Mirror arrays for maskless photolithography and image display

• US 8,610,986 B2
• Filed: 04/06/2009
• Issued: 12/17/2013
• Est. Priority Date: 04/06/2009
• Status: Active Grant

• Current Assignee: Board of Trustees of The University of Illinois
• Original Assignee: Board of Trustees of The University of Illinois
• Inventors: Jain, Kanti, Chae, Junghun, Lin, Kevin, Jin, Hyunjong
• Primary Examiner(s): Allen, Stephone B.
• Assistant Examiner(s): Kakalec, Kimberly N
• Application Number:
  US12/419,210
• Publication Number:
  US 20100255426A1
• Time in Patent Office: 1,716 Days
• Field of Search: 3591981-1994, 3592006-2008, 359/202.1, 359/221.2, 3592231-2251, 359/226.2, 359290-295, 359/584, 359/838, 359/846, 359/871, 359/872, 359/586, 359/588, 359/589, 359354-359, 359726-732, 250/204, 250/559.06, 250/559.29, 250/230, 250/234, 347225-260, 353/39, 353 98- 99, 385 15- 18, 385/22, 398/12, 398/19, 398/45, 378 34- 35, 1014501-473, 430302-305
• 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 5/0833 comprising inorganic materials only
• CPC Class Codes: G02B 5/0858 the reflecting layers comprising a single metallic layer with one or more dielectric layers
• CPC Class Codes: G03F 7/70291 Addressable masks, e.g. spatial light modulators [SLMs], digital micro-mirror devices [DMDs] or liquid crystal display [LCD] patterning devices

Abstract

Micromirrors and micromirror arrays described herein are useful, for example in maskless photolithography systems and methods and projection display devices and methods. According to one aspect, the micromirrors comprise a polymer structural layer and a reflective dielectric multilayer for selective reflection and/or redirection of incoming electromagnetic radiation. According to another aspect, incorporation of a reflective dielectric multilayer allows for use of polymer structural materials in micromirrors and prevents damage to such polymer materials due to excessive heating from absorption of electromagnetic radiation, as the reflective dielectric multilayers are highly reflective and minimize heating of the micromirror components. According to yet a further aspect, top down fabrication methods are described herein for making a micromirror comprising a polymer structural layer and a reflective dielectric multilayer.

Claims

1. A micromirror having an exposed surface area, the micromirror comprising:

a polymeric micromirror base;

a reflective dielectric multilayer disposed over the polymeric micromirror base, wherein the reflective dielectric multilayer comprises 10 or more dielectric layers;

a device layer positioned below the polymeric micromirror base for adjusting a position of the micromirror; and

a resistive heating element in thermal contact with the reflective dielectric multilayer;

wherein the reflective dielectric multilayer covers more than 50% of the exposed surface area and the reflective dielectric multilayer has a reflectivity selected over the range of 95% to 100% for at least a portion of electromagnetic radiation having wavelengths in the range of 150 to 1100 nm.

2. The micromirror of claim 1, further comprising a thermally conductive or heat dispersing layer in thermal contact with the reflective dielectric multilayer and the resistive heating element.

3. The micromirror of claim 2, wherein the thermally conductive or heat dispersing layer is provided between the reflective dielectric multilayer and the resistive heating element.

4. The micromirror of claim 1, wherein the resistive heating element maintains a temperature of the reflective dielectric multilayer within a 5°

C. window.

5. The micromirror of claim 1, wherein the reflective dielectric multilayer has a reflectivity selected over the range of 98% to 100% for at least a portion of electromagnetic radiation having wavelengths in the range of 150 to 1100 nm.

6. The micromirror of claim 1, wherein the reflective dielectric multilayer has a reflectivity selected over the range of 95% to 100% for at least a portion of electromagnetic radiation having wavelengths in the range of 600 to 750 nm.

7. The micromirror of claim 1, wherein the reflective dielectric multilayer has a reflectivity selected over the range of 95% to 100% for at least a portion of electromagnetic radiation having wavelengths in the range of 500 to 600 nm.

8. The micromirror of claim 1, wherein the reflective dielectric multilayer has a reflectivity selected over the range of 95% to 100% for at least a portion of electromagnetic radiation having wavelengths in the range of 400 to 500 nm.

9. The micromirror of claim 1, wherein the reflective dielectric multilayer does not include a metal layer.

10. The micromirror of claim 1, wherein the reflective dielectric multilayer comprises a plurality of dielectric layers selected from the group consisting of:

oxides, nitrides, fluorides, and sulfides.

11. The micromirror of claim 1, wherein the reflective dielectric multilayer comprises a plurality of dielectric layers selected from the group consisting of:

silicon dioxide, titanium dioxide, hafnium oxide, silicon nitride, magnesium fluoride and zinc sulfide.

12. The micromirror of claim 1, wherein the reflective dielectric multilayer comprises a plurality of dielectric layers, wherein adjacent dielectric layers have different refractive indices and wherein the plurality of dielectric layers alternates between higher and lower refractive index dielectric layers.

13. The micromirror of claim 12, wherein the reflective dielectric multilayer comprises 10 to 1000 of said higher and lower refractive index dielectric layers.

14. The micromirror of claim 12, wherein each of the higher refractive index dielectric layers has a refractive index selected over the range of 1.2 to 2.9 and each of the lower refractive index dielectric layers has a refractive index selected over the range of 1.1 to 2.8.

15. The micromirror of claim 12, wherein each of the dielectric layers has a thickness selected over the range of 10 nm to 100 μ

m.

16. The micromirror of claim 1, wherein the polymeric micromirror base comprises a polymer selected from the group consisting of:

SU-8, polyimide, photoresists, polydimethylsiloxane (PDMS), polymethyl methacrylate (PMMA), polyparaxylene (parylene), polytetrafluoroethylene (Teflon), liquid crystal polymers and any combination of these.

17. The micromirror of claim 1, having a width selected over the range of 5 to 100 μ

m.

18. The micromirror of claim 1, having a length selected over the range of 5 to 100 μ

m.

19. The micromirror of claim 1, wherein the exposed surface area of the micromirror is greater than or equal to 25 μ

m².

20. The micromirror of claim 1, wherein the exposed surface area of the micromirror is selected over the range of 25 μ

m² to 1 mm².

21. The micromirror of claim 1, wherein the reflective dielectric multilayer covers 90% to 100% of the exposed surface area of the micromirror.

22. The micromirror of claim 1, wherein the resistive heating element is a MEMS-based resistive heater.

23. The micromirror of claim 1, comprising four resistive heating elements in thermal contact with said reflective dielectric multilayer.

24. The micromirror of claim 1, wherein the resistive heating element maintains a temperature of the reflective dielectric multilayer within a 1°

C. window.

25. The micromirror of claim 1, further comprising a temperature sensor in thermal contact with the reflective dielectric multilayer.

26. A large area micromirror array comprising a plurality of micromirror elements, wherein each micromirror element has an exposed surface area and comprises a polymeric micromirror base, a reflective dielectric multilayer disposed over the polymeric micromirror base and a resistive heating element in thermal contact with the reflective dielectric multilayer, wherein the reflective dielectric multilayer comprises 10 or more dielectric layers, wherein the reflective dielectric multilayer covers 50% to 100% of the exposed surface area and wherein the reflective dielectric multilayer has a reflectivity selected over the range of 95% to 100% for at least a portion of electromagnetic radiation having wavelengths in the range of 150 to 1100 nm.

27. A digital micromirror display device comprising:

a source of electromagnetic radiation; and

a micromirror array comprising a plurality of micromirror elements, wherein each micromirror element has an exposed surface area exposed to electromagnetic radiation from the source and comprises a polymeric micromirror base and a reflective dielectric multilayer disposed over the polymeric base and a resistive heating element in thermal contact with the reflective dielectric multilayer, wherein the reflective dielectric multilayer comprises 10 or more dielectric layers, wherein the reflective dielectric multilayer covers 50% to 100% of the exposed surface area and wherein the reflective dielectric multilayer has a reflectivity selected over the range of 95% to 100% for at least a portion of electromagnetic radiation having wavelengths in the range of 150 to 1100 nm.

28. A method of displaying an image, the method comprising the steps of:

providing a surface for displaying the image;

providing a source of electromagnetic radiation;

providing an array of micromirror elements, wherein each micromirror element has an exposed surface area exposed to electromagnetic radiation from the source and comprises a polymeric micromirror base, a reflective dielectric multilayer disposed over the polymeric micromirror base and a resistive heating element in thermal contact with the reflective dielectric multilayer, wherein the reflective dielectric multilayer comprises 10 or more dielectric layers, wherein the reflective dielectric multilayer covers 50% to 100% of the exposed surface area and wherein the reflective dielectric multilayer has a reflectivity selected over the range of 95% to 100% for at least a portion of electromagnetic radiation having wavelengths in the range of 150 to 1100 nm;

controlling a position of each micromirror element of the array such that electromagnetic radiation from the source is reflected from each micromirror element to a location either on or off of the surface; and

directing electromagnetic radiation from the source onto the micromirror array, thereby displaying an image on the surface.