Thin film actuated mirror array for use in an optical projection system

• US 5,757,539 A
• Filed: 02/16/1996
• Issued: 05/26/1998
• Est. Priority Date: 04/21/1995
• Status: Expired due to Term

• Current Assignee: Wi-LAN Inc.
• Original Assignee: Daewoo Electronics (Government of South Korea)
• Inventors: Min, Yong-Ki
• Primary Examiner(s): Ben, Loha
• Application Number:
  US08/602,928
• Time in Patent Office: 830 Days
• Field of Search: 359/290, 359/291, 359/295, 359/221, 359/222, 359/224, 359/846, 359/848, 310/328, 310/333, 310/366
• US Class Current: 359/290
• CPC Class Codes: G02B 26/0858 the reflecting means being moved or deformed by piezoelectric means
• CPC Class Codes: Y10S 359/904 Micromirror

Abstract

An inventive array of M×N thin film actuated mirrors includes an active matrix, an insulating layer, an etchant stopping layer, and an array of M×N actuating structures. Each of the actuating structures has a tip at a distal end thereof and an etching aperture traversing therethrough, and further includes a first thin film electrode with a horizontal stripe, a thin film electrodisplacive member, a second thin film electrode, an elastic member and a conduit. The horizontal stripe, the tip and the etching aperture are created in order to increase the optical efficiency of each of the thin film actuated mirrors, facilitate the removal of the rinse and allow easy removal of the thin film sacrificial layer, respectively.

Claims

1. An array of M×

N thin film actuated mirrors, wherein M and N are integers, for use in an optical projection system, the array comprising;

an active matrix including a substrate, an array of M×

N transistors and an array of M×

N connecting terminals, wherein each of the connecting terminals is electrically connected to a corresponding transistor in the array of transistors;

a passivation layer formed on top of the active matrix;

an etchant stopping layer formed on top of the passivation layer; and

an array of M×

N actuating structures, each of the actuating structures being provided with a proximal and a distal ends, each of the actuating structures having a tip at the distal end thereof and an etching aperture traversing therethrough, each of the actuating structures including a first thin film electrode, a thin film electrodisplacive member, a second thin film electrode, an elastic member and a conduit, wherein the first thin film electrode is located on top of the thin film electrodisplacive member and is divided into an actuating and a light reflecting portions by a horizontal stripe, the horizontal stripe disconnecting electrically the actuating and the light reflecting portions thereof, the actuating portion thereof being electrically connected to ground, thereby allowing the actuating portion and the light reflecting portion thereof to function as a mirror and a bias electrode and as a mirror, respectively, the thin film electrodisplacive member is positioned on top of the second thin film electrode, the second thin film electrode is formed on top of the elastic member, the second thin film electrode being electrically connected to a corresponding transistor through the conduit and the connecting terminal, and being disconnected electrically from the second thin film electrode in other thin film actuated mirrors, to thereby allow it to function as a signal electrode, the elastic member is located at bottom of the second thin film electrode and a bottom portion at the proximal end thereof is attached on top of the active matrix with the etchant stopping and the passivation layers partially intervening therebetween, thereby cantilevering the actuating structure, and the conduit extends from top of the thin film electrodisplacive member to top of a corresponding connecting terminal, connecting electrically the second thin film electrode to the connecting terminal.

2. The array of claim 1, wherein the passivation layer is made of a phosphor-silicate glass (PSG) or silicon nitride.

3. The array of claim 1, wherein the etchant stopping layer is made of silicon nitride.

4. A method for manufacturing an array of M×

N thin film actuated mirrors, wherein M and N are integers and each of the thin film actuated mirrors corresponds to a pixel, for use in an optical projection system, the method comprising the steps of;

providing an active matrix including a substrate, an array of M×

N connecting terminals and an array of M×

N transistors, wherein each of the connecting terminals is electrically connected to a corresponding transistor in the array of transistors;

depositing a passivation layer on top of the active matrix;

depositing an etchant stopping layer on top of the passivation layer;

depositing a thin film sacrificial layer on top of the etchant stopping layer, wherein the thin film sacrificial layer has a top surface;

flattening the top surface of the thin film sacrificial layer;

creating an array of M×

N pairs of empty cavities in the thin film sacrificial layer in such a way that one of the empty cavities in each pair encompasses one of the connecting terminals;

depositing an elastic layer and a second thin film layer, successively, on top of the thin film sacrificial layer including the empty cavities;

iso-cutting the second thin film layer into an array of M×

N second thin film electrodes, wherein each of the second thin film electrodes is electrically disconnected from one another;

depositing a thin film electrodisplacive layer and a first thin film layer, successively, on top of the array of M×

N second thin film electrodes to thereby form a multiple layered structure;

patterning the multiple layered structure into an array of M×

N actuated mirror structures, until the thin film sacrificial layer is exposed, in such a way that each of the actuated mirror structures has a tip at a distal end thereof and an etching aperture traversing therethrough, each of the actuated mirror structures including a first thin film electrode, a thin film electrodisplacive member, a second thin film electrode and an elastic member, wherein the first thin film electrode is divided into an actuating and a light reflecting portions by a horizontal stripe, the horizontal stripe disconnecting electrically the actuating and the light reflecting portion thereof, the actuating portion thereof being electrically connected to ground;

creating an array of M×

N holes, each of the holes extending from top of the thin film electrodisplacive member to top of a corresponding connecting terminal;

filling each of the holes with a metal to thereby form a conduit therein, to thereby form an array of M×

N semifinished actuated mirrors;

semi-dicing the active matrix by forming an incision at the active matrix;

covering completely each of the semifinished actuated mirrors with a thin film protection layer;

removing the thin film sacrificial layer using an etchant or a chemical, wherein the etchant or the chemical is inserted into the etching aperture in each of the semifinished actuated mirrors and gaps between the semifinished actuated mirrors;

removing the thin film protection layer; and

dicing completely the active matrix into a desired shape to thereby form the array of M×

N thin film actuated mirrors.

5. The method of claim 4, wherein the passivation layer is made of a phosphor-silicate glass (PSG) os silicon nitride.

6. The method of claim 5, wherein the passivation layer is formed in a thickness of 0.1-2 μ

m.

7. The method of claim 6, wherein the passivation layer is formed by using a CVD or a spin coating method.

8. The method of claim 4, wherein the etchant stopping layer is made of silicon nitride.

9. The method of claim 8, wherein the etchant stopping layer is formed in a thickness of 0.1-2 μ

m.

10. The method of claim 9, wherein the etchant stopping layer is formed by using a sputtering or a CVD method.

11. The method of claim 8, wherein the thin film electrodisplacive layer is heat treated by using a rapid thermal annealing (RTA) method.

12. The method of claim 4, wherein the top surface of the thin film sacrificial layer is flattened by using a spin on glass (SOG) method or a chemical mechanical polishing (CMP) method, followed by a scrubbing method.

13. The method of claim 4, wherein the array of empty cavities is created by using a dry or a wet etching method.

14. The method of claim 4, wherein the second thin film layer is iso-cut by using a dry etching method.

15. The method of claim 4, wherein the incision at the active matrix is formed in a depth of one third of the thickness of the active matrix.

16. The method of claim 4, wherein the incision is formed by using a photolithography method.

17. The method of claim 4, wherein the active matrix is completely diced by using a photolithography or a laser trimming method.