note3 - Handout 3 Overview of BJT and MOSFET Devices What...

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Handout 3 ECE 315, Cornell University 1 Overview of BJT and MOSFET Devices What you will learn: • BJT device structure and design • BJT IV and operating regions • BJT large-signal and small-signal models • MOSFET device structure and design • MOSFET IV and operating regions • MOSFET as a large-signal switch and as a small-signal amplifier Handout 3
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Handout 3 ECE 315, Cornell University 2 3.1. The Bipolar Junction Transistor (BJT) • The electrostatics of BJT. • The current components in BJT and the bipolar amplification effects. • The basic BJT design • The viewpoints of current and voltage amplification in BJT IV. (Sedra and Smith, Appendix A and Chapter 5.1 – 5.3)
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Handout 3 ECE 315, Cornell University 3 Bipolar Junction Transistors (BJT) • For a reverse-biased diode, the saturation current is small, not because that there is no field for drift current, but there are very few carriers in the depletion region under reverse bias . • For forward bias, there are quite a few carriers injected into and cross the depletion region, though usually smaller than the doping level. F log (n), log (p)
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Handout 3 ECE 315, Cornell University 4 Bipolar Junction Transistors (BJT) • Can we inject carriers from a forward- bias junction to a reverse- bias junction? (Shockley’s original words!) V D I D Carriers injected to the depletion region of the reverse-biased junction will be swept across. I D will depend only on the number of carriers being injected, instead of V D . IV in active mode F
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Handout 3 ECE 315, Cornell University 5 Two Choices: NPN and PNP Fig. 5.1 NPN Bipolar Junction Transistor Mirror image is fine too. E C B
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Handout 3 ECE 315, Cornell University 6 PNP Bipolar Junction Transistors Fig. 5.2 E B C
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Handout 3 ECE 315, Cornell University 7 Physical Mechanisms Inside PNP in the Active Mode Emitter (p) base (n) Collector (p) EB junction forward-biased BC junction reversed-biased i E i B i C v BE v CB Injected holes Diffusing holes Collected holes Swept holes Injected electrons Recombined holes
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Handout 3 ECE 315, Cornell University 8 Physical Mechanisms Inside NPN in the Active Mode Fig. 5.3 Emitter (n) base (p) Collector (n) EB junction forward-biased BC junction reversed-biased i E i B i C v BE v CB Injected electrons Diffusing electrons Collected electrons Swept electrons Injected holes Recombined electrons
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Handout 3 ECE 315, Cornell University 9 Minority Carrier Concentration Inside NPN in the Active Mode p n not important here due to reverse bias base p emitter n n p 0 0 << Fig. 5.4 Carrier Concentration (cm -3 ) Distance ( μ m) Emitter ( n ) EB depletion region Base ( p ) Collector ( n ) CB depletion region p n (0) n p (0) n p when recombination significant Effective base width W Minority hole concentration p n (x) p n0 Minority electron concentration n p (x) ignoring recombination CB depletion width W CB
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Handout 3 ECE 315, Cornell University 10 Why Focus on Minority, Not Majority?
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note3 - Handout 3 Overview of BJT and MOSFET Devices What...

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