JPS6191969A - Non linear element - Google Patents

Abstract

PURPOSE:To increase the threshold value by improving the normal and reverse symmetricalness of voltage-current characteristics by a method wherein two diodes made of pin or nip laminated film of the same amorphous silicon formed into the same type by patterning process are connected in series in the reverse direction. CONSTITUTION:P type (or N type) amorphous silicon films 23, i-type amorphous silicon films 24 and N type (or P type) amorphous silicon films 15 are successive ly laminated on two lower electrodes 21, 22 formed at adjoining position on a glass substrate 20. Next this three layer structure amorphous silicon films are formed into island type parts by etching process to be left only on the lower electrodes 21, 22. Besides, silicon nitride or silicon dioxide insulating films are formed into passivation films 26 and then a contact hole for leaving out electrodes is opened. Finally two pin (or nip) diodes may be connected with each other by upper electrodes 27 through the intermediary of the connecting hole.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a nonlinear element including an amorphous silicon pin or nip mill diode.

[Prior art and its problems]

Nonlinear elements such as semiconductor varistors, whose voltage-current characteristics change nonlinearly, have traditionally been used in overvoltage suppression and noise absorption circuits, but recently they have been used to realize large-capacity liquid crystal displays. It has also started to attract attention as a t-th element. As a nonlinear element for this purpose, it is necessary that a large number of elements can be formed uniformly over a large area, and various materials and element structures have been proposed.

Now, the nonlinear element exhibits symmetrical voltage-current characteristics as shown in FIG. 3, for example. When such a nonlinear element is applied to a liquid crystal display, the nonlinear element is connected in series with a liquid crystal cell 43 via a trap, a signal line 41, and a data line 42, as shown in the circuit shown in FIG. This nonlinear element 4
A voltage ■ larger than the threshold voltage Vth of 4. When n is added between the signal line and the data line, the liquid crystal cell 43 has approximately ■. . -V
A voltage of th is applied and the liquid crystal turns on. Also, the threshold voltage V
When a voltage Voff smaller than th is applied, all of Voff is applied to the nonlinear element K, so no voltage is applied to the liquid crystal cell 43 and the liquid crystal does not turn on. In this manner, the ratio of the voltage effectively applied to the liquid crystal cell 43 is much larger than the ratio of the voltage applied from outside the trap Von i Vo f f, and the on-off ratio is greatly improved. As a result, in the conventional multiplayer and box drive of liquid crystal displays, the number of signal lines was limited to about 60, but by using nonlinear elements, the number of signal lines can be increased to several hundred, making it possible to use liquid crystal displays with large display capacity. realizable.

As such a nonlinear element, an n1 pin or pinip five-layer stacked back-to-back diode using amorphous silicon has already been proposed (Japanese Patent Application Laid-Open No. 130081/1981). The respective equivalent circuits are shown in FIG. 5 [a), 1b) VC. When forming amorphous silicon, the area surrounded by the dotted line in Figure 5 can be obtained by simply changing the doping gas for one impurity.

Clara back diode 51 or 52 can be formed at one time. However, although this element exhibits nonlinear characteristics almost similar to those shown in FIG. 3, it has the disadvantage that the symmetry of the forward and reverse characteristics is poor.

The reason for this is that the symmetry of the multi-element structure is lost due to the incorporation of impurities into the i-layer. If the nonlinear element characteristics are poorly symmetrical, the voltage applied to the liquid crystal cell will be asymmetrical], and a DC component will remain in the voltage applied to the liquid crystal. Under such conditions, the lifespan of the liquid crystal is short and it is not of practical use.

As a nonlinear element with improved symmetry of voltage-current characteristics, PIN or NIP 3 also uses amorphous silicon.
A configuration in which two stacked diodes are connected in parallel in opposite directions has been proposed (Japanese Patent Laid-Open No. 59-57
273). An equal number of circuits of this element are patterned at adjacent positions, so that the diode characteristics are exactly the same, and the symmetry of the nonlinear characteristics is significantly improved. However, since this nonlinear element utilizes the layer direction characteristics of the diode, the threshold voltage Vth as a nonlinear element is 0.7.
It has the disadvantage of being small, about v. If the threshold voltage Vth is small, the on/off ratio of the voltage applied to the liquid crystal cell is not much different from the on/off ratio of the voltage applied from the outside, and the number of signal lines of the liquid crystal display cannot be significantly increased.

[Purpose of the invention]

The purpose of the present invention is to improve the characteristics of conventional nonlinear elements made of amorphous silicon, which have the above-mentioned drawbacks, and to
The object of the present invention is to provide a nonlinear element made of amorphous silicon that has good forward and reverse symmetry in current characteristics and a relatively large threshold voltage.

[Structure of the invention]

The nonlinear element of the present invention consists of two pin laminated films or nip laminated films of the same amorphous silicon and patterned in the same shape at adjacent positions on an insulating substrate.
It consists of in diodes or nip mill diodes connected in opposite directions to each other. [Operation] FIG. 2 (al and bl are equivalent circuit diagrams showing the configuration of a nonlinear element according to the present invention.

In the present invention, as shown in the above structure, a structure in which two diodes of the PIN or NLPA layer stacked type using amorphous silicon are connected in series in opposite directions is used as the nonlinear element. PIN diode 11 or nip mill diode 12# surrounded by two dotted lines in the same figure
The same shape is patterned at adjacent positions of the i- pin laminated film or nip laminated film, and the symmetry of the nonlinear characteristics is significantly improved. Moreover, since these nonlinear elements utilize the reverse characteristics of diodes, the threshold voltage Vth as a nonlinear element can be set to a relatively large value, and the threshold value can be adjusted according to the specifications of the required nonlinear element characteristics. It is possible to control the voltage from about "Vth*iv." to about 10-odd volts.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view showing the structure of an embodiment of the present invention.

A p-type (or n-type) amorphous silicon film 23 and an i-type amorphous silicon film 23 are deposited on two lower electrodes 21 and 22 formed at adjacent positions on a glass substrate 20 by plasma CVD. A crystalline silicon film 24 and an n-type (or p-type) amorphous silicon film 25 are sequentially laminated. Next, this three-layered amorphous silicon film is etched to form an island shape so that it remains only above the lower electrodes 21 and 22. After forming an insulating film 26 made of silicon nitride or silicon dioxide by the plasma CVD method, a contact hole for taking out the electrode is made. Finally, the two pin (or nip) diodes are connected by the upper electrode 27 through this contact hole to complete this embodiment.

The nonlinear characteristics of this example obtained in this way are based on the third
As shown in the figure, the threshold value tEVth is relatively large, and the symmetry of the forward and reverse characteristics is very good. The threshold voltage Vth can be varied from about 1 V to about 20-odd V by changing the thickness of the i-type amorphous silicon film 24. For example, if the thickness of the i-type layer is 10001O and tkVthti8V, zoooo
Xo and a became 20V. The p-type (or n-type) and n-type (or p-type) amorphous silicon films 23.25 are for making ohmic contact with the lower and upper electrodes 21 and 22.27, respectively, and have a thickness of 300X. It is enough.

Also, the symmetry of the forward and reverse characteristics depends on the patterning accuracy of the area of the two diodes, but for example, if the junction area is 10μ
When the above nonlinear element of mXIQμm was formed, the positive direction Vth was 8. OIV and reverse direction Vth are the same <8. OI
Good symmetry with V could be obtained.

When incorporated into a liquid crystal display, one of the lower 11° C. poles 21 and 22 of the nonlinear element 44 of this embodiment is connected to the signal line 41 or the data line 42, and the other one is connected to the liquid crystal cell 43. This liquid crystal display was capable of multiplex drive with 500 signal lines, and good images without crosstalk were obtained.

〔Effect of the invention〕

As described in detail above, according to the present invention, by using a structure in which pin or nip three-layer diodes using an amorphous silicon film are connected in series in opposite directions, It is possible to obtain a nonlinear element having voltage-current characteristics with good symmetry and a relatively large threshold value tFE.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the structure of an embodiment of the present invention, FIG. 2 is an equivalent circuit diagram showing the structure of a nonlinear element according to the present invention, and FIG. A current characteristic diagram, FIG. 4 is an equivalent circuit diagram of a liquid crystal display using one embodiment, FIG. 5 (al, (bl), and FIG. 6 are equivalent circuit diagrams showing the configuration of a conventional nonlinear element. 11. ...pin diode, 12...
nip mill diode 0...Glass substrate, 21
, 22...lower electrode, 23...p type (
or n-type) amorphous silicon film, 24... i-type amorphous silicon film, 25... n-type (or) p-type amorphous silicon film, 26... ... Passivation film, 27 ... Upper electrode, 41 ... Signal line, 42 ... Data line, 43 ... Liquid crystal cell, 44 ... ...Nonlinear element, 51...p
inip diode, 52...N1 pin diode, 61...pin or nip mill diode,', Agent Patent attorney Susumu Uchihara (1 son 2 Leap /l!T half 31!T $ 4 Diagram de→-ku 1 (&) 1+kidney--groan---J Sensei 5 Mycology 6 times

Claims (1)

[Claims] Two PIN diodes or NI made of the same amorphous silicon PIN laminated film or NIP laminated film and patterned in the same shape at adjacent positions on an insulating substrate
A nonlinear element characterized by p-diodes connected in series in opposite directions.