JPH036507B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an active matrix liquid crystal display device using vertically structured junction transistors.

[Conventional technology]

Active matrix substrates drive display devices in a quasi-static manner, so they are attracting attention as a method for producing large panels with high contrast. In this method, a transistor is placed on one electrode of a display medium (liquid crystal or electroluminescent element), and switching is performed directly within the matrix. FIG. 1 shows a conventional matrix cell circuit. The address line X in the matrix of X rows and xy columns controls ON/OFF of the transistor 2 of the cell, and the data line Y transfers data as a voltage signal from the source to the drain 5 of the transistor. Capacity 3 is a transistor
The signal level is maintained from the time it is turned off until the next refresh. The liquid crystal body 4 is driven between the common electrode potential Vc and the cell drive output 5.

Figure 2 is a plan view of this cell, and the transistors and capacitors are formed on a silicon wafer in exactly the same way as in the IC process using normal silicon gate technology. The portion 14 from which the field film is removed has the thickness of the gate film and constitutes an address line, and the gate 10 of the transistor and the electrode 11 of the capacitor are made of polycrystalline silicon. In addition, the data line and drive electrode 13 are
It is Al. Also, contact holes 7, 8, and 9 are made of Al.
and the substrate or Al and polycrystalline silicon.

FIG. 5 shows a cross section of one element formed from this substrate into a panel shape. On the silicon wafer 35, there is an Al drive electrode 37 in a film type, forming a lower electrode.
Further, the Nesa film 39 on the glass substrate 36 serves as a common electrode, and the liquid crystal body 38 is sandwiched between these two electrodes. Further, a polarizing plate 32 is used in the direction of light incidence to increase contrast.

Although the above example uses a silicon wafer as the substrate, an insulating substrate such as quartz glass may also be used as the substrate. That is, a similar configuration can be achieved by using a thin film of silicon such as polycrystalline silicon formed on an insulating substrate such as quartz glass.

As is clear from Figure 2, in this type of active matrix liquid crystal display device, most of the MOS transistor components, address lines, and data lines do not contribute to driving the liquid crystal. The only portion that contributes to driving is the drive electrode 13 portion. Therefore, according to this configuration, the aperture ratio of the liquid crystal (area driven and displayed/total area of the display panel) is only 50% even with efficient design. 50% of the display area does not contribute to the liquid crystal display.

Furthermore, the data storage capacitor was intentionally formed below the drive electrode section between the silicon gate electrode, the SiO ₂ film, and the semiconductor layer.

Furthermore, the above conventional example requires a large number of manufacturing steps and has a complicated structure, resulting in a significantly low yield.

[Problem to be solved by the invention]

However, with the above-mentioned conventional technology, the aperture ratio of the liquid crystal display device is small, it is necessary to create a storage capacity to drive the liquid crystal, and the manufacturing process is large and the structure is complicated, so the yield is extremely low. The problem is that it is low.

Therefore, the present invention is intended to solve such problems, and its purpose is to significantly improve the aperture ratio of active matrix liquid crystal display devices, eliminate the need to create a data storage capacity, and improve manufacturing efficiency. The goal is to significantly reduce the number of steps and significantly improve yield.

[Means to solve the problem]

The active matrix liquid crystal display device of the present invention has a liquid crystal sealed in a pair of insulating substrates, a transparent electrode formed on one of the insulating substrates,
In an active matrix display device having a data line, an address line formed on the other substrate of the insulating substrate, and an intersection switching transistor formed at an orthogonal intersection of the data line and the address line, the switch The switching transistor includes a first silicon thin film of a first conductivity type provided on the insulating substrate, a second silicon thin film of a second conductivity type provided on the first silicon thin film, and a second silicon thin film of a second conductivity type provided on the first silicon thin film. a junction transistor comprising a third silicon thin film of a first conductivity type provided, the first silicon thin film being supplied with a data signal, the second silicon thin film being supplied with an address signal, and the third silicon thin film being supplied with a data signal; The thin film is characterized in that it is connected to a liquid crystal drive electrode.

〔Example〕

FIG. 3 is a cell diagram of a matrix used in the present invention. The transistor 19 is a vertical thin film transistor, and may be a junction type or bipolar transistor. The conduction of the source 16 and drain 18 is controlled by the gate or base 17. Unlike in FIG. 1, the data holding capacitor 20 uses the address line as one electrode and drives the liquid crystal 21.

FIG. 4A shows a plan view of the cell 24, in which 26 is an address line, 25 is a data line, and 27 is a liquid crystal drive electrode that also serves as the drain of a transistor and one electrode of a capacitor. B is a cross-sectional view, and the method for manufacturing this substrate includes, for example, forming on a substrate 28 an amorphous or polycrystalline silicon layer 29 doped with phosphorus to serve as a collector or a source. When patterning is performed using a photo process or the method of the present invention, the pattern is simple and precision is not required, so the silicon layer may be formed using a mask. Furthermore, a thin amorphous or polycrystalline silicon layer 3 doped with boron serves as a gate or base.
0 is formed by photoetching or mask deposition method. Thereafter, an amorphous or polycrystalline silicon layer 31 doped with phosphorus and serving as an emitter or drain is formed by photo-etching or mask deposition. If the characteristics are still insufficient, further annealing is performed. For example, when the entire surface is irradiated with a pulsed laser, grains of amorphous or polycrystalline silicon grow, resulting in properties close to those of single crystal. As a result, the silicon layers 29, 30, and 31 form a transistor, and a junction capacitance is formed between the silicon layers 30 and 31, and at the same time, the silicon layer 31 becomes a driving electrode for the liquid crystal.

FIG. 6 shows an example in which a vertical transistor is formed as a junction type punch-through transistor. The polycrystalline silicon layer 41 on the source side has a thickness of approximately 1500 mm.
Å, concentration is 5×10 ¹⁹ /cm ³ , gate polycrystalline silicon layer 42 has a thickness of 5000 Å, concentration is 1×10 ¹⁷ /cm 3
cm ³ , polycrystalline silicon layer 40 on the drain side
has a thickness of 2000 Å and a concentration of 1×10 ¹⁸ /cm ³ , and the P-type silicon layer 42 has N-type silicon layers 41 and 42.
- bias against. As a result, depletion layer regions 43 and 44 spread at the junction surface, and the width of this spread varies depending on the bias potential of the polysilicon layer 42 serving as the gate. If a deep bias is applied, the depletion layer 44 expands and reaches the depletion layer 43, causing a punch-through current between the source and drain. This characteristic is shown in FIG. The voltage applied to the source and drain is 0~
If it is 5V, if you want to turn off the transistor, you can set the gate to OV and it will turn off in any state, and if you want to turn the transistor on, you can set the gate to -10V and it will turn on for any signal level.

Figure 8 shows the signal waveform when this transistor is used to drive a cell.Unlike in the conventional case, the data storage capacitor is located between the address line
Even if the data Vy is written, when the X signal returns the transistor to the OFF level, the drive level also increases at the same time as △VG. Therefore, the data is set lower than the desired drive voltage by ΔVG in advance.

The structure shown in Figure 6 is of the P-N-P type,
Actually, it may be an N-P-N type, and other variations are also conceivable as long as they are vertical types that comply with the spirit of the present invention. In FIG. 9, a second semiconductor layer 52 is further formed on a first semiconductor layer 53 on a substrate 49. In FIG. Furthermore, a third semiconductor layer 51 is formed thereon, and at the same time Al 50 is used as a drive electrode. The first and second layers are preferably amorphous or polycrystalline silicon thin films. The third layer is a semiconductor film such as a Nesa film (SnO ₂ ), and Al may not be formed thereon. Further, a Schottky junction using a metal layer such as Al may be used instead of the third semiconductor layer.

〔Effect of the invention〕

As described above, the active matrix liquid crystal display device made of vertically structured junction transistors of the present invention has the following effects compared to the active matrix liquid crystal display device using conventional horizontally structured MOS transistors.

b) According to the above configuration, it is possible to fill almost the entire display area of the liquid crystal display device with a plurality of drive electrodes, and the portion that does not contribute to driving the liquid crystal can be reduced to almost zero, so that the liquid crystal display The aperture ratio of the device is close to 100%. Therefore, the active matrix liquid crystal display device of the present invention has twice the brightness and contrast compared to the conventional active matrix liquid crystal display device using MOS transistors, which can only obtain an aperture ratio of 50%. It becomes possible to provide an excellent display device.

(b) Furthermore, in the liquid crystal display device using the vertically structured junction transistor of the present invention, the floating capacitance of the transistor itself can be used as the storage capacitor for driving the liquid crystal, so there is no need to create a storage capacitor. Therefore, it is necessary to create a storage capacity to drive the liquid crystal.
Compared to liquid crystal display devices using MOS transistors, this device is superior in terms of man-hours and yield.

c) In addition, a junction transistor with a vertical structure is
Since the structure is simpler than that of a MOS transistor, the manufacturing process can be simplified and the yield can be significantly improved. For example, in the case of a conventional MOS transistor, the mask process requires 4
However, the vertical structure junction transistor of the present invention requires only three times.

[Brief explanation of the drawing]

FIG. 1 is a cell diagram of a conventional active matrix, and FIG. 2 is a plan view of the conventional cell.
FIG. 3 is a diagram of a matrix cell according to the present invention, and FIGS. 4A and 4B are specific examples thereof. FIG. 5 is a cross section of the matrix panel. FIG. 6 shows a specific example of a transistor used in the present invention, and FIG. 7 shows an example of its characteristics. Further, FIG. 8 shows an example of the operating waveforms of the matrix cell of the present invention, and FIG. 9 shows another specific example of the transistor used in the present invention. 4, 21... Liquid crystal, 10... Gate, 11... Capacitor electrode, 13... Al drive electrode, 7, 8, 9... Contact hole, 25, 35... First layer semiconductor layer, 26, 53... Second layer layer semiconductor layer, 27,5
1... Third semiconductor layer, 28... Substrate, 43, 4
4...depletion layer region, 50...Al.

Claims (1)

[Claims] 1. A transparent electrode formed on one of the pair of insulating substrates, in which a liquid crystal is sealed;
In an active matrix display device having a data line formed on the other substrate of the insulating substrate, an address line, and a switching transistor formed at an orthogonal intersection of the data line and the address line, the switching The transistor includes a first silicon thin film of a first conductivity type provided on the insulating substrate, a second silicon thin film of a second conductivity type provided on the first silicon thin film, and a second silicon thin film provided on the second silicon thin film. a junction transistor comprising a third silicon thin film of a first conductivity type, the first silicon thin film being supplied with a data signal, the second silicon thin film being supplied with an address signal, and the third silicon thin film being supplied with a data signal;
An active matrix liquid crystal display device characterized in that the silicon thin film also serves as a liquid crystal drive electrode.