JP2004310123A - Active type display unit, and television, camera and computer using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an active type display unit with excellent display performance. <P>SOLUTION: A pixel electrode 88 comprises a thin-film transistor formed on a glass substrate, a flattening film 85 formed on the thin-film transistor, and a transparent conductive film which comes into contact with the drain electrode of the thin-film transistor; and the drain electrode is provided on an inter-layer insulator and connected directly to the drain of the thin-film transistor through a 1st contact hole formed in the inter-layer insulator, and the pixel electrode 88, on the other hand, is provided on the flattening film 85 and connected directly to the drain electrode through a plurality of 2nd contact holes formed in the flattening film 85. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an active display device, particularly to an active electro-optical device, a television, and a wall-mounted television, in which a clear gradation level can be set.

  Liquid crystal compositions have different dielectric constants in the horizontal and vertical directions with respect to the molecular axis due to their material properties, so that they can be easily aligned horizontally or vertically with an external electric field. Can be. The liquid crystal electro-optical device displays ON / OFF by controlling the amount of transmitted light or the amount of dispersion by utilizing the anisotropy of the dielectric constant.

  FIG. 2 shows the electro-optical characteristics of the nematic liquid crystal. When the applied voltage is small Va (point A 101), the transmitted light amount is almost 0%, when Vb (point B 102) is about 30%, and when Vc (point C 103) is about 80%, Vd ( In the case of D point 104), it is about 100%. In other words, if only the points A and D are used, monochrome gray scale display can be performed, and if the rising portion of the electro-optical characteristic is used like the points B and C, intermediate gray scale display can be performed. As specific voltages confirmed by the present inventors, Va = 2.0 V, Vb = 2.18 V, Vc = 2.3 V, and Vd = 2.5 V.

  Conventionally, in the case of gradation display of a liquid crystal electro-optical device using a TFT, gradation display is performed by changing a gate applied voltage of the TFT or a voltage applied between a source and a drain to adjust the voltage in an analog manner.

  A more detailed description will be given of a gradation display method of a liquid crystal electro-optical device using a TFT. Conventionally, an n-channel thin film transistor used in a liquid crystal electro-optical device has a voltage-current characteristic as shown in FIG. The voltage-current characteristics shown in FIG. 3 are a characteristic 201 of an n-channel thin film transistor using amorphous silicon and a characteristic 202 of an n-channel thin film transistor using polysilicon.

  By controlling the voltage applied to the gate electrode in an analog manner, the drain current can be controlled, and the resistance value between the source and the drain can be changed. As a result, the magnitude of the electric field applied to the liquid crystals connected in series can be arbitrarily changed by the resistance division. Thereby, gradation display is possible. Conversely, there is a method of connecting the gate electrode to the scanning signal line and changing the source-drain voltage to arbitrarily control the electric field applied to the liquid crystal.

  Whichever method is used, there is no difference in that it is an analog gradation display method that largely depends on the characteristics of the TFT. However, it is difficult to make a large number of TFT elements in a matrix configuration to have uniform characteristics. In particular, fine adjustment of an intermediate voltage required for gray scale display is very difficult with the current technology. What is needed is the current situation. As can be seen from the electro-optical characteristics of the nematic liquid crystal shown in FIG. 2, all the values are between 0.32 V from around 2.08 V which is the boundary value in the dark state to around 2.40 V which is the boundary value in the bright state. A gradation display must be performed. Assuming 16 gradations, control at an average 0.02 V interval is required.

  If the control is performed in a portion where the liquid crystal is completely turned on / off, such as a point A 101 and a point D 104 shown in FIG. 2, the voltage difference can be 0.5 V or more. It is worth degrading internal characteristic variations sufficiently. Using a plurality of writing frames, for example, by turning on (2.5 V) 6 frames out of 10 frames and turning off (2.0 V) the remaining 4 frames, the writing average voltage becomes 2.3 V. , Half-tone display is possible.

  However, in such a case, since a plurality of frames are used, there is a risk that a display of 30 Hz or less that can be visually confirmed by humans may occur, and depending on conditions, a display defect such as flicker may be caused. . As a method for preventing this, increasing the driving frequency has been proposed, but the data transfer speed of the driver IC is limited to about 20 MHz, which is difficult.

  In view of the above, the present invention proposes a means for supplying a clear gradation display level to the liquid crystal by performing digital gradation display instead of the conventional analog gradation display. Conventionally, instead of a method of simply increasing the driving frequency to perform gradation display as proposed, digital gradation is performed without changing the frame frequency by making the data transfer frequency and the gradation display frequency independent. It is characterized by displaying.

  According to the present invention, in an active matrix type liquid crystal display device, a gradation display of a display device using a display driving method having a display timing related to a unit time t for writing to an arbitrary pixel and a time F for writing one screen is described. The signal during the writing time at the time t is time-division-changed without changing the time F, whereby the average value of the electric field applied to the liquid crystal of the pixel at the time t is changed according to the division ratio, and the gradation is changed. It is characterized in that it can be displayed.

  In the case of the conventional display device, the electric field applied to the pixel electrode is determined by the strength of the electric field of the signal line in the data direction, and thereby the transmittance of the liquid crystal is determined.

  In the present invention, instead of performing such analog gradation control, a signal during a writing time of a unit time t to be written to an arbitrary pixel is time-divided, and gradations corresponding to the number of divisions can be displayed. . At this time, the electric field change during the writing time becomes the average value during the non-writing time, and a clear gradation display is possible.

  As for the data transfer speed on the information signal side, for example, in the case of a 1920 × 400 dot liquid crystal electro-optical device, a clock frequency of 5.76 MHz is required for 8-bit parallel transfer. On the other hand, when the conventional multiple frame system is used, if 10 frames are used, a clock frequency of 57.6 MHz is simply required. However, in the case of the present invention, since the clock frequency for gray scale display is independently taken, up to about 166 gray scales can be displayed when an IC having a driving capability of 8 MHz at the maximum is used. If a 12.3 MHz drive IC is adopted, the value becomes sufficiently possible up to 256 gray scale display required for visual use, and is significantly superior to the conventional analog and multi-frame digital gray scale display. Nature occurs. A more detailed description will be given below with reference to examples.

  The present invention is characterized in that digital gray scale display is performed using two independent driving frequencies, as compared with the conventional analog gray scale display. As an effect, assuming a liquid crystal electro-optical device having a number of pixels of, for example, 640 × 400 dots, it is extremely difficult to manufacture all the 256,000 TFTs without variation in characteristics. In consideration of mass productivity and yield, 16-gradation display is considered to be the limit. However, in order to clarify the applied voltage level, the controller uses the reference voltage instead of the analog value as a signal instead of an analog value. The present invention employs a method of controlling the voltage applied to the TFT by controlling the timing of inputting the reference signal and connecting the reference signal to the TFT with a digital value, thereby controlling the variation in the characteristics of the TFT. The feature is that clear digital gradation display is possible.

  Another advantage is that by using two driving frequencies, clear digital gradation display can be performed without changing the number of frames for screen rewriting. It is possible to avoid the occurrence of flicker and the like due to the decrease in the number of frames.

  When digital gradation display according to the present invention is performed, since it is hard to be affected by variation in characteristics of TFT elements, it is possible to have up to about 64 gradations, and in color display, a variety of 262,144 colors and display of subtle colors Has been realized. When projecting software such as a television image, for example, even a “rock” made of the same color has a slightly different color due to its minute dents and the like. If an attempt is made to display a color close to natural colors, it is difficult to achieve 1696 gradations of 4096 colors. The gradation display according to the present invention makes it possible to impart these minute color tone changes.

  [Example 1] (Image display device / TV) In this example, a wall-mounted TV was manufactured using a liquid crystal display device having a circuit configuration as shown in FIG. The TFT at that time was a staggered type made of polycrystalline silicon using laser annealing.

  FIG. 5 shows an actual arrangement of electrodes and the like corresponding to this circuit configuration. For simplicity, only portions corresponding to 2 × 2 (or less) are described. FIG. 1 shows an actual drive signal waveform. For the sake of simplicity, the description will be made using signal waveforms in the case of a 2 × 2 matrix configuration.

  First, a method for manufacturing a liquid crystal panel used in this embodiment will be described with reference to FIGS. In FIG. 6A, a silicon oxide film as a blocking layer 51 is formed on a glass 50 which can withstand a heat treatment at an inexpensive temperature of 700 ° C. or less, for example, about 600 ° C. by a magnetron RF (high frequency) sputtering method. It is made to a thickness of 3000 mm. The process conditions were an oxygen 100% atmosphere, a film formation temperature of 15 ° C., an output of 400 to 800 W, and a pressure of 0.5 Pa. The film formation rate using quartz or single crystal silicon as a target was 30 to 100 ° / min.

A silicon film was formed thereon by a plasma CVD method. The film formation temperature was set at 250 ° C. to 350 ° C., and was set to 320 ° C. in this example, and monosilane (SiH ₄ ) was used. Not only the monosilane (SiH _4), disilane (Si ₂ H _6), or may be used trisilane (Si ₃ H _8). These were introduced into the PCVD apparatus at a pressure of 3 Pa, and high-frequency power of 13.56 MHz was applied to form a film. At this time, an appropriate high-frequency power is 0.02 to 0.10 W / cm ² , and in this example, 0.055 W / cm ² was used. The flow rate of monosilane (SiH ₄ ) was set to 20 SCCM, and the deposition rate at that time was about 120 ° / min. NTFT of Suresshuho - to control the field voltage (Vth), boron may be added during deposition as the concentration of ^{1 × 10 15 ~1 × 10 18} cm -3 with diborane. In addition, not only the plasma CVD method but also a sputtering method or a low pressure CVD method may be used for forming the silicon layer to be a channel region of the TFT, and the method will be briefly described below.

In the case of performing the sputtering method, the back pressure before the sputtering was set to 1 × 10 ⁻⁵ Pa or less, and single crystal silicon was used as a target in an atmosphere in which hydrogen was mixed with 20 to 80% of argon. For example, argon was 20% and hydrogen was 80%. The film formation temperature was 150 ° C., the frequency was 13.56 MHz, the sputter output was 400 to 800 W, and the pressure was 0.5 Pa.

When forming by a reduced pressure gas phase method, disilane (Si ₂ H ₆ ) or trisilane (Si ₃ H ₈ ) is supplied to a CVD apparatus at 450 to 550 ° C., for example, 530 ° C., which is 100 to 200 ° C. lower than the crystallization temperature. Was formed. The pressure in the reactor was 30 to 300 Pa. The deposition rate was 50-250 ° / min.

The coating formed by these methods preferably has an oxygen concentration of 5 × 10 ²¹ cm ⁻³ or less. In order to promote crystallization, it is desirable that the oxygen concentration be 7 × 10 ¹⁹ cm ⁻³ or less, preferably 1 × 10 ¹⁹ cm ⁻³ or less. This concentration was selected because the peak current would increase. If the oxygen concentration is high, crystallization is difficult, and the laser annealing temperature must be high or the laser annealing time must be long. Hydrogen was 4 × 10 ²⁰ cm ⁻³ , which was 1 atomic% as compared with silicon 4 × 10 ²² cm ⁻³ .

In order to promote crystallization of the source and the drain, the oxygen concentration is set to 7 × 10 ¹⁹ cm ⁻³ or less, preferably 1 × 10 ¹⁹ cm ⁻³ or less, and a channel forming region of a TFT constituting a pixel is formed. Oxygen may be added only to a concentration of 5 × 10 ^{20 to} 5 × 10 ²¹ cm ⁻³ by ion implantation.

  By the above method, the amorphous silicon film 52 was formed to a thickness of 500 to 5000 Å, in this embodiment, 1000 実 施.

Thereafter, as shown in FIG. 6B, a pattern was formed by opening only the source / drain regions of the photoresist 53 using the mask P1. A silicon film to be an n-type active layer was formed thereon by a plasma CVD method. The film is formed at a temperature of 250 ° C. to 350 ° C. In this example, a film having a concentration of 320 ° C. and a concentration of monosilane (SiH ₄ ) and phosphine (PH ₃ ) based on monosilane of 3% was used. These were introduced into the PCVD apparatus at a pressure of 5 Pa, and high-frequency power of 13.56 MHz was applied to form a film. At this time, high frequency power, 0.05~0.20W / cm ² are suitable, in the present embodiment, a 0.120W / cm ^2. The specific conductivity of the n-type silicon layer obtained by this method was about 2 × 10 ⁻¹ [Ωcm ⁻¹ ]. The film thickness was 50 °.

On the other hand, as shown in FIG. 6C, a pattern was formed in which only the source / drain regions were opened in the photoresist 54 using the mask P2. A silicon film to be a p-type active layer was formed thereon by a plasma CVD method. The film formation temperature is from 250 ° C. to 350 ° C., and in this embodiment, it is 320 ° C., and monosilane (SiH ₄ ) and monosilane-based diborane (B ₂ H ₆ ) having a concentration of 2% are used. These were introduced into the PCVD apparatus at a pressure of 4 Pa, and high-frequency power of 13.56 MHz was applied to form a film. At this time, high frequency power, 0.05~0.20W / cm ² are suitable, in the present embodiment, a 0.080W / cm ^2. The specific conductivity of the p-type silicon layer completed by this method was about 1 × 10 ⁻¹ [Ωcm ⁻¹ ]. The film thickness was 50 °.

  Thereafter, source / drain regions 55 and 56 and 57 and 58 were formed by using a lift-off method. Thereafter, an N-channel type thin film transistor island region 63 and a P-channel type thin film transistor island region 64 were formed using the mask (P3) 62. (FIG. 6 (D))

Thereafter, using a XeCl excimer laser, the source / drain / channel regions were laser-annealed, and at the same time, the active layer was laser-doped. At this time, the laser energy has a threshold energy of 130 mJ / cm ² , and 220 mJ / cm ² is required to melt the entire film thickness. However, when an energy of 220 mJ / cm ² or more is irradiated from the beginning, hydrogen contained in the film is rapidly released, so that the film is destroyed. For this purpose, it is necessary to first dissipate hydrogen with low energy and then melt it. In this embodiment, after performing the purging of the hydrogen in the first 150 mJ / cm ^2, crystallization was performed at 230 mJ / cm ^2.

Due to the annealing, the silicon film shifts from an amorphous structure to a highly ordered state, and a part of the silicon film exhibits a crystalline state. In particular, a region having a relatively high order in a state after the formation of silicon is particularly likely to be crystallized into a crystalline state. However, since the silicon existing between these regions is bonded to each other, the silicon mutually pulls each other. When measured by laser Raman spectroscopy, a peak shifted from the peak of 522 cm ^-1 of single crystal silicon to a lower frequency side is observed. The apparent particle size thereof is calculated to be 50 to 500 ° when calculated from the half-value width. However, in actuality, there are a large number of regions having high crystallinity and a cluster structure. A coating having a bonded (anchored) structure could be formed.

As a result, the coating exhibits a state that may be substantially free of grain boundaries (hereinafter referred to as GB). Carriers can easily move from one cluster to another through anchored locations, resulting in higher carrier mobility than so-called polycrystalline silicon having a distinct GB. That is, electron mobility (μe) = 15 to 300 cm ² / VSec and hole mobility (μe) = 5 to 100 cm ² / VSec were obtained.

  On this, a silicon oxide film was formed as a gate insulating film to a thickness of 500 to 2000 例 え ば, for example, 1000 Å. This was performed under the same conditions as those for forming the silicon oxide film as the blocking layer. During this film formation, a small amount of fluorine may be added to fix sodium ions.

Thereafter, a silicon film containing phosphorus in a concentration of 1 to 5 × 10 ²¹ cm ^-3 or a multilayer of molybdenum (Mo), tungsten (W), MoSi ₂ or WSi ₂ is formed on the silicon film. A film was formed. This was patterned using a fourth photomask 69 to obtain FIG. Gate electrodes 66 and 67 were formed, for example, a channel length of 7 .mu.m, a gate electrode of 0.2 .mu.m of phosphorus silicon and a thickness of 0.3 .mu.m of molybdenum thereon.

  If aluminum (Al) is used as the gate electrode material, the surface is anodized after patterning with a fourth photomask 69, so that the self-alignment method can be applied. Since the drain contact hole can be formed at a position closer to the gate, the characteristics of the TFT can be further improved from the reduction of the mobility and the threshold voltage.

  Thus, a C / TFT can be manufactured without applying a temperature to 400 ° C. or more in all steps. Therefore, it is not necessary to use an expensive substrate such as quartz as a substrate material, and it can be said that the process is extremely suitable for the large-screen liquid crystal display device of the present invention.

  In FIG. 6F, a silicon oxide film was formed on the interlayer insulator 68 by the above-described sputtering method. This silicon oxide film may be formed by an LPCVD method, a photo CVD method, or a normal pressure CVD method. For example, a thickness of 0.2 to 0.6 μm was formed, and then a window 79 for an electrode was formed using the fifth photomask 70. After that, further, aluminum is formed on the whole by sputtering to a thickness of 0.3 μm, and a lead 74 and a contact 73 are formed using a sixth photomask 76. The silicon oxide film was formed by the sputtering method described above. This silicon oxide film may be formed by an LPCVD method, a photo CVD method, or a normal pressure CVD method. After that, patterning was performed using the seventh photomask 81. Thereafter, aluminum was further formed on the entire surface to a thickness of 0.3 μm by sputtering, and leads 83 and contacts 84 were formed using an eighth photomask 82. (FIG. 6 (G))

  The surface was coated with a flattening organic resin 85, for example, a translucent polyimide resin, and an electrode hole was formed again using a ninth photomask 86. Further, ITO (indium oxide / tin) was formed to a thickness of 0.1 μm on all of them by sputtering, and a pixel electrode 88 was formed using a tenth photomask 87. This ITO film was formed at room temperature to 150 ° C., and was achieved by oxygen at 200 to 400 ° C. or annealing in air. (FIG. 6 (H))

The mobility of NTFT, which is an electrical characteristic of the obtained TFT, is 80 (cm ² / Vs), Vth is 5.0 (V), the mobility of PTFT is 30 (cm ² / Vs), and Vth is 5. 5 (V). One substrate for a liquid crystal electro-optical device manufactured according to such a method was obtained.

  FIG. 7 illustrates a method for manufacturing the other substrate. A 1 μm-thick polyimide resin in which a black pigment was mixed with polyimide was formed on a glass substrate 900 by a spin coating method, and a black stripe 901 was formed using the first photomask 11. Thereafter, a polyimide resin mixed with a red pigment was formed into a film having a thickness of 1 μm by a spin coating method, and a red filter 902 was manufactured using the second photomask 12. Similarly, a green filter 903 was manufactured using the third photomask 13 and a blue filter 904 was manufactured using the fourth photomask 14. During the production, each filter was baked at 350 ° C. in nitrogen for 60 minutes. After that, the leveling layer 905 was formed using a transparent polyimide, also using the spin coating method.

  Thereafter, ITO (indium tin oxide) was formed on the entire surface by sputtering to a thickness of 0.1 μm, and a common electrode 906 was formed using the fifth photomask 15. This ITO was formed at a temperature of from room temperature to 150 ° C., and was achieved by oxygen at 200 to 300 ° C. or annealing in the air to obtain a second substrate.

  A polyimide precursor was printed on the substrate by using an offset method, and baked at 350 ° C. for 1 hour in a non-oxidizing atmosphere such as nitrogen. Thereafter, a known rubbing method was used to modify the polyimide surface, and at least initially, a means for aligning liquid crystal molecules in a certain direction was provided.

  Thereafter, the nematic liquid crystal composition was sandwiched between the first substrate and the second substrate, and the periphery was fixed with an epoxy adhesive. A drive IC having a TAB shape and a PCB having a common signal and potential wiring were connected to leads on the substrate, and a polarizing plate was attached on the outside to obtain a transmission type liquid crystal electro-optical device.

  FIG. 8 is a schematic structural diagram of the electro-optical device according to the present embodiment. The liquid crystal panel 1000 obtained in the above process was installed in combination with a rear lighting device 1001 in which three cold cathode tubes were arranged. Thereafter, a tuner 1002 for receiving television waves was connected to complete an electro-optical device. Compared to a conventional CRT type electro-optical device, the device has a planar shape, so that it can be installed on a wall or the like.

  Next, a peripheral circuit of the liquid crystal electro-optical device for completing the present invention will be described with reference to FIG. The configuration is such that a drive circuit 352 is connected to the information signal side wirings 350 and 351 connected to the matrix circuit of the liquid crystal electro-optical device. The drive circuit 352 has two parts when divided by a drive frequency system. One is a data latch circuit system 353 similar to that of the conventional driving system, which mainly has a basic clock φH355 for sequentially transferring data 356, and performs 1-bit to 12-bit parallel processing. The other is a component according to the present invention, which comprises a clock CLK 357, a magnitude comparator circuit 358, and a panel driving buffer 360 according to the division ratio required for gradation display. The counter 359 generates a pulse corresponding to the gradation display data sent from the data latch circuit system 353.

  The features of the present invention are exactly these parts. By taking two drive frequencies, clear digital gradation display is possible without changing the number of frames for screen rewriting. is there. It is possible to avoid the occurrence of flicker and the like due to the decrease in the number of frames.

10 and 11 show operation waveforms of the C / TFT according to the present embodiment. FIG. 10 is an oscilloscope photograph showing the input signal waveform to the C / TFT and the output signal waveform from the C / TFT. FIGS. 10A to 11B show the case where the drive frequency of the input signal is increased to 5 KHz, 50 KHz, 500 KHz, and further to 1 MHz. As is clear from FIG. 11B, even at 1 MHz, the output signal waveform did not so much, and a sufficiently practical output signal could be obtained.
Therefore, the number of gray scales can be calculated by dividing the driving frequency by the number of duty cycles and the number of frames. In this case, the number of gray scales of 42 obtained by dividing 1 MHz by 400 and 60 is obtained. ing.

  When analog gray scale display is performed, 16 gray scale display is the limit due to variation in TFT characteristics. However, when the digital gradation display according to the present invention is performed, since it is hard to be affected by the variation in the characteristics of the TFT elements, it is possible to display up to 42 gradations. Color display has been realized.

  Example 2 (View Finder) In this example, a view finder for a video camera using a liquid crystal electro-optical device having a diagonal of 1 inch was manufactured and the present invention was implemented.

  In the present embodiment, the number of pixels is 387 × 128, and the first substrate is provided by using the same process as in “Example 1”. In addition, a color filter and a transparent conductive film ITO were formed to a thickness of 1000 上 on the insulating substrate by the same method as in “Example 1” to obtain a second substrate.

  A polyimide precursor was printed on the substrate using an offset method, and baked at 350 ° C. for 1 hour in a non-oxidizing atmosphere, for example, nitrogen. Then, the surface of the polyimide was modified using a known rubbing method, and at least initially, a means for aligning liquid crystal molecules in a certain direction was provided to obtain first and second substrates.

  Thereafter, the nematic liquid crystal composition was sandwiched between the first substrate and the second substrate, and the periphery was fixed with an epoxy adhesive. Since the pitch of the leads on the substrate was as fine as 46 μm, they were connected using the COG method. In this embodiment, a method is used in which gold bumps provided on an IC chip are connected with an epoxy silver palladium resin, and the IC chip and the substrate are filled and fixed with an epoxy modified acrylic resin for the purpose of fixing and sealing. Using. Thereafter, a polarizing plate was adhered on the outside to obtain a transmission type liquid crystal display device.

  In the TFT according to the present embodiment, since the channel length was 5 μm, the driving frequency could be increased to about 2 MHz. Therefore, it is possible to display up to 260 gradations obtained by dividing 2 MHz by 128 and 60, that is, to display about 256 gradations. For example, when a normal analog gradation display is performed on a liquid crystal electro-optical device in which 49,152 sets of 384 × 128 dot TFTs are formed in a 50 mm square (36 sheets from a 300 mm square substrate). Since there is about ± 10% variation in the characteristics of the amorphous TFT, 16 gradation display has been limited. However, when the digital gradation display according to the present invention is performed, it is hard to be affected by the variation in the characteristics of the TFT elements, so that it is possible to display 256 gradations or more. The display of subtle colors has been realized.

"Example 3" (projection type image display device)
In this embodiment, a projection-type image display device as shown in FIG.

  In this embodiment, a projection unit for a projection type image display device is assembled using three liquid crystal electro-optical devices 1300. Each of them has a configuration of 640 × 480 dots, and 307,200 pixels were produced in a diagonal of 4 inches. The size per pixel was 127 μm square.

  As a configuration of the projection type image display device, a liquid crystal electro-optical device 1300 is divided and installed for three primary colors of light, red, green and blue, and a red filter 1301, a green filter 1302, a blue filter 1303, The plate 1304 includes a 150 W metal halide light source 1307 and a focusing optical system 1308.

  The substrate of the liquid crystal electro-optical device used in the electro-optical device of this example was a substrate having a matrix circuit of a C / TFT configuration. An element using a high-mobility TFT by a low-temperature process was formed to constitute a projection-type liquid crystal electro-optical device. A method for manufacturing a liquid crystal display device used in this embodiment is described with reference to FIGS. In FIG. 13A, a silicon oxide film as a blocking layer 602 is formed on a non-expensive glass 601 such as quartz glass which can withstand a heat treatment at 700 ° C. or less, for example, about 600 ° C. by using a magnetron RF (high frequency) sputtering method. It is manufactured to a thickness of 1000 to 3000 mm. The process conditions were an oxygen 100% atmosphere, a film formation temperature of 15 ° C., an output of 400 to 800 W, and a pressure of 0.5 Pa. The film formation rate using quartz or single crystal silicon as a target was 30 to 100 ° / min.

A silicon film was formed thereon by an LPCVD (low pressure gas phase) method, a sputtering method, or a plasma CVD method. In the case of forming by a reduced pressure gas phase method, disilane (Si ₂ H ₆ ) or trisilane (Si ₃ H ₈ ) is supplied to a CVD apparatus at 450 to 550 ° C., for example, 530 ° C. lower than the crystallization temperature by 100 to 200 ° C. To form a film. The pressure in the reactor was 30 to 300 Pa. The deposition rate was 50-250 ° / min. In order to control the threshold voltage (Vth) of the PTFT and the NTFT substantially the same, boron may be added during the film formation at a concentration of 1 × 10 ¹⁵ to 1 × 10 ¹⁸ cm ⁻³ using diborane. .

In the case of performing the sputtering method, the back pressure before the sputtering was set to 1 × 10 ⁻⁵ Pa or less, and single crystal silicon was used as a target in an atmosphere in which hydrogen was mixed with 20 to 80% of argon. For example, argon was 20% and hydrogen was 80%. The film formation temperature was 150 ° C., the frequency was 13.56 MHz, the sputter output was 400 to 800 W, and the pressure was 0.5 Pa.

When a silicon film is formed by a plasma CVD method, the temperature is, for example, 300 ° C., and monosilane (SiH ₄ ) or disilane (Si ₂ H ₆ ) is used. These were introduced into a PCVD apparatus, and a high-frequency power of 13.56 MHz was applied to form a film.

The coating formed by these methods preferably has an oxygen concentration of 5 × 10 ²¹ cm ⁻³ or less. If the oxygen concentration is high, it is difficult to crystallize, and the thermal annealing temperature must be increased or the thermal annealing time must be increased. If the amount is too small, the leakage current in the off state increases due to the backlight. Therefore, the range is set to 4 × 10 ¹⁹ to 4 × 10 ²¹ cm ⁻³ . Hydrogen was 4 × 10 ²⁰ cm ⁻³ , which was 1 atomic% as compared with silicon 4 × 10 ²² cm ⁻³ .

  After a silicon film in an amorphous state is formed to a thickness of 500 to 5000 °, for example, 1500 ° by the above method, a heat treatment at a medium temperature in a non-oxide atmosphere at a temperature of 450 to 700 ° C. for 12 to 70 hours, for example, a hydrogen atmosphere It was kept at a temperature of 600 ° C. below. Since a silicon oxide film having an amorphous structure is formed on the surface of the substrate below the silicon film, no specific nucleus is present in this heat treatment, and the whole is annealed uniformly. That is, at the time of film formation, it has an amorphous structure, and hydrogen is simply mixed.

Due to the annealing, the silicon film shifts from an amorphous structure to a highly ordered state, and a part thereof exhibits a crystalline state. In particular, a region having a relatively high order in a state after the silicon film is formed tends to be crystallized to be in a crystalline state. However, since the silicon existing between these regions is bonded to each other, the silicon mutually pulls each other. When measured by laser Raman spectroscopy, a peak shifted from the peak of 522 cm ^-1 of single crystal silicon to a lower frequency side is observed. The apparent grain size of the crystal is 50 to 500 ° when calculated from the half width, which is like a microcrystal. However, in actuality, there are a large number of regions having high crystallinity and a cluster structure. Was able to form a coating 603 having a semi-amorphous structure in which silicon was mutually bonded (anchored).

As a result, the coating exhibits a state substantially free of grain boundaries (GB). The carriers can easily move from each other through the anchored portions between the clusters, so that the carrier mobility is higher than that of polycrystalline silicon in which GB is clearly present. That is, hole mobility (μh) = 10 to ²⁰⁰ cm ² / VSec and electron mobility (μe) = 15 to 300 cm ² / VSec are obtained.

On the other hand, when the film is polycrystallized by high-temperature annealing at 900 to 1200 ° C. instead of annealing at medium temperature as described above, segregation of impurities in the film occurs due to solid phase growth from nuclei, resulting in GB. Although impurities such as oxygen, carbon, and nitrogen are increased, and the mobility in the crystal is large, a barrier is formed in GB and the movement of carriers there is hindered. As a result, a mobility of 10 cm ² / Vsec or more cannot be easily obtained. That is, in the present embodiment, a silicon semiconductor having a semi-amorphous or semi-crystalline structure is used for such a reason.

  A silicon oxide film 604 was formed thereon as a gate insulating film to a thickness of 500 to 2000 Å, for example, 1000 Å. This was performed under the same conditions as those for forming the silicon oxide film as the blocking layer. During this film formation, a small amount of fluorine may be added to fix sodium ions.

Thereafter, a silicon film containing phosphorus in a concentration of 1 to 5 × 10 ²¹ cm ^-3 or a multilayer of molybdenum (Mo), tungsten (W), MoSi ₂ or WSi ₂ is formed on the silicon film. A film 605 was formed. This was patterned using a first photomask (P1) to obtain FIG. 13 (B). In this embodiment, the channel length is 10 μm, and molybdenum is formed as a gate electrode to a thickness of 0.3 μm. At this time, the metal of the gate electrode was over-etched 600 by about 3 μm. Thereafter, a positive photoresist 607 was applied to the entire substrate.

  The resist 608 can be obtained by performing exposure and development from the back surface of the substrate using the photomask (P2). Thereafter, an n-layer was deposited by a sputtering method. After that, by lifting off the resist 608, FIG. 13D is obtained.

  Similarly, after a positive photoresist 610 is applied to the entire substrate, exposure and development are performed from the back surface of the substrate using a photomask (P3), whereby the resist 610 can be obtained. Thereafter, a p-layer was deposited by a sputtering method. After that, the resist 610 is lifted off to obtain FIG.

Next, annealing was performed again at 600 ° C. for 10 to 50 hours. Impurities of the sources 612 and 614 and the drains 613 and 615 were activated to produce N ⁺ or P ⁺ . Channel formation regions 618 and 619 are formed below the gate electrodes 616 and 617 as semi-amorphous semiconductors.

  In this way, a C / TFT can be manufactured without applying a temperature to 700 ° C. or more in all the steps even though the self-alignment method is used. Therefore, it is not necessary to use an expensive substrate such as quartz as a substrate material, which is a process very suitable for the large pixel liquid crystal display device of the present invention. In this example, thermal annealing was performed twice in FIGS. 13A and 13E. However, the annealing in FIG. 13A may be omitted depending on the desired characteristics, and both may be replaced by the annealing in FIG. 13E to shorten the manufacturing time.

  In FIG. 13F, a silicon oxide film was formed on the interlayer insulator 620 by the above-described sputtering method. This silicon oxide film may be formed by an LPCVD method, a photo CVD method, or a normal pressure CVD method. For example, it was formed to a thickness of 0.2 to 0.6 μm, and then a window 621 for an electrode was formed using a photomask (P4). Further, as shown in FIG. 13 (F), aluminum is formed on the entire surface by sputtering, and leads 622 and contacts 623 are formed using a photomask (P5). For example, a translucent polyimide resin was applied and formed, and the electrode drilling was performed again using a photomask (P6) as shown in FIG.

In order to connect the output end to the electrode of one pixel of the liquid crystal device as a transparent electrode, ITO (indium tin oxide film) was formed by a sputtering method. It was etched using a photomask (P7) to form an electrode 625. This ITO was formed at a temperature of from room temperature to 150 ° C., and was achieved by oxygen at 200 to 400 ° C. or annealing in the air. Thus, the NTFT 626, the PTFT 627, and the electrode 625 of the transparent conductive film were formed on the same glass substrate 601. The mobility of the electrical characteristics of the obtained NTFT 626 is 120 (cm ² / Vs), Vth is 5.0 (V), the mobility of the electrical characteristics of the PTFT 627 is 50 (cm ² / Vs), and Vth is 5.3 (V). (FIG. 13 (G))

  FIG. 14 shows an outline of the structure. A mixture of a fumaric acid-based polymer resin and nematic liquid crystal dissolved in xylene as a common solvent in a ratio of 65:35 to a thickness of 10 μm was formed on the substrate 1500 by die casting. Thereafter, the solvent was removed at 120 ° C. for 180 minutes in a nitrogen atmosphere to form a liquid crystal dispersion layer 1501. In this case, it was found that if the pressure was slightly reduced from the atmospheric pressure, the tact time could be reduced.

  Thereafter, ITO (indium tin oxide film) was formed by a sputtering method to obtain a counter electrode 1502. This ITO was formed at a temperature from room temperature to 150 ° C. Thereafter, a translucent silicone resin was applied to a thickness of 30 μm using a printing method, and baked at 100 ° C. for 30 minutes to obtain a liquid crystal electro-optical device.

  The functional configuration of the driving IC used in this embodiment is the same as that of the first embodiment. When a normal analog gray scale display is performed on a liquid crystal electro-optical device in which 307 × 200 sets of 640 × 480 dot TFTs are formed in a 300 mm square, there is about ± 10% variation in TFT characteristics. 16 gradation display was the limit. Since the driving frequency of the TFT according to the present embodiment could be increased to 2.5 MHz, the number of gray scales displayed could be up to 86 gray scales where 2.5 MHz is divided by 480 scanning lines and 60 frames. Therefore, when performing digital gradation display according to the present embodiment, it is possible to display up to 64 gradations because it is hardly affected by the variation in the characteristics of the TFT elements. The display of various colors has been realized.

  In the case of displaying software such as a television image, for example, even a “rock” having the same color has a slightly different color due to the degree of light corresponding to the minute depression or the like. When an attempt is made to display a color close to natural colors, it is difficult to perform the display with 16 gradations, and it is not suitable for expressing these subtle depressions. The gradation display according to the present invention makes it possible to impart these minute color tone changes.

  This liquid crystal electro-optical device can be used not only for the front type projection television shown in FIG. 12, but also for the rear type projection television.

"Example 4" (portable computer)
In this embodiment, an electro-optical device for a portable computer using a reflective liquid crystal display device as shown in FIG.

  As the first substrate used in this example, a substrate prepared in the same process as in "Example 1" was used. A mixture obtained by dissolving a nematic liquid crystal in which 15% of a fumaric acid-based polymer resin and a black dye were mixed in xylene as a common solvent at a ratio of 65:35 on the substrate to a thickness of 10 μm using a die casting method. Then, the solvent was removed at 120 ° C. for 180 minutes in a nitrogen atmosphere to form a liquid crystal dispersion layer.

  Here, a flat panel display, which was difficult with a dispersion-type liquid crystal display due to the use of a black dye, can display black when light is scattered (when there is no electric field) and display white when transmitting (when an electric field is applied). , It can be displayed like characters written on paper.

  In addition, as a reverse structure, it is possible to express white when scattering and black when transmitting without mixing a black pigment. However, in this case, the back side shown below needs to be black. This is also possible to display like a character written on paper.

  Thereafter, ITO (indium tin oxide film) was formed by a sputtering method to obtain a counter electrode. This ITO was formed at a temperature from room temperature to 150 ° C. Thereafter, using a printing method, a white silicone resin was applied in a thickness of 55 μm and baked at 100 ° C. for 90 minutes to obtain a liquid crystal electro-optical device.

4 shows a driving waveform according to the present invention. 4 shows the electro-optical characteristics of a nematic liquid crystal. The electric characteristics of a TFT made of polysilicon and amorphous silicon are shown. 1 shows a matrix circuit according to the present embodiment. 2 shows a planar structure of an element according to the present embodiment. The manufacturing process of the TFT according to the present embodiment will be described. 4 shows a process of manufacturing a counter substrate according to the present embodiment. 1 shows a configuration of a liquid crystal display device (television) according to the present embodiment. 1 shows a system configuration of a drive circuit according to the present embodiment. 4 is a photograph showing an oscilloscope waveform of TFT characteristics according to the present embodiment. 4 is a photograph showing an oscilloscope waveform of TFT characteristics according to the present embodiment. 1 shows a structure of a projection type liquid crystal electro-optical device according to the present embodiment. The manufacturing process of the TFT according to the present embodiment will be described. 1 shows a sectional view of a liquid crystal electro-optical device according to the present embodiment. 1 shows a configuration of a portable computer according to the present embodiment.

Explanation of reference numerals

50: Glass substrate 51: Blocking layer 66: NTFT gate electrode 67: PTFT gate electrode 88: Pixel electrode

Claims (23)

A thin film transistor formed on a glass substrate, a pixel electrode made of a transparent conductive film in contact with a drain electrode of the thin film transistor and a planarization film formed on the thin film transistor,
The drain electrode is provided on the interlayer insulator, and is directly connected to a drain of the thin film transistor via a first contact hole formed in the interlayer insulator,
Wherein the pixel electrode is provided on the flattening film and is directly connected to the drain electrode through a second plurality of contact holes formed in the flattening film. Type display device. A thin film transistor formed on a glass substrate, a pixel electrode made of a transparent conductive film in contact with a drain electrode of the thin film transistor and a planarization film formed on the thin film transistor,
The drain electrode is provided on the interlayer insulator, and is directly connected to a drain of the thin film transistor via a first contact hole formed in the interlayer insulator,
The pixel electrode is provided on the flattening film, and is directly connected to the drain electrode via a second plurality of contact holes formed in the flattening film,
An active display device having a curved surface from an upper surface of the planarization film to an inner surface of the second contact hole. A thin film transistor formed on a glass substrate, a pixel electrode made of ITO in contact with a drain electrode of the thin film transistor and a planarization film formed on the thin film transistor,
The drain electrode is made of aluminum, provided on an interlayer insulator, and directly connected to a drain of the thin film transistor via a first contact hole formed in the interlayer insulator;
The pixel electrode is provided on the flattening film, and is directly connected to the drain electrode via a second plurality of contact holes formed in the flattening film. Display device. A thin film transistor formed on a glass substrate, a pixel electrode made of ITO in contact with a drain electrode of the thin film transistor and a planarization film formed on the thin film transistor,
The drain electrode is made of aluminum, provided on an interlayer insulator, and directly connected to a drain of the thin film transistor via a first contact hole formed in the interlayer insulator;
The pixel electrode is provided on the flattening film, and is directly connected to the drain electrode via a second plurality of contact holes formed in the flattening film,
An active display device having a curved surface from an upper surface of the planarization film to an inner surface of the second contact hole.   5. The active display device according to claim 1, wherein the interlayer insulator is a silicon oxide film.   6. The active display device according to claim 1, wherein the flattening film is made of an organic resin.   The active display device according to any one of claims 1 to 6, wherein the active display device is an active liquid crystal display device. A television using an active display device,
The active display device,
A thin film transistor formed on a glass substrate, a pixel electrode made of a transparent conductive film in contact with a drain electrode of the thin film transistor and a planarization film formed on the thin film transistor,
The drain electrode is provided on the interlayer insulator, and is directly connected to a drain of the thin film transistor via a first contact hole formed in the interlayer insulator,
A television, wherein the pixel electrode is provided on the flattening film and is directly connected to the drain electrode via a second plurality of contact holes formed in the flattening film. . A television using an active display device,
The active display device,
A thin film transistor formed on a glass substrate, a pixel electrode made of a transparent conductive film in contact with a drain electrode of the thin film transistor and a planarization film formed on the thin film transistor,
The drain electrode is provided on the interlayer insulator, and is directly connected to a drain of the thin film transistor via a first contact hole formed in the interlayer insulator,
The pixel electrode is provided on the flattening film, and is directly connected to the drain electrode via a second plurality of contact holes formed in the flattening film,
A television having a curved surface from an upper surface of the flattening film to an inner surface of the second contact hole.   10. The television according to claim 8, wherein the interlayer insulator is a silicon oxide film.   The television according to any one of claims 8 to 10, wherein the flattening film is made of an organic resin.   12. A television, wherein the active display device according to claim 8 is an active liquid crystal display device. A camera using an active display device,
The active display device,
A thin film transistor formed on a glass substrate, a pixel electrode made of a transparent conductive film in contact with a drain electrode of the thin film transistor and a planarization film formed on the thin film transistor,
The drain electrode is provided on the interlayer insulator, and is directly connected to a drain of the thin film transistor via a first contact hole formed in the interlayer insulator,
The camera, wherein the pixel electrode is provided on the flattening film, and is directly connected to the drain electrode via a second plurality of contact holes formed in the flattening film. . A camera using an active display device,
The active display device,
A thin film transistor formed on a glass substrate, a pixel electrode made of a transparent conductive film in contact with a drain electrode of the thin film transistor and a planarization film formed on the thin film transistor,
The drain electrode is provided on the interlayer insulator, and is directly connected to a drain of the thin film transistor via a first contact hole formed in the interlayer insulator,
The pixel electrode is provided on the flattening film, and is directly connected to the drain electrode via a second plurality of contact holes formed in the flattening film,
A camera having a curved surface from an upper surface of the flattening film to an inner surface of the second contact hole.   The camera according to claim 13, wherein the camera is a video camera.   16. The camera according to claim 13, wherein the interlayer insulator is a silicon oxide film.   17. The camera according to claim 13, wherein the flattening film is made of an organic resin.   18. A camera, wherein the active display device according to claim 13 is an active liquid crystal display device. A computer using an active display device,
The active display device,
A thin film transistor formed on a glass substrate, a pixel electrode made of a transparent conductive film in contact with a drain electrode of the thin film transistor and a planarization film formed on the thin film transistor,
The drain electrode is provided on the interlayer insulator, and is directly connected to a drain of the thin film transistor via a first contact hole formed in the interlayer insulator,
The computer, wherein the pixel electrode is provided on the flattening film, and is directly connected to the drain electrode through a second plurality of contact holes formed in the flattening film. . A computer using an active display device,
The active display device,
A thin film transistor formed on a glass substrate, a pixel electrode made of a transparent conductive film in contact with a drain electrode of the thin film transistor and a planarization film formed on the thin film transistor,
The drain electrode is provided on the interlayer insulator, and is directly connected to a drain of the thin film transistor via a first contact hole formed in the interlayer insulator,
The pixel electrode is provided on the flattening film, and is directly connected to the drain electrode via a second plurality of contact holes formed in the flattening film,
A computer having a curved surface from an upper surface of the planarization film to an inner surface of the second contact hole.   21. The computer according to claim 19, wherein the interlayer insulator is a silicon oxide film.   22. The computer according to claim 19, wherein the flattening film is made of an organic resin.   23. A computer, wherein the active display device according to claim 19 is an active liquid crystal display device.

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