Tektronix Keithley 4200A-SCS User manual

User’s Manual
4200A-SMU-900-01 Rev. A December 2020
*P4200A-SMU-900-01A*
4200A-SMU-900-01A
tek.com/keithley
Model 4200A-SCS
Source-Measure Unit (SMU)

Source-Measure Unit (SMU)
User's Manual
Model 4200A-SCS

© 2020, Keithley Instruments
Cleveland, Ohio, U.S.A.
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Document number: 4200A-SMU-900-01 Rev. A December 2020

Safety precautions
The following safety precautions should be observed before using this product and any associated instrumentation. Although
some instruments and accessories would normally be used with nonhazardous voltages, there are situations where hazardous
conditions may be present.
This product is intended for use by personnel who recognize shock hazards and are familiar with the safety precautions required
to avoid possible injury. Read and follow all installation, operation, and maintenance information carefully before using the
product. Refer to the user documentation for complete product specifications.
If the product is used in a manner not specified, the protection provided by the product warranty may be impaired.
The types of product users are:
Responsible body is the individual or group responsible for the use and maintenance of equipment, for ensuring that the
equipment is operated within its specifications and operating limits, and for ensuring that operators are adequately trained.
Operators use the product for its intended function. They must be trained in electrical safety procedures and proper use of the
instrument. They must be protected from electric shock and contact with hazardous live circuits.
Maintenance personnel perform routine procedures on the product to keep it operating properly, for example, setting the line
voltage or replacing consumable materials. Maintenance procedures are described in the user documentation. The procedures
explicitly state if the operator may perform them. Otherwise, they should be performed only by service personnel.
Service personnel are trained to work on live circuits, perform safe installations, and repair products. Only properly trained
service personnel may perform installation and service procedures.
Keithley products are designed for use with electrical signals that are measurement, control, and data I/O connections, with low
transient overvoltages, and must not be directly connected to mains voltage or to voltage sources with high transient
overvoltages. Measurement Category II (as referenced in IEC 60664) connections require protection for high transient
overvoltages often associated with local AC mains connections. Certain Keithley measuring instruments may be connected to
mains. These instruments will be marked as category II or higher.
Unless explicitly allowed in the specifications, operating manual, and instrument labels, do not connect any instrument to mains.
Exercise extreme caution when a shock hazard is present. Lethal voltage may be present on cable connector jacks or test
fixtures. The American National Standards Institute (ANSI) states that a shock hazard exists when voltage levels greater than
30 V RMS, 42.4 V peak, or 60 VDC are present. A good safety practice is to expect that hazardous voltage is present in any
unknown circuit before measuring.
Operators of this product must be protected from electric shock at all times. The responsible body must ensure that operators
are prevented access and/or insulated from every connection point. In some cases, connections must be exposed to potential
human contact. Product operators in these circumstances must be trained to protect themselves from the risk of electric shock. If
the circuit is capable of operating at or above 1000 V, no conductive part of the circuit may be exposed.
Do not connect switching cards directly to unlimited power circuits. They are intended to be used with impedance-limited
sources. NEVER connect switching cards directly to AC mains. When connecting sources to switching cards, install protective
devices to limit fault current and voltage to the card.
Before operating an instrument, ensure that the line cord is connected to a properly-grounded power receptacle. Inspect the
connecting cables, test leads, and jumpers for possible wear, cracks, or breaks before each use.
When installing equipment where access to the main power cord is restricted, such as rack mounting, a separate main input
power disconnect device must be provided in close proximity to the equipment and within easy reach of the operator.
For maximum safety, do not touch the product, test cables, or any other instruments while power is applied to the circuit under
test. ALWAYS remove power from the entire test system and discharge any capacitors before: connecting or disconnecting
cables or jumpers, installing or removing switching cards, or making internal changes, such as installing or removing jumpers.
Do not touch any object that could provide a current path to the common side of the circuit under test or power line (earth)
ground. Always make measurements with dry hands while standing on a dry, insulated surface capable of withstanding the
voltage being measured.

For safety, instruments and accessories must be used in accordance with the operating instructions. If the instruments or
accessories are used in a manner not specified in the operating instructions, the protection provided by the equipment may be
impaired.
Do not exceed the maximum signal levels of the instruments and accessories. Maximum signal levels are defined in the
specifications and operating information and shown on the instrument panels, test fixture panels, and switching cards.
When fuses are used in a product, replace with the same type and rating for continued protection against fire hazard.
Chassis connections must only be used as shield connections for measuring circuits, NOT as protective earth (safety ground)
connections.
If you are using a test fixture, keep the lid closed while power is applied to the device under test. Safe operation requires the use
of a lid interlock.
If a screw is present, connect it to protective earth (safety ground) using the wire recommended in the user documentation.
The symbol on an instrument means caution, risk of hazard. The user must refer to the operating instructions located in the
user documentation in all cases where the symbol is marked on the instrument.
The symbol on an instrument means warning, risk of electric shock. Use standard safety precautions to avoid personal
contact with these voltages.
The symbol on an instrument shows that the surface may be hot. Avoid personal contact to prevent burns.
The symbol indicates a connection terminal to the equipment frame.
If this symbol is on a product, it indicates that mercury is present in the display lamp. Please note that the lamp must be
properly disposed of according to federal, state, and local laws.
The WARNING heading in the user documentation explains hazards that might result in personal injury or death. Always read
the associated information very carefully before performing the indicated procedure.
The CAUTION heading in the user documentation explains hazards that could damage the instrument. Such damage may
invalidate the warranty.
The CAUTION heading with the symbol in the user documentation explains hazards that could result in moderate or minor
injury or damage the instrument. Always read the associated information very carefully before performing the indicated
procedure. Damage to the instrument may invalidate the warranty.
Instrumentation and accessories shall not be connected to humans.
Before performing any maintenance, disconnect the line cord and all test cables.
To maintain protection from electric shock and fire, replacement components in mains circuits —including the power
transformer, test leads, and input jacks —must be purchased from Keithley. Standard fuses with applicable national safety
approvals may be used if the rating and type are the same. The detachable mains power cord provided with the instrument may
only be replaced with a similarly rated power cord. Other components that are not safety-related may be purchased from other
suppliers as long as they are equivalent to the original component (note that selected parts should be purchased only through
Keithley to maintain accuracy and functionality of the product). If you are unsure about the applicability of a replacement
component, call a Keithley office for information.
Unless otherwise noted in product-specific literature, Keithley instruments are designed to operate indoors only, in the following
environment: Altitude at or below 2,000 m (6,562 ft); temperature 0 °C to 50 °C (32 °F to 122 °F); and pollution degree 1 or 2.
To clean an instrument, use a cloth dampened with deionized water or mild, water-based cleaner. Clean the exterior of the
instrument only. Do not apply cleaner directly to the instrument or allow liquids to enter or spill on the instrument. Products that
consist of a circuit board with no case or chassis (e.g., a data acquisition board for installation into a computer) should never
require cleaning if handled according to instructions. If the board becomes contaminated and operation is affected, the board
should be returned to the factory for proper cleaning/servicing.
Safety precaution revision as of June 2017.

Introduction..............................................................................................................1-1
Introduction .......................................................................................................................... 1-1
Source-measure unit (SMU) ................................................................................................ 1-1
Preamplifier.......................................................................................................................... 1-2
Ground unit (GNDU) ............................................................................................................ 1-2
Connections and configuration ..............................................................................2-1
Basic source-measure connections..................................................................................... 2-1
SMU connections......................................................................................................................2-2
Preamplifier local sense connections......................................................................................2-11
Using the ground unit..............................................................................................................2-12
Basic SMU circuit configuration...............................................................................................2-16
Test fixture and device under test (DUT) connections....................................................... 2-20
Testing with less than ±20 V with SMUs.................................................................................2-20
Testing with more than ±20 V..................................................................................................2-21
Recommended connecting cables .......................................................................................... 2-21
Setting up SMUs in Clarius......................................................................................3-1
Introduction .......................................................................................................................... 3-1
Set up a simple project......................................................................................................... 3-1
Select project components........................................................................................................3-1
Add a device and test to the project.......................................................................................... 3-2
Configure a simple test ........................................................................................................ 3-3
Set the key parameters.............................................................................................................3-5
Set the test parameters.............................................................................................................3-6
Run a simple test ................................................................................................................. 3-8
Operation Mode (SMU)........................................................................................................ 3-9
Open operation mode - SMU ..................................................................................................3-10
Voltage Bias operation mode..................................................................................................3-10
Voltage Linear Sweep operation mode - SMU........................................................................3-10
Voltage Segment Sweep operation mode...............................................................................3-11
Voltage List Sweep operation mode........................................................................................3-12
Voltage Log Sweep operation mode.......................................................................................3-12
Voltage Step operation mode..................................................................................................3-13
Current Bias operation mode ..................................................................................................3-13
Current Linear Sweep operation mode - SMU ........................................................................3-13
Current Segment Sweep operation mode - SMU....................................................................3-14
Current List Sweep operation mode - SMU.............................................................................3-14
Current Log Sweep operation mode - SMU............................................................................3-15
Current Step operation mode..................................................................................................3-16
Common operation mode - SMU............................................................................................. 3-16
SMU - all terminal parameters ........................................................................................... 3-16
Base Current...........................................................................................................................3-16
Base Voltage...........................................................................................................................3-16
Bias.........................................................................................................................................3-16
Column Name (Measure Current)........................................................................................... 3-17
Column Name (Measure Voltage)...........................................................................................3-17
Table of contents

Table of contents Model 4200A-SCS Source-Measure Unit (SMU) User's Manual
Compliance.............................................................................................................................3-17
Dual Sweep.............................................................................................................................3-18
Force Range (Source Range).................................................................................................3-19
List Values...............................................................................................................................3-19
Low Range..............................................................................................................................3-19
Measure Current.....................................................................................................................3-19
Off Time ..................................................................................................................................3-19
On Time ..................................................................................................................................3-20
Overvoltage protection............................................................................................................3-20
Points (list or segment sweep)................................................................................................3-20
Points (log sweep)...................................................................................................................3-20
Points......................................................................................................................................3-21
Power On Delay...................................................................................................................... 3-21
Pulse Mode.............................................................................................................................3-21
Range (Measure Current) .......................................................................................................3-23
Report Status (SMU)...............................................................................................................3-24
Report Value (Measure Current or Report Current)................................................................3-24
Report Value (Report Voltage or Measure Voltage)................................................................3-24
Segments................................................................................................................................3-24
Start (step) ..............................................................................................................................3-25
Start (sweep)...........................................................................................................................3-25
Step (step)...............................................................................................................................3-25
Step (voltage sweep) ..............................................................................................................3-26
Step (voltage sweep) ..............................................................................................................3-26
Stop (step)...............................................................................................................................3-27
Stop (sweep)...........................................................................................................................3-27
Voltage (Report Voltage).........................................................................................................3-27
Voltage Range ........................................................................................................................3-27
SMU Test Settings ............................................................................................................. 3-27
Speed......................................................................................................................................3-27
Report Timestamps.................................................................................................................3-28
Delay Factor............................................................................................................................3-29
Filter Factor.............................................................................................................................3-30
Auto A/D Aperture...................................................................................................................3-31
A/D Aperture Time .................................................................................................................. 3-31
Test Mode...............................................................................................................................3-31
Sweep Delay...........................................................................................................................3-32
Interval ....................................................................................................................................3-32
Number of Samples ................................................................................................................3-32
Hold Time - SMU.....................................................................................................................3-32
SMU Power On Sequence......................................................................................................3-32
Disable outputs at completion - SMU......................................................................................3-33
Output Values .........................................................................................................................3-33
Compliance exit-condition options...........................................................................................3-34
Source-measure hardware ......................................................................................4-1
Source-measure units.......................................................................................................... 4-1
Source-measure hardware overview................................................................................... 4-1
Basic SMU circuit configuration ........................................................................................... 4-2
SMU terminals and connectors............................................................................................ 4-3
SENSE LO terminal ..................................................................................................................4-4
SENSE terminal........................................................................................................................4-5
FORCE terminal........................................................................................................................4-5
PA CNTRL connector................................................................................................................4-5
Source-measure unit (SMU) with 4200-PA overview .......................................................... 4-5
Basic SMU/preamplifier circuit configuration............................................................................. 4-6

Model 4200A-SCS Source-Measure Unit (SMU) User's Manual Table of contents
Compliance limit for a SMU with a 4200-PA..............................................................................4-6
Using minimum compliance ......................................................................................................4-7
Operating boundaries................................................................................................................4-7
Preamplifier terminals and connectors......................................................................................4-8
FORCE terminal......................................................................................................................4-10
SENSE terminal......................................................................................................................4-11
Preamplifier CONTROL connector.......................................................................................... 4-11
SMU circuit COMMON connections........................................................................................4-11
Ground unit (GNDU) overview........................................................................................... 4-12
Basic characteristics ...............................................................................................................4-12
Ground unit connections .........................................................................................................4-13
Ground unit DUT connections.................................................................................................4-14
Ground unit terminals and connectors ....................................................................................4-15
FORCE terminal......................................................................................................................4-15
SENSE terminal......................................................................................................................4-16
COMMON terminal..................................................................................................................4-16
Source-measure concepts ......................................................................................5-1
Source-measure concepts................................................................................................... 5-1
Guarding .............................................................................................................................. 5-1
Guard connections....................................................................................................................5-2
Guarding concepts....................................................................................................................5-3
Test fixture guarding .................................................................................................................5-4
Local and remote sensing.................................................................................................... 5-5
Local sensing............................................................................................................................5-7
Remote sensing........................................................................................................................5-8
Source or sink ...................................................................................................................... 5-8
4200-SMU and 4201-SMU source or sink.................................................................................5-9
4210-SMU or 4211-SMU source or sink .................................................................................5-10
4200-SMU and 4201-SMU sink boundaries............................................................................5-11
4210-SMU and 4211-SMU sink boundaries............................................................................5-12
Source-measure considerations ........................................................................................ 5-12
Source I, measure V or I .........................................................................................................5-12
Source V, measure I or V........................................................................................................5-13
Measure only (V or I)............................................................................................................... 5-14
I-Source operating boundaries................................................................................................5-15
I-Source operation examples ..................................................................................................5-16
V-Source operating boundaries...............................................................................................5-17
V-Source operation examples.................................................................................................5-18
Source I measure I and source V measure V..........................................................................5-19
Sweep concepts................................................................................................................. 5-19
Source-delay-measure cycle...................................................................................................5-20
Sweep waveforms................................................................................................................... 5-20
Operation mode timing....................................................................................................... 5-22
Sampling mode timing.............................................................................................................5-23
Optimizing SMU measurements.............................................................................. 6-1
Introduction .......................................................................................................................... 6-1
Making stable measurements with SMUs............................................................................ 6-1
Single SMU stability considerations.......................................................................................... 6-1
Multiple SMU stability considerations........................................................................................6-2

Table of contents Model 4200A-SCS Source-Measure Unit (SMU) User's Manual
Eliminating oscillations..............................................................................................................6-3
Low-current measurements ................................................................................................. 6-4
Leakage currents ......................................................................................................................6-5
Generated currents...................................................................................................................6-5
Voltage burden..........................................................................................................................6-8
Noise and source impedance....................................................................................................6-9
Cable capacitance...................................................................................................................6-10
Test system performance........................................................................................................6-10
Interference........................................................................................................................ 6-11
Electrostatic interference.........................................................................................................6-11
Radio-frequency interference..................................................................................................6-11
Ground loops and other SMU grounding considerations.........................................................6-12
Make I-V measurements on a solar cell.................................................................. 7-1
Introduction .......................................................................................................................... 7-1
Equipment required.............................................................................................................. 7-1
Device connections.............................................................................................................. 7-2
Device connection schematic.................................................................................................... 7-2
Connect the 4200A-SCS to the DUT.........................................................................................7-3
Setting up measurements in the Clarius software ............................................................... 7-4
Create a new project.................................................................................................................7-4
Search for and select a test.......................................................................................................7-5
Configure the test......................................................................................................................7-6
Run the test...............................................................................................................................7-8
Analyze the test results.............................................................................................................7-9
Additional tests........................................................................................................................7-10

In this section:
Introduction .............................................................................. 1-1
Source-measure unit (SMU)..................................................... 1-1
Preamplifier.............................................................................. 1-2
Ground unit (GNDU) ................................................................ 1-2
Introduction
This document provides information about the 4200-SMU, 4201-SMU, 4210-SMU, and 4211-SMU
source-measure units and related instruments, including:
•Connections and configuration (on page 2-1): Basic information on connecting source-measure
units (SMUs), the preamplifier, and the ground unit to devices under test (DUTs), making test
equipment connections, and making control and data connections.
•Setting up SMUs in Clarius (on page 3-1): Describes the SMU operation modes, the options
available for each mode, and the SMU test settings.
•Source-measure hardware (on page 4-1): Provides information about the SMUs and related
instruments, including 4200-PAs and ground units, and provides information
•Source-measure concepts (on page 5-1): Provides information on guarding, remote sensing, sink
operation, and sweep concepts.
•Optimizing SMU measurements (on page 6-1): Includes information on improving measurement
stability, making low-current measurements, and reducing interference.
Source-measure unit (SMU)
The fundamental instrument module used by the 4200A-SCS is the source-measure unit (SMU). The
basic function of a SMU is to perform one of the following source-measure operations:
•Source voltage and measure current or voltage
•Source current and measure voltage or current
Section 1
Introduction

Section 1: Introduction Model 4200A-SCS Source-Measure Unit (SMU) User's Manual
1-2 4200A-SMU-900-01 Rev. A December 2020
The source of the SMU can be configured to sweep or step voltages or currents, or to output a
constant bias voltage or current.
There are medium-power and high-power source-measure units available. The 2 W medium-power
SMUs are models 4200-SMU and 4201-SMU. The 20 W high-power SMUs are models 4210-SMU
and 4211-SMU. The following table lists the maximum limits of the SMUs.
Source-measure units
Model
Maximum voltage
Maximum current
Maximum power
4200-SMU
4201-SMU
210 V
105 mA
2.2 W
4210-SMU
4211-SMU
210 V
1.05 A
22 W
Preamplifier
A 4200-PA preamplifier adds five low-current source-measure ranges to a SMU. Without a
preamplifier, the 100 nA range (100 fA resolution) is the lowest current source-measure range for a
SMU. With a preamplifier installed, the 10 nA, 1 nA, 100 pA, 10 pA, and 1 pA source-measure ranges
are added.
If preamplifiers are ordered, the 4200A-SCS is shipped from the factory with the preamplifiers
installed on the rear panel of the mainframe.
Ground unit (GNDU)
The ground unit on the rear panel of the 4200A-SCS provides a convenient method of making ground
connections. This eliminates the need to use a SMU for this purpose.

In this section:
Basic source-measure connections ......................................... 2-1
Test fixture and device under test (DUT) connections ........... 2-20
Basic source-measure connections
This section describes basic information on connecting source-measure units (SMUs), the
preamplifier, and the ground unit to devices under test (DUTs).
The 4200A-SCS is provided with an interlock circuit that must be positively activated for the
high voltage output to be enabled. The interlock helps facilitate safe operation of the
equipment in a test system. Bypassing the interlock could expose the operator to hazardous
voltages that could result in personal injury or death.
Asserting the interlock allows the SMU and preamplifier terminals to become hazardous,
exposing the user to possible electrical shock that could result in personal injury or death.
SMU and preamplifier terminals should be considered hazardous even if the outputs are
programmed to be low voltage. Precautions must be taken to prevent a shock hazard by
surrounding the test device and any unprotected leads (wiring) with double insulation that is
rated for 250 V, Category O.
The maximum allowed voltage between circuit COMMON and chassis ground is ±32 V dc. The
maximum allowed voltages between the preamplifier signals are:
COMMON to chassis ground: 32 VPEAK
GUARD to COMMON: 250 VPEAK
SENSE or FORCE to GUARD: 40 VPEAK
Section 2
Connections and configuration

Section 2: Connections and configuration Model 4200A-SCS Source-Measure Unit (SMU) User's Manual
2-2 4200A-SMU-900-01 Rev. A December 2020
SMU connections
The following topics explain how to connect the source-measure units (SMUs) to the device under
test (DUT).
The SMU can be connected directly to the device under test (DUT) with triaxial cables using either
local or remote sensing, as described in the following topics. Remote sensing is typically used when
currents exceed 1 mA and the FORCE path resistance is large (around 1 Ω). In this case, as much as
1 mV (= 1 mA × 1 Ω) of measurement error is generated due to FORCE path resistance. Remote
sensing eliminates these errors.
When using more than one SMU, use the ground unit for circuit COMMON connections instead of
the outer shield of the SMU terminals. Refer to Using the ground unit (on page 2-12).
Do not touch test cables or connectors when powering up the 4200A-SCS. Hazardous voltage
may be output momentarily, posing a safety hazard that could result in personal injury or
death.
Do not turn on the 4200A-SCS until you have reviewed the safe power-up procedure in
“Powering the 4200A-SCS” in Model 4200A-SCS Setup and Maintenance.
Do not connect the DUT to the 4200A-SCS before powering it up, because the hazardous
voltage that may be output momentarily at power-up could damage the DUT.
If your 4200A-SCS includes preamplifiers, all tests should be performed using the preamplifiers, as
the installed SMUs were optimized at the factory to use them.

Model 4200A-SCS Source-Measure Unit (SMU) User's Manual Section 2: Connections and configuration
4200A-SMU-900-01 Rev. A December 2020 2-3
Triaxial cables
Triaxial cables are supplied to make connections to the DUT (device under test). With preamplifiers
installed, use the low-noise triaxial cables, which are terminated with 3-slot triaxial connectors on both
ends. One end of the cable connects to the preamplifier and the other end connects to the DUT test
fixture or probe station.
Figure 1: Triaxial cable 4200-TRX-X
If your system does not have preamplifiers installed, use the cables that have a miniature triaxial
connector on one end and a standard 3-slot triaxial connector on the other end. The cable end that is
terminated with the miniature connector connects directly to the SMU, and the other end connects to
the test fixture or probe station.
Figure 2: Triaxial cable 4200-MTRX-X
With preamplifiers installed, never make connections directly to any of the miniature triaxial
connectors on the SMU modules. This may result in damage to the SMU or DUT or may
produce corrupt data.

Section 2: Connections and configuration Model 4200A-SCS Source-Measure Unit (SMU) User's Manual
2-4 4200A-SMU-900-01 Rev. A December 2020
SMU local sense connections
The simplest method to connect SMUs to the device under test (DUT) is to use one SMU for each
terminal of the device. When setting up a test, the FORCE terminal (center conductor) of the SMU is
used to apply voltage or current to the device. The FORCE terminal or ground unit can also be used
to connect the device terminal to the COMMON circuit.
The following figure shows typical SMU connections using local sensing. Use a triaxial cable such as
the 4200-MTRX-Xto make your connections as follows:
•Connect SMU FORCE (center conductor of FORCE terminal) to DUT HI.
•Connect circuit COMMON (outer shield of FORCE terminal) to DUT LO.
Figure 3: SMU local sense connections
Figure 4: SMU local sense connections - equivalent circuit

Model 4200A-SCS Source-Measure Unit (SMU) User's Manual Section 2: Connections and configuration
4200A-SMU-900-01 Rev. A December 2020 2-5
Basic device connections for SMUs
The following figures show the basic connections to 2-terminal, 3-terminal, and 4-terminal devices.
Notice that only the FORCE HI terminal of each SMU is connected to the device terminal. FORCE HI
is the center conductor of the triaxial cable.
Connecting the SMU or ground unit SENSE terminal without the FORCE terminal may damage
the instrument and return erroneous results.
Figure 5: Two-terminal device connections to SMUs and preamplifiers
Figure 6: Three-terminal device connections to SMUs and preamplifiers

Section 2: Connections and configuration Model 4200A-SCS Source-Measure Unit (SMU) User's Manual
2-6 4200A-SMU-900-01 Rev. A December 2020
Figure 7: Four-terminal device connections to SMUs and preamplifiers
Shielding and guarding
Many test situations require that the device under test (DUT) be shielded or guarded (or both) to
avoid detrimental effects caused by electrostatic interference, parasitic capacitance, system leakage
currents, and so forth.
See Guarding (on page 5-1) for more information on the principles and advantages of guarding.
A safety shield must be used whenever hazardous voltages (>30 VRMS, 42 VPEAK) will be
present in the test circuit. To prevent electrical shock that could cause injury or death, never
use the 4200A-SCS in a test circuit without a properly installed and configured safety shield.
To shield, but not guard, the device, connect the DUT shield to COMMON as shown in the following
figure.

Model 4200A-SCS Source-Measure Unit (SMU) User's Manual Section 2: Connections and configuration
4200A-SMU-900-01 Rev. A December 2020 2-7
Figure 8: Device shielding
Figure 9: Device shielding basic circuit

Section 2: Connections and configuration Model 4200A-SCS Source-Measure Unit (SMU) User's Manual
2-8 4200A-SMU-900-01 Rev. A December 2020
To guard the device, connect the DUT shield to GUARD. GUARD is the inner shield of triaxial cable,
as shown in the following figure.
Figure 10: Device guarding
Figure 11: Device guarding basic circuit

Model 4200A-SCS Source-Measure Unit (SMU) User's Manual Section 2: Connections and configuration
4200A-SMU-900-01 Rev. A December 2020 2-9
Signal integrity
To maintain signal integrity, especially at low current levels, consider the following when making
signal connections between the 4200A-SCS instrumentation and the device under test (DUT):
•Use only low-noise triaxial cables such as those provided with the SMU (4200-MTRX-X) and
preamplifier (4200-TRX-X).
•Keep connecting cables as short as possible.
•Avoid flexing or vibrating connecting cables while making measurements.
•Do not touch connector insulators. Be sure to keep all connector insulators clean to minimize
contamination-induced leakage currents.
•Avoid stresses in cables. Do not allow large portions to hang under their own weight. Place on a
table or flat surface if possible. Avoid tight bends in the cables.
Refer to the “Maintenance” section of Model 4200A-SCS Setup and Maintenance or the Keithley
Instruments Low Level Measurements Handbook for more information about measurement integrity.
Using the ground unit with more than two SMUs
Use the ground unit for circuit COMMON connections when using more than two SMUs. Make your
connections using the same basic connections shown in the previous figures for the ground units. Be
sure to connect all your DUT LO terminals to the GNDU FORCE terminal. If you are using remote
sensing, also connect the DUT LO terminals to the SENSE terminal.
SMU circuit COMMON connections
Some tests require SMUs to be connected to each DUT terminal. In these tests, circuit COMMON is
not hardwired to any of the DUT terminals. Each SMU must be able to internally connect circuit
COMMON to its FORCE signal when the test requires a DUT terminal to be connected to COMMON.
The following figure shows typical SMU connections using three SMUs to test a transistor. You can
use any one of the SMUs to provide access to circuit COMMON by programming the SMU
accordingly. See the Model 4200A-SCS Clarius User's Manual for detailed instructions on configuring
a SMU to provide a COMMON connection.