JPH03233973A - Composite thyristor - Google Patents

Abstract

PURPOSE:To increase a surge breakdown strength by forming two sets of PNPNP layer structure provided with a lower breakdown strength region than other part at the part of a junction for determining a forward breakdown strength. CONSTITUTION:An N11 layer, a P11 layer and an N21 layer are provided on one side surface of a substrate with a P-type semiconductor as the common substrate, and an N13 layer, a P13 and an N23, a P23 layer are provided on the other side surface. a 5-layer structure S1S2 provided with a low breakdown strength region L is formed of a P<+> type layer on an exposed part of junctions J12, J21 and junctions J13, J23 to the surface. The P11 layer is short-circuited to the N11 via a first metal electrode T1, the P21 layer is short-circuited to the N21 layer via a second metal electrode T2, and the P13 layer, the N13 layer of the other surface are commonly short-circuited to the P23 layer, the N23 layer via a third metal electrode T3. Thus, a low breakdown strength can be obtained without reducing the thickness of the P-type layer, characteristics are uniform, and an initial arc igniting position becomes constant. Accordingly, an irregularity in a surge protective breakdown strength can be reduced, and a surge current breakdown strength can be increased.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a composite thyristor suitable for surge protection of low voltage circuits.

(Prior art and problems to be solved) As shown in the cross-sectional view in Fig. 1, 5 of P, N, PN2 P2
A two-way shorted emitter type two-terminal thyristor, which has a configuration in which the Pl and N3 layers are short-circuited by a metal electrode T1 and the N2 and 22 layers are short-circuited by a metal electrode T2, is used in electronic equipment connected to communication circuits and other circuits. It is becoming widely used as a surge protection device in circuits.

However, in order to use the above-mentioned PNPNP type thyristor to exert a protective effect against both horizontal and vertical surges, the line to which the protected device circuit M is connected, as shown in FIG. , L2, a series vertical surge thyristor 2. whose midpoint is grounded E. ．． 22 must be connected, and thyristor Z3 must be connected for lateral surge. Therefore, the circuit configuration becomes complicated.

Furthermore, the recent integration of electronic device circuits has required lower breakdown voltage (VB.) of thyristors, and the digitalization of electronic device circuits has strongly required lower capacitance of thyristors. However, in the structure shown in Figure 1, the withstand voltage is determined by the thickness (resistivity) of P, which is the common substrate. tends to cause non-uniformity.

Further, in a normal structure, the capacitance is determined by the area of the junction J2 in FIG. 1 and the resistivity of the P layer, which is a common substrate, and as the resistivity decreases, the capacitance increases. Therefore, as mentioned above, when the thickness of the P layer is reduced in order to lower the breakdown voltage, the capacitance increases. Therefore, it is impossible to create a thyristor with low breakdown voltage and capacitance, and it is difficult to realize a thyristor that can protect digitalized integrated circuits.

In addition, the surge resistance of a thyristor is determined by the power loss in the turn-on transition region and the speed at which the initial firing spreads over the entire region, but the initial firing position is determined by the junction JIJ shown in Figure 1.
2 or due to subtle non-uniformities that occur during manufacturing, such as lateral resistance.

Therefore, it is difficult to manufacture a device with uniform surge current resistance. Therefore, as shown in FIG. 2, the three thyristors 2, 22
2. This tends to cause non-uniformity of characteristics, leading to a risk of malfunction.

(Objective of the Invention) The present invention applies the thyristor structure previously proposed by the present inventor, and is capable of providing protection against both vertical and horizontal surges with a single thyristor. The aim is to realize a composite thyristor with uniform characteristics such as low breakdown voltage, low capacitance, and high surge resistance that can protect circuits.

(Means of the Invention for Solving the Problems) The present inventor has previously proposed a thyristor that solves various problems of the thyristor shown in FIG. This thyristor is shown in Figure 3(a).
As shown in the cross-sectional view shown in Figure 3(b), a part of the joint J2J is exposed on the surface, or as shown in the cross-sectional view shown in Figure 3(b), P
Immediately below the tPs layer, a region having a lower breakdown voltage than other parts of the junction J2J2 is provided, for example, by a P+ layer, so that the following operations are performed. Note that in FIG. 3, ■ is an insulating film.

That is, in the unidirectional thyristor shown in FIG. 4 (al), when a current is passed in the forward direction from T to T2, a reverse voltage is applied to junction J2, which first causes the low breakdown voltage region to rise. Breakdown occurs at voltage VB in Figure 5, and current flows concentrated in this part.As this current increases, the left side of junction J1 becomes forward biased due to the voltage generated in the lateral resistance R of the N2 layer directly below the 21st layer. The bias value is maximum in the low breakdown voltage region.This is the junction J,
When the diffusion potential exceeds , holes are injected from the 21st layer, and the breakover current I in FIG.

72 is configured to shift to the turn-on state.

Furthermore, when a voltage in the opposite direction to that described above is applied, the same operation is performed in the unidirectional thyristor shown in FIG. 4(b).

According to this structure, the withstand voltage is determined by the withstand voltage in the low withstand voltage region, so it is possible to obtain a thyristor with the required withstand voltage by its design, and the capacitance value, and therefore the junction capacitance value of junction J2, is Since the capacitance is determined outside the breakdown voltage region, the capacitance is lower than that of a conventional structure, making it possible to realize a thyristor with a low breakdown voltage and low capacitance.

The present invention applies this short-circuit emitter type thyristor structure to provide a thyristor that provides surge protection with a single thyristor, has low breakdown voltage, low capacitance, and has a large surge current capacity. Next, the present invention will be explained in detail with reference to examples.

FIG. 6 is a sectional view showing an embodiment of the present invention, in which a P-type semiconductor is used as a common substrate, Nl1 and 213 layers, N21 and P21 layers are provided on one side, and NI2 and P21 layers are provided on the other side.
A layer, a Pus layer, an N23 layer, and a P2z layer are provided.

Also junctions JI2 and tLI and junctions J +x and J 2z
A five-layer structure S, S2 is formed in which a low breakdown voltage region is provided by a P+ layer on the exposed portion of the surface. and the pH layer and r
'tL+ layer is short-circuited by the first metal electrode T, the P21 layer and the N2□ layer are short-circuited by the second metal electrode T2,
Pl on the other side, 3 layers and N12 layer, and P22 layer and N22
The layers are commonly short-circuited by a third metal electrode T3 to form one electrode, and the composite thyristor having the equivalent circuit shown in FIG. 7 operates as described below.

In FIG. 7, parts with the same symbols as those in FIG. 6 indicate equivalent parts, and the resistance R'z RF P23 in the figure indicates the lateral resistance of each layer along the current flow path. Furthermore, the Zener diode Z D l 22 D 23 exhibits a breakdown voltage in a low breakdown voltage region.

In this thyristor, when a voltage is applied in the direction from electrode T to T2, PIINIIP N2+ is essentially a short-circuit base type thyristor, but if there is no low breakdown voltage region, the relative positional relationship of each layer Junction J 12
When the diode breaks down, current flows through the N,,P,N,,layers and it becomes the characteristic of a three-layer diode and does not turn on.

However, if a low breakdown voltage region exists, the Zener diode ZD
I2 breaks down and the current (T.

→Nll→R11→→Z D I 2→P-R, →P-
N2→T2). And when this current increases,
Due to the voltage drop due to the lateral resistance Rp of the P layer, CP-N
,→N23→R23→→ZD2. →P] is also in a state where voltage is applied.

In this state, in the equivalent circuit shown in FIG. 7, the thyristor [PN, , P N, .
) and (P23 N25P N21:1 are connected in series, which corresponds to the ignition current flowing in and out of (N++P gate) and CN2sP gate), so the path of electrodes T1→T2→T3 leads to electrode T172. The area between the electrodes T and 72 shifts to the on state. This operating state also holds true when the direction of voltage application is reversed. Therefore, between the electrodes T and 72,
A bidirectional thyristor action with substantially equal breakdown voltage is performed between T2T3 and TIT2.

Therefore, for example, if the electrodes T and T2 are connected as shown in FIG.
If the thyristor 2, 222.2 shown in FIG. 2 is connected between the thyristors 2, 222. One piece can fulfill a total of three roles.

Further, each of the five layer thyristors forming this composite thyristor has a low breakdown voltage region. Therefore, the above-mentioned FIG. 3,
As explained in FIG. 4, it is possible to lower the withstand voltage without reducing the thickness of the P layer, and it is possible to obtain a composite thyristor with uniform characteristics and low capacitance. In addition, since the initial ignition position is also constant, variations in surge protection capability are reduced and surge current capability is increased. Therefore, the present invention provides a composite thyristor that is easier to use than conventional ones, operates more reliably, has a low withstand voltage that is easy to manufacture, and is suitable for surge protection of digitalized electronic equipment circuits. I'll come.

Although the present invention has been described above with respect to the PNPNP type, it goes without saying that it would also be possible to create a device with the conductivity type reversed. Further, in order to improve the reliability of the thyristor, conventionally known means such as not providing a PL layer serving as a channel stopper as shown in FIG. 3 can be applied.

(Effects of the Invention) As is clear from the above, according to the present invention, it is possible to provide a surge protection element for an electronic device circuit comprising a digitized integrated circuit that is easy to use and operates reliably.

[Brief explanation of drawings]

1 and 2 are explanatory diagrams of a conventional element, and FIG. 3 is an explanatory diagram of a conventional element. FIG. 4 is an explanatory diagram of a composite thyristor proposed by the present invention, and FIGS. 5, 6, 7, and 8 are detailed explanatory diagrams of the present invention.

Claims (1)

[Claims] Using a P(N) type semiconductor as a common substrate, two sets of PNPNP (NPNPN) five-layer structures are formed in which a region with a lower breakdown voltage than other parts is provided in a part of the junction part that determines the forward breakdown voltage. 2, each exposed on one surface.
Two pairs of P(N) emitters and N(P) bases are short-circuited independently to serve as first and second electrodes, and two pairs of P(N) emitters and N(P) bases are exposed on the other surface. ) A composite thyristor characterized in that its base is short-circuited in common to serve as a third electrode.