JPH05136328A - Electrostatic protective circuit for semiconductor device - Google Patents

Abstract

PURPOSE:To display an intrinsic function for protecting an internal circuit for a semiconductor device from an electrostatic breakdown and to enhance the surge breakdown strength of a electrostatic protective device itself. CONSTITUTION:At the inside of a semiconductor device 10, a common route X at the outside, a first branch route A, a second branch route B and a common route Y at the inside are formed individually in such a way that one route form an input/output terminal 7 to an input/output circuit 6 is once branched to two routes and that the routes are joined to one. A diode 2 on the VSS side and a P-ch off-transistor 3 on the VDD side as protective elements on the positive side which are used to relax a stress caused by a positive-polarity surge voltage are arranged on the first branch route A; a diode 1 on the VDD side and an N-ch off-transistor 4 on the VSS side as protective elements on the negative side which are used to relax a stress caused by a negative-polarity surge voltage are arranged on the second branch route B. In addition, a protective resistance 5 used to relax a stress caused by a surge voltage of both positive and negative polarities is arranged in series on the common route Y at the inside.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of surge withstand voltage of an electrostatic protection circuit incorporated in a semiconductor device.

[0002]

2. Description of the Related Art The layout configuration of a conventional electrostatic protection circuit for a semiconductor device will be described.

FIG. 2 is a circuit diagram schematically showing the layout of a conventional electrostatic protection circuit. As shown in the figure, a semiconductor device 10 having an input / output circuit 6 inside has an input / output terminal 7 for external connection. One path from the input / output terminal 7 to the input / output circuit 6 for the purpose of protecting the input / output circuit 6 from electrostatic breakdown by alleviating the stress caused by the surge voltage entering through the input / output terminal 7. A diode 1 on the VDD side, a diode 2 on the VSS side, a Pch (P channel) off transistor 3 on the VDD side, an Nch (N channel) off transistor 4 on the VSS side, and a protection resistor 5 are provided on X. Of these, the diodes 1 and 2 and the transistors 3 and 4 are arranged between the path X and the power source and the ground, and the protective resistor 5 is connected to the path X.
They are arranged in series above.

When the surge voltage applied to the input / output terminal 7 has a positive polarity, when the surge voltage becomes higher than the power source voltage VDD by the threshold voltage of the Pch-off transistor 3 or more, the VDD side Pch-off is performed. The transistor 3 turns on, and a current flows through the VDD side Pch off transistor 3 and the VSS side diode 2. In other words, the VSS side diode 2 and the VDD side Pch off transistor 3 act as a positive side protection element for alleviating the stress caused by the positive surge voltage, and release positive charges from the outside.

On the contrary, when the surge voltage applied to the input / output terminal 7 has a negative polarity, the surge voltage is higher than the ground voltage VSS by N.
When the voltage becomes lower than the threshold voltage of the ch-off transistor 4, the VSS side Nch-off transistor 4 turns on,
A current flows through the diode 1 on the VDD side and the Nch off transistor 4 on the VSS side which is turned on. In other words, the VDD side diode 1 and the VSS side Nch off transistor 4 are
It acts as a negative-side protection element for relieving the stress caused by the negative surge voltage and releases negative charges from the outside.

Further, the protection resistor 5 has a function of further reducing the stress caused by the surge voltage with respect to the surge voltage of either positive or negative polarity.

Due to the respective functions of the positive side protection elements 2 and 3, the negative side protection elements 1 and 4, and the protection resistor 5, surge voltage of either positive or negative polarity enters the semiconductor device 10 through the input / output terminal 7. I / O circuit 6
Resists electrostatic damage.

[0008]

In the conventional electrostatic protection circuit for a semiconductor device, the plus side protection elements 2 and 3 and the minus side protection elements 1 and 4 for protecting the input / output circuit 6 have the same path. Since it is arranged on X, when the surge voltage applied to the input / output terminal 7 has a positive polarity, the VDD side diode 1 or the VSS side Nch off transistor 4 as a negative side protection element may be destroyed. Terminal 7
If the surge voltage applied to the negative polarity is negative, VSS side diode 2 or VDD side Pch as a positive side protection element
The off transistor 3 was sometimes destroyed. That is, there is a problem that the surge withstand voltage of the electrostatic protection circuit itself is low.

An object of the present invention is to improve the surge withstand voltage of the electrostatic protection circuit itself.

[0010]

In order to achieve the above object, the present invention is intended to protect the internal circuit of a semiconductor device from electrostatic breakdown by alleviating the stress caused by a surge voltage that intrudes through an input / output terminal. In the electrostatic protection circuit for semiconductor device, the path from the input / output terminal to the internal circuit is branched into two, and a positive side protection element and a negative side protection element are arranged in each of these branched paths, This is a configuration in which protective resistors are arranged in series on a common path.

More specifically, as shown in FIG. 1, the present invention is so common that one path from the input / output terminal 7 to the internal circuit 6 is once branched into two and then joined. It is assumed to have the routes X and Y and the first and second branch routes A and B. Then, on the first branch path A, positive side protection elements 2 and 3 for easing the stress caused by the positive surge voltage penetrating through the input / output terminal 7 are arranged,
Negative-side protection elements 1 and 4 are provided on the second branch path B to relieve the stress caused by the negative surge voltage that enters through the input / output terminal 7, and the common path X and Y are connected. A protective resistor 5 for alleviating the stress caused by the surge voltage with respect to the surge voltage of either positive or negative polarity that enters through the output terminal 7 is arranged in series.

[0012]

According to the present invention, when the surge voltage applied to the input / output terminal 7 has a positive polarity, the plus side protection elements 2 and 3 are provided.
Reduces the concentration of charges so as to relieve the stress caused by the positive surge voltage on the first branch path A. Further, the protective resistance 5 on the common paths X and Y serves to further alleviate the stress caused by the positive surge voltage. As a result, the internal circuit 6 is protected from electrostatic breakdown. Moreover, since the second branch path B is a path different from the first branch path A, the stress applied to the negative side protection elements 1 and 4 on the second branch path B is reduced and the elements are destroyed. Get rid of.

On the contrary, when the surge voltage applied to the input / output terminal 7 has a negative polarity, the negative side protection elements 1 and 4 relieve the stress caused by the negative surge voltage on the second branch path B. Relieve the concentration of electric charges as you do. Also,
The protective resistor 5 on the common paths X and Y has a function of further relieving the stress caused by the negative surge voltage.
As a result, the internal circuit 6 is protected from electrostatic breakdown. Moreover, since the first branch path A is a path different from the second branch path B, the stress applied to the positive side protection elements 2 and 3 on the first branch path A is reduced and the positive side protection elements 2 and 3 are destroyed. Get rid of.

As described above, when a positive or negative polarity surge voltage enters the semiconductor device through the input / output terminal 7, not only the input / output circuit 6 is protected from electrostatic breakdown,
Positive side protective elements 2, 3 and negative side protective elements 1, 4
Will not be destroyed.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a circuit diagram schematically showing a layout of an electrostatic protection circuit for a semiconductor device according to an embodiment of the present invention. As shown in the figure, a semiconductor device 10 having an input / output circuit 6 inside has an input / output terminal 7 for external connection as in the case of FIG. However, input / output terminal 7
From the input / output terminal 7 side, the outer common path X, the first and second branches are arranged in order from the input / output terminal 7 side so that one path from the input / output circuit 6 to the input / output circuit 6 is once branched into two. This is different from the case of FIG. 2 in that the routes A and B and the inner common route Y are respectively formed. Then, on the first branch path A, a VSS side diode 2 and a VDD side Pch off transistor 3 are provided as a positive side protection element for relieving the stress caused by the positive surge voltage that enters through the input / output terminal 7. And are arranged. Further, on the second branch path B, a VDD side diode 1 and a VSS side Nch are provided as negative side protection elements for relieving stress caused by a negative surge voltage entering through the input / output terminal 7.
The off-transistor 4 is arranged. Further, on the inner common path Y, a protection resistor 5 for relieving the stress caused by the surge voltage with respect to the surge voltage of either positive or negative polarity entering through the input / output terminal 7 is arranged in series. There is.

The operation of the electrostatic protection circuit of the present embodiment having the above layout will be described below.

First, the common path X from the input / output terminal 7 to the outside.
When the surge voltage that has entered the inside of the semiconductor device 10 through the positive electrode has a positive polarity, V as the positive side protection element is used.
SS side diode 2 and VDD side Pch off transistor 3
Reduces the concentration of electric charges in the same manner as in the case of FIG. 2 so as to relieve the stress caused by the positive surge voltage on the first branch path A. Further, the protection resistor 5 on the inner common path Y has a function of further relaxing the stress caused by the positive surge voltage. As a result, the input / output circuit 6 is protected from electrostatic breakdown. Moreover, since the second branch path B is a path different from the first branch path A, the VDD side diode 1 and the VSS side Nch off transistor 4 as the negative side protection element on the second branch path B are provided. Is
The stress applied to them is reduced, and both are protected from destruction.

On the contrary, when the surge voltage that has entered the inside of the semiconductor device 10 from the input / output terminal 7 through the outer common path X has a negative polarity, V as a minus side protection element is provided.
DD side diode 1 and VSS side Nch off transistor 4
In the same manner as in the case of FIG. 2, the electric charge concentration is softened so that the stress caused by the negative surge voltage is relieved on the second branch path B. Further, the protective resistance 5 on the inner common path Y has a function of further relieving the stress caused by the negative surge voltage. As a result, the input / output circuit 6 is protected from electrostatic breakdown. Moreover, since the first branch path A is a path different from the second branch path B, the VSS side diode 2 and the VDD side Pch off transistor 3 as the positive side protection element on the first branch path A are provided. Will be less stressed and will not be destroyed.

As described above, according to this embodiment, even if the surge voltage of either positive or negative polarity enters the semiconductor device 10 through the input / output terminal 7, not only the input / output circuit 6 is protected from electrostatic breakdown, but also the positive voltage is applied. The side protection elements 2 and 3 and the minus side protection elements 1 and 4 are not destroyed. Moreover, it is possible to improve the surge withstand voltage of the electrostatic protection circuit itself as compared with the conventional case without changing the number of protection elements only by changing the layout so that the path from the input / output terminal 7 to the input / output circuit 6 is branched. You can

[0021]

As described above, according to the present invention, the route from the input / output terminal of the semiconductor device to the internal circuit is branched into two, and the positive side protection element and the negative side are provided in each of these branched routes. Since the protection element and the protection element are respectively arranged and the protection resistor is arranged in series on the common path, not only can the original function of protecting the internal circuit from electrostatic damage be exerted, but also the positive side protection element and It is also possible to prevent the negative side protective element from being destroyed. That is, according to the present invention, the surge withstand voltage of the electrostatic protection circuit itself can be improved.

[Brief description of drawings]

FIG. 1 is a circuit diagram schematically showing an electrostatic protection circuit for a semiconductor device according to an exemplary embodiment of the present invention.

FIG. 2 is a circuit diagram schematically showing a conventional example of an electrostatic protection circuit for a semiconductor device.

[Explanation of symbols]

1 VDD side diode (minus side protection element) 2 VSS side diode (plus side protection element) 3 VDD side Pch off transistor (plus side protection element) 4 VSS side Nch off transistor (minus side protection element) 5 Protection resistor 6 Input / output Circuit (internal circuit) 7 Input / output terminal 10 Semiconductor device A First branch path B Second branch path X Outer common path Y Inner common path

Claims (1)

[Claims] 1. An electrostatic protection circuit for a semiconductor device for protecting an internal circuit of the semiconductor device from electrostatic breakdown by relieving stress caused by a surge voltage entering through an input / output terminal. The first branch path has a common path and first and second branch paths so that one path from the output terminal to the internal circuit once branches into two and then joins. A positive side protection element for relieving stress caused by a positive surge voltage penetrating through the input / output terminal is arranged above, and a negative polarity protection element penetrating through the input / output terminal is provided on the second branch path. A negative side protection element for alleviating the stress caused by the surge voltage is disposed on the common path for positive or negative surge voltage entering through the input / output terminals. Electrostatic discharge protection circuit for a semiconductor device in which the protection resistor for mitigating stress caused by the surge voltage is equal to or arranged in series.