JPH0945892A - Surge protection element - Google Patents

Abstract

(57) Abstract: A surge current withstand capability is improved and high reliability is obtained by reducing power loss due to a resistor disposed between a diffused emitter layer region and an electrode to suppress heat generation. The resistor is formed of a resistor having a negative temperature coefficient. The resistance value of the resistor having a negative temperature coefficient decreases as the temperature rises, and the power loss due to the resistor decreases.

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 element using a pnpn four-layer thyristor has a breakdown voltage (breakover voltage).
When the above abnormal voltage is applied, a low impedance current path is formed in the device, and the thyristor operation that changes from the forward blocking state to the conducting state absorbs the large current accompanying the abnormal voltage and reduces 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 an equivalent circuit of FIG. 4, two thyristors 51 and 52 sharing a floating base layer are connected in anti-parallel. FIG. 5 is a sectional view showing the structure of a conventional surge protection element. 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. In the n-type diffusion base layer regions 2 and 2 ', p-type diffusion emitter layer regions 3 and 3'are alternately formed on both surfaces of the substrate, and if necessary, to form ohmic junctions, the diffusion base layer regions are formed. The n-type ohmic regions 5, 5'having a concentration higher than the diffusion surface concentration of 2, 2'are formed alternately. Also,
Protective films 6, 6 ′ such as a silicon oxide film are formed on their surfaces by an oxidation method, a deposition method or another method, and n type diffusion base layer regions 2, 2 ′ and p type diffusion emitter layer regions 3, 3 are formed. A window is opened at the positions of the ', n-type ohmic regions 5, 5', and electrodes 7, 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. 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 2 constitute a reverse thyristor 9 having a pnpn structure.

Here, 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 reverse biased, and until the applied voltage exceeds the junction breakdown voltage. The current flows only through leakage current and is usually in a high impedance state. However, when a surge exceeding the junction breakdown voltage enters, charges are injected into the p-type semiconductor substrate 1 by 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, and the charge injection therein turns the thyristor on. That is, the thyristor is turned on by the application of the surge voltage, the impedance becomes low, and the surge current is passed. In a steady state after passing an abnormal current due to the surge, the thyristor cannot automatically maintain the ON state and automatically returns to the OFF state due to charge disappearance due to charge recombination in the p-type semiconductor substrate 1 constituting the base layer. (For example, JP-A-1-307264).

On the other hand, even when a positive voltage surge is applied to the lower electrode 7 'due to the symmetry of the structure, the reverse thyristor 9 operates similarly. FIG. 6 is a diagram showing voltage-current characteristics when a lightning surge is applied. In the figure, the horizontal axis is voltage,
The vertical axis represents current. V _b0 are breakover voltage, is I _H holding current, V _T is the on-voltage in 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

[0009]

[Equation 1]

Can be expressed as Note that this is equal to the calorific value Q of the surge protection element. Incidentally, destruction of the element depends on the heat generation temperature inside the element. Since the lightning surge is a short-time pulse, the internal heat generation of the element when the lightning surge is applied is instantaneous, whereas the heat transmitted to the outside has a large thermal time constant. 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 shows the position of the surge protection element shown in FIG. 5 in the x-axis direction, and the vertical axis shows the temperature at each position. When the forward thyristor 8 generates heat, the reverse thyristor 9 functions as a 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 destruction of the element depends on the heat generation temperature (peak temperature) inside the element. However, the conventional structure cannot reduce the element itself, so that the surge current resistance is reduced.

The surge protection element described in Japanese Patent Application Laid-Open No. 5-74321 solves this problem. FIG. 8 shows an example of the cross-sectional structure. 8, components having the same functions as those of the respective parts of the surge protection element in FIG. 5 are denoted by the same reference numerals. This device is characterized in that the diffused emitter layer regions 3, 3 'are formed in a stripe shape, and a plurality of forward thyristors and reverse thyristors connected to the same electrodes 7, 7' are alternately arranged. The miniaturized forward thyristors 11, 12, 13 are provided with p-type diffusion emitter layer regions 3, 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 thyristors 14, 15, 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. 2
It consists 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 thyristors are provided. Forward thyristors 11, 12, 1
3 generates heat, and the heat source is dispersed. FIG. 9 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 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. A plurality of miniaturized forward thyristors 11,
Since 12 and 13 disperse and generate heat, the amount of heat generation (peak temperature) per forward thyristor becomes small.
Further, the adjacent reverse thyristors 14, 15 and 16 absorb heat as a heat sink, but since they are also miniaturized, the heat conduction distance is short and the temperature of the entire element is quickly made uniform. 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 is lowered, the reliability of the surge protection element and the surge current withstand capability can be improved.

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

In the surge protection element shown in FIG. 8, as in a general thyristor, when a lightning surge is applied, the forward thyristors 11 to 13 or the reverse thyristors 14 to 16 are applied.
Of these, the first switching is a minute portion of a certain point, and the adjacent regions are sequentially switched to expand the operation region. However, when the emitter width W is longer than the diffusion length d of the majority carriers in the base layer in the horizontal direction, the plurality of thyristors of the same polarity are independent from each other. Under such circumstances, only one of the thyristors may operate, and in such a case, a lightning surge is concentrated on the thyristor, and the heat generation is remarkably increased, resulting in a decrease in surge current resistance. 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 'are integrated in a comb shape to ensure that all thyristors of the same polarity operate. That is, one thyristor is provided in each of the forward direction and the reverse direction by the comb-shaped structure, and the lightning surge current is prevented from being partially concentrated. However, there is no change in the structure in which the operation region is expanded by the diffusion of carriers from the first switching occurring at a minute portion of one point. Therefore, although the entire surface is eventually switched by the comb-shaped structure, it takes time to spread the operation region due to the diffusion of carriers, so that it takes time until the entire surface is switched.

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
In this technology, when current concentrates on one transistor, the other transistor is switched by the potential rise due to the resistance to flow current evenly to avoid current concentration. Similarly, when a plurality of thyristors are used in parallel, FIG.
As in the equivalent circuits shown in (1) and (2), the current concentration can be avoided by connecting the resistor 62 between the anode or cathode and the ground. However, the thyristor shown in FIG. 5 or FIG. 8 has the electrodes 7, 7 'formed on the entire surface, and does not have a structure in which a resistor can be externally attached.

In the surge protection element of Japanese Patent Application No. 6-137661, a resistor is provided between a diffusion emitter layer region and an electrode in a thyristor structure which is miniaturized in a stripe shape or a comb shape. If the diffused emitter layer region has a stripe shape, even if the current is concentrated in one thyristor, another thyristor is switched by the potential increase due to the resistance,
The thyristors can be reliably operated in parallel. In addition, if the diffusion emitter layer region has a comb shape, even if switching starts from a minute portion of one point of the thyristor, the operating region can be spread over the entire device in a short time by the voltage effect of the resistor. In this way, the function of the resistor makes it possible to operate the entire element reliably and in a short time,
As a result, the surge current resistance can be improved and high reliability can be obtained.

[0020]

However, in a surge protection element having a resistor, a large current of lightning surge flows through the resistor, so that power loss due to the resistance cannot be avoided.
For example, the power loss is the square of the current multiplied by the resistance value. Therefore, if the lightning surge current is 1000 A and the resistance value is 0.01 Ω, a very large power loss of 10000 W occurs. As a result, if the element locally generates heat and becomes equal to or higher than the melting point of silicon, the element may be broken.

It is an object of the present invention to provide a surge protection element capable of improving surge current withstanding capability and obtaining high reliability by reducing power loss due to such resistance and suppressing heat generation. .

[0022]

According to the present invention, a resistor is provided between a diffused emitter layer region and an electrode in Japanese Patent Application No. 6-137.
In the surge protection element of No. 661, the resistor is composed of a resistor having a negative temperature coefficient. At the initial stage of operation, the same mechanism as that of the thyristor element of the prior application allows the entire element to operate reliably and in a short time by the action of resistance.
Further, when a large current of lightning surge flows, the self-heating of the thyristor element is transmitted to the resistor. Here, the resistance value of a resistor having a negative temperature coefficient decreases as the temperature rises,
Power loss due to the resistor is reduced.

The diffused emitter layer region of this surge protection element is an emitter layer in which current concentrates on the periphery of the emitter region.
In consideration of the crowding effect and transient heat diffusion, the shape is set such that the ratio A / L of the area A and the peripheral length L becomes small (for example, stripe shape or comb shape). When the surge protection element has stripe-shaped diffusion emitter layer regions, a plurality of miniaturized thyristors corresponding to the diffusion emitter layer regions tend to operate in parallel. When the surge protection element has a comb-shaped diffusion emitter layer region, it operates as one thyristor.

[0024]

FIG. 1 is a diagram showing a first embodiment of a surge protection element of the present invention. (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. 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 surfaces of a p-type semiconductor substrate 1. A striped p-type diffusion emitter layer region 3 is formed in the n-type diffusion base layer region 2, and a stripe-shaped p-type diffusion emitter layer region 3 is formed in the n-type diffusion base layer region 2 'so as to be alternate with the diffusion emitter layer region 3. To form a p-type diffused emitter layer region 3 '. Amorphous silicon, for example, is formed as the resistors 10 and 10 'so as to cover the diffusion emitter layer regions 3 and 3'. Further, protective films 6, 6 ', such as a silicon oxide film, are formed on the surfaces of the n-type diffusion base layer regions 2, 2', resistors 10, 10 'by the oxidation method, the deposition method, or another method. I gave a window to
Electrodes 7 and 7'are formed on the entire surface of the window. In the top and bottom views, the protective films 6, 6 'and the electrodes 7, 7' are omitted.

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 'forms a forward thyristor having a pnpn structure. 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 having a pnpn structure. Since the structure is such that these forward thyristors and reverse thyristors are alternately arranged, it is thermally equivalent to the surge protection element described in Japanese Patent Application Laid-Open No. 5-74321 (temperature distribution in FIG. 9). Can be obtained.

Further, since the diffusion 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, the action of the resistors 10 and 10 'prevents the current from being concentrated on some thyristors,
The entire device can be operated reliably and in a short time.

Further, although the lightning surge current increases with the passage of time, since the resistors 10, 10 'are formed in contact with the thyristor element, heat is conducted to the resistor by self-heating of the thyristor. I will do it. Resistor 10,
Since the amorphous silicon forming 10 'has a negative temperature coefficient as shown in FIG. 2, the resistance value decreases as the temperature rises, and the loss due to the resistor can be reduced.

FIG. 3 is a diagram showing a second embodiment of the surge protection element of the present invention. (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.
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 surfaces 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, 3 'have a small ratio A / L between the area A and the peripheral length L, similarly to the stripe-shaped diffusion emitter layer regions 3, 3' of the first embodiment. This is an example of the shape, and 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 ′ therein, a diffusion base layer region 2 and an ohmic junction are formed.
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 negative temperature coefficient as in the first embodiment are formed so as to cover the diffusion emitter layer regions 3 and 3'. In addition, a protective film 6 such as a silicon oxide film
6'is formed by an oxidation method, a deposition method, or another method, and the resistors 10, 10 ', the n-type ohmic region 5,
A window is opened at the 5'position, and electrodes 7, 7'are formed on the entire surface of the window.
To form In the top and bottom views, 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 the 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
Constitutes a reverse thyristor having a pnpn structure.
By forming the n-type ohmic regions 5, 5 ', the contact potential difference (loss due to the Schottky barrier) between the semiconductor portion and the electrode can be reduced, and the surge current withstand capability can be improved. Thermally, the same effect as that of the surge protection element described in JP-A-6-53487 can be obtained.

In the present 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 diffusion emitter layer regions 3, 3' and the electrodes 7, 7 'work effectively. That is, the switching of the thyristor starts from a minute portion at a certain point, but when current concentration occurs there, the thyristor in the non-operating portion switches due to a voltage drop of the resistors 10 and 10 '. Therefore, the effect of expanding the switch region due to the drift of the electric field is further added to the effect of expanding the switch region due to the conventional carrier diffusion, so that the time required for switching over the entire surface can be significantly reduced.

Further, although the lightning surge current increases with the passage of time, since the resistors 10, 10 'are formed in contact with the thyristor element, heat is conducted to the resistor by self-heating of the thyristor. To do. However, since the resistor has a negative temperature coefficient, the resistance value is reduced and the loss due to the resistor is reduced. 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 can surely operate the entire element in a short time. Further, as shown in FIG. 9, the thyristor element generates heat with the passage of time, and the heat is transmitted to the resistor to raise the temperature of the resistor, but the resistance value decreases due to the negative temperature coefficient, Power loss due to resistance can be reduced.

[0033]

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 quickly made uniform and the peak temperature can be reduced. . Furthermore, current loss due to resistance can be reduced. Therefore, the reliability as a protection element against lightning surge or static electricity to which a high-voltage pulse having a short time width is applied, and as a switching noise and other absorbing elements can be improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram showing temperature dependence of electric conductivity of amorphous silicon.

FIG. 3 is a diagram showing a second embodiment of the present invention.

FIG. 4 is a diagram showing an equivalent circuit of the 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 a temperature distribution inside the element when a lightning surge is applied.

FIG. 8 shows a conventional surge protection element (JP-A-5-74321).
FIG.

FIG. 9 is a diagram showing a time change of a 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 Direction thyristor 9 Reverse thyristor 10 Resistor 11, 12, 13 Forward thyristor 14, 15, 16 Reverse thyristor 51, 52 Thyristor 61, 62 Resistance

Claims (4)

[Claims] A first conductive type semiconductor substrate on both surfaces thereof;
Conductive type diffusion base layer regions are formed, and a plurality of first conductivity type diffusion emitter layer regions are formed in each of the diffusion base layer regions so as to have a staggered relationship on both sides of the semiconductor substrate. A resistor is formed on the upper surface of each diffused emitter layer region, and a resistor is formed on both surfaces and a surge protection element in which electrodes are connected to the diffused base layer region, respectively, wherein the resistor has a negative temperature coefficient. A surge protection element characterized by being composed of a resistor. 2. The surge protection device according to claim 1, wherein the diffusion emitter layer region has a ratio A / A of its area A to its peripheral length L.
A surge protection element formed in a diffusion base layer region so as to reduce L. 3. The surge protection device according to claim 2, wherein the diffused emitter layer region is formed in a stripe shape. 4. The surge protection device according to claim 2, wherein the diffusion emitter layer region is formed in a comb shape.