Conductivity

Conductivity Measurements

The Conductivity measurement type allows you the perform (four-wire) conductivity measurements. This page serves to detail what means what on the configuration panel.

Instrument Channels

Name	Required?	Description
Ground	Only for SPA use	SMU channel to use as ground/common - only relevant if using an SPA
Source-Drain	Always required	SMU channel to use for sourcing source-drain current and measuring source-drain voltage
Source-Gate	Only if gate voltage set	SMU channel to use for sourcing source-gate voltage and measuring source-gate/leakage current
Four-Point Probe 1	Optional	Voltmeter channel to use for measuring a four-point probe voltage
Four-Point Probe 2	Optional	Voltmeter channel to use for measuring a second four-point probe voltage
Thermometer	Optional	Thermometer channel to use for measuring temperature during the measurement

Measurement Logic

In general the measurement works by sweeping over values of source-drain current then measuring the voltages that develop across the device as a result. (i.e. source current, measure voltage). The voltage value that is eventually used for fitting and extracting a value of conductivity will depend on how the instruments are configured. This is defined below in the step-by-step logic.

Before explaining the logic step-by-step, we shall define the following abbreviations:

SDC: Source-Drain Channel

SGC: Source-Gate Channel

FPP1: Four-Point Probe Channel 1

FPP2: Four-Point Probe Channel 2

1. Switch off all configured channels (SDC, SGC, FPP1, FPP2)
2. Configure all channels to use the specified integration time for measurements
3. If gate voltage is enabled, set SGC to source specified source-gate voltage
4. Generate list of current values to sweep over
5. Set SDC to source first current value in list
6. Turn on all channels
7. Select first value in current list to be I
8. Set SDC to source I amps of current
9. Wait for the specified delay time
10. Measure voltages:
    • SDC voltage
    • FPP1 voltage (if configured)
    • FPP2 voltage (if configured)
11. Determine voltage to use for conductivity calculation
    • If neither FPP1 nor FPP2 are configured, use SDC voltage
    • If only one of FPP1 or FPP2 is configured, use its voltage
    • If both FPP1 and FPP2 are configured, use the difference between their voltages
12. If values are left, select next value in current list to be I and go to step 8
13. Turn off all channels
14. End measurement

Parameters

Conductivity measurements have three "groups" of parameters:

1. Basic
2. Source-Drain
3. Source-Gate

1. Basic

This is where we configure the basic parameters of the measurement. These are:

Name: The name to give the measurement.

Integration Time: The integration time, in seconds, to use when measuring.

Delay Time: The time, in seconds, to wait between setting the source-drain current and measuring the resultant voltages.

2. Source-Drain

This is where we configure the set of current values to sweep over for the measurement.

Start Current: The current value to start the sweep at, in Amps.

Stop Current: The current value to end the sweep at, in Amps.

No. Steps: The total number of current values to use going from Start to Stop.

Scaling: How the current values in the sweep should be spaced. Linear means equal step sizes, for instance.

Sweep Both Ways: If checked, two current sweeps will be run. One going from Start to Stop followed by another going from Stop to Start.

3. Source-Gate

This panel lets you optionally define a source-gate voltage to apply during the measurement.

Active: If checked, then the configured source-gate voltage will be used during the measurement.

Voltage: The source-gate voltage to use, in Volts - ignored if "Active" is not checked.