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.
- 1 Drivers/Devices
- 2 Sweep modes
- 3 Supported parameters
- 4 Pulsed mode
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.
Every Device Class that is implemented as SMU should have at at least two Sweep modes: 'Voltage [V]' and 'Current [A]'. Please choose the mode according to what you like to apply. If you like to apply voltages and read currents, then select 'Voltage [V]'. If you like to apply currents and read voltages, please select 'Current [A]'
Additional parameters can be supported by a Device Class, depending on the functionality of the device. The exact implementation of the provided options can be seen in the code of the Device Class by clicking 'Open/Modify'.
Device Class 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]
Device Class 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.
Device Class 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:
- '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.
Device Class 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. At the moment 'Range' is related to current. A range for voltage is not yet supported.
Device Class 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
Stop value [V] or [A]
The SweepEditor of the SMU module allows to set a stop time. If this stop time is not zero, SweepMe! will set the applied Sweep value, correponding to the Sweep mode, to the given Stop value after taking a measurement point. This functionality is provided by SweepMe! so that there is no need to implement it via the Device Class.
Device Class 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 [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.
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.
After selecting pulse mode, four further options pop up:
Off level in V or A
Here, you can choose the off 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
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
This is the time between two pulses.
Measurement ratio in %
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.