JP2006215060A - Liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transflective liquid crystal display of an active matrix type wherein the distance at which backlight light passes through a liquid crystal layer when the liquid crystal display is used as a transmission type and the distance at which external light passes through the liquid crystal layer when the display is used as a reflection type can be made nearly equal to each other by the presence of a level difference formed film (34), and power consumption is not increased even when auxiliary capacitance is made large. <P>SOLUTION: Reflection films 6 are provided on an upper surface of a thin film transistor substrate 1 on which scanning lines 2 are formed and auxiliary capacitance electrodes 7 are provided on an upper surface of an interlayer insulating film 19. At least a part of the auxiliary capacitance electrode 7 and at least a part of the reflection layer 6 are superposed on each other in a state in which a gate insulating film 12 and the interlayer insulating film 19 are interposed therebetween. Since the auxiliary capacitance electrodes 7 and the reflection layers 6 are electrically insulated from each other by the gate insulating film 12 and the interlayer insulating film 19 interposed therebetween though auxiliary capacitance is formed by superposition parts of the auxiliary capacitance electrodes 7 and the reflection layers 6, power consumption is not increased even when auxiliary capacitance is made large. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a liquid crystal display device.

  In a conventional transflective liquid crystal display device, the distance through which the backlight passes through the liquid crystal layer when used as a transmissive type and the distance through which the external light passes through when used as a reflective type are substantially the same. Further, a step forming film is provided in a region corresponding to a reflection portion of one pixel on the inner surface of the front surface side substrate, and a color filter and a common electrode are provided in this order on the inner surface of the front side substrate including the step forming film. A reflective layer is provided in a region corresponding to the reflective portion of one pixel on the inner surface of the substrate, and a protective film and a transmissive electrode are provided in this order on the inner surface of the back side substrate including the reflective layer. In some cases, the thickness of the liquid crystal layer in the reflective portion of the pixel is approximately half the thickness of the liquid crystal layer in the transmissive portion of one pixel (see, for example, Patent Document 1).

JP 2004-102243 A

  By the way, the above-mentioned patent document 1 does not describe an auxiliary capacitance electrode for forming an auxiliary capacitance with the pixel electrode. On the other hand, in an active matrix type transflective liquid crystal display device having a thin film transistor as a switching element, the gate of the thin film transistor is generally made of a highly reflective metal such as an aluminum-based metal in order to improve productivity. The electrode, the auxiliary capacitance electrode, and the reflective layer are formed on the same surface. In this case, in order to increase the auxiliary capacity, a part of the auxiliary capacity electrode may also serve as a reflective layer. However, when a part of the auxiliary capacitance electrode is also used as a reflective layer, the auxiliary capacitance can be increased, but there is a problem that power consumption increases accordingly.

  Therefore, an object of the present invention is to provide a liquid crystal display device that can prevent power consumption from increasing even if the auxiliary capacity is increased.

  In order to achieve the above object, the present invention provides a liquid crystal display device in which one pixel has a reflective portion and a transmissive portion, and the liquid crystal layer thickness of the reflective portion is smaller than the liquid crystal layer thickness of the transmissive portion. On the substrate, an auxiliary capacitance electrode for forming an auxiliary capacitance with a pixel electrode provided in a region corresponding to one pixel on the substrate and a reflective layer for forming the reflecting portion are interposed therebetween. It is characterized in that at least a part thereof is overlapped with an insulating film interposed.

  According to this invention, since the auxiliary capacitance electrode and the reflective layer are overlapped at least partially with the insulating film interposed therebetween, the auxiliary capacitance is formed by the overlapping portion of the auxiliary capacitance electrode and the reflective layer. Although formed, the auxiliary capacitance electrode and the reflective layer are electrically insulated by an insulating film interposed between them, so that even if the auxiliary capacitance is increased, the power consumption can be prevented from increasing.

(First embodiment)
FIG. 1 is a transmission plan view of a main part on the thin film transistor substrate side in an active matrix type transflective liquid crystal display device as a first embodiment of the present invention, and FIG. 2 is taken along line II-II in FIG. FIG. 3 shows a cross-sectional view corresponding to the portion along the line III-III in FIG. The liquid crystal display device includes a thin film transistor substrate 1 made of a glass substrate or the like and a counter substrate 31.

  First, the thin film transistor substrate 1 side will be described with reference to FIG. On the upper surface side of the thin film transistor substrate 1 (the inner surface side facing the counter substrate 31), scanning lines 2 and data lines 3 are provided in a matrix, and thin film transistors 4, pixel electrodes 5, and a reflective layer 6 are provided in the vicinity of each intersection. Further, a substantially lattice-shaped auxiliary capacitance electrode 7 is provided in parallel with the scanning line 2 and the data line 3. Here, for the purpose of clarifying FIG. 1, diagonal short solid hatching is written at the edge of the pixel electrode 5.

  In this case, the reflective layer 6 is disposed on one lower side of the pixel electrode 5 so as to overlap with a part of the pixel electrode 5. The four sides of the pixel electrode 5 are overlapped with a substantially lattice-shaped auxiliary capacitance electrode 7 disposed around the pixel electrode 5. The reflection layer 6 described above is entirely formed in the area of the pixel electrode 5 in plan view, and the three sides excluding the one side on the center side of the pixel electrode 5 are substantially lattices arranged around it. Is overlapped with the auxiliary capacitance electrode 7. In the pixel electrode 5, a region excluding the reflective layer 6 formation region, the auxiliary capacitance electrode 7 formation region, and a source electrode 17 formation region described later is a substantial transmission pixel region. Further, in the reflective layer 6, a region excluding the auxiliary capacitance electrode 7 formation region is a substantial reflective pixel region.

  The substantially lattice-shaped auxiliary capacitance electrode 7 includes a first auxiliary capacitance electrode portion 7a including a portion overlapped with the data line 3, a second auxiliary capacitance electrode portion 7b including a portion overlapped with the scanning line 2, and The third auxiliary capacitance electrode portion 7c includes a portion overlapped with the thin film transistor 4. In this case, as will be described later, the auxiliary capacitance electrode 7 is provided on a layer different from the scanning line 2, and the first auxiliary capacitance electrode 7a among them is in the thickness direction, that is, FIG. Are provided between the data line 3 and the pixel electrode 5 via an insulating film, respectively.

  The width of the first auxiliary capacitance electrode 7a is somewhat larger than the width of the data line 3. As a result, even if there is a positional shift in the direction orthogonal to the data line 3, the first auxiliary capacitance electrode 7 a is configured to reliably cover the data line 3 so that the data line 3 does not directly face the pixel electrode 5. It has become. Further, the first auxiliary capacitance electrode 7 a is arranged over almost the entire arrangement area of the data line 3. As a result, the first auxiliary capacitance electrode 7a reliably overlaps with the left and right sides of the pixel electrode 5 even if there is a positional shift in the direction parallel to the data line 3 with respect to the pixel electrode 5. Auxiliary capacity fluctuations due to deviation are reliably prevented.

  The width of the second auxiliary capacitance electrode 7b is somewhat larger than the width of the scanning line 2. As a result, the second auxiliary capacitance electrode 7b surely overlaps the scanning line 2 even if there is a positional shift in the direction orthogonal to the scanning line 2. Further, the second auxiliary capacitance electrode 7 b is arranged over almost the entire arrangement area of the scanning line 2. As a result, the second auxiliary capacitance electrode 7b surely overlaps with the upper and lower sides of the pixel electrode 5 even if there is a positional shift in the direction parallel to the scanning line 2 with respect to the pixel electrode 5, and the alignment in this direction is performed. Auxiliary capacity fluctuations due to deviation are reliably prevented.

  The third auxiliary capacitance electrode 7 c including the second auxiliary capacitance electrode 7 b is provided so as to cover the thin film transistor 4. Thereby, the incidence of external light to the thin film transistor 4 is surely prevented. In FIG. 1, a region surrounded by a dotted line larger than the pixel electrode 5 is an opening 32a of a black mask 32 for preventing light leakage provided on the inner surface of a counter substrate 31 described later. In this case, the black mask 32 is provided so as to cover a predetermined part of the scanning line 2, the data line 3, and the thin film transistor 4. However, since the scanning line 2, the data line 3, and the thin film transistor 4 are covered with the substantially grid-like auxiliary capacitance electrode 7, the black mask 32 may not be provided on the counter substrate 31.

  Next, a specific structure of the liquid crystal display device will be described with reference to FIGS. A scanning line 2 including a gate electrode 11 made of a highly reflective metal such as an aluminum-based metal and a reflective layer 6 are provided at predetermined locations on the upper surface of the thin film transistor substrate 1. A gate insulating film 12 made of silicon nitride is provided on the upper surface of the thin film transistor substrate 1 including the gate electrode 11, the scanning line 2, and the reflective layer 6.

  A semiconductor thin film 13 made of intrinsic amorphous silicon is provided at a position corresponding to the gate electrode 11 on the upper surface of the gate insulating film 12. A channel protective film 14 made of silicon nitride and having an outer shape smaller than the outer shape of the gate electrode 11 is provided at a position corresponding to the substantially central portion of the gate electrode 11 on the upper surface of the semiconductor thin film 13. Ohmic contact layers 15 and 16 made of n-type amorphous silicon are provided on both sides of the upper surface of the channel protective film 14 and on the upper surface of the semiconductor thin film 13 on both sides thereof. A source electrode 17 and a drain electrode 18 made of chromium or the like are provided on the upper surfaces of the ohmic contact layers 15 and 16.

  The thin film transistor 4 is constituted by the gate electrode 11, the gate insulating film 12, the semiconductor thin film 13, the channel protective film 14, the ohmic contact layers 15 and 16, the source electrode 17 and the drain electrode 18.

  A data line 3 made of chromium or the like is connected to the drain electrode 18 at a predetermined location on the upper surface of the gate insulating film 12. An interlayer insulating film 19 made of silicon nitride is provided on the upper surface of the gate insulating film 12 including the source electrode 17, the drain electrode 18 and the data line 3. An auxiliary capacitance electrode 7 made of chromium or the like is provided at a predetermined location on the upper surface of the interlayer insulating film 19.

  An overcoat film 20 made of silicon nitride is provided on the upper surface of the interlayer insulating film 19 including the auxiliary capacitance electrode 7. A contact hole 21 is provided in the interlayer insulating film 19 and the overcoat film 20 on the source electrode 17. A pixel electrode 5 made of a transparent conductive material such as ITO is connected to the source electrode 17 through the contact hole 21 on the upper surface of the overcoat film 20.

  On the other hand, a black mask 32 made of a light-shielding metal such as chromium is provided on the lower surface of the counter substrate 31 (inner surface on the side facing the thin film transistor 1) corresponding to the periphery of each pixel electrode 5. On the lower surface of the counter substrate 31 including the black mask 32, a color filter 33 made of red, green, and blue resin is provided. The lower surface of the color filter 33 is substantially flat.

  On the lower surface of the color filter 33, a step forming film 34 made of a transparent resin such as an epoxy resin or a polyimide resin is provided in a region other than a region substantially corresponding to the pixel region for transmission of the pixel electrode 5. In this case, the step forming film 34 has a trapezoidal cross-sectional shape in which both side surfaces are inclined surfaces in FIG. A counter electrode 35 made of a transparent conductive material such as ITO is provided on the lower surface of the color filter 33 including the step forming film 34.

  The thin film transistor substrate 1 and the counter substrate 31 are bonded to each other via a sealing material (not shown), and a liquid crystal 36 is sealed between the substrates 1 and 31 inside the sealing material. In this state, due to the presence of the step forming film 34, the layer thickness d 1 of the liquid crystal 36 layer in the region corresponding to the substantial reflective pixel region (reflecting portion) of the reflective layer 6 is substantially equal to the transparent pixel of the pixel electrode 5. In the region corresponding to the region (transmission portion), the thickness d2 of the liquid crystal 36 layer is 1/3 to 2/3, preferably about 1/2.

  When this liquid crystal display device is used as a transmission type, when a backlight (not shown) disposed on the lower surface side of the thin film transistor substrate 1 is turned on, the light from the backlight is insulated from the thin film transistor substrate 1 and the gate insulation. The upper surface of the counter substrate 31 through the film 12, the interlayer insulating film 19, the overcoat film 20, the substantial transmission pixel region of the pixel electrode 5, the liquid crystal 36, the counter electrode 35, the color filter 33 and the counter substrate 1. The light is emitted to the side, thereby displaying.

  On the other hand, when this liquid crystal display device is used as a reflection type, the backlight is not turned on, and external light incident from the upper surface side of the counter substrate 31 is opposed to the counter substrate 31, the color filter 33, the step forming film 34, and the counter The electrode 35, the liquid crystal 36, the pixel electrode 5, the overcoat film 20, the interlayer insulating film 19, and the gate insulating film 12 are transmitted and reflected by the reflective layer 6, and the reflected light passes through the optical path opposite to the above and the counter substrate 31. The light is emitted to the upper surface side of the display, thereby displaying.

  As described above, in this liquid crystal display device, when used as a transmission type, the backlight passes through the liquid crystal layer 36 once, and when used as a reflection type, external light passes through the liquid crystal layer 36 twice. However, due to the presence of the step forming film 34, the layer thickness d1 of the liquid crystal 36 layer in the region corresponding to the substantial reflective pixel region (reflective portion) of the reflective layer 6 is substantially equal to the transparent pixel region (for the pixel electrode 5). Since the thickness d2 of the liquid crystal 36 in the region corresponding to the transmission portion is 1/3 to 2/3, preferably about 1/2, the multi-gap structure in which both the reflectance and the transmittance are optimum can do. As an example, if the layer thickness d2 is about 4 μm, the layer thickness d1 is set to about 2 μm.

  In this liquid crystal display device, the reflective layer 6 is provided on the upper surface of the thin film transistor substrate 1 provided with the scanning lines 2, the auxiliary capacitance electrode 7 is provided on the upper surface of the interlayer insulating film 19, and the auxiliary capacitance electrode 7, the reflective layer 6, Since at least a part of them is overlapped with the gate insulating film 12 and the interlayer insulating film 19 interposed therebetween, an auxiliary capacitance is formed by the overlapping portion of the auxiliary capacitance electrode 7 and the reflective layer 6. The auxiliary capacitance electrode 7 and the reflective layer 6 are electrically insulated by the gate insulating film 12 and the interlayer insulating film 19 interposed between them, so that the power consumption does not increase even if the auxiliary capacitance is increased. can do. In this case, since the auxiliary capacitance is also formed by the overlapping portion of the reflective layer 6 and the pixel electrode 5, the auxiliary capacitance can be further increased.

(Second Embodiment)
4 shows a cross-sectional view similar to FIG. 2 of a liquid crystal display device as a second embodiment of the present invention, and FIG. 5 shows a cross-sectional view similar to FIG. 3 of the liquid crystal display device as the second embodiment. In this liquid crystal display device, the difference from the case shown in FIGS. 2 and 3 is that the reflective layer 6 is not the upper surface of the thin film transistor substrate 1 provided with the scanning lines 2 but the gate insulating film 12 provided with the data lines 3. It is a point provided on the upper surface of the.

  Therefore, in this case, the reflective layer 6, the data line 3, the source electrode 17 and the drain electrode 18 are made of a highly reflective metal such as an aluminum-based metal. The scanning line 2 including the gate electrode 11 may be formed of a highly reflective metal such as an aluminum-based metal, but is not limited thereto, and may be formed of chromium or the like.

  In this liquid crystal display device, the reflective layer 6 is provided on the upper surface of the gate insulating film 12 provided with the scanning lines 2, the auxiliary capacitive electrode 7 is provided on the upper surface of the interlayer insulating film 19, and the auxiliary capacitive electrode 7 and the reflective layer 6 are provided. Are overlapped at least partially with the inter-layer insulating film 19 interposed therebetween, so that an auxiliary capacitance is formed by the overlapping portion of the auxiliary capacitance electrode 7 and the reflective layer 6. 7 and the reflective layer 6 are electrically insulated by an interlayer insulating film 19 interposed therebetween, so that even if the auxiliary capacity is increased, the power consumption can be prevented from increasing. Also in this case, since the auxiliary capacitance is formed by the overlapping portion of the reflective layer 6 and the pixel electrode 5, the auxiliary capacitance can be further increased.

(Other embodiments)
In the above-described embodiment, the pixel electrodes 5 (and the reflective layer 6) are arranged in stripes in a straight line in the column direction, and the data lines 3 and the first auxiliary capacitance electrodes 7a are straight in the column direction between the pixel electrodes 5. However, the present invention can also be applied to a so-called delta arrangement in which the pixel electrodes 5 are shifted by a half pitch for each row. The first auxiliary capacitance electrode 7 a is formed in a zigzag shape extending between the rows of the pixel electrodes 5 by a half pitch of the pixel electrodes 5 in parallel with the scanning lines 2. Further, although the thin film transistor is used as the switching element, other switching elements such as a diode can be applied.

FIG. 3 is a transmission plan view of the main part on the thin film transistor substrate side in the liquid crystal display device as the first embodiment of the present invention. Sectional drawing equivalent to the part in alignment with II-II of FIG. Sectional drawing corresponded in the part in alignment with III-III of FIG. Sectional drawing similar to FIG. 2 of the liquid crystal display device as 2nd Embodiment of this invention. Sectional drawing similar to FIG. 3 of the liquid crystal display device as the said 2nd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Thin-film transistor substrate 2 Scan line 3 Data line 4 Thin-film transistor 5 Pixel electrode 6 Reflective layer 7 Auxiliary capacity electrode 31 Opposite substrate 32 Black mask 33 Color filter 34 Step formation film 35 Common electrode 36 Liquid crystal

Claims (9)

  In a liquid crystal display device in which one pixel has a reflective portion and a transmissive portion, and the layer thickness of the liquid crystal layer of the reflective portion is smaller than the layer thickness of the liquid crystal layer of the transmissive portion, one pixel on the substrate At least one of an auxiliary capacitance electrode for forming an auxiliary capacitance with a pixel electrode provided in a corresponding region and a reflective layer for forming the reflective portion with an insulating film interposed therebetween. A liquid crystal display device characterized in that the portions are provided in an overlapping manner.   In a liquid crystal display device in which liquid crystal is sealed between a thin film transistor substrate and a counter substrate, and one pixel has a reflective portion and a transmissive portion, a step forming film is formed in a region corresponding to the reflective portion on the inner surface side of the counter substrate. Providing a common electrode on the inner surface side of the counter substrate including the step forming film, covering the thin film transistor provided on the inner surface side of the thin film transistor substrate with an overcoat film, and corresponding to one pixel on the overcoat film Provided with a pixel electrode, and an auxiliary capacitance electrode for forming an auxiliary capacitance with the pixel electrode and a reflective layer for forming the reflective portion under the overcoat film on the inner surface side of the thin film transistor substrate. A liquid crystal display device characterized in that at least a part thereof is overlapped with an insulating film interposed therebetween.   3. The liquid crystal display device according to claim 1, wherein all of the reflective layers are overlapped with a part of the pixel electrode and an insulating film interposed therebetween.   3. The liquid crystal display device according to claim 1, wherein the auxiliary capacitance electrode is overlapped with an entire peripheral portion of the pixel electrode and an insulating film interposed therebetween.   5. The liquid crystal display according to claim 4, wherein a part of the peripheral part of the reflective layer is overlapped with a part of the peripheral part of the pixel electrode and an insulating film interposed therebetween. apparatus.   6. The liquid crystal display device according to claim 5, wherein the auxiliary capacitance electrode is overlapped with a peripheral portion of the reflective layer that is overlapped with a peripheral portion of the pixel electrode.   The scanning line connected to the gate electrode of the thin film transistor is provided below the overcoat film on the inner surface side of the thin film transistor substrate, and the reflective layer is provided on the same plane as the scanning line. A liquid crystal display device characterized by that.   The data line connected to the drain electrode of the thin film transistor is provided on the inner surface side of the thin film transistor substrate below the overcoat film, and the reflective layer is provided on the same plane as the data line. A liquid crystal display device characterized by that.   In the invention according to claim 2, the thickness of the liquid crystal layer of the reflective portion is 1/3 to 2/3 of the thickness of the liquid crystal layer of the transmissive portion due to the presence of the step forming film. A characteristic liquid crystal display device.

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