Mars optical modulators

• US 5,949,571 A
• Filed: 07/30/1998
• Issued: 09/07/1999
• Est. Priority Date: 07/30/1998
• Status: Expired due to Term

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: Goossen, Keith Wayne, Walker, James Albert
• Primary Examiner(s): Epps, Georgia
• Assistant Examiner(s): BURKE, MARGARET A
• Application Number:
  US09/126,352
• Time in Patent Office: 404 Days
• Field of Search: 359/223, 359/224, 359/290, 359/291, 359/295, 359/318, 430/321
• US Class Current: 359/291
• CPC Class Codes: G02B 26/001 based on interference in an adjustable optical cavity interference filters G02B5/28; devices or arrangements using multiple reflections in spectrometry or monochromators G01J3/26
• CPC Class Codes: G02B 26/02 for controlling the intensity of light G02B26/004 takes precedence

Abstract

The specification describes a double poly Mechanical Anti-Reflection Switch (MARS) device in which shorting between the lower poly metallization and the silicon substrate is prevented by providing an insulating layer on the surface of the silicon substrate.

Claims

1. An electrooptic device comprising:

(a) a conductive substrate having a refractive index η

,

(b) an insulating layer on said substrate, said insulating layer having a thickness t,

(c) a membrane having an optically transparent portion and comprising at least three layers i,ii, and iii, wherein

layer i has a refractive index approximately equal to η

,

layer ii has a refractive index approximately equal to η

^1/2,

layer iii has a refractive index approximately equal to η

,

(d) a flexible support for positioning the optically transparent portion of said membrane at a first position spaced from said substrate and defining an air gap d₁ between said optically transparent portion of said membrane and said insulating layer, and a second position spaced from said substrate defining an air gap d₂ between said optically transparent portion of said membrane and said insulating layer, and

(e) means for applying an electrical bias between said conductive substrate and said membrane to switch said optically transparent portion of said membrane from said first position to said second position.

2. The device of claim 1 wherein d₁ and d₂ are approximately equal to mλ

/4-t, and m is an odd integer for d₁ and an even integer for d₂.

3. An electrooptic modulator comprising:

(a) a conductive substrate having a refractive index η

,

(b) an insulating layer on said substrate, said insulating layer having a thickness t,

(c) means for directing a beam of light on said substrate, said light having a wavelength λ

,

(d) a membrane having an optically transparent portion and comprising at least three layers i,ii, and iii, wherein

layer i has a refractive index approximately equal to η

, and a thickness approximately equal to λ

/4,

layer ii has a refractive index approximately equal to η

^1/2, and a thickness approximately equal to λ

/4,

layer iii has a refractive index approximately equal to η

, and a thickness approximately equal to λ

/2,

(e) a flexible support for positioning the optically transparent portion of said membrane at a first position spaced from said substrate and defining an air gap d₁ between said optically transparent portion of said membrane and said insulating layer, and a second position spaced from said substrate defining an air gap d₂ between said optically transparent portion of said membrane and said insulating layer, and

(f) means for applying an electrical bias between said conductive substrate and membrane to switch said optically transparent portion of said membrane from said first position to said second position.

4. The modulator of claim 3 wherein d₁ and d₂ are approximately equal to mλ

/4-t, and m is an odd integer for d₁ and an even integer for d₂.

5. The modulator of claim 3 wherein said conductive substrate is a semiconductor.

6. The modulator of claim 3 wherein said conductive substrate is silicon.

7. The modulator of claim 4 wherein said insulating layer comprises SiN_x.

8. The modulator of claim 3 wherein λ

is 1.55 μ

m.

9. The modulator of claim 3 wherein layer(i) is polysilicon.

10. The modulator of claim 3 wherein layer(iii) is polysilicon.

11. The modulator of claim 10 wherein layer(i) is polysilicon.

12. A method for modulating light comprising:

(a) directing a beam of light with a wavelength λ

on a conductive substrate, said substrate having a refractive index η

, and an insulating layer on said substrate with a thickness t,

(b) providing a membrane spaced from said substrate, said membrane having an optically transparent portion and comprising at least three layers i,ii, and iii, wherein

layer i has a refractive index approximately equal to η

, and a thickness approximately equal to λ

/4,

layer ii has a refractive index approximately equal to η

^1/2, and a thickness approximately equal to λ

/4,

layer iii has a refractive index approximately equal to η

, and a thickness approximately equal to λ

/2,

(c) providing a flexible support for positioning said optically transparent portion of said membrane at a first position spaced from said substrate and defining an air gap d₁ between said optically transparent portion of said membrane and said insulating layer, and a second position spaced from said substrate defining an air gap d₂ between said optically transparent portion of said membrane and said insulating layer, and

(d) applying an electrical bias between said conductive substrate and said membrane to switch said optically transparent portion of said membrane from said first position to said second position.

13. The method of claim 12 wherein d₁ and d₂ are approximately equal to mλ

/4-t, where m is an odd integer for d₁ and an even integer for d₂.

14. The method of claim 12 wherein said conductive substrate is a semiconductor.

15. The method of claim 14 wherein said conductive substrate is silicon.

16. The method of claim 12 wherein said insulating layer comprises SiN_x.

17. The method of claim 12 wherein λ

is 1.55 μ

m.

18. The method of claim 12 wherein layer(i) is polysilicon.

19. The method of claim 12 wherein layer(iii) is polysilicon.

20. The method of claim 19 wherein layer i is polysilicon.

21. A method for fabricating an electrooptic modulator comprising the steps of:

(a) depositing an insulating layer on a semiconductor substrate,

(b) depositing a glass layer on said insulating layer,

(c) depositing a first layer of polysilicon on said glass layer,

(d) depositing a dielectric layer on said first polysilicon layer, said dielectric layer selected from the group consisting of silicon dioxide and silicon nitride,

(e) depositing a second layer of polysilicon on said dielectric layer,

(f) masking said second polysilicon layer with a photomask having a central membrane feature and at least three arms extending from said central membrane feature to a peripheral frame, leaving exposed portions corresponding with spaces between said arms,

(g) etching through said second polysilicon layer, said dielectric layer and said first polysilicon layer using a plasma etch and using said photomask as an etch mask, to form openings corresponding with said spaces between said arms and expose portions of said glass layer in said openings, and

(h) etching through said glass layer in said exposed portions and under said arms using a wet etchant, thereby forming an air gap between said insulating layer and said central membrane feature and leaving said central membrane feature supported by said arms.

22. The method of claim 21 wherein the glass is phosphosilicate glass and the wet etchant comprises HF.