JPS5879749A - Semiconductor integrated circuit - Google Patents

Abstract

PURPOSE:To obtain a protective circuit with voltage limiting effect both in the positive and negative directions by a method wherein two diodes are connected in series in the transistor circuit connecting Zener diode between collector and base. CONSTITUTION:One end of Zener diode 6, collector of transistor 7 and one end of diode 8 are connected to terminal 1 while emitter of transistor 7 and the other end of diode 8 are connected to terminal 2. Then the other end of Zener diode 6 and the base of transistor 7 are connected to constitute a protective circuit. When said circuit is connected to an element 3 to be protected, and the terminal 1 is supplied with positive surge voltage, the voltage between the terminal 1 and 2 is limited by the Zener voltage of Zener diode 6 and the voltage between emitter and base of transistor, while if the terminal 1 is supplied with negative surge voltage, the voltage between the terminals 1 and 2 may be limited by the voltage in the forward direction of the diode 8 protecting the element 3.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a protection circuit for protecting an integrated circuit from surge voltage or static electricity.

Static electricity applied during the testing process or assembly of integrated circuits can cause damage to internal elements of the integrated circuit. Conventionally, as a measure to protect against damage caused by static electricity, the electrostatic energy applied to the internal elements of an integrated circuit was limited and protected by inserting a protective resistor in series with the internal elements of the integrated circuit or by inserting a diode in parallel. . However, the resistance value of the protective resistor cannot be made very large, so the protective effect on elements destroyed by electric fields is small, and the protective diode cannot protect elements with low withstand voltage, so a sufficient protective effect cannot be expected.

SUMMARY OF THE INVENTION An object of the present invention is to provide an integrated circuit equipped with a protection circuit having sufficient protection functions to protect internal circuits from excessive inputs applied to terminals.

According to the present invention, the Zener diode, the collector of the transistor, and the diode are connected to the terminal, and the other end of the Zener diode is connected to the base of the transistor,
A semiconductor integrated circuit is obtained which includes a protection circuit in which the emitter of a transistor and the other end of a diode are connected to a reference potential terminal.

Next, the present invention will be explained in more detail with reference to the drawings.

Figures 1 and 2 show examples of the configuration of conventional protection circuits when excessive static voltage is applied between terminals 1 and 2. In the case of Figure 1, internal element 3 is protected by protective resistor 4. It limits the flowing current, and in the case of Fig. 2, the voltage drop of the protection diode 5 is
By limiting the voltage applied to the internal element 3,
The electrostatic energy applied to each internal element 3 is limited to protect it.

In the protection by resistor 4 in Fig. 1, due to characteristic restrictions,
It has the disadvantage that it may not be able to protect internal elements that are destroyed by electric fields, such as oxide film capacitors and reverse Schittky barrier diodes, or when the resistance value cannot be increased.

In addition, in the diode protection shown in Fig. 2, if the protection diode 5 is composed of a substrate, an insulating layer, and an epitaxial layer, or an epitaxial layer and a base diffusion layer, the reverse breakdown voltage is high, so a positive static electricity is generated at the terminal 1. Or, if a surge voltage is applied, internal elements with low withstand voltage such as emitter base junctions may be
It has the disadvantage that it has no voltage limiting effect and may be destroyed.

Furthermore, if the protection diode shown in Fig. 2 is constructed of a Zener diode with an insulating layer and an emitter diffusion layer, or a base diffusion layer and an ivy diffusion layer, the above drawbacks can be overcome to some extent;
In order to ensure the breakdown strength of the Zener diode when a surge voltage or static electricity is applied, and to limit the voltage of internal elements, it is necessary to design the operating resistance to be small. Therefore, the area of the high concentration PN junction must be increased,
Since the parasitic capacitance between terminals 1 and 2 becomes large, this method has a drawback that it may not be applicable to high frequency circuits or high impedance circuits.

The present invention overcomes these drawbacks of conventional structures.

FIG. 3 is an equivalent circuit of a protection circuit according to an embodiment of the present invention. When positive static electricity or surge voltage is applied to terminal 1, the voltage between terminals 1 and 2 is limited by the sum of the Zener voltage of Zener diode 6 and the voltage between the base of transistor 7, and a negative voltage is applied to terminal 2. When static electricity or surge voltage is applied, the voltage between terminals 1 and 2 is limited by the forward voltage of diode 8, which has a voltage limiting effect on positive and negative static electricity or surge voltage.

Also, compared to the case where the protection diode 5 is configured with a Zener diode in Figure 2, the Zener diode 6 is configured in Figure 3.
Since only the base current of the transistor 70 is supplied, the current value is reduced to 1/hFIif times that of the transistor 7. Therefore, the operating resistance can be tolerated up to hrr+ times, and the junction area of the Zener diode can be reduced. This shows that even if a high concentration junction is used to lower the withstand voltage of the Zener diode 6, sufficient operation is possible with a small junction area.

FIG. 4 is a cross-sectional structural diagram when the protection circuit of FIG. 3 is constructed on a semiconductor substrate. The internal element 3 in FIG. 3 is assumed to be an arbitrary element and cannot be specified, so it is omitted in FIG. 4. In FIG. 4, after a buried layer (a) is diffused into a semiconductor substrate (a) to form an epitaxial layer, an epitaxial layer (d) isolated by an insulating diffusion layer (C) is obtained. A base region e is formed in the epitaxial layer d by a base diffusion process, and a high concentration region f for a Zener diode and an emitter region g are formed by diffusion in an emitter diffusion process. In Figure 4, emitter area g
, a base region, an epitaxial layer d, and a high concentration region f for a Zener diode constitute the transistor 7 shown in FIG. 3, and correspond to the emitter, base, and collector, respectively.

A Zener diode 6 is constituted by the Zener diode high concentration region f and the base region, and a diode 8 is constituted by the semiconductor substrate a, the isolation diffusion region C, the epitaxial layer d, and the Zener diode high concentration region f. These steps may be the same as those for manufacturing normal transistors of integrated circuits. As shown in FIG. 4, by configuring the protection circuit of FIG. 3 into one island, and by making the collector of the transistor 7, the cathode of the Zener diode 8, and the base of the transistor 70 and the collector of the Zener diode 8 common, the pellet The occupied area can be reduced and parasitic capacitance can be reduced.

In the above explanation, only damage caused by surge voltage or static electricity applied to the ground terminal and other terminals of an integrated circuit has been described, but if the present invention is applied to any terminal other than the ground terminal, the ground terminal However, since it has a voltage limiting effect in both positive and negative directions, it is possible to limit the voltage between any two terminals, and it can be used as protection between any two terminals.

Furthermore, it is clear that the effect of the present invention can be obtained even if a protective resistor is further added to the protective circuit shown in FIG.

As explained above, according to the present invention, it is possible to limit voltages in both the positive and negative directions for the ground terminal and other terminals of an integrated circuit without changing the manufacturing method, and to realize a protection circuit with low parasitic capacitance. .

[Brief explanation of drawings]

1 and 2 are circuit diagrams showing examples of conventional protection circuits, FIG. 3 is an equivalent circuit diagram of a protection circuit according to an embodiment of the present invention, and FIG. 4 is a circuit diagram showing an example of a protection circuit according to an embodiment of the present invention. FIG. 3 is a cross-sectional structural diagram showing an example of the structure of various circuits. 1... Any terminal of the integrated circuit, 2...
Ground terminal, 3...Internal element to be protected, 4
...Principle resistance, 5...Protection diode, 6...Zener diode, 7...
Transistor, 8...Diode, a...
...Semiconductor substrate, b...Buried layer, C...
・Insulation L d・・・Epitaxial layer, e・
... Heath region, f ... Emitter region,
g...High concentration area for Zener diode.

Claims (1)

[Claims] 1) The collector of the transistor and the cathode of the Zener diode on one side between the terminals to be protected. and ``a semiconductor integrated circuit, characterized in that the cathode of the diode is connected, and the ivy of the transistor described above and the anode of the diode are connected. 2) The protection circuit is an island of an epitaxial layer independently insulated a Tze diode formed by a collector contact region of the transistor and a space layer; and a diode formed by a junction between an island region of the epitaxial layer and at least an insulating isolation region. A semiconductor integrated circuit according to claim 1, characterized in that: