JPH02268460A - Electrostatic breakdown preventing circuit - Google Patents

Abstract

PURPOSE:To prevent electrostatic breakdown by connecting two diodes in a specified direction between an outer input terminal and an inner circuit of an IC device and by realizing specified relationship between a driving voltage range of the IC and a threshold voltage of the diode. CONSTITUTION:Diodes D13 and D22 are connected to an outer connecting terminal 4 of a gate electrode busbar of an inner circuit 1 which consists of an aSi thin film transistor array formed on a glass substrate. The other ends 5, 6 of the diode are connected to a source electrode busbar. A threshold voltage of the diode is made Vt1, and Vt2; and -Vt2<Vd<Vt1 is selected as a range of a driving voltage Vd of the inner circuit. According to this constitution, when a voltage not less than the inner driving voltage Vd is applied to an external terminal 4, a current flows through the diode and a high surge voltage is not applied to the inner circuit 1. When a voltage is not exceeding the threshold of the diode, it is transmitted to the inner circuit. A diode can be realized by n<+>aSi/iaSi/SiNx and composition of SiNx can control a threshold by film thickness.

Description

[Detailed description of the invention] Industrial applications The present invention relates to an electrostatic damage prevention circuit.

Conventional technology FIG. 3 shows an example of a conventional electrostatic damage prevention circuit.

The electrostatic damage prevention circuit shown in the figure is installed between an external input terminal 4 and an internal circuit 1 of a semiconductor integrated circuit. A diode Doll connected from the external input terminal 4 to the ground potential in the reverse direction, and a diode D210 connected from the external input terminal 4 to the power supply potential in the forward direction are grounded.

According to this, a high voltage surge of negative polarity is clamped to the ground potential by the first diode D111, and a high voltage surge of positive polarity is clamped to the power supply potential V c c by the second diode D212. Sufficient electrostatic damage prevention effects can be obtained even against surges.

Electrostatic breakdown has been a serious problem, particularly in thin film transistor (TPT) array substrates formed on insulating layers. Therefore, methods have been proposed in which gate busbars and source busbars are connected with metal, or gate busbars and source busbars are connected with metal, and the metal is removed after the creation process is completed.

Problems to be Solved by the Invention In the conventional method of connecting diodes as described above, it was necessary to connect one side of the diode to a power supply potential and a ground potential. Therefore, there is a drawback that the internal circuit may be damaged by electrostatic discharge during the process of creating the internal circuit or during subsequent handling.

Furthermore, the method of connecting busbars provides protection against electrostatic damage after the process is completed.

In view of the above, an object of the present invention is to provide an electrostatic breakdown prevention circuit for a semiconductor integrated circuit that can prevent breakdown against both positive and negative high voltage surge voltages without using a power supply voltage.

Means for Solving the Problems The present invention provides an interface between an external input terminal and an internal circuit of a semiconductor integrated circuit device, the range of the driving voltage vd of the internal circuit and the threshold of the forward current of the first and second diodes. Voltage Vtl,
The relationship with Vt2 is the sum of the relationship of V t 2 < V d < V tr , and the first diode is connected in the forward direction from the external input terminal to the first potential side, and the first diode is connected from the external input terminal to the first potential side. This is an electrostatic breakdown prevention circuit in which a second diode is connected in the opposite direction toward the potential side.

The present invention also provides a range of the driving voltage Vd of the internal circuit, a positive threshold voltage Vt(+) and a negative threshold voltage Vt(-) of the group of diodes connected in series in opposite directions.
This is an electrostatic breakdown prevention circuit in which a group of diodes having a relationship of Vt(-)<Vd<Vt(+) are connected between the external input terminal and a first potential.

According to the above-described configuration, the present invention allows current to flow through the diode connected to the terminal when a voltage higher than the driving voltage of the internal circuit is applied to the external connection terminal, thereby preventing high surge voltage from being applied to the internal circuit. If a voltage below the threshold of the diode is applied, that voltage is transmitted to the internal circuit.

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

Example 1 FIG. 1 shows an explanatory diagram of Example 1. A first terminal is connected to an external connection terminal 4 of a gate electrode bus of an internal circuit 1 consisting of an aSi thin film transistor (TPT) array formed on a glass substrate.
Diode DI, D23, exhibiting the characteristics shown in figure (b)
．． Connect 2. The other end 5.6 of the diode is connected to the source electrode bus. The threshold voltages V th of the diodes DI and D23.2 are each Vt+5Vt2. The diode shown in FIG. 1(b) is n”-aSi/1-aS
The eVth that can be achieved with i/SiNx can be controlled by the composition or film thickness of S+NX. For example, if the film thickness of SiNx is 9
In the case of 0 nm, a diode with a threshold voltage of 30 V can be realized. Another implementation method is to utilize the TPT structure of the array, which is an internal circuit, so that at least one source or drain electrode and the gate electrode of a transistor do not overlap with each other through an insulating layer and a semiconductor layer.
It can also be realized by connecting either the source or drain electrode and the gate electrode in the "offset transistor" structure. The threshold voltage Vth in FIG. 1(b) can be controlled by the distance of the portion where at least one of the source or drain electrodes and the gate electrode do not overlap with the insulating layer and the semiconductor layer interposed therebetween. The threshold voltage is 50V with a gap of 2 μm. The gate voltage required to drive the TPT array is in the range of -10V to 15V, and the diode connections are not affected by normal drive.

If a diode is installed on the source electrode bus as in the case of the gate electrode bus described above and the other end is connected to the gate electrode bus, surge voltage entering the source electrode bus can be prevented.

Example 2 FIG. 2 shows a diagram explaining Example 2. Diodes 7.8 connected in series in opposite directions are connected to the external connection terminal 4 of the internal circuit 1, which is a semiconductor integrated circuit. other terminal 9
may be at ground potential. Ve(
+) and Vt(-) are determined by the reverse breakdown voltage of each diode. If it is desired to increase this voltage, it is sufficient to connect a plurality of diodes in series, and the internal circuit can be driven in the range from V t (J to Vt (+)).

The diodes 7.8 connected in series in opposite directions to each other function in the same manner as so-called MIM diodes made of metal/insulator/metal.

Effects of the Invention According to the present invention, it is possible to avoid electrostatic discharge damage without connecting one of the diodes to the power supply potential and the ground potential. Therefore, it can be connected to the internal circuit even after the process of creating the internal circuit, and there is no disadvantage that the internal circuit will be damaged by static electricity during handling.It is effective against both positive and negative high voltage surges, and its practical use. The value is high.

[Brief explanation of drawings]

1(a) and (b) are a circuit diagram and a characteristic diagram for explaining an embodiment of the electrostatic breakdown prevention circuit of the present invention, and FIG. 2(a) and (b) are respectively FIG. 3 is a circuit diagram for explaining a conventional electrostatic discharge prevention circuit. l◆・Middle white circuit, 2.3.7.8.1O111...
Diode, 4...External connection terminal. Name of agent Patent attorney Shigetaka Awano Hakaichi Takazu (α) Figure 2 C (L) Rakuzu

Claims (6)

[Claims] (1) In an electrostatic breakdown prevention circuit provided between an external input terminal and an internal circuit of a semiconductor integrated circuit device, a first diode connected in a forward direction from the external input terminal toward a first potential side. and a second diode connected in a reverse direction from the external input terminal toward the first potential side, the range of the drive voltage V_d of the internal circuit and the first,
Threshold voltage of forward current of second diode V_t_
1. An electrostatic damage prevention circuit characterized in that the relationship with V_t_2 satisfies the following relationship: -V_t_2<V_d<V_t_1. (2) In the first and second diodes, at least one of the source or drain electrode of the transistor and the gate electrode do not overlap with each other with an insulating layer and a semiconductor layer interposed therebetween, 2. The electrostatic damage prevention circuit according to claim 1, characterized in that the circuit is formed by connecting electrodes. (3) The first and second diodes are composed of a semiconductor layer and an insulating layer.
The electrostatic breakdown prevention circuit according to claim 1, having a layered structure. (4) In an electrostatic breakdown prevention circuit provided between an external input terminal and an internal circuit of a semiconductor integrated circuit device, a threshold voltage V_t in the positive direction between the external input terminal and a first potential is applied in both positive and negative directions. (+) and negative threshold voltage V_t(
), the range of the drive voltage V_d of the internal circuit and the threshold voltage of the two-terminal element, V
The relationship between _t(-) and V_t(+) is V_t(-)<V_
An electrostatic breakdown prevention circuit characterized by satisfying the relationship: d<V_t(+). (5) The electrostatic breakdown prevention circuit according to claim 4, wherein the two-terminal elements are a group of diodes connected in series in opposite directions. (6) The electrostatic breakdown prevention circuit according to claim 4, wherein the two-terminal element has first and second metals with an insulating layer sandwiched therebetween.