GIMBAL-LESS MICRO-ELECTRO-MECHANICAL-SYSTEM TIP-TILT AND TIP-TILT-PISTON ACTUATORS AND A METHOD FOR FORMING THE SAME

• US 20080061026A1
• Filed: 11/09/2007
• Published: 03/13/2008
• Est. Priority Date: 12/02/2003
• Status: Active Grant

• Current Assignee: Adriatic Research Institute
• Original Assignee: Adriatic Research Institute
• Inventors: Milanovic, Veljko, Matus, Gabriel
• Granted Patent: US 8,043,513 B2
• Time in Patent Office: Days
• US Class Current: 216/2
• CPC Class Codes: B81B 3/0062 Devices moving in two or more dimensions, i.e. having special features which allow movement in more than one dimension
• CPC Class Codes: G02B 26/0841 the reflecting element being moved or deformed by electrostatic means

Abstract

Fully monolithic gimbal-less micro-electro-mechanical-system (MEMS) devices with large static optical beam deflection and fabrications methods are disclosed. The devices can achieve high speed of operation for both axes. Actuators are connected to a device, or device mount by linkages that allow static two-axis rotation in addition to pistoning without the need for gimbals, or specialized isolation technologies. The device may be actuated by vertical comb-drive actuators, which are coupled by bi-axial flexures to a central micromirror or device mount. Devices may be fabricated by etching an upper layer both from the top side and from the bottom side to form beams at different levels. The beams include a plurality of lower beams, a plurality of full-thickness beams, and a plurality of upper beams, the lower, full-thickness and upper beams That form vertical combdrive actuators, suspension beams, flexures, and a device mount.

Claims

1. A method for fabricating a micro-electro-mechanical system (MEMS) device, the method comprising the steps of:

(a) preparing a substrate including an upper layer; and

(b) etching the upper layer both from the top side and from the bottom side to form beams at different levels, the beams including a plurality of lower beams, a plurality of full-thickness beams, and a plurality of upper beams, the lower, full-thickness and upper beams forming vertical combdrive actuators, suspension beams, flexures, and a device mount.

2. The method of claim 1, further comprising the step of (c) oxidizing the upper layer to protect front side features on the upper layer and improve sidewall quality of the beams.

3. The method of claim 1, wherein the step (a) comprises the steps of:

double-side-polishing a first wafer to form a lower layer;

single- or double-side polishing a second wafer to form the upper layer;

growing a wet thermal oxide on one or both of the first and second wafers to form an oxide layer;

patterning the upper layer with a photoresist and/or oxide mask;

etching a surface of the upper layer to a depth of less than one half of a final desired upper layer thickness; and

after removing the mask from the upper layer, bonding the first and second wafers to form a bonded substrate with the etched surface of the upper layer facing a polished surface of the lower layer.

4. The method of claim 3 further comprising grinding and/or polishing the bonded substrate to achieve the final desired upper layer thickness.

5. The method of claim 3, wherein the two wafers are bonded by fusion bonding, metal bump bonding or general adhesive bonding.

6. The method of claim 3, wherein the step (b) comprises the steps of:

on the bonded substrate, preparing two front-side masks, wherein the two front-side masks are aligned with a buried mask and the two front-side masks are aligned with each other.

7. The method of claim 6 wherein the two front-side masks include oxides of two thicknesses

8. The method of claim 6 wherein the two front-side masks include an oxide mask and a photoresist mask

9. The method of claim 3, further comprising the step of (e) etching the lower layer of the bonded substrate from a backside to form a cavity.

10. The method of claim 9, wherein the step (e) comprises:

on a backside of the bonded substrate, employing a single mask which is aligned to one or more front-side features.

11. The method of claim 1, wherein (b) includes

i) selectively etching the upper layer from one of the top side to etch portions of the upper layer corresponding to the upper and middle beams, but not the lower beams and full beams, to a first depth;

ii) selectively etching the upper layer from the bottom side to etch portions of the upper layer corresponding to the lower and middle beams, but not the upper beams and full beams, to a second depth; and

iii) selectively etching through selected portions of the upper layer from the top side to the bottom side.