Laboratory Exercise Manual in
TFFY 34 Semiconductor Technology
SEMICONDUCTOR TECHNOLOGY
Device Measurements
Laboratory Exercise Manualin
TFFY 34 Semiconductor Technology
Page 1(9) -- Device Measurement
Preparatory Exercises
for
Device Measurements
• Why is a diode conducting when it is forward biased but not when it is reverse biased?
• Which are the two main mechanisms that cause breakdown in a diode? Describe them:
• Why is the collector current IC increasing when you increase the base current IB in a
bipolar transistor? Explain the physics behind it:
• Why is a MOSFET a voltage controlled transistor?
Laboratory Exercise Manualin
TFFY 34 Semiconductor Technology
Sept. 11, 2013
Page 2(9) -- Device Measurement
Laboratory Exercise 1
Device Measurements
Location: see webside
1.1. Purpose of this Exercise
During this laboratory exercise the I-V characteristics for some of the most common semiconductor devices will be measured and analyzed. The goal of this exercise is to give you a better
understanding of the devices and the formulae that you have encountered during the lectures.
During this exercise you will learn how to use the “curve tracer” which can be a very useful
instrument in measuring different devices.
You probably already know some of the devices that you will be measuring: diodes,
bipolar transistors, JFET and MOSFET. In order to be well prepared for this exercise we suggest
that you browse through the corresponding chapters in the main textbook.
1.2. The Curve Tracer
The curve tracer can be used for characterizing a two- or three-terminal semiconductor device,
for checking a certain device that has been fabricated, for comparison with another device or for
analyzing errors. It shows the current through the device as a function of the applied voltage
I=f(V) and is suitable to determine the I-V characteristics of semiconductor devices.
For a transistor characterization the curve tracer HM6042 used in this laboratory exercise, displays a set of five curves at a time. In a bipolar transistor test, the measurement is performed using the common-emitter circuit. The collector current is measured as a function of the
collector-emitter voltage IC=f(VC) for the different base currents. Investigating a MOSFET, the
drain current dependence on the drain-source voltage ID=f(VD) is measured for the five different
gate voltage values. To evaluate a selected point on a curve (defined by the cursor point), the
corresponding voltage and current is displayed on a LCD (Liquid Crystal Display). Together
with the voltages and currents, the following transistor parameters can be displayed by the curve
tracer: β-current gain, the hybrid h-parameters and admittance parameters.
NOTE: Voltages up to 50V DC can be present at the DUT (Device Under Test) terminals. So keep your fingers away from the terminals during the measurement!
1.3. Resistor Measurement
Your first assignment is to investigate the I-V characteristics of a common resistor.
Connect the given resistor between the E/S and C/D terminals. Set the switch DUT 1/
DUT 2 to the corresponding position where the resistor is connected. Set the BIP/FET switch
Laboratory Exercise Manualin
TFFY 34 Semiconductor Technology
Sept. 11, 2013
Page 3(9) -- Device Measurement
to the FET position (locked switch). To limit the maximal test current Imax, voltage Vmax and
power Pmax, set them to the minimal values. Press the DUT switch to start the measurement and
adjust Imax, Vmax and Pmax settings to get the desired I-V characteristic. To read the voltage or
current values on the LCD, select VD or ID with the push buttons ← →. The screen cursor (high▲
▲
lighted dot) indicates the point where the voltage or current is measured. To move the cursor,
select
with the FUNCTION button and turn the rotary knob.
• Calculate the resistance from the measured I-V characteristic.
1.4. The Diode
Start by studying the I-V characteristics of the different diodes that you can find in the laboratory
room. Connect each diode between E/S and C/D terminals and use FET position of the switch
as you did for the resistance measurement. Choose forward or reverse bias, using the NPN/PNP
switch, and study the corresponding I-V characteristics.
For each diode, write down answers to the following questions: What kind of diode is
it, what is the knee voltage Vknee and what material is the diode made of (Si or Ge)? Note that
the knee voltage Vknee is defined as the forward voltage over the diode when the current flowing
through it is 1 mA.
• Fill in the table and find out which of the diodes is a Zener diode.
Diode
Vknee [V]
Material
• What are the differences between the I-V characteristics of the Si diode and the Ge diode? Explain why:
The I-V characteristics of diodes are strongly dependent on the temperature. Measure the knee
Laboratory Exercise Manualin
TFFY 34 Semiconductor Technology
Sept. 11, 2013
Page 4(9) -- Device Measurement
voltage and breakdown voltage of Zener diodes at room temperature (T=25°C). Place the Zener
diodes in liquid nitrogen to measure the knee voltage and breakdown voltage dependence on the
temperature.
LIQUID N2 HAS A TEMPERATURE OF ABOUT -200°C.
BEWARE!
• Fill in the table.
Zener diode
Vknee [V]
(T=25°C)
Vknee [V]
(T=-200°C)
VBR [V]
(T=25°C)
VBR [V]
(T=-200°C)
• Explain the temperature dependence of the knee and breakdown voltages of the Zener
diodes:
• Connect the LED and check what happens if we cool it down. Explain why:
1.5. Transistor Identification
Analyzing an unknown device, you always start by measuring two connections in order to try
to find out what kind of device you are measuring and the function of the two connections. Now
you shall analyze the devices that you have in the laboratory room.
• Try to find out what devices are there in the lab (bipolar transistors, JFET or MOSFET). Write down the transistor serial number, type and polarity (Ex.: BDX34C, Bi-
Laboratory Exercise Manualin
TFFY 34 Semiconductor Technology
Sept. 11, 2013
Page 5(9) -- Device Measurement
polar, PNP.):
Transistor
Type
Polarity
• Are the collector and the emitter interchangeable in a bipolar transistor or is there a
difference between them? Motivate your answer.
• Are the source and the drain interchangeable in a JFET or a MOS transistor or is there
a difference between them? Motivate your answer.
1.6. The Bipolar Transistor
For a bipolar transistor the I-V characteristics can be measured for different base currents. Connect the emitter to the E/S, base to the B/G and collector to the C/D terminals. Check if the BIP/
NPN switch is set to the BIP position, you should notice it on the LCD. Select the appropriate
position of the NPN/PNP switch. Set the maximum current Imax, maximum voltage Vmax and
maximum power Pmax to the lowest values. Press the DUT switch. You must get five curves of
the collector current as a function of the collector-emitter voltage IC=f(VC) for the different base
currents IB. Set the suitable ranges for the maximum current Imax, maximum voltage Vmax and
Laboratory Exercise Manualin
TFFY 34 Semiconductor Technology
Sept. 11, 201
Page 6(9) -- Device Measurement
maximum power Pmax. To change the base current of the top curve, select MAX with the
FUNCTION button and turn the rotary knob. The base current of the bottom curve can be adjusted by selecting MIN and turning the rotary knob. Use the CURSOR key to move the cursor
from one curve to the next. You can measure the voltage and current on the base and collector
terminals (VB, IB, VC, IC) or evaluate the current gain β. The hybrid h-parameters and admittance parameters are not so important in this lab, so we don’t address these now.
Choose one of the parameters to be displayed on the LCD with the push buttons ← →.
• The bipolar transistor has a saturation region and an active region. Sketch the I-V
characteristics and show where these regions are located:
• Calculate the common-emitter current gain at VC=2VB for the top curve:
• Cool down the transistor by using liquid nitrogen. What happens and why? Is it still
functioning?
Laboratory Exercise Manualin
TFFY 34 Semiconductor Technology
Sept. 11, 2013
Page 7(9) -- Device Measurement
1.7. Field Effect Transistors
To investigate the I-V characteristics of a field effect transistor (FET), connect its source to the
E/S, gate to the B/G and drain to the C/D terminals. Set the BIP/FET switch to the FET position.
Choose the type of the FET channel with the NPN/PNP switch. The channel type will be displayed on the LCD. Check so that Imax, Vmax and Pmax are switched to the lowest levels. Press
the DUT switch and adjust the Imax, Vmax and Pmax to reasonable ranges. You must get five
curves with the drain current as a function of the drain voltage ID=f(VD) for the five different
gate voltages VG. The gate voltage of the top curve can be adjusted with FUNCTION set to
MAX and turning the rotary knob. To adjust the vertical position of the bottom curve, press
FUNCTION and select MIN, turn the rotary knob. Select the FET parameters to be displayed
on the LCD by the two push buttons ← →.
• The MOSFET is said to have a linear region and a saturation region. Sketch the I-V
characteristics and show where these regions are located:
• Calculate the threshold voltage VT and the transconductance gm at VD=2(VG-VT):
• In the saturation region of a FET the drain current ID is said to be proportional to (VG
Laboratory Exercise Manualin
TFFY 34 Semiconductor Technology
Sept. 11, 2013
Page 8(9) -- Device Measurement
- VT)2. Check this dependence at VDsat=VG-VT and fill in the table.
• Cool the MOSFET in nitrogen. What happens? What are the differences compared to
the bipolar transistor?
•
Laboratory Exercise Manualin
TFFY 34 Semiconductor Technology
Sept. 11, 2013
Page 9(9) -- Device Measuremen
date and signature of the student
signature of the lab assistant