JPH0281468A - Input protective circuit - Google Patents

Abstract

PURPOSE:To avoid concentration of a current and make the current flow uniformly and facilitate effective input protection with small dimensions by a method wherein distances between a first conductivity type diffused region and contacts in a second conductivity type diffused region are large on an input contact side and small on an output contact side. CONSTITUTION:As distances between an input protective resistor 1 and contacts 6 are large on an input contact 3a side and small on an output contact 3b side, the resistance of an n-type well 4 is high near the input contact 3a and a current flowing through a region near the input contact 3a in the n-type well 4 is approximately equal to a current flowing through a region near the output contact 3b in the n-type well 4. As the current flowing in the n-type well 4 is made to be uniform and heat generation is dispersed, a protective circuit can be constituted in a small size as a whole. Moreover, as the resistance of the n-type well 4 near the output contact 3b is small, a sufficient voltage drop can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an input protection circuit for a semiconductor device that protects internal circuits from, for example, surges.

[Conventional technology]

FIG. 7 is a plan view showing a conventional input protection circuit. In this figure, numeral 1 denotes an input protection resistor formed by p0 diffusion, 2 denotes a guard ring (under the n region), and is connected to a power source through a plurality of contacts 6 and metal wiring 7. 3a and 3b are the input and output contacts of the input protection resistor 1, respectively, 4 is an n-well, and 5 is
a.

5b is a metal wiring.

This input protection circuit can be represented isometrically by the area surrounded by the dotted line in FIG. In this figure, 10a to 10
n is a resistance formed by the input protection resistor 1, 11a to 11n are resistances formed by the n well 4, and 12a to 12n are diodes formed by the input protection resistor 1 and the n well 4. Together with the diode 13, these are used to protect the gate of the transistor 15 from an overvoltage applied to the input terminal 14.

Next, the operation will be explained.

First, consider a case where a voltage equal to or lower than the ground potential is applied to the input terminal 14. In this case, the diode 13 is turned on, and the resistors 10a to Ion and the diode 13 are connected to the input terminal 14.
A current flows through the transistor 15, and the gate potential of the transistor 15 is kept at the ground potential. Next, consider a case where a voltage higher than the power supply potential is applied to the input terminal 14. In this case, the diodes 12a to 12n are turned on, and the current flows to the input terminal 14.
, resistors 10a to 10n, diodes 12a to 12n,
The voltage flows through the resistors 11a to 11n and the guard ring 2 shown in FIG. 7, and the gate potential of the transistor 15 is maintained at the power supply potential. In other words, no matter what potential the input terminal 14 has, the gate potential of the transistor 15 is maintained within the range from the ground potential to the power supply potential, and the transistor 15 can be protected from gate breakdown.

[Problem to be solved by the invention]

In the conventional input protection circuit as described above, the input protection resistor 1
Since the distance between the input contact 3a side and the guard ring 2 is equal on the input contact 3a side and the output contact 3b side, the current flowing through the area near the output contact 3b of the n-well 4 is caused by the input protection resistor 1 of the n-well 4. The current was smaller than the current flowing in the area near the input contact 3a. In other words, the current will concentrate in the area near the input contact 3a of the n-well 4, and if the distance between the input protection resistor 1 and the guard ring 2 is made small, an excessive current will flow near the input contact 3a, and the metal There was a risk that the wiring 5a would be burnt out. However, conversely, if the distance between the input protection resistor 1 and the guard ring 2 is increased, the resistance value of the resistors 11a to 11n due to the n-well 4 increases, and the transistor 1
There was a problem in that a voltage drop sufficient for input protection could not be obtained at the gate potential of No. 5.

This invention was made in order to solve the above-mentioned problems.The current flowing through the resistor of the input protection circuit is not concentrated in one part, but flows on average, thereby providing effective input protection in a small area. The purpose of this invention is to obtain an input protection circuit that can perform the following steps.

[Means to solve the problem]

In the input protection circuit according to the present invention, the distance between the contacts in the first conductivity type diffusion region and the second conductivity type diffusion region is made larger on the input contact side and smaller on the output contact side.

(Function) In this invention, the resistance value of the first conductivity type diffusion region constituting the diode is high near the input contact and low near the output contact, and the resistance value of the diffusion region of the second conductivity type and the input/output contact are high in the vicinity of the input contact and low in the vicinity of the output contact. The current flowing between them is averaged.

(Embodiment) FIG. 1 is a plan view showing an embodiment of the input protection circuit of the present invention. In this figure, the same reference numerals as in FIG. 7 indicate the same parts.

In this invention, the distance between the input protection resistor 1 and the contact 6 is made larger near the input contact 3a and smaller near the output contact 3b. Therefore, the equivalent circuit becomes as shown in FIG.
The resistance values of a to lln are large on the resistor 11a side;
It becomes smaller toward the n side.

Next, the operation will be explained.

First, consider the case where a voltage equal to or lower than the ground potential is applied to the input terminal 14. In this case, the diode 13 is turned on, current flows to the input terminal 14 via the resistors 10a to 10n and the diode 13, and the gate potential of the transistor 15 is maintained at the ground potential. Next, consider a case where a voltage higher than the power supply potential is applied to the input terminal 14. In this case, the die-totes 12a to 12n are turned on, and current flows from the input terminal 14 to the resistors 10a to 10n and the diodes 12a to 12n.
2n, resistors 11a to 11n, and the guard ring 2 shown in FIG. 1, the gate potential of the transistor 15 is maintained at the power supply potential. At this time, the distance between the input protection resistor 1 and the contact 6 is large on the input contact 3a side and small on the output contact 3b side, so the resistance value of the n-well 4 is high near the input contact 3a, and the resistance value of the n-well 4 is high near the input contact 3a. The current flowing through the region near the input contact 3a and the current flowing through the region near the output contact 3b of the n-well 4 are approximately equal. That is, the input protection circuit of the present invention can also obtain the same protection effect as the conventional one shown in FIG.
Since the current flowing through the protection circuit is averaged and the heat generation is dispersed, the entire protection circuit can be made smaller. Also,
Since the resistance value of the n-well 4 near the output contact 3b is reduced, a sufficient voltage drop can be obtained.

Although the input protection resistor 1 is shown here as having a rectangular shape, the input protection resistor 1 may have a shape that protrudes around the input contacts 3a and output contacts 3b, as shown in FIG. As shown in FIG. 4, it is also possible to have a shape bent in the middle. Further, although the guard ring 2 is shown as having a shape that covers the periphery of the input protection resistor 1, it may be simply arranged in parallel as shown in FIG.

Furthermore, although the example in which the input protection resistor 1 is made of a p-type semiconductor is shown here, if the input protection resistor 1 is made of an n-type semiconductor, and the n-well 4 and the guard ring 2 are made of p-type, as shown in FIG.
A similar input protection circuit can also be formed by combining it with the diode 13 connected to the power supply.

[Effects of the Invention] As explained above, in this invention, the distance between the contacts in the first conductivity type diffusion region and the second conductivity type diffusion region is made larger on the input contact side and smaller on the output contact side. The current flowing between the contact in the second conductivity type diffusion region and the human output contact is averaged, heat generation is dispersed, and the entire input protection circuit can be made smaller. Furthermore, since the resistance value near the output contact is reduced, there is also the effect that a sufficient voltage drop can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a plan view showing one embodiment of the input protection circuit of the present invention, Fig. 2 is an equivalent circuit diagram of the input protection circuit shown in Fig. 1, and Figs. 3 to 5 are other embodiments. Fig. 6 is an equivalent circuit diagram of another embodiment, Fig. 7 is a diagram showing a conventional input protection circuit, and Fig. 8 is an equivalent circuit diagram of the input protection circuit shown in Fig. 7. be. In the figure, 1 is the input protection resistor, 2 is the guard ring, and 3 is the input protection resistor.
a is an input contact, 3b is an output contact, 4 is an n-well, 5a, 5b, and 7 are metal wiring lines, and 6 is a contact. Note that the same reference numerals in each figure indicate the same or corresponding parts. Figure 1 Agent: Masuo Oiwa (2 others) Figure 1 Figure Figure 1

Claims (1)

[Claims] a first conductivity type diffusion region that serves as an input protection resistor;
a second conductivity type diffusion region formed near the conductivity type diffusion region and forming a diode together with the first conductivity type diffusion region, and an input contact and an output contact within the first conductivity type diffusion region. In an input protection circuit comprising a contact connected to a power supply or ground in the second conductivity type diffusion region, between the contact in the first conductivity type diffusion region and the second conductivity type diffusion region. An input protection circuit characterized in that the distance is larger on the input contact side and smaller on the output contact side.