Semiconductor device

Details Semiconductor device Semiconductor device

2000-03-08

2002-06-11

Flynn, Nathan (Department: 2826)

Active solid-state devices (e.g., transistors, solid-state diode

Field effect device

Having insulated electrode

C257S350000, C257S356000, C257S360000, C327S310000

Reexamination Certificate

active

06404016

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor device, and more particularly to a protection circuit for electrostatic breakdown (it may be called as electrostatic discharge “ESD”) in the semiconductor device including two or more kinds of power source systems in a single unit.
Now referring to the drawings, an explanation will be given of a semiconductor device according to a prior art. Many semiconductor devices, represented by a device incorporating a digital section and an analog section in the single unit, have two or more individual power source systems, which may be set at equal voltages.
An example of such a semiconductor device is shown in FIG.
3
. As seen from
FIG. 3
, this device includes first circuitry which is an analog section composed of an analog circuit
1
, an output circuit
3
and an input protection circuit
5
, and second circuitry which is a digital section composed of a digital circuit
2
and an input circuit
4
. Both sections are connected to each other by a signal line S
1
.
A power source voltage for the analog section is supplied from power source lines Vdd
1
and Vss
1
, whereas a power source voltage for the digital section is supplied from power source lines Vdd
2
and Vss
2
. The power source lines Vdd
1
and Vdd
2
are separated from each other, and the power source lines Vss
1
and Vss
2
are also separated from each other.
In the above device, an output signal is produced from the analog circuit
1
through the output circuit. The output signal is transferred to the digital circuit
2
of the digital section through the signal line S
1
. Specifically, the output signal is supplied to the input circuit
4
made of an inverter.
Because of any cause, where a surge input is supplied from an applying terminal NT which is an input terminal to the analog section, a rushing current SR occurs along the passage as shown in
FIG. 3
so that the potential at the power source line Vss
1
rises. Correspondingly, the potential in the signal line S
1
also rises. This applies to the case where the surge input is supplied from the power source line Vss
1
.
In this case, the following problem occurs. The gate potential of a MOS transistor Q
1
constituting an inverter of the input circuit
4
rises excessively so that the gate-source voltage of the MOS transistor Q
1
increases excessively. As a result, the gate oxide film of the MOS transistor Q
1
will be broken.
In order to prevent such electrostatic breakdown in the above circuit configuration, i.e. a semiconductor device in which a multiple power system having two or more kinds of power sources and first circuitry and second circuitry are contained therein and the first circuitry and the second circuitry are connected by a signal line, it is proposed to place a protection circuit (e.g. MOS transistor) between the first power source line Vss
1
and the second power source line Vss
2
. In such a proposed circuit configuration, when the potential difference between the first power source line Vss
1
and the second power source line Vss
2
exceeds a prescribed value, the protection circuit becomes conductive so that both power source lines are made the same potential, thereby preventing occurrence of the electrostatic breakdown in the MOS transistor Q
1
.
However, in the above device configuration, the direction of the MOS transistor is determined based on which of the first power source line Vss
1
and second source line Vss
2
is larger or smaller than the other is determined. In a case where the direction of the MOS transistor is incorrectly set, the first power source line Vss
1
and second power source line Vss
2
are short-circuited to each other even if the protection circuit is provided.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a semiconductor device capable of protecting electrostatic breakdown when a surge input occurs irrespectively of the magnitude relationship between the first power source line and second power source line.
According to the invention, a semiconductor device includes an N-type semiconductor substrate on which an analog section to which power source lines Vdd
1
and Vss
1
are supplied and a digital section to which power source lines Vdd
2
and Vss
2
are supplied. The analog section and the digital section are mounted and connected to each other by a signal line S
11
. The device also has a protection circuit HK
1
located between the power source line Vss
1
and Vss
2
. The protection circuit becomes conductive when a potential difference between the power source lines Vss
1
and Vss
2
exceeds a prescribed value irrespectively of the direction of the a surge input. Therefore, the power source lines Vss
1
and Vss
2
are placed at substantially the same potential.


REFERENCES:
patent: 5886558 (1999-03-01), Iijima et al.
patent: 9 172146 (1997-06-01), None

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