Problem 1. Consider the low frequency Clf/Cox versus CG curve in figure 1. It is for a MOS capacitor with a p-type substrate (NA = NA1), a metal gate and VFB = 0. Draw the Cif/CCox versus VG curve for the device if the metal gate is replaced with a p-type poly-Si gate doped to NA = NA1. Explain your answer.
Figure 1. lf CV characteristics of a MOS capacitor
Problem 2. The subthreshold ID-VG curves of a MOSFET are shown in Figure 2 before and after stressing the device. Determine the interface trap density change DDit (in cm-2eV-1) induced by the stress. T = 300K, eox = 3.9, tox = 10 nm. (Read off the relevant values from the semi-log plot below)
Figure 2. Transfer characteristics of a MOSFET before and after stress
You may find the following useful: ΔDit = Cox/2.3kT (1/slope before -1/slope after)
3. Why do the low frequency and high frequency CV curves differ in inversion?
4. Using the transfer characteristics shown in Figure 3 (VD = 2V; W/L = 10:1).
Calculate the following:
a. The threshold voltage
b. The field effect mobility
Figure 3. Transfer characteristics of a TFT