomic clock apparatus as recited in claim 15 wherein the given initial pressure is approximately 0.1 mBar or less.

17. The millimeter wave atomic clock apparatus as recited in claim 16 wherein the dipolar molecular gas comprises water vapor.

18. The millimeter wave atomic clock apparatus as recited in claim 17 wherein the secondary hermetic cavity comprises a first region that surrounds the perimeter of the primary hermetic cavity and a second region that lies under the primary hermetic cavity, the first and second regions being conjoined.

19. The millimeter wave atomic clock apparatus as recited in claim 17 wherein the secondary hermetic cavity comprises a plurality of secondary hermetic cavities, a first secondary hermetic cavity of the plurality of secondary hermetic cavities surrounding the perimeter of the primary hermetic cavity and each successive secondary hermetic cavity of the plurality of secondary hermetic cavities surrounding an outside perimeter of a previous secondary hermetic cavity.