JPH0770609B2 - Protection circuit for complementary MIS integrated circuit - Google Patents

Description

The present invention relates to a complementary MIS (Metal Insulator S / S) such as a CMOS circuit.
The present invention relates to a protection circuit for an integrated circuit, and more particularly to a protection circuit capable of reducing reverse breakdown voltage and resistance after breakdown.

[Prior Art] Conventionally, for example, as shown in FIG. 6, a protection circuit for protecting a power supply terminal from static electricity stress and for forming a network is provided with a low potential side power supply terminal 3 and a low potential side power supply terminal 3 of an internal circuit 2 of a chip 1. In general, a PN junction diode 5 is reversely connected to the power source terminal 4 on the potential side.

[Problems to be Solved by the Invention] However, in the above-described conventional protection means, since the reverse breakdown voltage of the PN junction diode 5 is high, the high potential power supply terminal 3
When a high electric field with a high electric potential is applied, there is a drawback that it does not function sufficiently as a protective element. Moreover, the PN junction diode has a drawback that it has a low protection ability because of high series resistance after breakdown.

The present invention has been made in view of the above problems, and provides a protection circuit for a complementary MIS integrated circuit, which has a low reverse breakdown voltage and a small series resistance after breakdown, instead of a PN junction diode. To aim.

[Means for Solving Problems] A protective circuit for a complementary MIS integrated circuit according to the present invention uses an N-channel MI instead of the above-mentioned PN junction diode as a protective element.
It is composed mainly of diodes by S-transistors.

That is, the protection circuit according to the present invention includes an N-channel MIS transistor having a drain connected to the high-potential-side power supply terminal and a source and a back gate connected to the low-potential-side power supply terminal, and a gate of the N-channel MIS transistor and the low-voltage side MIS transistor. And a resistor interposed between the power source terminal and the potential side power supply terminal.

[Operation] FIG. 2 shows reverse voltage-current characteristics of a conventionally used PN junction diode and a diode (hereinafter, referred to as a BV _DSN diode) including an N-channel MIS transistor used in the present invention. Normally, comparing the reverse breakdown voltage with that of a PN junction diode (hereinafter referred to as BV _J ) and that of a BV _DSN diode (BV _DS ), BV _DS <BV due to electric field concentration near the drain gate. _The relationship _J is established. Also BV
After reverse breakdown, the _DSN diode turns on a parasitic NPN transistor whose drain is a collector, source is an emitter, and back gate is a base, and after showing negative resistance characteristics, shows extremely low impedance characteristics. When viewed as the on resistance as a diode, BV
_{The DSN} diode has a resistance value that is 1/10 to 1/20 that of the PN junction diode. Therefore, the BV _DSN diode has far superior advantages over the PN junction diode from the viewpoint of low impedance and low clamp voltage required as a protection element, and can significantly improve the protection capability. You can Further, the characteristics of the inter-power supply diode are important from the viewpoint of networking the protection circuit, and the above-mentioned advantages greatly contribute to the high reliability of the integrated circuit. Further, in the present invention, since the resistor or the inverter is connected to the gate of the MIS transistor forming the protection circuit, it is possible to suppress the increase of the gate electric field due to the electrostatic stress applied through the power supply terminal. As a result, it is possible to reliably prevent damage to the protection circuit itself.

[Examples] Next, examples of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a block diagram of a protection circuit composed of one MIS transistor. The protection circuit 11 is connected between the high potential side power supply terminal 3 and the low potential side power supply terminal 4 of the internal circuit 2 of the chip 1. The protection circuit 11 has an N-channel MIS transistor 12 whose drain is connected to the high potential side power supply terminal (V _DD ) 3 and whose source, gate and back gate are connected to the low potential side power supply terminal (V _SS ) 4. . In this embodiment, the N-channel MIS transistor 12 constitutes the first means, and the metal wiring 5 between the gate of the transistor 12 and the terminal 4 constitutes the second means.

In such a protection circuit 11 , as shown in FIG. 2, since the reverse voltage is low and the impedance after breakdown is low, it functions well as a protection element.

FIG. 3 shows a first embodiment of the present invention. In FIG. 3, the same parts as those in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted. In this embodiment, by using the resistor 13 connected between the gate of the transistor 12 and the low-potential-side power supply terminal 4, destruction by the gate electric field when electrostatic stress is applied is prevented. As the resistor, a non-matching resistor such as polycrystalline silicon, or a source / drain diffusion layer,
A substrate or a junction type resistor such as a well of opposite conductivity type can be used.

A second embodiment is shown in FIG. This embodiment is an example in which the gate of the N-channel MIS transistor 12 has a high impedance by an inverter 14 of the same power supply system, and the input of the inverter 14 is protected by the resistor 13 described above.

FIG. 5 is a block diagram showing a third embodiment of the present invention. In this embodiment, a P-channel MIS transistor 15, a gate protection inverter 16 thereof, and a resistor 17 are added to the circuit 11 shown in FIG. P channel
The MIS transistor 15 has a source and a back gate connected to the high potential side power supply terminal 3, and a drain connected to the low potential side power supply terminal 4.

According to this circuit, the diode formed by the P-channel MIS transistor 15 (hereinafter referred to as "BV _DSP diode") is connected in parallel. Therefore, when a reverse stress is applied, first,
Clamping is possible with either the BV _DSN diode or BV _DSP diode, whichever has the lower reverse breakdown voltage. Also, P
In the case of the N-type substrate, the PNP vertical transistor based on the N-type well also operates as a protective element, and in the case of the N-type substrate,
Since the NPN vertical transistor based on the P-type well can also operate as a protection element, there is an advantage that the protection capability is further improved.

[Effect of the Invention] As described above, according to the present invention, by using an N-channel MIS transistor as a diode as a protection element between power supplies, it has a low clamp voltage and a low on-resistance protection capability. It is possible to obtain a complementary MIS integrated circuit whose reliability is remarkably improved as compared with the conventional one.

[Brief description of drawings]

FIG. 1 is a block diagram showing a protection circuit composed of one MIS transistor, and FIG. 2 is a reverse voltage-current characteristic diagram of a conventional PN junction diode and a diode using an N-channel MIS transistor used in the present invention. 3 to 5 are block diagrams showing the first to third embodiments of the present invention, respectively, and FIG. 6 is a block diagram showing a conventional protection means. 1: Chip, 2; Internal circuit, 3; High potential side power supply terminal, 4; Low potential side power supply terminal, 5; PN junction diode, 11 ; Protection circuit, 12; N
Channel MIS transistor (BV _DSN diode), 13,17;
Resistors, 14, 16; Inverter, 15; P-channel MIS transistor (BV _DSP diode)

Claims (5)

[Claims] 1. An N-channel MIS transistor having a drain connected to a high potential side power supply terminal and a source and a back gate connected to a low potential side power supply terminal, a gate of the N channel MIS transistor and the low potential side power supply terminal. Complementary MIS, comprising a resistor interposed between
Integrated circuit protection circuit. 2. The protection circuit for a complementary MIS integrated circuit according to claim 1, wherein the resistor is a non-junction type resistor made of polycrystalline silicon or the like. 3. The complementary MIS according to claim 1, wherein the resistor is a junction-type resistor formed by any one of a source / drain diffusion layer, a substrate, and a well of opposite conductivity type. Integrated circuit protection circuit. 4. An N-channel MIS transistor having a drain connected to a high-potential-side power supply terminal and a source and a back gate connected to a low-potential-side power supply terminal, and the potential of the high-potential-side power supply terminal is inverted to reverse the N-channel MIS transistor. A protection circuit for a complementary MIS integrated circuit, comprising: an inverter applied to the gate of a channel MIS transistor. 5. A P-channel MIS transistor having a source and a back gate connected to the high-potential-side power supply terminal and a drain connected to the low-potential-side power supply terminal, and the P-channel MIS transistor inverting the potential of the low-potential-side power supply terminal. The protection circuit for a complementary MIS integrated circuit according to claim 4, further comprising a second inverter provided to the gate of the channel MIS transistor.