Mars optical modulators

• US 20050225835A1
• Filed: 02/18/2005
• Published: 10/13/2005
• Est. Priority Date: 04/24/2001
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: David John Bishop, Dennis S. Greywall, James Albert Walker, Keith Wayne Goossen
• Inventors: Goossen, Keith Wayne, Greywall, Dennis S., Walker, James Albert, Bishop, David John
• Granted Patent: US 7,180,652 B2
• Time in Patent Office: Days
• US Class Current: 359/291
• CPC Class Codes: G02B 26/0825 the reflecting element being a flexible sheet or membrane, e.g. for varying the focus flexible mirrors for cosmetic use A45D42/24

Abstract

The specification describes an improved Moving Anti-Reflection Switch (MARS) device structure that largely eliminates charge build up on the movable membrane, and reduces stresses that cause curling of the membrane. The improved device uses a movable membrane made of single crystal silicon.

Claims

1. An electrooptic device comprising:

a. an electrically conductive substrate having a surface s₁,

b. a movable membrane having a top surface and a bottom surface s₂, the movable membrane comprising a single crystal silicon layer,

c. a laser for directing light onto the movable membrane, the light having a wavelength λ

,

d. a support for positioning the movable membrane at a first position spaced from said substrate by an air gap d₁ between surface s₁ and s₂, and

e. bias means for applying an electrical bias across the air gap to move the movable membrane from the first position to a second position having an air gap d₂, where the change from the first to the second position causes a change in the amount of light that is reflected from the movable membrane.

2. The device of claim 1 wherein the single crystal silicon layer has a thickness in the range 1000-5000 Angstroms.

3. The device of claim 1 wherein the conductive substrate is a semiconductor.

4. The device of claim 3 wherein the conductive substrate is silicon.

5. The device of claim 1 wherein the laser has a wavelength λ

in the range 1500-1600 nm.

14. The device of claim 1 where d₂-d₁ is in the approximate range 1500 to 5000 angstroms.

6. A method for switching light comprising:

a. directing a beam of laser light with a wavelength λ

on a substrate,

b. providing a movable membrane spaced from said substrate, the movable membrane consisting of single crystal silicon,

c. providing a support for positioning said membrane at a first position spaced from said substrate by an air gap mλ

/4, where m is an even number, and a second position spaced from said substrate by an air gap nλ

/4 and n is an odd number, and

d. applying an electrical bias across said air gap to move said membrane from said first position to said second position where the change from the first to the second position changes the light that is reflected from the movable membrane from anti-reflecting to reflecting.

7. The method of claim 10 wherein said substrate is silicon.

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

a. providing a substrate comprising;

i. a silicon substrate,

ii. an SiO₂ layer on the substrate,

iii. a single crystal silicon layer on the SiO₂ layer,

b. masking the single crystal layer with a mask having a central membrane feature and at least two arms extending from said central membrane feature to a peripheral frame, leaving exposed portions corresponding with spaces between said arms,

c. etching through the single crystal silicon layer etch using the mask as an etch mask to form openings corresponding with the spaces between the arms and expose portions of the SiO₂ layer in the openings, and

d. etching through the SiO₂ layer in the exposed portions and under the arms using a wet etchant, thereby forming an air gap between the substrate and the central membrane feature and leaving the central membrane feature supported by the arms.

11. The method of claim 10 wherein the single crystal silicon layer has a thickness in the range 1000-5000 Angstroms.

8. The method of claim 11 wherein λ

is approximately 1.55 μ

m.

12. The method of claim 10 wherein the SiO₂ layer has a thickness in the range 7000-15000 Angstroms.

13. The method of claim 10 wherein the etchant used in etch step d. is a wet etchant.

15. The device of claim 10 where the first position and the second position are both in the approximate range 1500 to 5000 angstroms.