Performing Very Low Frequency
Capacitance-Voltage Measurements
on High Impedance Devices Using the4200A-SCS Parameter Analyzer––
APPLICATION NOTE

Performing Very Low Frequency Capacitance-Voltage Measurements on
High Impedance Devices Using the 4200A-SCS Parameter Analyzer

Introduction
Capacitance measurements on semiconductor devices
are usually made using an AC technique with a bridgetype instrument. These AC instruments typically make

APPLICATION NOTE

shows how to use the provided software, and describes
optimizing VLF C-V measurements using the 4200A-SCS.

Very Low Frequency C-V Techniquecapacitance and impedance measurements at frequencies

Figure 1 is a simplified diagram of the SMU instrument

ranging from megahertz down to possibly tens of hertz.

configuration used to generate the low frequency impedance

However, even lower frequency capacitance measurements

measurements. This configuration requires a 4200A-SCS

are often necessary to derive specific test parameters ofsystem with two SMU instruments installed, with 4200-PA

devices such as MOScaps, thin film transistors (TFTs), andpreamps connected to either side of the device under test.

MEMS structures. Low frequency C-V measurements are

SMU1 outputs the DC bias with a superimposed AC signal

also used to characterize the slow trapping and de-trapping

and also measures the voltage. SMU2 measures the resulting

phenomenon in some materials. Instruments capable of

AC current while sourcing 0V DC.

making quasistatic (or almost DC) C-V measurements are
Capacitor

often used for these low frequency impedance applications.
However, the 4200A-SCS Parameter Analyzer uses a
new narrow-band technique that takes advantage ofthe low current measurement capability of its integrated
source measure unit (SMU) instruments to perform C-V
measurements at specified low frequencies in the range of
10mHz to 10Hz. This new method is called the Very Low

Test Device

Force HISMU1
smu_src

A

Force HIA

SMU2
smu_sense

Frequency C-V (VLF C‑V) Technique.
The VLF C-V Technique makes it possible to measurevery small capacitances at a precise low test frequency.
This patent-pending, narrow-band sinusoidal techniqueallows for low frequency C-V measurements of very highimpedance devices, up to >1E15 ohms. Other AC impedance
instruments are usually limited to impedances up to about

Force LO
(Internally Connected)
SMU2 with preamp:
SMU1 with preamp:
Measures AC current
Outputs DCV with
at 0V DC.
superimposed ACV andmeasures AC voltage.

1E6 to 1E9 ohms. The VLF C-V approach also reduces thenoise that may occur when making traditional quasistatic C-V
measurements.

Figure 1. Connections for very low frequency C-V measurements.

Basically, while the voltage is forced, voltage and current

The 4200A-SCS Parameter Analyzer comes withmeasurements are obtained simultaneously over several

preconfigured tests and a user library to perform impedancecycles. The magnitude and phase of the DUT impedance ismeasurements automatically using this very low frequency

extracted from the discrete Fourier transform (DFT) of a ratio

technique. Because this approach uses the 4200A-SCS’sof the resultant voltage and current sinusoids. This narrow-

SMU instruments, no additional hardware or software isband information can be collected at varying frequencies

necessary if low current I-V characterization is already(10mHz to 10Hz) to create a complex, multi-element of therequired. This application note describes the VLF C-V

DUT. The resulting output parameters include the impedancetechnique, explains how to make connections to the DUT,

(Z), phase angle (θ), capacitance (C), conductance (G),resistance (R), reactance (X), and the dissipation factor (D).

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Performing Very Low Frequency Capacitance-Voltage Measurements on
High Impedance Devices Using the 4200A-SCS Parameter Analyzer

APPLICATION NOTE

Because the very low frequency method works over a

to measure the AC current should be connected to the highlimited frequency range, the capacitance of the device under

impedance terminal of the device (Figure 2).

test (DUT) should be in the range of 1pF to 10nF. Table 1
summarizes the VLF C-V specifications (see Appendix A for

MOSCaps on wafer

complete specifications).
Table 1. Very Low Frequency C-V specifications.
Measurement
Parameters
Frequency Range

Cp, Gp, F, Z, θ, R, X, Cs, Rs, D, time
10mHz to 10Hz

Measurement Range 1pF to 10nF
Typical Resolution

3.5 digits, minimum typical 10fF

AC Signal

10mV to 3V RMS

DC Bias±20V on the High terminal, minus the AC signal,
1µA maximum

Required Hardware for VLF C-V
Measurements
To make very low frequency impedance measurements, thefollowing hardware is required:

Prober Chuck

Force HISMU1
smu_src

Force HIPreAmp

PreAmpAA

SMU2
smu_sense

Force LO
(Internally Connected)
smu_sense issmr.src is connectedto the chuck. This SMU connected to the gateof the MOScap andapplies the DC and AC
voltage and measures measures the current.
the voltage.

• 4200A-SCS with Clarius software• Two 4200 SMU instruments (4200-SMU or 4210-SMU)• Two 4200-PA Preamps• Optional: 4210-CVU Capacitance Voltage Unit (for making
high frequency C-V measurements)

Making Connections to the Device

Figure 2. VLF C-V measurement setup for a MOScap on wafer.

An example of a MOSCap circuit connected for VLF C-V
measurements is shown in Figure 2. Most MOSCaps have
only a single pad on the top of the wafer, with the backsideof the wafer used as the common contact for all MOSCaps.
SMU1 outputs the AC+DC voltage and is connected tothe chuck. The SMU that outputs the voltage is known as

To make VLF C-V measurements on a device, connect“smu_src” in the software that is included with the system.

the DUT between the two Force HI terminals of two SMU

The high impedance terminal of the MOSCap is the gate

instruments (either 4200-SMU or 4210-SMU) with 4200-PA

and is connected to SMU2, which is called “smu_sense” inPreamps (Figures 1, 2). The preamp option is necessary

the software.

because measuring very high impedances requires
measuring very small currents. With the 4200-PAs, currentsof <1E‑12A can be measured. Because the VLF C-V method
requires measuring small currents, it is best to use the triax
cables that come with the SMU instruments to make theseconnections. The method does not support any switching
instrumentation between the SMU instrument preamp andthe device under test (DUT). One SMU outputs both the DC
and AC voltage (SMU1 in Figures 1 and 2) and measures
the AC voltage. The other SMU instrument measures the AC
current (SMU2 in Figures 1 and 2). The SMU instrument used

Using the Clarius Software to Perform
VLF C-V Measurements
The system includes a user library called VLowFreqCV that
contains several user modules that you can use to make low
frequency C-V measurements. Clarius includes example tests
and projects that are based on these user modules that you
can use as templates to develop tests. The example tests andprojects are available in the Library.
You can also build custom tests using these user modules.
The VLowFreqCV User Library contains several modules,

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Performing Very Low Frequency Capacitance-Voltage Measurements on
High Impedance Devices Using the 4200A-SCS Parameter Analyzer

APPLICATION NOTE

listed in Table 2, that can be used in a test in a project. To

library (UTM)”. Select Configure. In the right pane, for thebuild a custom test, in the Library, select Custom Test andUser Library, select VLowFreqCV User Library and thenselect the option “Choose a test from the pre-programmed

select the appropriate User Module.

Figure 3. Screen capture of vlfcv_measure_dual_sweep_bias_fixed_range user module
Table 2. User Modules in the VLowFreqCV User Library.
User Module

Description

vlfcv_measure

Measures C, G, Z, theta, R+jX at a fixed DC bias.

vlfcv_measure_dual_
sweep_bias

Measures C, G, Z, theta, R+jX, time while
sweeping the DC voltage. Optional dual sweep
allows sweeping from dcv_bias_start to dcv_
bias_stop, with 1 measure point at dcv_bias_
stop, then back down to dcv_bias_start.

vlfcv_measure_dual_
sweep_bias_fixed_
range

Measures C, G, Z, theta, R+jX, time while
sweeping the DC voltage. Measurements
are made on a fixed current range which isdetermined by the expected_C, expected_R
and maximum DC voltage. Optional dual sweep
allows sweeping from dcv_bias_start to dcv_
bias_stop, with 1 measure point at dcv_bias_
stop, then back down to dcv_bias_start.

vlfcv_measure_sweep_
freq

Measures C, G, Z, theta, R+jX, time at multiple
user-specified test frequencies.

vlfcv_measure_sweep_time

Measures C, G, Z, theta, R+jX, time as a functionof time.

Once you’ve added a new module to a project, you needto input a few parameters. Many of the parameters arecommon to all the modules; however, each module has some

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unique parameters. Figure 3 illustrates the Key Parameters
view of the vlfcv_measure_dual_sweep_bias_fixed_range
User Module showing all the user-defined parameters. The
adjustable parameters for all the modules are listed in Tables
3 through 6.
The values of the expected capacitance (expected_C) andthe expected parallel resistance (expected_R) determine
which current range will be used to make the measurement.
However, choosing specific values is generally not required,as setting expected_C = 0 will allow the test routines toestimate the C and R to use.
The simplest module is vlfcv_measure. It is used in the
Capacitor VLF C-V Measurement (vlf-cap-one-point) test in
the Capacitor VLF-CV Project. This test performs a single
measurement. The module does not perform any sweeping,but it allows for all test parameters to be controlled (Table
3). Note that the maximum voltage possible is a combinationof both the AC and DC voltages. The maximum negative DC

Performing Very Low Frequency Capacitance-Voltage Measurements on
High Impedance Devices Using the 4200A-SCS Parameter Analyzer__
bias voltage = –20 + (acv_RMS * √ 2 ). The maximum positive__
DC bias voltage = +20 – (acv_RMS * √ 2 ). Use expected_C = 0
to have the routine auto-detect the estimated C and R values.
Table 3. Adjustable parameters in vlfcv_measure User Module.
Parameter
smu_src

Range
SMUn

Description
SMU instrument to source DC + AC voltage
waveform and measure AC volts: SMU1,
SMU2, SMU3…

smu_sense

SMUn

SMU t instrument o measure AC current:
SMU1, SMU2, SMU3…

frequency

0.01 to 10

Test frequency in hertz, from 0.01 to 10.

APPLICATION NOTE

Table 5. Adjustable parameters in the vlfcv_measure_dual_sweep_freq
user module.
Parameter
smu_src

Range
SMUn

Description
SMU instrument to source DC + AC voltage
waveform and measure AC volts: SMU1,
SMU2, SMU3…

smu_sense SMUn

SMU instrument to measure AC current:
SMU1, SMU2, SMU3…

frequency

Array of Test frequencies in Hertz. Maximum
number of entries limited to 512, from 0.01
to 10.

0.01 to 10

expected_C 1e-12 to 1e-8

Estimate of DUT capacitance in Farads, use
0 for auto-detect of DUT C and R.

expected_C 1e-12 to 1e-8

Estimate of DUT capacitance in Farads,
use 0 for auto-detect of DUT C and R.

expected_R 1e6 to 1e14

Estimate of resistance parallel to DUT,
in ohms

expected_R 1e6 to 1e14

Estimate of resistance parallel to DUT,
in ohms

acv_RMS30e-3 to 3

AC drive voltage in volts RMS

acv_RMS30e-3 to 3

AC drive voltage in volts RMS

dcv_bias±20 less_ The DC Voltage applied to the device(acv_RMS * √ 2)

dcv_bias±20 less_ The DC voltage applied to the device(acv_RMS * √ 2)

Table 6. Adjustable parameters in the vlfcv_measure_sweep_time
user module.
Parameter

Table 4. Adjustable parameters in the vlfcv_measure_dual_sweep_bias_fixed_range User Modules.
Parameter
smu_src

Range
SMUn

smu_sense SMUnfrequency

Test frequency in hertz, from 0.01 to 10.

expected_C 1e-12 to 1e-8

Estimate of DUT capacitance in Farads,
use 0 for auto-detect of DUT C and R.

expected_R 1e6 to 1e14

Estimate of resistance parallel to DUT, inohms

acv_RMS30e-3 to 3

AC drive voltage in volts RMS

dcv_start±20 less_ Starting DC voltage of the sweep(acv_RMS * √ 2)

dcv_stop±20 less_ Stop DC voltage of the sweep(acv_RMS * √ 2)

dcv_step±20 less_ Step size of the DC voltage. Number of(acv_RMS * √ 2) steps limited to 512.

dual_sweep 0 or 1

SMUn

Description
SMU instrument to source DC + AC voltage
waveform and measure AC volts: SMU1,
SMU2, SMU3…
SMU instrument to measure AC current:
SMU1, SMU2, SMU3…

0.01 to 10

smu_src

Range

Enter 0 for single sweep; enter 1 fordual sweep

Description
SMU instrument to source DC + AC voltage
waveform and measure AC volts: SMU1,
SMU2, SMU3…

smu_sense SMUn

SMU instrument to measure AC current: :SMU1, SMU2, SMU3…

frequency

Test frequency in Hertz, from 0.01 to 10.

0.01 to 10

expected_C 1e-12 to 1e-8

Estimate of DUT capacitance in Farads, use
0 for auto-detect of DUT C and R.

expected_R 1e6 to 1e14

Estimate of resistance parallel to DUT,
in ohms

acv_RMS30e-3 to 3

AC drive voltage in volts RMS

dcv_bias±20 less_ The DC Voltage applied to the device(acv_RMS * √ 2)

num_points 1 to 512

Number of points to take as a functionof timeOnce any test is executed, several test parameters will be
returned to the Sheet in the Analyze view and can be saved
as an .xls file. These test parameters can also be plotted on
the Graph. Table 7 lists the returned test parameters andtheir descriptions. From these returned test parameters, more
device extractions can be performed using the mathematical
functions in the Formulator. Note that the tests return all
typical C-V measurement parameters. For example, both
Cp-Gp and Cs-Rs are always returned, even if the test device
response only matches the parallel (Cp-Gp).

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Performing Very Low Frequency Capacitance-Voltage Measurements on
High Impedance Devices Using the 4200A-SCS Parameter Analyzer

APPLICATION NOTE

Table 7. Measurements returned for the modules in the
VLowFreqCV Library.

MOSFET VLF-CV Project

Returned Test
Parameters

In the MOSFET VLF-CV Project, there are three tests for

Description

the n-fet devices, as shown in Figure 4. Figure 6 shows

StatusError code from test module execution. Definitions of the
returned errors are listed at the bottom of the Definition
tab in the UTM Description.

the results of generating a very low frequency dual C-V

times

Calculated time difference between readings.

terminal and the Drain/Source/Bulk terminals tied together

dcv_bias

Programmed DC voltage applied to the device.

(Figure 5). This C-V sweep was generated using themeas_Cp

Measured capacitance in parallel (Cp-Gp).

MOSFET VLF-CV Sweep (vlf-nmosfet-vsweep-dual) test.

meas_Gp

Measured conductance in parallel (Cp-Gp)

Tests for measuring capacitance as a function of frequency

meas_freq

Measured test frequency.

(vlf-nmostfet-freq-sweep), as well as a high frequency

meas_Z

Measured impedance (Z-theta).

C-V test (cvu-nmostfet, taken with the 4210-CVU) are also

meas_Theta

Measured phase angle in degrees (Z-theta).

included in the project.

meas_R

Real component of the impedance (R + jX).

meas_X

Imaginary component of the impedance (R + jX).

meas_Cs

Measured AC capacitance in series (Cs-Rs).

meas_Rs

Measured resistance in series (Cs-Rs).

meas_D

Calculated dissipation factor, D.

meas_irange

The SMU instrument current range that the measurement
was taken.

Using the Example Tests and Projects
in the Library

sweep on an n‑MOSFET measured between the Gate

4200-SMU 1
smu_src

4200-SMU 2
smu_sense

PreAmp
SENSE
FORCE

Force
Triax cable

PreAmp
SENSE
FORCE

S
Force

B
G

D

DUT

Triax cable

Figure 5. Connection for MOSFET with the gate connected to SMU2
and, with the drain-source-bulk tied together and connected to SMU1
(smu_sense).

The Clarius software comes with example tests of very low
frequency C-V measurements on various devices. Choose
Select to search for the examples in either the Test or Project
Libraries. Enter VLF in the search box from either the Test
or Project tab. The Tests or Projects will automatically bedisplayed in the Library. Select the desired Test or Project
and add it to the Project tree on the left. Even though thetest and projects were created using specific devices, theseexamples can be used on other devices. Descriptions of thevery low frequency C-V projects that can be found in the
Project Library are described in the following paragraphs.

Figure 6. VLF C-V Sweep of an n-MOSFET measured between thegate to drain/source/bulk. This graph is from the vlf_nmosfet_vsweep_
dual test (user module vlfcv_measure_dual_sweep_bias_fixed_range).

Figure 4. Project tree of MOSFET VLF-CV project

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Performing Very Low Frequency Capacitance-Voltage Measurements on
High Impedance Devices Using the 4200A-SCS Parameter Analyzer

APPLICATION NOTE

Capacitor VLF-CV Project
Using the VLF C-V method, capacitors can be measured
in the range of 1pF to 10nF, and connections are made asshown in Figure 7. The project has four tests for measuring
capacitors (Figure 8). The Capacitor VLF-CV C-t Sweep (vlfcap-time) Test measures the capacitance of a 1pF capacitor
as a function of time (Figure 9). The results of performing a
C-V sweep on a 1pF capacitor are shown in Figure 10. This
small capacitance was measured at a test frequency of 1Hz
with capacitance measurement noise levels at less than
±5E-15F. The Formulator can be used to determine the noise
and average capacitance readings easily.
4200-SMU 1
smu_src

4200-SMU 2
smu_sense

PreAmp
SENSE
FORCE

Force
Triax cable

PreAmp
SENSE
FORCE

DUT

Figure 9. Results of C-t measurements of nominal 1pF reference
capacitor, using VLF capacitance technique at a test frequency of
1Hz. This graph is from the vlf-cap-time test (user module vlfcv_
measure_sweep_time).

Force
Triax cable

Figure 7. VLF C-V connections for the capacitor. If the test device ison wafer, see the MOSCap diagram (Figure 2) for connections.

Figure 10. VLF C-V results, at 1Hz, of a voltage sweep on a 1pF
reference capacitor. This graph is from the vlf-cap-vsweep test (vlfcv_
measure_dual_sweep_bias_fixed_range user module).

Figure 8. Capacitor tests in the Capacitor VLF-CV Project.

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Performing Very Low Frequency Capacitance-Voltage Measurements on
High Impedance Devices Using the 4200A-SCS Parameter Analyzer

APPLICATION NOTE

To compare the results of both low and high C-V measure­ments on one graph, the data can be copied from one
test module into another. Just select and copy the C-V
measurements from the Sheet of one test module andthen paste the data into the columns of the CALC Sheet ofthe other test module. The data in the CALC Sheet can beselected on the graph to plot. To do this, make sure to checkthe “Enable Multiple Xs” box in the Graph Definition window.
An example showing both the low and high frequency C-V
measurements on one graph is shown in Figure 12.

Figure 11. A VLF C-V sweep of a MOScap at various frequences from
100mHz to 10Hz created using the MOS Capacitor VLF-CV Project.
This graph is from the vlf-moscap-vsweep-dual test (vlfcv_measure_
sweep_bias_fixed_range user module).

MOS Capacitor VLF-CV Project
The MOScap Project has three tests; all are DC bias sweeps
with two using SMUs for the VLF C-V test DC bias voltage
sweep (vlf-moscap-vsweep-dual and vlf-moscap-vsweep)
and the other using the 4210-CVU for higher frequency
testing (cvu-moscap-vsweep). An example of a MOScap
VLF-CV dual sweep generated with various test frequencies
ranging from 0.1 Hz to 10 Hz is shown in Figure 11. This test
was performed on a chuck at room temperature. This sweepis the result of executing the vlf-moscap-vsweep-dual test in

Figure 12. This graph is from the moscap-vsweep-hif-lof test, showing
the high frequency data from the 4210-CVU card along with the VLF
C-V data from the vlf-moscap-vsweep test.

the project. From the low frequency C-V data, characteristics
about the MOScap can be determined. The built-in mathfunctions are helpful in performing the analysis of thesedevices from the C-V data. The connection diagram for the
MOSCap is shown in Figure 2. The dual sweep functionality
aids in determining any hysteresis behavior in the inversion
region of the MOScap device, where frequency dependence
is also observed. Note that the SMU instrument measuring
the low current is not connected to the chuck. Connecting
the sensitive (i.e., low-current measurement) instrument to thechuck will result in noisier measurements.
In addition to the test that generates VLF C-V measurementson the MOScap, the project includes a test to measurehigh frequency C-V on the MOScap. The high frequency
C‑V measurements were generated using the 4210-CVU,
which has a test frequency range of 1kHz to 10MHz, with theexample data taken at 100kHz.

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R-C Circuit VLF-CV ProjectSome devices can be modeled as a parallel RC combination(connection diagram in Figure 13). The parallel resistanceis usually the leakage resistance of the device. In the R-C
Circuit VLF-CV Project, there are two tests for the RC device:
one is the test for a VLF C-V DC bias sweep (vlf-1nf-1gohm)
and the other tests sweeps votage and measures current
using an SMU (smu-vsweep). Figure 14 shows the resultsof performing a low frequency sweep on a 1.5nF and
1GΩ parallel combination. From the bias voltage and theresistance (1/Gp) of the device, the current can be calculated
in the Formulator and displayed on the graph. Excessive
leakage current can cause erroneous results if the current
exceeds the maximum current range for the particular RC
combination. To determine the DC leakage current of an
unknown DUT, use the smu-vsweep test, as describedin the section titled “Testing a Device with VLF C-V.”Performing Very Low Frequency Capacitance-Voltage Measurements on
High Impedance Devices Using the 4200A-SCS Parameter Analyzer

APPLICATION NOTE

More information about making optimal measurements is

Guidance for measurement performance across a range ofdescribed in the next section of this note.

D values is shown in Table 8. As the table shows, higher Dvalues reduce the accuracy of the reported C measurement.

4200-SMU 1
smu_src

4200-SMU 2
smu_sense

PreAmpSENSE
FORCE

Table 8. VLF C-V typical accuracy vs. D and current measure range forthe sense SMU instrument.
Force

PreAmp
SENSE
FORCE

0.01 D

0.1 D

1D

10 D

0.6 %

1.6 %

Not Recommended

Not Recommended

100 nA

1.4 %

10 %

Not Recommended

Not Recommended

10 nA

0.7 %

4%

6%

Not Recommended

1 nA

0.4 %

2%

2.6 %

3%

100 pA

0.8 %

0.6 %

0.6 %

2%

Triax cable
DUT
Force
Triax cable

Figure 13. Connection diagram for parallel RC test device.

1 µA“Not Recommended” means that the typical error is >10%.
For details on specific capacitance and frequency values, see
the VLF C-V Typical Specifications in Appendix A.
If the device is purely capacitive (very low to almost no
leakage current, a D <0.1), then just connect the DUT as
shown in Figure 7 (or Figure 2 if the DUT is on a wafer). After
connection, run the desired test(s). However, if the device
type is new, or its electrical characteristics are unknown,
then use the following procedure. This procedure provides
a guideline for determining reasonable parameter values forunknown test devices using the parallel (Figure 13). It also
Figure 14. Results of measuring parallel RC combination of 1.5nF
capacitor and 1GΩ resistor. This graph is from the vlf-1nF-1gohm test
(vlfcv_measure_dual_sweep_bias_fixed_range user module).

Testing a Device with VLF C-Vprovides guidance for evaluating results.

Setup
1.

must be direct with the supplied triax cables. No
switching or 4225-RPMs may be in the cable path from

Dissipation Factor

the SMU instrument Preamp to the DUT. The VLF C-V

The parallel resistance of the device under test is a key

method utilizes low current measurements, so ensure

aspect that determines the quality of the capacitancethat appropriate shielding and guarding are used. Use

measurement because it causes additional DC current totriax cable and eliminate, if possible, or minimize any

flow, which reduces measurement accuracy. This parallelunshielded or unguarded cable runs. For on-wafer

resistance at a given frequency is otherwise expressed asmeasurements, use triax probe manipulators andD, the dissipation factor. Here is the equation for the simple

guarded probe arms.

parallel model.
D = Reactance/Resistance = 1/ωRC = 1/2πfRC
where:
f is the test frequency, in Hz
R is the parallel resistance of the test device, in Ω
C is the capacitance of the test device, in farads

Connect the DUT as shown in Figure 2. The connection

2.

Open one of the example very low frequencyy tests or
project examples in the Library.

Initial Screening of DUT characteristics
3.

Choose the SMU instrument IV sweep, smu-vsweep
test, R-C Circuit VLF-CV Project. Choose voltage startand stop values for the sweep that match the desired
minimum and maximum DC bias voltages to be used for

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Performing Very Low Frequency Capacitance-Voltage Measurements on
High Impedance Devices Using the 4200A-SCS Parameter Analyzer

4.

VLF C-V tests. This test will help determine if the DUT

measurements to ensure that the results are reasonable

leakage is too high for repeatable, accurate results.

by evaluating the data in the Sheet as well as the

Run the smu-vsweep test. Review the results on thegraph or in the Sheet. For best results, the maximum

plotted values.
a.

current should be <±1µA. If the current >±1µA, reducethe bias voltages until the current <±1µA. Note thesevoltages for later testing. These voltages may need to beb.

means that the routine did not detect any errors, but
the validity of the data must still be assessed; go to
the next step. If there is a non-zero status value, refer

VLF-CV Project. Enter the desired test frequencies, using

to the Table 9 Error Codes to see the explanation

just five to ten points to span the desired frequency

and troubleshooting suggestions.

point test vlf-cap-one-point instead. Use the defaultc.

side of the Sheet, shows the current measure range= 0.3V and dcv_bias = 0.0V. This test will help determine

used for each point. If this range is 1E-6 (1µA) or

the dissipation factor D of the DUT.

lower, skip to the next step. If any of the measure

Run the vlf-cap-freq-sweep test. Review the results inrange values is 10E-6 (10µA) or larger, the results for

the Sheet. Review the value(s) in the meas_D column. If

these rows are suspect. Change the DC bias voltage|meas_D| <1, then the results are reasonable for the test

to reduce the current measure range used for thefrequencies and DC bias values that had <±1µA with thetest. For example, when running a voltage bias

smu_vsweep test. If |meas_D| <10 then results should

sweep, reduce the start and stop voltage used, forbe reasonable for dcv_bias = 0V. If |meas_D| >10, thenexample from ±5V to ±2V, and re-run the test. Verify

this present implementation of VLF C-V may providethat the new test uses a meas_irange 1E-6 (1µA) or

unacceptable results or results with fairly large errors

lower, then compare the results to the previous run(see Table 8). Note that reasonable values with a low D

taken with the 10µA range. Generally, the results withvalue at dcv_bias = 0 may provide larger errors as the DC

the 1 µA range are more accurate.

bias is increased.

VLF C-V Characterization of DUT
Configure the desired test, such as the bias sweep vlfcap-vsweep (Table 4) or frequency sweep vlf-cap-freqsweep (Table 5) in the Capacitor VLF-CV Project. Use thevoltage values determined in the previous step. As statedearlier, using expected_C = 0 will perform an auto-detect

8.

In the Sheet, check the current measurement range
used. The column meas_irange, located on the rightexpected_C = 0 and expected_R = 1E+12. Use acv_RMS

7.

Check the status returned from the test. Status = 0

Next, choose the vlf-cap-freq-sweep test, Capacitor

range. If only one test frequency is desired, use the single

6.

Review the plotted data, noting the overall shapeand Y-axis values.

adjusted again as described later in this procedure.
5.

APPLICATION NOTEd.

If the Y-axis scale shows the maximum of 7E22 or70E21, then an overflow has occurred on one ormore measurements in the test. Review the datain the Sheet, in the meas_Cp column, for entriesof 70E21 or 7E22. There are a few causes ofthe overflow:i.

If the overflow values are only at the start andof both the C and R values. For the other parameters,

end of the test, consider reducing the range

follow the description in the table corresponding to theof sweep values to omit the sweep points thattest (Tables 3 through 6).

cause the overflow values. Another option is

Run the test. Because of the Run History feature,
repeating the test keeps the old data, allowing forcomparison across multiple tests. The test parameters
used for each run are in the Settings tab of each Run
History. For unknown or new devices, review the

10 | WWW.TEK.COM

to specify appropriate values for expected_Cand expected R. Before choosing values for
expected_C and expected_R, let’s briefly
explain how these values affect the test. If theoverflow values are most or all of the rows inPerforming Very Low Frequency Capacitance-Voltage Measurements on
High Impedance Devices Using the 4200A-SCS Parameter Analyzer

the meas_Cp column, it is possible that an

2.

incorrect measure range was used for the test.
This means that the current measure range used

to the corresponding row in Table 8.

for the test was too small for the test parameters

Note that the higher D values are moreand DUT. The measure range used for the test

difficult to test.
3.

The current measure range for the sense SMUb) increase the acv_RMS = 0.3V; c) increase

expected_R values.

the test frequency.

To change the current measure range for a test,4.

supply an expected_C value that is larger thanidentical parameter values and review themeas_Cp column and choose a representative,

data. If the results are different across

non-overflow value and use it to calculate theeach run, this indicates that the system is

expected_C = 2 * chosen meas_Cp value. To

operating at or near the noise floor, whichchoose a value for expected_R, review themeans that the capacitance value of themeas_Gp column for a representative value. Set

test device is small, or the test device has aexpected_R = 1/(2 * chosen meas_Gp).

higher D value (Table 8).

If one or more of the meas_Cp values is negative:
Ensure that the DUT connections are good.

ii.

The D may be too high, or the DC current
leakage is too high compared to thecapacitance.
1.

Review the Sheet for meas_D andmeas_irange values. If D > ~10 and or
meas_irange is ≥10nA, the results may have

If the meas_Cp values seem noisy or
inconsistent, append several tests withthe meas_Cp value. Review the values in thei.

Try one or more of the following
adjustments: a) reduce the DC bias voltage;

instrument is based on the expected_C ande.

Consult Table 8. Compare the current
measure range (in the meas_irange) column

is contained in the meas_irange in the Sheet.

ii.

APPLICATION NOTE

5.

If none of these adjustments provides
reasonable results, try a higher frequency
C-V test using the 4210-CVU, if available.

9.

Add tests, such as the capacitance vs. time (test vlfcap-time) or more DC bias sweeps at additional test
frequencies. Recall that data may be saved in .xls or.csv file formats by using the Save Data button in the
Analyze pane.

a larger error.

WWW.TEK.COM | 11

Performing Very Low Frequency Capacitance-Voltage Measurements on
High Impedance Devices Using the 4200A-SCS Parameter Analyzer

APPLICATION NOTE

Table 9. VLF C-V error codes and descriptions.
Error
Code
0

Description

Explanation and Troubleshooting Recommendation

Test executed with no errors

No software or operational errors were detected.

-16001

smu_src is out of range

Specified SMU instrument is not available in the chassis. For example, if SMU5 is entered, but there are only
four SMU instruments in the 4200 chassis, then this error will occur. Modify SMU instrument string to anavailable SMU instrument number: SMU1, SMU2, SMU3 …

-16002

smu_sense is out of range

Specified SMU instrument is not available in the chassis. For example, if SMU5 is entered, but there are only
four SMU instruments in the 4200 chassis, then this error will occur. Modify SMU instrument string to anavailable SMU number: SMU1, SMU2, SMU3 …

-16003Frequency is out of range.

Ensure that the test frequency is within the range of 10mHz to 10Hz, inclusive-16004

acv_RMS is out of range

Make sure that the RMS voltage is within the range of 0.01V to 3.0V, inclusive-16005dcv_bias is out of range

Modify the DC or AC voltage bias to ensure that the ±20V maximum is not exceeded. Maximum negative
voltage = –20 + (AC voltage * )Maximum positive bias voltage = 20 – (AC voltage * √_2)

-16006

hold_time is out of range

This error is unused for the VLowFreqCV routines.

-16007delay_time is out of range

This error is unused for the VLowFreqCV routines.

-16008

Too few points per period

This error indicates that the test was aborted by the operator.

-16009Output array sizes are not equal,
Make sure all output array sizes are the same value and are not greater than 4096.
or are larger than 4096.

-16010Over range indication detected.

-16011Results array size is less than the
Increase the size of all output arrays to be equal to the number of points in the sweep.
number of points in the sweep.

-16012

Cannot estimate expected_C or expected_R. This error occurs only when expected_C = 0. Input a estimated
Could not collect enough data to
non-zero value for expected_C. Review the meas_Cp values in the Sheet for non-overflow values. Set
perform measurement.
estimated_C = 2 * non-overflow meas_Cp-16013

Unable to allocate memory.

This error is unused for the VLowFreqCV routines.

-16014Current range is out of range.

This error is unused for the VLowFreqCV routines.

-16015

Irange_sense and expected_C
cannot be 0 at the same time

This error is unused for the VLowFreqCV routines.

-16016

expected_C is out of range

expected_C must be 0 (auto-detect C) or between 1E-15 and 1E-3, inclusive.

-16017This test requires preamp isconnected to smu_sense

Make sure preamp is connected to each SMU used in the test. If reconnecting preamps, run run KCON andchoose “Update PreAmp and RPM Configuration” in the Tools menu.

-16018Invalid start, stop, step DC bias
sweep values.

Correct the values for the voltage bias sweep. dcv_bias_step cannot be 0, unless dcv_bias_start = dcv_bias_
stop. If dcv_bias_start = dcv_bias_stop, then dcv_bias_step must = 0.

-16019Output array sizes are less thannumber of points in sweep.

Increase the size of all output arrays to be equal to the number of points in the sweep.

-16020Invalid combination of start, stop, Correct the values for the voltage bias sweep. dcv_bias_step cannot be 0, unless dcv_bias_start = dcv_bias_
step dc bias sweep values.
stop. If dcv_bias_start = dcv_bias_stop, then dcv_bias_step must = 0.

12 | WWW.TEK.COM

Current measurement over-range occurred and returned values are set to 7E22 (70E21).
Troubleshooting:
Review the value in the meas_CP column of the Sheet, looking for the overflow values (7E22 or 70E21). Follow
the process given in Step 8d.

Performing Very Low Frequency Capacitance-Voltage Measurements on
High Impedance Devices Using the 4200A-SCS Parameter Analyzer

APPLICATION NOTE

Guidelines for Making Optimal
Measurements and Troubleshooting
Techniques

C and R of the device under test. The estimated R and C

When making high impedance, very low frequency C-V

code -16010 for more information). However, in some cases,

measure­ments using the SMU instruments, various

entering a non-zero estimated capacitance for expected_C

techniques must be used to optimize measurement accuracy.

may provide better results for higher D devices or larger DC

These techniques include implementing low current

bias tests. To calculate a value of expected_C, multiply a non-measurement practices and choosing the appropriate

overflow value from the meas_Cp column by two and entersettings in the software.

values determine the SMU instrument measurement range. If
these values are chosen incorrectly, measurement errors or
measurement range overflow may result (see Table 9, error

this value into the test definition expected_C.

Implementing Low Current Measurement
Techniques

To determine if a device is compatible with the present

Because using the very low frequency impedance

performing an I-V test using the smu-vsweep test, R-C

measurement method involves measuring picoamp

Circuit VLF-CV Project. Use the same test voltages in the I-V

to femtoamp current levels, low current measurement

sweep that will be used in the impedance measurements.

techniques must be implemented. Use the triax cables

Additionally, performing a single measurement (test vlf-cap-

VLF C-V approach, measure the DC resistance of the DUT,

that come with the 4200A-SCS, which are shielded andone-point) or frequency sweep (test vlf-cap-freq-sweep) at

will allow making a guarded measurement, if necessary.

a DC bias of 0V will determine the D of the device. Refer to

To reduce the noise due to electrostatic interference,“Testing a Device with VLF C-V” and Table 8 for additional

make sure the device is shielded by placing it in a metal

information.

enclosure with the shield connected to the Force LO terminalof the 4200A-SCS. Detailed information on low current
measurement techniques can be found in Keithley’s Low

Conclusion

Level Measurements Handbook. Also, ensure that the triax

The 4200A-SCS contains a tool for performing very low

cable is directly connected to the DUT or probe pins; do notfrequency C-V measurements using the SMU instruments

use any switching matrix or 4225-RPM in the SMU instrument

and preamps. This method enables the user to perform low

signal path.

capacitance measurements at a precise test frequency in therange of 10mHz to 10Hz. The Clarius software included with

Choosing the Correct “expected_C” and“expected_R” Values

the system enables the user to execute these low impedance

In most cases, expected_C should be 0 and the expected_R

the DUT. When combined with the 4210-CVU Capacitance= 1E12 (both are the default values). When expected_C = 0,

Voltage Unit, the 4200A-SCS offers the user a single system

the VLF C-V routine will determine estimated values for boththat can perform both high and low frequency measurements.

measurements easily and extract important parameters about

WWW.TEK.COM | 13

Performing Very Low Frequency Capacitance-Voltage Measurements on
High Impedance Devices Using the 4200A-SCS Parameter Analyzer

Appendix A
Very Low Frequency C-V Typical Specifications
MEASUREMENT FUNCTIONS
Measurement Parameters: Cp+Gp, Cp+D, Cs, Rs+Cs, R+jX, Z,
theta, frequency, voltage, time.
Connector Type: Two triax (female) connectors.
TEST SIGNAL
Frequency Range: 10mHz to 10Hz.
Minimum Resolution: 10mHz
Signal Output Level Range: 10mV rms to 3V rms.
DC BIAS FUNCTION
DC Voltage Bias:
Range: ±20V1.
Resolution: 0.5mV.
Accuracy: ±(0.02% + 1.5mV).
Maximum DC Current: 1µA.

TYPICAL MEASUREMENT ACCURACY2Frequency

10 Hz

1 Hz

100 mHzSWEEP CHARACTERISTICS
Available Test Types: Linear bias voltage sweep (up or down),
frequency list sweep, sample (time), single point
Maximum Number of Measurement Points: 512.
INCLUDED LIBRARIES• C-V, C-t and C-f modules• Includes test and projects for:–– Capacitor–– MOSCAP–– nMOS FET–– R-C circuit
REQUIRED HARDWARE and SOFTWARE• 4200A-SCS• Two SMU instruments, either 4200-SMU or 4210-SMU, with Preamplifiers (4200-PA)

14 | WWW.TEK.COM

APPLICATION NOTE

10 mHzMeasured
CapacitanceC Accuracy @300 mV rms1

C Accuracy @30 mV rms1

1 pF

10%

13%

10 pF

10%

10%

100 pF

5%

5%
9%

1 nF

5%

10 nF

5%

5%

1 pF

2%

2%

10 pF

1%

2%

100 pF

2%

1%

1 nF

2%

1%

10 nF

2%

2%

1 pF

2%

3%

10 pF

2%

2%

100 pF

2%

2%
2%

1 nF

1%

10 nF

2%

1%

1 pF

5%

10%

10 pF

1%

2%

100 pF

1%

1%

1 nF

1%

1%

10 nF

2%

2%

NOTES
1. ±20V maximum includes the DC Bias and the AC Test Signal peak__voltage. Maximum negative bias voltage = –20 + (AC __voltage * √ 2 ).
Maximum positive bias voltage = 20 – (AC voltage * √ 2 ).
2. Test device must have dissipation factor DX <0.1. All data shown for
DC Bias voltage = 0V.
All specifications apply at 23°C ±5°C, within one year of calibration, RH
between 5% and 60%, after 30 minutes of warmup.

Performing Very Low Frequency Capacitance-Voltage Measurements on
High Impedance Devices Using the 4200A-SCS Parameter Analyzer

APPLICATION NOTE

WWW.TEK.COM | 15

Performing Very Low Frequency Capacitance-Voltage Measurements on
High Impedance Devices Using the 4200A-SCS Parameter Analyzer

APPLICATION NOTE

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