JP2007212560A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an OCB type liquid crystal display device capable of displaying an image without applying initial transfer voltage. <P>SOLUTION: In the semitransmission type liquid crystal display device 10 wherein thicknesses of a liquid crystal layer in a reflection part and a transmission part are different from each other, a liquid crystal of the liquid crystal layer 50 has an OCB mode and shows twist alignment in an initial alignment state, which is transferred to bend alignment in an image display state. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a transflective liquid crystal display device.

Recently, OCB type liquid crystal display devices have been used in liquid crystal televisions and the like (for example, see Non-Patent Document 1). This OCB type liquid crystal display device is characterized by a wide viewing angle and a high-speed response. However, this OCB mode liquid crystal has a splay alignment when no voltage is applied, and must be transferred to a bend alignment by applying an initial transition voltage when the power is turned on (see Non-Patent Document 2).
Nikkei Flat Panel Display Strategy 2005 Page 110 Nikkei Business Publications High-Speed Bend Transition Method using Electrical Twist Field in OCB Mode TFT-LCDs Kenji nakao, Daiichi Suzuki, Tetsuya Kojima, Midori Tsukane, Hirofumi Wakemoto 1416 ・ SID 04 DIGEST

  When power is turned on in the conventional OCB type liquid crystal display device as described above, it is necessary to apply an initial transition voltage having a transition waveform as shown in FIG. 8 between the pixel electrode and the counter electrode. This initial transition voltage is a relatively high voltage of about ± 25V. On the other hand, the thickness of the liquid crystal layer in the pixel reflection portion of the transflective liquid crystal display device is about half of the thickness of the liquid crystal layer in the pixel transmission portion. Occurs, resulting in pixel defects and bright spots.

  In view of the above problems, an object of the present invention is to provide an OCB type transflective liquid crystal display device capable of displaying an image without applying an initial transition voltage.

  In the present invention, a plurality of pixels are formed on an array substrate, each of the plurality of pixels has a reflective portion and a transmissive portion, and the thickness of the liquid crystal layer in the reflective portion and the thickness of the liquid crystal layer in the transmissive portion. In a transflective liquid crystal display device having different liquid crystal cells, the liquid crystal of the liquid crystal layer is OCB mode, twist alignment in the initial alignment state, and transition to bend alignment in the image display state. The liquid crystal display device.

According to the present invention, a plurality of pixels are formed on an array substrate, each of the plurality of pixels has a reflective portion and a transmissive portion, and the thickness of the liquid crystal layer in the reflective portion and the liquid crystal layer in the transmissive portion In a transflective liquid crystal display device having liquid crystal cells with different thicknesses,
In the liquid crystal display device, the liquid crystal of the liquid crystal layer is in an OCB mode, and the bend alignment of the liquid crystal is maintained in an initial alignment state by an alignment film having a pretilt angle of a predetermined angle or more.

  According to the present invention, a plurality of pixels are formed on an array substrate, each of the plurality of pixels has a reflective portion and a transmissive portion, and the thickness of the liquid crystal layer in the reflective portion and the liquid crystal layer in the transmissive portion In a transflective liquid crystal display device having liquid crystal cells having different thicknesses, the liquid crystal of the liquid crystal layer is in an OCB mode, and the liquid crystal polymer is networked in the liquid crystal to bend the liquid crystal in an initial alignment state. This is a liquid crystal display device characterized in that

  According to the present invention, the OCB mode liquid crystal spontaneously becomes bend alignment without applying an initial transition voltage.

  Hereinafter, an OCB type liquid crystal display device 10 according to an embodiment of the present invention will be described with reference to the drawings.

  An OCB type transflective liquid crystal display device 10 according to a first embodiment will be described with reference to FIGS.

  The liquid crystal cell of the liquid crystal display device 10 includes an array substrate 12 and a counter substrate 14. As shown in FIG. 1, a plurality of signal lines 16 to which image signals are input and scanning lines 18 arranged so as to be orthogonal to the signal lines 16 are wired on the glass substrate 20 on the array substrate 12. A thin film transistor (hereinafter referred to as TFT) 22 made of amorphous silicon or polysilicon is formed near the intersection of the signal line 16 and the scanning line 18. The TFT 22 has a source electrode connected to the signal line 16, a gate electrode connected to the scanning line 18, and a drain electrode connected to the pixel electrode 24.

  Each signal line 16 is connected to a signal line driver circuit 26, and each scanning line 18 is connected to a scanning line driver circuit 28.

  As shown in FIG. 2, the liquid crystal display device 10 is a semi-transmissive type, and each pixel 29 is composed of two types of regions, a pixel reflection unit 30 and a pixel transmission unit 32. The pixel reflection unit 30 is configured by a reflection electrode 34 made of a metal film such as aluminum as the pixel electrode 24. Further, the pixel electrode 24 of the pixel transmission portion 32 is formed of a transparent electrode 36 such as ITO. The thickness A of the liquid crystal layer in the pixel reflection unit 30 is half of the thickness B of the liquid crystal layer in the pixel transmission unit 32.

  Further, on the glass substrate 20 constituting the array substrate 12, the array wiring layer 38 on which the signal lines 16, the scanning lines 18, and the TFTs 22 described above are formed is formed. Pixels 29 (pixel electrodes 24) are formed in a matrix on the wiring layer 38. A resin layer 40 is formed at a location where the pixel reflection portion 30 is formed, and a reflective electrode 34 is formed thereon. In this way, the thickness of the liquid crystal layer 50 is adjusted to be thin by the pixel reflection unit 30. On the other hand, a transparent electrode 36 is formed at a position where the pixel transmission portion 32 is formed. An alignment film 42 is formed on the reflective electrode 34 and the transparent electrode 36.

  A color filter layer 44 made of R, G, and B is formed on the lower surface of the glass substrate 43 constituting the counter substrate 14, and a counter electrode layer 46 is formed on the lower surface of the color filter layer 44. An alignment film 48 is formed. A liquid crystal layer 50 is formed between the array substrate 12 and the counter substrate 14 with an OCB mode liquid crystal described below interposed therebetween. The thickness B of the liquid crystal layer 50 in the pixel transmission part 32 is 4.6 μm, and the thickness of the liquid crystal layer 50 in the pixel reflection part 30 is 2.3 μm.

  A phase difference plate 52, a λ / 4 plate 54, and a polarizing plate 56 are attached to the lower surface of the glass substrate 20 constituting the array substrate 12. On the other hand, a phase difference plate 58, a λ / 4 plate 60, and a polarizing plate 62 are attached to the upper surface of the glass substrate 43 constituting the counter substrate 14.

  In this embodiment, as shown in FIGS. 3 and 4, the overall retardation of the composite of the liquid crystal layer 50 and the retardation plates 52 and 58 is black when the retardation is approximately 0, and the retardation is approximately λ. Displayed white when / 2. However, since the pixel reflection unit 30 passes through the liquid crystal layer 50 twice as shown in FIG. 3, the thickness of the liquid crystal layer 50 is improved to be approximately ½ that of the pixel transmission unit 32. The polarizing plate 62 and the λ / 4 plate 60 form a circularly polarizing plate, which is for realizing conversion between circularly polarized light and linearly polarized light as shown in FIG. As shown in FIG. 4, the same applies to the pixel transmission unit 32.

  In this embodiment, an OCB mode liquid crystal that is twisted in the initial alignment state is used for the liquid crystal layer 50. This is for transition to bend alignment without applying an initial transition voltage. That is, as shown in Non-Patent Document 1, when a liquid crystal that is twisted in the initial alignment state is used, bend alignment easily occurs. Therefore, a chiral agent is added to the liquid crystal material of the liquid crystal layer 50 to realize 180 ° twist alignment in the initial alignment state as shown in FIG. As a result, without applying an initial transition voltage, a voltage based on an image signal is applied for image display, thereby quickly transitioning to bend alignment. Therefore, pixel defects and bright spots due to the initial transition voltage do not occur.

  In the present embodiment, twist-aligned liquid crystals are used for all the pixel reflection units 30 and the pixel transmission units 32 on the entire display screen. However, the present invention is not limited to this, and the inside of the pixel reflection unit 30 and the pixel transmission unit 32 is used. If there is even a portion of twisted liquid crystal, the liquid crystal layer 50 is spread over the entire surface, so that the twist alignment region may be a part of the pixel transmission portion 32 or the pixel reflection portion 30.

  Next, the OCB type liquid crystal display device 10 of the second embodiment will be described with reference to FIG. The difference between the first embodiment and the second embodiment is that the structure for transition to bend alignment without applying an initial transition voltage is different.

  In this embodiment, the bend orientation is maintained even in the initial transition state as shown in FIG. 6 by setting the pretilt angle of the orientation film 42 and the orientation film 48 to 30 ° or more.

  Specifically, if the alignment films 42 and 48 of the side chain type polyimide resin are used and have a pretilt angle of 30 ° or more in the initial state, the bend alignment is spontaneously performed without applying the initial transition voltage. The OCB type liquid crystal display device 10 can be realized.

  Next, an OCB type liquid crystal display device 10 according to a third embodiment will be described with reference to FIG. The difference between this embodiment and the first embodiment is also the structure that maintains the bend alignment in the initial transition state.

  In the present embodiment, the liquid crystal polymer is networked in the liquid crystal so as to maintain the bend alignment state, and the bend alignment is stabilized.

  Specifically, as shown in FIG. 7, a polymerizable liquid crystal monomer material is dissolved in liquid crystal, and a voltage is applied to form a bent orientation. When ultraviolet rays are irradiated in this state, the liquid crystal monomer material is polymerized and deposited to form a network structure. Since this network structure is formed in the bent alignment state, the bent alignment can be maintained even when the electric field is turned off.

  In order to maintain this vent alignment, the concentration of the liquid crystal polymer is required to be 5% or more, and it is effective to include a liquid crystal monomer having a functional unit.

  Also in the present embodiment, the OCB type liquid crystal display device 10 can be realized without spontaneously becoming bent orientation and applying an initial transition voltage.

It is explanatory drawing of the liquid crystal display device concerning the 1st Embodiment of this invention. It is a longitudinal cross-sectional view of the liquid crystal display device of FIG. It is explanatory drawing of the pixel reflection part of the liquid crystal display device of FIG. It is explanatory drawing of the pixel transmissive part of the liquid crystal display device of FIG. FIG. 2 is an explanatory diagram showing a state where the liquid crystal display device of FIG. 1 transitions from twist alignment to bend alignment. It is explanatory drawing whose pretilt angle in the liquid crystal display device concerning 2nd Embodiment is 30 degrees or more. It is explanatory drawing which polymerizes the liquid crystal monomer in the liquid crystal display device concerning 3rd Embodiment. It is a waveform of the initial transition voltage in the conventional OCB type liquid crystal display device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Liquid crystal display device 12 Array substrate 14 Counter substrate 30 Pixel reflection part 32 Pixel transmission part 34 Reflection electrode 36 Transparent electrode 42 Alignment film 48 Alignment film 50 Liquid crystal layer

Claims (6)

A plurality of pixels are formed on the array substrate, each of the plurality of pixels has a reflective portion and a transmissive portion, and the thickness of the liquid crystal layer in the reflective portion is different from the thickness of the liquid crystal layer in the transmissive portion. In a transflective liquid crystal display device having
A liquid crystal display device, wherein the liquid crystal of the liquid crystal layer is in an OCB mode, twist alignment in an initial alignment state, and transition to bend alignment in an image display state. The liquid crystal display device according to claim 1, wherein a part of the liquid crystal in the reflection portion or the transmission portion is twisted. A plurality of pixels are formed on the array substrate, each of the plurality of pixels has a reflective portion and a transmissive portion, and the thickness of the liquid crystal layer in the reflective portion is different from the thickness of the liquid crystal layer in the transmissive portion. In a transflective liquid crystal display device having
The liquid crystal display device, wherein the liquid crystal of the liquid crystal layer is in an OCB mode, and the bend alignment of the liquid crystal is maintained in an initial alignment state by an alignment film having a pretilt angle of a predetermined angle or more. The liquid crystal display device according to claim 3, wherein the predetermined angle is 30 °. A plurality of pixels are formed on the array substrate, each of the plurality of pixels has a reflective portion and a transmissive portion, and the thickness of the liquid crystal layer in the reflective portion is different from the thickness of the liquid crystal layer in the transmissive portion. In a transflective liquid crystal display device having
The liquid crystal display device, wherein the liquid crystal of the liquid crystal layer is in an OCB mode, and a liquid crystal polymer is networked in the liquid crystal to maintain the bend alignment of the liquid crystal in an initial alignment state. The liquid crystal polymer is
A polymerizable liquid crystal monomer is dissolved in the liquid crystal;
Applying voltage to the liquid crystal to bend alignment,
The liquid crystal display device according to claim 5, wherein the liquid crystal is polymerized by irradiating the liquid crystal with ultraviolet rays in the bend alignment state.

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