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Thermistor Evaluation Using the
Agilent B2900A Series of SMUs
Technical Overview
Agilent B2901/02/11/12A Precision Source/Measure Unit
Agilent B2901A Precision SMU, 1ch, 100 fA resolution, 210 V, 3 A DC/10.5 A pulse
Agilent B2902A Precision SMU, 2ch, 100 fA resolution, 210 V, 3 A DC/10.5 A pulse
Agilent B2911A Precision SMU, 1ch, 10 fA resolution, 210 V, 3 A DC/10.5 A pulse
Introduction Agilent B2912A Precision SMU. 2ch, 10 fA resolution, 210 V, 3 A DC/10.5 A pulse
The thermistor is a resistor with
resistivity that varies as a function
of temperature. Typical thermistor
applications are thermal sensing
and electric circuitry protection.
However, the thermistor's sensitivity
to temperature changes can work
against measurement accuracy since
Joule self-heating during measure-
ment can alter device characteristics.
This means that accurate thermistor
characterization requires both precise
low-current resistance measurement
capability and pulsed bias measure-
ment capability (to minimize tempera-
ture change during measurement).
The Agilent B2901/02/11/12A
Precision Source/Measure Unit is a
compact and cost-effective bench-
top Source/Measure Unit (SMU)
with the capability to output and
measure both voltage and current.
The B2900A Series of SMUs also
supports a resistance measurement
function that facilitates both low and
Figure 1. Using the B2900A Series of SMUs to characterize a thermistor
high resistance measurements. The
B2900A Series of SMUs enables you
to make a wide range of resistance that make it easy for you to begin Figure 1 illustrates the connections
measurements more accurately and making productive measurements necessary for measuring a thermistor
quickly than ever before. immediately. using a member of the B2900A Series
of SMUs. The B2900A Series of SMUs
In addition, the B2900A Series These features make the B2900A allows you to accurately and easily
of SMUs comes with an intuitive Series of SMUs the best solution measure the resistance of thermistor.
graphical user interface (GUI) and for accurate characterization of
free PC-based application software thermistor and other devices.
B2901/02/11/12A B2901/02/11/12A
RLead
High force IMeas High force IMeas
RLead
High sense High sense A
VMeas VSet RDUT VMeas VSet RDUT
Low sense Low sense B
RLead
Low force Low force
a) 2-wire connection b) 4-wire connection
Figure 2. A 4-wire connection eliminates the measurement error caused by residual lead resistance
What is the B2900A Series Eliminating residual measurement results. In this case
a 4-wire connection scheme (remote
of SMUs? resistance effects sensing) can be used to eliminate this
An SMU combines the capabilities of A basic 2-wire connection is the most error. A 4-wire measurement uses
a current source, a voltage source, common scheme used for resistance one pair of leads to force current and
a current meter and a voltage meter measurements. In this configuration the other pair of leads to monitor volt-
along with the capability to switch (shown in Figure 2a) the same pair age. This eliminates cable resistance
easily between these various func- of test leads is used to both force effects so that only the voltage drop
tions into a single instrument. This current and measure voltage. This across the DUT is measured (please
gives it the ability to evaluate the IV arrangement is suitable for resistance see Figure 2b). In addition, the 4-wire
characteristics of devices across all measurements as long as the residual measurement scheme of the B2900A
four measurement quadrants without lead resistance is negligible compared Series of SMUs keeps the voltage
the need for any additional equipment. to the resistance of the device under between the sense points (A and B
Besides being able to output and test (DUT). in Figure 2b) at exactly the specified
measure voltage or current very voltage Vset, thereby ensuring that
accurately, SMUs also possess a However, for very low resistance your device is characterized exactly
compliance feature that allows a limit measurements where the residual under the measurement conditions
to be placed on the voltage or current lead resistance is comparable to you specify. The B2900A Series of
output to prevent device damage. The the DUT resistance, the 2-wire SMUs supports both connection
members of the B2900A Series of measurement will give erroneous schemes and it is easy to switch
SMUs are single or dual channel SMU between them.
units that offer a wide range of IV
measurement capability for a variety
of two-terminal and three-terminal
devices. They cover currents from
10 fA to 3 A (DC)/10.5 A (pulse) and
voltages from 100 nV to 210 V. In
addition to their DC operation mode,
the B2900A Series of SMUs also has
the ability to perform pulsed measure-
ments in order to prevent device
self-heating from distorting the mea-
surement results. Finally, the B2900A
Series of SMUs also has a built-in
resistance measurement function.
2
Leakage current prevention Banana-to-triax adaptor Banana-to-triax adaptor
for 4-wire (kelvin) connection for 2-wire (kelvin) connection
Leakage currents in the cables and
test fixturing can cause significant High High Low High Low
sence force sence force Guard force
measurement errors, especially when
measuring large resistances where
the measurement current is small Guard Low
(less than a nanoamp). In this case, force
the guard function of the B2900A
Series of SMUs can be used by
employing banana-to-triaxial adaptors
and triaxial cables. The SMU circuitry
maintains the guard terminal at same
voltage potential as the high force
line, which prevents current from
leaking into the cable and the
surrounding measurement path
(please see Figure 3). Figure 3. The active guard of the B2900A Series of SMUs eliminates leakage currents
when used with the proper triaxial connectors and cabling
Powerful GUI and
convenient PC control
options 1) Set the measurement condition
and the measurement range
The wide QVGA LCD display of the
B2900A Series of SMUs supports an
easy-to-use GUI that provides easy
instrument control from the front
panel. This makes it simple to perform
both spot resistance measurements
using constant voltage or current and
sweep measurements to obtain an IV
curve. After measurement completion 2) Execute
you can use the front panel GUI to
graphically view measurement results
such as IV curves using Graph View,
and display a list of the measurement Figure 4. The GUI of the B2900A Series of SMUs makes it easy to take a quick
data using the Measure Result dialog measurement
window (please see Figure 4).
The B2900A Series of SMUs has a USB
interface on the front panel so that a
USB flash memory device can be used
with the B2900A Series of SMUs to
save and load measurement setups
as well as to save measurement
results.
3
If you have specialized programming and languages so that you can Summary
needs then both Standard Commands develop programs without having
for Programmable Instruments (SCPI) to use low-level commands. The Agilent B2901/02/11/12A
and IVI-COM drivers are available for The Agilent B2900A Quick I/V Precision Source/Measure Unit is the
the B2900A Series of SMUs. SCPI Measurement Software is available best solution for IV characterization
is an industry-standard command for download from the Agilent Web of thermistor and a variety of other
set for basic instruments, and it has site for free (Please see Figure 5). devices. Its wide current and volt-
a uniform structure that supports a The Agilent B2900A Graphical Web age measurement ranges (from 10
common set of commands. The SCPI Interface is also available, and it fA/100 nV to 10.5 A/210 V) provide
command set of the B2900A Series of provides functionality to allow access superior measurement performance
SMUs not only supports its advanced to the B2900A Series of SMUs over a and allow you to characterize devices
features but also general-purpose LAN connection. The B2900A Series more accurately and easily than ever
SMU commands (such as those used of SMUs is fully compliant with the before.
by the Keithley 2400) to simplify LXI class C specification, making it
test program migration. In addition easy to take measurements using a The easy-to-use GUI of the B2900A
to SCPI, the IVI-COM drivers for the standard web browser by just con- Series of SMUs has a variety of capa-
B2900A Series of SMUs work in a necting the B2900A Series of SMUs bilities and features that make it easy
variety of programming environments to a PC using a LAN cable. to take measurements quickly and
to save both the measurement setup
conditions and data to USB-based
flash memory devices.
In addition to being able to control
the B2900A Series of SMUs remotely
over GPIB, USB and LAN interfaces,
Agilent supplies PC-based Agilent
B2900A Graphical Web Interface
and Agilent B2900A Quick I/V
Measurement Software for free to
simplify controlling the B2900A Series
of SMUs from your PC.
For more detailed information on the
various models of the B2900A Series
of SMUs, please refer to the data
sheet of the B2900A Series of SMUs
(5990-7009EN).
The B2900A Series of SMUs enables
you to quickly debug and accurately
Figure 5. It is easy to make a quick measurement on a PC using the Agilent B2900A characterize a wide variety of devices
Quick I/V Measurement software using only a single bench-top SMU.
4
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