JPH0458696B2 - - Google Patents

Description

Detailed Description of the Invention The present invention provides a TFT formed on an insulating substrate.
The present invention relates to a protection circuit for a semiconductor integrated circuit device having (Thin Film Trs) as a component.

Since TFT semiconductor integrated circuits are usually formed on insulating substrates, there is no common conductive substrate that has the same potential. Therefore, a protection circuit for preventing destruction of circuit devices due to static electricity or the like cannot be configured with the same structure as the protection circuit normally employed in LSIs formed on single-crystal silicon substrates. From the configuration of the protection circuit used in the LSI, only the input protection resistor can be used as the protection circuit for TFTLSI. Therefore, conventional TFTLSI has low resistance to element destruction due to static electricity and the like. The present invention proposes a protection circuit for TFTLSI in order to improve the durability.

The details of the present invention will be explained below along with Examples.

FIG. 1 shows one embodiment according to the present invention,
Part of TFTLSI is shown. 1 is the power supply wiring that becomes the common GND potential (V _ss ) of TFTLSI, and 2
is a power supply wiring that has a constant potential with respect to _Vss . 3
is one of the input wirings. There are two input wiring
It is connected to Vss via TFTs (T ₁ , T ₂ ), and also connected to V _DD via two TFTs (T ₃ , T ₄ ). The two TFTs are connected in series, the gate of the TFT closer to the input wiring is connected to the input wiring, and the gate of the TFT farther from the input wiring is connected to V _ss.
connected to _VDD . When static electricity or the like is applied from the input wiring 3, one of T ₁ and T ₂ is turned on and the other is turned off, and similarly, one of T ₃ and T ₄ is turned on and the other is turned off. Therefore, the static electricity flows to the V _ss to V _DD wiring due to the breakdown between the source and drain of the TFT that is turned off, and the voltage due to the static electricity applied to the gate of the TFT (T ₅ ) becomes a sufficiently small value. This will prevent the gate from being destroyed.

In the voltage range in which TFTLSI normally operates, T ₁ and T ₃ in Figure 1 are always OFF, so no unnecessary current flows through the protection circuit according to the present invention, and the input signal remains at the initial signal level inside the LSI. Can be transmitted to the circuit.

TFTLSI can also be destroyed by static electricity during assembly processes such as dicing and wiring. In a normal LSI formed using single-crystal silicon as a substrate, all terminals of the LSI are connected to a conductive substrate via a PN junction, so static electricity may be input to any of the terminals during the assembly process. too,
Due to the breakdown of the PN junction, static electricity eventually reaches the substrate. Therefore, the potential difference between each part of the LSI does not become very large. Further, the conductive substrate serves as a capacitor and absorbs input static electricity. Therefore, ordinary LSIs using single-crystal silicon as substrates are unlikely to be destroyed by static electricity during the assembly process. On the other hand, TFTLSI does not have a conductive substrate equivalent to the single-crystal silicon, so it is particularly vulnerable to electrostatic damage during the assembly process. In the protection circuit according to the present invention shown in FIG.
Since each input terminal is connected to V _SS to V _DD via a TFT, basically all terminals of TFTLSI are connected via several PN junctions. Therefore, even if static electricity is applied to any terminal, the static electricity will be transmitted to the entire TFTLSI circuit due to the breakdown of the PN junction or the source/drain, and the potential difference between each part of the TFTLSI will not become very large, so the static electricity will not be affected by static electricity. Become more resistant to destruction.

FIG. 2 shows another embodiment according to the invention,
An input resistor 4 is added compared to FIG.
The input resistor serves to blunt the waveform of input static electricity and lower the peak voltage. With respect to FIG. 1, the incidence of breakdown due to static electricity decreases as the peak voltage decreases. The numbers and symbols shown in Figure 2 correspond to those in Figure 1, where 1 is V _ss and 2 is
V _DD , 3 is an input wiring, T ₁ to _{T 4} are TFTs forming a protection circuit, 4 is an input resistor, and T ₅ is a TFT into which an input signal should be input.

FIG. 3 shows a third embodiment according to the invention.
The numbers in FIG. 3 correspond to those in FIG. 2. D ₁ to _{D 4} indicate diodes inserted between the input wiring 3 and V _ss to V _DD . Two diodes are inserted between the input wiring and V _SS , and two diodes are inserted between the input wiring and V _DD , and each two diodes are connected in opposite directions. The input resistor 4 is intended to lower the peak voltage of input static electricity, and is inserted before the four diodes. In Fig. 3, when static electricity is generated from input 3, the peak voltage of static electricity is lowered by resistor 4, and the breakdown of one of the diodes _D1 and _D2 , which becomes a reverse voltage, reduces the static electricity. A portion of the input static electricity flows to V _ss , and due to the breakdown of one of the diodes D ₃ and D ₄ , which becomes a reverse voltage, a portion of the input static electricity also flows to V _DD . Therefore, due to the static electricity, the voltage applied to the gate of the TFT 5 in the input section becomes a sufficiently low value, and gate destruction can be prevented.

FIG. 4 shows a fourth embodiment according to the invention.
The numbers and symbols in FIG. 4 are the same as in FIG. 2. In Fig. 4, the peak voltage of static electricity is lowered by the input resistor 4, and the static electricity is released to the _Vss line through a TET ( _T2 ) whose gate is connected to _Vss .

As explained above, the present invention eliminates static electricity ignited from the input terminal of TFTLSI by the breakdown between the source and drain of the turned-off TFT or the reverse breakdown of the PN _junction . V _DD ). In addition to the illustrated embodiments, various structures having the above characteristics are possible. Since it has the above characteristics, the gate breakdown of the TFT connected to the input terminal is
This should be a dramatic improvement.

[Brief explanation of the drawing]

Embodiments of the present invention are shown in FIGS. 1 to 4. Figures 1, 2, and 4 are protection circuits that utilize the breakdown between the source and drain of a TFT.
The figure shows a protection circuit that uses the breakdown of a PN junction. 1...V _ss , 2...V _DD , 3...input, 4...
Input resistance, T ₁ to T ₄ ... TFT for protection circuit, T ₅ ...
Input TFT, D ₁ ~ D ₄ ~ PN diode for protection circuit.

Claims (1)

[Claims] 1. In a semiconductor device formed on an insulating substrate, a plurality of thin film transistors are connected in series between a reference potential wiring and a signal input terminal, and a plurality of thin film transistors are connected in series between a reference potential wiring and a signal input terminal. A gate of the thin film transistor is connected to the signal input terminal, a gate of the thin film transistor at an end on the reference potential wiring side is connected to the reference potential wiring, and a constant voltage having a constant potential difference with respect to the reference potential wiring is connected. A plurality of thin film transistors are connected in series between the potential wiring and the signal input terminal, the gate of the thin film transistor at the end on the signal input terminal side is connected to the signal input terminal, and the gate of the thin film transistor at the end on the signal input terminal side is connected to the constant potential wiring side. A semiconductor device characterized in that a gate of the thin film transistor at an end has an input protection circuit connected to the constant potential wiring. 2. The semiconductor device according to claim 1, wherein a resistor is connected between the signal input terminal and the internal circuit.