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Four-Point Probe User Manual


Four-Point Probe

  • Easy-to-Use
  • Non-Destructive Testing
  • Built-In SMU

Available From £2200

1. Overview


The Ossila Four-Point Probe System is part of the Institute of Physics award-winning Solar Cell Prototyping Platform*. It is a low-cost solution for rapid and reliable measurement of the sheet resistance, resistivity, and conductivity of materials.

Click for more information about The Ossila Solar Cell Prototyping Platform and to see related products.

The system includes a four-point probe, source measure unit, and easy-to-use PC software — enabling more laboratories to measure sheet resistance for an affordable price. The probe head uses gentle spring-loaded contacts instead of sharp needles, minimising damage to delicate samples (e.g., polymer films that are only a few nanometres thick).

It is operated via the specifically designed PC software, which automatically calculates appropriate geometrical correction factors for the sample to give accurate values for the sheet resistance. If the sample thickness is provided, the software will further calculate resistivity and conductivity.

Ossila Four-Point Probe

2. EU Declaration of Conformity (DoC)


Please refer to the full PDF or print user manual for the EU Declaration of Conformity (DoC).

3. Safety


3.1 Warning

The absolute maximum input voltage for the Vsense channels is ±12 V. Do NOT apply input while not powered.

3.2 Use of Equipment

The Ossila Four-Point Probe System is designed to be used as instructed. It is intended for use under the following conditions:

  • Indoors in a laboratory environment (Pollution Degree 2).
  • Altitudes up to 2000m.
  • Temperatures of 5°C to 40°C; maximum relative humidity of 80% up to 31°C.

The unit is supplied with a 24 VDC power adapter with a power cord for the country of purchase, in accordance with European Commission regulations and British Standards. Use of any other electrical power cables, adaptors, or transformers is not recommended.

3.3 Hazard Icons

The following symbols can be found at points throughout the rest of the manual.

Table 3.1 Hazard warning labels used in this manual.

Symbol Associated Hazard
Electrical shock warning symbol Electrical shock

3.4 General Hazards

Before installing or operating the Ossila Four-Point Probe System there are several health and safety precautions which must be followed and executed to ensure safe installation and operation.

3.5 Power Cord Safety

Electrical shock warning symbol

Emergency power disconnect options: use the power cord as a disconnecting method and remove from wall. To facilitate disconnect, make sure the power outlet for this cord is readily accessible to the operator.

3.6 Servicing

If servicing is required, please return the unit to Ossila Ltd. The warranty will be invalidated if:

  • Modification or service has been carried out by anyone other than an Ossila engineer.
  • The Unit has been subjected to chemical damage through improper use.
  • The Unit has been operated outside the usage parameters stated in the user documentation associated with the Unit.
  • The Unit has been rendered inoperable through accident, misuse, contamination, improper maintenance, modification, or other external causes.

3.7 Health and Safety - Servicing

Electrical shock warning symbol

Servicing should only be performed by an Ossila engineer. Any modification or alteration may damage the equipment, cause injury, or death. It will also void your equipment’s warranty.

4. Requirements


Table 4.1 details the power requirements for the system, and the minimum computer specifications for the Ossila Sheet Resistance software.

Four-Point Probe System requirements.

Power 24 VDC
Operating Systems Windows 10 or 11 (32-bit or 64-bit)
CPU Dual Core 2 GHz
RAM 2 GB
Available Hard Disk Space 194 MB
Monitor Resolution 1440 x 900
Connectivity

USB 2.0

Ethernet (requires DHCP)

5. Unpacking


5.1 Packing List

The standard items included with the Ossila Four-Point Probe System are:

  • The Ossila Four-Point Probe.
  • 24 VDC power adapter.
  • USB-B cable.
  • USB memory stick pre-loaded with the user manual, software installer, QC data, and USB drivers.
  • 400 – 450 nm FTO coated glass substrate (60 x 60 x 2.2 mm).
  • 10 kΩ resistor test head.

5.2 Damage Inspection

Examine the components for evidence of shipping damage. If damage has occurred, please contact Ossila directly for further action. The shipping packaging will come with a shock indicator to show if there has been any mishandling of the package during transportation.

6. Specifications


The Four-Point Probe System measurement specifications are shown in Table 6.1 and Table 6.2, and the physical specifications are shown in Table 6.3.

Table 6.1 Four-Point Probe System measurement specifications.

Voltage Range ±100 μV to ±10 V
Current range ±1 µA to ±200 mA (5 ranges)
Sheet resistance range 100 mΩ/square to 10 MΩ/square

Table 6.2 Accuracy and precision of the Four-Point Probe System at each resistance range. Accuracy is the maximum deviation from the true value. Precision is the maximum deviation between identical measurements (useful for comparative measurements).

Sheet Resistance Accuracy Precision Measured at Range
100 mΩ/square ±8% ±3% 200 mA
1 Ω/square ±2% ±0.5% 200 mA
10 Ω/square ±1% ±0.5% 200 mA
100 Ω/square ±1% ±0.05% 20 mA
1 kΩ/square ±1% ±0.03% 20 mA
10 kΩ/square ±1% ±0.02% 2 mA
100 kΩ/square ±2% ±0.05% 200 μA
1 MΩ/square ±8% ±0.5% 20 μA
10 MΩ/square ±30% ±5% 20 μA

Table 6.3 Four-Point Probe System physical specifications.

Probe Spacing 1.27 mm
Rectangular Sample Size Range

Long Edge Minimum: 4 mm

Short Edge Maximum: 60 mm

Circular Sample Size Range (Diameter) 4 mm to 76.2 mm
Maximum Sample Thickness 10 mm
Overall Dimensions

Width: 145 mm

Height: 150 mm

Depth: 240 mm

7. System Components


The Four-Point Probe System is comprised of: the Ossila Four-Point Probe System (Figure 7.1) and the Ossila Sheet Resistance Software (Figure 7.2).

Ossila Four-Point Probe
Figure 7.1 The Ossila Four-Point Probe.
The Ossila Sheet Resistance Lite software
Figure 7.2 The Ossila Sheet Resistance Lite software.

8. Installation


  1. Install the Ossila Sheet Resistance Lite software on your PC.
    1. Run the file ‘Ossila-Sheet-Resistance-Lite-Installer-vX-X-X-X.exe’ on the USB memory stick provided.
    2. Follow the on-screen instructions to install the software.
  2. Connect the 24 VDC power adaptor to the power socket on the rear of the unit.
  3. Connect the unit to your PC using the provided USB-B cable, or an Ethernet cable if preferred. If you are using a USB connection and the unit is not detected, please refer to the SMU USB Driver Installation Guide found on the USB memory stick.
The Ossila Sheet Resistance Lite software and Source Measure Unit USB drivers can also be downloaded from the Software and Drivers page.

9. Operation


9.1 Taking a Measurement

  1. Place your sample in the centre of the vertical stage.
  2. Raise the platform until the probes have retracted approximately half-way into their housing.
    1. One full turn of the micrometer (after initial contact is made) is a good way to ensure that there is good electrical contact between the probes and your sample.
    2. Ensure that the probes make contact with the centre of the sample.
    3. For rectangular samples, the longest edge should be aligned parallel to the probes.
  3. Start the Ossila Sheet Resistance Lite software. The window shown in Figure 9.1 will open.
  4. Set the appropriate settings in the software (explained in more detail in Section 9.2).
  5. Click the on/off toggle button.
    1. The system will attempt to pass a current between through the sample.
    2. If a current can be passed though the sample, the system will measure the sheet resistance, which will be displayed in the program.
    3. If a thickness has been provided, the resistivity and conductivity will also be displayed.
    4. The measurement will continue until the on/off toggle button is clicked or the software is closed.
The Ossila Sheet Resistance Lite software
Figure 9.1 Ossila Sheet Resistance Lite software.

9.2 Software Settings

There are several settings in the program which must be filled in before taking a measurement. These are found in the column on the left of the window, as shown in Figure 9.1.

9.2.1 Basic Settings

Basic settings menu
Figure 9.2 Basic settings.
(I) System Address

Select the COM port or IP address of the connected unit you intend to use (USB and Ethernet connection respectively). This box will be populated automatically with the addresses of any units connected to the computer or network.

(II) Geometry

Select the geometry of the sample being measured. This is required to calculate the geometrical correction factor for the current sample.

If the shape of the sample is irregular, consider whether it is closer to rectangular or circular and then estimate what size of that shape could fit within the sample

(III) Long Side (Rectangular Sample)

Sets the length of the long side of the sample in mm (if the sample is rectangular). This is required for calculating the appropriate geometrical correction factor.

(IV) Short Side (Rectangular Sample)

Sets the length of the short side of the sample in mm (if the sample is rectangular). This is required for calculating the appropriate geometrical correction factor.

(V) Diameter (Circular Sample)

Sets the diameter of the sample in mm (if the sample is circular). This is required for calculating the appropriate geometrical correction factor.

(VI) Thickness (Optional)

Sets the thickness of the conductive layer being measured in µm.

This enables the calculation of the resistivity and conductivity of the sample, as well as calculating a thickness correction factor for samples with a thickness greater than 40% of the probe spacing. It is not needed for sheet resistance measurements of samples with a thickness less than 40% of the probe spacing, thus can be set to 0 if not known.

9.2.2 Saving Results

Quantity of readings to save
Figure 9.3 Save Settings.
(I) Readings to Save

Set the number of measurements to save.

(II) Save

Opens a file dialog window to choose where to save the data.

(III) Saved Data Format

The applied current, measured voltage, and measured sheet resistance are saved to the file. The mean and standard deviation of the sheet resistance measurements are saved to the same file, placed after the data readings.

If a thickness is provided, the resistivity and conductivity values are also saved.

9.2.3 Advanced Settings

Advanced settings can be found by checking the “Use Advanced Settings” box below the basic settings. This will also show the voltage and current set between the outer probes, and voltage measurements between the inner probes. Note that these settings will only be used whilst “Use Advanced Settings” box is ticked, default settings will be used when not ticked.

Advanced settings options
Figure 9.4 Ossila Sheet Resistance software showing advanced settings options.
Advanced settings menu
Figure 9.5 Advanced settings.
(I) Probe Spacing

Sets the spacing between each of the probes in mm. This is required to determine the appropriate geometric correction factors for the sample being measured.

(II) Samples per Point

Select the number of samples to be taken for each measurement. A higher number of samples per point will improve the accuracy and precision of the measurement. However, this will increase the time taken for it to be performed.

(III) Current Range

Select whether the appropriate range should be automatically determined or whether a specific range of currents is used. This defines the upper limit and accuracy of current measurements that can be performed by the unit.

Autorange will enable the measurement to automatically switch ranges as needed. The maximum current values for each range are shown in the range selection box.

(IV) Polarity

Sets whether the measurement polarity is positive or negative.

(V) Voltage Limit

Sets the maximum voltage the measurement can apply to the sample in volts. If the voltage limit is exceeded the measurement will stop.

(VI) Current Limit

Sets the maximum current the measurement can apply to the sample in mA. If the current limit is exceeded the measurement will stop.

(VII) Reset to Default

Clicking this button will reset all advanced settings to their default values.

10. Test Head


The system is shipped with a test head that can be used to verify the correct operation the system by providing a reference measurement. It is designed to give a response of 10 kΩ when a sheet resistance measurement is performed on it using the system.

Four-Point Probe test head
Figure 10.1 Four-Point Probe test head.

10.1 Taking a Measurement

  1. Replace the four-point probe head on the system with the test head.
    1. To do this first disconnect the cables, then remove the 5 screws attaching the head to the system.
    2. Remove the four-point probe head and place the test head on the system.
    3. Attach the test head using the screws, then connect the cables.
  2. Plug in and switch on the system.
  3. Allow at least 30 minutes for the system to warm up.
  4. Start the Sheet Resistance Lite software and enter the settings in Figure 10.2. The Long Side and Short Side can be any value greater than 55 mm, this is to ensure that no correction factor is applied to the measurement.
  5. Measurement settings for the test head
    Figure 10.2 Measurement settings for the test head.
  6. Start the measurement.
  7. The system should measure a sheet resistance between 9.9 and 10.1 kΩ/square (within 1% of 10 kΩ/square).
Example measurement of the test head
Figure 10.3 Example measurement of the test head.

11. Troubleshooting


Most of the issues that may arise will be detailed here. However, if you encounter any issues that are not detailed here, then please contact Ossila.

11.1 Installation and Setup

Problem Possible Cause Action
No power/display The power supply may not be connected properly. Ensure the system is firmly plugged into the power supply, and that the plug is connected to both the adaptor and a working power socket.
The power supply adaptor has a fault. Contact Ossila for a replacement power supply adaptor.
Software does not start The wrong version of Windows is installed on the computer. Install the software on a computer with Windows Vista or newer.
The software has not installed properly. Try reinstalling the software.
Cannot connect to the system via USB The USB cable may not be connected properly. Ensure the USB cable is firmly plugged in at both ends.
The USB cable may not be connected to a working USB port. Try connecting the unit to a different USB port on the computer.
The USB cable is defective. Try using a different USB-B cable, and contact Ossila if necessary.
Cannot connect to the system via network The MAC address of the unit is not registered with the internal network. Register the system on the network using the MAC address obtained via a USB connection (see Source Measure Unit manual).
The Ethernet cable may not be connected properly. Ensure the Ethernet cable is firmly plugged in at both ends.
The Ethernet cable is defective. Try using a different Ethernet cable.

11.2 Error Messages and Warnings

Message Description
Current limit exceeded The measured current is greater than the set current limit.
Voltage limit exceeded The output voltage is greater than the set voltage limit.
Unable to measure sample, resistance outside of measurable range The system is unable to pass a current through the sample under test.
Long edge must be able to fit all probes The long edge of a rectangular sample is shorter than 3 times the probes spacing.
Diameter must be able to fit all probes The diameter of a circular samples is shorter than 3 times the probes spacing.
Short edge cannot be longer than the long edge The short edge is greater than the long edge for a rectangular sample.
Sample removed, stopping measurement The system has detected that the sample has been removed.
Error communicating with system The software is unable to connect to the system.
Unable to open file: permission was denied The software does not have the necessary permissions to access the given file path, or the file is already open in other software.
Unable to save file: permission was denied The software does not have the necessary permissions to access the given file path, or the file is already open in other software.

12.1 Related Consumables

12.2 Related Processing Equipment

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