JPH06103744B2 - Optical trigger thyristor - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical trigger thyristor in which the amplification gate structure of a conventional optical trigger thyristor is improved and the optical trigger sensitivity is drastically increased as compared with the conventional optical trigger thyristor. The present invention relates to an optical trigger thyristor that can be used not only as a power converter but also as a switching element in a large power converter.

[0002]

2. Description of the Related Art Conventionally, it has been widely practiced to trigger a thyristor with light, such as LASCR and Light Act.
It is a well-known fact that it is implemented under the names such as Ivated Thyristor and Photothyristor.

FIG. 4 shows an example of a conventional optical trigger thyristor, which has a structure in which amplification thyristors are integrated. In order to allow light to enter the inside of the base and to increase the photosensitivity of the amplifying thyristor, the p base layer in the portion to be irradiated with light is dug in and thinned. Also,
In order to improve the dv / dt withstand capability, the structure in which the cathode and the base of the amplification thyristor and the main thyristor are short-circuited is common. The n-cathode region 811, the p-base layer 803, the n-base layer 802 and the p-anode layer 801 form an amplification gate auxiliary thyristor having an npnp four-layer structure, and at the same time, the n-cathode layer 804 and the p-base layer 8 are formed.
03, the n base layer 802, and the p anode layer 801 form a main thyristor. Auxiliary thyristor n
The cathode 811 and the p base layer 803 are short-circuited by the electrode 833, and the n cathode 804 and the p base layer 803 of the main thyristor are short-circuited by the electrode 832.

Incident light 861 introduced by an optical fiber or the like is transmitted through the thin n-cathode layer 811 to form electron-hole pairs in the depletion layer formed at the junction of the p-base layer 803 and the n-base layer 802. To generate. The generated holes flow through the base resistance portion 850 in the thinned p base layer, while the generated electrons are generated in the n base layer 802 and the p anode layer 8.
01 accumulates at the junction interface and causes hole injection from the p anode layer 801. The current due to the injected holes and the holes generated by the light flows through the thinned base resistance portion 850 in the p base layer, and the base potential of the auxiliary thyristor rises to reach the turn-on threshold. The thyristor turns on. In the ON state, the hole current flows in the n cathode 811, passes through the electrode 833, and in turn the base resistance portion 8 in the p base layer 803 of the main thyristor.
It will flow through 54. Electron current is n cathode 811
Flow through diffusion in the thinned p base layer, flow through the strong electric field portion of the p base layer 803 and the n base layer 802, accumulate at the junction portion of the n base layer 802 and the p anode layer 801, and further from the positive electrode of the p anode 801. The hole injection is promoted and it flows out to the p anode electrode 831.

When the auxiliary thyristor is turned on, an overwhelming number of hole currents are injected from the p anode 801 toward the p base 803, so that the base resistance portion in the base layer 803 of the main thyristor. When a large amount of hole current flows through 854 and the base potential of the main thyristor exceeds the turn-on threshold value, the main thyristor turns on. In the ON state of the main thyristor, the hole current flows through the n cathode 804 and is continuously absorbed by the cathode electrode 832, and the electron current flows from the n cathode 804 to the p electrode 804.
It flows in the base 803 by diffusion, drifts in the n base layer 802, flows in the p anode 801 and is absorbed by the anode electrode 831. 851 is an anode terminal, 852
Represents the cathode terminal of the main thyristor.

[0006]

As described above, the conventional optical trigger thyristor uses the auxiliary amplification thyristor as the trigger mechanism, but the auxiliary amplification thyristor has the bipolar base structure. The DC optical amplification factor (current amplification factor) β of the uniform base bipolar base structure can be expressed by the following equation in the approximation that the incident light intensity is small.

[0007]

[Equation 1]

In the equation (1), D _n and D _p are diffusion constants of electrons and holes, L _p is a diffusion distance of holes, W _b is a base width, n _e is an impurity density of the emitter, and p _b is It is the impurity concentration of the base. Actually, the value of β is at most 10 ² to 1
It is about 0 ³ . Therefore, in order to trigger the amplification thyristor with light, considerably high optical power is required. As described above, the conventional optical trigger thyristor has a problem that an extremely high output light source is required as the trigger light source because the optical sensitivity of the amplification gate is small. Therefore, an attempt has been made to increase the optical amplification degree by thinning the base layer of the amplification auxiliary thyristor as shown in FIG. 4 or by connecting a plurality of devised auxiliary thyristors to such a base layer. However, it was structurally complicated.

In view of the above problems, the present invention is to provide an optical trigger thyristor with dramatically improved optical trigger sensitivity as compared with the conventional optical trigger thyristor.

[0010]

In order to achieve the above object, an optical trigger thyristor according to the present invention applies a static induction transistor (SIT) gate structure as an amplification gate. One of the thyristors is a first conductivity type high impurity density anode region,
A first base region of a second conductivity type formed on the anode region, and a first base region formed on the first base region.
A four-layer structure main thyristor formed of a conductive second base region and a cathode region formed in a part of the upper part of the second base region, and the first layer in a part of the upper part of the first base region. A drain region of the first conductivity type having a high impurity density, which is formed so as to be connected to at least a part of the second base region;
The first conductivity type low impurity density channel region formed on the drain region, the first conductivity type high impurity density source region formed on a part of the channel region, and the source region are sandwiched. And the isolation region provided between the second base region and the channel region, and the static induction phototransistor formed on the channel region with the second conductivity type high impurity density gate region. And at least a region. Further, another one of the optical thyristors according to the present invention is the first conductivity type high impurity concentration anode region, the second conductivity type first base region formed on the anode region, and the first base. A second conductivity type high impurity density buried region formed inside the region, a first conductivity type second base region formed above the first base region, and an upper part of the second base region. A four-layer structure main thyristor formed of a cathode region formed in the first part, and a first part formed in at least a part of the upper part of the first base region so as to be connected to the second base region. A drain region having a high conductivity type conductivity, a channel region having a first conductivity type low impurity density formed on the drain region, and a first conductivity type high impurity density formed on a part of the channel region. Source area of
Between an electrostatic induction phototransistor formed of a second conductivity type high impurity density gate region formed above the channel region so as to sandwich the source region, and between the second base region and the channel region. And a separation region provided in the.

[0011]

In the SIT gate structure, the potential barrier when the holes in the gate escape to the source side is larger than the potential barrier that the source side overcomes when the electrons flow to the drain. It is easily accumulated in the region, and the current amplification factor β becomes very large. Moreover, there is a characteristic that the smaller the input light intensity is, the larger it is. The maximum value of the direct-current optical amplification of the SIT gate structure corresponds to the limit where the incident light intensity is equivalent to the dark current hole current,

[0012]

[Equation 2]

In equation (2), W _G is the effective value of the gate potential barrier, n _S is the source impurity density, p _G is the gate impurity density, k is the Boltzmann constant, T is the absolute temperature, and q is the unit charge amount. , V _biGS is the potential barrier height between the gate and the source that should be exceeded when holes in the gate region escape to the source side, and V _biG ^* _S is the true gate point G ^* that should be exceeded when electrons on the source side flow to the drain ^. The height of the potential barrier between the source and the source. The true gate is unique to the SIT gate structure and is the saddle point of the potential generated in the channel.

As is clear from the equation (2), the difference in potential barrier between the gate and the source and between the true gate point G ^* and the source has a great influence on the optical amplification factor (current amplification factor). Therefore, the optical amplification factor (current amplification factor) of the SIT gate structure is
This is much higher than the optical amplification factor (current amplification factor) of the bipolar base structure described above. As a result of the experiment, values exceeding 10 ⁸ have been obtained for extremely weak light of 10 ⁻¹⁰ (W / cm ² ), and if the SIT gate structure is applied to the amplification gate of the conventional optical trigger thyristor, the optical trigger sensitivity is increased. Is dramatically improved, and an optical trigger thyristor that can be driven at high speed with weak light can be realized. That is, the integration of the static induction phototransistor and the main thyristor improves the trigger sensitivity of the conventional optical trigger thyristor.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the present invention. The main feature of this embodiment is that the amplification gate structure is composed of a planar gate type static induction phototransistor (SIPT).

In FIG. 1, the main thyristor comprises an n ⁺ cathode region 704 and a second base region p base region 7.
03, first base region n ⁻ high resistance layer 702, n ⁺
It is formed from the second gate region 705 and the p ⁺ anode region 701, and the n ⁺ second gate region 705 forms a SIT gate structure with the p ⁺ anode region 701. Regions 732 and 731 are cathode electrodes,
An anode electrode is shown, and 751 and 752 are an anode terminal and a cathode terminal, respectively.

In FIG. 1, a p-channel SIP for amplification is used.
T is composed of p ⁺ source region 711, p ⁻ low impurity density channel region 713, p ⁺ drain region 714 and n ⁺ gate region 712, and p ⁺ drain region 714 is the second base region of the main thyristor. Base region 703
And n ⁻ base region 702 which is the first base region. p ⁺ source region 711 and n ⁺ gate region 712
A source electrode 733 and a gate electrode 734 are provided on the exposed surface portion of each.

The p ⁺ source region 711 of the amplifying p-channel SIPT has a positive voltage (source bias voltage) V _st 7
Biased to 55, the n ⁺ gate region 712 is biased to the gate bias voltage V _Gt 753 through the resistor R _Gt 754. There is a beveled groove between the p base region 703 and the p ⁻ channel region 713, which serves as a separation region. By adjusting the size of the resistor R _Gt, the optical trigger sensitivity and response time can be controlled.

The amplification SIPT is off when the trigger light pulse LT760 is not incident via the optical transmission medium such as an optical fiber. Light pulse for trigger LT76
As the wavelength of 0, a GaAs infrared light emitting diode or the like having a long light penetration distance is suitable. Optical pulse LT for trigger
When 760 is irradiated, the amplification SIPT turns on, the p-base region 703 of the main thyristor is positively biased by the positive bias voltage V _st 755, and the main thyristor turns on. Turn-on of the main thyristor occurs as follows.

The amount of holes injected from the p ⁺ anode region 701 increases and contributes as a hole current flowing through the base resistance of the p base region 703 of the main thyristor, but due to the base resistance drop in the p base region 703. When the potential of the p base region 703 exceeds the turn-on threshold value, the main thyristor turns on, and electrons from the n ⁺ cathode region 704 flow in the p base region 703 by diffusion and drift in the n ⁻ high resistance layer 702. It runs and is accumulated at the interface between the n ⁺ gate region 705 or the n ⁻ high resistance layer 702 and the p ⁺ anode region 701. In the ON state of the main thyristor, holes flowing into the p base region 703 are n ⁺ cathode region 704.
Through which the electron current continues to be absorbed by the cathode electrode 732 and through the p ⁺ anode region 701 to the p ⁺ anode electrode 731. Therefore, in order to quickly turn on the main thyristor, the p ⁺ anode region 70
It is necessary to increase the amount of hole injection from 1. Therefore, it is desirable that the n ⁺ gate region 705 has a SIT gate structure. That is, the optical amplification degree of the static induction phototransistor is very high as described in the equation (2), and the SI phototransistor having the SIT gate structure is used as the amplification auxiliary transistor in the embodiment shown in FIG. Therefore, the optical trigger sensitivity is very high.

Regarding the embodiment of the present invention described above, S
The experimental result of the direct current optical amplification factor (current amplification factor) of the IT gate structure will be described in comparison with the experimental result of the bipolar base structure.

FIG. 2 shows the dependency of the direct-current optical amplification degree G of SIPT on the incident light intensity P _i . The drain bias voltage V _D is used as a parameter, and at the same time, the change ΔV _G in the gate potential of the SIPT is shown.

FIG. 3 shows a bipolar phototransistor (B
12 shows the dependency of the direct current optical amplification degree G of (PT) on the incident light intensity P _i . The collector bias voltage V _C is used as a parameter, and the change ΔV _B of the base potential of the BPT is also shown.

As is clear from FIGS. 2 and 3, the SIPT
And the tendency of the direct current optical amplification degree G of the BPT to depend on the light intensity P _i are completely different. In BPT, the optical amplification degree G is DC.
Gradually increases as the light intensity P _i increases, but P _i =
It is 10 ² μW / cm ² and at most about 3 × 10 ² . on the other hand,
In the SIPT, the weaker the light intensity is, the more the direct-current optical amplification degree G tends to increase, and at P _i = 10 ⁻⁴ μW / cm ² , G exceeding 10 ⁸ is obtained.

As described above, in the SIT gate structure,
A much larger optical amplification factor (current amplification factor) can be obtained as compared with the bipolar base structure. Therefore, if the SIT gate structure is applied to the amplification gate structure of the optical trigger thyristor, a high photosensitivity and high speed trigger thyristor can be realized.

As an example, in the case of an optical trigger of 400V-10A, when the amplification gate structure of the SIT gate structure according to the present invention is used, the turn-on delay is 1.8 μs and the turn-on rise time is about 123 μW of light. It was 1.1 μs. When an amplification gate structure having a bipolar base structure is used instead of the SIT gate structure,
At the same light intensity, the gate potential of the main thyristor is 0.6
It was only able to rise to eV and could not trigger light.

[0027]

As described above, the optical trigger thyristor according to the present invention has a dramatically improved optical trigger sensitivity as compared with the conventional optical trigger thyristor. Therefore, if the optical trigger thyristor according to the present invention is used in a switching device to which the conventional optical trigger thyristor is applied, extremely high speed,
A highly sensitive switching device can be realized. Further, it broadens the application range of the optical trigger thyristor from high power to medium and low power fields, and has high industrial utility value.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of an embodiment of an optical trigger thyristor according to the present invention in which an optical amplification section is formed of a static induction phototransistor.

FIG. 2 is a graph showing experimental data of direct-current optical amplification and gate potential change, and incident light intensity Pi dependence on the SIT gate structure.

FIG. 3 is a graph showing experimental data of direct-current optical amplification and gate potential change, and incident light intensity Pi dependence for a bipolar base structure.

FIG. 4 is a schematic cross-sectional view showing the structure of an optical trigger thyristor having a conventional amplification gate structure.

[Explanation of symbols]

701 p ⁺ anode region 702 first base region of main thyristor 703 second base region of main thyristor 704 n ⁺ cathode region of main thyristor 705 n ⁺ second gate region 711 p ⁺ source region 712 p channel of SIPT n ⁺ gate region 713 p channel SIPT p ⁻ low impurity density channel region 714 p channel SIPT p ⁺ drain region 731 main thyristor p ⁺ anode electrode 732 main thyristor cathode electrode 751 anode terminal 752 cathode terminal 753 gate bias voltage V _Gt 754 Gate resistance R _Gt 755 Source bias voltage _Vst 760 Trigger light pulse LT

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location H01L 31/111

Claims (2)

[Claims] 1. A first conductivity type high impurity concentration anode region (701), and a second region formed on the anode region.
A first base region (702) of a conductivity type and a second base region (7) of a first conductivity type formed on the first base region (7).
03) and a cathode region (704) formed in a part of the upper part of the second base region, and a second base in a part of the upper part of the first base region. A first conductivity type high impurity density drain region (714) formed so as to be connected to at least a part of the region, and a first conductivity type low impurity density channel region (713) formed on the drain region. ), A first conductivity type high impurity density source region (711) formed in a part of the upper part of the channel region, and a second conductivity type formed in the upper part of the channel region so as to sandwich the source region. At least a static induction phototransistor including a high impurity density gate region (712) and an isolation region provided between the second base region and the channel region. Wherein the optical trigger thyristor. 2. An anode region (701) of the first conductivity type and a high impurity density, and a second region formed on the anode region.
A conductive type first base region (702), a second conductive type high impurity density buried region (705) formed inside the first base region, and a first conductive region formed above the first base region. A four-layer main thyristor formed of a second base region of one conductivity type (703) and a cathode region (704) formed in a part of the upper part of the second base region; A first conductivity type high impurity density drain region (714) formed to be connected to at least a part of the second base region, and a first conductivity formed on the drain region. Type low impurity density channel region (713), a first conductivity type high impurity density source region (711) formed in a part of the upper portion of the channel region, and the channel region of the channel region so as to sandwich the source region. Formed on top And a separation region provided between the second base region and the channel region. An optical trigger thyristor characterized in that