Method of manufacturing flexible metallic photonic band gap structures, and structures resulting therefrom

• US 6,274,293 B1
• Filed: 05/28/1998
• Issued: 08/14/2001
• Est. Priority Date: 05/30/1997
• Status: Expired due to Fees

• Current Assignee: Iowa State University Research Foundation Incorporated (Iowa State University)
• Original Assignee: Iowa State University Research Foundation Incorporated (Iowa State University)
• Inventors: Sigalas, Mihail, Ho, Kai-Ming, McCalmont, Jonathan S., Gupta, Sandhya, Tuttle, Gary L.
• Primary Examiner(s): Duda, Kathleen
• Application Number:
  US09/086,790
• Time in Patent Office: 1,174 Days
• Field of Search: 430/320, 430/311, 430/315, 430/324, 430/329, 427/566, 427/124, 427/372.2
• US Class Current: 430/315
• CPC Class Codes: B82Y 20/00 Nanooptics, e.g. quantum optics or photonic crystals
• CPC Class Codes: G02B 6/1225 comprising photonic band-gap structures or photonic lattices

Abstract

A method of manufacturing a flexible metallic photonic band gap structure operable in the infrared region, comprises the steps of spinning on a first layer of dielectric on a GaAs substrate, imidizing this first layer of dielectric, forming a first metal pattern on this first layer of dielectric, spinning on and imidizing a second layer of dielectric, and then removing the GaAs substrate. This method results in a flexible metallic photonic band gap structure operable with various filter characteristics in the infrared region. This method may be used to construct multi-layer flexible metallic photonic band gap structures. Metal grid defects and dielectric separation layer thicknesses are adjusted to control filter parameters.

Claims

1. A method of manufacturing a flexible metallic photonic band gap structure operable in the infrared region, comprising the steps of:

spinning on a substrate a first layer of dielectric to a first thickness;

imidizing said first layer of dielectric;

forming a first metal pattern on said first layer of dielectric;

spinning on said metal pattern a second layer of dielectric to a second thickness;

imidizing said second layer of dielectric; and

removing said substrate.

2. The method of claim 1, wherein said dielectric comprises a fluorinated polyamic acid polyimide.

3. (Once amended) The method of claim 1, wherein said steps of spinning on a first layer of dielectric and a second layer of dielectric are performed at a speed of at least approximately 2000 RPM for approximately 45 seconds.

4. The method of claim 3, wherein said steps of spinning on a first layer of dielectric and said step of spinning on a second layer of dielectric are performed at approximately 4000 RPM.

5. The method of claim 1, wherein said step of imidizing comprises the steps of:

softbaking said dielectric at approximately 120°

-150°

C. for approximately 30 minutes to produce partial imidization of said dielectric; and

curing said dielectric at approximately 350°

-4000°

C. for approximately 30-15 minutes respectively to complete imidization and consolidation of said dielectric.

6. The method of claim 5, wherein said step of curing said dielectric comprises the steps of:

placing said dielectric in an oven at a temperature of approximately 200°

C.;

ramping the temperature from approximately 200°

C. to 350°

-400°

C.;

soaking said dielectric at approximately 350°

-400°

C. for approximately 30-15 minutes;

ramping the temperature from approximately 350°

-400°

C. to approximately 200°

C.; and

removing said dielectric from the oven.

7. The method of claim 1, wherein said step of forming a metal pattern on said first layer of dielectric comprises the steps of:

spinning on said first layer of dielectric a layer of photoresist;

exposing said layer of photoresist with a negative of said metal pattern with UV light;

hardening said layer of photoresist;

developing said pattern;

depositing a layer of metal on said layer of photoresist; and

removing metal from areas of said photoresist which were not patterned by said exposing step.

8. The method of claim 7, wherein said step of spinning on a layer of photoresist comprises the steps of:

spinning-on said photoresist at a speed of at least approximately 2000 RPM; and

baking at approximately 90°

C. for approximately 30 minutes.

9. The method of claim 8, wherein said step of spinning-on is performed at approximately 3000+/−

100 RPM for approximately 45 seconds.

10. The method of claim 7, wherein said step of depositing a layer of metal on said layer of photoresist comprises the steps of:

e-beam evaporating aluminum; and

depositing said aluminum at a rate not to exceed 50 angstroms per second.

11. The method of claim 10, wherein said step of depositing said aluminum is performed at a rate of approximately 7-10 angstroms per second to a thickness of approximately 2000 angstroms.

12. The method of claim 7, wherein said step of removing metal from areas of said photoresist which were not patterned by said exposing step comprises the step of dissolving said areas of said photoresist which were not patterned by said exposing step in an ultrasonic bath of acetone.

13. The method of claim 1, wherein said substrate is GaAs and wherein said step of removing said substrate comprises the step of soaking in a solution of citric acid and hydrogen peroxide of concentration approximately 4:

1.

14. The method of claim 1, further comprising, before performing said step of removing said substrate, the steps of:

forming a second metal pattern on said second layer of dielectric;

spinning on said second metal pattern a third layer of dielectric to a third thickness; and

imidizing said third layer of dielectric.

15. The method of claim 14, wherein said second thickness is approximately equal to or less than approximately 11 micrometers.

16. The method of claim 14, wherein said second thickness exceeds approximately 11 micrometers, and wherein said step of spinning on said second layer of dielectric comprises the steps of:

spinning on a first sub-layer of dielectric of thickness not greater than approximately 11 micrometers;

softbaking said first sub-layer;

spinning on a second sub-layer of dielectric of thickness not greater than approximately 11 micrometers; and

repeating said spinning on, said softbaking, and said spinning on steps until a desired thickness is reached.

17. The method of claim 14, further comprising the steps of:

forming a third metal pattern on said third layer of dielectric;

spinning on said third metal pattern a fourth layer of dielectric to a fourth thickness; and

imidizing said fourth layer of dielectric.

18. The method of claim 17, further comprising the steps of:

forming a fourth metal pattern on said fourth layer of dielectric;

spinning on said fourth metal pattern a fifth layer of dielectric to a fifth thickness; and

imidizing said fifth layer of dielectric.

19. The method of claim 18, further comprising the steps of:

forming a fifth metal pattern on said fifth layer of dielectric;

spinning on said fifth metal pattern a sixth layer of dielectric to a sixth thickness; and

imidizing said sixth layer of dielectric.

20. The method of claim 17, wherein said step of spinning on said second layer of dielectric and said step of spinning on said third layer of dielectric are performed such that said second thickness and said third thickness are approximately equal.

21. The method of claim 17, wherein said step of spinning on said second layer of dielectric and said step of spinning on said third layer of dielectric are performed such that said second thickness and said third thickness are not equal.

22. The method of claim 17, wherein said step of spinning on said second layer of dielectric and said step of spinning on said third layer of dielectric are performed to control a parameter of filter characteristic.

23. The method of claim 17, wherein said step of forming a second metal pattern includes the step of introducing a defect in said metal pattern.

24. The method of claim 23, further comprising the step of adjusting a parameter of said defect to control a parameter of filter characteristic.

25. The method of claim 17, wherein said step of forming a first metal pattern, said step of forming a second metal pattern, and said step of forming a third metal pattern each include the step of introducing a defect in said metal pattern.

26. The method of claim 25, further comprising the steps of adjusting a parameter of said defects to control a parameter of filter characteristic.

27. A method of manufacturing a flexible metallic photonic band gap structure, comprising the steps of:

providing a GaAs substrate;

applying a bottom encapsulation layer of polyimide dielectric to said substrate;

forming a first metal pattern on said bottom encapsulation layer;

applying a first polyimide dielectric separation layer on said first metal pattern;

forming a second metal pattern on said first separation layer;

applying a second polyimide dielectric separation layer on said second metal pattern;

forming a third metal pattern on said second separation layer;

applying a top encapsulation layer of polyimide dielectric on said third metal pattern; and

removing said substrate from said bottom encapsulation layer, resulting in the flexible metallic photonic band gap structure.

28. The method of claim 27, wherein said step of applying said bottom encapsulation layer and said step of applying said top encapsulation layer comprise the steps of:

spinning on said dielectric at approximately 4000 RPM for approximately 45 seconds;

softbaking said dielectric at approximately 120°

-150°

C. for approximately 30 minutes;

placing said dielectric in an oven at a temperature of approximately 200°

C.;

ramping the temperature from approximately 200°

C. to 350°

-400°

C.;

soaking said dielectric at approximately 350°

-400°

C. for approximately 30-15 minutes;

ramping the temperature from approximately 350°

-400°

C. to approximately 200°

C.; and

removing said dielectric from the oven.

29. The method of claim 27, wherein said step of applying said first dielectric separation layer and said step of applying said second dielectric separation layer comprise the steps of:

spinning on said dielectric at a predetermined speed based on a desired thickness of said layer for approximately 45 seconds;

softbaking said dielectric at approximately 120°

-150°

C. for approximately 30 minutes;

placing said dielectric in an oven at a temperature of approximately 200°

C.;

ramping the temperature from approximately 200°

C. to 350°

-400°

C.;

soaking said dielectric at approximately 350°

-400°

C. for approximately 30-15 minutes;

ramping the temperature from approximately 350°

-400°

C. to approximately 200°

C.; and

removing said dielectric from the oven.

30. The method of claim 27, wherein said steps of forming a first metal pattern, of forming a second metal pattern, and of forming a third metal pattern comprise the steps of:

spinning on a layer of photoresist;

exposing said layer of photoresist with a negative of said metal pattern with UV light;

hardening said layer of photoresist;

developing said pattern;

depositing a layer of aluminum on said layer of photoresist by e-beam evaporation at a rate of approximately 7-10 angstroms per second to a thickness of approximately 2000 angstroms; and

dissolving areas of photoresist which were not patterned by said exposing step in an ultrasonic acetone bath to remove metal deposed therefrom.

31. The method of claim 27, wherein said step of removing said substrate from said bottom encapsulation layer comprises the step of dissolving the GaAs substrate in a solution of citric acid and hydrogen peroxide.

32. The method of claim 27, wherein said step of forming a second metal pattern on said first separation layer includes the step of introducing a defect in said metal pattern.

33. The method of claim 32, further comprising the step of adjusting a parameter of said defect to control a parameter of filter characteristic.

34. The method of claim 27, wherein said steps of forming a first metal pattern, of forming a second metal pattern, and of forming a third metal pattern include the step of introducing a defect in said metal pattern.

35. The method of claim 34, further comprising the step of adjusting a parameter of said defect to control a parameter of filter characteristic.

36. The method of claim 27, wherein said step of applying said first dielectric separation layer and said step of applying said second dielectric separation layer are performed to control a parameter of filter characteristic.

37. The method of claim 36, wherein said step of applying said first dielectric separation layer and said step of applying said second dielectric separation layer are performed such that said first dielectric separation layer and said second dielectric separation layer are of unequal thicknesses.

38. The method of claim 27, further comprising the step of adjusting critical frequencies of the metallic photonic band gap structure by varying spatial periodicity of said metal patterns and interlayer separation thereof.