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– ID increases ~ linearly with input voltage (VG), because the carrier
concentration in the channel is proportional to (VGVTH)
In order to understand how MOSFET design parameters affect MOSFET
performance, we first need to understand how a MOS capacitor works... EE105, Fall 2013 Lecture 15 – Slide 8 Prof. Ming C. Wu 4 MOS Capacitor §༊ A metaloxidesemiconductor structure can be considered as a
parallelplate capacitor, with the top plate being the positive plate,
the gate insulator being the dielectric, and the ptype
semiconductor substrate being the negative plate. §༊ The negative charges in the semiconductor (for VG > 0) are
comprised of conduction electrons and/or acceptor ions.
§༊ In order to understand how the potential and charge distributions within
the Si depend on VG, we need to be familiar with electrostatics...
EE105, Fall 2013 Lecture 15 – Slide 9 Prof. Ming C. Wu Gauss’s Law ∇⋅E = ρ
ε ρ is the net charge density
ε is the dielectric permittivity à༎ If the magnitude of electric ﬁeld changes, there must be charge! §༊ In a charge free region, the electric ﬁeld must be constant. §༊ Gauss’ Law equivalently says that if there is a net electric ﬁeld leaving a region, there must be posiNve charge in that region: ∫ E ⋅ dS =
EE105, Fall 2013 Q ε Lecture 15 – Slide 10 The integral of the electric field over a
closed surface is proportional to the
charge within the enclosed volume Prof. Ming C. Wu 5 Gauss’s Law in 1 D ∇⋅E = dE ρ
=
dx ε ρ
dx
ε
x
ρ ( x' )
E ( x) = E ( x0 ) + ∫
dx '
ε
x
dE = 0 §༊ Consider a pulse charge distribuNon: ρ ( x)
0 Xd x E ( x) 0 − qNA x Xd Lecture 15 – Slide 11 EE105, Fall 2013 Prof. Ming C. Wu ElectrostaNc PotenNal §༊ The electric ﬁeld (force) is related to the potenNal (energy): dV
E=−
dx ⇒ d 2V ( x)
ρ ( x)
=−
2
dx
ε – N...
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This note was uploaded on 01/22/2014 for the course EE 105 taught by Professor Kingliu during the Fall '07 term at University of California, Berkeley.
 Fall '07
 KingLiu
 Volt

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