JPH04106935A - Dual direction thyristor - Google Patents

Abstract

PURPOSE:To make it possible to manufacture a low pressure resistance and low capacitance device easily by further reducing punch-through voltage so that it is smaller than PN junction pressure resistance between a P (n)-type common substrate semiconductor and an N (p)-type base. CONSTITUTION:P<+> regions C and C' are installed on an exposed portion on the surface of a P-type substrate. This region is so formed that the punch-through voltage determined by a span 1 between an N1 base and N2 base is lower than an avalanche yield voltage of junctions J2 and J3. The breakdown strength of a device is determined by the impurity concentration of a P layer and a span 1 between punch-through portions C and C' and an N base. The breakdown strength is determined only by the span l in the case of the same impurity concentration. Therefore, a required lower breakdown strength is available by the selection of a thickness l. The capacitance of the device can be determined by the concentration of impurities. However, the thickness of the P layer portion which excludes the C and C' portions related with the capacitance value is greater while the concentration of impurities is smaller, which makes it possible to minimize the capacitance. It is, therefore, possible to obtain a dual directional thyristor characteristic of lower breakdown strength and a smaller capacitance as well.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a PNPNP (NPNPN) bidirectional thyristor, particularly to lowering the breakdown voltage (Vao) and reducing the capacitance.

(Prior art) A bidirectional thyristor having the basic structure as shown in FIG. The exposed P...
22 layers are formed, and the metal electrode T IIT2
A bidirectional thyristor is well known, which has a five-layer structure in which the first layer and the N1 layer and the 22nd layer and the N2 layer are short-circuited, respectively, and operates as follows.

It is assumed that a voltage is applied in a direction that causes a current to flow in the direction of the arrow shown in the diffusion cross-sectional view of FIG. 1(a). When this voltage exceeds the withstand voltage (V, .) of junction J3, current begins to flow through junction J3. Then, the current component I2 flowing laterally through the N2 layer of this current and the voltage drop based on the lateral resistance R or the junction J are forward biased to cause holes to be injected from the 22nd layer. For this purpose, the electrodes T, T2 are turned on as shown in the voltage-current characteristic diagram shown in FIG.

When a voltage in the opposite direction to the above is applied, the junction J1 is forward biased by the current component flowing in the lateral direction in the N1 layer, turning on the electrode T1°72 as shown in FIG. I do.

Since this bidirectional thyristor has two terminals and is easy to use, and is also small and lightweight, it is becoming widely used as a surge protection element for various electronic circuits connected to low-power circuits, such as communication lines.

However, as electronic circuits have recently become more integrated and their withstand voltages have become lower, there has been a strong demand for bidirectional thyristors with low withstand voltages (V,...), and the recent progress in digitalization has increased. Demand for elements with low capacitance is increasing.

(Prior art and its problems) However, in the conventional bidirectional cross-risk structure based on such avalanche breakdown, T of 18+ in FIG.

The breakdown voltage V B O between 72 and 72 is almost uniquely determined by the specific resistance of the P layer, that is, the impurity concentration, and as the impurity concentration decreases, vao increases.

On the other hand, the junction J2 which determines the capacitance of the element. The capacitance of J3 is almost uniquely determined by the impurity concentration of the P layer,
As is well known, as the impurity concentration decreases, the capacitance decreases in proportion.

Therefore, if the impurity concentration of the P layer is increased in order to lower the breakdown voltage, the capacitance also increases, resulting in a so-called one-doff relationship, making it difficult to realize a bidirectional thyristor with low breakdown voltage and low capacitance.

Therefore, as a means to solve this problem, the thickness W of the P layer shown in FIG. Instead, it may be possible to obtain it by punching through two layers of N and PN.

However, when trying to obtain a device with the required low breakdown voltage and low capacitance using this method, the thickness W of the P layer in FIG. 1(a),
However, it becomes too thin and difficult to manufacture, making it difficult to realize it.

For example, if the impurity concentration of the P layer is 1014/cc, N+,
N = layer surface concentration 10”/cc, its diffusion depth 3
0μ, assuming the impurity distribution to be an error function type, and setting the punch-through voltage to 150V, the spread of the depletion layer to the P layer, and therefore the thickness W of the P layer in the N2 layer, is 35μ.
It will be about. As a result, the thickness of the entire device including the N, N2 layers is approximately 100 μm, which poses significant difficulties in manufacturing using 4-inch wafers, which are commonly used at present.

(Objective of the Invention) The present invention provides a structure in which an element with a required low breakdown voltage and low capacitance can be easily manufactured by a known means such as ordinary selective diffusion using the punch-through method, The present invention aims to realize a bidirectional thyristor that can reliably provide surge protection for this type of circuit, such as the integrated circuit having the digitalization processing function.

(Means of the present invention for solving the problems) The present invention is characterized by a bidirectional thyristor having a five-layer structure.
By providing a region determined by its breakdown voltage or punch-through in a part of the NF2 (N, PN2) layer, the thickness of the main portion of the P layer, and therefore the thickness of the device, can be maintained the same as that of conventional devices due to avalanche breakdown. This makes it possible to realize an element with a low breakdown voltage, thereby making it possible to easily manufacture an element with the required low breakdown voltage and low capacitance. Next, the present invention will be explained by way of an example.

(Embodiment) FIGS. 2(a), 2(b), and 2(c) are a plan view showing an embodiment of the present invention, a diffusion cross-sectional view taken along line A-A' in the plan view, and an equivalent circuit diagram thereof. In the present invention, P' regions c and c' are provided on the exposed surface of the P-type substrate, and these regions are N, , N
The punch-through voltage determined by the distance β between the two bases or the junction J2. It is designed to be lower than the avalanche breakdown voltage of J3.

Next, its operation will be explained.

It is assumed that a voltage is applied with a polarity that causes a current to flow in the direction of the arrow in Figure 2 (b). Then, when the applied voltage reaches a punch-through voltage corresponding to the distance r, a current I begins to flow through C. When the current I increases, the junction J4 is forward biased due to the voltage drop due to the effective lateral resistance R of N2@ directly under the 22nd layer, so holes are injected from the 22nd layer in the portion J4 near the region C. This can be seen in the main thyristor N1PN2P, N2. This corresponds to the ignition current I flowing in and out of the PC punch-through diode.
The main thyristor starts turning on from this vicinity, and the turn-on region spreads over the entire surface. Since the above operation is symmetrical in structure, the same operation is performed from the C' detail even when the voltage is applied in the opposite direction.

As described above, the breakdown voltage V8o of the device of the present invention is determined by the impurity concentration of the P layer and the distance l between the punch holes c and c' and the N base, and for the same impurity concentration, it is determined only by l,
By selecting the thickness l, it is possible to achieve a desired low breakdown voltage.

Also, the capacitance of the element and hence the junction J2. The capacitance of J3 is determined only by the impurity concentration, or the thickness of the P layer portion other than the C2C portion related to the capacitance value, and therefore the main portion of the P layer, is large and the impurity concentration is small. By reducing the capacitance, the trade-off problem described above is solved at once, and it becomes possible to provide a bidirectional thyristor with low breakdown voltage and small capacitance.

In addition, in the present invention, the punch sle part c, P other than c'
The thickness of the layer portion, that is, the main portion of the P layer, can be made as thick as in the conventional device based on avalanche breakdown, and the thickness of the device itself can be increased. Therefore, the difficulties in manufacturing process are significantly reduced compared to the case where a punch-through structure is obtained by reducing the overall thickness of the P layer described above.

In addition, according to the present invention, it is possible to obtain an element with less variation in surge current withstand capacity, which is a performance required for surge protection. In other words, the surge current withstand capacity is determined by the power loss in the turn-on transition region shown in Figure 1 (bl),
It is greatly influenced by the speed at which the turn-on area spreads over the entire surface from the initial turn-on position, that is, the initial ignition position.

However, in conventional elements, the ignition position is not constant, which tends to cause variations in surge current withstand capacity.

However, in the present invention, the initial firing position is the punch-through portion c,
Since the current is always localized to c', it is possible to provide a bidirectional thyristor with almost no variation in surge current resistance.

One embodiment of the present invention has been described above, and FIG.
l (The plan view and diffusion cross-sectional view shown in bl are
Using the commonly used channel stopper C8,
This is an embodiment in which a punch-through region is formed by partially reducing the distance to the N base layer.In addition, in the embodiment of the present invention, the P+
It is possible to provide the region on the exposed surface portion of the P substrate or to provide it inside by buried diffusion, etc., and various modifications are possible. For example, when viewed from the surface side, they may be connected in a ring shape or discontinuously provided in a dotted manner.

Furthermore, various known manufacturing methods can also be used. Furthermore, the present invention can be effectively applied to a composite thyristor whose basic structure is a PNPNP (NPNPN) bidirectional thyristor.

(Effects of the Invention) As is clear from the above description, the present invention is suitable for surge protection of integrated circuits that handle digital signals that have low withstand voltage, small capacitance, and less variation in surge current withstand capacity. Bidirectional thyristors can be provided.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a conventional element, FIG. 2 is an explanatory diagram of one embodiment of the present invention, and FIG. 3 is an explanatory diagram of another embodiment of the present invention.

Claims (2)

[Claims] (1) Both sides of the common substrate semiconductor P(N) type have N(
P) base and P(N) base are provided, and N(P) of each surface is
A part of the base is exposed on the surface and short-circuited with the P(N) emitter to form one electrode, and an impurity region P^+ (N^+) of the same conductivity type is provided in the common substrate semiconductor. , the punch-through voltage determined by the distance between this P^+(N^+) region and the N(P) base is set to be smaller than the breakdown voltage of the PN junction between the P(N) type common substrate semiconductor and the N(P) type base. A bidirectional thyristor characterized by: (2) The bidirectional thyristor according to claim 1, wherein the P^+(N^+) region is provided in a portion exposed on the surface of the P(N) type substrate.