8. 바이폴라 트랜지스터 (Bipolar Transistor) 1

Bipolar Junction Transistors (BJTs) Over the past 3 decades, the higher layout density and low-power advantage of CMOS technology has eroded away the BJT’s dominance in integrated-circuit products. (higher circuit density  better system performance) BJTs are still preferred in some digital-circuit and analog-circuit applications because of their high speed and superior gain. faster circuit speed larger power dissipation  limits integration level to ~104 circuits/chip

8-1. BJT 소자 공정 그림 8.1 BJT 소자공정 3

8-2. 동작원리 용어정리 회로심볼 4

Common-emitter output characteristics Modes of Operation Common-emitter output characteristics (IC vs. VCE) Mode Emitter Junction Collector Junction CUTOFF reverse bias Forward ACTIVE forward bias reverse bias* Reverse ACTIVE SATURATION EE130 Lecture 23, Slide 5 *or not strongly forward biased

PNP BJT Operation (Qualitative) “Active Bias”: VEB > 0 (forward bias), VCB < 0 (reverse bias) ICn “Emitter” “Collector” “Base” ICp

BJT Performance Parameters (PNP) Emitter Efficiency: Decrease (5) relative to (1+2) to increase efficiency Base Transport Factor: Decrease (1) relative to (2) to increase transport factor Common-Base d.c. Current Gain: EE130 Lecture 23, Slide 7

Collector Current (PNP) The collector current is comprised of Holes injected from emitter, which do not recombine in the base  (2) Reverse saturation current of collector junction  (3) where ICB0 is the collector current which flows when IE = 0 Common-Emitter d.c. Current Gain: EE130 Lecture 23, Slide 8

Performance parameters: Emitter efficiency Base transport factor Common base d.c. current gain Common emitter d.c. current gain EE130 Lecture 23, Slide 9

BJT Design Important features of a good transistor: Injected minority carriers do not recombine in the neutral base region Emitter current is comprised almost entirely of carriers injected into the base (rather than carriers injected into the emitter

그림 8.4 Common Base pnp BJT 특성 8-3. I-V 특성 이론(이상적인)으로 구한 I-V특성 그림 8.4 Common Base pnp BJT 특성 11

Measurement I-V

8-3. 이론과 측정의 오차 Base width modulation Geometrical effect 13

8-3. Figure merit 그림 8.5 그림 8.6 14

Summary: BJT Performance Requirements High gain (bdc >> 1) One-sided emitter junction, so emitter efficiency g  1 Emitter doped much more heavily than base (NE >> NB) Narrow base, so base transport factor aT  1 Quasi-neutral base width << minority-carrier diffusion length (W << LB) IC determined only by IB (IC  function of VCE,VCB) One-sided collector junction, so quasi-neutral base width W does not change drastically with changes in VCE (VCB) Based doped more heavily than collector (NB > NC) (W = WB – xnEB – xnCB for PNP BJT)

8-5. 등가회로 그림 8.11 BJT 전류모델 16