EL ENG 130 Study Guide - Midterm Guide: Gate Oxide, Polycrystalline Silicon, Mosfet
Document Summary
Professor c. hu: consider a pmosfet with a p+ poly-silicon gate and a n-type body. Ee 130, midterm #2, spring 2000, solutions (c) calculate the flat band voltage. (7 pts) Vfb = eg/2 + delta = eg/2+k*t/q * ln(nsub/ni) = 0. 55+0. 026*ln(2. 0*10^17/(1. 0*10^10)) = 0. 55. +0. 44 = 0. 99v (d) calculate the threshold voltage. (7 pts) Phib = k*t/q * ln(nsub/n1) = 0. 44 (= delta in (d) ) Cox = epsilonox/tox = 3. 9*8. 85*10^-14/10^-6 = 3. 45*10^-7 (f/cm^2) Vt = 0. 99-2*0. 44-2. 41*10^-7)/(3. 45*10^7) = -0. 59v (e) a sheet of electrons (6. 9*10^-8c/cm^2) is trapped at the center of the gate oxide. How much is the threshold voltage changed? (7 pts) Delta vt = -q/coxe = -q/(epsilonox/(tox/2)) = -q/(2*cox) = -(-6. 9*10^-8)/(2*3. 45*10^-7) = Problem #2 file:///c|/documents%20and%20settings/jason%20raft20-%20spring%202000%20-%20hu%20-%20midterm%202. htm (2 of 6)1/27/2007 4:21:49 pm. Qualitatively sketch the c-v, id-vg, and id-vd curves for an nmosfet to indicate how the curves would differ in response to the changes given below. Source and body are tied to ground (0v).
