Self-aligned vertical combdrive actuator and method of fabrication

• US 6,713,367 B2
• Filed: 08/27/2002
• Issued: 03/30/2004
• Est. Priority Date: 08/28/2001
• Status: Expired due to Fees

• Current Assignee: Board of Trustees of the Leland Stanford Junior University (Stanford University)
• Original Assignee: Board of Trustees of the Leland Stanford Junior University (Stanford University)
• Inventors: Solgaard, Olav, Krishnamoorthy, Uma
• Primary Examiner(s): Niebling, John F.
• Assistant Examiner(s): Simkovic, Viktor
• Application Number:
  US10/229,578
• Publication Number:
  US 20030073261A1
• Time in Patent Office: 581 Days
• Field of Search: 438/50-53, 438/455, 438/459, 438/7, 735/140.1, 735/143.2, 310/309, 200/181, 200/600, 385/16
• US Class Current: 438/459
• CPC Class Codes: B81B 2201/042 Micromirrors, not used as optical switches
• CPC Class Codes: B81B 2203/0136 Comb structures
• CPC Class Codes: B81C 3/002 Aligning microparts
• CPC Class Codes: G02B 2006/12104 Mirror; Reflectors or the like
• CPC Class Codes: G02B 2006/12145 Switch
• CPC Class Codes: G02B 6/122 Basic optical elements, e.g. light-guiding paths
• CPC Class Codes: G02B 6/3518 the reflective optical element being an intrinsic part of a MEMS device, i.e. fabricated together with the MEMS device MEMS devices in general B81B; manufacture of MEM devices in general B81C; micromechanical devices controlling the direction of light G02B26/0833
• CPC Class Codes: G02B 6/357 Electrostatic force electrostatic forces controlling reflecting elements in general G02B26/0841
• CPC Class Codes: G02B 6/3584 constructional details of an associated actuator having a MEMS construction, i.e. constructed using semiconductor technology such as etching MEMS per se B81B, B81C

Abstract

A method of fabricating a self-aligned vertical combdrive is described. The method includes the steps of etching in a semiconductor wafer a first comb with a coarse set of teeth. A second semiconductor wafer is bonded to the first set of teeth. A set of accurately positioned teeth is etched in the second wafer with teeth overlapping the teeth in the first comb. The lower teeth are etched using the overlapping teeth as a mask to assure proper alignment. One variation in this fabrication method whereby the first coarse comb teeth are etched on semiconductor-on-insulator instead, allows creation of double-sided comb actuators with increased torsional deflection range. Another variation to this fabrication method that keeps the electrically isolated upper masking teeth allows creation of dual-mode vertical comb actuators after an initial assembly step.

Claims

1. A method of fabricating a self-aligned combdrive actuator comprising the steps of:

etching, in a wafer of semiconductive material, spaced electrode teeth extending upwardly from a base to form a fixed comb,

oxidizing at least one surface of a second wafer of semiconductive material,

fusing the oxidized surface of said second wafer to the upper surface of said fixed comb teeth,

masking and etching accurately spaced electrode teeth through said second wafer to form a movable comb with tooth spacing such that alternate teeth overlap the fixed comb teeth, and

etching the fixed comb teeth using the overlapping teeth as a mask to thereby provide accurately aligned upper and lower teeth.

2. A method of fabricating a self-aligned combdrive actuator as in claim 1 which includes the additional step of removing the overlapping teeth from the movable comb to permit movement of the movable comb with respect to the fixed comb.

3. A method of fabricating a self-aligned combdrive as in claim 1 which includes the additional step of detaching the overlapping teeth from the movable comb to permit movement of the movable comb with respect to the fixed comb.

4. A method of fabricating a self-aligned combdrive which comprises the steps of:

selecting a wafer of semiconductive material having a base layer and an upper layer separated by an oxide layer,

etching the upper layer down to the oxide layer to form spaced electrode teeth extending upwardly from said oxide layer to form at least one fixed comb isolated from the base layer,

selecting a second wafer of semiconductive material and oxidizing at least one surface of said second wafer,

fusing the oxidized surface of said second wafer to the upper surface of said fixed comb teeth,

masking and etching accurately spaced electrode teeth through said second wafer to form a movable comb with tooth spacing such that alternate teeth overlap the fixed comb teeth, and

etching the fixed comb teeth using the overlapping teeth as a mask to thereby provide accurately aligned upper and lower teeth.

5. A method of fabricating a self-aligned combdrive actuator as in claim 4 which includes the additional step of removing the overlapping teeth from the movable comb to permit movement of the movable comb with respect to the fixed comb.

6. A method of fabricating a self-aligned combdrive as in claim 4 which includes the additional step of detaching the overlapping teeth from the movable comb to permit movement of the movable comb with respect to the fixed comb.

7. A method of fabricating a combdrive actuator as in claim 6 in which said fixed comb wafer is etched to form first and second spaced fixed combs isolated from one another and in which said second wafer is etched to form a movable comb with teeth that interleave with each of said first and second spaced comb teeth.