JPH03114029A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To improve the adhesion of a semiconductor layer and a gate electrode to a glass substrate by forming an insulating film on the substrate and a thin film transistor on the insulating film. CONSTITUTION:A polysilicon film is formed on a glass substrate 40, a gate 43 and a capacitor electrode 42 are formed on the polysilicon film and an insulating film 44 is further formed. A second polysilicon film 45 is then formed and annealed by irradiation with laser beams. Al is deposited on the film 45 and photoetched to form source and drain electrodes 46, 47. The adhesion of the resulting thin film transistor to the glass substrate 40 is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid crystal display device equipped with a thin film transistor.

[Prior Art] A display panel using a conventional active matrix allows the matrix size to be much larger than that of a dynamic method, and is attracting attention as a method capable of realizing a large panel with a large number of dots.

Particularly in light-receiving devices such as liquid crystals, there is a limit to the driving duty of the dynamic method, and active matrix applications are being considered for television displays and the like.

FIG. 1 shows one cell of a conventional active matrix.

The address line X is input to the gate of the transistor 2, and the transistor is turned on to cause the signal on the data line Y to be stored as a charge in the holding capacitor 3. This capacitor 3 holds the data until data is written again, and at the same time drives the liquid crystal 4.

Here, VC is a common electrode signal. Since liquid crystal leakage is very low, it is sufficient to hold charge for a short period of time. The manufacturing method for transistors and capacitors here is exactly the same as the normal IC process.

FIG. 2 is an example in which the cell shown in FIG. 1 is produced by a silicon gate process.

A transistor 10 and a capacitor 11 are constructed on a single crystal silicon wafer. The address line X and the upper electrode 11 of the capacitor are made of polycrystalline silicon (polysilicon), the data line Y and the liquid crystal drive electrode 13 are made of A1, and the contact holes 7, 8. 9 connects the substrate and A1, and the polysilicon and A1, respectively.

However, since such a structure requires a complicated process and has problems such as difficulty in controlling yield, a display body in which thin film transistors are formed on a transparent substrate has been considered.

When using such a thin film transistor, amorphous silicon, polysilicon, or the like has been used as the semiconductor thin film.

[Problems and objects to be solved by the invention] When such a thin film transistor is formed on a glass substrate, there is a drawback that the semiconductor layer or gate electrode of the thin film transistor and the glass substrate have poor adhesion and are easily peeled off. there were. Another drawback is that impurities from the glass substrate diffuse into the channel portion of the thin film transistor, disrupting the characteristics of the transistor.

[Means for Solving the Problems] The present invention provides a liquid crystal that includes a liquid crystal sealed between a pair of substrates, a pixel electrode arranged in a matrix on the substrate, and a thin film transistor connected to the pixel electrode. In the display device, the substrate is made of a glass substrate, an insulating film is formed on the substrate, and the thin film transistor is formed on the insulating film.

[Embodiment] FIG. 3 shows a matrix cell used in the present invention.

The only difference from FIG. 1 is that a capacitor GND wiring is newly provided, and the basic circuit is the same.

The GND potential in this case means a constant bias, and the bias level does not matter.

FIG. 4 shows an example of cell structure.

(A) is a plan view in which the address line 26 is the data line 25.
, and serves as the gate of a channel 28 of a transistor whose source and drain are the driving electrode and the electrode 29 of the capacitor. Further, the GND line 27 is constructed at the same time as the address line 26, and forms a capacitor between the GND line 27 and the electrode 29. Figure 4 (
B) shows a cross section taken along the AE line of (A).

To explain an example of the manufacturing process, approximately 3000 polysilicon films are grown as a silicon thin film on a high melting point glass substrate 31 such as quartz, and then P ions are implanted into the entire surface to make it N type. However, in some cases, a thin layer of SiO2 may be formed in advance to improve adhesion.

Furthermore, after forming the gate 26 and the capacitor electrode 27 by photo-etching, the S
An i02 film 30 is grown as a gate insulating film and a dielectric film for a capacitor. After that, a second layer of polysilicon is applied and a pattern is formed by photo-etching, and then P ions are implanted again in areas other than the channel area 28 using a resist mask to create a liquid crystal that also serves as source/drain electrodes, data line wiring areas, and capacitor electrodes. form a drive electrode.

By irradiating the channel portion 28 with a laser locally or uniformly over the entire substrate to melt and solidify the polysilicon in a short time to grow grains, performance such as threshold value and conductance can be improved. can be done. This is what is called laser annealing.

In the structure shown in FIG. 4, an electrode that transmits light is used, but an A1 electrode may be further placed on this electrode.

FIG. 5 shows a simple cross section of a liquid crystal display device using the matrix substrate of the present invention.

A liquid crystal body 38 is sandwiched between a quartz substrate 35 on which a polysilicon electrode 37 is placed and a glass 36 on which a common electrode 39 made of a Nesa film is placed, and further sandwiched between polarizing plates 32 and 33, and then a reflecting plate 34 is attached to the lower side.

In this case, most of the light incident from above passes through the polysilicon electrode 37, is reflected by the reflection plate 34, and is sensed by the human eye. This method uses a regular FE type liquid crystal, so it has high contrast and a wide viewing angle.

FIG. 6 shows a cross section of a cell formed on an ordinary glass substrate as another example of the present invention. A polysilicon film is formed on a glass substrate 40 by a low-temperature film formation method such as sputtering or plasma CVD. Then, a gate 43 and a capacitor electrode 42 are formed by zero-order photoetching in which P ions or B ions are implanted into the entire surface. Furthermore, an insulating film 44 is formed.

This also uses 5i02 or the like grown at low temperature.

Furthermore, a second layer of polysilicon, which also serves as the source/drain of the transistor, the capacitor, and the drive electrode, is formed at a low temperature.

The polysilicon is either completely undoped or implanted with B ions in sufficient quantities to provide an enhancement of the threshold value.

Thereafter, a laser beam is applied locally or to the entire surface to anneal it. A portion of the laser beam is absorbed by the first layer of polysilicon, but is transmitted through the glass substrate 40. Therefore, in order to activate the ion-implanted impurities in the first layer of polysilicon and to grow the grains of the second layer of polysilicon (particularly in the channel region 48), the energy of the beam is appropriate and the period of time (pulsed laser If the pulse interval, C
When processed with a W laser (depending on the scanning speed), annealing is possible within a range that has almost no effect on the glass substrate.

The feature of this method is that laser annealing has much less effect on the glass substrate than conventional thermal annealing, so it is possible to use low-cost glass.
Laser annealing is capable of simultaneously activating impurities and growing polysilicon grains in the channel region, thereby improving transistor characteristics (particularly mobility).

Thereafter, A1 is attached and photoetched to form source/drain electrodes 46 and 47. Since it is difficult to make contact between Al and polysilicon as they are, it may be necessary to perform some heat treatment or irradiate them with a weak laser beam.

[Effects] The present invention provides a liquid crystal display device having a liquid crystal sealed between a pair of substrates, a pixel electrode arranged in a matrix on the substrate, and a thin film transistor connected to the pixel electrode. is made of a glass substrate, an insulating film is formed on the substrate, and the thin film transistor is formed on the insulating film. Therefore, when forming the thin film transistor on the glass substrate, the glass substrate and the thin film transistor are This has the effect of greatly improving adhesion.

Further, since it is possible to prevent impurities from the glass substrate from diffusing into the channel portion of the thin film transistor, it has the effect of stabilizing the characteristics of the transistor.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a cell used in a conventional active matrix. FIG. 2 is a plan view of a cell using bulk silicon. FIG. 3 is a cell diagram of the present invention. FIGS. 4(A) and 4(B) are a plan view and a sectional view of an example of its implementation. FIG. 5 is a sectional view when the substrate of the present invention is mounted on a panel. FIG. 6 is a diagram showing another embodiment of the present invention. 7, 8. 9...Contact hole 10...Polysilicon gate 11...Polysilicon upper electrode 13 of capacitor 3...Drive electrode by A1 26.27...First layer polysilicon 25.29...
・Second layer polysilicon 28...Channel 31...Quartz substrate 32, 33...Polarizing plate 34...Reflector 35, 36...Transparent substrate 39...Nesa film 37... Polysilicon drive electrode 38...Liquid crystal body 40...Glass substrate 42, 43...First layer polysilicon 45...Second layer polysilicon 46, 47...Al 48... Channel

Claims (1)

[Scope of Claims] A liquid crystal display device having a liquid crystal sealed between a pair of substrates, pixel electrodes arranged in a matrix on the substrates, and thin film transistors connected to the pixel electrodes, the substrates being made of glass. 1. A liquid crystal display device comprising a substrate, an insulating film formed on the substrate, and a thin film transistor formed on the insulating film.