ECEN 2060 Electronic and Semiconductor Device Laboratory
Fall 2021
Lab 10: Field Effect Transistors I
Written lab report due to Canvas on Monday, 11/8/21, at 11:59 pm
Description
In this lab you will learn concepts about field effect transistors (FETs) commonly used in circuits
for signal gating and amplification and as the basis for Boolean logic gates used in integrated
circuits. Here you will probe the different regimes of operation of an N-Channel MOSFET (active,
cutoff, and saturation) and characterize its IV characteristics for appropriate combinations of
drain, source, and gate terminals. You will then build a simple switching circuit to drive an LED,
as you did in the previous lab on BJTs.
Background reading
- Sparkfun transistor tutorial [1]
-
Various MOSFET tutorials found online [2, 3, 4]
-
Chapter 5 / MOS Field Effect Transistors of Neudeck and Pierret Modular Series on Solid
State Devices, Volume IV Field Effect Devices, Addison-Wesley (1983).
-
IRF510 N-Channel MOSFET datasheet [5]
Equipment and materials list
- From your ADALP2000 Analog Parts kit:
o IRF510 N-Channel MOSFET
- Breadboard and assorted cables and connectors
- Standard benchtop equipment: Keysight DSOX404A Oscilloscope, 33400B WaveForm
Generator, E36313A Triple Output Programmable DC Power Supply, and U3401A Digital
Multimeter. Some minor variations in model numbers may exist at different benches
around the lab.
- Keysight U2722A SMU (supplied by the instructors via sign-out sheet)
References
[1] https://learn.sparkfun.com/tutorials/transistors/
[2] https://www.electronics-tutorials.ws/transistor/tran_6.html
[3] http://www.learningaboutelectronics.com/MOSFETs/
[4] https://www.instructables.com/id/Transistor-Basics-MOSFETs/
[5] https://www.mouser.com/datasheet/2/427/sihf510-1768607.pdf
1
Concept 0: Fundamentals (5 points)
1. MOSFETs explained (Short answer essay). Based on the background reading in
Neudeck and Pierret Volume IV, Chapter 5, answer the following questions in your
own words using a few sentences and/or images for each.
Problem 5.1 in Chapter 5 / MOS Field Effect Transistors of Neudeck and Pierret. (1/2
point each)
(a) Precisely what is the “channel” in MOSFET terminology?
(b) Define “threshold voltage.”
(c) Sketch an outline of the inversion layer and depletion region inside a MOSFET
biased at the pinch-off point.
(d) Why does the VG = constant drain current in short channel devices increase
somewhat with increasing VD > VDsat?
(e) Why is the mobility in the surface channel of a MOSFET different from the carrier
mobility in the semiconductor bulk?
(f) Explain what is meant by the term "depletion mode" transistor.
(g) What is the difference between the "field-oxide" and the "gate-oxide"?
(h) Precisely what is the “body effect”?
(i) What is the mathematical definition of the drain conductance? the
transconductance?
(j) Why is the observed MOSFET CG – VG (VD = 0) curve typically a low-frequency
characteristic even at a measurement frequency of 1 MHz?
2
Concept 1: Demonstrate the regimes of operation of a MOSFET. (12 points)
Objective
Demonstrate the saturation, cutoff, active, and reverse active modes of operation for a Nchannel MOSFET.
Methods
a. Using two channels on the U2722A SMU, bias the devices in the appropriate
regimes of relative values of VB, VC, and VE (the specific values are up to you) and
record the collector currents for each.
b. Make a diagram similar to that below, but show the specific voltage values and
indicate the resulting currents you measure. Display the plot as a “heat map”, with
the value of the current showed in color. Take extra data points near the boundaries
between the regime to explore these regions. (That can be done easily in Excel*).
*https://www.excel-easy.com/examples/heat-map.html
Concept question(s)
How sensitive is the response of the device in the vicinity of the boundaries between
modes of operation?
3
Concept 2: Demonstrating the forward active mode of a MOSFET. (13 points)
Objective
Duplicate the series of curves that is typical for the forward active mode of a MOSFET,
which demonstrate the transition from ohmic to saturation regimes as ID is measured
versus VDS curves for different values of VGS
Methods
a. Reproduce a similar figure to that below for your N-channel MOSFET device (the
exact voltage and current values will differ).
https://www.electronics-tutorials.ws/transistor/tran_6.html
b. Fit your results to the square-law theory, given by equation 5.17 in Neudeck and
Pierret Volume IV.
Note: The test configuration is similar to what you did in the BJT lab:
However, you will need to choose the range of VGS values carefully, to exceed the
threshold voltage VGS(th) (see the datasheet) but remain below the current limit of the
SMU (120 mA), in order to see the desired trends in the curves.
Concept question(s)
Did the MOSFET behave as expected? If there were deviations, what could be the
explanations?
4
Concept 3: Switching a device on and off with a MOSFET. (10 points)
Objective
With the N-Channel MOSFET, make a simple switching circuit and demonstrate that it
can turn an LED on and off.
Methods
a. Duplicate the circuit shown in the image below.
b. Record the current through the LED in the on and off conditions of the MOSFET,
along with the applied voltages.
c. With the circuit turned on, verify that Kirchoff’s law is satisfied for the currents
through the MOSFET.
d. With the circuit turned on, determine how much power is being consumed in the
control line of your circuit.
e. Demonstrate that a pulsed signal can be used to turn the LED on and off with the
circuit. Capture the LED current on the oscilloscope and verify that it is
coincident with the input waveform.
f. Explore how fast a frequency you can drive the LED with this circuit.
https://www.electronics-tutorials.ws/transistor/tran_7.html
*Note, the “Flywheel Diode” aka “Flyback Diode” is good practice but is not critical to
the operation. For more information, see
https://en.wikipedia.org/wiki/Flyback_diode
https://www.electronicshub.org/flyback-diode-or-freewheeling-diode/
Concept question(s)
Did the MOSFET and circuit behave as expected? If there were deviations, what could
be the explanations? How fast were you able to drive the circuit, and what do you think
limited the speed?
5
Concept X1: Amplifying a signal with an N-channel MOSFET (5 points extra credit)
Objective
Amplify a waveform signal with an N-channel MOSFET.
Methods
a. Construct the circuit as show below. The choice of resistance values, input
voltages, etc. is up to you, noting that VG will need to exceed the gate threshold
voltage).
https://www.electronics-tutorials.ws/transistor/tran_6.html
b. Apply an input waveform of any shape you like (it doesn’t have to be a sine
wave as shown) and measure the output on the oscilloscope. Determine the gain
of the circuit.
Concept question(s)
How large can the gain be made? How does the input frequency influence the behavior
of the circuit?
6
Concept X2: Constructing Boolean logic gates with MOSFETs (6 points extra credit)
Objective
Construct prototypcal Boolean logic gates (NAND and NOR) from circuits with multiple
MOSFETs.
Methods
a. Construct the NAND and NOR circuits as shown below
https://www.ece.jhu.edu/~andreou/216/Archives/2014/Handouts/POP_Ch3-4.pdf
b. Apply appropriate voltages and measure the output of the circuits in order to
generate a truth table of the results for each circuit.
Concept question(s)
How accurate are your logic gates? In what modes of operation are the MOSFETs during
the operation of the circuit (considering the three cases of inputs: 00, 01, and 11).
7