Description

The high-frequency C−V characteristic curve of a MOS capacitor is shown in Figure 1. The area of the device is 2×10−3 cm2. The metal-semiconductor work function difference is ϕms = −0.50 V, the oxide is SiO2, the semiconductor is silicon, and the semiconductor doping concentration is 2 × 1016 cm−3.
(a) Is the semiconductor n or p type?
(b) What is the oxide thickness?
(c) What is the equivalent trapped oxide charge density?(d) Determine the flat-band capacitance.

Figure 1: Figure for Problem 8.1
Exercise 8.2
Consider the high-frequency C − V plot shown in Figure 2.
(a) Indicate which points correspond to flat-band, inversion, accumulation, threshold,and depletion modes.
(b) Sketch the energy-band diagram in the semiconductor for each condition.

Figure 2: Figure for Problem 8.2
Exercise 8.3
A p-channel MOSFET has the following parameters: = 15,
and VT = −0.4 V. Calculate the drain current ID for
(a) VSG = 0.8 V,VSD = 0.25 V;
(b) VSG = 0.8 V,VSD = 1.0 V ;
(c) VSG = 1.2 V,VSD = 1.0 V; (d) VSG = 1.2 V,VSD = 2.0 V.
Exercise 8.4
Consider a p-channel MOSFET with the following parameters: and W/L = 20. The drain current is 100µA with applied voltages of VSG = 0, VBS = 0, and
VSD = 1.0 V.
(a) Determine the VT value.
(b) Determine the drain current ID for VSG = 0.4 V,VSB = 0, and VSD = 1.5 V. (c) What is the value of ID for VSG = 0.6 V,VSB = 0, and VSD = 0.15 V?
Exercise 8.5
One curve of an n-channel MOSFET is characterized by the following parameters:
ID(sat) = 2 × 10−4 A,VDS( sat ) = 4 V, and VT = 0.8 V (a) What is the gate voltage?
(b) What is the value of the conduction parameter?
(c) If VG = 2 V and VDS = 2 V, determine ID.
(d) If VG = 3 V and VDS = 1 V, determine ID.
(e) For each of the conditions given in (c) and (d), sketch the inversion charge density and depletion region through the channel.
Exercise 8.6
An NMOS device has the following parameters: n+poly gate, tox = 400˚A,Na =
1015 cm−3, and cm−2.
(a) Determine VT.
(b) Is it possible to apply a VSB voltage such that VT = 0 ? If so, what is the value of VSB ?
Exercise 8.7
Draw the ID − VSD relationship for a p-type MOSFET at different gate voltages, assuming the source is grounded. Explain why there is the saturation region, and how the saturation point changes with different gate voltages.
Reference
1. Neamen, Donald A. Semiconductor physics and devices: basic principles. McGrawhill, 2003.