Bipolar Junction Transistors HBTs, Circuits, and MOSFETs (Ch. 11: pp. 407 – 432 Ch. 12 443-449)
Professor Mark Lundstrom Electrical and Computer Engineering Purdue University, West Lafayette, IN USA [email protected]
12/10/14 1
BJT doping profiles
FB RB
IEn n+ p n n+ emitter base collector
IEp
++ N D N DE N AB
log10 {N D (N A )} N DC
Lundstrom 12.10.14 2 2 transistor doping
I B I B
n+
n-collector n+ light collector doping increases the breakdown voltage high base doping lowers the base resistance high sub-collector doping lowers the collector series 3 resistance
about the collector doping
FB RB
IEn n+ p n n+ emitter base coll
IEp
+ ρ = qN D
Dn ICn = qAE Δn(0) WB
IC = qAW nυsat n ≈ N D “base push out” Kirk effect 4 emitter-base doping
FB RB n2 I ∝ i I En N En AB n+ p n n+ emitter base collector n2 i I IEp ∝ Ep N DE
1 Emitter must be γ = F N DE >> N AB doped more DpE WB N AB 1+ heavily than the DnB WE N DE base. Lundstrom 12.10.14 5 5
HBT (wide gap emitter)
FB RB
IEn n+ p n n+ emitter base collector
IEp
EGE EGB EGC
n2 iB 1 IEn ∝ γ F = 2 2 −EG kBT N AB ni ∝ e DpE WB N AB niE 1+ 2 2 DnB WE N DE niB niE IEp ∝ N DE
6 Freedom to dope the base heavily 6 “inverted” base doping
FB RB
IEn Wide gap p n n+ emitter base collector
IEp
++ N AB N D
log10 {N D (N A )} N DC N DE
Lundstrom 12.10.14 7 7
SiGe HBTs
Martin Claus
8 TU-Dresden 8 SiGe HBTs
FB RB
Si SiGe Si n+
EG (Si) = 1.12 eV EG (Si) = 1.12 eV
EG (Ge) = 0.66 eV
Lundstrom 12.10.14 9 9
outline
1) HBTs 2) MOSFETs vs. BJTs
Lundstrom 12.10.14 10 transconductance
terminal 1
I12 I12 +δi
black I12 + gmδv V32 +δv V32 box δi control g = m δv
∂I12 A gm ≡ (S) terminal 2 ∂V12 V
Lundstrom 12.10.14 11
transconductance
VGS = 1.2 V
VGS = 1.1V
ΔI D A gm = = S ΔVGS V VDS
gm = 1000 µS µm (1180 −1080) ×10−6 g = = 0.001S µm gm = 1000 mS mm m 0.1 12 Lundstrom 12.10.14 gm = 1000 S m MOSFETs vs. BJTs
MOS (saturated) Bipolar (active)
gm = ∂I D ∂VGS gm = ∂IC ∂VBE VDS VCE
I WC 0 V V qVBE /kBT D = ox υ( ) ( GS − T ) IC = α F IF0e
gm = WCox υ(0) gm = IC (kBT / q)
gm I D = 1 (VGS − VT ) gm IC = 1 (kBT / q)
-1 -1 gm I D = 1 (1.0 − 0.2) ≈ 1.25 V gm IC = 1 (0.026) ≈ 40 V
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MOSFETs vs. BJTs
I D IC
D C I 0 G ≈ I B
G VDS B VCE E V BE VBE siliconS IE
• simple to make • more complex to make • no gate current • base current • moderate gm • large gm • low capacitance • high capacitance 14 course outline
Course objectives: To introduce students to the fundamentals of semiconductors and semiconductor devices.
Part 1: Semiconductor Fundamentals: 5 weeks
Part 2: PN diodes, MS diodes, and devices 5 weeks
Part 3: Transistors 5 weeks
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transistors
"The transistor was probably the most important invention of the 20th Century, and the story behind the invention is one of clashing egos and top secret research.”
- Ira Flatow, Transistorized!
http://www.pbs.org/transistor/
16 the invention of the planar process
“The most important moment since humankind emerged as a life form.”
Isaac Asimov
(speaking about the “planar process” used to manufacture ICs -- invented by Jean Hoerni, Fairchild Semiconductor, 1959). 17 IEEE Spectrum Dec. 2007
modern electronics
CMOS transistors for logic BJTs for RF A/D and D/A convertors Digital Signal processor Microprocessor ROM and FLASH memory
CMOS imager Gyroscope MEMS devices www.apple.com Magnetometer Microphone, speaker LCD display and touch screen MOSFETs vs. BJTs
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