JPS6254458A - Input protecting circuit - Google Patents

Abstract

PURPOSE:To realize higher speeds and to improve voltage-withstanding capability by a method wherein an input protecting resistor is made to present resistance that is sufficiently lower at its end portion than at other portions. CONSTITUTION:The resistance to be presented by an input protecting resistor R is so caused as to be lower at its end portion A measured from its input side than at other portions. For example, the width is enlarged at the end portion A of the protecting resistor R, which results in a decrease in the resistance to be presented by the resistor R. The end portion A made larger than the other portions causes fusing if any to take place in the other portions. The voltage causing such a fusion represents the true voltage-withstanding capability of the input-protecting circuit. The portion A with its width enlarged presents less resistance, generates less heat, and radiates more heat, which all contributes to the attainment of higher speeds and improved voltage-withstanding capability.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an input protection circuit, and particularly to an input protection circuit for MO8 integrated circuits. It is used for.

[Technical background of the invention and its problems]

A conventional input protection circuit of this type is shown in FIG.

In the figure, Tr1 is an aluminum field transistor;
D is a protection diode element, and R is a protection resistor. This is discharged through the transistor Tr when a positive surge voltage is applied to the input. Further, when a negative surge voltage is applied to the input, it is discharged through the diode element Dl.

FIG. 3 shows a plan view of the main turn of the protective resistor R. In the figure, 1 is the aluminum pad to which the mending wire is connected, 2 is the aluminum cover, and 3 is the transistor T.
4 and 5 are wiring contact holes. The protective resistor R is made of polysilicon, a diffusion layer, etc., and has a meandering shape in order to obtain a long length with a small area. FIG. 4 is a sectional view taken along the line B--B in FIG. 3, where 6 is a semiconductor substrate and 7 is an SlO□ film. In this case, the heat generated in the resistor R during surge discharge is transmitted through the aluminum 2 and escapes to the outside through the pad 1 and the denning wire, thereby preventing the resistor R from melting. .

Although there are various modifications, the essence of the input protection circuit according to the prior art can be summarized in FIGS. 2 through 4. In order to create a protection circuit with a high withstand voltage, the value of the protection resistor R may be increased, but since this hinders the speeding up of integrated circuits, it is desirable to reduce the resistance value to the bare minimum.

When the resistance part is lowered, the heat generated in the resistance part increases, causing fusing. In other words, higher speed circuits and higher voltage protection circuits are contradictory terms. Furthermore, in terms of patterns, the portion A in FIGS. 3 and 4 is particularly prone to fusing. This is because this part is near the end of the protective resistor R, where the aluminum cover 2 ends, and it is difficult for aluminum to efficiently absorb the Joule heat generated by the resistor R.

[Object of the Invention] An object of the present invention is to increase the voltage resistance without increasing the protective resistance in an input crop circuit, and to simultaneously achieve high speed and high voltage resistance.

[Summary of the invention]

In the present invention, by sufficiently lowering the resistance value (for example, making the resistor thicker) near the terminal end of the input protection resistor than in other parts, the amount of heat generated in this part is reduced and melting is prevented. Since the other portions are largely covered with aluminum, the amount of heat required for fusing is greater than that near the terminal portion, so there is no need to lower (increase) the resistance value.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. 1st
The figure is a lean plan view of the same embodiment, but since this is an example in which it corresponds to that of the conventional example, corresponding parts are given the same reference numerals and explanations are omitted, and the features are as follows. Let me explain the points. A feature of the present invention is that the resistance value of the terminal end of the input protection resistor R as seen from the input side of the input protection circuit is lowered compared to other parts of the input protection resistor R. Here, the resistance value is lowered by making the width of the terminal end of the input protection resistor R wider than other parts. That is, what is desired to be thicker is the edge portion of the aluminum cover (cover for improving heat dissipation effect) 2 and the portion of the protective resistor that is not covered with aluminum.

However, with the conventional input protection resistor (Figure 3), when the resistance value is lowered (the lower the resistance is, the more desirable it is for higher speeds), melting occurs at the input part, lowering the withstand voltage. Ta. The reason why the part A is easily fused is because the aluminum layer 2 does not cover the entire surface. Then, heat can only escape to one side of the aluminum layer 2 directly above the part A, and the heat dissipation efficiency decreases. Further, since contact is made with the aluminum wiring 3 through the contact hole 5, a resistive portion not covered by the aluminum layer 2 is inevitably formed. For example, if the thickness of this part is doubled, the calorific value will be (per unit length! +) 1/2, and the unit area will be 1/2.
/4. Therefore, as shown in FIG. 1, the person's part should be made sufficiently thick so that the melting occurs in other parts. The withstand voltage at this time is the true withstand voltage of input protection. That is, according to this embodiment, since the human part is made thicker, the resistance value becomes smaller and the amount of heat generated decreases, and the area becomes a dog, so that the amount of heat dissipated can be increased.

Note that the present invention is not limited to the embodiments, and can be applied in various ways. For example, if it is possible to somehow lower the resistance of the human part in Figure 3 compared to other parts (while keeping the same thickness) (for example, by making I-resilicon polycide only in this part), it will still be the same. can realize the purpose of

〔Effect of the invention〕

As described above, according to the present invention, it is possible to provide an input protection circuit that can achieve high breakdown voltage without increasing the input protection resistance value and can satisfy βJRK for high speed and high breakdown voltage.

[Brief explanation of drawings]

Fig. 1 is a pattern plan view of an embodiment of the present invention, Fig. 2 is an input protection circuit diagram, Fig. 3 is a plan view of a conventional input protection resistor portion, and Fig. 4 is a B of Fig. 3. - It is a sectional view along the B line. L...Ginding knob, 2...Aluminum cover, 4, 5...Contact hole, R...Input protection resistor, A...Near the terminal end of the input protection resistor. Applicant's agent Patent attorney Takehiko Suzue Figure 2 Figure 351

Claims (3)

[Claims] (1) An input protection circuit characterized in that the resistance value near the terminal end of the input protection resistor seen from the input side of the input protection circuit is lowered compared to other parts of the input protection resistor. (2) The input protection circuit according to claim 1, characterized in that the resistance value is lowered by making the width of the resistance near the terminal end of the input protection resistor thicker than in the other parts. . (3) A portion near the terminal end of the input protection resistor is not covered with aluminum, and the other portion is covered with aluminum. Input protection circuit.