Chapter 27 STATIC-INDUCTION TRANSISTOR

의료영상 연구실나기은

2003.05.31.

HISTORY 1972 : The static-induction transistor(SIT) was introduced by

Nishizawa el al. 1975 : More studies were reported by Ogawa et al. and

Yamaguchi et al. 1952 : Shockley proposed the analog transistor. 1963 : Roosild et al. – Realization of a vertical structure 1964 :

Buchanan et al. – Experimental results Teszner, Gicquel - Other devices include Zuleeg, Hinkle - Multichannel FET

The mid-1980s : The SIT began to be produced in the commercial market.

STRUCTURE All but Fig. 27.1(d) have

vertical current flow. The buried-gate structure

is the scheme proposed originally

The planar-gate structure in Fig. 27.1(b) is probably the mist common today.

The critical parameters The spacing between

gates(2a). The channel doping

level(ND).

STRUCTURE The doping

The depletion regions from the gates do not merge There exists a narrow, neutral channel opening with

zero gate bias. Gaps are a few microns,

with channel doping levels around the range.

The gates are formed by p-n junctions.

The SIT operations can be generalized to include metal gates or MIS gates.

31510 cm

depletion regions

CHARACTERISTICS SIT is a JFET or MESFET

Super-short channel length Multiple channels connected

in parallel

Difference The gates do not extend

close to the source or drain

Punch-through occurs with high drain bias even if the transistor is turned off

The depletion regions around the gates do not pinch off the gap

This condition (27.1)

The built-in potential of the p-n junction

(27.2)

A neutral region between the gates with zero gate bias provides a current path for a depletion-mode device

The current conduction is drift in nature and is similar to an FET

aqND

bis 2

2ln

i

DATbi n

NN

CHARACTERISTICS

CHARACTERISTICS

PbiT VV

s

DP

aqNV2

2

(27.4)

(27.3)

With negative gate bias The depletion regions widen Pinch off the channel Electrons from the source start to see a potential barrier

This begins when the gate voltage is more negative than

The pinch-off voltage VP is given by

CHARACTERISTICS

Negative gate voltage raises the barrier

Positive drain voltage lowers the barrier

The efficiency by which the terminal voltages affect the barrier is indicated by

Db V Gb V (27.5)

(27.6)

CHARACTERISTICS

s

s

WaW

ds

s

WWW

The factors and are geometry dependent

Different for different structures in Fig 27.1

example

(27.7)

(27.8)

The current of an SIT is given by the form

is the doping concentration is the source The term is the carrier diffusion velocity When becomes small giving a current of

The barrier height is given by

kTq

WDqNJ b

G

nD

exp

kTq

mkTqNJ b

D

exp

2

PbiGDPbiGD

DTb VVVVV

NN

,ln

DN

Gn WD /GW

(27.9)

(27.10)

(27.11)

CHARACTERISTICS

Diffusion current is exponential with The current can be put in the form

The I-V characteristics have the form

kT

VVqJJ DG exp0 (27.12)

3

2

89LVJ Dns

2

22LVvJ Dsats

2/32/1

*2

294

Ds Vmq

LJ

(27.13)(27.14)(27.15)

CHARACTERISTICSb

aqND

bis 2

CHARACTERISTICS Another mode of operation is the bipolar-mode SIT(BSIT) The gap is smaller The doping in the channel is lower

The output characteristics of a BSIT

(27.16)

APPLICATIONS Combination of high voltage, high speed

capability

Most applications of the SIT are in the power area.

Low noise, low distortion, and low output impedance

It can be used in high-power oscillators of microwave equipment

SIT 는 높은 파워 , 높은 주파수 , 높은 온도 application 을 위한 short channel FET 구조이다 SI(Static Induction) 소자는 접합게이트에 인가하는 전압에 의해 에미터전류를 제어하는 전압제어형 소자로서 , SI Transistor

는 수 10 ㎒의 고주파 발진기나 증폭기등에 이용되는 고속용소자인 한편 , SI-Thyristor 는 고내압용으로 적합하고 , GTO 보다 고속이며 dv/dt 및 di/dt 내량이 우수하기 때문에 고내압ㆍ고속의 스위치로 인버터 등에 주로 사용되고 있다 .

현재 4 ㎸ /400A 의 역도통 SI 싸이리스터가 사용되고 있지만 4.5 ㎸ /1 ㎄급 용량의 소자의 개발을 목전에 두고 있다 .

이러한 SIT 의 특징을 다음과 같이 요약할 수 있다 .

- 유니폴라 스위치로써 Tail 전류가 작고 , 고속 스위칭동작이 가능하다 .

- 고내압 /대용량의 제품제작이 가능하고 , 전력밀도를 높일 수 있다 .

- 파워 MOSFET 와 비교해서 On 저항이 크고 도통손실도 많지만 , SIT 는 병렬접속이 용이함으로써 , 병렬 합성저항을 저하시킬 수 있어 대전류화가 가능하다 .

- 파워 MOSFET 과 비교해 체널부분의 구조가 단순하므로 전류써지에 강하다 .

- 구동ㆍ보호회로가 복잡해진다 .

SIT 는 이러한 특징에 의해 , 정격이 큰 소자는 주파수가 100 ∼㎑ 400 ㎑대의 대전력 인버터에 사용되며 , 특히 고주파특성을 개선한 소자는 ㎒대의 고주파 인버터에 사용이 가능하다 .