Interferometric modulator and display unit

• US 7,113,339 B2
• Filed: 08/27/2004
• Issued: 09/26/2006
• Est. Priority Date: 08/29/2003
• Status: Expired due to Fees

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Taguchi, Tokio, Ueki, Shun, Tsuda, Kazuhiko
• Primary Examiner(s): Lester, Evelyn A.
• Application Number:
  US10/928,833
• Publication Number:
  US 20050046919A1
• Time in Patent Office: 760 Days
• Field of Search: 359/579, 359/578, 359/584, 359586-589, 359290-292, 359/295, 359/298, 359/302, 359/318
• US Class Current: 359/586
• CPC Class Codes: G02B 26/001 based on interference in an adjustable optical cavity interference filters G02B5/28; devices or arrangements using multiple reflections in spectrometry or monochromators G01J3/26

Abstract

The interferometric modulator of the invention includes a transparent substrate (refractive index: n₀) 12, an optical thin film (complex index of refraction: N₁=n₁−i·k₁) 13 provided on the transparent substrate 12, and an absorber layer (complex index of refraction: N_s=n_s−i·k_s) 14 opposed to the optical thin film 13, the distance of a gap to the optical thin film 13 being variable, wherein the relation n₁>n₀, k₁≅0 and n_s>n₀ is satisfied.

Claims

1. An interferometric modulator comprising:

a transparent substrate having a refractive index of n₀;

an optical thin film having a complex index of refraction of N₁=n₁−

i·

k₁, where n₁ is the refractive index of the optical thin film and k₁ is the extinction coefficient of the optical thin film, and provided on said transparent substrate; and

an absorber layer having a complex index of refraction of N_s=n_s−

i·

k_s, where n_s is the refractive index of the absorber layer and k_s is the extinction coefficient of the absorber layer, and opposed to said optical thin film;

wherein

a gap having a distance to said optical thin film is variable; and

the following relation is satisfied,

n₁n₀, k₁≅

0 and n_s>

n₀.

2. The interferometric modulator according to claim 1, wherein the following relation of expression (1) is satisfied,

$\begin{array}{c}{n}_1\cong \end{array}$

( n 0 ⁢

n s + n 0 ⁢

k s 2 n s - n 0 ) 1 / 2 . ( 1 )

3. The interferometric modulator according to claim 1, wherein for a wavelength λ

in a visible radiation region, a physical film thickness d₁ of said optical thin film satisfies the following expression (2), when n₁²−

n_s²−

k_s²>

0,

$\begin{array}{cc}{d}_1\cong <br><br>\frac{\mathrm{\lambda <br><br>}}{2<br><br>n_1}<br><br>\left\{j-\frac{1}{2<br><br>\mathrm{\pi <br><br>}}<br><br>{\tan }^{-1}<br><br>\left(\frac{-2<br><br>n_1<br><br>k_s}{n_1^2-n_s^2-k_s^2}\right)\right\}<br><br><br><br>j<br><br>\text{;<br><br>}<br><br><br><br>\mathrm{integer}& \left(2\right)\end{array}$

or satisfies the following expression (3), when n₁²−

n_s²−

k_s²<

0,

$\begin{array}{cc}{d}_1\cong <br><br>\frac{\mathrm{\lambda <br><br>}}{2<br><br>n_1}<br><br>\left\{\left(j-\frac{1}{2}\right)-\frac{1}{2<br><br>\mathrm{\pi <br><br>}}<br><br>{\tan }^{-1}<br><br>\left(\frac{-2<br><br>n_1<br><br>k_s}{n_1^2-n_s^2-k_s^2}\right)\right\}<br><br><br><br>j<br><br>\text{;<br><br>}<br><br><br><br>\mathrm{integer}.& \left(3\right)\end{array}$

4. The interferometric modulator according to claim 3, wherein d₁ is the smallest value in which the expression (2) or (3) is satisfied.

5. The interferometric modulator according to claim 1, wherein the refractive index n_v of a medium filling a gap formed between said optical thin film and said absorber layer is smaller than the refractive index n₁ of said optical thin film, and assuming that a physical distance of said gap is d_v, for wavelength λ

in the visible radiation region, the following expression (4) is satisfied,

$\begin{array}{cc}{d}_v\cong <br><br>\frac{\left(2<br><br>m+1\right)<br><br>\mathrm{\lambda <br><br>}}{4·<br><br>n_v}<br><br><br><br>m<br><br>\text{;<br><br>}<br><br><br><br>\mathrm{integer}.& \left(4\right)\end{array}$

6. The interferometric modulator according to claim 1, wherein said optical thin film is composed of an equivalent multilayer film.

7. The interferometric modulator according to claim 1, wherein the distance of said gap formed between said optical thin film and said absorber layer is changed within an interferometric range.

8. The interferometric modulator according to claim 1, wherein the distance of said gap formed between said optical thin film and said absorber layer is changed up to the optical distance at which no interference occurs.

9. The interferometric modulator according to claim 1, wherein said gap formed between said optical thin film and said absorber layer is changed stepwise.

10. The interferometric modulator according to claim 1, further comprising a driving element for changing the distance of said gap formed between said optical thin film and said absorber layer.

11. The interferometric modulator according to claim 10, wherein said driving element comprises a piezoelectric element.

12. The interferometric modulator according to claim 1, wherein said gap formed between said optical thin film and said absorber layer is vacuum or filled with gas.

13. The interferometric modulator according to claim 1, wherein said gap formed between said optical thin film and said absorber layer is filled with liquid.

14. The interferometric modulator according to claim 1, further comprising a color filter disposed on the transparent substrate for passing light having a specific wavelength.

15. The interferometric modulator according to claim 1, further comprising a light scattering layer disposed on the transparent substrate.

16. The interferometric modulator according to claim 1, wherein said optical thin film comprises at least one transparent conductive layer.

17. The interferometric modulator according to claim 16, wherein the distance of said gap formed between said optical thin film and said absorber layer is changed in accordance with a voltage applied to said at least one transparent conductive layer.

18. A display unit having a plurality of pixels, each of which comprises the interferometric modulator according to claim 1.

19. The display unit according to claim 18, wherein said plurality of pixels comprise a first pixel and a second pixel, in which said interferometric modulators provided for said first pixel and said second pixel are mutually different in the configuration of said optical thin film, or said absorber layer.

20. An electronic apparatus comprising the display unit according to claim 19.

21. An interferometric modulator comprising:

a transparent substrate having a refractive index of η

₀;

a stacked-layer film provided on said transparent substrate; and

an absorber layer having a complex index of refraction η

_s=n_s−

i·

k_s, where n_s is refractive index of the absorber layer and k_s is the extinction coefficient of the absorber layer, and opposed to said stacked-layer film;

wherein

a gap having a distance to said stacked-layer film is variable;

said stacked-layer film has M transparent thin film layers, where M is three or more, the complex indexes of refraction of two adjacent transparent thin film layers being mutually different, the complex index of refraction of a j-th thin film layer, where j is between one and M, from a side nearest to said transparent substrate is η

_j=n_j−

i·

k_j, where n_j is the refractive index of the j-th thin film layer and k_j is the extinction coefficient of the j-th thin film layer, a phase film thickness is δ

_j, and B and C are given by the following expression (5),

$\begin{array}{cc}\left(\begin{array}{c}B\\ C\end{array}\right)=\left\{\underset{j=1}{\overset{M}{\prod <br><br>}}<br><br><br><br>\left(\begin{array}{cc}\cos <br><br><br><br>{\mathrm{\delta <br><br>}}_j& i·<br><br>\sin <br><br>\left({\mathrm{\delta <br><br>}}_j\right)/{\mathrm{\eta <br><br>}}_j\\ i·<br><br>{\mathrm{\eta <br><br>}}_j·<br><br>\sin <br><br>\left({\mathrm{\delta <br><br>}}_j\right)& \cos <br><br>\left({\mathrm{\delta <br><br>}}_j\right)\end{array}\right)\right\}<br><br>\left(\begin{array}{c}1\\ {\mathrm{\eta <br><br>}}_s\end{array}\right)& \left(5\right)\end{array}$

k_j≅

0, and in a visible wavelength region, the following expression (6) is satisfied,

$\begin{array}{cc}\left(\frac{{\mathrm{\eta <br><br>}}_0·<br><br>B-C}{{\mathrm{\eta <br><br>}}_0·<br><br>B+C}\right)<br><br>{\left(\frac{{\mathrm{\eta <br><br>}}_0·<br><br>B-C}{{\mathrm{\eta <br><br>}}_0·<br><br>B+C}\right)}^{*}<<br><br>\left(\frac{{\mathrm{\eta <br><br>}}_0-{\mathrm{\eta <br><br>}}_s}{{\mathrm{\eta <br><br>}}_0+{\mathrm{\eta <br><br>}}_s}\right)<br><br>{\left(\frac{{\mathrm{\eta <br><br>}}_0-{\mathrm{\eta <br><br>}}_s}{{\mathrm{\eta <br><br>}}_0+{\mathrm{\eta <br><br>}}_s}\right)}^{*}& \left(6\right)\\ \mathrm{where}<br><br>*<br><br>\mathrm{denotes}<br><br><br><br>\mathrm{complex}<br><br><br><br>\mathrm{conjugate}.& \end{array}$

22. The interferometric modulator according to claim 21, wherein assuming that the refractive index of a medium filling said gap formed between said stacked-layer film and said absorber layer is η

_v, a physical distance of said gap is δ

_v, and D and E are given by the following expression (7),

$\begin{array}{cc}\left(\begin{array}{c}D\\ E\end{array}\right)=\left\{\underset{j=1}{\overset{M}{\prod <br><br>}}<br><br><br><br>\left(\begin{array}{cc}\cos <br><br><br><br>{\mathrm{\delta <br><br>}}_j& i·<br><br>\sin <br><br>\left({\mathrm{\delta <br><br>}}_j\right)/{\mathrm{\eta <br><br>}}_j\\ i·<br><br>{\mathrm{\eta <br><br>}}_j·<br><br>\sin <br><br>\left({\mathrm{\delta <br><br>}}_j\right)& \cos <br><br>\left({\mathrm{\delta <br><br>}}_j\right)\end{array}\right)\right\}<br><br>\left(\begin{array}{cc}\cos <br><br><br><br>{\mathrm{\delta <br><br>}}_v& i·<br><br>\sin <br><br>\left({\mathrm{\delta <br><br>}}_v\right)/{\mathrm{\eta <br><br>}}_v\\ i·<br><br>{\mathrm{\eta <br><br>}}_v·<br><br>\sin <br><br>\left({\mathrm{\delta <br><br>}}_v\right)& \cos <br><br>\left({\mathrm{\delta <br><br>}}_v\right)\end{array}\right)<br><br>\left(\begin{array}{c}1\\ {\mathrm{\eta <br><br>}}_s\end{array}\right)& \left(7\right)\end{array}$

in a visible wavelength region of wide band, the following expression (8) is satisfied,

$\begin{array}{cc}\left(\frac{{\mathrm{\eta <br><br>}}_0·<br><br>D-E}{{\mathrm{\eta <br><br>}}_0·<br><br>D+E}\right)<br><br>{\left(\frac{{\mathrm{\eta <br><br>}}_0·<br><br>D-E}{{\mathrm{\eta <br><br>}}_0·<br><br>D+E}\right)}^{*}><br><br>\left(\frac{{\mathrm{\eta <br><br>}}_0-{\mathrm{\eta <br><br>}}_s}{{\mathrm{\eta <br><br>}}_0+{\mathrm{\eta <br><br>}}_s}\right)<br><br>{\left(\frac{{\mathrm{\eta <br><br>}}_0-{\mathrm{\eta <br><br>}}_s}{{\mathrm{\eta <br><br>}}_0+{\mathrm{\eta <br><br>}}_s}\right)}^{*}& \left(8\right)\\ \mathrm{where}<br><br>*<br><br>\mathrm{denotes}<br><br><br><br>\mathrm{complex}<br><br><br><br>\mathrm{conjugate}.& \end{array}$

23. The interferometric modulator according to claim 21, wherein said stacked-layer film has an alternate stacked-layer film in which a first transparent thin film layer and a second transparent thin film layer having mutually different complex indexes of refraction are stacked alternately, and a third transparent thin film layer provided on said alternate stacked-layer film and opposed to said absorber layer.

24. The interferometric modulator according to claim 21, wherein the distance of said gap formed between said stacked-layer film and said absorber layer is changed within an interferometric range.

25. The interferometric modulator according to claim 21, wherein the distance of said gap formed between said stacked-layer film and said absorber layer is changed up to the optical distance at which no interference occurs.

26. The interferometric modulator according to claim 21, wherein said gap formed between said stacked-layer film and said absorber layer is changed stepwise.

27. The interferometric modulator according to claim 21, further comprising a driving element for changing the distance of said gap formed between said stacked-layer film and said absorber layer.

28. The interferometric modulator according to claim 27, wherein said driving element comprises a piezoelectric element.

29. The interferometric modulator according to claim 21, wherein said gap formed between said stacked-layer film and said absorber layer is vacuum or filled with gas.

30. The interferometric modulator according to claim 21, wherein said gap formed between said stacked-layer film and said absorber layer is filled with liquid.

31. The interferometric modulator according to claim 21, further comprising a color filter disposed on the transparent substrate for passing light having a specific wavelength.

32. The interferometric modulator according to claim 21, further comprising a light scattering layer disposed on the transparent substrate.

33. The interferometric modulator according to claim 21, wherein said stacked-layer film comprises at least one transparent conductive layer.

34. The interferometric modulator according to claim 33, wherein the distance of said gap formed between said stacked-layer film and said absorber layer is changed in accordance with a voltage applied to said at least one transparent conductive layer.

35. A display unit having a plurality of pixels, each of which comprises the interferometric modulator according to claim 21.

36. The display unit according to claim 35, wherein said plurality of pixels comprise a first pixel and a second pixel, in which said interferometric modulators provided for said first pixel and said second pixel are mutually different in the configuration of said stacked-layer film or said absorber layer.

37. An electronic apparatus comprising the display unit according to claim 35.