JPH0550727B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid crystal display device with a large display capacity used in information terminals, personal computers, etc.

[Conventional technology]

In recent years, the application of liquid crystal displays (LCDs), mainly twisted nematic type, has developed and is now being used in large quantities in the fields of wristwatches and calculators. In addition, matrix-type LCDs, which can display arbitrary characters, figures, etc., have recently been used. In order to expand the application fields of this matrix type LCD, it is necessary to increase the display capacity.

Conventional LCDs do not have a very steep rise in voltage-transmittance change characteristics, so crosstalk is likely to occur, and the number of scan lines is limited to about 100 in terms of contrast and viewing angle. In order to significantly improve this limitation, active matrix LCDs have recently been devised in which a switching element is arranged in each pixel of the LCD. Switching elements include thin film transistor elements (TFT) made of amorphous silicon (a-Si) or polysilicon (poly-Si) as semiconductor materials, and nonlinear resistors such as metal-insulator-metal elements (hereinafter abbreviated as MIM). There is an element. Figure 2 shows the basic circuit diagram of an LCD using these devices. FIG. 2A shows the nonlinear resistance element 11
is a circuit connected in series with the liquid crystal pixel 10 and further connected to the pixel row electrode 12 and the pixel column electrode 13. B, the gate of the thin film transistor element 14 is connected to the pixel row electrode 12, the source is connected to the pixel column electrode 13,
An example is shown in which the drain is connected to the liquid crystal pixel 10. Note that the other side of the liquid crystal pixel 10 becomes a counter electrode. For details, see Takahashi et al., “Liquid Crystal Display Device Using Nonlinear Active Elements,” Sharp Technical Review, Volume 24, Page 19.
(published in 1983) for details.

[Problem that the invention seeks to solve]

However, when the display capacity is increased by such a method, the number of terminals also increases accordingly. In the future, LCDs with approximately 1000 x 1000 pixels, which are about the size of an A4 sheet of paper, will not only have difficulty connecting terminals, but will also require an increase in the number of peripheral drive ICs.
This results in an increase in the volume occupied by peripheral circuit-related components, and also increases costs.

As a method to eliminate these drawbacks, a method has been proposed in which the peripheral drive IC is made into a TFT and laminated on the LCD substrate, and a prototype using poly-Si TFT has been announced. However, poly-SiTFT requires the use of a quartz substrate due to the element manufacturing temperature, and the manufacturing equipment is difficult to accommodate larger substrate areas, making it difficult to increase the area and reduce costs. . In addition, yields are expected to be low because the functions of silicon ICs are directly converted into TFTs.

SUMMARY OF THE INVENTION An object of the present invention is to provide a matrix terminal type liquid crystal display device that eliminates such conventional drawbacks and reduces the number of terminals connected to an external drive circuit.

[Means for solving problems]

The present invention provides a matrix terminal type liquid crystal display device in which at least one of a row decoder section and a column decoder section is formed on the same substrate as a display section, wherein the display section has a large number of row electrode terminals and a large number of columns. The display device is an active matrix liquid crystal display device having electrode terminals, and the row decoder section is connected to each row electrode terminal, and each row electrode terminal is connected to a terminal row electrode and a terminal column electrode by matrix wiring via peripheral two-terminal elements. The column decoder section is connected to each column electrode terminal, and each column electrode terminal is converted into a terminal row electrode and a terminal column electrode by matrix wiring via peripheral two-terminal elements. It is a terminal type liquid crystal display device. In the present invention, the two-terminal element typically refers to a capacitor element or a resistance element. In order to distinguish it from the nonlinear resistance elements connected to each liquid crystal pixel as shown in FIGS. 2A and 2B, such a two-terminal element used for forming a matrix of terminals will be hereinafter referred to as a peripheral two-terminal element.

Furthermore, the active matrix liquid crystal display device refers to an LCD in which a switching element is arranged in series for each liquid crystal pixel, as shown in FIGS. 2A and 2B.

A circuit array of a liquid crystal display device obtained by the present invention is shown in FIG. 1, and the structure of the present invention will be explained below based on FIG.

The present invention includes a display section 1, a row decoder section 2, a column decoder section 3, and a drive section 4. The display unit 1 may be a simple matrix LCD using a conventional twisted nematic (TN) type liquid crystal, but in terms of display capacity and contrast, each pixel 5 is
An active matrix LCD with the circuit configuration shown in (b) is desirable.

The row decoder section and the column decoder section are the main parts of the present invention. In the former, as shown in FIG. 1, pixel row electrode terminals 6 from which each pixel row electrode is drawn are formed into a matrix through peripheral two-terminal elements 28.
The terminal row electrodes 7 and terminal column electrodes 8 are converted into terminal row electrodes 7 and terminal column electrodes 8. It is a kind of decoder. When there are N pixel row electrode terminals 6, the number of terminal row electrodes and terminal column electrodes is √
A total of 2√ books is connected to the external drive unit 4. If √ is not an integer, the number of terminal row and column electrodes is an integer larger than √ and closest to it. Further, the numbers of terminal row and column electrodes do not need to be the same, and it is sufficient that the number of terminal rows and column electrodes is equal to or greater than the number of pixel row electrode terminals by multiplying them. The latter column decoder section also has basically the same configuration as the row decoder section.

A terminal row electrode and a terminal column electrode of the row decoder section and the column decoder section are connected to a driving section. The drive section is typically one or several integrated circuit devices (ICs).
Consists of.

A method for driving the matrix terminal type liquid crystal display device of the present invention will be described below.

Pixel row electrode terminal 6 and pixel column electrode terminal 9 of the display section
The voltage waveform applied to the LCD is basically the same as that of a normal simple matrix type or active matrix type LCD. Further, the voltage waveforms applied to the terminal row electrodes 8 and the terminal column electrodes 7 are set so that such voltage waveforms are obtained. Here, the relationship between the voltage applied to the terminal row/column electrodes 8 and 7 and the voltage applied to the pixel row or column electrode terminals 6 and 9 is as follows, regardless of whether the two-terminal element is a capacitor element or a resistor element. The relationship is the same as the relationship between the row and column terminal voltages of a simple matrix and the voltage applied to the liquid crystal. Therefore, the voltage averaging driving method is also used in the display device of the present invention. A driving method when the present invention is applied to a TFT-LCD in which thin film transistors (TFT) are stacked will be specifically explained.

First, the row decoder section will be explained. For simplicity, a case will be explained in which there are four pixel row electrode terminals 6, two terminal row electrodes 7, and two terminal column electrodes 8.
Naturally, this driving method can be applied when there are N pixel row electrode terminals and √ terminal row electrodes and terminal column electrodes each. An example of a main line decoder is shown in FIG. In this way, our decoder uses a capacitor as a two-terminal element, and the 2×
2 matrix. The pixel row electrode is 2
connected between two capacitors. This corresponds to a portion extracted from FIG. Next, FIG. 8 shows voltage waveforms applied to each of the first terminal row electrode A1, the second terminal row electrode A2, the first terminal column electrode B1, and the second terminal column electrode B2. The drive waveform example shown here is based on the so-called 1/3 bias multiplex drive method. When such a waveform is applied, the signals C1, C2, C3, and C4 applied to the first to fourth pixel row electrodes are the average values of the signals applied to the terminal row electrodes and the terminal column electrodes, respectively. The waveform is shown in FIG.

In this way, high voltages are applied to the first to fourth terminal row electrodes in response to T1, T2, T3, and T4, and in response to these high voltage pulses, the gates of the TFTs are turned on and the liquid crystal is charged. . The ratio of this peak voltage to the bias voltage is 3, and this peak voltage is
The on voltage and bias voltage applied to the TFT gate become the off voltage. Furthermore, the ratio of the voltages applied to the terminal row and column electrodes is only determined, and the absolute value is determined from the current-voltage characteristics of the TFT. Further, it is easy to add an offset, and it can correspond to any TFT current-voltage.

Based on the voltage waveforms C1, C2, C3, and C4 applied to the first to fourth pixel row electrodes shown in FIG.
The driving of the TFT-LCD will be explained next. The drain current-gate voltage characteristics shown in Figure 9 are
This is an example of a characteristic. Generally, to drive a TFT-LCD, the drain current of the TFT is about 10 ^-6 amperes or more when the TFT, which writes voltage to the liquid crystal pixels, is on, and about 10 ^-12 amperes or less when the TFT, which holds the voltage, is off. That's fine.
As shown in Figure 9, the drain current-gate voltage characteristics of TFTs have strong nonlinear characteristics, so the off voltage is 4V, the on voltage is 12V, and the ratio of the two is 1:
3, it is possible to satisfy the drain current condition of .

The above is an explanation of the driving method for the row decoder section.
The column decoder section can also be driven in a similar manner using the nonlinear electro-optic characteristics of the liquid crystal. Furthermore, although the above explanation relates to driving a TFT-LCD, the same applies when the present invention is applied to an active matrix LCD using a metal-insulator-metal (MIM) element, which is a nonlinear resistance element. A driving method is used.

〔Example〕

The present invention will be described in detail below based on Examples.

Example 1 This example is an example in which the present invention is applied to an active matrix type LCD using a metal-insulator-metal (MIM) element, which is a type of nonlinear resistance element. A capacitor element is used as the peripheral two-terminal element 28. FIG. 3 shows a cross-sectional view of a representative example of an MIM element and a liquid crystal pixel. A cross-sectional view of a typical example of a capacitor element of a decoder is shown in FIG.

First, the process of forming a film on the lower glass substrate 19 will be explained. In FIGS. 3 and 4, the lower glass substrate 19 is first coated with a protective layer 18 of Ta ₂ O ₅ , SiO ₂ or the like. Although this protective layer 18 prevents sodium ions and the like from entering from the glass, it is not essential and can be omitted. On top of this, tantalum (Ta) is formed to a thickness of 4000 Å using DC sputtering in ordinary argon (Ar). Patterned by photolithography using normal dry etching,
A pixel row electrode 12 and a peripheral lower electrode 21 were used. After coating with resist, anodic oxidation is performed in 0.1wt% citric acid to form a layer on the pixel row electrode 12.
An insulating layer 14 made of tantalum pentoxide (Ta ₂ O ₅ ) with a thickness of 500 Å and a layer of 2000 Å on the peripheral lower electrode 21.
A dielectric material 22 of Ta ₂ O ₅ was formed. The upper electrode 15 and the upper peripheral electrode 23 were made of chromium (Cr) and were formed by a normal vacuum deposition method and then patterned by photolithography. The pixel electrode 16 was made of a transparent indium oxide-tin oxide (ITO) electrode, formed by magnetron sputtering, and patterned by ordinary photolithography.

Film formation and patterning on the upper glass substrate 20 are almost the same as those on the lower glass substrate. However, Ta and Ta ₂ O ₅ are used only to form capacitor elements in the decoder and not to form MIM elements.
Furthermore, the pixel column electrodes 13 are made of ITO, and are formed in a stripe shape as in a normal simple multiplex.

By the above manufacturing method, 400 pixel row electrodes 12
and 400 pixel column electrodes 13 were formed to form a display section of 400×400 pixels with a pixel pitch of 0.3 mm. As shown in Figure 1, the capacitor element
A column decoder was formed, with 20 terminal rows and 20 column electrodes each. That is, according to the present invention, the number of external terminals is
There was a single-digit decrease from 800 to 80. This results in
The number of drive ICs was also reduced from 20 to 2, resulting in significant cost reductions.

These upper and lower glass substrates are connected to ordinary TN
TN type LCD (Merck, ZLI-1565) is pasted and sealed using the method used for type LCDs.
The LCD according to the present invention was completed by injecting the liquid and attaching a polarizing plate. The cell thickness is 8 μm, and the polarizing plate is NPF-1100H manufactured by Nitto Denko.

When the LCD according to this example was driven using a 1/5 bias voltage averaging method, the contrast ratio was 5:
The viewing angle obtained with No. 1 was as wide as ±50°, and display characteristics almost equivalent to that of a static display were obtained.

In this embodiment, the MIM is formed on the pixel row electrode side, but an LCD having the same function as this embodiment can also be realized by forming the MIM on the pixel column electrode side.

Furthermore, in this embodiment, decoders are provided for both the pixel row electrode terminals and the pixel column electrode terminals to form a matrix, but it is also possible to form only one of them into a matrix, and this alone can reduce the number of terminals by half. Decrease nearby.

Example 2 In this example, a prototype was manufactured using the same manufacturing method as in Example 1, except that the peripheral two-terminal element was changed from the capacitor element shown in FIG. 4 to the resistor element shown in FIG. 5. The thin film resistor 24 is Ta or tantalum nitride (TaN). The former was formed by DC sputtering of Ta in argon and the latter in argon containing some nitrogen. Patterning was performed by photolithography using dry etching. Further, in order to adjust the resistance value, a meandering pattern or the like was used for the thin film resistor 24 as appropriate.

Similarly to Example 1, the LCD according to this example also had display characteristics comparable to those obtained when statically driven.

Example 3 This example describes an active film using a-Si TFT.
This is an example in which the present invention is applied to a matrix LCD.
A capacitor element is used for the peripheral two-terminal element,
Section 6 shows a cross-sectional view of typical examples of TFT elements and liquid crystal pixels.
As shown in the figure. A cross-sectional view of a typical example of a capacitor element of a decoder is already shown in FIG.
In this embodiment, both the row and column decoders are formed on the lower glass substrate side. The steps are basically the same as in Example 1. Components that are the same as those in FIGS. 3 and 4 will be explained using the same numbers.

In this example, tantalum was first formed on the protective layer 18 by DC sputtering. It is patterned by dry etching, and the pixel row electrode 1
2 and the peripheral lower electrode of the capacitor. These were anodized to form Ta ₂ O ₅ with a thickness of 2000 Å, which served as the gate insulating layer 25 and a dielectric. After this, the a-Si layer 26 is formed and the pixel column electrodes and connection electrodes 26 are made of metal such as Cr, as in the normal TFT manufacturing method.
7 was formed. Furthermore, the upper peripheral electrode of the decoder section was also formed of Cr at the same time. After that, a pixel electrode was formed using ITO.

The upper glass substrate 20 has ITO on the protective layer 18.
The counter electrode 15 is simply attached solidly.

A TN type LCD was manufactured by combining these two substrates and using the same method as in Example 1. By driving this in the same manner as in Example 1, display characteristics comparable to static driving were obtained.

Example 4 This example was fabricated using the same manufacturing method as Example 1, except that the peripheral two-terminal element was replaced with the MIM element shown in FIG. 3 instead of a capacitor element. Similarly to Example 1, the LCD according to this example had a display performance comparable to that achieved when statically driven.

〔Effect of the invention〕

As explained above, according to the present invention, the number of terminals taken out to the outside from a large display capacity liquid crystal display device can be reduced by about one order of magnitude, thereby significantly reducing the number of terminal connection points and the number of driving ICs. This can be realized and has the effect of greatly contributing to cost reduction and downsizing of the device.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an embodiment of a matrix terminal type liquid crystal display device according to the present invention, and FIG.
A circuit diagram of one pixel of an active matrix type LCD, FIG. 3 is a cross-sectional view of the structure of one pixel of Examples 1 and 2, and FIG. 4 is a cross-sectional view of the structure of the peripheral two-terminal element of Examples 1 and 3. 5 is a structural sectional view of a peripheral two-terminal element of Example 2, and FIG. 6 is a structural sectional view of one pixel of Example 3. FIG. 7 is a diagram showing an example of a row decoder, and FIG. 8 is a diagram showing signals applied to terminal row electrodes and terminal column electrodes, and signals applied to pixel row electrode terminals accordingly. Figure 9 is
FIG. 3 is a diagram showing an example of drain current-gate voltage characteristics of a TFT. 1... Display section, 2... Row decoder section, 3... Column decoder section, 4... Drive section, 5... Pixel, 6...
Pixel row electrode terminal, 7...Terminal row electrode, 8...Terminal column electrode, 9...Pixel column electrode terminal, 10...Liquid crystal pixel, 11...Nonlinear resistance element, 12...Pixel row electrode, 13... Pixel column electrode, 14... Thin film transistor element, 15... Counter electrode (upper electrode), 16
... Pixel electrode, 17 ... Liquid crystal layer, 18 ... Pixel column electrode, 19 ... Lower glass substrate, 20 ... Upper glass substrate, 21 ... Lower peripheral electrode, 22 ... Dielectric, 23 ... Upper peripheral electrode, 24... thin film resistor, 25... gate insulating layer, 26... d-Si layer,
27... Connection electrode, 28... Peripheral two-terminal element.

Claims (1)

[Claims] 1. A matrix terminal type liquid crystal display device in which at least one of a row decoder section and a column decoder section is formed on the same substrate as a display section, wherein the display section has a large number of row electrode terminals and a large number of column electrode terminals. The row decoder section is connected to each row electrode terminal, and each row electrode terminal is converted into a terminal row electrode and a terminal column electrode by matrix wiring via peripheral two-terminal elements, The column decoder section is connected to each column electrode terminal, and each column electrode terminal is converted into a terminal row electrode and a terminal column electrode by matrix wiring via a peripheral two-terminal element. Display device.