lec10_05_10 - MOSFET Operation (VGS < VT) VDS = 0, VGS...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
MOSFET Operation (V GS < V T ) V DS = 0, V GS > 0 but < V T V GS > 0 + charge on gate - charge in substrate Electric field repels holes p leaving ionized acceptor atoms depletion region N φ ε qN ε ρ φ A 2 N A = density of acceptors in p-type substrate q = electron charge ( 1.6 10 -19 C ) S φ qg ( = permittivity of Si ( 1.04 10 -12 F/cm ) Integrating in x direction 2 x ε qN φ 2 d A S S d qN 2 εφ x x d x d = depletion layer depth Q dep = depletion region charge A s A d A dep εφ 2qN x qN Q x MOSFET Operation (V GS V T ) V DS = 0, V GS increasing and V T Depletion region becomes deeper; almost as deep as at under the N+ regions that under the N+ regions Surface is as attractive for electrons as N+ regions Electrons can enter from the N+ regions The induced n-region under the gate is of n-type Surface is inverted and the electron layer is called the inversion layer The inversion layer forms a channel for current flow when V DS > 0 MOSFET Operation (V GS >V T ) V DS = 0, V GS > V T Once surface is inverted lectrons can easily enter electrons can easily enter from the N+ regions All additional gate charge bl db l t i is balanced by electrons in the inversion layer Depletion layer depth and urface potential are fixed surface potential are fixed φ 2 φ 2 φ F S i A th n N ln V inversion) (strong V th = thermal voltage 26 mV @ 300 o K n i = intrinsic carrier conc. (undoped Si) ( 1.5 10 10 cm -3 ) = Fermi level φ F The gate voltage required to produce the inversion layer is called the threshold voltage V T F The Threshold Voltage V T x d = depletion layer depth
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 4

lec10_05_10 - MOSFET Operation (VGS &lt; VT) VDS = 0, VGS...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online