JPS6143863B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical thyristor that can be rendered conductive by applying light to a region corresponding to the gate of the thyristor.

The thyristor with the PNPN structure shown in Fig. 1 generally has a positive voltage applied to the anode 5, a negative voltage applied to the cathode 4, a positive voltage applied to the gate 9, and a predetermined current flowing between the gate and the cathode. The element can be brought into conduction. However, in such an element, it is very difficult to electrically insulate between the gate and cathode. For this reason, so-called optical thyristors, which can make elements conductive using optical signals, have recently come to be needed in circuits where the gate needs to be completely insulated from the cathode. In a photothyristor, when the reverse bias junction of a PNP is irradiated with light, the bare electrons and holes generated inside the junction are multiplied inside the depletion layer, increasing leakage current, which is further multiplied by the NPN transistor. This is an element that can change the element to a conductive state. In such an element, the smaller the electric power required to control the on/off of the element, the better, so the element is required to have high sensitivity to light. For this purpose, the h _FE of the NPN transistor must be increased and the area of the light receiving section must be increased. In addition, from other electrical characteristics, an element with a high dv/dt tolerance is required, which does not turn on even when a voltage with a large dv/dt, which is a temporal change in the voltage applied between the anode and cathode, is applied. For this purpose, the h _FE of the NPN transistor must be made small and the area of the light receiving section must be made small.

The above two requirements are clearly contradictory, and it is extremely difficult to simultaneously satisfy them in one element.

However, the present invention aims to eliminate such drawbacks and provide an element with high photosensitivity and high dv/dt tolerance.

In the present invention, in order to improve the dv/dt characteristics and increase the photosensitivity, an auxiliary thyristor is provided adjacent to the region that operates as the main thyristor, the junction of which is separated by a mesa groove, and the cathode of the auxiliary thyristor is connected to the main thyristor. The cathode of the auxiliary thyristor is connected to the gate region, and the cathode of the auxiliary thyristor is connected to the gate region of the main thyristor, and only the auxiliary thyristor region is selectively irradiated with an electron beam to form an element.
The main thyristor has a short circuit between the gate and the cathode, which can improve the dv/dt capability of the device by lowering the h _FE of the NPN transistor at small current levels. Furthermore, the auxiliary thyristor section has a structure that does not have a gate-cathode short circuit, thereby increasing the photosensitivity. However, without a short circuit, the dv/dt withstand capability will be reduced, so we selectively irradiate only the auxiliary thyristor with an electron beam using a metal mask to create strain within the crystal.
It is desirable to improve the dv/dt capability by somewhat lowering the h _FE of the NPN transistor. In this case, as an auxiliary thyristor, it is inevitable that the dv/dt withstand capacity will decrease when the light sensitivity is increased, but for this reason, even if the light sensitivity is slightly lowered and the dv/dt withstand capacity is improved, the light sensitivity will be lowered. The sensitivity is higher than that of the main thyristor. Further, by connecting the cathode of the auxiliary thyristor and the gate of the main thyristor to bring the auxiliary thyristor into conduction, the main thyristor can be brought into conduction. In addition, the dv/dt withstand capability is determined by reducing the junction area under reverse bias, because when a sudden voltage change occurs in the junction capacitance of a PNP during reverse bias, the current that flows as a displacement current flows through the element and leads to a conductive state. In order to reduce the junction capacitance, the area of the auxiliary thyristor may be made sufficiently smaller than that of the main thyristor, and from this point of view as well, a structure in which the main thyristor and the auxiliary thyristor are combined is desirable. Elements with such a structure have high sensitivity to light and can have high dv/dt tolerance.

Embodiments of the present invention will be described using the drawings.

An N-type silicon substrate 1 having a resistance of 15 to 30 Ωcm is selected, and boron is diffused from both sides to form an anode layer 3 and a gate layer 2 to a depth of 50 μm. Thereafter, the cathode layer 8 is selectively diffused using a known optical method. At this time, a short-circuit region 7 with the gate is provided at the cathode of the main thyristor. Further, mesa grooves 12 and 13 are respectively formed in the region between the main thyristor and the auxiliary thyristor and in the region surrounding the pellet, and the junctions 10 and 14 exposed on the surface are protected with glass 6. After that, electrodes 5, 4, 9,
11 by vapor deposition, many pellets
It is made in a continuous state within a single wafer. This wafer is selectively irradiated with an electron beam using a molybdenum mask only on the cathode region 17 of the auxiliary thyristor with an intensity such that the flux is 1×10 ¹⁵ ev/cm ² . The wafer thus prepared is separated into pellets using a laser scribe and assembled using a normal assembly method. At this time, the cathode electrode 11 of the auxiliary thyristor and the gate electrode 9 of the main thyristor are wired with an A line 15. By applying a positive voltage to the anode 5 of such an element and a negative voltage to the cathode, and applying infrared rays 16 with a wavelength of about 1 μm to the cathode region 17 of the auxiliary thyristor, the optical thyristor can be rendered conductive. An example of the electrical characteristics of this device is that the device has a breakdown voltage of 750V, dv/
We were able to obtain characteristics with a dt tolerance of 20V/μsec and a photosensitivity of 2mA.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a conventional thyristor.
FIG. 2 is a cross-sectional view of an optical thyristor according to an embodiment of the present invention. In the figure, 1... N type substrate, 2... P type gate layer, 3... P type anode layer, 4... cathode electrode, 5... anode electrode, 6... glass surface protective film, 7... Gate cathode short circuit part, 8... Cathode layer of main thyristor, 9... Main thyristor gate electrode, 10... Thyristor forward junction, 12
...Main thyristor, auxiliary thyristor separation section, 13
. . . pellet peripheral mesa portion, 14 . . . thyristor reverse junction, 15 . . . main thyristor gate electrode and auxiliary thyristor cathode electrode short-circuit conductor, 16 . . . external infrared rays, 17 .

Claims (1)

[Claims] 1 Can be made conductive using light
A PNPN thyristor has an auxiliary thyristor adjacent to a region that operates as a main thyristor, the junction of which is separated by a mesa groove, the cathode of the auxiliary thyristor is connected to the gate region of the main thyristor, and the auxiliary thyristor has a selective An optical thyristor comprising a region irradiated with an electron beam.