Quick and 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, the Ossila Four-Point Probe System is an easy-to-use tool for the rapid measurement of sheet resistance, resistivity, and conductivity of materials.
Built with a high-specification Ossila Source Measure Unit at its core, the Ossila Four-Point Probe is 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 price includes a four-point probe, in-built source measure unit, easy-to-use PC software, and an ITO-coated glass substrate. With free tracked worldwide shipping as standard, more laboratories across the globe can now measure sheet resistance to empower their materials characterisation and thin-film development programs.
The Ossila Four-Point Probe is now supplied with a global power cord that supports all major plug types (type G, type F, type A and type I). Please contact us for more information.
The Ossila Four-Point Probe is backed by the Ossila Guarantee and is covered by our FREE 2-year warranty.
What is a Four-Point Probe?
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.
Wide Current Range
The four-point probe is capable of delivering currents between 1 μA and 200 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.
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.
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.
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.
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 limited.
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.
Equipped with Soft Contact Probes
The Ossila Four-Point Probe System reduces the potential of damaging delicate thin films via three features. The probes, used to make contact, have rounded tips (unlike other probes which are like sharp needles). These rounded tips have a radius of 0.24 mm and give the probes a larger contact surface area than a needle would, therefore spreading out the downward force being applied to the sample. These probes are gold plated and mounted on springs to encourage electrical contact without excessive force as it enables them to retract into the probe head when making contact with the sample to ensure that a uniform force of 60 grams is applied. A schematic of the probes is shown in the figure below. The probe head can be purchased separately here.
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.
Sheet resistance is an important property of materials, which is commonly used in material characterisation and in the development of thin-film devices such as perovskite solar cells or organic LEDs.
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 require thin conducting electrodes that transport electrical charge laterally to be extracted, so materials with low sheet resistances are required to reduce potential losses. This becomes even more important when attempting to scale up these devices, as the electrical charges must travel further along the electrodes before they can be extracted.
Included with the Ossila Four-Point Probe
The Four-Point Probe Unit
Built-in Ossila Source Measure Unit
The Ossila Four-Point Probe is powered by our Source Measure Unit. Supplied with a 24 V / 2 A power adapter and USB-B cable.
For more information, please refer to the Source Measure Unit product page.
Four-point probe head
Providing a constant contact force of 60 grams, the spring-loaded four point probe head is perfect for delicate samples. The probes are gold-plated to ensure good electrical contact is made without excess force, and are rounded to further prevent them from causing damage to thin films and other fragile samples (note that they are not suitable for silicon or other materials with insulating oxide layers).
Linear translation stage
With micrometer height control and a sample stage with non-slip rubber.
Software and Accessories
Ossila Four-Point Probe Software
The Ossila Sheet Resistance Lite software is quick, simple and easy to use. Accurate results are assured by the automatic geometrical correction factors, and the software is able to calcuate the resistivity and conductivity of the sample on the fly for quick characterisation of materials.
The software is supplied on the included USB memory stick along with a copy of the user manual and QC data. In addition, the latest version is always available to download for free from our website.
ITO-coated glass substrate
100 nm ITO coated glass substrate (20 x 15 mm).
Also available seperately. Please refer to the ITO-coated glass substrate product page for more information.
Frequently Asked Questions
What sample thicknesses are compatible with the system?
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 measurement guide: How to Measure Sheet Resistance using a Four-Point Probe.
Do I need my own source measure unit (sourcemeter)?
The system has a built-in Ossila Source Measure Unit (SMU), so you don’t need to have one already.
What resistivity/conductivity range can the system measure?
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|
Do you offer other probe designs?
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. Replacement probe heads can be purchased online or contact us to request a quote.
What materials are not compatible with the system?
Materials that are not compatible with the system are those that can form oxide layers, causing no contact between probe and sample. Examples of such materials include semiconductors consisting of pure silicon and those that fall within the III-V category (GaAs, InP, AlAs, etc).
Getting Started with the Ossila Four-Point Probe
Sheet Resistance Equation
Sheet resistance can 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.
Resources and Support
Four-Point Probe Measurement Specifications
|Voltage range||±100 μV to ±10 V|
|Current range||±1 μA to ±200 mA (5 ranges)|
|Sheet resistance range||100 mΩ/□ to 10 MΩ/□ (ohms per square)|
|Sheet Resistance||Accuracy*||Precision**||Measured at Range|
|100 mΩ/□||±8%||±3%||200 mA|
|1 Ω/□||±2%||±0.5%||200 mA|
|10 Ω/□||±1%||±0.5%||200 mA|
|100 Ω/□||±1%||±0.05%||20 mA|
|1 kΩ/□||±1%||±0.03%||20 mA|
|10 kΩ/□||±1%||±0.02%||2000 µA|
|100 kΩ/□||±2%||±0.05%||200 µA|
|1 MΩ/□||±8%||±0.5%||20 µA|
|10 MΩ/□||±30%||±5%||20 µA|
*Accuracy is the maximum deviation from the true value.
** Precision is the maximum deviation between identical measurements (useful for comparative measurements).
Physical Device Specifications
|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|
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.
Key Software Features
- Clean and intuitively-designed interface
- Data saved to .csv file
- Calculates resistivity and conductivity for samples with a known thickness
- Automatic correction factor calculation
|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)|
The Ossila Four-Point Probe comes with everything you need, including a power adapter, a USB-B cable, a 400 – 450 nm FTO coated glass substrate (60 x 60 x 2.2 mm), a 10 kΩ resistor test head, and a USB memory stick pre-loaded with the user manual, software installer, QC data, and USB drivers. Spare probe heads can be bought seperately.
Four-Point Probe Spares and Accessories
Related Processing Equipment
To the best of our knowledge the information provided here is accurate. However, Ossila assume no liability for the accuracy of this page. The values provided are typical at the time of manufacture and may vary over time and from batch to batch. All products are for laboratory and research and development use only, and may not be used for any other purpose including health care, pharmaceuticals, cosmetics, food or commercial applications.