Electrical and Computer Engineering Undergraduate Laboratory
ECE 494 - Electrical Engineering Laboratory III

Part B - Semiconductor Devices
Experiment Series 5 – MOSFET

MOSFET – Pre-Laboratory Assignment

  1. For an n-channel MOSFET sketch ID (VDS) curves for three different gate voltages. Identify different regions of the transistor operation.
    What is the relation between VDS and VGS for the transistor to operate in the saturation region?
  2. For an n-channel or a p-channel MOSFET plot (ID)1/2 versus VGS for a value of VDS such that the transistor operates in saturation. Identify the threshold voltage VTh on the graph and comment on the meaning of the slope of plot.
  3. For this series of experiments (see below) design measurements with Agilent U2722A source measure unit: show schematics of the transistors with connections to voltage or current sources, show the sources polarity, and indicate which source output will be varied (stepped).

Reference: Jasprit Singh Semiconductor Devices, John Wiley & Sons 2001. pp. 393 - 415.

MOSFET – Experiments

  1. Measure the MOSFET output characteristics: IDS=f(VDS) for four different values of VGS > VTh. Plot the family of the I-V curves on the same graph. Identify the linear (ohmic) and saturation regions on the graph. Make the measurements for both n-type and p-type transistors.
  2. Measure IDS=f(VGS) in the saturation region for VDS ≥ VG. Note that this condition will be satisfied with the transistor in the "diode connection" (VD = VG), which will simplify measurements with Agilent U2722A source measure unit. The goal is to determine the threshold voltage VTh from the plot (IDS )1/2 vs. VGS determine of the and the factor Make the measurements for both n-type and p-type transistors.

Report and Analysis

Present clearly all graphs and include all relevant parameters. Derive the values of VTh from appropriate trend lines as well as the value of Eq for both types of transistors. Bases on these values, plot the transistor transconductance, gm, as a function of VGS. If you measured a complementary pair of trnsistors (such as in a CMOS ship), comment on the symmetry of their characteristics and the values of VTh.
Do you see the effect of the channel length modulation in the data of part 1?