JPH0777268B2 - Surge absorber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a surge absorbing element for protecting an electric circuit system from an abnormal voltage caused by various surge factors such as lightning, switching surge, etc., and particularly a punch through phenomenon. The present invention relates to a surge absorbing element using the.

<Prior Art> A surge absorbing element is formed by forming an equivalent low-impedance current line in itself in the subsequent process when a high voltage higher than a specified voltage value called “breakdown voltage” is applied. , Which absorbs a large current due to the high voltage and clamps the voltage across the element to a certain voltage value or less to prevent the influence of such abnormal voltage on the electric circuit system to be protected. Most of the equipment provided for the avalanche had a mechanism of avalanche breakdown.

That is, the avalanche breakdown voltage when a reverse bias is applied to the diode structure of the pn junction or the diode connection structure of the transistor is defined as the breakdown voltage as the surge absorbing element.

Also, as can be seen in Japanese Examined Patent Publication No. 51-5913, there were some that utilize the punch-through principle, but even in such cases, the avalanche breakdown type and so-called constant voltage diodes described above were also used. Was only provided.

<Problems to be Solved by the Invention> In the conventional surge absorbing element based on the avalanche breakdown principle,
As described above, the avalanche breakdown voltage itself directly defines the "breakdown voltage" used when the characteristics as the surge absorbing element are called.

However, on the other hand, the avalanche breakdown voltage in such a conventional device is almost uniquely determined depending on the impurity concentration of one of the two regions forming the pn junction, which is the one of the semiconductor regions forming the high resistivity side, that is, the semiconductor substrate in general. It will be fixed.

Therefore, in such a conventional avalanche breakdown type surge absorber, as long as semiconductor substrates with the same impurity concentration are used, the breakdown voltage cannot be arbitrarily changed or is extremely difficult, and if a product with a different breakdown voltage is to be obtained, Therefore, semiconductor substrates with different impurity concentrations must be used accordingly.

This is not only extremely irrational in itself, but changes in the breakdown voltage also change other electrical characteristics other than the breakdown voltage, such as junction capacitance and series resistance. In other words, the junction capacitance and series resistance cannot be designed independently of the breakdown voltage.

In addition, conversely, such a conventional element is not limited to the intentional case, and even though it is within the manufacturing tolerance range for each lot, a semiconductor having different impurity concentrations from the beginning between different lots. In the case where the board has been supplied, and even if it is known in advance, there is no simple way to correct it, and the result is that the surge absorber after it is completed as a product has a The variation or variation between the lots regarding the breakdown voltage will be reflected honestly as it is.

Furthermore, in this type of conventional avalanche breakdown type surge absorber, there are often restrictions on the actual physical structure.

This is because, in this type of surge absorbing element, when the second semiconductor region is embedded in the first semiconductor region by impurity diffusion or the like, avalanche breakdown is generally likely to occur from the electric field concentrated portions at both ends of the junction. This is because it becomes extremely difficult to flow a current evenly over the entire area of the junction when the input voltage is clamped after breakdown.

In addition to these drawbacks, the conventional element described above has a drawback that the voltage across the element (clamp voltage) does not become so low when the input voltage is clamped after breakdown. Rather, both the avalanche breakdown type and the punch-through type described above have constant voltage characteristics.
The clamp voltage is higher than the breakdown voltage.

Therefore, after breakdown, the power consumed in the device is the product of this clamp voltage and the absorption current, which is considerably high in absolute value, resulting in a large amount of heat generation in the device. In other words, this means that in terms of heat capacity, it creates a considerable limit on the absorption current that can be tolerated by the device.

The present invention has been made in view of the conventional circumstances as described above, and has an adequate breakdown width and a good designability regardless of the impurity concentration, the resistivity or the thickness of the semiconductor substrate used. Therefore, it is also possible to independently design other electrical characteristics such as junction capacitance and series resistance regardless of the breakdown voltage.Moreover, at the time of surge absorption, the clamp voltage is compared with the breakdown voltage, It is intended to provide a surge absorbing element capable of sufficiently lowering the voltage and flowing a large absorption current.

<Means for Solving Problems> In order to achieve the above object, in the present invention, instead of the conventional avalanche breakdown type, by introducing a parchthru phenomenon as a new operating principle, and as an element for breakover,
We propose surge absorbers A and B with the following configurations.

A: a first semiconductor region of the first conductivity type; formed on one surface side of the upper and lower surfaces of the first semiconductor region and having a conductivity type opposite to that of the first conductivity type described above. A second semiconductor region forming a pn junction diode between the first semiconductor region and the second semiconductor region; A third semiconductor region which defines an effective thickness of the semiconductor region and which has a conductivity type opposite to that of the second semiconductor region and forms a pn junction with the second semiconductor region in a direction opposite to the pn junction diode; Of the upper and lower surfaces of the first semiconductor region, a fourth region formed on the other surface side facing the one; a first terminal connected to the fourth region; a second semiconductor region and a third semiconductor A region and a second terminal connected to an electrode that shorts them at their surface; Note that the fourth region is the first semiconductor region after the first semiconductor region and the third semiconductor region are punched through as a surge having a voltage equal to or higher than the breakdown voltage is applied with a polarity that reversely biases the pn junction diode. A region for forming a minority carrier injection junction with the first semiconductor region to start absorbing the above surge current between the first and second terminals by injecting minority carriers for the first semiconductor region into the region. The third semiconductor region has a voltage that forward biases the pn junction between the second semiconductor region and the third semiconductor region in the second semiconductor region due to the increase in the current after the start of absorption of the surge current. From the time of occurrence, promoting the injection of minority carriers from the fourth region to the first semiconductor region by injecting minority carriers for the second semiconductor region into the second semiconductor region, Along with the further increase of the surge current to be accommodated, a breakover characteristic as a negative characteristic is generated between the first and second terminals, and the voltage between the first and second terminals in absolute value has a clamp voltage lower than the breakdown voltage. A surge absorbing element characterized by being a region for injecting minority carriers into the second semiconductor region in order to shift to.

B: a first semiconductor region of a first conductivity type; formed on one of the upper and lower surfaces of the first semiconductor region and having a conductivity type opposite to that of the first conductivity type described above. A second semiconductor region forming a first pn junction diode between the first semiconductor region and the second semiconductor region; Define the effective thickness of the second semiconductor region, and have the opposite conductivity type to the second semiconductor region and the first pn
A third semiconductor region forming a pn junction in a direction opposite to that of the junction diode; formed on the other surface of the first semiconductor region opposite to the one of the upper and lower surfaces, and has the first conductivity type. A fourth semiconductor region having an opposite conductivity type and forming a second pn junction diode opposite to the first pn junction diode from the first semiconductor region; and opposite to the first semiconductor region. By contacting the fourth semiconductor region from the side, the distance between the first semiconductor region and the fourth semiconductor region is defined to define the effective thickness of the fourth semiconductor region, and the fourth semiconductor region has a conductivity type opposite to that of the fourth semiconductor region. The second pn between the semiconductor region
A fifth semiconductor region forming a pn junction in a direction opposite to that of the junction diode; a first terminal connecting the fourth semiconductor region and the fifth semiconductor region to a first electrode short-circuiting at their surfaces; A second terminal connecting a semiconductor region and a third semiconductor region to a second electrode that short-circuits the surfaces thereof; the second pn junction diode is a reverse bias of the first pn junction diode. Injecting minority carriers for the first semiconductor region into the first semiconductor region after punch-through between the first semiconductor region and the third semiconductor region due to the application of a surge of voltage equal to or higher than the breakdown voltage. The first pn junction diode is a diode for injecting minority carriers into the first semiconductor region in order to start absorbing the surge current between the first and second terminals. After the punch-through between the first semiconductor region and the fifth semiconductor region due to the application of a surge of a voltage equal to or higher than the breakdown voltage with the polarity of reverse biasing the second pn junction diode, the first semiconductor region is formed in the first semiconductor region. By injecting minority carriers for the semiconductor region to start absorbing the surge current between the first and second terminals, it is a diode that injects minority carriers into the first semiconductor region; and the third semiconductor region is After the start of absorption of the surge current, an increase in the current causes a voltage that forward-biases the pn junction between the second semiconductor region and the third semiconductor region in the second semiconductor region. By injecting minority carriers for the second semiconductor region into the region, injection of minority carriers from the fourth semiconductor region to the first semiconductor region is promoted, and the above absorption As the surge current is further increased, a break-over characteristic as a negative characteristic is generated between the first and second terminals, and the voltage between the first and second terminals becomes a clamp voltage lower in absolute value than the breakdown voltage. The fifth semiconductor region is a region in which minority carriers are injected into the second semiconductor region in order to make a transition; and the fifth semiconductor region is a fourth semiconductor region in the fourth semiconductor region due to an increase in the current after the start of absorption of the surge current. After the voltage for forward-biasing the pn junction with the fifth semiconductor region is generated, minority carriers for the fourth semiconductor region are injected into the fourth semiconductor region to inject from the second semiconductor region to the first semiconductor region. The injection of minority carriers is promoted, and a breakover characteristic as a negative characteristic is generated between the first and second terminals with further increase of the surge current absorbed. And a region for injecting minority carriers into the fourth semiconductor region in order to shift the voltage between the first and second terminals to a clamp voltage lower than the breakdown voltage in absolute value. .

<Operation> In the above-described surge absorbing element A according to the first invention of the present application, when a reverse bias is applied to the pn junction diode composed of the first semiconductor region and the second semiconductor region due to the application of surge, the pn junction diode is formed in the pn junction. The depletion layer extends in the first semiconductor region toward the fourth region and at the same time in the second semiconductor region toward the third semiconductor region. Then, this depletion layer continues to expand in the transient voltage rise process accompanying the surge application, and when it reaches the third semiconductor region, the first semiconductor region and the third semiconductor region punch through, and the punch through region is passed through. The surge current begins to be absorbed. The start voltage of this pulse-through operation is the "breakdown voltage" in FIG.

The fourth region is made of a material capable of injecting minority carriers into the first semiconductor region (for example, a semiconductor of a conductivity type opposite to that of the first semiconductor region, a silicide, or the first semiconductor, as described in the summary configuration). In the case where the region is p-type, it may be made of a metal capable of injecting electrons, etc., but here, in order to facilitate understanding of the operation of this element, it is assumed that it is a p-type semiconductor, for example. Therefore, in this case, the conductivity type of the first semiconductor region is n-type, the conductivity type of the second semiconductor region is p-type, and the conductivity type of the third semiconductor region is n-type, in accordance with the limitation regarding the conductivity type of each region in the gist configuration of the present application. It will be a mold.

However, the holes injected from the fourth semiconductor region at the start of the above-mentioned breakdown are partially combined with the electrons that have flowed into the first semiconductor region by punching through the second semiconductor region from the third semiconductor region. However, most of them reach the second semiconductor region, which is a space charge layer, and the current path is generated in the presence of an electric field due to the surge application between the electrode and the electrode in contact with the surface of the second semiconductor region. Therefore, after moving laterally in the second semiconductor region so as to lick the lower surface of the third semiconductor region, it reaches the surface electrode of the second semiconductor region, and the device current (current absorbed surge) ) Begins to be taken out.

According to the present invention, the electrode provided on the surface of the second semiconductor region is in contact with the surface of the third semiconductor region to short-circuit the surfaces of the second and third semiconductor regions, and as a result, The surfaces of the second and third semiconductor regions are both at the same potential, but since holes flow in the second semiconductor region along the third semiconductor region as described above, this hole flow (current)
Due to the presence of the resistance component along the path of, the voltage drop occurs with respect to the surface potential inside the second semiconductor region. And
The turn-on of the pn junction starts at a point where this voltage drop becomes equal to the forward bias of the pn junction formed by the second semiconductor region and the third semiconductor region, and the turn-on of the pn junction starts from the third semiconductor region through the second semiconductor region. An electron flow that does not depend on punch-through begins to flow toward one semiconductor region.

In this way, the electron flow injected into the first semiconductor region promotes the injection of minority carriers (holes in this description) from the fourth semiconductor region into the first semiconductor region, and the device current increases accordingly. In the pn junction formed by the second semiconductor region and the third semiconductor region, the number of sites turned on by forward bias increases, and the number of holes injected from the fourth semiconductor region increases more and more. The electron injection amount from is also increasing.

By repeating such a carrier injection process continuously, a positive feedback phenomenon related to the carrier injection becomes remarkable, and a breakover as an element is reached, resulting in a voltage across the element (refer to the first term in the constitution of the present invention). , The voltage between the second terminals) shifts to an extremely low “clamp voltage” as shown in FIG. The element current value at this time is the value shown as "breakover current" in FIG. 2, and in the state after the breakover, almost all surge current is absorbed in the first semiconductor region. Therefore, the current flows through almost the entire pn junction formed by the second semiconductor region and the third semiconductor region.

As described above, in the surge absorbing element A of the present invention, although there is a restriction on the polarity of the surge that can be absorbed (in the above-described example of the combination of the conductive types, the fourth semiconductor region side is the third semiconductor region side), the simple two Although it is a terminal element, it is possible to suppress heat generation of the element and absorb a large surge current.
The voltage value at the time of exhibiting the breakover can be called "breakover voltage" as shown in FIG. 2, and this breakover voltage itself is generally higher than the breakdown voltage.

On the other hand, unlike the teaching of the present invention, when the surface of the second semiconductor region and the surface of the third semiconductor region are used as a two-terminal element without being short-circuited, no breakover characteristic is shown, but Even so, the breakover current becomes extremely small.

For example, when electrodes are provided only on the surface of the second semiconductor region and the surface of the fourth semiconductor region, and the first and second terminals are taken out from these, the first and second semiconductor regions are used as a model when a surge is applied. When a reverse voltage is applied to the pn junction composed of and the absolute value is increased, the space charge region first spreads in the second semiconductor region between the first semiconductor region and the third semiconductor region, and this When the third semiconductor region reaches the semiconductor region, the potential of the third semiconductor region changes from the floating state up to that point. When the absolute value of the reverse voltage further increases in that state, the pn junction formed by the second semiconductor region and the third semiconductor region reaches a voltage at which it "breaks down". In this case, the second semiconductor region moves to the third semiconductor region. , The punch-through region, the first semiconductor region, and then the fourth semiconductor region, the current flows along the route, and the voltage between the two terminals becomes a “constant voltage”. Breakover cannot occur because the second semiconductor region and the third semiconductor region are reverse biased.

Further, if an electrode is provided only on the surface of the third semiconductor region and the surface of the fourth semiconductor region and it is operated as a two-terminal element, a pn junction composed of the first semiconductor region and the second semiconductor region is formed. When a voltage as a surge application model is applied with a polarity that is a reverse bias and the absolute value is increased,
Eventually, punch-through occurs between the first semiconductor region and the third semiconductor region. Then, carriers from the third semiconductor region are supplied to the first semiconductor region via the second semiconductor region, which promotes injection of minority carriers from the fourth semiconductor region to the first semiconductor region. However, since the second semiconductor region is in a floating state, the second semiconductor region and the third semiconductor region are immediately forward-biased, and punch-through does not depend on the third semiconductor region to the second semiconductor region. Even if there is no carrier flow and, as a result, the breakover characteristic is generated, the breakover current becomes a very small value. Devices with low breakover current have various problems.

For example, the displacement current id that tries to charge the junction capacitance Cj of the reverse bias pn junction flows with the application of the surge whose rising sharpness is represented by dV / dt, and this magnitude is id = Cj (dV / dt) ………… It is expressed by (1). However, when the breakover current is small, the absolute value of the peak voltage is smaller than the standard operating voltage of the device, and although it is a “small surge” that should not normally be absorbed, its rise dV / d
Although t is not too sharp, the device may turn on due to the displacement current id. Further, in this case, since the holding current is also small for the same reason that the breakover current is small, once the device is turned on, the element current does not recover until the element current becomes almost zero even if the surge disappears (see A "flow effect" occurs).

As apparent from the above-mentioned invention, it is clear that the present invention is effective in constructing a two-terminal surge absorbing element by short-circuiting the second semiconductor region and the third semiconductor region.
High breakover current required to obtain / dt resistance,
It is possible to obtain a high holding current for avoiding the follow current effect.

Moreover, since the second semiconductor region and the third semiconductor region are short-circuited at their surfaces rather than simply short-circuited, the surface potentials of the second semiconductor region and the third semiconductor region are affected by external factors. Can be made to have the same electric potential. This is extremely significant in device design. If terminals are separately drawn from the surface of the second semiconductor region and the surface of the third semiconductor region by separate lead wires and these are short-circuited outside the device, this lead may be used for the purpose of the surge absorbing device. It is common for a line to be noisy. In addition, considering the existence of the inductance component and contact resistance of the lead wire, and the fact that the dV / dt of the surge described above varies, the breakover characteristics between the two terminals become unstable with each surge application. Inconveniences such as fluctuations are possible. On the other hand, as in the present invention, by providing electrodes for short-circuiting them on the surfaces of the second and third semiconductor regions and taking out terminals from them, the above problems are solved or at least alleviated. .

The value of the break-over current is determined by the resistance of the second semiconductor region and the shape of the third region and the first semiconductor region, the shape of the fourth region with respect to the first semiconductor region, and further described below. As described above, when the first semiconductor region is directly connected to the external terminal, it can be determined depending on the resistance of the first semiconductor region and the shape of the vicinity of the fourth region.

On the other hand, considering the breakdown voltage that causes the punch-through operation to start, in the surge absorbing element of the present invention, what is the height position of the third semiconductor region, which is in contact with the second semiconductor region on the opposite side to the first semiconductor region ,? It is possible to arbitrarily change and control the punch-through voltage between the first and third regions, that is, the breakdown voltage, by setting or in other words, by setting the effective thickness of the intermediate second semiconductor region. Will be things.

For example, when the effective thickness of the intermediate second semiconductor region is set to be thick, if the other conditions are the same, a larger reverse bias is required to extend the generated depletion layer to the third region. Eventually, the breakdown voltage at which the device breaks down is increased, and conversely, if the effective thickness of the intermediate second semiconductor region is set to be thin, the generated depletion layer can easily be generated at a relatively low applied voltage. Since it reaches the region, the breakdown voltage is set to a low value.

Of course, such a breakdown voltage can be controlled also by the impurity concentration of the intermediate second semiconductor region, but in any case, according to the present invention, according to the present invention, a suitable commercially available first semiconductor region is obtained. It can be seen that the surge absorbing element having any desired breakdown voltage can be obtained by using the semiconductor substrate wafer of 1) as it is, or by using the same type of semiconductor substrate as the starting member.

Further, by appropriately controlling the control of the effective thickness of the second semiconductor region and the control of the impurity concentration thereof, the junction capacitance and series resistance can be designed independently of the breakdown voltage.

Furthermore, for the semiconductor substrate itself, or on the semiconductor substrate, or for the first semiconductor region formed in the semiconductor substrate,
The method itself of sequentially forming the second semiconductor region and the third region may be based on existing epitaxial growth technology, ion implantation, selective diffusion, or the like. Since the control of the effective thickness and the impurity concentration can be extremely high even with the current technology, the surge absorbing element manufactured according to the present invention can have extremely high accuracy if necessary.

Even from a structural point of view, the effective thickness of the second semiconductor region can be set to be small regardless of the thickness of the first region. It can be used as it is without thickening (though it is more general), so that it does not cause an increase in the number of steps and does not cause a decrease in physical strength. It is also possible to form a plurality of elements, which has an effect of easy integration.

In contrast to the above-described surge absorbing device A as the first invention of the present application, the surge absorbing device B as the second invention is capable of absorbing a bipolar surge current.

That is, assuming that the fourth region is limited to the semiconductor, this is considered to be a region corresponding to the second semiconductor region in the first invention, and similarly, the fifth semiconductor region (hereinafter, also simply referred to as the fifth region) is included in the first invention. Considering a region corresponding to the third semiconductor region (hereinafter, also simply referred to as a third region), the pn junction diode in the first invention composed of the first semiconductor region and the second semiconductor region as described above is used. The punch-through phenomenon that can occur in the corresponding first pn junction diode in the second invention is that the reverse bias of the second pn junction diode composed of the first semiconductor region and the fourth semiconductor region with respect to the surge current of opposite polarity. The same will occur as a result of.

That is, when punch through occurs in the second pn junction diode between the first semiconductor region and the fourth semiconductor region, the second semiconductor region is made of a semiconductor in the description of the first invention above. The fourth area of the case will perform the function.

Therefore, the respective explanations regarding the second semiconductor region regarding the fourth semiconductor region and regarding the third region regarding the fifth region can be applied as they are without any change, and also regarding other considerations. Become.

Therefore, the advantages of the surge absorbing element of the first invention, such as a sufficiently low clamp voltage and good designability of the breakdown voltage, are exhibited in the surge absorbing element of the second invention as well. can do.

<Examples> Hereinafter, some of the illustrated examples of the present invention will be described in detail.
Of course, there are respective examples for the first invention and the second invention, but as already mentioned, since the two are extremely closely related, they can be referred to each other.

The surge absorbing element 10 shown in FIG. 1 is one of the basic embodiments according to the first invention, in which the semiconductor substrate is used as it is as the first semiconductor region 1 of the first conductivity type, and the upper and lower surfaces thereof are The second semiconductor region 2 and the third region 3 are sequentially formed on one surface by the double diffusion technique, and the fourth region 4 is made of a semiconductor on the other surface, that is, the back face, and this is formed by the diffusion technique. It was formed.

In such a relationship, for example, when the semiconductor substrate to the first semiconductor region 1 is an n-type semiconductor, the second semiconductor region 2 and the fourth semiconductor region 4 are p-typed by an appropriate impurity diffusion technique such as boron. Use as a mold.

Since the third region 3 forms one end of the main current line when punch-through occurs, it preferably has a high conductivity. In this embodiment, a high impurity concentration n type, that is,
The n ⁺ type region is formed by double diffusion of impurities into the second semiconductor region 2. In practice, this can be obtained by high-concentration phosphorus diffusion or the like.

An ohmic lead terminal is attached to each region to complete the device, but the lead terminal 2t of the second semiconductor region 2 and the lead terminal 3t of the third region 3 are imaginary lines Ls in the figure. Although it is shown, it is actually short-circuited at the stage of production, and such a surface short circuit line Ls
Can be formed of a metal layer or the like that is in ohmic contact with the exposed surface of the second semiconductor region 2 and the exposed surface of the third region 3 by vapor deposition in series.

Here, first, both terminals 2t and 3t are thus short-circuited by the line Ls, and they and the lead terminal of the fourth semiconductor region 4 are connected.
The description will be made assuming that the surge voltage is applied between 4 tons.

In such a surge absorbing element 10, since it has already been described in detail in the section of the operation, its operation will be briefly described here. A reverse bias is applied to the pn junction between the first semiconductor region 1 and the second semiconductor region 2. Then, the depletion layer generated thereby extends not only toward the first semiconductor region 1 side but also toward the third region 3 side.

Therefore, if a surge voltage is applied between the terminals 2t, 3t and the terminal 4t, and it is considerably large in the phase of applying a reverse bias to the pn junction, the upper end of the depletion layer becomes the third region. It is possible to reach 3.

This state is the start of the punch-through state between the first semiconductor region 1 and the third region 3, and is the low impedance state in which a large current can flow, or the breakdown state of the present surge absorbing element. This starting point is shown in FIG. 2 as a breakdown voltage on the voltage axis.

When such a breakdown start state is realized, terminals 2t, 3t and terminal 4
A surge current flows out during t, holes are injected from the fourth semiconductor region 4 into the first semiconductor region 1, and the holes are collected in the second semiconductor region 2 and transferred to the external current (device current) via the external terminal 2t. Become.

Therefore, the product of the resistance value along the current path in the second semiconductor region 2 sandwiched between the third region 3 and the first semiconductor region 1 and the above current is the pn junction diode constituted by the regions 2 and 3. When the voltage becomes equal to the forward voltage of, the electrons are injected from the third region 3 into the second semiconductor region 2 this time, which causes an increase in current, and the holes are again injected from the fourth semiconductor region 4. A positive feedback phenomenon that occurs is generated.

The current value at which such a positive feedback phenomenon begins is the breakover current described above, and the voltage across the element (voltage between the external terminals 4t and 3t) at this time becomes the breakover voltage.

As described above, the breakover voltage has a value somewhat higher than the breakdown voltage, but once positive feedback starts to occur, the voltage across the element transits to a significantly low value. This value is shown as a clamp voltage in FIG. 2, but it is approximately the value obtained by adding one forward voltage of the pn junction to the product of the absorption current and the series resistance of each part.ゞ Equal.

As can be understood from such a mechanism, the surge absorbing element 10 of the present invention maintains a high breakdown voltage when a surge is not applied and suppresses the current flowing through the element to the minimum limit. While preventing current consumption, once a surge above the breakdown voltage is applied, it will soon exhibit an extremely low clamp voltage, thus absorbing large currents and ensuring the protection of subsequent circuitry. Become.

The breakdown voltage of the surge absorbing element 10 that operates in this manner is determined not only by the resistivity or impurity concentration of the first semiconductor region 1 but also by the distance between the first semiconductor region 1 and the third region 3. Whether the effective thickness Dt of the second semiconductor region 2 is
And / or the punch through voltage can be controlled depending on the impurity concentration, so that the punch through voltage can be arbitrarily set within a considerably wide design width. In fact, experiments by the applicant have confirmed that this design width covers a very wide range from several volts to several hundreds of volts.

In the case of the first illustrated embodiment, as described above, the second semiconductor region 2 and the third region 3 are formed in the semiconductor substrate 1 by the double diffusion technique. In this case, the effective thickness Dt of the second semiconductor region 2 is directly controlled by controlling the diffusion depth Dd of the third region forming impurities from the surface after the formation of the second semiconductor region 2. Will be done. That is, when using the double diffusion technique,
The variation or change setting of the height position of the third region 3 with respect to the first semiconductor region directly changes the effective thickness Dt of the second semiconductor region 2.

On the other hand, when the second semiconductor region 2 and the third region 3 are formed by the epitaxial growth technique, the effective thickness Dt of the second semiconductor region 2 is the growth film thickness itself determined based on the conditions in the epitaxy. However, even in that case, the existence of the third region 3 still defines the effective thickness Dt for punch-through.

Whether the diffusion technique or the epitaxy is used, the effective thickness Dt of the second semiconductor region 2 can be controlled with extremely high precision even with the existing technique. The breakdown voltage can be set with extremely high accuracy.

Similarly, the punch-through voltage, and consequently the impurity concentration of the second semiconductor region 2, which is another factor that regulates the breakdown voltage of the present device, are adjusted with extremely high precision using existing techniques.
Can be controlled.

In the case of the device of the present invention, the above also has two variables for designing the breakdown voltage, namely, the effective thickness Dt of the second semiconductor region 2 and the impurity concentration, which have good designability and are independent of each other. It means that you are doing. Therefore, not only can you set the breakdown voltage over an extremely wide range by using only one of these variables or by using both variables appropriately, but you can also set other electrical characteristics such as junction capacitance and series resistance. It can be seen that it can also be designed independently of the breakdown voltage.

Of course, the fourth semiconductor region 4 can also be formed with good controllability by utilizing conventional techniques such as impurity diffusion and epitaxy, and, as described above, the first invention is not limited to this. The fourth region 4 is the first semiconductor region 1
However, as long as it is formed of a material that forms an injection junction capable of injecting minority carriers, it is not limited to a semiconductor having a conductivity type opposite to that of the first semiconductor region 1 as in the illustrated embodiment. Moreover, when the first semiconductor region 1 is p-type, it may be made of metal capable of injecting electrons.

In principle, in the surge absorbing element of the present invention, the current distribution of the surge current after punch-through between the first and third regions is relatively uniform. However, if it is intended to ensure evenness, a configuration as shown in FIG. 3 can be adopted.

That is, in the second embodiment shown in FIG. 3, a plurality of third regions 3 are formed for the semiconductor substrate to the second semiconductor region 2 of the opposite conductivity type formed on the surface of the first semiconductor region 1. Each of the area elements 31 to 3n is composed of a set of divided third area elements 31, 32, 33, ...
Is designed to be electrically connected to the outside from the common lead terminal 3t.

With such a structure, it is possible to avoid the concentration effect of the electric field, which is seen in the conventional avalanche breakdown type element, and obtain a uniform current distribution. Therefore, the current capacity can be increased substantially in proportion to the element area.

In this third illustrated embodiment as well, the other considerations mentioned for the first embodiment can be adopted as well. Note that the two terminals 2t and 3t are not only short-circuited on the operating principle as described above, but also have the effect of avoiding a transient phenomenon when they are short-circuited.

In the surge absorbing element having the structure like the present invention, when the breakdown voltage, which should be defined by the punch-through phenomenon, approaches the avalanche breakdown voltage of the first semiconductor region 1 and the second semiconductor region 2, the controllability is improved. May be worse.

When there is such a fear, in order to prevent or suppress the avalanche breakdown starting at the joining of the ends of the second semiconductor region 2 in the initial stage, as shown in FIG. 4 as an embodiment of the second invention described later. And forming a guard ring region 2G of the same conductivity type as the second semiconductor region so as to surround the second semiconductor region 2 or similarly as a second embodiment of the second invention.
As shown in the figure, the end edge portion 6a of the ohmic electrode 6 formed in series on the surfaces of the second semiconductor region 2 and the third semiconductor region 3 is connected to the end portion of the second semiconductor region via the insulating film 8. It is preferable to further project so as to exceed the junction with the first semiconductor region in.

By doing so, the concentration of the electric field at the end of the second semiconductor region is relaxed, and the avalanche breakdown voltage is effectively increased. Therefore, the designability of the breakdown voltage only by punch-through is achieved in accordance with the idea of the present invention. Can be expanded and improved.

Next, an embodiment of the second invention shown in FIGS. 4 and 5 will be described.

Also in the embodiment shown in FIGS. 4 and 5, the first semiconductor region 1, the second semiconductor region 2, the third region 3 and the third region element
For 31,32, 33, ..., 3n, the same configuration, shape, and arrangement relationship as in the embodiment according to the first invention shown in FIGS. 1 and 3 can be applied. Rather, in the embodiment of the second invention, in addition to the configuration of the surge absorbing element shown in FIG. 3, the third region element 31, 32, 33, ... Fifth area element 51,5 which is substantially similar to
You can think that 2,53, ..., 5n have been added.

Therefore, in the surge absorbers shown in FIGS. 4 and 5,
Depending on the polarity of the surge voltage applied between the terminals 3t and 5t, the punch-through diode may be the first diode composed of the first semiconductor region 1 and the second semiconductor region 2, It may be a second diode composed of the semiconductor region 1 and the fourth semiconductor region 4, but even if a bunch-through phenomenon occurs in any of the diodes, its operation mechanism is already the same as that of the first invention. This is exactly the same as that described with respect to the diode constituted by the one semiconductor region 1 and the second semiconductor region 2.

In other words, the surge absorbing element according to the second embodiment of the present invention can exhibit a function of absorbing bipolar surge voltage or surge current. Of course, the fact that the breakdown voltage can be determined with respect to the surge voltage with good designability, the clamp voltage can be made sufficiently smaller than the breakdown voltage, etc. are exactly the same as in the surge absorbing element described in the first invention. Is.

The difference between the embodiment shown in FIG. 4 and the embodiment shown in FIG. 5 is that the avalanche breakdown that begins at the junction of the end portions of the second semiconductor region and the fourth semiconductor region is the initial consideration. Only the means to prevent or suppress it in stages differ.

That is, in the embodiment shown in the fourth illustration, as described above, the same conductivity type as the second and fourth semiconductor regions is provided so as to surround the second semiconductor region 2 and the fourth semiconductor region 4. Guard ring regions 2G and 4G are formed, and in the fifth embodiment shown, the surfaces of the second semiconductor region 2 and the third semiconductor region 3 and the fourth semiconductor region 4 and the fifth region 5 are formed. Edges 6 of ohmic electrodes 6 and 7 formed in series on the surface.
The a and 7a are further extended so as to extend beyond the junction end with the first semiconductor region through the insulating films 8 and 9.

Of course, in the embodiments shown in the fourth and fifth embodiments, the third and fifth areas 3 and 5 are each a plurality of area element groups 31 to 3 for that area.
It is composed of a set of n, 51 to 5n.
As typified by the third region 3 shown in the figure, most basically, the third region 5 and the fifth region 5 may each be formed as a single region.

In the case of the surge absorbing element of the present invention as shown in each of the embodiments described so far, after the element is completed, as a general rule, incidental treatment such as end face polishing which is required in the conventional avalanche breakdown type is not necessary. Therefore, a plurality of the configurations of the above-described embodiments can be simultaneously formed in one semiconductor substrate 1.

However, on the contrary, when it is not necessary to accumulate many,
As another means for increasing the avalanche breakdown voltage described above, as shown in FIG. 6, first and second semiconductor regions 1, 2
A portion corresponding to the joint end portion between the two may be etched or cut with a slope perpendicular to the surface or having an angle.
The case shown in FIG. 6 relates to the surge absorbing element corresponding to the first invention of the present invention, but the same idea can be applied to the second invention. However, when such a simple method is used, it is common to require a suitable protective film (not shown) on the cut-off surface.

Finally, as an example, the effect of the present invention is confirmed by comparison with an actual device.

First, the surge absorber of the present invention shown in FIG. 1 without the fourth semiconductor region 4 was prepared for comparison by the steps described below.

A silicon wafer having a resistivity of 5 Ω-cm, a conductivity type of n-type, a 111 plane, and a thickness of 300 μm was used as a starting member for the first semiconductor region 1, and 6000 Å SiO ₂ films were first formed on the front and back surfaces thereof.

Among them, only the SiO ₂ film on the back surface was removed, and high-concentration phosphorus diffusion was performed to a depth of 3 μm.

Next, in order to define the planar shape of the second semiconductor region 2, a photo-etching process was applied to the surface silicon oxide film according to a predetermined pattern to open an impurity diffusion window.

Boron is diffused through this diffusion window and its depth is 2.5μ.
A p-type region extending over m was formed.

After newly forming a silicon oxide film on the wafer surface, in order to define the planar shape of the plurality of third region elements 31 to 3n, the silicon oxide film is photo-etched in accordance with a predetermined pattern, An impurity diffusion window for each third region element was formed.

Highly concentrated phosphorus is diffused through this diffusion window and its depth is 1.2μ.
A third region 3 was formed consisting of a set of n ⁺ type third region elements 31-3n over m. Therefore, at the same time, the second semiconductor region 2 was formed and its effective thickness Dt was 1.3 μm.

After that, the electrodes 6 to terminals 2t and 3t were formed through photo etching for forming a common ohmic contact in the second and third regions, metal thin film deposition, and the etching process. The electrodes or terminals 1t on the semiconductor substrate side were simultaneously formed in the metal thin film deposition step.

The comparative surge absorption element made by this process has a breakdown voltage of 120V and maximum surge absorption current.
It was possible to obtain up to 300A / cm ² .

On the other hand, as a surge absorbing element according to the idea of the present invention, the manufacturing steps up to the third region are the same as those in the comparative surge absorbing element, but as a fourth semiconductor region on the back side of the n-type semiconductor substrate. In the surge absorption element in which the P ⁺ region was formed by impurity diffusion and the electrode or terminal 4t was formed by metal thin film deposition, the breakdown voltage was about the same as 121V, but the breakover current was 4A / cm ^2. The maximum surge absorption current was 10,000 A / cm ² . From this characteristic example, it can be seen that the function of the fourth semiconductor region provided by the present invention is extremely large.

Further, under the same conditions as above, except that the breakdown voltage at the time of forming the n ⁺ -type third region, which substantially defines the effective thickness of the second semiconductor region 2, is changed, the breakdown voltage is changed. Could be varied between 30V and 170V. Of course,
It is also confirmed that this variation width is not the maximum variation width, and an extremely wide variation range from several volts to several hundreds of volts can be obtained in consideration of other conditions.

It was also confirmed that the breakdown mechanism of this device can be controlled without fail by tunneling or avalanche breakdown only by the punch-through phenomenon.

If the breakover current is further increased and a "small surge" such as a transient noise that has a large voltage time derivative but a very short duration is introduced, it may be detected below the DC breakdown voltage. In order to prevent the response, the contact area of the second semiconductor region and / or the fourth semiconductor region with the metal thin film is increased, or the fourth semiconductor region 4 is formed into a plurality of region elements 4 as shown in FIG.
A first semiconductor region portion which is composed of a set of 1,42, ..., 4n and is laterally sandwiched between adjacent fourth semiconductor region elements.
11,12, ..., 1n _-1 are formed so that an electrode in common ohmic contact with the first semiconductor region portion 11, 12, ..., 1n _-1 is provided as a terminal 1t, and A common line is formed in the fourth semiconductor region element group 41, 42, ...
It is good to pull out t and use it.

In any case, the breakover current can be arbitrarily designed within a considerable range, and in the above, in particular,
The electrodes 1t and 4t which make ohmic contact with the respective surfaces of the first semiconductor region portion 11, 12, ... 1n _-1 and the fourth semiconductor region element 41, 42 ,. The structure used by short-circuiting each other as shown by the line Ls of the line can be similarly adopted in the embodiments shown in FIGS. 1 and 3 in which there is only one fourth semiconductor region 4.

<Effects of the Invention> According to the present invention, as described below, various excellent effects can be obtained as compared with existing avalanche breakdown type devices.

The semiconductor substrate or the semiconductor wafer is the most expensive and inflexible member as the component value of each part of this kind of element, but according to the present invention, even if the starting wafers having the same material constant have different breakdown voltages. A surge absorbing element can be obtained.

Since the set of the second semiconductor region and the third region and the set of the fourth semiconductor region and the fifth region can be formed from the same side with respect to the first semiconductor region, the change of the breakdown voltage and the set breakdown voltage are set. The control for setting the voltage is extremely simple and can be performed with high accuracy.

Other electrical characteristics such as junction capacitance and series resistance can be designed independently with respect to the breakdown voltage, so that, for example, other electrical characteristics can be substantially the same even when the breakdown voltage is different.

It is easy to integrate a plurality of devices in a common semiconductor substrate.

It has a design principle that the terminal voltage (clamp voltage) is much smaller than the breakdown voltage in the large current region, so it can absorb an extremely large surge current.
It has an extremely high capability in terms of circuit protection.

When the terminals are taken out from the second semiconductor region and the third region independently and short-circuited outside the device, the surge applied depending on the resistance value or inductance value expected in the short-circuit line or short-circuit means. The breakover voltage is likely to change due to the time differential value of the voltage of the waveform, but in the surge absorbing element of the present invention, the second semiconductor region and the third region are short-circuited on the surface thereof. Note that this is not the case, and a stable breakover voltage can be obtained.

According to the second invention of the present application, in addition to the above effects,
It is possible to absorb bipolar surge currents.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a first embodiment according to the first invention of the present invention, FIG. 2 is an operation characteristic diagram of the first illustrated embodiment, and FIG. 3 is a schematic configuration diagram of a second embodiment according to the first invention. , Figures 4 and 5
The figure is a schematic configuration diagram of each embodiment according to the second invention of the present invention,
FIG. 6 is an explanatory view of an example for eliminating the influence of avalanche breakdown voltage in the surge absorbing element of the present invention, and FIG. 7 is a schematic configuration diagram of still another modification of the surge absorbing element according to the first invention. In the figure, 1 is a first semiconductor region to a semiconductor substrate, 2 is a second semiconductor region, 3 is a third region, 31 to 3n are third region elements, 4 is a fourth semiconductor region, and 41 to 4n are a fourth semiconductor region. Elements 5 are fifth areas, 51-5n are fifth area elements, 2G and 4G are guard rings, and 10 is the surge absorbing element of the present invention as a whole.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Masaaki Sato, 1-12 Miyashita, Sagamihara-shi, Kanagawa Sankosha Sagami factory (72) Inventor, Hiroaki Yoshihara 3-12, Fujihashi, Aomi-shi, Tokyo No. Judgment body of the referee at Mitaka Institute of Electronic Science, Inc. Judgment Chair Haruo Asukai Judge Masayuki Ishikawa Judge Toshiaki Aoki (56) References JP51-5913 (JP, B1)

Claims (3)

[Claims] 1. A first-conductivity-type first semiconductor region; formed on one of the upper and lower surfaces of the first semiconductor region and having a conductivity type opposite to that of the first-conductivity type. A second semiconductor region that forms a pn junction diode with the first semiconductor region; and between the first semiconductor region and the second semiconductor region by contacting the second semiconductor region from a side opposite to the first semiconductor region. To define the effective thickness of the second semiconductor region, and in a direction opposite to that of the pn junction diode between the second semiconductor region and the second semiconductor region with a conductivity type opposite to that of the second semiconductor region. a third semiconductor region forming a pn junction; a fourth region formed on the other surface side opposite to the one of the upper and lower surfaces of the first semiconductor region; and a fourth region connected to the fourth region A terminal; and a surface of the second semiconductor region and the third semiconductor region. And a second terminal connected to the short-circuited electrode; the fourth region has a polarity that reverse-biases the pn junction diode, and a surge having a voltage equal to or higher than a breakdown voltage is applied to the first semiconductor. After punching through between the region and the third semiconductor region, by injecting minority carriers for the first semiconductor region into the first semiconductor region, the surge current is generated between the first and second terminals. The third semiconductor region is a region that forms an injection junction of the minority carriers with the first semiconductor region in order to start absorption; the third semiconductor region is the second semiconductor region due to the increase of the current after the absorption start of the surge current. After the voltage for forward-biasing the pn junction between the second semiconductor region and the third semiconductor region is generated in the semiconductor region, a minority capacitor for the second semiconductor region is generated in the second semiconductor region. By injecting a rear, the injection of the minority carriers from the fourth region to the first semiconductor region is promoted, and as the surge current absorbed is further increased, a negative characteristic is provided between the first and second terminals. In order to cause the break-over characteristic of the second semiconductor region and to shift the voltage between the first and second terminals to a clamp voltage lower in absolute value than the breakdown voltage, in the region where the minority carriers are injected into the second semiconductor region. There is a surge absorption element. 2. The first terminal connected to the fourth region is connected to an electrode that short-circuits the surface of the fourth region and the surface of the first semiconductor region. A surge absorber according to range 1). 3. A first semiconductor region of the first conductivity type; formed on one of the upper and lower surfaces of the first semiconductor region and having a conductivity type opposite to that of the first conductivity type. A second semiconductor region forming a first pn junction diode with the first semiconductor region; and contacting the second semiconductor region from the side opposite to the first semiconductor region, To define the effective thickness of the second semiconductor region, and has a conductivity type opposite to that of the second semiconductor region and the first pn junction with the second semiconductor region. A third semiconductor region forming a pn junction in a direction opposite to that of the diode; formed on the other surface side facing the one of the upper and lower surfaces of the first semiconductor region, and having the first conductivity type It has a reverse conductivity type and is opposite to the first pn junction diode with the first semiconductor region. A fourth semiconductor region forming a second pn junction diode; and a distance between the first semiconductor region and the fourth semiconductor region by contacting the fourth semiconductor region from a side opposite to the first semiconductor region. To define the effective thickness of the fourth semiconductor region, and in a direction opposite to that of the second pn junction diode between the fourth semiconductor region and the fourth semiconductor region with a conductivity type opposite to that of the fourth semiconductor region. a fifth semiconductor region forming a pn junction; a first terminal connected to a first electrode short-circuiting the fourth semiconductor region and the fifth semiconductor region on their surfaces; the second semiconductor region and the above A third semiconductor region and a second terminal connected to a second electrode that shorts them at their surface; the second pn junction diode is of a polarity that reverse biases the first pn junction diode. A surge with a voltage higher than the breakdown voltage is applied Accordingly, after the first semiconductor region and the third semiconductor region are pulse-through, by injecting minority carriers for the first semiconductor region into the first semiconductor region, between the first and second terminals. Is a diode that injects the minority carriers into the first semiconductor region in order to start absorbing the surge current at; and the first pn junction diode is a diode that reverse-biases the second pn junction diode. Injecting minority carriers for the first semiconductor region into the first semiconductor region after punching through between the first semiconductor region and the fifth semiconductor region as a surge of a voltage equal to or higher than the voltage is applied. In order to start absorbing the surge current between the first and second terminals by doing so, it is a diode that injects the minority carriers into the first semiconductor region. Together; the third semiconductor region forward biases the pn junction between the second semiconductor region and the third semiconductor region in the second semiconductor region due to an increase in the current after the start of absorption of the surge current. From the time when the voltage to be generated is generated, promoting the injection of the minority carriers from the fourth semiconductor region to the first semiconductor region by injecting the minority carriers for the second semiconductor region into the second semiconductor region, Along with the further increase of the absorbed surge current, a breakover characteristic as a negative characteristic is generated between the first and second terminals, and the voltage between the first and second terminals is greater in absolute value than the breakdown voltage. While it is a region for injecting the minority carriers into the second semiconductor region in order to shift to a low clamp voltage; the fifth semiconductor region is provided after the start of absorption of the surge current. In the fourth semiconductor region, a voltage that forward-biases the pn junction between the fourth semiconductor region and the fifth semiconductor region is generated in the fourth semiconductor region, and thereafter, the fourth semiconductor region is provided with the voltage. The injection of minority carriers from the second semiconductor region to the first semiconductor region is promoted by injecting minority carriers into the four semiconductor regions, and the first and second surge currents are further increased together with the surge current absorbed. In order to cause a breakover characteristic as a negative characteristic between the terminals and to shift the voltage between the first and second terminals to a clamp voltage that is lower in absolute value than the breakdown voltage, It is a region for injecting minority carriers;