JPH06268236A - Composite static induction type transistor - Google Patents

Abstract

PURPOSE:To provide a normally-on type composite static induction transistor possessed of such various SIT features that drive voltage and drive power are small, a current temperature characteristic is negative, a current can be easily intensified, and the transistor has a current-unsaturated characteristic. CONSTITUTION:A composite static induction type transistor is of multiple series connection (Darlington connection) structure composed of a normally-ON type static induction transistor 9 provided in front and a normally-OFF type static induction transistor 10 provided in rear.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite static induction transistor.

[0002]

2. Description of the Related Art Conventionally, static induction type transistors (Static
As an induction transistor (hereinafter abbreviated as SIT), a normally-on type SIT (normally SIT), a normally-off type SIT (bipolar mode SIT; Bipola)
r Mode SIT; hereinafter abbreviated as B.SIT), and Darlington structure B.SIT.

FIG. 3 is a sectional view of a conventional buried gate structure type SIT, and FIG. 4 is a schematic sectional view of a conventional buried gate structure type SIT with further improved frequency characteristics. Further, FIG. 5 is a schematic cross-sectional view of a similarly improved conventional surface wiring type SIT. 3 to 5, reference numeral 1 is an N ⁺ silicon substrate to be a drain ohmic layer, reference numeral 2 is an N ⁻ drain layer, reference numerals 4 and 4 ′ are P ⁺ gate regions, and reference numeral 5 is N.
The source layer, reference numeral 6 is an N ⁺ source ohmic layer. In any SIT of the gate structure, the electrical characteristics are determined by the channel portion A, and the characteristics are governed by the impurity density Nd of the channel portion A, the width W of the channel portion A, and the length L of the channel portion A. .

6 and 7 are enlarged views of the channel portion A of FIGS. 3 and 4, respectively. In FIG. 6 showing the case of the buried gate structure, the channel length L is usually 5 to 8 μm.
The value of m is taken. The channel width W is 5 when the impurity density Nd of the N ⁻ drain layer 2 is 5 × 10 ¹³ cm ^−3.
It is set to μm or more.

On the other hand, FIG. 7 showing a case of a cut gate structure.
, The channel length L is usually selected to be 1 to 4 μm, and the channel width W is the impurity density N of the N ⁻ drain layer 2.
When d is 5 × 10 ¹³ cm ⁻³ , it is set to 5 μm or more.

In the case of the normal normally-on type SIT as described above, the depletion layer in the channel protrudes from the opposite gate ends when the gate bias V _G is zero, regardless of the gate structure. It is usually formed in a just pinch-off state where the edges of the depletion layer just touch, or in a state where the depletion layer edges overlap slightly. In this case, the drain current I _D flows, and the relationship between the drain current I _D and the drain voltage V _DS becomes as shown in FIG. 8 when the gate bias V _G is used as a parameter.

On the other hand, when the channel width W is further narrowed (or the channel width W is made constant and the impurity density in the channel portion is reduced), the depletion layer between the opposite gates has a gate bias V _G of zero. , SIT is a normally-off type bipolar mode SIT in which drain current does not flow at zero gate bias by making it so that it overlaps greatly.
(B / SIT). Its current is shown in Figure 9 I _D - voltage V _DS
Show the characteristics. FIG. 10 shows symbol diagrams of SIT and B.SIT.

[0008]

The points to be noted in the I _D -V _DS characteristics of the SIT characteristic of FIG. 8 and the B.SIT characteristic of FIG. 9 are that the former is the current unsaturated characteristic and the latter is the current saturated characteristic. In addition to showing the characteristics, the latter has a smaller value of the internal resistance R _D (or R _on ) than the former by one digit or more.

The characteristics of SIT are that it is a voltage drive type device, so the drive power is small, and since injection of carriers to the gate for turning it on is unnecessary, there is no storage time in switching operation, and high speed operation is possible. However, there is a drawback that R _D is large.

[0010] B · SIT Features include, but is that R _D is small, a limit to the long switching speed storage time for injecting the driving power is large because it requires the carrier to the gate to turn on the There is also a drawback that there is a limit to the improvement of the current amplification factor h _fs . There is a B · SIT Darlington structure shown in FIG. 11 as an improvement over the drive power and h _fs of the B · SIT.
FIG. 12 shows the current _ID -voltage _VDS characteristic. B. shown in FIGS. The SIT Darlington structure requires a small driving power and a large h _fs, but
There is a drawback that R _D becomes large because a voltage of about 0.6 V is required for the drain current to rise.
This is because there are two pn junctions in series that require carrier injection to drive the Darlington structure B / SIT.

Therefore, the technical problem of the present invention is to provide the characteristics of various conventional SITs such as voltage driving, small driving power, negative temperature characteristic of current, easy large current, and current unsaturated characteristic. An object is to provide a normally-on type composite static induction transistor capable of saving energy.

[0012]

In order to eliminate the drawbacks of the above device, the composite static induction transistor of the present invention has a normally-on type SIT in the front stage and a normally-off type B.SIT in the rear stage, which are connected in series. It features a Darlington structure.

[0013]

In the present invention, the current unsaturation characteristic similar to that of the conventional SIT is exhibited, and the driving power is the same as that of the conventional SI because it is voltage driven.
T is about the same, R _D is about the same as that of the B / SIT Darlington structure, and the switching speed is faster than that of the B / SIT Darlington structure.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing the structure of a composite static induction transistor according to an embodiment of the present invention. Reference numeral 9 is a normally-on type SIT, reference numeral 10 is a normally-off type B / S
The IT is a normally-on type SIT in the front stage, and a normally-off type B / SIT in the rear stage, which is connected in a Darlington connection. The current unsaturated characteristic, voltage drive, and drive power are small.
It has an advantage that a large current can be easily obtained. With the configuration of this embodiment, it is possible to realize this structure by connecting a normally-on type SIT and a normally-off type B / SIT alone externally, or to build this structure on one chip.

FIG. 2 is a diagram showing the I _D -V _DS characteristics of the composite static induction transistor having the structure of FIG. Figure 2
It is apparent that the characteristic of 1 has both the characteristics of FIG. 8 and FIG.

Since the former stage is a normally-on type SIT,
When the gate voltage V _G1 is zero V, I _D1 (= I _S1 ) flows, and this becomes the gate current I _{G2 of the} latter-stage normally-off type B / SIT, the B / SIT turns on, and the main drain current I _D2 flows, and the composite type The static induction transistor turns on. V _G1
If a negative voltage is applied to, I _D1 becomes difficult to flow, that is, I _G2 becomes difficult to flow, and I _D2 eventually _stops flowing. In other words, the composite static induction transistor is a voltage drive type current unsaturated type device. Since it is a voltage-driven type, the driving power is similar to that of the conventional SIT, and the main drain current flows through the conventional B / SIT in the latter stage, so the resistance value is similar to R _{D of} the conventional Darlington structure B / SIT, and the large current Can be converted. The present structure and characteristics can be realized regardless of whether the gate structure is a buried gate structure, a cut gate structure, or a surface wiring structure SIT.

By the way, at present, there is an increasing need for protection of the natural environment and energy saving on a global scale, and as a part of this, there is an increasing need for electric vehicles and electric vehicles that do not emit exhaust gas. Since energy saving is also required, it is required to reduce the drive power of these automobiles, that is, to reduce the loss of the switching device of the drive system. Therefore, the composite static induction transistor according to the embodiment of the present invention is used in the energy saving field because it has a current unsaturated characteristic, has a small driving power, and has a large current and a low R _D as compared with the conventional SIT, and thus has a small loss. It is a possible device.

[0019]

As described above, according to the present invention, the normally-on type has current unsaturation characteristics, the driving power is small by voltage driving, the large current can be easily achieved, and the temperature characteristic of the current is negative. As compared with the conventional SIT, the loss is small because of the large current and low R _D , so that it is possible to provide the composite static induction transistor which can save energy.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a composite static induction transistor according to an embodiment of the present invention.

[2] a diagram showing a transistor I _D -V _DS characteristics of FIG. 1, (a) a small current, high-voltage region, shows respectively the (b) high current low voltage region.

FIG. 3 is a view showing a buried gate structure of a conventional SIT.

FIG. 4 is a view showing a cut gate structure of a conventional SIT.

FIG. 5 is a diagram showing a surface wiring gate structure of a conventional SIT.

6 is an enlarged view of the vicinity of the channel of FIG.

FIG. 7 is an enlarged view of the vicinity of the channel of FIG.

FIG. 8 is a diagram showing current-voltage characteristics of a conventional normally-on type SIT, in which (a) shows a small current high voltage region and (b) shows a large current low voltage region.

9A and 9B are diagrams showing current / voltage characteristics of a conventional normally-off type B / SIT, in which FIG. 9A shows a small current high voltage region, and FIG. 9B shows a large current low voltage region.

FIG. 10: Normally-on type SIT and normally-off type B
-SIT symbol diagram.

FIG. 11 is a diagram showing a configuration of a normally-off type B / SIT Darlington connection.

12 is a diagram showing I _D -V _DS characteristics of the Darlington connection of FIG. 11.

[Explanation of symbols]

1 N ⁺ Silicon Substrate (N ⁺ Drain Ohmic Layer) 2 N ⁻ Drain Layer 4, 4 ′ P ⁺ Gate Layer 5 N Source Layer 6 N ⁺ Source Ohmic Layer 7, 8, 10 Normally Off Type B / SIT 9 Normally On Type SIT

Claims (2)

[Claims] 1. A composite static induction transistor comprising a normally-on static induction transistor in the front stage and a normally-off static induction transistor in the rear stage in a multistage series connection (Darlington connection) structure. 2. The composite static induction transistor according to claim 1, wherein each of the static induction transistors is formed on the same chip.