SMU

The SMU module can be used to interface with source-measuring units that can apply voltages and read currents at the same time (and vice versa). Such devices are typically used to investigate semiconductor devices such as LEDs, solar cells, and transistors.

Drivers/Devices

A list of available drivers can be found here: https://sweep-me.net/devices/ The documentation for a particular instrument be found on the webpage of each driver.

Sweep modes

Every Driver that is implemented for the module "SMU" should have at at least two Sweep modes: 'Voltage in V' and 'Current in A'. Please choose the mode according to what you like to apply. If you like to apply voltages and read currents, then select 'Voltage in V'. If you like to apply currents and read voltages, please select 'Current in A'

Options

Additional parameters are supported by the SMU driver, depending on the functionality of the device. The exact implementation of the provided options can be seen in the code of the SweepMe! driver by clicking 'Open/Modify'.

Route out

Driver parameter key: 'RouteOut'

Some SMUs provide output connectors at the front panel and at the rear side of the instrument. We recommend to use 'Front' and 'Rear' as selectable options.

Compliance [A] or [V]

Driver parameter key: 'Compliance'

Compliance is feature that most SMUs support. The SMU will automatically make sure that in any case a current or a voltage is not exceeded, preventing damage to your device under test. In case you use Sweep mode = "Voltage [V]", the compliance is a current in A. In case you use Sweep mode = "Current [V]", the compliance is a voltage in V.

Speed/Integration

Driver parameter key: 'Speed'

This parameter can be used to adjust the time used for integration of one measurement value and thus influences the speed of the measurement. The integration time is often given in terms of 'Number of Power-Line-Cycles' (NPLC). The period of a 'Power-Line-Cycle' (PLC) is related to the power frequency. For example, a power frequency of 50 Hz corresponds to 20 ms. Typically, 'Fast', 'Medium' and 'Slow' are provided as options in the graphical user interface and we recommend to following relation:

• 'Very fast' = 0.01 NPLC
• 'Fast' = 0.1 NPLC
• 'Medium' = 1 NPLC
• 'Slow' = 10 NPLC

Please note that the implementation might differ in each Device Class and one should look up the code of the Device Class to see what is actually done.

CUstom NPLCs have to be implemented by modifying the corresponding Device Class. Just copy the folder of the Device Class you like to modify and give it a new name. You can add further options to the ComboBox of 'Speed/Intgration' and then you have to modify the DeviceClass accordinfly if your custom NPLC condition is chosen by the user.

Current range

Driver parameter key: 'Range'

SMUs have different ranges for measuring voltages and currents to ensure accurate results when these parameters change over many orders of magnitude. Most users use some kind of auto ranging function that is provided by the SMU. However, in some case it might be needed to use a fixed range to prevent the change of the range during the measurement or to limit the lower range that is automatically used by the SMU. 'Range' is related to current.

Voltage range

Driver parameter key: 'RangeVoltage'

Similar to the current range, one can set the range for the voltage.

Average

Driver parameter key: 'Average'

The quality of noisy measurements can be improved by using averaging over multiple measurement results. Most SMUs provide this functionality via an internal operation. If an instrument does not provide such a function, one has to create a Device Class that measures multiple time and just returns the averaged values

4wire

Driver parameter key: '4wire'

4wire measurements, 4-point measurements, Four-terminal sensing, or 4-point probes method are different names for a method that can drastically reduce the influence of a series resistance if the device under test has a resistance that is already close or below the resistance of cables, connectors, electrodes, etc. If this option is selected, one has to use a special wiring as explained in this Link

Skip if compliance is reached

This functionality is internally provided by the Module. For example, the Sweep mode is "Voltage in V" and the compliance is set to 100 mA. Once, the compliance is reached, defined by a current that exceeded 99% of the compliance value, i.e. > 99 mA in this example, SweepMe! will remember the critical voltage of this point. All further voltages that are higher than the critical voltage will be automatically skipped, preventing unnecessary stress to your device. 'Skip if compliance is reached' used different critical voltages for positive and negative applied voltages or currents. This functionality works best if your device has a monotonically increasing current-voltage characteristic. In case your devices has a regime of negative differential resistance, values might be skipped that are still of interest.

Please test this functionality first in a safe operation environment, e.g. at low compliance and with an inexpensive test device to make sure it works correctly in your case.

Pulsed mode

To switch on the pulse mode, the check box at the bottom of the module can be used. Pulse mode is only available if a driver for the SMU module supports this. Otherwise, the check box is greyed out.

The sequence of pulses and their levels is still programmed via Sweep mode and Sweep value of the SMU module. For example, if you select the Sweep editor, you can program number of pulses or pulsed IV curves just as it is done normally.

The following GUI options are available:

Enable pulse

Driver parameter key: 'CheckPulse'

Check the box "Use pulse mode" to tell the driver to do a pulsed measurement.

Pulse count

Driver parameter key: 'PulseCount'

Use this field to enter the number of consecutive pulses that are performed for the parameters below.

Off level in V or A

Driver parameter key: 'PulseOffLevel'

Here, you can choose the off level/ base level of the pulse in V or A according to your sweep mode. For example, if you make a voltage sweep, the off level is given in V. In order to go back to 0 V after each pulse, plesase insert 0 V.

On time in s

Driver parameter key: 'PulseOnTime'

This is the time that the pulse has the voltage given by the value that is selected in the Sweep value field of the SMU module. If you use the Sweep editor, each value that is programmed is also applied as pulse, one after another.

Off time in s

Driver parameter key: 'PulseOffTime'

This is the time between two pulses.

Pulse period

Driver parameter key: 'PulsePeriod'

This parameter can be available as alternative to "On time in s" and "Off time in s" to define the length of the entire pulse including on and off state.

Pulse delay

Driver parametewr key: 'PulseDelay'

This field can be used to delay the pulse with respect to the trigger which can be important to optimize the pulsing of two synchronize channels.

Measurement start

Driver parameter key: 'PulseMeasStart'

This field can be used to define the start of the measurement in % related to the on time of the pulse. The measurement is typically done at the end of a pulse where the current and voltage settle to a constant value. This parameter allows to define when acquiring data can start.

Measurement ratio in %

Driver parameter key: 'PulseMeasTime'

Some SMUs can specify which ratio of the pulse is used to measure voltage and current. For example, 50% means that the second half of the pulse is used to perform the measurement. The first part of the pulse is discarded because the device to be measured might need some time to reach a certain steady state after charging.

Rise time

Driver parameter key: 'PulseRiseTime'

This field can be used to define in which time the pulse changes from off to on level.

Fall time

Driver parameter key: 'PulseFallTime'

This field can be used to define in which time the pulse changes from on to off level.

Impedance

Driver parameter key: 'PulseImpedance'

This field can be used to define the impedance of the device/sample that some instruments need to apply the correct voltage.

List sweep

Some SMUs support the measurement of a full list sweep or also called staircase sweep. In contrast to a single-spot measurement, the SMU takes the values of the entire sweep before data is returned to the computer. This leads to faster measurements and more accurate timing between the adjacent points, but also reduces the flexibility and data is only available after the sweep.

If the driver supports it, one can select "List sweep" in the field Sweep value. Then, the sweep is not created by the Sweep editor or any external source but by the fields in the section List sweep of the module.

Type

Driver parameter key: 'ListSweepType'

Use this dropdown box to select whether a linear sweep or a a custom sweep is created. The selection depends on whether the driver provides these options.

Start value

Driver parameter key: 'ListSweepStart'

Use this field to enter the start voltage or current of the sweep.

End value

Driver parameter key: 'ListSweepEnd'

Use this field to enter the end voltage or current of the sweep.

Step width or points

Driver parameter key: 'ListSweepStepPointsType'

Use the fields to indicate whether you want to enter a step width or points that can be linearly or logarithmically distributed. The options here also depend on the driver. Then, enter the step width of the voltage/current or enter the number the points depending on the selected mode.

Step value

Driver parameter key: 'ListSweepStepPointsValue'

Use this field to enter the step width value or the number of points depending on the selection in the field "Step width or points".

Dual sweep

Driver parameter key: 'ListSweepDual'

If checked, the sweep will contain of a forward and a backward sweep, going from start value to end value and back to start value.

Hold time in s

Driver parameter key 'ListSweepHoldtime'

The hold time specifies the time each voltage or current is applied, but the exact definition can be different for each driver and instrument. Please check the driver documentation and the manual of the instrument.

Delay time in s

Driver parameter key 'ListSweepDelaytime'

The delay time can specify the time before the measurement is taken for each point the time after the measurement before the next value is applied. The exact definition can be different for each driver and instrument. Please check the driver documentation and the manual of the instrument.

Custom values

Driver parameter key: 'ListSweepCustomValues'

Use this text box to enter comma-separated values for the list sweep. Whether the text box is visible depends on the selection of the sweep type and whether the driver supports this option.