Quick & accurate characterisation for a wide range of materials.
Experience effortless sheet resistance measurements with the system's easy-to-use PC software.
Part of the Institute of Physics award-winning Ossila Solar Cell Prototyping Platform , Ossila's Four-Point Probe System is an easy-to-use tool for the rapid measurement of sheet resistance, resistivity, and conductivity of materials.
Using our own source measure unit, we have been able to create a low-cost system that allows a wide measurement range. The probe head uses spring-loaded contacts instead of sharp needles, preventing damage to delicate samples, such as polymer films with thicknesses on the order of nanometres*.
The system includes a four-point probe, source measure unit, and easy-to-use PC software - enabling more laboratories to measure sheet resistance for the affordable price of £1800.00. It is also covered by our FREE 2-year warranty .
* The system is not suitable for measuring the properties of materials that form a native insulating oxide e.g. silicon.
Wide Current Range - The four-point probe is capable of delivering currents between 1 μA and 150 mA, and can measure voltages from as low as 100 μV up to 10 V. The system can measure sheet resistances in the range of 100 mΩ/□ to 10 MΩ/□, enabling the characterisation of a wide range of materials.
Easy-to-Use - Just plug in the system, install the software, and you're ready to go! The intuitive interface and clean design makes the four-point probe easy-to-use, simplifying the measurement of sheet resistance. Substrates of various shapes and sizes can be used.
High Accuracy - Positive and negative polarity measurements can be performed using the PC software. This enables you to calculate the average sheet resistance between positive and negative currents - eliminating any voltage offsets that may have occurred, hence increasing the accuracy of your measurements.
Non-Destructive Testing - Designed with the measurement of delicate samples in mind, the four-point probe head utilises gold-plated, gentle spring-loaded contacts with rounded tips. This results in a constant contact force of 60 grams, preventing the probes from piercing fragile thin films, whilst still providing good electrical contact.
Space-Saving Design - Through careful design consideration, we have been able to keep the footprint of the four-point probe to a minimum (total bench area of 14.5 cm x 24 cm), allowing it to be used even in busy labs where shelf space is lacking.
Rapid Material Characterisation - The PC software (included with the system) performs all the necessary measurements and calculations for sheet resistance, resistivity, and conductivity - making material characterisation effortless. It also automatically performs correction factor calculation.
|Voltage range||±100 μV to ±10 V|
|Current range||±1 μA to ±150 mA|
|Sheet resistance range||100 mΩ/□ to 10 MΩ/□ (ohms per square)|
|Sheet Resistance||Accuracy*||Precision**||Measured at Range|
*Accuracy is the maximum deviation from the true value.
** Precision is the maximum deviation between identical measurements (useful for comparative measurements).
|Probe Spacing||1.27 mm|
|Rectangular Sample Size Range||Long Edge Minimum: 5 mm
Short Edge Maximum: 60 mm
|Circular Sample Size Range (Diameter)||5 mm to 76.2 mm|
|Maximum Sample Thickness||10 mm|
|Overall Dimensions||Width: 145 mm
Height: 150 mm
Depth: 240 mm
- Clean and intuitively-designed interface
- Data saved to .csv file
- Calculates resistivity and conductivity for samples with a known thickness
- Automatic correction factor calculation
An intuitive and user-friendly standalone PC program is used to control the four-point probe measurement, enabling rapid characterisation of materials without the need for the user to write any code themselves. This PC software calculates appropriate geometrical correction factors for the given sample geometry, ensuring accurate results. It can also calculate the resistivity and conductivity of the sample, if the thickness is provided, to allow for extensive electrical characterisation of materials.
The software saves data to comma-separated value (.csv) files, facilitating importing the data into your preferred analysis software. Advanced settings give you greater control over the measurment, allowing you to set voltage and current limits, perform negative polarity measurements, or use probes with different spacings.
|Operating System||Windows 10 (32-bit or 64-bit)|
|CPU||Dual Core 2 GHz|
|Available Hard Drive Space||178 MB|
|Monitor Resolution||1440 x 900|
|Connectivity||USB 2.0, or Ethernet (requires DHCP)|
Material Characterisation - Resistivity is an inherent characteristic of a material, and an important electrical property. It can be determined by measuring the sheet resistance of a thin film with a known thickness, making the four-point probe measurement a key technique for the electrical characterisation of materials.
Thin-Film Solar Cells and LEDs - Thin-film devices (such as perovskite solar cells or organic LEDs) require thin conducting electrodes that transport electrical charge laterally to be extracted. Therefore, materials with low sheet resistances are required to reduce potential losses at this stage. This becomes even more important when attempting to scale up these devices, as the electrical charges will have to travel further along the electrodes before they can be extracted.
Please note, this system is not suitable for silicon or other materials which naturally form insulating oxide layers. To measure such materials, the oxide layer needs to be penetrated by the probes, which may not be possible with the spring-loaded, round tipped probes utilised by this system.
The four-point probe is the most commonly-used piece of equipment for measuring the sheet resistance of a material. Sheet resistance is the resistivity of a material divided by its thickness, and represents the lateral resistance through a thin square of conducting/semiconducting material. This measurement uses four probes arrayed in a line, with equal spacing between each probe. A current is passed between the outer two probes, causing a reduction in voltage between the inner two probes. By measuring this change in voltage, the sheet resistance can then be calculated using the following equation:
Here, I is the applied current and ΔV is the decrease in voltage between the inner probes. The result of this equation must further be multiplied by a geometric correction factor based upon the shape, size, and thickness of the sample. This accounts for limitations to the possible current pathways through the sample, which affects the values that are measured.
A more in-depth explanation of the theory behind sheet resistance, geometric correction factors, and the four-point probe technique can be found in our Guide to Sheet Resistance Theory.
Frequently Asked Questions
The Four-Point Probe System is specifically designed to enable the measurement of thin films in the nanometre range. For example, we have successfully measured 30 – 40 nm films of PH 1000 PEDOT:PSS and < 100 nm silver nanowire films on PET, without creating holes in the thin films. For a more in-depth explanation, please see our application note: Sheet Resistance Measurements of Thin Films.
The system has a built-in Ossila Source Measure Unit (SMU), so you don’t need to already have one.
As the system measures the sheet resistance of a sample, a general range of measurable resistivities or conductivities cannot be given. This is because the measurable resistivity range depends on the thickness of the sample being tested. The resistivity of a sample can be calculated from its sheet resistance and thickness using the following equation:
The system is capable of measuring between 100 mΩ/□ and 10 MΩ/□, so if we use these values in the formula above with a sample 50 nm thick, then the resistivity (conductivity) range that can be measured by the system will be 5 nΩ.m to 500 mΩ.m (2 S/m to 200 MS/m). If the sample is 400 µm thick, then the resistivity (conductivity) range of the system is 40 µΩ.m to 4 kΩ.m (250 µS/m to 25 kS/m). Below is a table of the resistivity and conductivity ranges of the system for samples with thicknesses of different orders of magnitude:
|Sample Thickness||Resistivity Range||Conductivity Range|
|10 nm||1 nΩ.m - 100 mΩ.m||10 S/m - 1 GS/m|
|100 nm||10 nΩ.m - 1 Ω.m||1 S/m - 100 MS/m|
|1 µm||100 nΩ.m - 10 Ω.m||100 mS/m - 10 MS/m|
|10 µm||1 µΩ.m - 100 Ω.m||10 mS/m - 1 MS/m|
|100 µm||10 µΩ.m - 1 kΩ.m||1 mS/m - 100 kS/m|
|1 mm||100 µΩ.m - 10 kΩ.m||100 µS/m - 10 kS/m|
Currently we offer a single probe layout, i.e. linear with 1.27 mm spacing between the probes, 0.48 mm probe diameter, and 60 g spring pressure. This allows us to maintain the affordable price of the Four-Point Probe System, whilst still providing reliable and accurate measurements of sheet resistance.
To the best of our knowledge the technical information provided here is accurate. However, Ossila assume no liability for the accuracy of this information. The values provided here are typical at the time of manufacture and may vary over time and from batch to batch.