5.0.3 Summary to: Required Reading to Chapter 5

	Essentials of the bipolar transistor:
		High emitter doping (NDon for npn transistor here) in comparison to base doping NAc for large current amplification factor g = IC/IB.
		NDon/NAc » k = injection ratio.
		g   »   NDon NAc   ·   æ ç è   1  –  dbase L ö ÷ ø
		Small base width dbase (relative to diffusion length L) for large current amplification.
		Not as easy to make as the band-diagram suggests!
	Essentials of the MOS transistor:			Band diagram for inversion
		Gate voltage enables Source-Drain current
		Essential process. Inversion of majority carrier type in channel below gate by: Drive intrinsic majority carriers into bulk by gate voltage with same sign as majority carriers. Reduced majority concentration nmaj below gate increases minority carrier concentration nmin via mass action law
		nmaj · nmin  =  ni2
		An inversion channel with nmin > nmaj develops below the gate as soon as threshold voltage UTh is reached. Current now can flow because the reversely biased pn-junction between either source or drain and the region below the gate has disappeared.
	The decisive material is the gate dielectric (usually SiO2). Basic requirement is:
		High capacity CG of the gate electrode - gate dielectric - Si capacitor = high charge QG on electrodes = strong band bending = low threshold voltages UG		QG  =  CG · UG
		It follows: Gate dielectric thickness dDi Þ High breakdown field strength UBd Large dielectric constant er No interface states. Good adhesion, easy to make / deposit, easy to structure, small leakage currents, ...		Example: U = 5 V, dDi = 5 nm  Þ  E = U/dDi = 107 V/cm !! er(SiO2)  =  3.9

© H. Föll (Electronic Materials - Script)