JP2005326881A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the size and weight of a liquid crystal display device and to improve portability. <P>SOLUTION: The liquid crystal display device contains: a glass substrate which mounts a display region by an active matrix system having a plurality of scanning signal lines and a plurality of video signal lines, a video signal side peripheral circuit connected to the video signal lines and having thin film transistors, a scanning signal side peripheral circuit connected to the scanning signal lines and having thin film transistors, and one driver connected to the scanning signal side peripheral circuit and to the video signal side peripheral circuit; a counter substrate opposing the above substrate; and a liquid crystal layer held between the glass substrate and the counter substrate. The driver is fixed with a resin to the glass substrate. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a liquid crystal display device, and more particularly to an active matrix liquid crystal display device using a thin film transistor.

  An active matrix liquid crystal display device has a thin film transistor (TFT) and a liquid crystal pixel driven by the thin film transistor (TFT) in the vicinity of the intersection of a plurality of scanning lines and signal lines on a substrate. A scanning signal and a video signal are respectively supplied to the scanning wiring and the signal wiring by connecting an external driver IC. A video signal is applied to the liquid crystal by the TFT turned on by the scanning signal, and a predetermined image is displayed.

  The method of connecting the external driver to the wiring on the substrate is a TAB method using an organic resin film having a metal wiring pattern for display, and COG (Chip On Glass) directly bonding on the substrate using a metal paste, solder, or the like. There is a law. An example of the COG method is described in Patent Document 1.

  Non-Patent Document 1 and Non-Patent Document 2 include examples in which all or some of the functions of the external driver are built in the substrate to reduce the number of external drivers.

Japanese Patent Laid-Open No. 5-113574 Electronic Technology, June 1993, pages 6 to 8 1993 International Electron Devices Meeting Technical Digest, pp389-392

  However, in the above-mentioned invention, sufficient consideration is not given to cost reduction, power consumption reduction, pixel improvement, and reduction of the outer shape of the liquid crystal display device.

  An object of the present invention is to reduce the outer dimensions of a high-definition active matrix liquid crystal display device and to reduce the manufacturing cost.

  According to the liquid crystal display device of the present invention, a part of the function of the drive circuit is built in the glass substrate, a driver for driving it is connected to the glass substrate, the counter substrate facing the glass substrate, and the glass And a liquid crystal layer sandwiched between the substrate and the counter substrate, and the driver is fixed to the glass substrate with a resin.

  The scanning signal side peripheral circuit and the video signal side peripheral circuit are arranged below the counter substrate and below the seal of the liquid crystal layer or on the display region side.

  The use of TFTs with high operating speed in the peripheral circuit increases the degree of circuit integration. Even in a high-definition liquid crystal display device, the number of external drivers is reduced to two or less. The driver can be concentrated on one side of the substrate, and the external dimensions of the liquid crystal display device are reduced. The connection wiring between the driver and the external signal can be shortened, and the device can be reduced in size, weight and cost.

  Further, by using the COG method for connecting the driver, the outer shape of the liquid crystal display device becomes almost equal to that of the glass substrate, and the outer size is further reduced. Although the COG junction has a high connection failure rate in the past, the number of drivers to be connected is one or two, so connection failures can be reduced. For example, if the connection failure rate per driver is 1%, when the number of drivers is 10 with no circuit built-in, the success rate for all 10 is 90%, whereas with the circuit built-in is 99%. . This yield improvement effect becomes more prominent when the defect rate per piece increases. Repair in the case of poor connection, that is, inspection, disconnection, and reconnection becomes easy. Manufacturing cost can be reduced by reducing the defect rate.

  Mounting with COG improves earthquake resistance and impact resistance. The case material of the liquid crystal display device can be thinned. The external dimensions of the liquid crystal display device are reduced.

  The external interface and the driver are connected by a thick film wiring such as FPC and a thin film wiring on a glass substrate. Since there are one or two drivers, the wiring length on the glass substrate can be reduced. Since the wiring is usually a thin film like the electrode material of the TFT, the sheet resistance is large, but the voltage drop and voltage fluctuation due to the wiring resistance is short. Moreover, since the wiring is short, the amount of electromagnetic field radiation is small. A shielding material for shielding radiation can be omitted or reduced, and the liquid crystal display device can be thinned. There are cases where minute cracks, cracks, debris adhesion, etc. may occur in the periphery of the substrate due to strain stress at the time of cutting the substrate. This can prevent disconnection and short circuit between wirings.

  It is possible to reduce the number of crossing points and crossing areas between wirings on the glass substrate connecting the external interface and the driver. The probability of disconnection due to the step over the wiring at the intersection and the short-circuit failure probability between the intersecting wirings is reduced.

  It is possible to reduce the number of places where different layers of wiring are connected. The connection failure rate is reduced and the manufacturing cost can be reduced.

  By reducing the process temperature, the amount of shrinkage of the glass substrate of the substrate is reduced. Since the dimensional variation of the pattern formed on the substrate is small, the alignment accuracy of each connection terminal of the substrate and the driver is improved. It is possible to reduce connection resistance by reducing the connection pitch, increasing the effective connection area, reducing defects in the connection process, and shortening the connection time.

  The thermal expansion coefficient of the glass substrate is a little larger than the thermal expansion coefficient of the quartz substrate, and is almost equal to the thermal expansion coefficient of the driver made of single crystal silicon. The alignment accuracy of the connection between the driver and the board is improved, and the connection pitch can be reduced, the connection resistance can be reduced by expanding the effective connection area, the connection process can be reduced, and the connection time can be shortened. Damage to the driver and the board due to thermal stress and peeling of the connection part can be reduced.

21 and 22 show an equivalent circuit and driving waveform of one pixel. The operation of the TFT is as follows: (1) a period for charging the signal voltage to the liquid crystal capacitor through the pixel TFT; (2) a period for holding the charged voltage;
(3) It is divided into three moments from (1) to (2). The liquid crystal capacitor CLC is connected to the source of the TFT in parallel with the holding capacitor CAD. A video signal VDn for driving the liquid crystal is applied to the drain of the TFT. The TFT is turned on by the gate signal Vgn. The liquid crystal capacitor is charged by the conductive TFT, and the potential Vs rises to the level of Vd. A difference voltage between the potentials VCOM and Vs of the common electrode on the counter substrate side is applied to the liquid crystal. The transmittance of the liquid crystal is controlled by the time average value of the differential voltage, that is, the effective voltage. The transmittance is controlled independently for each pixel, and an image is displayed on the entire LCD. In order to perform normal image display, it is ideal that the voltage Vdn supplied from the outside is equal to the electrode potential Vs of the liquid crystal. Actually, the Vs waveform is distorted with the above operations (1), (2), and (3), and a difference is generated between Vd and Vs. To reduce the distortion of (1),
Increase the charging capacity of TFT. That is, the mobility is improved. It is also effective to increase the TFT channel width to channel length ratio (W / L). In order to reduce the distortion of (2), the off-current of the TFT is lowered and the W / L is reduced. Normally, since the off-current is linked with the mobility, a TFT with a low off-current tends to have a low mobility. In order to reduce the distortion of (3), it is effective to reduce the overlap width of the gate and the source and the channel width. The smaller the area of the TFT, the smaller the defect due to a short circuit between wirings. Further, the aperture ratio increases as the TFT becomes smaller. Therefore, in the case of a transmissive liquid crystal display device, the luminance of the display surface is improved. In addition, the smaller the TFT, the smaller the distortion (3). Therefore, it is desirable to reduce the TFT occupation area WL by reducing the TFT W and L as much as possible. Ideally, both W and L are set to the minimum processing size of the TFT manufacturing process. However, considering conventional TFT characteristics, W and L cannot be equalized. For an a-Si TFT having a mobility as low as 0.4 cm ² / Vsk or less, the W / L ratio was set by setting L to the minimum processing dimension and W to be greater than this L, usually about 5 times. On the other hand, in a p-Si TFT having a high mobility of 10 or more but a high off-current, L is set to the minimum processing dimension, W is set to about 5 times or more, and the W / L ratio is set. As a result, the area occupied by the TFT is usually more than 5 times the minimum processing area WL. In particular, p-Si has a multi-gate structure (multiple TFTs connected in series) or LDD to reduce off-current.
(Lightly Doped Drain) structure is adopted. Such a p-Si TFT structure is larger than the area occupied by the TFT. In contrast, when the mobility of the TFT of the pixel is in the range of 0.6 cm ² / Vs to 5 cm ² / Vs, the W / L ratio of the TFT becomes about 2. The area occupied by the TFT can be reduced to half or less of the conventional area. When a peripheral circuit is incorporated, it is necessary to consider the signal delay time by the peripheral circuit. In other words, when the peripheral circuit is built-in, it is necessary to complete the charging of the liquid crystal in about half or less of the pixel TFT. For this reason, it is necessary to increase the charging capability of the TFT of the pixel, that is, the mobility, as compared with a case where no circuit is incorporated. In particular, when the mobility of TFTs in the peripheral circuit is low, the delay time due to the peripheral circuit becomes long, so that it is necessary to further increase the mobility of the TFTs in the pixel. When the mobility of the peripheral circuit TFT is 100 to 300 cm, liquid crystal driving without voltage distortion is possible by setting the mobility of the pixel TFT to 0.4 or more and 5 or less. Further, when the mobility of the peripheral circuit TFT is 30 to 100 cm, the mobility of the pixel TFT is set to 0.7 or more and 5 or less. Further, when the mobility of the peripheral circuit TFT is 10 or more and 30 or less, the mobility of the pixel TFT is set to 1 or more and 5 or less, thereby enabling liquid crystal driving without voltage distortion.

Among the three voltage distortion causes classified above, the voltage fluctuation (hereinafter referred to as the through voltage Vcgs) due to (3) is a change in the gate voltage that appears on the source electrode via the gate-source capacitance of the TFT. . That is, Vs is lower by Vcgs than the level charged until Vs = Vd in (1). When the gate voltage is a rectangular wave without distortion, Vcgs is expressed as Vcgs = Vgh · Cgs / (Cgs + CL). Here, Cgs is the drain-source capacitance of the TFT, CL is the liquid crystal capacitance (and the sum of the holding capacitance) CL, and Vgh is the height of the gate voltage. In practice, it takes some time for the gate voltage to completely switch from the high level to the low level. Meanwhile, the TFT shows a weak conducting state. This conduction state works in the direction of charging Vs again to the level of Vd. Actual Vcgs is smaller than the value of the above formula. The voltage increase Vr due to the recharging is proportional to the product of the distortion amount of the gate signal and the charging capability of the TFT, that is, the mobility. The amount of distortion of the gate signal changes within the display surface. That is, the gate voltage is supplied to the first end of the scanning line of the display portion, and the amount of distortion increases until reaching the end of the scanning line due to the wiring capacitance and the wiring resistance. For this reason, Vcgs has a distribution in the plane. That is, the display becomes non-uniform. In particular, when the display area increases to 3 inches or more, particularly 5 inches or more, and the resistance and capacitance of the wiring increases, the non-uniformity of the display becomes significant. Further, when the charging ability of the TFT is high, the cloth uniformity becomes more remarkable. When the peripheral circuit is built-in, the distortion amount of the scanning signal supplied to the display unit is larger than that when the peripheral circuit is not built-in. Inhomogeneity becomes a more serious problem. In addition, when the number of gradations to be displayed increases, inversion between gradations occurs, and normal display becomes impossible. In order to solve such a problem, the mobility of the TFT of the pixel is preferably 5 cm ² / Vs or more, preferably 3 cm ² / Vs or less.

By setting the dynamic range of the liquid crystal driving power supply voltage of the video signal driver to 5 V or less, preferably 3 V or less, the processing rule of the driver pattern can be set to 1 μm or less, preferably 0.5 μm or less. Thereby, the chip area can be greatly reduced. The processing dimension of the driver is an order of magnitude smaller than the processing dimension of the TFT. Compared to the case where all driver functions are built into the board, the size and power consumption can be greatly reduced. The external dimensions of the liquid crystal display device can be greatly reduced. The chip area can be reduced to 0.1 mm ² or less per pin output. One driver can output more than 200 pins or more than 300 pins. The liquid crystal display device can be driven by one or two drivers and a peripheral circuit. One driver can include a display information generating circuit and a memory circuit for generating display information. A display information generation circuit and a memory circuit for generating display information can be collectively formed in the same process as the liquid crystal drive voltage generation circuit.

  When the peripheral circuit is not built in, data input / output is shared by 10 or more drivers, so the amount of heat generated per driver is small. In a circuit built-in, since one or two drivers are all driven, the amount of heat generated per driver is increased. The amount of heat generated can be reduced by setting the dynamic range of the driver's liquid crystal driving voltage to 5 V, preferably 3 V or less. Even if the driver is mounted on a glass substrate with poor thermal conductivity, it will not be destroyed by heating. Even if the substrate is mounted on a plastic having a low heat-resistant temperature, the substrate is not deformed or disconnected by heating. The amount of heat generation increases with the driving frequency. However, since the voltage is low, the driver is not destroyed by heating even at a frequency of 40 MHz or higher. Even if the driver includes a large-scale display information generation circuit and a memory circuit for generating display information, thermal damage or malfunction will not occur.

By reducing the voltage, the leakage current of the high mobility circuit and pixel TFT is reduced exponentially. A TFT with high mobility can be used. Photocon current is reduced. The threshold voltage shift of the peripheral circuit TFT is reduced, and the circuit operation is stabilized. Lowering the voltage reduces the amount of heat generated by the peripheral circuits.

  In particular, in a peripheral circuit with a large amount of heat generation such as an NMOS shift register circuit, the temperature rise of the circuit is reduced. Peripheral circuit operation is stable. High-density circuit arrangement is possible. The area of the peripheral circuit is reduced. The circuit operates at high speed. Peripheral circuits can operate in a high temperature environment. There is no increase in the temperature of the liquid crystal in the display area near the peripheral circuit and the pixel TFT. In-plane uniformity of display is improved. The driver power supply can be reduced in voltage and current. The power consumption of the entire system is reduced. The power supply volume can be reduced. Weight is reduced. Case strength can be lowered. Case weight and volume are reduced. The liquid crystal display device can be made lighter and thinner, and the outer shape of the device can be made smaller.

  As described above, according to the present invention, the active matrix liquid crystal display device can be reduced in size and the portability of the liquid crystal display device can be improved.

  Hereinafter, the present invention will be described in detail with reference to examples.

(Example 1)
FIG. 1 is a plan view showing a first embodiment of a liquid crystal display device according to the present invention. On the glass substrate 10, an active matrix display area 40, and a video signal side peripheral circuit 51 and a scanning signal side peripheral circuit 52 are built in the outer periphery thereof. Furthermore, one video signal driver 21 is mounted on the substrate by the COG method. Although not shown, a signal from the interface circuit located on the back surface of the substrate is guided by the FPC and connected to one end of the thin film wirings 55 and 56 on the glass substrate. The other ends of the thin film wirings 55 and 56 are connected to the video signal side driver 51 and the scanning side built-in circuit 52, respectively. The above members are housed in the case 4 and constitute a liquid crystal display device.

  FIG. 4 shows an equivalent circuit of a display area of 240 × 320 pixels (240 × 320 × 3 color dots) and peripheral circuits. Both the video signal side peripheral circuit 51 and the scanning side signal circuit 52 are of a switch matrix type. Taking the video signal side circuit as an example, the video signal from the driver and Vdd1 to Vdd240 are dispersed by TFTs and supplied to the video signal line and scanning signal line of the display unit. The branching of the signal is controlled by the switching operation of the sampling TFT by the clock pulses CL1 to CL4. The scanning signal side circuit has the same configuration, and the scanning signals Vgd1 to Vgd24 from the driver are branched into 240 scanning signal lines from Vg1 to Vg240 by 10 clock pulses. 240 video signal lines can be driven by 240 video signal terminals of the driver, and 24 scanning signal terminals can drive 960 video signal lines and 240 scanning signal lines. That is, the driver IC and the number of connections can be reduced to ¼ or less.

FIG. 2 shows a planar structure of one pixel in the display area. FIG. 3 shows a cross-sectional structure between (A) and (B) of FIG. TFTs 101 are inverted staggered TFTs using hydrogenated amorphous silicon (a-Si) as an active layer 110. The active layer is connected to the source electrode 120 and the drain electrode 130 through n + -type a-Si contact layers 125 and 135. The source electrode 120, the drain electrode 130, and the video signal line 137 have a two-layer structure of molybdenum 10a and ITO 10b. The gate electrode 110 and the scanning signal line 111 are aluminum. The gate insulating film 140 is SiN. The liquid crystal 200 is a TN liquid crystal and is sealed between the glass substrates 10 and 12. The alignment films 205 and 207 are formed on the opposing surfaces of the respective glass substrates, and the alignment direction of the liquid crystal is rotated by 90 degrees between the glass gaps. Although not shown, a backlight is positioned on the back surface of the glass substrate 10 and irradiates the liquid crystal with light. Polarizing films 210 and 212 are attached to the outer surface of the glass substrate. The amount of transmitted light is controlled by the voltage applied to the liquid crystal, and an image is displayed. One end of the scanning signal line and the video signal line is connected to the peripheral circuit at the peripheral part of the glass substrate.

  FIG. 5 shows a planar structure of the peripheral circuit on the video signal side. The video signal line 137 from the display unit is connected to the source electrode 120c of the circuit TFT 101c. The basic structure of TFT101c is almost the same as TFT101 of the display unit. However, TFT 101c differs only in that polycrystalline silicon is used as an active layer. A circuit TFT that requires a high driving capability uses a poly-Si TFT by laser annealing, and an a-Si TFT uses a pixel TFT that requires uniform characteristics and low off-current. By this combination, the peripheral circuit is built in without impairing the display uniformity. The drain electrodes 120 c of the four TFTs 101 c are connected to one connection terminal 51. Although not shown, the connection terminal 51 is connected to a video signal driver. The driver is mounted on the glass substrate by the COG method.

Next, a method for manufacturing a liquid crystal display device will be described. FIG. 6 shows a cross-sectional structure in the main manufacturing process of the TFT of the display unit according to the present invention. As described below, the TFTs in the circuit portion are manufactured by substantially the same process. In either case, the TFT 101 is formed on the glass substrate 10. The glass substrate 10 contains SiO ₂ as a main component, contains Al ₂ O ₃ and B ₂ O ₃ of 11% and 15%, and 25% of other oxides, respectively, and has a strain point of 593 ° C. The coefficient of thermal expansion is 46 × 10 ⁻⁷ / K. First, a Cr film is deposited to a thickness of 120 nm on the glass substrate 10 by sputtering, unnecessary portions are removed by photo etching, and the gate electrode 11 is formed. The etching solution is a cerium nitrate-based etching solution. Subsequently, the SiN film 145 and the a-Si film 110 are continuously deposited by the plasma CVD method at a substrate temperature of 300 ° C., 270 ° C., a thickness of 350 nm, and 40 nm, respectively. Subsequently, the a-Si film is crystallized by laser annealing only in the region where the peripheral circuit is formed. The laser is a XeCl excimer laser. Irradiation was performed in vacuum at an energy density of 200 mJ / cm ² . In order to prevent deterioration of the characteristics of the a-Si TFT, the heat dehydrogenation treatment before irradiation is not performed. Also, the substrate is not heated during irradiation for the same reason. On the other hand, when a-Si is deposited, if the hydrogen concentration in the film is 15% or more, and especially the concentration of hydrogen bonded to silicon atoms in a chain (SiH ₂ ) is high, poly- having good characteristics is obtained. A SiTFT was obtained. The bonding state of hydrogen can be evaluated by an infrared absorption spectrum, but the peak wave number of absorption is 2020 / cm to 2060 / cm, preferably 2030 to 2050. This makes the TFT mobility 10
cm ² / Vs.

  Subsequently, the laminated film of SiN 140 and a-Si 110 is processed into an island shape so as to cover the gate electrode by photolithography (FIG. 6A). For the etching, a dry etching method using a mixed gas of trifluorochlorocarbon and oxygen was used. In the peripheral circuit portion, when a-Si containing a large amount of hydrogen is laser-annealed, the surface becomes rough, and pinholes are sometimes generated. In this case, the etchant may come into contact with the gate insulating film. In this embodiment, the etching is a dry method with a low etch rate for SiN. Even if there is a pinhole in silicon, there is no damage to the gate insulating film.

Subsequently, a Mo film having a thickness of 200 nm is deposited at a substrate temperature of 160 ° C. by sputtering. Silicide layers MoSi and 125 are formed at the interface between a-Si and Mo by solid-phase reaction of both. Subsequently, Mo is etched and etched using a phosphoric acid / acetic acid mixed solution (PAN solution). That is, the portions other than the channel portion 125, the source electrode portion 120b, the drain electrode portion 130b, and the signal wiring portion 10b are removed (FIG. 6B). Since MoSi, 127 is insoluble in the PAN solution, it remains on the surface of the a-Si without being removed. Subsequently, P is implanted into a-Si by ion doping to form a high-concentration impurity silicon layer (contact region) 135 (FIG. 6C). For ion doping, a non-mass separation type ion irradiation apparatus was used, and helium diluted phosphine was used as a source gas. The acceleration voltage was 10 kV and the dose was 10 ¹⁵ pieces / cm ² . At this time, if the substrate temperature is heated to, for example, 300 ° C., P implanted into a-Si is activated, and activation treatment such as new laser irradiation or heat treatment can be omitted. Needless to say, activation treatment by thermal annealing or the like may be separately performed to further improve the characteristics.

  Subsequently, an ITO film is deposited by sputtering at a substrate temperature of 220 ° C. and a thickness of 140 nm.

This ITO is processed into the shape of the pixel electrode 150, the source 120a, the electrode drain electrode 130a, and the signal line 10a by photolithography using an HBr solution (FIG. 6D). Subsequently, using each ITO electrode as a mask, the Mo film is removed by etching with a PAN solution. That is, Mo in the channel portion of the TFT not covered with ITO is removed (FIG. 6E). Subsequently, the MoSi in the channel portion is removed by oxygen plasma asher or dry etching such as chlorine or trifluorocarbon. In this case, the characteristics of the TFT using the oxygen asher are good, and it is preferable to use this. The reason is considered to be that plasma damage to the a-Si film and overetching can be prevented and the surface capture order can be reduced by forming a very thin oxide film that is stable on the surface simultaneously with the removal of the silicide. In this case, the thickness of the oxide film is about 30 nm or less, preferably 10 nm or less in order to suppress the generation of stress. Although not shown in the drawings, an SiN film 145 is subsequently deposited by plasma CVD as a protective film for the TFT. Finally, the SiN film is etched and etched in the same manner as the gate insulating film to expose the signal line and gate line terminals, thereby completing the TFT.

  In this embodiment, as shown in the plan view of FIG. 2, the storage capacitor 102 is formed using the gate line 112 in the row adjacent to the pixel electrode 150 as an electrode. This storage capacitor is connected in parallel with the liquid crystal capacitor when the liquid crystal is driven by the active matrix substrate of this embodiment, and has an effect of preventing the voltage effect due to the leakage current. FIG. 6 shows a partial plan view of the drive circuit according to the present embodiment (range related to the pixels in the two columns of the display unit). From one drain terminal DLT at the end of the glass substrate to two drain lines (video signal lines) (even column DL0, odd column DL1) of the display unit (pixel unit) via two TFTs, TC0, TC1 Branch connected. A pattern CROS made of a two-layer film of Si and SiN is sandwiched between the gate lines GC0 and GC1 and the drain line to insulate the wirings from each other. Two gate lines GC1 and GC1 for switching the TFTs are connected to the even-numbered and odd-numbered TFTs TC0 and TC1, respectively.

  Even if the changes listed below in the first and second embodiments are added, the gist of the present invention is not impaired.

  In the embodiment, the source and drain electrodes are provided on the gate electrode and the semiconductor, but even if this shape is changed, the gist of the present invention is not impaired. That is, the source / drain metal layers 130b and 120b may not be left on the silicon film but may be a contact having only a laminated structure of n + Si, silicide and ITO.

  In the embodiment, Cr is used as the gate electrode material, but other metals such as Al, Cu, Ta, Ti and the like, laminated films thereof, alloys, or the like may be used. When Al or Cu is used, the wiring resistance is lowered, and the in-plane uniformity of the display image of the LCD using this can be improved.

In the embodiment, the SiN film is used as the gate insulating film material, but other films such as SiO ₂ and SiON may be used. In addition, when Al or Ta is used as the gate line material, the insulation film may be improved in breakdown voltage and short circuit prevention as a laminated film obtained by anodizing the gate line material.

  In the embodiment, the semiconductor film is an a-Si film formed by plasma CVD or a polycrystalline Si film obtained by laser annealing, but it may be formed of other materials or other manufacturing methods. For example, the characteristics of the TFT may be improved as a Ge film obtained by depositing germane gas as a material gas by plasma CVD, a mixed crystal film of Ge and Si, or a superstructure film.

  The semiconductor film may be deposited by using a low pressure CVD method without plasma damage, a sputtering method capable of reducing the amount of hydrogen in the film, or an ECR-CVD method to prevent instability of the film and reduce the process temperature. High mobility may be achieved by using a Si microcrystal film as the semiconductor film. The semiconductor film may be annealed with laser or heat to be polycrystallized to increase the mobility of the TFT. In this case, as described in the section of action, even if there is a lot of hydrogen in the film before annealing, the defect of the gate insulating film due to pinholes in the crystallized film hardly occurs.

  In the embodiment, Mo is used for the source / drain electrodes, but other metal materials that react with semiconductors such as Ti, Ta, Mo, Cr, Ti, Pd, Mn, Co, Ni, Ta, and Pt to form silicide or germanium compounds. It may be used. Furthermore, an alloy containing these and a laminated film may be used.

  FIG. 3 is a cross-sectional view of one pixel of a cell in which an active matrix substrate faces another substrate and liquid crystal is sealed. In the TFT substrate 10, a TFT, a pixel electrode 150, a protective film 145 and the like are formed on the surface in contact with the liquid crystal by the method described in the above embodiment. On top of that, a wiring film 145 for aligning liquid crystal molecules is formed by spinner coating and rubbing. A deflection plate 210 is attached to the opposite surface. On the inner surface of the counter substrate, a black matrix 160 of Cr for blocking light leaking from areas other than the pixel electrodes, a color filter 152 formed by dyeing an organic resin after roll coating, and counter electrodes 170r, 170g of ITO The alignment film 207 is sequentially formed. An alignment film 212 is attached to the outer surface. Beads are dispersed between the two substrates to have a gap length of about 5 μm. Although not shown in the drawing, the periphery of the substrate is bonded with resin, and then nematic liquid crystal is filled and sealed. The deflection directions of the deflection plates 210 and 212 are orthogonal to each other, and the rubbing directions of the alignment films 205 and 207 are orthogonal to each other. The display mode is a normally white mode in which light is transmitted when no voltage is applied to the liquid crystal.

FIG. 5 shows a planar structure of the peripheral circuit on the video signal side. A circuit portion corresponding to four video signal lines from 4n + 1 to 4n + 4 columns is shown. Circuit with 4 connection terminals with driver
Connected to the drain electrode 330 of the TFT 301. On the other hand, the source electrode 320 of the circuit TFT is connected to the corresponding storage capacitor 302 and video signal line 137, respectively. The clock lines CL1, CL2, CL3, and CL4 correspond to the scanning signal lines of the display unit and are connected to the gate electrode of the circuit TFT. The clock line has a bent wiring shape to reduce the circuit area. This increases the wiring length. The wiring width of these two wires was increased so that the wiring resistance would be the same as the other two wires. Variations in display colors due to differences in delay time can be prevented. The structure and process of the circuit TFT are the same as those of the display unit TFT except that the active layer is poly-Si by laser annealing. That is, the source / drain electrodes and the wiring are two-layer wiring of metal and ITO, and the silicon layer is laid under the wiring. The shape of the TFT channel 310 was U-shaped. As a result, the channel width can be doubled without increasing the parasitic capacitance between the gate and the source. That is, the driving capability of the circuit can be improved without increasing the influence of the gate voltage waveform. The structure of the storage capacitor 302 is the same as that of the display unit. A total of 240 such circuit patterns are arranged for every four video signal lines. At that time, as shown in FIG. 1, the entire circuit may be divided into blocks having a width equal to or smaller than the width of the laser beam, and the intervals between the blocks may be separated by about 100 to 500 μm. In this case, it is possible to reduce the influence of TFT characteristic variations in the laser beam overlapping portion during laser annealing. The peripheral circuit on the scanning side has the same configuration as that in FIG. The difference is that the source of the circuit TFT and the scanning signal line, that is, the gate metal layer are connected. That is, it is a point of connecting different layers of wiring.

  FIG. 20 shows an outline of the leftmost four columns of the display unit in the drive waveform of the liquid crystal display device. In the first half tL1 of the pixel line selection time t1 (35 μs), the circuit TFTs are sequentially turned on by the clock signals CL1, CL2, CL3, and CL4. In accordance with this, the driver switches the data Vdd1 in a time 1/8 of tL. The video signals Vd1, Vd2, Vd3, and Vd4 are charged to the video signal lines. This video signal is charged in the liquid crystal capacitor by the TFT of the pixel in the second half tL2. An image given from a signal line (drain line) by applying a voltage to the gate line (scanning line) sequentially (VGn-1 to VGn or less, but not shown, to the next row) to make the pixel (line sequential scanning) TFT conductive. A signal VD is applied to the liquid crystal. The liquid crystal is driven by the difference voltage between the potentials VCOM and VDn of the common electrode on the counter substrate side, and the light transmittance of the pixel changes. The transmittance is controlled independently for each pixel, and an image is displayed on the entire LCD.

  FIG. 11 is a general outline of a liquid crystal display using the above liquid crystal cell. A driver 21 is COG mounted on the active matrix substrate of the liquid crystal cell. The driver has a function of generating a scanning signal, a video signal, and a clock signal thereof. An output terminal of the driver is connected to the scanning side peripheral circuit 51 and the video signal side peripheral circuit 52. Signals and power for driving the driver IC are supplied from the printed circuit board 430 via an FPC (flexible printed circuit). A signal processing circuit 400 including an IC such as a timing converter and a gradation voltage generation circuit 410 corresponding to each gradation displayed on the liquid crystal are mounted on the printed circuit board. The backlight 440 was installed on the back surface of the active matrix substrate. The above members are mounted in the case 90.

  FIG. 7 is a cross-sectional view of a driver and a glass substrate connected by the COG method. There are various types of COG methods, but this is based on the microbonding method. An Au bump 350 is formed on the output terminal of the driver 51, and this is directly connected to the video signal line I terminal 351 on the glass substrate 10. The driver is fixed by an ultraviolet curable resin 358 applied between the driver and the substrate. The Au bump and the ITO terminal 351 are press-contacted by shrinkage and compressive stress when the resin is cured. The contact resistance of micro bump bonding is about 1 ohm. Low wiring resistance was realized by laminating the gate wiring material Cr, the video signal line material Mo, and ITO. The liquid crystal panel terminal and the interface circuit are connected by FPC (base material 80a, copper foil 80b). The peripheral circuit is formed within a width of 2 mm in the vicinity of the seal 352 of the liquid crystal cell. In the vicinity of the seal, the display characteristics of the liquid crystal become non-uniform due to impurity contamination, rubbing unevenness, and the like. In consideration of seal processing accuracy, the non-display area is about 2 mm inside the seal and the seal. Conventionally, this area has been a dead space, but in this embodiment, a peripheral circuit is provided here, so that the external dimensions of the display area of the liquid crystal display device can be reduced. In this embodiment, a switch matrix circuit is used as the peripheral circuit. The power consumption of this circuit is smaller than that of a shift register circuit using an inverter. Therefore, the amount of heat generated in the circuit is small. Even if the circuit is formed in the liquid crystal cell, the liquid crystal is not locally heated and the temperature is uniform. Therefore, a uniform display without display unevenness can be obtained.

  In this embodiment, the liquid crystal may be PDLC liquid crystal (Polymer Dispersed Liquid Crystal). PDLC is a liquid crystal material filled in the pores of a polymer film. This is obtained by phase-separating a uniform solution of liquid crystal and polymer material by polymerization. For example, the liquid crystal is E-8 manufactured by BDH. As the polymer material, a mixed solution of 2-ethylhexyl acrylate, urethane acrylate, and a photopolymerization initiator was used. After the liquid mixture was filled in the liquid crystal cell, PDLC was obtained by photopolymerization. In this case, the deflection plates 212 and 210 and the alignment films 207 and 205 in FIG. 3 are not necessary. Due to the absence of the deflecting plate, the transmittance is improved twice, which is effective in improving display luminance and reducing power consumption.

  The area per connection terminal can be increased, malfunctions are prevented, and power consumption is reduced. Such an improvement in manufacturing yield is significant in a multi-terminal large-sized, very small driver chip, a so-called string-shaped chip. For this reason, it is possible to further increase the number of terminals and the width of the string chip. The width of the non-display area in the outer peripheral portion of the liquid crystal display device can be reduced. The display area size can be increased with respect to the external size of the liquid crystal display device.

In this embodiment, when the TFT of the display portion is moved from 1 to 3 cm ² / Vs and the off-current is 100 pA, the ratio of the channel width and the channel length of the TFT of the pixel can be made 1. As a result, the aperture ratio of the display area can be improved, the panel luminance can be improved, and the power consumption of the backlight can be reduced. A 30 MHz signal can be generated by setting the driver mobility to 800 cm ² / Vs. When the mobility of the peripheral circuit is 10 to 30 cm ² / Vs, the switch matrix circuit can be operated. Further, by setting the mobility of the built-in circuit to 100 or more and 300 or less, it is possible to reduce the in-plane variation of the voltage change due to the source-drain capacitance when the TFT is off.

  Power consumption due to the switching time of the thin film transistor of the display pixel being 30 μs to 60 μs, the switching time of the thin film transistor of the built-in circuit on the video signal side being 3 μs to 12 μs, and the switching time of the driver transistor being 0.01 μs to 0.03 μs Can be reduced. Electromagnetic radiation can be reduced. The amount of heat generated by the circuit can be reduced. The calorific value of silicon can be reduced. The element area of silicon can be reduced.

  The switching time of the thin film transistor of the display pixel is 30 μs to 60 μs, the switching time of the thin film transistor of the built-in circuit on the video signal side is 3 μs to 12 μs, and the switching time of the driver transistor is 0.01 μs to 0.03 μs. The above can be further obtained.

  The number of connection processes is simplified because the drivers are integrated. When the short stories are aggregated, the frame area relative to the display area can be small. Since the area of the glass substrate is small, a large number of active matrix substrates that can be taken from a single glass motherboard can be reduced. In the case of being integrated into a long story, there is a light guide type backlight fluorescent tube in the area under the driver. The phosphor sky light travels in the short side direction of the backlight. Therefore, variation in light intensity distribution is small. The light emission intensity of the fluorescent tube may be small. Other elements can be mounted next to the driver. For example, the timing converter substrate for converting a CRT signal into an ICD can be made smaller or eliminated. This is because the liquid crystal display device is small and light.

  Electromagnetic radiation from the liquid crystal display device is reduced. Data leakage to others due to interception of electromagnetic radiation can be prevented.

(Example 2)
As a second embodiment, an embodiment of a horizontal electric field type liquid crystal display device will be described. FIG. 14 is a partial plan view of one pixel of a liquid crystal display device using a horizontal electric field method. FIG. 15 is a cross-sectional view taken along the line (a)-(b). The scanning signal line 111 and the gate electrode 113 are Cr films. The video signal line 111, the source electrode 120, the drain electrode 130, the pixel electrode 150, and the common electrode 154 are a laminated film of Al and Cr. The active layer 110 of the TFT 101 is a film in which a-Si is deposited in two layers of 40 nm and 180 nm. However, in the peripheral circuit portion, only the lower layer is a poly-Si film by laser annealing. In other words, the TFT of the circuit uses a two-layer film of poly-Si and a-Si as an active layer. An n + a-Si layer 135 is formed between the source / drain electrodes and the active layer. The pixel electrode 150 is formed in a strip shape parallel to the video signal line 137. The common line 154 is formed in the vicinity of the video signal line in the adjacent row in parallel therewith. The common line supplies a common voltage in the column direction within the display surface. The alignment of the liquid crystal is controlled between the pixel electrode 150 and the common electrode 154 by an electric field parallel to the substrate surface.

According to the lateral electric field of this embodiment, the birefringence of the liquid crystal depending on the viewing angle is small. Wide viewing angle range for image display. The liquid crystal capacity is 1/5 or less of the conventional vertical electric field. Further, the capacity of the signal wiring and the scanning signal line is reduced to about half. For this reason, the writing time by the TFT of the pixel can be improved to 5 times or more than the conventional one. Therefore, charging is possible even if the mobility of the TFT of the pixel is low. Therefore, the performance of poly-Si in the peripheral circuit can be improved without considering the deterioration of the characteristics of the a-Si in the pixel. For example, the substrate can be heated to near 400 ° C. during laser annealing. In addition, the formation conditions of the a-Si film as the starting material can be optimized so that the characteristics of the poly-Si film after laser annealing are improved. For example, a film having many Si—H ₂ bonds is used. Alternatively, a hydrogen-free Si film formed by sputtering may be laser-annealed, and then hydrogen may be introduced by plasma hydrogenation. Although the characteristics of the a-Si TFT are lowered by these methods, the mobility of the poly-Si TFT can be improved to 30 cm ² / Vs or more. A high-definition liquid crystal display device can be realized by high-speed operation for forming off-current poly-Si. Since there is a sufficient charge capacity, the channel width of the TFT can be reduced. The area of the peripheral circuit can be reduced, and the area of the outer periphery other than the display area of the liquid crystal display device can be reduced. Reduction of the pixel TFT increases the aperture ratio of the pixel, thereby improving the luminance of the liquid crystal display device and reducing the power consumption of the backlight. The voltage held in the liquid crystal capacitance while the TFT is off, the lower the liquid crystal capacitance, the lower. The horizontal electric field type liquid crystal capacity is small and easily affected. However, in this embodiment, the pixel TFT is an a-Si inverted staggered TFT and originally has a low off-state current. Therefore, there is no influence of voltage drop due to off-current. According to the present embodiment, the power consumption can be reduced because the wiring capacity and the capacity of the peripheral circuit for driving the wiring capacity are small. When this is mounted on a portable information processing apparatus, it has the effect of increasing battery life, reducing dimensions, and reducing weight.

  FIG. 9 shows a portable information processing apparatus equipped with a liquid crystal display. An electronic notebook with a communication function. CPU board 950 equipped with an information processing function centered on a microprocessor, rechargeable battery 920 for supplying power to the entire system in an electronic notebook, numeric data input keyboard 904, information processing menu selection switch 901, data recording memory Contains card 960. The liquid crystal display 1 is a transmission type having a backlight on the back. Since the aperture ratio of the active matrix substrate was improved, the utilization factor of backlight light was improved and the brightness of the LCD was improved. Moreover, sufficient brightness was obtained even with a low-power backlight, making it possible to reduce the backlight thickness and weight, and to reduce the size and weight of the battery used as the power source. As a result, the size and weight can be reduced directly and indirectly (and structural members for storing and holding them), and the portability of the notebook personal computer can be improved. In addition, the time that can be used with a single charge has been extended, and usability has been improved.

  According to the present invention, the LCD is effective not only in the notebook personal computer described in this embodiment, but also in other portable information processing devices that are reduced in size, weight, and battery life. For example, the LCD of the present invention is based on the power of the battery for information processing using an integrated circuit, such as a portable information processor for sales / order management used in portable telephones, portable game machines, retail stores, etc. It is effective in the equipment to be used.

(Example 3)
As a third embodiment, a liquid crystal display device which is a reflection type node and does not use a counter substrate will be described. FIG. 16 shows a cross-sectional structure of the liquid crystal cell. A coplanar TFT 101 is formed on the glass substrate 10. The surface of the TFT protective film 145 is flattened by spin coating and drying of polyimide resin. The reflective pixel electrode 520 is formed on the protective film 145. As the liquid crystal, PDLC (Polymer Dispersed Liquid Crystal) is used. PDLC is formed by coating on a TFT substrate. In PDLC, the liquid crystal material 200 is filled in the pores of the polymer film 510. This is obtained by phase-separating a uniform solution of liquid crystal and polymer material by polymerization. The liquid crystal is E-8 from BDH. As the polymer material, a mixed solution of 2-ethylhexyl acrylate, urethane acrylate, and a photopolymerization initiator was used. After applying the mixed solution, the polymer component was cured by photopolymerization to obtain PDLC. An organic film 204 was applied and formed as a protective layer on the surface of the PDLC film. The material of the protective film was the same as the polymer material of PDLC. The counter electrode 165 made of ITO is formed by sputtering at a low temperature.

  PDLC may be formed by an immersion method. The porous polymer film is formed by applying a polymer film containing fine particles and removing the fine particles therefrom. For example, a polyvinyl alcohol solution containing polymethyl methacrylate having a particle size of 1 μm is used. Application is by a spinner method. The coating film is dried and then immersed in chloroform. Fine particles are eluted to form pores, and when this is impregnated with liquid crystal, PDLC is obtained. Since there is no counter substrate, the liquid crystal cell can be reduced in weight and thickness. Further, according to the present embodiment, it is not necessary to seal the liquid crystal cell at the periphery. Therefore, the liquid crystal display device can be downsized by a width corresponding to the seal width.

Example 4
FIG. 9 shows a portable information processing apparatus equipped with a liquid crystal display device. An electronic notebook with a communication function. CPU board 950 equipped with an information processing function centered on a microprocessor, rechargeable battery 920 for supplying power to the entire system in an electronic notebook, numeric data input keyboard 904, information processing menu selection switch 901, data recording memory Contains card 960. The liquid crystal display 1 is a transmission type having a backlight on the back. Since the aperture ratio of the active matrix substrate was improved, the utilization factor of backlight light was improved and the brightness of the LCD was improved. Moreover, sufficient brightness can be obtained even with a low-power backlight, making it possible to reduce the thickness and weight of the backlight, or to reduce the size and weight of the battery serving as the power source. As a result, the size and weight can be reduced directly and indirectly (and structural members for storing and holding them), and the portability of the notebook personal computer can be improved. In addition, the time that can be used with a single charge has been extended, and usability has been improved.

  The LCD according to the present invention is not limited to the notebook personal computer described in this embodiment, and is effective in reducing the size and weight of other portable information processing apparatuses and improving the battery life.

  For example, the LCD of the present invention is based on the power of the battery for information processing using an integrated circuit such as a portable information processing device for sales / order management used in portable telephones, portable game machines, retail stores, etc. It is effective in the equipment to be used.

(Example 5)
FIG. 17 shows a card type information processing apparatus using a liquid crystal display device according to the present invention. A display area 10 is formed on an opaque plastic substrate 17. The active layer of the pixel TFT is an a-Si: HTFT by substrate temperature 150 ° C. ECR plasma CVD. The peripheral circuit is a poly-Si TFT obtained by this a-Si film laser annealing. Since the laser is instantaneously heated, there is no damage to the plastic substrate. Because it is a plastic substrate, it is safe without worrying about cracking. Moreover, since the specific gravity of plastic is about 1/2 that of glass, the weight of the device was further reduced. The display mode of the liquid crystal is a reflection type. Since it is opaque, it is not necessary to consider light shielding from the lower surface of the substrate. The liquid crystal is a PDLC liquid crystal formed by coating. The driver 630 is a string type and incorporates a CPU function. A solar cell 600 is built on the substrate to supply power for the entire apparatus. Transmission / reception of information with the outside is performed by an input / output sensor 610 (for example, an LED and a photodiode) built in the substrate. In this embodiment, most members such as a power supply, a backlight, a substrate on which a control circuit is mounted, an FPC, and a case can be eliminated, and the apparatus is remarkably reduced in weight, size, and thickness. The portability of the information processing apparatus is dramatically improved. FIG. 19 shows an example in which a CPU 630 is mounted on a substrate using a string driver as a similar embodiment. FIG. 18 shows all the elements built on the substrate. In both cases, the portability of the device can be dramatically improved.

1 is a structural diagram of a liquid crystal display device. The partial top view of an active matrix substrate. The figure which shows the cross-section of a liquid crystal cell. FIG. 6 is a diagram illustrating an equivalent circuit of a pixel and a peripheral circuit of a liquid crystal display device. The partial top view of a peripheral circuit. The figure which shows the cross-section of the manufacture process of TFT. The figure which shows the cross-section of the connection part of a peripheral circuit and a driver. The figure which shows the cross-section of a liquid crystal cell. 1 is a structural diagram of a liquid crystal display device. 1 is a structural diagram of a liquid crystal display device. 1 is a structural diagram of a liquid crystal display device. 1 is a structural diagram of a liquid crystal display device. 1 is a diagram illustrating a structure of an information processing device. The partial top view of an active matrix substrate. The figure which shows the cross-section of a liquid crystal cell. The figure which shows the cross-section of a liquid crystal cell. 1 is a diagram illustrating a structure of an information processing device. 1 is a diagram illustrating a structure of an information processing device. 1 is a diagram illustrating a structure of an information processing device. The figure which shows the drive waveform of a liquid crystal display device. The figure which shows the equivalent circuit of one pixel. The figure which shows the drive waveform of one pixel.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Board | substrate, 12 ... Opposite board | substrate, 15 ... Card board | substrate, 40 ... Display area, 51 ... Video signal side peripheral circuit, 52 ... Scanning signal side peripheral circuit, 51 ... Driver, 55 ... Wiring, 80 ... Connection line,
90 ... Case, 101, 301 ... TFT, 102,302 ... Retention capacitance, 110,310 ... Semiconductor layer, 111,311 ... Scanning signal line, 113 ... Gate, 120a, 120b, 320a, 320b ... Source, 125 ... Doping mask 127, silicide, 130a, 130b, 330a, 330b, drain, 135, 335, high-concentration impurity layer, 137a, 137b, 337a, 337b, video signal line, 140, gate insulating film, 145, protective film, 146, holding Capacitance insulating film, 150 ... pixel electrode, 152 ... counter electrode, 154 ... common electrode, 170r, 170g, 160 ... black matrix, 165,520 ... reflection film, 200 ... liquid crystal, 204 ... polymer film, 205,207 ... orientation Membrane, 210, 212 ... Polarizing plate, 351 ... Valve, 352 ... Sealing material, 358 ... Adhesive, 40 DESCRIPTION OF SYMBOLS 0 ... Timing converter 410 ... Gradation voltage generation circuit, 430 ... Printed circuit board, 440 ... Back light, 510 ... Polymer matrix, 530 ... Shield pattern, 600 ... Solar cell, 630 ... Microprocessor, 610 ... I / O sensor, 640 ... Touch sensor, 904 ... Push switch, 901 ... Menu selection switch, 904 ... Numeric keypad, 902,903 ... Connector, 910 ... Battery, 920 ... Printed circuit board, 950 ... CPU board, 960 ... Memory card.

Claims (5)

An active matrix display region having a plurality of scanning signal lines and a plurality of video signal lines, a video signal side peripheral circuit having a thin film transistor connected to the video signal line, and a scanning signal having a thin film transistor connected to the scanning signal line A glass substrate on which a side peripheral circuit and one driver connected to the scanning signal side peripheral circuit and the video signal side peripheral circuit are mounted;
A counter substrate facing the glass substrate;
A liquid crystal layer sandwiched between the glass substrate and the counter substrate,
The one driver is a liquid crystal display device fixed to a glass substrate with a resin. An active matrix display region having a plurality of scanning signal lines and a plurality of video signal lines, a video signal side peripheral circuit having a thin film transistor connected to the video signal line, and a scanning signal having a thin film transistor connected to the scanning signal line A glass substrate on which a side peripheral circuit and one driver connected to the scanning signal side peripheral circuit and the video signal side peripheral circuit are mounted;
A counter substrate facing the glass substrate;
A liquid crystal layer sandwiched between the glass substrate and the counter substrate,
The scanning signal side peripheral circuit and the video signal side peripheral circuit are a liquid crystal display device disposed below the counter substrate and below a seal of the liquid crystal layer or on the display region side. The liquid crystal display device according to claim 1 or 2,
The liquid crystal display device in which the video signal side peripheral circuit distributes the video signal output from the one driver by the clock pulses output from the thin film transistor and the one driver and supplies the dispersed video signal to the plurality of video signal lines . The liquid crystal display device according to claim 1 or 2,
The scanning signal side peripheral circuit disperses the scanning signal output from the one driver by the clock pulse output from the thin film transistor and the one driver, and supplies it to the plurality of scanning signal lines. . The liquid crystal display device according to claim 1 or 2,
The liquid crystal display device in which the one driver is concentrated on a short side or a long side of the substrate.

Images