Abstract

We devised a novel buried inverse-trapezoidal (BIT) micropattern that can enable light extracting to both front and back sides of the backlight unit (BLU). The proposed BLU comprised of only a single-sheet light-guide plate (LGP) having the BIT micropatterns only on the top surface of the LGP. The proposed BLU shows normal directional light emitting characteristics to both the front and back sides of the LGP and successfully acts as a planer light source for a dual-sided LCD. The proposed BLU has the potential to dramatically reduce the thickness, weight and cost of the dual-sided LCD thanks to its single-sheet nature.

© 2014 Optical Society of America

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References

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  1. H. T. Huang, C. C. Tsai, and Y. P. Huang, “Ultraviolet excitation of remote phosphor with symmetrical illumination used in dual-sided liquid-crystal display,” Opt. Lett. 35(15), 2547–2549 (2010).
    [Crossref] [PubMed]
  2. J. Han, D. Kang, S. Byun, J. Moon, and J. Lee, “Bidirectional LCD monitor using single backlight unit,” in SID Symposium Digest (2011), 42, pp. 793–796.
  3. H. Higashiyama, and Hachioji, ” Surface light source for emitting light from two surfaces and double-sided display device using the same,” U.S. patent 7,156,546 (2007).
  4. K. Käläntär, S. Matsumoto, T. Katoh, and T. Mizuno, “Backlight unit with double‐surface light emission using a single micro‐structured lightguide plate,” Journal of the SID 12, 379–387 (2004).
  5. J.-H. Lee, H.-S. Lee, B.-K. Lee, W.-S. Choi, H. Y. Choi, and J. B. Yoon, “Simple liquid crystal display backlight unit comprising only a single-sheet micropatterned polydimethylsiloxane (PDMS) light-guide plate,” Opt. Lett. 32(18), 2665–2667 (2007).
    [Crossref] [PubMed]
  6. J.-H. Lee, H.-S. Lee, B.-K. Lee, W.-S. Choi, H.-Y. Choi, and J.-B. Yoon, “Design and fabrication of a micropatterned polydimethylsiloxane (PDMS) light-guide plate for sheet-less LCD backlight unit,” Journal of the SID. 16, 329–335 (2008).
  7. G.-W. Yoon, “A Novel microstructure for the backlight unit of a dual-sided display,” M.S. Thesis, Korea Advanced Institute of Science and Technology (KAIST), Korea (2011).
  8. H.-D. Kim, G.-W. Yoon, J. Yeon, J.-H. Lee, and J.-B. Yoon, “Fabrication of a uniform microlens array over a large area using self-aligned diffuser lithography (SADL),” J. Micromech. Microeng. 22(4), 045002 (2012).
    [Crossref]
  9. J.-H. Lee, W.-S. Choi, K.-H. Lee, and J.-B. Yoon, “A simple and effective fabrication method of various 3-D microstructures: Backside 3-D diffuser lithography,” J. Micromech. Microeng. 18(12), 960–1317 (2008).
    [Crossref]
  10. K. Kim, D. S. Park, H. M. Lu, W. Che, K. Kim, J. B. Lee, and C. H. Ahn, “A tapered hollow metallic microneedle array using backside exposure of SU-8,” J. Micromech. Microeng. 14(4), 597–603 (2004).
    [Crossref]
  11. S. W. Lee and S. S. Lee, “Shrinkage ratio of PDMS and its alignment method for the wafer level process,” Microsyst. Technol. 14(2), 205–208 (2008).
    [Crossref]

2012 (1)

H.-D. Kim, G.-W. Yoon, J. Yeon, J.-H. Lee, and J.-B. Yoon, “Fabrication of a uniform microlens array over a large area using self-aligned diffuser lithography (SADL),” J. Micromech. Microeng. 22(4), 045002 (2012).
[Crossref]

2010 (1)

2008 (3)

J.-H. Lee, H.-S. Lee, B.-K. Lee, W.-S. Choi, H.-Y. Choi, and J.-B. Yoon, “Design and fabrication of a micropatterned polydimethylsiloxane (PDMS) light-guide plate for sheet-less LCD backlight unit,” Journal of the SID. 16, 329–335 (2008).

J.-H. Lee, W.-S. Choi, K.-H. Lee, and J.-B. Yoon, “A simple and effective fabrication method of various 3-D microstructures: Backside 3-D diffuser lithography,” J. Micromech. Microeng. 18(12), 960–1317 (2008).
[Crossref]

S. W. Lee and S. S. Lee, “Shrinkage ratio of PDMS and its alignment method for the wafer level process,” Microsyst. Technol. 14(2), 205–208 (2008).
[Crossref]

2007 (1)

2004 (2)

K. Käläntär, S. Matsumoto, T. Katoh, and T. Mizuno, “Backlight unit with double‐surface light emission using a single micro‐structured lightguide plate,” Journal of the SID 12, 379–387 (2004).

K. Kim, D. S. Park, H. M. Lu, W. Che, K. Kim, J. B. Lee, and C. H. Ahn, “A tapered hollow metallic microneedle array using backside exposure of SU-8,” J. Micromech. Microeng. 14(4), 597–603 (2004).
[Crossref]

Ahn, C. H.

K. Kim, D. S. Park, H. M. Lu, W. Che, K. Kim, J. B. Lee, and C. H. Ahn, “A tapered hollow metallic microneedle array using backside exposure of SU-8,” J. Micromech. Microeng. 14(4), 597–603 (2004).
[Crossref]

Byun, S.

J. Han, D. Kang, S. Byun, J. Moon, and J. Lee, “Bidirectional LCD monitor using single backlight unit,” in SID Symposium Digest (2011), 42, pp. 793–796.

Che, W.

K. Kim, D. S. Park, H. M. Lu, W. Che, K. Kim, J. B. Lee, and C. H. Ahn, “A tapered hollow metallic microneedle array using backside exposure of SU-8,” J. Micromech. Microeng. 14(4), 597–603 (2004).
[Crossref]

Choi, H. Y.

Choi, H.-Y.

J.-H. Lee, H.-S. Lee, B.-K. Lee, W.-S. Choi, H.-Y. Choi, and J.-B. Yoon, “Design and fabrication of a micropatterned polydimethylsiloxane (PDMS) light-guide plate for sheet-less LCD backlight unit,” Journal of the SID. 16, 329–335 (2008).

Choi, W.-S.

J.-H. Lee, H.-S. Lee, B.-K. Lee, W.-S. Choi, H.-Y. Choi, and J.-B. Yoon, “Design and fabrication of a micropatterned polydimethylsiloxane (PDMS) light-guide plate for sheet-less LCD backlight unit,” Journal of the SID. 16, 329–335 (2008).

J.-H. Lee, W.-S. Choi, K.-H. Lee, and J.-B. Yoon, “A simple and effective fabrication method of various 3-D microstructures: Backside 3-D diffuser lithography,” J. Micromech. Microeng. 18(12), 960–1317 (2008).
[Crossref]

J.-H. Lee, H.-S. Lee, B.-K. Lee, W.-S. Choi, H. Y. Choi, and J. B. Yoon, “Simple liquid crystal display backlight unit comprising only a single-sheet micropatterned polydimethylsiloxane (PDMS) light-guide plate,” Opt. Lett. 32(18), 2665–2667 (2007).
[Crossref] [PubMed]

Han, J.

J. Han, D. Kang, S. Byun, J. Moon, and J. Lee, “Bidirectional LCD monitor using single backlight unit,” in SID Symposium Digest (2011), 42, pp. 793–796.

Huang, H. T.

Huang, Y. P.

Käläntär, K.

K. Käläntär, S. Matsumoto, T. Katoh, and T. Mizuno, “Backlight unit with double‐surface light emission using a single micro‐structured lightguide plate,” Journal of the SID 12, 379–387 (2004).

Kang, D.

J. Han, D. Kang, S. Byun, J. Moon, and J. Lee, “Bidirectional LCD monitor using single backlight unit,” in SID Symposium Digest (2011), 42, pp. 793–796.

Katoh, T.

K. Käläntär, S. Matsumoto, T. Katoh, and T. Mizuno, “Backlight unit with double‐surface light emission using a single micro‐structured lightguide plate,” Journal of the SID 12, 379–387 (2004).

Kim, H.-D.

H.-D. Kim, G.-W. Yoon, J. Yeon, J.-H. Lee, and J.-B. Yoon, “Fabrication of a uniform microlens array over a large area using self-aligned diffuser lithography (SADL),” J. Micromech. Microeng. 22(4), 045002 (2012).
[Crossref]

Kim, K.

K. Kim, D. S. Park, H. M. Lu, W. Che, K. Kim, J. B. Lee, and C. H. Ahn, “A tapered hollow metallic microneedle array using backside exposure of SU-8,” J. Micromech. Microeng. 14(4), 597–603 (2004).
[Crossref]

K. Kim, D. S. Park, H. M. Lu, W. Che, K. Kim, J. B. Lee, and C. H. Ahn, “A tapered hollow metallic microneedle array using backside exposure of SU-8,” J. Micromech. Microeng. 14(4), 597–603 (2004).
[Crossref]

Lee, B.-K.

J.-H. Lee, H.-S. Lee, B.-K. Lee, W.-S. Choi, H.-Y. Choi, and J.-B. Yoon, “Design and fabrication of a micropatterned polydimethylsiloxane (PDMS) light-guide plate for sheet-less LCD backlight unit,” Journal of the SID. 16, 329–335 (2008).

J.-H. Lee, H.-S. Lee, B.-K. Lee, W.-S. Choi, H. Y. Choi, and J. B. Yoon, “Simple liquid crystal display backlight unit comprising only a single-sheet micropatterned polydimethylsiloxane (PDMS) light-guide plate,” Opt. Lett. 32(18), 2665–2667 (2007).
[Crossref] [PubMed]

Lee, H.-S.

J.-H. Lee, H.-S. Lee, B.-K. Lee, W.-S. Choi, H.-Y. Choi, and J.-B. Yoon, “Design and fabrication of a micropatterned polydimethylsiloxane (PDMS) light-guide plate for sheet-less LCD backlight unit,” Journal of the SID. 16, 329–335 (2008).

J.-H. Lee, H.-S. Lee, B.-K. Lee, W.-S. Choi, H. Y. Choi, and J. B. Yoon, “Simple liquid crystal display backlight unit comprising only a single-sheet micropatterned polydimethylsiloxane (PDMS) light-guide plate,” Opt. Lett. 32(18), 2665–2667 (2007).
[Crossref] [PubMed]

Lee, J.

J. Han, D. Kang, S. Byun, J. Moon, and J. Lee, “Bidirectional LCD monitor using single backlight unit,” in SID Symposium Digest (2011), 42, pp. 793–796.

Lee, J. B.

K. Kim, D. S. Park, H. M. Lu, W. Che, K. Kim, J. B. Lee, and C. H. Ahn, “A tapered hollow metallic microneedle array using backside exposure of SU-8,” J. Micromech. Microeng. 14(4), 597–603 (2004).
[Crossref]

Lee, J.-H.

H.-D. Kim, G.-W. Yoon, J. Yeon, J.-H. Lee, and J.-B. Yoon, “Fabrication of a uniform microlens array over a large area using self-aligned diffuser lithography (SADL),” J. Micromech. Microeng. 22(4), 045002 (2012).
[Crossref]

J.-H. Lee, W.-S. Choi, K.-H. Lee, and J.-B. Yoon, “A simple and effective fabrication method of various 3-D microstructures: Backside 3-D diffuser lithography,” J. Micromech. Microeng. 18(12), 960–1317 (2008).
[Crossref]

J.-H. Lee, H.-S. Lee, B.-K. Lee, W.-S. Choi, H.-Y. Choi, and J.-B. Yoon, “Design and fabrication of a micropatterned polydimethylsiloxane (PDMS) light-guide plate for sheet-less LCD backlight unit,” Journal of the SID. 16, 329–335 (2008).

J.-H. Lee, H.-S. Lee, B.-K. Lee, W.-S. Choi, H. Y. Choi, and J. B. Yoon, “Simple liquid crystal display backlight unit comprising only a single-sheet micropatterned polydimethylsiloxane (PDMS) light-guide plate,” Opt. Lett. 32(18), 2665–2667 (2007).
[Crossref] [PubMed]

Lee, K.-H.

J.-H. Lee, W.-S. Choi, K.-H. Lee, and J.-B. Yoon, “A simple and effective fabrication method of various 3-D microstructures: Backside 3-D diffuser lithography,” J. Micromech. Microeng. 18(12), 960–1317 (2008).
[Crossref]

Lee, S. S.

S. W. Lee and S. S. Lee, “Shrinkage ratio of PDMS and its alignment method for the wafer level process,” Microsyst. Technol. 14(2), 205–208 (2008).
[Crossref]

Lee, S. W.

S. W. Lee and S. S. Lee, “Shrinkage ratio of PDMS and its alignment method for the wafer level process,” Microsyst. Technol. 14(2), 205–208 (2008).
[Crossref]

Lu, H. M.

K. Kim, D. S. Park, H. M. Lu, W. Che, K. Kim, J. B. Lee, and C. H. Ahn, “A tapered hollow metallic microneedle array using backside exposure of SU-8,” J. Micromech. Microeng. 14(4), 597–603 (2004).
[Crossref]

Matsumoto, S.

K. Käläntär, S. Matsumoto, T. Katoh, and T. Mizuno, “Backlight unit with double‐surface light emission using a single micro‐structured lightguide plate,” Journal of the SID 12, 379–387 (2004).

Mizuno, T.

K. Käläntär, S. Matsumoto, T. Katoh, and T. Mizuno, “Backlight unit with double‐surface light emission using a single micro‐structured lightguide plate,” Journal of the SID 12, 379–387 (2004).

Moon, J.

J. Han, D. Kang, S. Byun, J. Moon, and J. Lee, “Bidirectional LCD monitor using single backlight unit,” in SID Symposium Digest (2011), 42, pp. 793–796.

Park, D. S.

K. Kim, D. S. Park, H. M. Lu, W. Che, K. Kim, J. B. Lee, and C. H. Ahn, “A tapered hollow metallic microneedle array using backside exposure of SU-8,” J. Micromech. Microeng. 14(4), 597–603 (2004).
[Crossref]

Tsai, C. C.

Yeon, J.

H.-D. Kim, G.-W. Yoon, J. Yeon, J.-H. Lee, and J.-B. Yoon, “Fabrication of a uniform microlens array over a large area using self-aligned diffuser lithography (SADL),” J. Micromech. Microeng. 22(4), 045002 (2012).
[Crossref]

Yoon, G.-W.

H.-D. Kim, G.-W. Yoon, J. Yeon, J.-H. Lee, and J.-B. Yoon, “Fabrication of a uniform microlens array over a large area using self-aligned diffuser lithography (SADL),” J. Micromech. Microeng. 22(4), 045002 (2012).
[Crossref]

Yoon, J. B.

Yoon, J.-B.

H.-D. Kim, G.-W. Yoon, J. Yeon, J.-H. Lee, and J.-B. Yoon, “Fabrication of a uniform microlens array over a large area using self-aligned diffuser lithography (SADL),” J. Micromech. Microeng. 22(4), 045002 (2012).
[Crossref]

J.-H. Lee, W.-S. Choi, K.-H. Lee, and J.-B. Yoon, “A simple and effective fabrication method of various 3-D microstructures: Backside 3-D diffuser lithography,” J. Micromech. Microeng. 18(12), 960–1317 (2008).
[Crossref]

J.-H. Lee, H.-S. Lee, B.-K. Lee, W.-S. Choi, H.-Y. Choi, and J.-B. Yoon, “Design and fabrication of a micropatterned polydimethylsiloxane (PDMS) light-guide plate for sheet-less LCD backlight unit,” Journal of the SID. 16, 329–335 (2008).

J. Micromech. Microeng. (3)

H.-D. Kim, G.-W. Yoon, J. Yeon, J.-H. Lee, and J.-B. Yoon, “Fabrication of a uniform microlens array over a large area using self-aligned diffuser lithography (SADL),” J. Micromech. Microeng. 22(4), 045002 (2012).
[Crossref]

J.-H. Lee, W.-S. Choi, K.-H. Lee, and J.-B. Yoon, “A simple and effective fabrication method of various 3-D microstructures: Backside 3-D diffuser lithography,” J. Micromech. Microeng. 18(12), 960–1317 (2008).
[Crossref]

K. Kim, D. S. Park, H. M. Lu, W. Che, K. Kim, J. B. Lee, and C. H. Ahn, “A tapered hollow metallic microneedle array using backside exposure of SU-8,” J. Micromech. Microeng. 14(4), 597–603 (2004).
[Crossref]

Journal of the SID (1)

K. Käläntär, S. Matsumoto, T. Katoh, and T. Mizuno, “Backlight unit with double‐surface light emission using a single micro‐structured lightguide plate,” Journal of the SID 12, 379–387 (2004).

Journal of the SID. (1)

J.-H. Lee, H.-S. Lee, B.-K. Lee, W.-S. Choi, H.-Y. Choi, and J.-B. Yoon, “Design and fabrication of a micropatterned polydimethylsiloxane (PDMS) light-guide plate for sheet-less LCD backlight unit,” Journal of the SID. 16, 329–335 (2008).

Microsyst. Technol. (1)

S. W. Lee and S. S. Lee, “Shrinkage ratio of PDMS and its alignment method for the wafer level process,” Microsyst. Technol. 14(2), 205–208 (2008).
[Crossref]

Opt. Lett. (2)

Other (3)

J. Han, D. Kang, S. Byun, J. Moon, and J. Lee, “Bidirectional LCD monitor using single backlight unit,” in SID Symposium Digest (2011), 42, pp. 793–796.

H. Higashiyama, and Hachioji, ” Surface light source for emitting light from two surfaces and double-sided display device using the same,” U.S. patent 7,156,546 (2007).

G.-W. Yoon, “A Novel microstructure for the backlight unit of a dual-sided display,” M.S. Thesis, Korea Advanced Institute of Science and Technology (KAIST), Korea (2011).

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Figures (9)

Fig. 1
Fig. 1 Schematic of the proposed dual-sided light emitting BLU and its optical light-path. The buried inverse-trapezoidal (BIT) microstructures in the figure are exaggerated in size and spacing for viewing purposes. The propagating light inside of the LGP can be extracted to both forward and backward directions by the total internal reflection that occurs at the inner or outer sidewall of the BIT microstructures.
Fig. 2
Fig. 2 Relationship between the forward and backward extracting light angles (θf and θb) and the sidewall angle (θs) of the BIT microstructures. Interestingly, the forward and backward extracted lights have the same directionality (θf = θb).
Fig. 3
Fig. 3 Simulation results of the forward and backward angular luminance distribution. (a) Forward luminance with respect to the sidewall angle θs of the BIT microstructures and (b) the forward and backward luminances when θs was optimally set to 55°.
Fig. 4
Fig. 4 Possible optical loss paths caused by the air-gap surrounding the BIT structure (all solid lines). The original contributing light paths are drawn with the dotted lines. Upper left inset shows the refraction loss and upper right inset indicates the reflection loss.
Fig. 5
Fig. 5 Simulated forward and backward luminances with respect to the air-gap thickness.
Fig. 6
Fig. 6 Simulation results of the spatial and angular luminance distributions of the front and back sides of (a) the previous protruding inverse-trapezoidal (PIT) micro-patterned LGP and (b) the proposed buried-inverse-trapezoidal (BIT) micro-patterned LGP.
Fig. 7
Fig. 7 Overall fabrication process of the proposed single-sheet dual-sided light extracting PDMS LGP. (a) Self aligned diffuser lithography (SADL) process on the Ti (500 Å)/Au (500 Å) deposited Si wafer. (b) Photoresist development to form hollow truncated-conical photoresist mold. (c) Cu electroplating for making a truncated-conical shape (d) Ni electroplating for forming a metallic shell mold and photoresist coating for protecting the microstructures during CMP. (e) Ni CMP process to open up the cap of the shell. (f) Etching out the Cu structure. (g) PDMS curing and removing the metallic shell mold. (h) Separation of the PDMS LGP.
Fig. 8
Fig. 8 Scanning electron microscope (SEM) images of (a) the hollow metallic (Ni) micro-shell array, and (b) the fabricated PDMS LGP having BIT microstructures.
Fig. 9
Fig. 9 Optical characteristics of the fabricated BLUs: one BLU has BIT microstructures and the other BLU has PIT microstructures. (a) Ratio of the backward luminance (Lb) to forward luminance (Lf) of the two BLUs in six positions, and (b) angular luminance distribution of the two BLUs at the center position.

Equations (3)

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θ i = θ s θ t
θ f   = θ i + θ s = 2 θ s θ t  
θ b = 2 θ s θ t  

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