Anodically bonded cell, method for making same and systems incorporating same

• US 20050184815A1
• Filed: 01/05/2005
• Published: 08/25/2005
• Est. Priority Date: 01/06/2004
• Status: Active Grant

• Current Assignee: SRI International, Inc.
• Original Assignee: Sarnoff Corporation (SRI International, Inc.)
• Inventors: Braun, Alan Michael, Lipp, Steven Alan, Zanzucchi, Peter J., McBride, Sterling Eduard, Abeles, Joseph H., Riganati, John P., Whaley, Ralph Doud Jr.
• Granted Patent: US 7,400,207 B2
• Time in Patent Office: Days
• US Class Current: 331/94.100
• CPC Class Codes: G04F 5/14 using atomic clocks

Abstract

A cell suitable for use with an atomic clock and a method for making the same, the cell including: a silicon wafer having a recess formed therein; at least one amorphous silicate member having an ion mobility and temperature expansion coefficient approximately that of silicon sealing the recess; and, an alkali metal containing component and buffer gas contained in the recess. The method includes: providing a silicon wafer; forming a cavity through the silicon wafer; introducing an alkali metal containing component and buffer gas into the cavity; and, anodically bonding at least one amorphous silicate member having an ion mobility and temperature expansion coefficient approximately that of silicon to the wafer to close the cavity.

Claims

1. A cell suitable for use with an atomic clock comprising:

a silicon wafer having a recess formed therein;

an alkali metal containing component and buffer gas in said recess; and

,

at least one amorphous silicate member having an ion mobility and temperature expansion coefficient approximately that of silicon closing said recess.

2. The cell of claim 1, further comprising at least a second amorphous silicate member having an ion mobility and temperature expansion coefficient approximately that of silicon sealing said recess.

3. The cell of claim 1, wherein said amorphous silicate member comprises borosilicate glass.

4. The cell of claim 1, wherein said alkali metal component comprises a Cs vapor.

5. The cell of claim 4, wherein said buffer gas comprises at least one of argon, neon and nitrogen.

6. The cell of claim 1, further comprising at least one heater positioned substantially adjacent to said at least one amorphous silicate member.

7. The cell of claim 6, wherein said heater comprises a patterned indium tin oxide heater.

8. The cell of claim 1, further comprising a photo detector being integrated with said silicon wafer.

9. The cell of claim 1, further comprising a laser suitable for emitting optical energy having a center wavelength of about 894 nm into said cavity.

10. The cell of claim 9, further comprising at least one wave plate between said laser and said alkali metal containing component.

11. The cell of claim 9, further comprising an amplitude modulator positioned between said laser and said alkali metal containing component.

12. The cell of claim 9, further comprising a neutral density filter positioned between said laser and said alkali metal containing component.

13. The cell of claim 9, further comprising a reflector positioned with respect to said cavity to reflect emissions from said laser back through said cavity.

24. The process of claim 13, wherein said buffer gas consists essentially of about 79% argon and about 21% nitrogen.

14. A process for fabricating a cell suitable for use with an atomic clock comprising:

providing a silicon wafer;

forming a cavity through said silicon wafer;

introducing an alkali metal containing component and buffer gas into said cavity; and

,

anodically bonding at least one amorphous silicate member having an ion mobility and temperature expansion coefficient approximately that of silicon to said wafer.

15. The process of claim 14, wherein said introducing is prior to bonding at least one of said members to said wafer.

16. The process of claim 14, wherein said introducing comprises forming an aperture through one of said members.

17. The process of claim 16, wherein said introducing further comprises flowing an alkali metal atomic stream through said aperture.

18. The process of claim 16, wherein said aperture is between about 100 micrometers and about 125 micrometers in diameter.

19. The process of claim 16, wherein said aperture is at an angle of about 60 degrees to a surface plane of said cell.

20. The process of claim 14, wherein said amorphous silicate member comprises borosilicate glass.

21. The process of claim 14, further comprising anodically bonding a second amorphous silicate member having an ion mobility and temperature expansion coefficient approximately that of silicon to said wafer to close said cavity.

22. The process of claim 14, wherein said alkali metal containing component comprises Cs.

23. The process of claim 22, wherein said buffer gas comprises at least one of argon, neon and nitrogen.

25. The process of claim 22, wherein said introducing comprises providing Cs salt and a reducing agent.

26. The process of claim 14, wherein said introducing comprises providing liquid cesium near a periphery of said cavity.

27. The process of claim 14, wherein said introducing comprises a liquid Cs pin transfer.

28. The process of claim 14, further comprising providing a protectant within said cavity.

29. The process of claim 28, wherein said providing a protectant comprises depositing at least one of SiO₂, Al₂O₃ or Si_xN_y.

30. The process of claim 14, wherein said forming comprises at least one of:

providing an etch mask over said silicon wafer and caustic etching said silicon wafer dependently upon said etch mask; and

,

physical eroding of said silicon wafer.

31. The process of claim 14, further comprising forming a second cavity in said silicon wafer and in physical communication with said first cavity.

34. The cell of claim 31, further comprising at least one heater positioned substantially adjacent to at least one of said borosilicate glass members.

35. The cell of claim 21, further comprising at least one of SiO₂ and Al₂O₃ coating at least a portion of an interior surface of said recess.

32. A cell suitable for use with an atomic clock comprising:

a first amorphous silicate member having an ion mobility and temperature expansion coefficient approximately that of silicon and a recess;

an alkali containing component and buffer gas in said recess;

a silicon containing layer over said first borosilicate glass member and around a periphery of said recess; and

,

a second amorphous silicate member having an ion mobility and temperature expansion coefficient approximately that of silicon and being anodically bonded to said silicon containing layer and closing said recess.

33. The cell of claim 32, wherein said alkali metal component comprises a Cs vapor and said buffer gas comprises at least one of argon, neon and nitrogen.

36. A process for fabricating a cell suitable for use with an atomic clock comprising:

providing a first amorphous silicate member having an ion mobility and temperature expansion coefficient approximately that of silicon and a recess;

providing a silicon containing layer over said first member and around a periphery of said recess;

introducing an alkali containing component and buffer gas into said recess; and

,

anodically bonding a second amorphous silicate member having an ion mobility and temperature expansion coefficient approximately that of silicon to said silicon containing layer to close said recess.

37. The process of claim 36, wherein said component comprises Cs and said buffer gas comprises at least one of argon, neon and nitrogen.

38. The process of claim 36, wherein said introducing comprises a liquid Cs pin transfer.

39. The process of claim 36, wherein said introducing is prior to said closing said recess.

40. A system comprising:

a clock comprising a silicon wafer having a recess formed therein;

at least one amorphous silicate member having an ion mobility and temperature expansion coefficient approximately that of silicon closing said recess; and

, an alkali metal containing component and buffer gas contained in said recess; and

,

a device having an input coupled to said clock and being operatively responsive to said input.

41. The system of claim 40, wherein said device comprises at least one of a distributed computing system nodal computing element, a global positioning system signal receiver and a communications transceiver.

42. A system comprising:

a clock comprising a first amorphous silicate member having an ion mobility and temperature expansion coefficient approximately that of silicon and a recess;

an alkali containing component and buffer gas in said recess;

a silicon containing layer over said first borosilicate glass member and around said recess; and

, a second amorphous silicate member having an ion mobility and temperature expansion coefficient approximately that of silicon anodically bonded to said silicon containing layer and closing said recess; and

,

a device having an input coupled to said clock and being operatively responsive to said input.

43. The system of claim 42, wherein said device comprises at least one of a distributed computing system nodal computing element, a global positioning system signal receiver and a communications transceiver.

44. A system suitable for use with an atomic clock comprising:

a cell defining a cavity having an interior volume of less than about 1 microliter; and

,

an atomic vapor and buffer gas in said cavity and at a pressure greater than about an atmosphere.