JPH01307264A - Pnpn surge-preventing device - Google Patents

Abstract

PURPOSE:To provide an antisurging device improved characteristics for preventing lighting surge, by specifying resistivity of a P-type semiconductor substrate, diffused surface concentration of base regions, diffused depth and overlapping width between emitter regions. CONSTITUTION:A breaker voltage VBO is generally dependent on a thickness of a semiconductor substrate 1, resistivity rho thereof, a diffusion surface concentration NSB of base regions and diffusion depth XJB. In order to satisfy all the characteristics required for a lightening surge preventing device, device parameters must be designed properly. Thus, resistivity of the P-type semiconductor substrate 1 is specified in a range of 1.0-3.5OMEGAcm, the diffused surface concentration NSB of the base regions 2, 2' is specified in a range of 3X10<17>-7X10<18>cm<-3>, the diffusion depth XjB is specified in a range of 20-50mum and the mutual overlapping width (d) between the emitter regions 3 and 3' is specified in a range of 200-800mum. In this manner, it is possible to obtain a highly reliable surge-preventing device having all the characteristics required for preventing lightening surge.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical field to which the invention pertains) The present invention relates to PNPPN having excellent characteristics in lightning surge protection.
It relates to surge protection devices.

(Prior Art) As is well known, two-terminal bidirectional thyristors have been widely used as power or trigger elements for AC dimmers, instantaneous fluorescent lamp starters, and starting elements for sodium lamps. There is. In addition, in recent years, it has been characterized by high short-term overcurrent capability, and is small and inexpensive.
Moreover, since it has two terminals and is easy to use, it tends to be widely used as a lightning surge protection element. In particular, its performance has begun to draw attention as it is the most suitable of all surge absorption devices for lightning surge protection for telephone exchanges and terminal telephones. By the way, for example, in the case of items such as telephones, which are difficult to maintain because they are distributed in large numbers, there is a need for products that are highly reliable and have few breakdowns, and at the same time, it is necessary to ensure that the telephone circuits are in good working condition by ensuring reliable lightning protection. Severe operating characteristics are required in order not to impede normal operation.

For example, (1) Breakover voltage stable against lightning surge■
Must have an angle of 8°.

(2) Must have a large lightning surge current withstand capacity.

(3) Have a large holding current.

(4) Capacitance must be as small as possible.

The following characteristics are required. However, the structural parameters and the above-mentioned characteristics of current PNPN surge protection devices are in a contradictory relationship with each other. Therefore, satisfying one characteristic deteriorates the other characteristic, so it has been very difficult to obtain a conventional PNPN surge protection device that satisfies all the characteristics. The basic structure of this semiconductor device has already been published in Japanese Patent Publication Nos. 41-15902 and 14254-1973.
However, the quantitative relationship between structural parameters and properties was not clear.

(Object of the Invention) The present invention has been made for the purpose of providing a PNPN lightning surge protection element that can satisfy the severe requirements for lightning surge protection for telephones as described above. The details will be explained below using the drawings.

(Structure of the Invention) (Characteristics of the Invention and Differences between the Prior Art) A cross-sectional structural diagram of a PNPN surge protection device is shown in FIG. P-type semiconductor substrate 1, N-type base region 2.2° formed by diffusion, P-type emitter region 3.3', ohmic region 5.5°, surface inactive film 6, 6', electrode 7.7', etc. A PNPN structure is constructed from .

FIG. 2 shows an equivalent model diagram of FIG. 1. It is a bidirectional device in which two cyrisks 8.9 are arranged in antiparallel, and each gate is short gated by lateral resistors R1, R2, and R3. Next, the operation will be explained.

When a voltage is applied between terminals 7 and 7'' so that the terminal 7 side is positive, junction JR becomes reverse biased and junction Js becomes forward biased.On the other hand, junction J1 becomes forward biased due to the voltage drop across resistor R1. In this state, when the applied voltage is low, a current limited by the reverse characteristic of the junction J2 flows from the electrode 7 and is shunted from the thyristor 9 side to the thyristor 8 side by the resistors R, , R, , R, etc., and the shunt current i4 When the applied voltage that flows into the electrode 7 at the same time exceeds the breakover voltage V, the reverse current increases rapidly,
Along with this, a voltage drop (i+XR+) occurs due to the resistor R1 directly under the emitter region 3 and the shunt current iI, and the junction J becomes forward biased. And this voltage drop is the junction J+
When the diffusion potential of
Holes begin to be injected into.

On the other hand, in the thyristor 8 of Fig. 2, the current amplification factor α of the PNP) run risk formed from 3.2.1 and the NPN) run risk formed from 2.1.2'.

α2 increases with current. When α1+αt==1, the thyristor 8 is turned on. Further, when the polarity of the voltage applied to the electrode 7 is reversed, the thyristor 9 is turned on based on the same principle. FIG. 3 shows the above characteristics. I3 is the current transitioning to the on state, that is, the transition point current, V! is the on-voltage at the on-current tc.

Next, we quantitatively describe the relationship between device parameters and characteristics.

■ Breakover voltage VIO is generally applied to semiconductor substrate 1.
, its specific resistance ρ, and the diffusion surface concentration N5 in the base region.
ll, depends on diffusion depth x mouth. In addition, the current amplification factor α depends on the impurity concentration of each region and its vertical dimension relationship.
, it changes depending on the situation.

FIG. 4 shows N8 in the base area 2,2''. Assuming that X is constant,
■, determined through experiments using the mouth as a parameter. This shows the relationship between and ρ. vlo becomes higher as ρ increases. It also increases as Xj becomes larger. Figure 5 shows V, which is determined by keeping ρ constant and using the X opening of the base area 2.2" as a parameter. The relationship diagram of NSB is shown. As Ns becomes higher from curve A (solid line),

can be seen to be lower.

(2) The holding current (2) depends on the conductivity σ of the base region 2 immediately below the emitter region 3. σ is ■N31+XJI forming base region 2.2', ■emitter.

Ratio between diffusion depth XJt and Xj, xjE/XJ1%■
It depends on the current amplification factor αhα2. Curve B (dotted line) in FIG. 5 shows NsB and 1° using XJI as a parameter. However, X j t/X mouth is kept constant.

It can be seen that as NSB becomes higher, 111 increases.

(2) FIG. 6 shows a cross-sectional structure of a device having an overlapping width d at the mutual positions of the emitter regions 3, 3'.

FIG. 7 shows the relationship between d and IC+ turn-on time ton. However, ρ, N, and □Xj were kept constant.

The optimum value is d between 200 and 700, and thereafter it decreases due to the influence of the reduction in the effective area of the emitter. In this way, d
By selecting , an appropriate l(,,ton) can be obtained.

■ Capacitance C4 is: ■ Area of base region 2,2", ■
is the specific resistance ρ of the semiconductor substrate 1, ■N of the base region 2゜2゛
5Il relationship is shown. C4 increases as N5Il increases, and decreases as ρ increases.

The relationship between device parameters and characteristics has been described above.

Therefore, in order to satisfy each characteristic required of a lightning surge protection device, it is necessary to design device parameters in consideration of the above-mentioned items. Therefore, V2
O 100-220V, lightning surge current withstand capacity Ic>150
^, holding current 1. ≧75mA, capacitance (0 bias)
The device parameters that satisfy the characteristic of Cj≦400PF are as follows from FIGS. 4, 5, 7, and 8.

■ Set the specific resistance range of P-type semiconductor substrate 1 to 1.0 to 3.5.
Ωcm.

■ Diffusion surface concentration N31 of base region 2.2゛ is 3×1
0" to 7 XIO"cm-', diffusion depth Xj8 to 20
-50 .mu.m. The overlapping width d of the mutual positions of the emitter regions 3, 3' is 200 to 800 pr11 (Embodiment) The structure of the embodiment of the present invention shown in FIG. 6 is manufactured as follows.

■P-type silicon substrate 1 with smooth both sides and within the above specific resistance range
A 5iOz film is applied to the surface using the steam oxidation method.

(2) Next, the Sin film is selectively removed by double-sided photolithography to open a window that will become the base region 2,2''.

Then, selective phosphorus deposition was performed using 5iozv as masking to remove phosphorus glass, and then the base area 2.2 to a specified depth was removed.
” to spread the word.

■After that, the base areas 2 and 2 are also
An ohmic region 5,5' is formed within 100°.

■Remove the phosphorus glass on the SiO□ film and remove the emitter area 3.
P-type diffusion layers are simultaneously formed in the 3° and channel stopper regions 4.4'' by selective diffusion.

■After that, a semiconductor inert glass film is baked on the entire surface on both sides of the semiconductor substrate 1, and ■Finally, the outer glass film 6.6" is left by photo-etching and the window of the electrode 7,7" is opened by vapor deposition and photo-etching. By law,
Electrodes 7, 7' are formed.

In addition, ■. The above resistivity range is too wide. Therefore, in practice, select specific resistance values in divisions of about 0.2 Ωctn, and select N, Xj, or Xj within the above range suitable for each ρ.
It is preferable to adjust the angle to obtain the required angle of 1.8 degrees, and to maintain the required conductivity of 1.1 by creating an emitter region that maintains the conductivity constant just below the emitter region 3.3 degrees. Also the 6th
As shown in the figure, P-type channel stopper regions 4, 4''
By providing a brainer structure using semiconductor glass, the PNPN protection device can be made highly reliable.

(Effects of the Invention) As is clear from the above, according to the present invention, a highly reliable PNPN having the characteristics required for lightning surge protection.
Can provide surge protection devices.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional structural diagram of the above-mentioned PNPN surge protection device, FIG. 2 is its equivalent model diagram, FIG. 3 is its V-1 characteristic diagram, and FIGS. 4, 5, and 7. FIG. 8 is a diagram for determining the characteristics of the present invention, and FIG. 6 is a cross-sectional structural diagram showing one embodiment of the present invention. Patent applicant: 1 person other than Nippon Telegraph and Telephone Corporation

Claims (1)

[Claims] In the PNPN surge protection device, the semiconductor substrate is P type, the emitter region thereof is overlapped at the center of the base region, the specific resistance ρ of the P type semiconductor substrate is 1.0 to 3.5 Ωcm, and the base region is diffused. Surface area concentration N_S_B is 3 x 10^1^7 ~ 7 x 10^1^8
cm^-^3, a diffusion depth xgm of 20 to 50 μm, and an overlapping width d of emitter regions of 200 to 800 μm.