Optical reflector for micro-machined mirrors

• US 6,392,775 B1
• Filed: 01/26/2000
• Issued: 05/21/2002
• Est. Priority Date: 01/13/1998
• Status: Expired due to Term

• Current Assignee: Seagate Technology LLC (Seagate Technology Holdings Plc)
• Original Assignee: Seagate Technology LLC (Seagate Technology Holdings Plc)
• Inventors: Drake, Joseph D, Jerman, John H.
• Primary Examiner(s): Spyrou, Cassandra
• Assistant Examiner(s): Juba, Jr., John
• Application Number:
  US09/491,427
• Time in Patent Office: 846 Days
• Field of Search: 257/431, 257/432, 359/223, 359/224, 359/225, 359/295, 359/291, 359/582, 359/584, 359/585, 359/883
• US Class Current: 359/224.1
• CPC Class Codes: G02B 26/0833 the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD G02B26/0825 takes precedence; micromechanical devices in general B81B
• CPC Class Codes: G02B 26/0841 the reflecting element being moved or deformed by electrostatic means
• CPC Class Codes: G02B 5/0858 the reflecting layers comprising a single metallic layer with one or more dielectric layers
• 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 6/4216 incorporating polarisation-maintaining fibres polarisation-maintaining fibres per se G02B6/105
• CPC Class Codes: G11B 11/10543 using optical beam of radiation
• CPC Class Codes: G11B 7/08564 using galvanomirrors
• CPC Class Codes: G11B 7/122 Flying-type heads, e.g. analogous to Winchester type in magnetic recording
• CPC Class Codes: G11B 7/1362 Mirrors
• CPC Class Codes: G11B 7/1365 Separate or integrated refractive elements, e.g. wave plates
• CPC Class Codes: G11B 7/1384 Fibre optics
• CPC Class Codes: H02N 1/008 Laterally driven motors, e.g. of the comb-drive type

Abstract

The present invention includes a structure, apparatus, and method by which the reflectivity of a micro-machined reflector can be improved. The present invention increases the mirror'"'"'s reflectivity at 650 nm, increases its reflectivity at 410 nm, and improves its long-term reliability. The reflectivity at other wavelengths may also be improved. Also, the present invention minimizes mirror plate distortion while providing a suitable fabrication approach.

Claims

1. A micromachined reflector comprising a planar substrate, a reflective layer, means for securing the reflective layer to the planar substrate, the reflective layer and the means for securing the reflective layer to the planar substrate having an aggregate stress, an additional layer of material secured to the reflective layer, the additional layer having a stress substantially opposing the aggregate stress of the reflective layer and the means for securing the reflective layer to the planar substrate whereby the stress of the additional layer substantially offsets the aggregate stress of the reflective layer and the means for securing the reflective layer to the planar substrate so as to enhance the planarity of the micromachined reflector.

2. The micromachined reflector of claim 1 wherein the reflective layer and the means for securing the reflective layer to the planar substrate have a tensile stress and the additional layer has a compressive stress.

3. The micromachined reflector of claim 1 for use with laser light having a wavelength, wherein the additional layer includes first and second layers each having an optical pathlength equal to one quarter the wavelength of the laser light.

4. The micromachined reflector of claim 1 wherein the additional layer includes a first dielectric layer of a material having a relatively low index of refraction overlying the reflective layer and a second dielectric layer of a material having a relatively high index of refraction overlying the first dielectric layer.

5. The micromachined reflector of claim 4 wherein the additional layer includes a third dielectric layer of a material having a relatively low index of refraction overlying the second dielectric layer and a fourth dielectric layer of a material having a relatively high index of refraction overlying the third dielectric layer.

6. The micromachined reflector of claim 1 wherein the means for securing the reflective layer to the planar substrate is an adhesion layer.

7. The micromachined reflector of claim 6 wherein the adhesion layer is made from chromium.

8. The micromachined reflector of claim 1 wherein the reflective layer is made from a material selected from the group consisting of gold and aluminum.

9. A micromachined reflector for use with laser light having a wavelength comprising a planar substrate, a reflective layer, means for securing the reflective layer to the planar substrate, the reflective layer and the means for securing the reflective layer to the planar substrate having an aggregate stress, an additional layer of material secured to the reflective layer and including a layer having an optical pathlength equal to one half the wavelength of the laser light, the additional layer having a stress substantially opposing the aggregate stress of the reflective layer and the means for securing the reflective layer to the planar substrate whereby the stress of the additional layer substantially offsets the aggregate stress of the reflective layer and the means for securing the reflective layer to the planar substrate so as to enhance the planarity of the micromachined reflector.

10. The micromachined reflector of claim 9 wherein the additional layer includes a layer made from silicon nitride.

11. A micromachined reflector for use with laser light having a wavelength, comprising a planar substrate, a reflective layer, means for securing the reflective layer to the planar substrate, the reflective layer and the means for securing the reflective layer to the planar substrate having an aggregate stress, a first additional layer of material secured to the reflective layer and including a first dielectric layer of a material having a relatively low index of refraction overlying the reflective layer and a second dielectric layer of a material having a relatively high index of refraction overlying the first dielectric layer, a second additional layer overlying the first additional layer and having an optical pathlength equal to one half the wavelength of the laser light, the first additional layer and the second additional layer having a stress substantially opposing the aggregate stress of the reflective layer and the means for securing the reflective layer to the planar substrate whereby the stress of the first additional layer and the second additional layer substantially offsets the aggregate stress of the reflective layer and the means for securing the reflective layer to the planar substrate so as to enhance the planarity of the micromachined reflector.

12. A micromachined reflector comprising a planar substrate, a reflective layer, means for securing the reflective layer to the planar substrate and an additional layer of material secured to the reflective layer, the additional layer including a layer of silicon dioxide overlying the reflective layer and a layer of silicon nitride overlying the layer of silicon dioxide.

13. The micromachined reflector of claim 12 wherein the reflective layer and the means for securing the reflective layer to the planar substrate have an aggregate stress and wherein the additional layer has a stress substantially opposing the aggregate stress of the reflective layer and the means for securing the reflective layer to the planar substrate whereby the stress of the additional layer substantially offsets the aggregate stress of the reflective layer and the means for securing the reflective layer to the planar substrate so as to enhance the planarity of the micromachined reflector.

14. A micromachined reflector for use with laser light having a wavelength comprising a planar substrate, a reflective layer, means for securing the reflective layer to the planar substrate and a dielectric layer secured to the reflective layer for protecting the reflective layer, the reflective layer having a sidewall extending upwardly from the planar substrate, the dielectric layer extending over the sidewall of the reflective layer and having an optical pathlength equal to one half the wavelength of the laser light.

15. A micromachined reflector for use with laser light having a half wavelength comprising a planar substrate, a reflective layer, means for securing the reflective layer to the planar substrate and a dielectric layer of silicon nitride secured to the reflective layer for protecting the reflective layer, the dielectric layer having an optical pathlength equal to one half the wavelength of the laser light.

16. The micromachined reflector of claim 15 wherein the reflective layer is made from gold and the means for securing the reflective layer to the planar substrate is a layer of chromium.