Optical microswitch printer heads

• US 20040081498A1
• Filed: 10/25/2002
• Published: 04/29/2004
• Est. Priority Date: 10/25/2002
• Status: Active Grant

• Current Assignee: Xiang Zheng Tu
• Original Assignee: Xiang Zheng Tu
• Inventors: Tu, Xiang Zheng
• Granted Patent: US 6,809,753 B2
• Time in Patent Office: Days
• US Class Current: 400/118.2
• CPC Class Codes: B41J 2/465 using masks, e.g. light-switching masks

Abstract

An optical microswitch printer head comprising a micromachined optical microswitch array with optical microswitches extending in a main scanning direction. The optical microswitch is based on a variable air gap Fabry-Perot cavity that is defined by two non-absorbing distributed Bragg reflectors. One of the distributed Bragg reflectors is supported by flexible beams so that the length of the Fabry-Perot cavities can be set to be equal to an odd or even multiple of a quarter wavelength of a working optical wave by applying a voltage. As a result, the optical microswitches can be pushed into a transmission state or “on” state for letting a light pass through or a reflection state or “off” state for blocking the light. The optical microswitch printer head can utilize a gas discharge lamp such as a cold cathode fluorescent lamp as a light source. The light irradiated from the gas discharge lamp shines over all the optical microswitches, but the optical microswitches are selectively switched “on” or “off” so as to generate light signals for graphic image formation Since the fabrication process of the optical microswitch array is based on standard IC technology, it can be batch-produced at lower cost

Claims

1. An optical microswitch printer head, comprising:

an optical microswitch array with optical microswitches extending in a main scanning direction;

a driver circuit for switching the optical microswitches on and off on demand;

a light source for providing light that passes through selectively switched-on optical microswitches for generating light signals,

a reflector condensing the light onto the optical microswitch array;

a collimator converting the condensed light into collimated light that is normal to the main scanning direction;

a filter only allowing the light with a selected wavelength to illuminate the optical microswitches;

a light-sensitive material covering the periphery surface of a drum that can be rotated around an axis parallel to the main scanning direction; and

a cylindrical lens configured such that the light signals generated by the optical microswitches can be condensed onto the light-sensitive material to form a latent image thereon.

2. The optical microswitch printer head of claim 1, wherein each of the optical microswitches comprises a variable air gap Fabry-Perot cavity that is defined by two non-absorbing distributed Bragg reflectors.

3. The optical microswitch printer head of claims 1 and 2, wherein the optical microswitches can be switched on and off by setting the length of the air gap of the variable Fabry-Perot cavities to be equal to an odd or even multiple of a quarter wavelength of a working optical wave.

4. The optical microswitch printer head of claim 1, wherein the light sources comprise gas discharge lamps.

5. An optical microswitch array, comprising:

a silicon substrate,

a plurality of optical microswitches each comprising

a bottom supporting layer disposed on the silicon substrate;

a bottom distributed Bragg reflector comprising a stack of alternating layers of non-absorbing high refractive index dielectric material and low refractive index dielectric material and disposed on the bottom supporting layer,

a bottom electrode disposed on the bottom distributed Bragg reflector;

a middle air gap disposed on the bottom electrode;

a separating layer surrounding the middle air gap;

a top electrode disposed above the middle air gap and on the separating layer,

a top supporting structure having a central plane and at least two side inflexible beams and disposed on the top electrode; and

a top distributed Bragg reflector comprising a stack of alternating layers of high refractive index dielectric material and low refractive index dielectric material and disposed on the top supporting structure;

a driver circuit electrically connected to the variable air Fabry-Perot cavities and selectively turning the optical microswitches “

on”

or “

off”

;

a plurality of light guiding holes disposed in the silicon substrate and each perpendicularly extending to a corresponding variable air gap Fabry-Perot cavity, and

an electrical connection means for interfacing to a printer'"'"'s CPU.

6. The optical microswitch array of claim 5, wherein the air gap of the variable air gap Fabry-Perot cavities can be set to be equal to an odd or even multiple of a quarter wavelength of a working optical wave by applying a voltage.

7. The optical microswitch array of claim 5, wherein the bottom supporting layer comprises SiO₂ or the like.

8. The optical microswitch array of claim 5, wherein the separating layer comprises SiO₂ or the like.

9. The optical microswitch array of claim 5, wherein the distributed Bragg reflectors comprise a stack of alternating layers of SiO₂ and TiO₂ having the thickness equal to λ

₀/4n, where λ

₀ is the working optical wavelength and n is the refractive index.

10. The optical microswitch array of claim 5, wherein the distributed Bragg reflectors comprise a stack of alternating layers of SiO₂ and Ta₂O₅ with the thickness of each layer being equal to λ

₀/4n, where λ

₀ is the working optical wavelength and n is the refractive index.

11. The optical microswitch array of claim 5, wherein the distributed Bragg reflectors comprise a stack of alternating layers of SiO₂ and SiN_x with the thickness of each layer being equal to λ

₀/4n, where λ

₀ is the working optical wavelength and n is the refractive index.

12. The optical microswitch array of claim 5, wherein the electrodes comprise In₂O₃:

SnO₂(5-10%) or the like.

13. The optical microswitch array of claim 5, wherein the top supporting structure comprises Si₃N₄.

14. The optical microswitch array of claim 5, wherein the top supporting structure comprises amorphous SiC.

15. The optical microswitch array of claim 5, wherein the top supporting structure comprises polysilicon recrystallized from amorphous silicon.

16. The optical microswitch array of claim 5, wherein the driver circuit is integrated with the optical microswitch array by monolithic integration.

17. The optical microswitch array of claim 5, wherein the driver circuit is integrated with the optical microswitch array by hybrid packaging.

18. The optical microswitch array of claim 5, wherein the light guiding holes have a metal reflecting layer coated on the sidewalls.

19. An optical microswitch array, comprising

a glass substrate;

a plurality of variable air gap Fabry-Perot cavities disposed on the glass substrate and each comprising;

a bottom distributed Bragg reflector comprising a stack of alternating layers of non-absorbing high refractive index dielectric material and low refractive index dielectric material and disposed on the glass substrate;

a bottom electrode disposed on the bottom distributed Bragg;

a middle air gap disposed on the bottom electrode;

a separating layer surrounding the middle air gap;

a top electrode disposed above the middle air gap and on the bottom electrode;

a top supporting structure consisting of a central plane and at least two side flexible beams and disposed on the top electrode, and

a top distributed Bragg reflector comprising a stack of alternating layers of high refractive index dielectric material and low refractive index dielectric material and disposed on the top supporting structure;

a driver circuit disposed on the glass substrate and electrically connected to the variable air Fabry-Perot cavities,

a light block layer with a plurality of light windows each situated under a corresponding variable air gap Fabry-Perot cavity; and

an electrical connection means for interfacing to a printer'"'"'s CPU.

20. The optical microswitch array of claim 19, wherein the length of the air gap of the variable air gap Fabry-Perot cavity can be set to be equal to odd or even multiple of a quarter wavelength of a working optical wave by applying a voltage.

21. The optical microswitch array of claim 19, wherein the separating layer comprises SiO₂ or the like.

22. The optical microswitch array of claim 19, wherein the distributed Bragg reflectors comprise a stack of alternating layers of SiO₂ and TiO₂ having the thickness equal to λ

₀/4n, where λ

₀ is the working optical wavelength and n is the refractive index.

23. The optical microswitch array of claim 19, wherein the distributed Bragg reflectors comprise a stack of alternating layers of SiO₂ and Ta₂O₅ having the thickness equal to λ

₀/4n, where λ

₀ is the working optical wavelength and n is the refractive index.

24. The optical microswitch array of claim 19, wherein the distributed Bragg reflectors comprise a stack of alternating layers of SiO₂ and SiN_x having the thickness equal to λ

₀/4n, where λ

₀ is the working optical wavelength and n is the refractive index.

25. The optical microswitch array of claim 19, wherein the electrodes comprise In₂O₃:

SnO₂(5-10%) or the like.

26. The optical microswitch array of claim 19, wherein the top supporting structure comprises Si₃N₄.

27. The optical microswitch array of claim 19, wherein the top supporting structure comprises amorphous SiC.

28. The optical microswitch array of claim 19, wherein the top supporting structure comprises polysilicon recrystallized from amorphous silicon.

29. A method of fabricating an optical microswitch array comprising the steps:

forming a CMOS driver circuit in a predetermined region of a silicon substrate using standard CMOS circuit fabrication technologies,

depositing a bottom supporting layer in another predetermined region of the silicon substrate;

fabricating a plurality of bottom distributed Bragg reflectors on the supporting layer;

forming a plurality of bottom electrodes each disposed on and aligned with an underlying bottom Bragg reflector;

depositing a separating layer covering the bottom electrodes;

forming a plurality of top electrodes each disposed on the separating layer and aligned with an underlying bottom electrode;

defining a plurality of top supporting structures each disposed on and aligned with an underlying top electrode;

fabricating a plurality of top distributed Bragg reflectors each disposed on and aligned with an underlying top supporting structure;

forming a plurality of vertical holes disposed in the backside of the silicon substrate and each aligned with a corresponding Fabry-Perot cavity on the front side;

depositing a metal layer on the sidewalls of the vertical holes by electroplating; and

releasing the top supporting structures and top electrodes by selectively etching the underlying separating layer so as to form a plurality of variable air gap Fabry-Perot cavities each defined by two non-absorbing distributed Bragg Reflectors and one of distributed Bragg reflector supporting by the released top supporting structure.

30. The method of fabricating an optical microswitch array of claim 29, wherein the bottom supporting layer comprises SiO₂ or the like.

31. The method of fabricating an optical microswitch array of claim 29, wherein the separating layer comprises SiO₂ or the like.

32. The method of fabricating an optical microswitch array of claim 29, wherein the electrodes comprise In₂O₃:

SnO₂(5-10%) or the like.

33. The method of fabricating an optical microswitch array of claim 29, wherein the distributed Bragg reflectors comprise a stack of alternating layers of SiO₂ and TiO₂ having the thickness equal to λ

₀/4n, where λ

₀ is the working optical wavelength and n is the refractive index.

34. The method of fabricating an optical microswitch array of claim 29, wherein the distributed Bragg reflectors comprise a stack of alternating layers of SiO₂ and Ta₂O₅ having the thickness equal to λ

₀/4n, where λ

₀ is the working optical wavelength and n is the refractive index.

35. The method of fabricating an optical microswitch array of claim 29, wherein the distributed Bragg reflectors comprise a stack of alternating layers of SiO₂ and SiN_x having the thickness equal to λ

₀/4n, where λ

₀ is the working optical wavelength and n is the refractive index.

36. The method of fabricating an optical microswitch array of claim 29, wherein the top supporting structure comprises Si₃N₄.

37. The method of fabricating an optical microswitch array of claim 29, wherein the top supporting structure comprises amorphous SiC.

38. The method of fabricating an optical microswitch array of claim 29, wherein the top supporting structure comprises polysilicon recrystallized from amorphous silicon.

39. The method of fabricating an optical microswitch array of claim 29, wherein the released top supporting structure comprises a central plane and at least two side flexible beams disposed on the edge of the central plane.

40. A method of fabricating an optical microswitch array comprising the steps:

preparing a glass substrate,

fabricating a plurality of bottom distributed Bragg reflectors in a predetermined region of the glass substrate,

forming a plurality of bottom electrodes each disposed on and aligned with an underlying bottom Bragg reflector,

depositing a separating layer covering all the bottom electrodes;

forming a plurality of top electrodes each disposed on and aligned with an underlying bottom electrode;

defining a plurality of top supporting structures each disposed on and aligned with an underlying top electrode;

fabricating a plurality of top distributed Bragg reflectors each disposed on and aligned with an underlying top supporting structure, and

releasing the top electrode and top supporting structure by selectively etching the underlying separating layer so as to form a plurality of variable air gap Fabry-Peron cavities each defined by two non-absorbing distributed Bragg reflectors and one of the distributed Bragg reflector supported by the released top supporting structure.

41. The method of fabricating an optical microswitch array of claim 40, wherein the separating layer comprises SiO₂ or the like.

42. The method of fabricating an optical microswitch array of claim 40, wherein the electrodes comprise In₂O₃:

SnO₂(5-10%) or the like.

43. The method of fabricating an optical microswitch array of claim 40, wherein the distributed Bragg reflectors comprise a stack of alternating layers of SiO₂ and TiO₂ having the thickness equal to λ

₀/4n, where λ

₀ is the working optical wavelength and n is the refractive index.

44. The method of fabricating an optical microswitch array of claim 40, wherein the distributed Bragg reflectors comprise a stack of alternating layers of SiO₂ and Ta₂O₅ having the thickness equal to λ

₀/4n, where λ

₀ is the working optical wavelength and n is the refractive index.

45. The method of fabricating an optical microswitch array of claim 40, wherein the distributed Bragg reflectors comprise a stack of alternating layers of SiO₂ and SiN_x having the thickness equal to λ

₀/4n, where λ

₀ is the working optical wavelength and n is the refractive index.

46. The method of fabricating an optical microswitch array of claim 40, wherein the top supporting structure comprises Si₃N₄.

47. The method of fabricating an optical microswitch array of claim 40, wherein the top supporting structure comprises amorphous SiC.

48. The method of fabricating an optical microswitch array of claim 40, wherein the top supporting structure comprises polysilicon recrystallized from amorphous silicon.

49. The method of fabricating an optical microswitch array of claim 40, wherein the released top supporting structure comprises a central plane and at least two flexible beams disposed on the edge of the central plane.