JP3193386B2 - Bidirectional thyristor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an emitter short-circuit type PNPN.
P (NPNPN) is suitable as a bidirectional thyristor, particularly as a surge protection element.

[0002]

P ₁ N ₁ PN as the sectional view shown in the Related Art FIG. 9
_It consists of five layers of ₂ P ₂ (the same applies to the reverse conductivity type, and the following description is omitted), and has a structure in which P ₁ N ₁ is short-circuited by the metal electrode T ₁ and P ₂ N ₂ by the metal electrode T _2. , bidirectional thyristor Z having the characteristics shown in FIG. 10, as the basic operation circuit diagram shown in FIG. 11, in order to protect the communication circuit from a surge is connected in parallel to the input end of the protection circuit, for example a communication circuit G Is being widely used as an element. By the way, in this case, as a minimum function required as a surge protection element, when a surge voltage S penetrates into the circuit of FIG. 11 and is superimposed, (a) the surge S flows through the surge protection element Z and its withstand voltage A voltage higher than V _BO is prevented from flowing into the protected circuit G, and (b) the circuit voltage E
Is required to be able to immediately cut off the subsequent flow through the surge protection element Z. For this reason, (1) the withstand voltage V _BO (upper and lower limits) and (2) the holding current (lower limit) are regulated, and (3) the device must have a current capacity to prevent breakdown due to surge current. It is required that the capacitance C of the element Z shown in FIG. 11 be kept low in order to guarantee the communication performance of the circuit.

[0003]

However, the above requirements for the surge protection element are in a severe trade-off relationship in the design and manufacture of the surge protection element. It is not easy to manufacture with good yield. For example, the holding current I
The _H as a means for causing better follow current interrupt in the large, as a short portion C _1, an effective method is to constitute a C ₂ (plurality may be provided) as shown in the sectional view shown in FIG. 12 Be taken. When this structure of the element turned, but current flows in the figure, the initial electric current only joined J ₄ of of this and forward biased to cause injection of electrons from J _4, from one part based on this Firing is started to turn on the entire device. Thus a completely reactive current current is not at all involved in turn except this case, the current I _S that this is substantially as shown in FIG. 10
Increases, causing a decrease in current withstand capability. In addition, the initial firing position fluctuates due to subtle fluctuations at the time of manufacturing the junction J ₃ (J ₂ ) shown in FIG. 12 and causes variations in the spread time of the turn-on region and also causes variations in the surge current capacity. become. 9 or FIG.
When the N ₁ P ₁ and N ₂ P ₂ layers having the structure 2 are formed by a diffusion method or the like, the withstand voltage V _BO capacitance C is substantially determined by the impurity concentration of the P substrate, and the higher the impurity concentration, the lower the V _BO becomes. However, the capacitance C becomes large. That is, V _BO and C are in a trade-off relationship, and V _BO small and C small cannot be produced.

[0004]

And satisfying various requirements described above it is an object of the present invention is an object of the invention, the presentation of a new structure and design means problems to be solved, in particular (1) without an increase in the reactive current I _S Providing means for increasing the holding current I _H , (2) Providing a simple means for realizing a device having a small capacitance C independent of V _BO , (3) Stable increase in surge current withstand by determining the initial firing position In providing means for conversion.

[0005]

FIG. 1 is a cross-sectional view showing an example of a basic structure for explaining the principle of the present invention, in which the N ₁ and N ₂ layers are formed of ordinary B ₁ and B ₂ portions. Other than C ₁ ,
The figure in which the metal electrodes T ₁ and T ₂ are short-circuited at the C ₂ part, respectively .
In 9 the same structure, in that further provided shorting portion B ₁ and C ₁ and B ₂ and C junction J ₂ apart from _2, low reverse breakdown voltage than the other places part of the J ₃ D _1, D ₂ There, as a method of forming a low reverse breakdown voltage portion D _1, D _2, a method is taken to be described below with reference to example FIG. 2 (a) (b).
(Since D ₁ and D ₂ are the same in this description, only D ₂ is shown.) The examples of FIGS. 2A and 2B are examples in which N ⁺ and P ⁺ are formed in the junction J ₃ by buried diffusion, respectively. In this case, the breakdown voltage is determined by PN ⁺ and N ₂ -P ⁺ , respectively.

[0006]

[Action] Consider the T ₁ direction of movement from the metal electrode T ₂ of the Figure 1. When the applied voltage rises reaches the breakdown voltage of the low voltage portion D _2, current as in figure i is all flows through the low-voltage portion D _2, the reactive current as in FIG. 12 does not flow. This current causes a voltage drop by the lateral resistance of N ₂ layers, this voltage drop biases the junction J _4, the forward bias is maximum just below the low-voltage portion D _2. Thus the injection of holes from the junction J ₄ in this portion is maximized. Since also becomes maximum amount of electrons injected from the junction J _2, so that the turn-on than the portion begins.
As a result, an increase in the reactive current can be prevented. Since the initial firing position is limited, it is possible to prevent a variation in the amount of surge current. Also, the withstand voltage V _BO is determined by the withstand voltage of the low withstand voltage portion D ₂ (D ₁ ), and the capacitance C is determined by the other region of the junction J ₃ (J ₂ ), so that the specific resistance of the P layer is increased. Thus, a surge protection element having a low withstand voltage V _{BO and} a small capacitance C can be realized. In the turn-off process, turn-on starts around the short-circuit portion C ₂ (C ₁ ), and is not affected by the presence of the low breakdown voltage portion D ₂ (D ₁ ). Therefore
The low breakdown voltage portion D ₂ (D ₁ ) does not affect the holding current I _H , and the holding current I _H can be increased without increasing the reactive current I _S by providing the low breakdown voltage portion D ₂ (D ₁ ). Such problems of the prior art can be solved at once. Next, examples of the present invention will be described.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS.
In the part shown in A ', the N ₁ layer is surrounded by the P ₁ layer, and the short-circuit portion C
₁ and C ₂ are formed on the opposing portions to form a low withstand voltage portion
When D ₁ and D ₂ are seen through from above and below,
And a junction J at a position corresponding to a substantially central portion of the P ₁ and P ₂ layers.
It is an example of forming a _2, J _3. In the example of the partial top view and the partial cross-sectional view shown in FIGS. 4A and 4B, the N ₁ layer surrounding the P ₁ layer is provided with a short-circuit portion of the convex portion N ₁ ′ from both sides thereof (illustration shown).
Or to not but also N ₂ layer surrounding the P ₂ layer on both sides
Convex portion N ₂ ′), and the low breakdown voltage portions D ₁ and D ₂ are vertically
In the see-through state from, approximately the P ₁ and P ₂ layers respectively
In the example formed at the joints J ₂ and J ₃ at the position corresponding to the central part
5 (a) and 5 (b) show the N ₁ and N ₂ layer projections of the embodiment of FIG.
In place of N ₁ ', N ₂ ', a plurality of hole-shaped short-circuit portions N ₁ ", N ₂ "
Provided there Te examples, an example which aimed improvement, i.e. an increase in <br/> holding current I _H of the respective turn-off performance. FIG. 6 (a)
Top view (b) and that shown in the A-A 'section cross section, P _1, N ₁ these are separated P ₂ layers diagonally, N
Surround with _two layers and see through from the top and bottom.
Joining at a position corresponding to the approximate center of the P ₁ and P ₂ layers
This is an example in which low breakdown voltage parts D ₁ and D ₂ are provided in J ₂ and J ₃ .
In each of these embodiments, the same operation as described above with reference to FIG. 1 can be performed to achieve the object of the present invention. Regardless of the embodiment exemplified above, the shape, relative position, etc. of the short-circuit portion and the low-breakdown-voltage portion are variously considered within the scope of the present invention for the purpose, and are conventionally used for the purpose of ensuring reliability and the like. Needless to say, the known structures can be used in combination. 7 is an example of a composite thyristor that can be used as a surge protection element according to the circuit of FIG. 8 , and uses two semiconductor thyristors T ₁ -T ₃ , sharing one semiconductor substrate P. T ₂ -T ₃ are combined, and the low breakdown voltage portion N ⁺
(D ₁ , D ₂ , D ₃ ) are formed. In this example, each short-circuit portion is one place, but as in the above-described embodiment,
Of course, various modifications can be applied. By connecting the composite thyristor Z in the circuit of FIG. 8, when positive or a negative surge voltage is applied between the ground and L ₁ or L _2, both thyristors T ₁ -T _3, or T ₂ -T ₃ Apparently operates as a surge protection device. Also,
When a surge voltage is applied between the lines L ₁ and L ₂ ,
As shown by the dotted line in FIG. 7 , the T ₁ D ₁ T ₃
Since a current flows through D ₃ T ₂ , this is the thyristor T ₁ −
T ₃ and T ₃ -T ₂ are turned on to bypass the surge current and protect the protected circuit G from surge voltage. The illustration of the metal electrode and the insulating layer of SiO ₂ or the like in the top view of each of the above-mentioned embodiments is omitted.

[0008]

According to the present invention, it is possible to increase the holding current without increasing the reactive current. By limiting the initial firing position, it is possible to prevent variations in the surge current withstand capability. With low withstand voltage and low capacitance,
An excellent advantage is obtained in that a short-emitter type five-layer bidirectional thyristor capable of satisfying various performances required as a surge protection element for a communication circuit or the like can be manufactured with high yield.

[Brief description of the drawings]

FIG. 1 is a basic configuration diagram of a bidirectional thyristor of the present invention.

FIG. 2 is an explanatory diagram of another embodiment of a low breakdown voltage portion.

FIG. 3 is an explanatory diagram of another embodiment of the present invention.

FIG. 4 is an explanatory diagram of another embodiment of the present invention.

FIG. 5 is an explanatory diagram of another embodiment of the present invention.

FIG. 6 is an explanatory diagram of another embodiment of the present invention.

FIG. 7 is an explanatory diagram of another embodiment of the present invention.

8 is a circuit diagram of a surge protection circuit using the elements shown in FIG . 7;

FIG. 9 is an explanatory diagram of a conventional bidirectional thyristor.

FIG. 10 is a VI characteristic.

FIG. 11 is a surge protection circuit diagram.

FIG. 12 is a diagram illustrating the operation of a conventional bidirectional thyristor.
is there.

[Explanation of symbols]

T ₁ , T ₂ , T ₃ Metal electrode J ₁ junction J ₂ junction J ₃ junction J ₄ junction V _BO withstand voltage I _H holding current I _S reactive current Z Surge protection element G Protected circuit C Capacitance S Surge E Power supply C ₁ Short-circuit part C ₂ Short-circuit part D ₁ Low withstand voltage part D ₂ Low withstand voltage part I Insulating layer

Claims (3)

(57) [Claims] A first conductive type semiconductor layer serving as a common substrate;
And a second conductive type formed on one surface of the common substrate.
A first base layer, and a first conductive layer on the first base layer.
And a first emitter layer of the same type.
A second conductive type second base formed on the other surface of the substrate;
And a second conductive layer of a first conductivity type on the second base layer.
An emitter layer is formed, and a part of the first base layer and a part of the second base layer are respectively formed.
Exposed on the surface, the first base layer and the first
Between the second base layer and the second emitter layer.
And a second electrode for short-circuiting between the first and second layers, respectively.
And the first base layer exposed on the one surface and the other base layer.
A second emitter layer exposed on one surface, and the other
The second base layer exposed on the surface and the second base layer exposed on the one surface
Each of the first emitter layers is transparent in a vertical direction.
Bidirectional rhinoceros
In Lister, a junction between the common substrate and the first base layer
In the see-through state from above and below, the first
A substantially central portion of the emitter layer, the common substrate and the second
A junction between the base layer and the base layer;
In a viewing state, a substantially central portion of the second emitter layer
In addition, the breakdown voltage is lower than that of the other portions of each of the joints.
Bidirectional thyris characterized by the formation of a curved part
Ta. 2. A semiconductor device according to claim 1 , wherein said first conductive type semiconductor layer is a common substrate.
And a second separated substrate formed on one side of the common substrate.
A first base layer and a second base layer of a conductivity type of
Corresponding to the first base layer and the second base layer, respectively.
And a first emitter layer and a second emitter layer of a first conductivity type
Is formed, and a shape is formed on the other surface side of the common substrate.
A third base layer of the second conductivity type thus formed, and the third base layer;
A third emitter layer of a first conductivity type on the source layer;
Is a portion of the first base layer and second base layer it
Exposed on one surface, and a portion of the third base layer is
Exposed on the other surface, the first base layer and the first
Between the second base layer and the second
Between the emitter layer and the third base layer and the third
A first electrode and a second electrode, each of which short-circuits with the emitter layer.
And a third electrode provided on the first base layer and the second electrode exposed on the one surface.
Base layer and a third emitter exposed on the other surface
A third base layer exposed on said other surface and said one surface.
The first emitter layer and the second emitter
Substantially opposing in the see-through state from above and below
The common substrate and the first base layer and the second base layer in the bidirectional thyristor arranged as described above.
And in the see-through state from above and below.
The first and second emitter layers.
A central portion of the substrate and a contact between the common substrate and the third base layer.
In the joint part, in the see-through state from the above-mentioned vertical direction
At substantially the center of the third emitter layer,
Formed parts with lower withstand voltage than other parts of each joint
A composite thyristor characterized by the following: 3. A semiconductor device according to claim 1 , wherein the semiconductor layer of the first conductivity type is a common substrate.
And a second separated substrate formed on one side of the common substrate.
A first base layer and a second base layer of a conductivity type of
Corresponding to the first base layer and the second base layer, respectively.
And a first emitter layer and a second emitter layer of a first conductivity type
Is formed, and a shape is formed on the other surface side of the common substrate.
A third base layer of the second conductivity type thus formed, and the third base layer;
A third emitter layer of a first conductivity type on the source layer;
Is a portion of the first base layer and second base layer it
Exposed on one surface, and a portion of the third base layer is
Exposed on the other surface, the first base layer and the first
Between the second base layer and the second
Between the emitter layer and the third base layer and the third
A first electrode and a second electrode, each of which short-circuits with the emitter layer.
And a third electrode provided on the first base layer and the second electrode exposed on the one surface.
Base layer and a third emitter exposed on the other surface
A third base layer exposed on said other surface and said one surface.
The first emitter layer and the second emitter
Substantially opposing in the see-through state from above and below
And the third base layer exposed on the other surface.
Between the first base layer on the opposite side and the common substrate.
A bonding portion, and a connection between the second base layer and the common substrate.
Insulates the joint from the first electrode or the second electrode
Exposed on the one surface,
The joints have a higher breakdown voltage than the other joints.
A third base layer formed substantially at the center of the third emitter layer;
The joint between the layer and the common substrate is disconnected from the third electrode.
Rim and exposed to said other surface, said exposed third
The bonding portion between the base layer and the common substrate
Characterized by forming a part with lower withstand voltage compared to other parts
And a composite thyristor.