JPS6013311B2 - Semiconductor controlled rectifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to semiconductor controlled rectifiers, and more particularly to thyristors.

The structure of a generally known thyristor will be explained with reference to FIG. 1. In the figure, 1 is a relatively low concentration n
2 is a p+ conductivity type anode layer provided on one surface of the base layer 1; 3 is a p conductivity type base layer provided on the other surface of the base layer; 4 is a conductive light-type base layer; This p
This is a cathode layer of n+ conductivity type selectively provided on the conductivity type base layer 3.

Reference numeral 5 designates an anode electrode that makes ohmic contact with the anode layer 2, 6 a cathode electrode that makes ohmic contact with the cathode layer 4, and 7 a gate electrode that makes ohmic contact with the base layer 3 of the p conductivity type. An overview of the operation of a thyristor having such a structure will be explained.

When the main current is applied, a negative bias is applied to the cathode electrode 6 and a positive bias is applied to the anode electrode 5. At this time, the junction J between the anode layer 2 and the n-conductivity type base layer 1 and the junction J3 between the cathode layer 4 and the p-conductivity type base layer 3 are biased in the forward direction; The junction J2 between the shaped base layers 3 is reverse biased. Holes are injected from the gate electrode 7 , and electrons are injected from the cathode electrode 6 through the cathode layer 4 into the p-conductivity type base layer 3 . The injected electrons are collected in the n-type base layer 1 through the junction J2. At this time, holes are injected from the anode layer 2 into the n-conductivity type base layer 1, pass through the base layer 1, and are collected in the p-conductivity type base layer 3. These holes cause electrons to be injected from the cathode layer 4 into the p-conductivity type base layer 3 through the junction J3 again. By repeating this process, the joint J
By accumulating holes and electrons in the base layers on both sides of J2, the junction J2 changes from reverse bias to forward bias and becomes conductive. The process of transitioning to this conductive state is called turn-on, and its speed is determined by the speed at which holes injected from the gate electrode T enter the cathode layer 4, and the speed at which electrons injected from the cathode layer 4 into the p-conductivity type base layer 3 It depends on the speed of transmission to the conductivity type base layer 1, the speed at which holes injected from the anode layer 2 to the n conductivity type base layer 1 reach the p conductivity type base layer 3, etc. In addition, the reverse bias voltage is applied to the cathode electrode 6.
The process of changing from the conductive state to the blocking state when the fin flow is interrupted by applying between the anode electrode 5 and the anode electrode 5 is called turn-off.
This is limited to the speed at which the holes and electrons remaining in the vicinity of the junction J2 disappear and the forward blocking state is completely restored. However, although the conventional sirolith switch having the above-described structure has an excellent ability to control large electric power, its control speed is low, and a switching device with high speed and high withstand voltage cannot be obtained.

The present invention was made in view of these points, and its purpose is to increase the control speed and increase the d for high-speed operation.
The object of the present invention is to provide a semiconductor-controlled rectifier that can operate at high speed and withstand high voltage by increasing the i/dt and dv/dt withstand capacities.

To achieve this object, the present invention comprises an n-conductivity type base layer, a p-conductivity type anode layer and a base layer provided on both sides of this base layer, and ~ on this p-conductivity type base layer. In a semiconductor controlled rectifier comprising an n-conductivity type cathode layer provided, the p-conductivity type base layer is formed in a predetermined pattern adjacent to the p-conductivity crab-shaped base layer. A p conductivity type gate region having a higher impurity concentration than the base layer is provided, and a high concentration base region having a higher impurity concentration than the base layer is provided between the n conductivity type base layer and the anode layer. When the mutual spacing between the regions is 2a, the thickness and impurity concentration of the p-conductivity type base layer are W8 and Na, and the impurity concentration of the n-conductivity type base layer is Nd, Nd・a2<Na・
It is characterized by being made to be WB2. Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a sectional view of a main part of a thyristor showing an embodiment of the present invention,
The same numbers are used for the same or corresponding parts as in FIG. 1.

Here, the difference from the thyristor structure in FIG. 1 is that a p-conductor is formed on the n-conductor base layer 1 adjacent to the p-conductor base layer 3a in a comb-like or mesh shape in a fine pattern vertically and horizontally. A gate region 8 of the shape of a conductivity type is provided, and an n+ conductivity type base layer region 9 containing impurities at a higher concentration than the base layer wing is provided between the n conductivity type base layer layer and the p+ conductivity type anode layer 2. That's true. In this case, the p-conductivity type base layer 3a is formed sufficiently thinner than the p-conductivity type base layer 3 in FIG. can. The thickness WB of the p-conductivity type base layer 38 is defined as "Nd" between the mutual spacing 2a of the gate regions 8 and the impurity concentration Na of the p-conductivity type base layer 3a and the impurity concentration Nd of the n-conductivity type base layer 3a.
.

a2<Na. It is determined to satisfy the relationship W82.

The thickness of the p-conductivity type base layer 3a varies depending on the mutual spacing of the gate regions 8, the low resistivity of the p-conductivity type base layer 3a, the applied voltage of the device, etc.
It can be formed up to a base depth of '5. According to the thyristor having the structure of the above embodiment, when it is turned on, the gate electrode? Holes injected from the T-gate region 8 try to be injected into the cathode layer through the D conductivity type base layer 3a. Since the gate region 8 is formed in a tooth-like or mesh-like shape, the resistance is low, and the resistance is quickly transmitted through the gate region 8 to the entire surface of the device.

Therefore, electron injection from the cathode layer 4 occurs quickly.
In addition, the injected electrons reach the n-conductivity type base layer 1 after passing far through the p-conductivity type base layer 3a, which is thinner than the conventional structure. As a result, the injection of holes from the toanode layer 2 is made farther away, and the turn-on time is increased from 1'2 to
It can be reduced to 1'10. That is, the first
In the thyristor structure shown in the figure, the turn-on time of the thyristor is determined by the thickness WB of the p-conductivity type base layer 3 and the n
Depending on the thickness WB2 of the conductivity type base layer 1, and assuming the minority carrier transit time in the n and p conductivity type base layers, the evening on time (ton) is approximately equal to tonnizo-t2. Become.

However, Dn and Dp are minority carrier diffusion constants in each of the base layers. Therefore, the thicker the base layer, the longer the turn-on time, and the smaller the thickness of the p-conductivity type base layer 3, WB, is. Then, a problem arises in that the forward blocking voltage of the thyristor is controlled by the punch-through voltage VpT of its base layer.In contrast, the present invention has a method of suppressing the extension of the depletion layer in the p-conductivity type base layer 3a. Therefore, the thickness W8, of the base layer region 9 of the n+ conductivity type is reduced by 4.0 cm, and the thickness WB2 of the n conductivity type base region 1 is reduced by 4.0 cm. The extension of the depletion layer in the conductive base layer 3a is approximately 1 nom compared to the structure shown in FIG.
However, it is the cape xp (number), the distance between the gate areas 8 on this side, and L is the depth thereof.

Therefore, the thickness of the p-conductivity type base layer 3a (=WB, is 1/
can be screamed and therefore the turn-on time is 1
You can scream. For example, the back:. At -7, the turn-on time is reduced to about 1/degree. Furthermore, assuming that the thickness WB of the p-conductor crane-shaped base layer 3a is constant, the structure shown in Fig. 2 can apply a voltage twice as high as that of Fig. 1. It can be doubled.
On the other hand, when the current is cut off, the cathode electrode 6 and the anode electrode 5
A reverse bias voltage is applied between the junction J
, and J3 are reverse biased, whereas junction J2 remains inverted and forward biased, so
In the conventional structure, the excess carriers near the junction J2 had to disappear naturally by recombination, and it took a long time for turn-off.

In the present invention, the anode layer 2 is formed by the n+ conductivity type base layer 9 provided between the n conductivity type base layer 1 and the anode layer 2.
The injection of holes into the base layer 2 is controlled by "appropriately selecting the thickness and impurity concentration of the n+ conductivity type base layer 9 so as to reduce the amount of holes injected as much as possible and turn on the structure in the evening." Therefore, fewer carriers disappear during turn-off, and the turn-off speed can be increased. This will be explained with reference to FIG.

Here, FIG. 3 corresponds to the conventional thyristor shown in FIG. 1, and FIG. 4 corresponds to the thyristor exterior of the present invention shown in FIG. 2. In the conventional thyristor structure, when the thyristor changes from the off state to the on state, current concentrates in the area A shown in FIG. As time passes, the current flow area spreads over the entire surface of the cathode layer at a speed vs. On the other hand, in the structure of the present invention, B shown in FIG.
The current is concentrated in the peripheral portion of the p+ atomized gate region 8, and its area expands at a speed vs. Therefore, in the present invention, the effective emitter peripheral length becomes longer and "dv/dt
Tolerance is improved. Further, since the above vs is inversely proportional to the thickness WB2 of the n-conductivity type base layer 1, in the present invention, this vs
becomes larger, which also contributes to improvement of di/dt tolerance. In addition, an n-conductivity type cathode (emitter) layer 4
, a p-conductivity type base layer 3 and an n-conductivity type base layer 1, the current amplification factor Q of the npn transistor depends on the density of the current flowing through the thyristor, and generally the Q increases as the current density increases.

By reducing the current density dependence of Q, the dv/dt withstand capability is improved. When the thickness WB of the p-conductivity type base layer 3a becomes thinner, the base transport efficiency of the npn transistor comes to be dominated by carrier diffusion, and the influence of drift due to the electric field becomes relatively smaller. Therefore, in the structure of the present invention, the current dependence of Q becomes small ~d
The v/dt tolerance will be improved. As explained above, according to the semiconductor controlled rectifier according to the present invention, a p-conductivity type gate region formed in a predetermined pattern is provided adjacent to a p-conductivity type base layer on an n-conductivity hazy base layer. The thickness of the base layer is reduced by suppressing the extension of the depletion layer within the p-conductivity type base layer, and the base layer has a higher impurity concentration than the base layer provided between the base layer and the p-conductivity type anode layer. Since the structure is such that the thickness of the n-conductivity type base layer is reduced by the high concentration base region, the thickness of the p-conductivity type base layer can be sufficiently thinned by the gate region, and the breakdown voltage in the normal direction can be increased. This has the advantage that it is possible to provide a high-speed, high-voltage semiconductor-controlled rectifier.

[Brief explanation of drawings]

FIG. 1 is a sectional view of the main part of a conventional thyristor, FIG. 2 is a sectional view of the main part of a thyristor showing an embodiment of the present invention, and FIGS. dLd
FIG. 2 is an explanatory diagram for explaining v/dt tolerance. 1...n-conductivity type base layer 2...p+ conductivity type anode layer, 3, 3a...p conductivity type base layer, 4...n+ conductivity type cathode layer, 5... anode electrode,
6...Cathode electrode, 7...Gate electrode, 8...P+ conductivity type gate region, 9...
, base area of conductive type. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1 A base layer of n conductivity type, an anode layer and a base layer of p conductivity type provided on both sides of this base layer, and this p conductivity type base layer.
In a semiconductor controlled rectifier comprising a cathode layer of n conductivity type provided on a base layer of conductivity type, the base layer of n conductivity type is formed in a predetermined pattern adjacent to the base layer of p conductivity type. a p-conductivity type gate region having a higher impurity concentration than the p-conductivity type base layer;
A high concentration base region having an impurity concentration higher than that of the base layer is provided between the conductivity type base layer and the anode layer, the mutual spacing of the gate regions is 2a, and the thickness and impurity concentration of the p conductivity type base layer are respectively W_B and Na,
When the impurity concentration of the conductivity type base layer is Nd, N
A semiconductor-controlled rectifier device characterized in that d・a^2<Na・W_B^2.