JPH088420A - Surge protection element - Google Patents

Abstract

(57) [Abstract] [Purpose] Regarding a surge protection element, the entire element can be operated reliably and in a short time in a stripe-shaped or comb-shaped miniaturized thyristor structure, which improves surge current withstand capability. , Get high reliability. A second conductivity type diffusion base layer regions are formed on both surfaces of a first conductivity type semiconductor substrate, and first conductivity type diffusion emitter layer regions are formed alternately in each diffusion base layer region. Then, a resistor is formed on the upper surface of each diffusion emitter layer region, and electrodes are connected to the resistor and the diffusion base layer region formed on both surfaces, respectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surge protection element for protecting a communication terminal or a maintenance worker from a high voltage surge such as lightning induced on a telephone line or the like.

[0002]

2. Description of the Related Art A surge protection device using a pnpn four-layer thyristor has a breakdown voltage (breakover voltage).
When the above abnormal voltage is applied, a thyristor operation that forms a low impedance current path in the element to change from the forward blocking state to the conducting state is used to absorb the large current associated with the abnormal voltage and reduce the voltage across the element. It is an element that clamps below a certain voltage value to protect the electric circuit system.

The surge protection element has a structure in which two or more thyristors are connected in anti-parallel in the same substrate in order to perform an equivalent protection function against positive and negative surges. For example, as shown in the equivalent circuit of FIG. 4, two thyristors 51 and 52 sharing a floating base layer are connected in antiparallel.

FIG. 5 is a sectional view showing the structure of a conventional surge protection element. Note that here, the first conductivity type is p-type and the second conductivity type is n-type. In the figure, n-type diffusion base layer regions 2 and 2'are provided on both sides of a p-type semiconductor substrate 1.
To form. The p-type diffusion emitter layer regions 3 and 3'are alternately formed in the n-type diffusion base layer regions 2 and 2 ', and further, if necessary, for forming an ohmic junction, the diffusion base layer regions 2 and 2'. The n-type ohmic regions 5 and 5'having a concentration higher than the diffusion surface concentration are alternately formed.
Further, a protective film 6, such as a silicon oxide film, is formed on the surface of them.
6'is formed by an oxidation method, a deposition method, or another method, and positions of the n-type diffusion base layer regions 2 and 2 ', the p-type diffusion emitter layer regions 3 and 3', and the n-type ohmic regions 5 and 5 ' A window is opened in the substrate, and electrodes 7 and 7'are formed on the entire surface of the window.

That is, the p-type diffusion emitter layer region 3,
The n-type diffusion base layer region 2, the p-type semiconductor substrate 1, and the n-type diffusion base layer region 2'constitute a forward thyristor 8 having a pnpn structure. Further, the p-type diffusion emitter layer region 3 ', the n-type diffusion base layer region 2', the p-type semiconductor substrate 1, and the n-type diffusion base layer region 2 constitute a reverse thyristor 9 having a pnpn structure.

Now, the function of the surge protection element will be described. When a positive voltage is applied to the electrode 7 on the upper surface, the pn junction between the n-type diffusion base layer region 2 and the p-type semiconductor substrate 1 is reversely biased, and the applied voltage exceeds the junction breakdown voltage. Only leakage current flows, and the current is usually in a high impedance state. However, when a surge exceeding the junction breakdown voltage is applied, charges are injected into the p-type semiconductor substrate 1 due to the breakdown of the pn junction. Now, in the forward thyristor 8, the p-type semiconductor substrate 1 constitutes the base layer of the thyristor, so that the charge injection into this turns the thyristor into the ON state. That is, the application of the surge voltage causes the thyristor to be in the ON state, which results in a low impedance and allows the surge current to pass therethrough. In the steady state after the passage of the abnormal current due to this surge, the thyristor cannot maintain the on state and automatically returns to the off state because of the charge disappearance due to the charge recombination in the p-type semiconductor substrate 1 forming the base layer. (For example, JP-A-1-307264).

On the other hand, due to the symmetry of the structure, the reverse thyristor 9 also operates when a positive voltage surge is applied to the lower electrode 7 '. FIG. 6 is a diagram showing a voltage-current characteristic when a lightning surge is applied.

In the figure, the horizontal axis represents voltage and the vertical axis represents current. V _b0 is the breakover voltage, I _H is the holding current, and V _T is the on-voltage at the lightning surge current I _F.
V _b0 ′, I _H ′, V _T ′, and _IF ′ are values in the opposite directions.

Here, the energy loss E in the surge protection element when a lightning surge is applied is

[0010]

[Equation 1]

It can be expressed as This is equal to the heat generation amount Q of the surge protection element. By the way, the destruction of the element depends on the heat generation temperature inside the element. Since the lightning surge is a short-time pulse, the heat generation inside the element is instantaneous when the lightning surge is applied, whereas the thermal time constant for transmitting the heat to the outside is large.

FIG. 7 is a diagram showing the time variation of the temperature distribution inside the element when a lightning surge is applied. In the figure, the horizontal axis represents the position of the surge protection element shown in FIG. 5 in the x-axis direction, and the vertical axis represents the temperature at each position. When the forward thyristor 8 generates heat, the reverse thyristor 9 functions as its heat sink. However, since it takes time for the entire element to reach a uniform temperature, the temperature gradient inside the element becomes large as shown in FIG. Therefore, the occurrence of mechanical strain due to the difference in thermal expansion of the surge protection element is unavoidable, and the element may be destroyed depending on the magnitude of the surge current. That is, the breakdown of the device depends on the heat generation temperature (peak temperature) inside the device, but the conventional structure cannot reduce the device itself, resulting in a small surge current withstand capability.

The surge protection element described in Japanese Patent Application Laid-Open No. 5-74321 solves this problem. An example of the cross-sectional structure is shown in FIG. In FIG. 8, components having the same functions as those of the surge protection element of FIG. 5 are designated by the same reference numerals. This device is characterized in that the diffusion emitter layer regions 3 and 3'are formed in a stripe shape and a plurality of forward thyristors and reverse thyristors connected to the same electrode 7, 7'are alternately arranged. The miniaturized forward thyristors 11, 12 and 13 are the p-type diffusion emitter layer regions 3 and 3.
It is composed of an n-type diffusion base layer region 2, a p-type semiconductor substrate 1, and an n-type diffusion base layer region 2 '. Further, the miniaturized reverse direction thyristors 14, 15 and 16 include a p-type diffusion emitter layer region 3 ', an n-type diffusion base layer region 2', a p-type semiconductor substrate 1 and an n-type diffusion base layer region. Two
It is composed of

As described above, since the miniaturized forward thyristor and reverse thyristor are arranged adjacent to each other, for example, when a positive lightning surge is applied to the electrode 7, a plurality of electrodes are provided. Forward thyristors 11, 12, 1
3 generates heat and the heat sources are dispersed.

FIG. 9 is a diagram showing the change over time in the temperature distribution inside the element when a lightning surge is applied. In the figure, the horizontal axis shows the position of the surge protection element shown in FIG. 8 in the x-axis direction, and the vertical axis shows the temperature at each position. Since the plurality of miniaturized forward thyristors 11, 12, 13 disperse and generate heat, the amount of heat generation (peak temperature) per forward thyristor becomes small. In addition, the adjacent reverse thyristor 1
The heat sinks 4, 15 and 16 absorb heat as heat sinks, but since they are also miniaturized, the heat conduction distance is short and the temperature of the entire device becomes uniform quickly. Therefore, the temperature gradient generated inside the element when a surge is applied becomes gentle, and the mechanical strain generated due to the difference in thermal expansion can be reduced. Further, since the peak temperature also becomes low, the reliability of the surge protection element and the surge current withstand capability can be improved.

[0016]

However, this is the case where all the thyristors (11 to 16) have the same characteristics. In reality, the semiconductor substrate 1, the diffusion base layer region 2,
It is difficult to manufacture all of them to have the same characteristics due to the nonuniformity of the impurity concentration of 2'and the diffusion emitter layer regions 3 and 3 ', crystal defects, and other causes. In a general thyristor, due to such non-uniformity, the first switching occurs in one minute portion, the adjacent regions are sequentially switched, the operation region is expanded, and the entire region is switched.

In the surge protection element shown in FIG. 8, as in a general thyristor, the forward thyristors 11 to 13 or the reverse thyristors 14 to 16 are applied when a lightning surge is applied.
Of these, the first switching is a minute portion at a certain point, and adjacent regions are sequentially switched to expand the operation region. However, when the emitter width W is longer than the lateral diffusion length d of majority carriers in the base layer, the plurality of same-polarity thyristors are independent of each other, which is the same as when individual thyristors are connected in parallel. Under such circumstances, only one thyristor out of a plurality of thyristors may operate, and in that case, a thunder surge concentrates and flows into the thyristor, heat generation remarkably increases, and surge current resistance decreases. There was a point.

The surge protection element described in Japanese Patent Laid-Open No. 6-53487 discloses a stripe-shaped diffusion emitter layer region 3,
3'is integrated into a comb shape so that all the same-polarity thyristors can be operated reliably. That is, the comb structure is used to form one thyristor in each of the forward direction and the reverse direction to prevent the lightning surge current from being concentrated in a part. However, the structure does not change to the structure in which the operating region expands due to carrier diffusion from the first switching that occurs in one minute portion. Therefore, although the entire surface is eventually switched by the comb structure, it takes a long time to spread the operation region due to carrier diffusion, and there is a problem that it takes time to switch the entire surface.

By the way, there is a circuit configuration method in which a resistor 61 is connected between the emitter and the ground as shown in FIGS. 10 (1) and 10 (2) when a plurality of transistors are used in parallel. This is 1
This is a technique for avoiding current concentration by causing current to flow evenly by switching other transistors by a potential increase due to the resistance when current concentrates on one transistor. Similarly, when using a plurality of thyristors in parallel, FIG.
As in the equivalent circuits shown in (1) and (2), current concentration can be avoided by connecting the resistor 62 between the anode or cathode and the ground. However, in the thyristor shown in FIG. 5 or FIG. 8, the electrodes 7 and 7'are formed on the entire surface, and the structure does not have an external resistor.

According to the present invention, in a thyristor structure miniaturized in a stripe shape or a comb shape, the entire element can be operated reliably and in a short time, thereby improving the surge current withstanding capability and obtaining high reliability. It is an object of the present invention to provide a surge protection element capable of

[0021]

In the surge protection element of the present invention, diffusion base layer regions of the second conductivity type are formed on both sides of a semiconductor substrate of the first conductivity type, and the diffusion base layer regions of the second conductivity type are respectively formed. The first conductivity type diffusion emitter layer regions are formed alternately, resistors are formed on the upper surface of each diffusion emitter layer region, and electrodes are connected to the resistors and diffusion base layer regions formed on both surfaces, respectively. To do.

Further, the diffusion emitter layer region has an area A
And a shape in which the ratio A / L of the peripheral length L is reduced is formed in the diffusion base layer region. Further, the shape in which the ratio A / L of the area A of the diffusion emitter layer region and the peripheral length L is small is a stripe shape or a comb shape.

[0023]

When the surge protection element has stripe-shaped diffusion emitter layer regions, a plurality of miniaturized thyristors corresponding to the diffusion emitter layer regions try to operate in parallel. When the surge protection element has a comb-shaped diffusion emitter layer region, it operates as one thyristor.

In the surge protection element of the present invention, a resistor is provided between the diffused emitter layer region and the electrode. As a result, if the diffusion emitter layer region has a stripe shape, even if the current is concentrated in one thyristor, another thyristor can be reliably operated in parallel by switching the other thyristors by the potential increase due to the resistance. Further, if the diffused emitter layer region has a comb shape, even if switching is started from one minute portion of the thyristor, the operation region can be spread over the entire element in a short time due to the voltage effect of the resistor.
In this way, the function of the resistor allows the entire element to be operated reliably and in a short time.

[0025]

1 is a view showing the structure of a first embodiment of a surge protection element of the present invention. Note that (1) is a top view, (2) is a cross-sectional view taken along the line AA 'in the top view, and (3) is a bottom view.
Further, here, the first conductivity type is p-type and the second conductivity type is n-type.

In the figure, n-type diffusion base layer regions 2 and 2'are formed on both sides of a p-type semiconductor substrate 1. Stripe-shaped p-type diffusion emitter layer regions 3 are formed in the n-type diffusion base layer regions 2 and stripe-shaped so as to alternate with the diffusion emitter layer regions 3 in the n-type diffusion base layer regions 2 '. To form a p-type diffusion emitter layer region 3 '. So as to cover these diffusion emitter layer regions 3, 3 ',
Amorphous silicon, for example, is formed as the resistors 10 and 10 '. Alternatively, tungsten, molybdenum, or another metal may be used.

Further, a protective film 6, 6 ', such as a silicon oxide film, is formed on the surface of the n-type diffusion base layer regions 2, 2', resistors 10, 10 'by an oxidation method, a deposition method or another method. A window is opened at the position of ', and electrodes 7, 7'are formed on the entire surface of the window. Note that the protective films 6, 6'and the electrodes 7, 7'are omitted in the top view and the bottom view.

In this way, the p-type diffusion emitter layer region 3, the n-type diffusion base layer region 2, the p-type semiconductor substrate 1,
The n-type diffusion base layer region 2'constitutes a forward thyristor having a pnpn structure. Further, the p-type diffused emitter layer region 3 ', the n-type diffused base layer region 2', the p-type semiconductor substrate 1, and the n-type diffused base layer region 2 form a reverse thyristor having a pnpn structure. Since these forward thyristors and reverse thyristors are alternately arranged, they have the same thermal effect as the surge protection element described in JP-A-5-74321 (temperature distribution in FIG. 9). Can be obtained.

Further, since the diffused emitter layer regions 3 and 3'of each thyristor are connected to the electrodes 7 and 7'through the resistors 10 and 10 ', the circuit is shown in FIG. It is similar to the parallel operation configuration of multiple thyristors shown in (2). That is, it is possible to prevent the electric current from concentrating on a part of the thyristors by the action of the resistors 10 and 10 '.
The entire device can be operated reliably and in a short time.

FIG. 2 is a diagram showing the relationship between the width (emitter width) of the diffused emitter layer regions 3 and 3'and the peak temperature.
In the figure, the horizontal axis represents the emitter width (μm) and the vertical axis represents the peak temperature. The example shown here is a lightning surge waveform with a rise time of 15 μsec and a fall time of 100 μsec.
It is the result of performing the unsteady thermal analysis when 600 A was applied. As shown in the figure, it can be seen that the peak temperature can be significantly reduced by setting the emitter width to 500 μm or less.

On the other hand, the high-frequency high-power transistor also has a stripe-shaped or comb-shaped emitter, which has a ratio A / L of the emitter area A to its peripheral length L in order to effectively work the emitter. It is a small one. In this case, the emitter width W is determined by the lateral diffusion distance of majority carriers, and in the case of the npn structure, L _PB ≈ (D _PB τ _PB ) ^1/2 , and the emitter width of the diffusion base type silicon transistor is It will be about 10 μm. On the other hand, if the emitter width used in the surge protection element of the present invention is 500 μm or less, the peak temperature can be sufficiently reduced.

FIG. 3 is a diagram showing the structure of a second embodiment of the surge protection element of the present invention. In addition, (1) is a top view, (2)
Is a sectional view taken along the line AA 'in the top view, and (3) is a bottom view. Further, here, the first conductivity type is p-type and the second conductivity type is n-type.

In the figure, n-type diffusion base layer regions 2 and 2'are formed on both sides of a p-type semiconductor substrate 1. A comb-shaped p-type diffusion emitter layer region 3 is formed in the n-type diffusion base layer region 2, and a comb-shaped p-type diffusion emitter layer region 3 is formed in the n-type diffusion base layer region 2 ′ so as to be point-symmetric with the diffusion emitter layer region 3. A p-type diffusion emitter layer region 3'having a shape is formed. The comb-shaped diffusion emitter layer regions 3 and 3'have a small ratio A / L between the area A and the peripheral length L, like the stripe-shaped diffusion emitter layer regions 3 and 3'of the first embodiment. However, the present invention is not limited to this shape.

Further, the n-type diffusion base layer regions 2, 2 '
In order to fill the comb-shaped diffusion emitter layer regions 3 and 3'within the diffusion base layer region 2 for ohmic contact formation.
The n-type ohmic regions 5 and 5'having a concentration higher than the diffusion surface concentration of 2'are formed point-symmetrically. Further, resistors 10 and 10 'having the same composition as in the first embodiment are formed so as to cover the diffusion emitter layer regions 3 and 3'.

Further, a protective film 6, 6 ', such as a silicon oxide film, is formed on their surface by an oxidation method, a deposition method, or another method to form the resistors 10, 10' and the n-type ohmic regions 5, 5 '. A window is opened at the position, and electrodes 7 and 7'are formed on the entire surface of the window. In addition, in the top view and the bottom view,
The protective films 6 and 6'and the electrodes 7 and 7'are omitted and the shape of the diffusion layer region is shown.

As described above, the comb-shaped p-type diffusion emitter layer region 3, the n-type diffusion base layer region 2, the p-type semiconductor substrate 1, and the n-type diffusion base layer region 2'provide a forward direction of the pnpn structure. A thyristor is constructed. Also, a comb-shaped p-type diffusion emitter layer region 3 ', an n-type diffusion base layer region 2', a p-type semiconductor substrate 1, and an n-type diffusion base layer region 2 are provided.
A reverse direction thyristor having a pnpn structure is constituted by.
By forming the n-type ohmic regions 5 and 5 ', the difference in contact potential between the semiconductor portion and the electrode (loss due to the Schottky barrier) can be reduced, and the surge current withstand capability can be improved. Thermally, it is possible to obtain the same effect as the surge protection element described in JP-A-6-53487.

In this embodiment, the diffused emitter layer regions 3,
Since 3'has a comb shape, it operates as one thyristor in each of the forward and reverse directions. Here, the resistors 10, 10 'connecting the diffused emitter layer regions 3, 3'to the electrodes 7, 7'function effectively. That is, switching of the thyristor starts from a minute portion at a certain point, but when current concentration occurs at that point, the thyristor in the non-operating portion switches due to the voltage drop of the resistors 10 and 10 '. Therefore, in addition to the conventional effect of spreading the switch region due to carrier diffusion, the effect of spreading the switch region due to the drift of the electric field is added, and the time for switching the entire surface can be extremely shortened.

As described above, in the first embodiment, the parallel operation effect of a plurality of thyristors and in the second embodiment, the high speed expansion effect of the switch region of one thyristor ensures the operation of the entire element in a short time. You can

[0039]

As described above, according to the present invention, since the entire device can be operated reliably and in a short time, the temperature inside the device can be made uniform quickly and the peak temperature can be reduced. . Therefore, reliability as a lightning surge or static electricity protection element to which a high-voltage pulse with a short time width is applied, and as a switching noise or other absorption element can be improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a structure of a first embodiment of a surge protection element of the present invention.

FIG. 2 is a diagram showing a relationship between an emitter width and a peak temperature.

FIG. 3 is a diagram showing the structure of a second embodiment of the surge protection element of the present invention.

FIG. 4 is a diagram showing an equivalent circuit of a surge protection element.

FIG. 5 is a sectional view showing the structure of a conventional surge protection element.

FIG. 6 is a diagram showing voltage-current characteristics when a lightning surge is applied.

FIG. 7 is a diagram showing a time change of temperature distribution inside the element when a lightning surge is applied.

FIG. 8 is a conventional surge protection element (Japanese Patent Application Laid-Open No. 5-74321).
No.) sectional view showing the structure.

FIG. 9 is a diagram showing a time change of temperature distribution inside the element when a lightning surge is applied.

FIG. 10 is a diagram showing a circuit configuration when a plurality of conventional transistors are used in parallel.

FIG. 11 is a diagram showing a circuit configuration when a plurality of conventional thyristors are used in parallel.

[Explanation of symbols]

 1 p-type semiconductor substrate 2, 2'n-type diffusion base layer region 3, 3 'p-type diffusion emitter layer region 5, 5' n-type ohmic region 6, 6 'protective film 7, 7' electrode 8 sequence Directional thyristor 9 Reverse direction thyristor 10 Resistor 11, 12, 13 Forward direction thyristor 14, 15, 16 Reverse direction thyristor 51, 52 Thyristor 61, 62 Resistance

Claims (4)

[Claims] 1. A second conductive film is formed on both sides of a semiconductor substrate of a first conductivity type.
Conductive type diffusion base layer regions are formed, first conductive type diffusion emitter layer regions are alternately formed in the diffusion base layer regions, and resistors are formed on the upper surfaces of the diffusion emitter layer regions. The surge protection element is characterized in that electrodes are respectively connected to the resistor and the diffusion base layer region formed on both surfaces. 2. The surge protection device according to claim 1, wherein the diffused emitter layer region has a ratio A / A of its area A to a peripheral length L.
A surge protection element characterized in that it is formed in the diffusion base layer region in a shape such that L is small. 3. The surge protective element according to claim 2, wherein the diffused emitter layer region is formed in a stripe shape. 4. The surge protection element according to claim 2, wherein the diffused emitter layer region is formed in a comb shape.