JP6403478B2 - Liquid crystal display - Google Patents

Description

  The present invention relates to an active matrix liquid crystal display (LCD) having a thin film transistor (TFT) element having a channel portion made of polycrystalline silicon.

  2. Description of the Related Art Conventionally, an active matrix type LCD has a TFT array side substrate on which a large number of pixel electrode portions including TFT elements are formed and a color filter side substrate on which a color filter and a black matrix are formed facing each other. Are bonded together at a predetermined interval, and a liquid crystal is filled and sealed between the substrates.

  An example of the basic configuration of a conventional active matrix LCD is shown in FIG. For example, the TFT array side substrate has a plurality of gate signal lines GLl, GL2, GL3,... GLn formed in a first direction (for example, a row direction) thereon and a first crossing the first direction. A plurality of image signal lines SLl, SL2, SL3... SLm formed to intersect the gate signal lines GLl to GLn in two directions (for example, the column direction), and the gate signal lines GLl to GLn and the image signal lines. The pixel portion Pll, P12, P13... Pnm including the TFT element 41 and the pixel electrodes PE11, PE12, PE13... PEnm, which are formed at the intersections of SL1 to SLm. Further, the common electrode (not shown) and the common electrode line 42 that supplies a common voltage (Vcom) to the common electrode form a vertical electric field applied to the liquid crystal between the pixel electrodes PE11 to PEnm. Are provided on the color filter side substrate. The common electrode line 42 is a TFT array side substrate when a horizontal electric field (lateral electric field: In-Plane Field) and an edge electric field (Fringe Field) are applied between the pixel electrodes PE11 to PEnm. It is provided above. In FIG. 6, 43 is a gate signal line drive circuit, and 44 is an image signal (source signal) line drive circuit.

  The TFT element 41 has a semiconductor layer made of amorphous silicon (a-Si), low-temperature polycrystalline silicon (LTPS), or the like, and has three terminal portions including a gate electrode portion, a source electrode portion, and a drain electrode portion. It is the structure which has. Then, by applying a voltage (for example, 6 V) of a predetermined potential to the gate electrode portion, it functions as a switching element (gate transfer element) that causes a current to flow through the semiconductor layer (channel) between the source electrode portion and the drain electrode portion. . The pixel electrodes PE11 to PEnm are generally composed of a transparent conductor layer made of indium tin oxide (ITO) or the like.

The LTPS is silicon crystallized at 450 ° C. or lower, and a glass substrate can be used instead of an expensive quartz substrate. LTPS has a carrier mobility of 100 to ²⁰⁰ cm ² / Vs or higher, which is higher than 0.5 cm ² / Vs of amorphous silicon. As a result, the current drive capability is improved, and the TFT element 41 can be made smaller and higher definition can be achieved. In addition, since LTPS can be used to form an n-channel TFT element and a p-channel TFT element, a driving circuit based on a CMOS circuit, an SRAM circuit, a D / A converter, an image display unit, etc. are integrated on a glass substrate. It can be integrated. Therefore, an LCD equipped with an audio processing circuit and a microprocessor can also be manufactured using LTPS. Since the LCD and its peripheral drive circuit can be integrally formed on the glass substrate, the electrical reliability is improved. In other words, the number of electrical connections between the LCD panel and the drive circuit can be greatly reduced, and it is resistant to vibrations and light in weight, so that it is suitable for portable information terminals and the like. In addition, since the current driving capability is high, an LCD having high-definition pixels and pixel portions Pll to Pnm with a high aperture ratio can be manufactured.

  And the semiconductor layer which consists of LTPS is produced as follows. First, an amorphous silicon layer is formed on a glass substrate by a plasma CVD (Chemical Vapor Deposition) method. Next, in order to polycrystallize the amorphous silicon layer, the amorphous silicon layer is irradiated with excimer laser light at a glass substrate temperature of 450 ° C. or lower. The amorphous silicon is instantaneously melted and solidified by the energy of the excimer laser beam. As a result, it changes to an LTPS layer having an average particle size of about 0.3 μm.

  The LTPS layer produced by the above production method tends to have a relatively large number of crystal defects. Therefore, when a voltage of a predetermined potential (for example, 6 V) is applied to the gate signal lines GLl to GLn to the channel part (active part) that is an intersection of the LTPS layer with the gate signal lines GLl to GLn, a desired value is obtained. Current may not flow easily. That is, the operation reliability of the channel portion of the LTPS layer tends to be lowered.

  FIG. 4 is an enlarged plan view showing an enlarged portion 45 of the TFT element 41 having the semiconductor layer 13 made of LTPS and the intersections of the gate signal lines GLl to GLn and the image signal lines SL1 to SLm of FIG. . As shown in FIG. 4, the LCD includes a TFT element having double gate channel portions 13a and 13b made of LTPS formed in the vicinity of the intersection of the gate signal line 11 and the image signal line 12, and the upper surface of the glass substrate. The gate signal line 11, the channel portions 13a and 13b, and the light shielding film 16 formed through an insulating layer are provided at portions overlapping the channel portions 13a and 13b in plan view. The light shielding film 16 is provided in order to suppress light leakage current from flowing through the inactive channel portions 13a and 13b in a device using a high-brightness backlight such as a projector device or a head-up display.

  Since the operation reliability of the channel portion of the LTPS layer is likely to be lowered, a double gate structure having two channel portions that are intersections of the semiconductor layer made of LTPS and the gate signal lines GLl to GLn is formed. That is, the redundant structure is such that even if the operation reliability of one channel portion 13a (13b) is low, the operation reliability of the other channel portion 13b (13a) is sufficient. In FIG. 4, 14 is a drain electrode, 14a is a contact hole, 15 is a source electrode, 15a is a contact hole, and 17 is a pixel portion.

  FIG. 5 is a sectional view taken along line B1-B2 of FIG. On the upper surface of the glass substrate 30, a light shielding film 16, a light-transmitting first insulating layer 31, a gate signal line 11, a gate insulating layer 32, a semiconductor layer 13, a light-transmitting second insulating layer 33, and a drain electrode 14. The source electrode 15 is sequentially stacked.

  As another conventional example, a liquid crystal device having a single gate structure having a conductive light-shielding film provided at positions covering at least a channel region of a semiconductor layer made of polysilicon of a plurality of TFTs when viewed from the substrate side. Has been proposed (see, for example, Patent Document 1).

JP 2000-10120 A

  However, since the conventional LCD shown in FIG. 4 has the light shielding film 16 formed in a portion overlapping the channel portions 13a and 13b in a plan view of the upper surface of the glass substrate, the area of the light shielding film 16 is large. Thus, there is a problem that the aperture ratio of the pixel portion 17 is lowered.

  Accordingly, the present invention has been completed in view of the above-described conventional problems, and is to provide an LCD capable of reducing the area of the light shielding film and improving the aperture ratio of the pixel portion.

The liquid crystal display device of the present invention is formed by crossing a plurality of gate signal lines formed in the first direction on the upper surface of the substrate and the gate signal lines in a second direction intersecting the first direction. A plurality of image signal lines, a thin film transistor element having a single-gate channel portion made of polycrystalline silicon formed in the vicinity of an intersection of the gate signal line and the image signal line, and an upper surface of the substrate. A light-shielding film formed through an insulating layer in a portion overlapping with the channel portion in plan view, and the light-shielding film overlaps at least a part of the source electrode of the thin film transistor element in plan view. The source signal electrode is formed in a shape extending obliquely with respect to the image signal line, and the source electrode overlaps the gate signal line in plan view .

In the liquid crystal display device of the present invention, preferably, the channel portion is formed to extend in the oblique direction .

In the liquid crystal display device of the present invention, a plurality of gate signal lines formed in the first direction on the upper surface of the substrate intersect with the gate signal lines in a second direction intersecting the first direction. A plurality of image signal lines formed; a thin film transistor element having a single-gate channel portion made of polycrystalline silicon formed in the vicinity of an intersection of the gate signal line and the image signal line; and an upper surface of the substrate A light-shielding film formed through an insulating layer in a portion that overlaps the channel portion in plan view, and the light-shielding film overlaps at least a part of the source electrode of the thin film transistor element in plan view. The channel portion is formed to extend in an oblique direction with respect to the image signal line, and the channel portion is formed to extend in the oblique direction.

  In the liquid crystal display device of the present invention, preferably, the light shielding film is a metal film containing at least one of Al, Mo, Cr, Ti, Ta, W, and Pd.

The liquid crystal display device of the present invention includes a gate signal line of the plurality of formed in a first direction of the upper surface of the substrate, made form by intersecting with the gate signal line in a second direction intersecting the first direction A plurality of image signal lines, a thin film transistor element having a single-gate channel portion made of polycrystalline silicon formed in the vicinity of an intersection of the gate signal lines and the image signal lines, and a channel in a plan view of the upper surface of the substrate A light-shielding film formed through an insulating layer in a portion overlapping the portion, and the light-shielding film is oblique to the image signal line so as to overlap with at least a part of the source electrode of the thin film transistor element in plan view. Since it is formed in a shape extending in the direction, the area of the light shielding film can be reduced and the aperture ratio of the pixel portion can be improved.

  In the liquid crystal display device of the present invention, preferably, since the source electrode overlaps with the gate signal line in plan view, the light-shielding source electrode also overlaps with the gate signal line. As a result, the aperture ratio of the pixel portion is further improved.

  In the liquid crystal display device of the present invention, preferably, since the channel portion is formed to extend in an oblique direction, the drain electrode and the source electrode of the thin film transistor element are connected via the semiconductor conductive layer including the channel portion. It can be connected at a short distance. As a result, the source electrode can be disposed at a position closer to the intersection of the gate signal line and the image signal line, so that the aperture ratio of the pixel portion is further improved.

  In the liquid crystal display device of the present invention, it is preferable that the light shielding film is a metal film including at least one of Al, Mo, Cr, Ti, Ta, W, and Pd. It is possible to effectively block the light of the high-brightness backlight.

FIG. 1 is a diagram showing an example of an embodiment of a liquid crystal display device according to the present invention, and a TFT having a semiconductor conductive layer including a crossing portion of a gate signal line and an image signal line and a channel portion made of polycrystalline silicon. It is an enlarged plan view of the site | part of an element. 2 is a cross-sectional view taken along line A1-A2 of FIG. FIG. 3 is a diagram showing another example of the embodiment of the liquid crystal display device of the present invention, and a TFT having a semiconductor conductive layer including a crossing portion of a gate signal line and an image signal line and a channel portion made of polycrystalline silicon. It is an enlarged plan view of the site | part of an element. FIG. 4 is a diagram showing a conventional liquid crystal display device, and is an enlarged plan view of a portion of a TFT element having a semiconductor conductive layer including a crossing portion of a gate signal line and an image signal line and a channel portion made of polycrystalline silicon. is there. 5 is a cross-sectional view taken along line B1-B2 of FIG. FIG. 6 is a block circuit diagram showing a basic configuration of a conventional liquid crystal display device.

  Embodiments of an LCD according to the present invention will be described below with reference to the drawings. However, each drawing referred to below shows main components of the LCD of the present invention. Therefore, the LCD of the present invention may include well-known components such as a circuit board, a wiring conductor, a control IC, and an LSI that are not shown in the drawing.

  1 and 2 are diagrams showing an LCD of the present invention, and FIG. 1 is a diagram showing an example of an embodiment of the LCD of the present invention, where an intersection of a gate signal line 1 and an image signal line 2, And FIG. 7 is an enlarged plan view of a part of a TFT element (part indicated by reference numeral 45 in FIG. 6) having a semiconductor conductive layer 3 including a channel portion 3a made of polycrystalline silicon. 2 is a cross-sectional view taken along line A1-A2 of FIG.

  As shown in FIGS. 1 and 2, the LCD of the present invention includes a plurality of gate signal lines 1 formed in a first direction (for example, a row direction) on the upper surface of a substrate such as a glass substrate, A plurality of image signal lines 2 formed above the gate signal line 1 so as to intersect with the gate signal line 1 in a second direction (for example, a column direction) intersecting the direction, and the gate signal line 1 and the image signal line The TFT element having a single gate channel portion 3a made of polycrystalline silicon formed in the vicinity of the intersection of the two and the portion overlapping the channel portion 3a in plan view of the upper surface of the substrate is formed via an insulating layer 21. The light shielding film 6 is formed in a shape extending obliquely with respect to the image signal line 2 so as to overlap with at least a part of the source electrode 5 of the TFT element in plan view. It is the composition which is. With this configuration, the area of the light shielding film 6 can be reduced and the aperture ratio of the pixel portion 7 can be improved.

  That is, since the light shielding film 6 overlaps the channel portion 3a of the single gate in a plan view, the area of the light shielding film 6 is reduced and at least a part of the light-shielding source electrode 5 is overlapped in a plan view. Since there is this overlapping portion 8, the area of the light shielding film 6 with respect to the area of the pixel portion 7 is reduced by the amount of the overlapping portion 8. As a result, the aperture ratio of the pixel unit 7 is improved. The single gate means a structure in which one TFT element has one intersection (channel portion 3a) between the semiconductor conductive layer 3 and the gate signal line 1. A double gate means a structure having two intersections (channel portions 3a).

  Further, as shown in FIG. 2, the light shielding film 6, the light-transmitting first insulating layer 21, the gate signal line 1, the gate insulating layer 22, the semiconductor conductive layer 3, and the light-transmitting film are formed on the upper surface of the glass substrate 20. A second insulating layer 23, an image signal line 2 (the drain electrode 4 is not shown), and a source electrode 5 are sequentially stacked. In FIGS. 1 and 2, reference numerals 4a and 5a denote contact holes.

  The gate signal line 1, the image signal line 2, the drain electrode 4, and the source electrode 5 are made of conductive layers. For example, tantalum (Ta), tungsten (W), titanium (Ti), molybdenum (Mo), aluminum (Al), Elements selected from chromium (Cr), silver (Ag), copper (Cu), neodymium (Nd), etc., alloy materials containing these elements as main components, metal nitrides such as titanium nitride, tantalum nitride, and molybdenum nitride It is made of a material having electrical conductivity. The conductive layer can have a single-layer structure or a multilayer structure of these materials. A low resistance can be realized by using a laminated structure. Further, the gate signal line 1, the image signal line 2, the drain electrode 4, and the source electrode 5 generally have a light shielding property. The pixel electrode (not shown) is made of a light-transmitting conductive layer, and includes indium tin oxide (ITO), indium zinc oxide (IZO), indium tin oxide added with silicon oxide (ITSO), and zinc oxide. It is made of a conductive material such as (ZnO), silicon (Si) containing phosphorus or boron and having translucency.

  The first insulating layer 21, the gate insulating layer 22, and the second insulating layer 23 can have a single-layer structure or a stacked structure of a plurality of layers. As the material for these insulating layers, an inorganic material or an organic material can be used. As the inorganic material, silicon oxide or silicon nitride can be used. As the organic material, acrylic resin, polyimide, polyamide, polyimide amide, benzocyclobutene, siloxane, or polysilazane can be used. Siloxane has a skeleton structure formed by the bond of silicon (Si) and oxygen (O). As the substituent, an organic group containing at least hydrogen (for example, an alkyl group or an aromatic hydrocarbon) is used. As a substituent, a fluoro group, an organic group containing at least hydrogen, and a fluoro group may be used. Polysilazane is formed using a polymer material having a bond of silicon (Si) and nitrogen (N) as a starting material. When an organic material is used as the material of these insulating layers, the surface flatness can be improved, which is preferable. When an inorganic material is used as the material for these insulating layers, the semiconductor conductive layer 3 and the gate signal line 1 have surfaces that conform to the surface shape. Even in this case, the film becomes flat by increasing the film thickness.

  The semiconductor conductive layer 3 is made of polycrystalline silicon, which is low-temperature polycrystalline silicon (LTPS). The semiconductor conductive layer 3 made of LTPS is manufactured as follows. First, an amorphous silicon layer is formed on a substrate such as a glass substrate by a plasma CVD (Chemical Vapor Deposition) method. Next, in order to polycrystallize the amorphous silicon layer, the amorphous silicon layer is irradiated with excimer laser light at a glass substrate temperature of 450 ° C. or lower. The amorphous silicon is instantaneously melted and solidified by the energy of the excimer laser beam. As a result, it changes to an LTPS layer having an average particle size of about 0.3 μm. LTPS constituting the semiconductor conductive layer 3 may be either n-type LTPS or p-type LTPS, but n-type LTPS is preferable in that high charge (electron or the like) mobility can be obtained.

  The light shielding film 6 is formed by a thin film forming method such as sputtering or CVD, or a thick film method such as screen printing. The light shielding film 6 may be made of a light shielding material such as a metal, an alloy, a metal oxide, a metal nitride, or a black resin. For example, the light shielding film 6 is a metal containing at least one of aluminum (Al), molybdenum (Mo), chromium (Cr), titanium (Ti), tantalum (Ta), tungsten (W), and palladium (Pd). A membrane is preferred. In this case, it is possible to effectively block the light of the backlight having high luminance (1 million candela or more) irradiated from below the glass substrate 20. Therefore, the LCD having the light shielding film 6 is suitable for an LCD using a high-brightness backlight such as a head-up display or a projector device.

  Other materials for the light shielding film 6 include elements selected from silver (Ag), copper (Cu), neodymium (Nd), or the like, or alloy materials containing these elements as main components, and titanium nitride, tantalum nitride, A conductive material such as a metal nitride such as molybdenum nitride may be employed. The light shielding film 6 may have a single layer structure made of these materials or a multilayer structure of a plurality of layers.

  The thickness of the light shielding film 6 may be such that the optical density (Optical Density: OD) value of the light shielding film 6 is about 3 or more.

  The light shielding film 6 has a shape extending in an oblique direction with respect to the image signal line 2 so as to overlap with at least a part of the source electrode 5 of the TFT element in plan view. The shape of the light shielding film 6 in plan view is rectangular, Various shapes such as a rectangle with rounded corners, an ellipse, and an oval can be used. The angle formed by the longitudinal direction of the light shielding film 6 and the signal transmission direction (stretching direction) of the image signal line 2 is not particularly limited, but is about 30 to 60 degrees.

  Further, in the light shielding film 6, it is preferable that the distance between the shape line (outline) and the shape line (outline) of the channel portion 3a in plan view is equal to or greater than the light leakage current generation inhibiting distance in any direction. . This light leakage current generation inhibition distance is, for example, 4 μm or more. If the thickness is less than 4 μm, light leakage current tends to flow through the inactive channel portion 3a.

  The light shielding film 6 overlaps at least a part of the source electrode 5 of the TFT element in plan view, but the area of the overlapping portion 8 is preferably 30% or more of the area of the source electrode 5. In this case, the contribution to the improvement of the aperture ratio of the pixel portion 7 is easily manifested clearly.

  FIG. 3 is a diagram showing another example of the embodiment of the LCD of the present invention. The semiconductor conductive layer 3 including the channel part 3a made of polycrystalline silicon and the intersection part of the gate signal line 1 and the image signal line 2 is shown. It is an enlarged plan view of the site | part of the TFT element which has. As shown in FIG. 3, the source electrode 5 preferably overlaps the gate signal line 1 in plan view. In this case, the light-shielding source electrode 5 also overlaps with the gate signal line 1. As a result, the aperture ratio of the pixel unit 7 is further improved.

  As shown in FIG. 3, the channel portion 3 a is preferably formed so as to extend in an oblique direction that is the longitudinal direction of the light shielding film 6. Thereby, the drain electrode 4 and the source electrode 5 of the TFT element can be connected at a short distance via the semiconductor conductive layer 3 including the channel portion 3a. As a result, the source electrode 5 can be disposed at a position closer to the intersection of the gate signal line 1 and the image signal line 2, so that the aperture ratio of the pixel portion 7 is further improved. The longitudinal direction (stretching direction) of the channel portion 3a does not need to be completely parallel to the oblique direction, and may form an angle of about 20 degrees or less with the oblique direction.

When the channel portion 3a is made of n-type LTPS, the channel portion 3a is non-doped or contains phosphorus (P) or boron (B) of 5 × 10 ¹¹ to 2 × 10 ¹² / cm ² in order to control the threshold voltage of the TFT. It is doped to some extent. Further, a lightly doped drain (LDD) portion may be formed around the channel portion 3a of the semiconductor conductive layer 3 in order to reduce leakage current. This LDD portion is, for example, doped with phosphorus (P) at about 1 × 10 ^{12 to} 5 × 10 ¹³ / cm ² . The source electrode 5 portion and the drain electrode 4 portion of the semiconductor conductive layer 3 are formed of, for example, phosphorus (P) or boron (B) at 5 × 10 ^{14 to} 5 × 10 ¹⁵ / cm in order to improve the operation reliability of the transistor. ^{About 2} doped.

  When the semiconductor conductive layer 3 has an LDD portion, the distance in plan view between the shape line (outline) of the light shielding film 6 and the shape line (outline) of the LDD portion is suppressed in any direction. It is preferable that it is more than a distance. This light leakage current generation inhibition distance is, for example, 4 μm or more.

  The LCD of the present invention is manufactured as follows. In the LCD, a TFT array side substrate composed of a glass substrate or the like on which a large number of pixel portions including TFT elements are formed and a color filter side substrate composed of a glass substrate or the like on which a color filter and a black matrix are formed are opposed to each other. These substrates are bonded together at a predetermined interval, and a liquid crystal is filled and sealed between the substrates. In general, the color filter side substrate forms a vertical electric field to be applied to the liquid crystal with the pixel electrode on the entire main surface (main surface a) facing the TFT element and the pixel electrode. A common electrode (reference electrode) is formed. In the case of an IPS (In-Plane Switching) type LCD, this common electrode is formed in the same plane as the pixel electrode in the pixel portion of the TFT array side substrate, thereby generating a horizontal electric field. In the case of an FFS (Fringe Field Switching) type LCD, the common electrode is formed in the pixel portion of the TFT array side substrate with an insulating layer sandwiched above or below the pixel electrode, thereby generating an edge field (Fringe Field). It will be generated. In addition, red (R), green (G), and blue (B) color filters corresponding to the respective pixels are formed on the main surface a of the color filter side substrate, and light passing through the respective pixels is transmitted. A black matrix that prevents mutual interference is formed so as to surround the outer periphery of the color filter.

  The LCD of the present invention is not limited to the above-described embodiment, and may include appropriate design changes and improvements.

  The active matrix LCD of the present invention can be applied to various electronic devices. The electronic devices include a head-up display, a projector device, an automobile route guidance system (car navigation system), a ship route guidance system, an aircraft route guidance system, a smartphone terminal, a mobile phone, a tablet terminal, a personal digital assistant (PDA), a video Cameras, digital still cameras, electronic notebooks, electronic books, electronic dictionaries, personal computers, copying machines, terminal devices for game machines, televisions, product display tags, price display tags, industrial programmable display devices, car audio, digital audio There are players, facsimile machines, printers, automatic teller machines (ATMs), vending machines, digital display wristwatches, and the like.

DESCRIPTION OF SYMBOLS 1 Gate signal line 2 Image signal line 3 Semiconductor conductive layer 3a Channel part 4 Drain electrode 5 Source electrode 6 Light shielding film 7 Pixel part 8 Overlapping part

Claims (4)

A plurality of gate signal lines formed in the first direction on the upper surface of the substrate and a plurality of image signal lines formed so as to intersect with the gate signal lines in a second direction intersecting the first direction. And a thin film transistor element having a single-gate channel portion made of polycrystalline silicon formed in the vicinity of the intersection of the gate signal line and the image signal line, and overlapping the channel portion in plan view of the upper surface of the substrate A light-shielding film formed through an insulating layer at a site, and the light-shielding film is oblique to the image signal line so as to overlap with at least a part of the source electrode of the thin film transistor element in a plan view. The liquid crystal display device is formed in a shape extending in a direction, and the source electrode overlaps the gate signal line in plan view . The liquid crystal display device according to claim 1, wherein the channel portion is formed to extend in the oblique direction . A plurality of gate signal lines formed in the first direction on the upper surface of the substrate and a plurality of image signal lines formed so as to intersect with the gate signal lines in a second direction intersecting the first direction. And a thin film transistor element having a single-gate channel portion made of polycrystalline silicon formed in the vicinity of the intersection of the gate signal line and the image signal line, and overlapping the channel portion in plan view of the upper surface of the substrate A light-shielding film formed through an insulating layer at a site, and the light-shielding film is oblique to the image signal line so as to overlap with at least a part of the source electrode of the thin film transistor element in a plan view. is formed in a shape extending in the direction, the liquid wherein the channel portion that is formed so as to extend in front Symbol oblique direction crystal display device. 4. The liquid crystal display device according to claim 1, wherein the light shielding film is a metal film containing at least one of Al, Mo, Cr, Ti, Ta, W, and Pd.