Normally conducting dual thyristor

Miscellaneous active electrical nonlinear devices – circuits – and – Gating – Utilizing three or more electrode solid-state device

Reexamination Certificate

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Details

C327S439000, C257S133000, C257S132000

Reexamination Certificate

active

06188267

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a dual thyristor, that is, to a component, the features of which can be induced from those of a conventional thyristor by applying the duality principle to the current and voltage behaviors and to the control modes.
2. Discussion of the Related Art
FIG. 1A
shows a conventional thyristor Th including an anode A, a cathode K, and cathode and anode gates GK and GA.
The characteristic curve of a thyristor is illustrated in FIG.
1
B. This component exhibits the following features:
it is normally off,
it is a one-way component for the current, that is, it is likely to let through a positive current I
A
but blocks a negative current,
it is bidirectional for the voltage, that is, it is likely to withstand positive or negative voltages in the off state,
it can be triggered by a current pulse applied to its gate when the voltage thereacross is positive; this is illustrated in
FIG. 1B
by curve
10
, that is, when a gate current is applied thereto, it turns on by break over, and its characteristic becomes that indicated by curve
11
,
it is self-triggering when the voltage thereacross exceeds a value VBO in the absence of a gate current,
it spontaneously turns off when the current flowing therethrough becomes low (lower than a hold current value I
H
).
The symbol of a dual thyristor is illustrated in FIG.
2
A. This dual thyristor has current-voltage characteristics which are dual with respect to those of a conventional thyristor, as is shown in FIG.
2
B:
it is normally on,
it is bidirectional for the current, that is, a positive current as well as a negative current can flow therethrough (the flowing of a negative current is ensured by diode D illustrated in FIG.
2
A),
it is a one-way component for the voltage, that is, it is likely to withstand positive voltages only, in the off state, due to the presence of diode D,
it can be turned off by a voltage pulse applied to the gate, that is, if, while the operating point is on curve
20
, a control voltage is applied, the operating characteristic will become that designated with reference
21
,
it has a self turn-off characteristic, that is, if the current flowing therethrough exceeds a value I
BO
, it turns off by itself,
it spontaneously triggers at voltage zero crossing, that is, it turns on if, while in the off state, the voltage thereacross drops below a threshold voltage V
H
.
In other words, while a thyristor forms a normally off one-way component for the current, which can be triggered by a control current or be self-triggering beyond a given voltage threshold, a dual thyristor forms a normally on switch which can be turned off by a control voltage or be self-locking beyond a given voltage threshold.
In prior art, the implementation of a system having the function of a dual thyristor has been performed by associating a specific control circuit with a switching component. This solution has two disadvantages. The first one is that it is always difficult to monolithically associate control circuits with a power component. The second one is that it is necessary to provide for the control circuit a bulky auxiliary power supply, which is costly and possibly sensitive to surrounding disturbances. A simplified dual thyristor not controllable by pulses is described in EPE'95: 6TH European Conference on Power Electronics and Application, Seville, Sep. 19-21, 1995, vol. 1, Sep. 19, 1995, P. 1.637 to 1.642, X P OOO537596, J-L Sanchez et al.
SUMMARY OF THE INVENTION
Thus, an object of the present invention is to provide a simple assembly of components having the function of a dual thyristor.
Another object of the present invention is to provide such an assembly in the form of a monolithic component.
Another object of the present invention is to provide such a monolithic component which can be manufactured by usual technologies.
To achieve these objects as well as others, the present invention provides a component forming a dual thyristor, which is normally on and which can be turned off by a voltage pulse on the control electrode, including a thyristor, a resistive means formed of a first depletion MOS transistor, the gate of which is connected to the source, the substrate of this transistor being connected to the cathode gate terminal, connected between the anode gate and the thyristor cathode, and a controlled conduction switching means formed of a second enhancement MOS transistor, the gate of which is connected to a control terminal and the substrate of which is connected to the cathode gate terminal, connected between the cathode gate and the thyristor cathode.
According to an embodiment of the present invention, the component is pulse-controlled and further includes means for maintaining the conduction between the cathode gate and the cathode as soon as this conduction has been triggered by the switching means.
According to an embodiment of the present invention, the maintaining means include a third enhancement MOS transistor, the substrate of which is connected to the cathode gate terminal, in parallel on the second enhancement MOS transistor; a zener diode connected between the cathode of the thyristor and a node connected to the gate of the third transistor; and a fourth depletion MOS transistor connected between said node and the anode gate of the thyristor, the gate of the fourth transistor being connected to the cathode and its substrate being connected to said node.
According to an embodiment of the present invention, a low leakage current component is made by providing, in series with the first depletion MOS transistor, a second switching means, normally on and turned off after a control order has been applied to the second transistor.
According to an embodiment of the present invention, the second switching means is a floating substrate P-channel depletion MOS transistor, the gate of which is connected to said node.
According to an embodiment of the present invention, the thyristor is implemented in vertical form in a silicon substrate of a first conductivity type; the first depletion MOS transistor is implemented between the cathode region of the thyristor and the substrate; each of the second and third MOS enhancement transistors is formed between two regions of the first conductivity type formed in a first cathode gate well of the thyristor, one of these two regions corresponding to the cathode region of the thyristor; the fourth depletion MOS transistor is formed between a region of the first conductivity type, itself formed in a second well of the second conductivity type separated from the gate well of the thyristor, and the substrate; and the zener diode is formed in the second well.
According to an embodiment of the present invention, the component is formed from a substrate of the first conductivity type, the rear surface of which is coated with a layer of the second conductivity type coated with a first metallization and includes on its front surface side a first well of the second conductivity type containing first, second, third and fourth regions of the first conductivity type, the first and second regions being separated by a portion of the first well coated with a first insulated gate metallization, the third and fourth regions being separated by a portion of the first well coated with a second insulated gate metallization, a portion at least of the first well separating the first and/or the fourth region from the substrate including at its upper surface a first preformed channel region coated with a third insulated gate metallization, a second metallization coating the first region, a third metallization coating the second and third regions and a portion of the upper surface of the first well, a fourth metallization coating the fourth region; and a second well of the second conductivity type including fifth and sixth regions of the first conductivity type, the fifth region being separated from the substrate by a second preformed channel region coated with a fourth insulated gate metallization, the sixth region forming

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