What Four Point Probe Features Do You Need?
Building on the reliable source measure unit, the Ossila Four Point Probe is an instrument that makes measuring sheet resistance as straightforward as possible for users. Without complex calibration or set up, you just put your thin film into the four point probe station and immediately get reliable sheet resistance, conductivity and resistivity values for your thin films.
The Ossila Four Point Probe accesses all the measurement power and capability of the source measure unit. It will automatically try to find the appropriate measurement range for your sample, but you also have the option to select current range using the compatible Sheet Resistance software. As well current ranges, you can also set samples per point, voltage limits and current limits. This allows you to tailor your measurement to your need.
Do I Need the Four Point Probe Plus?
There are many situations where it becomes difficult to connect and control systems though a PC unit:
- In a glove box
- In a fume hood
- In any crowded lab where bench space is at a premium
For these instances, we recommend the Four Point Probe Plus. This is a standalone system with a display screen for even easier sheet resistance measurements. What's more this system still maintains the compact design, processing power and PC-connectability of the initial four point probe.
The Ossila Four Point Probe has a display screen integrated into the body, which displays sheet resistance data with just the touch of a button. You can input film information into the system to ensure your measurements are accurate.
This system can still be used with the compatible Sheet Resistance software via PC, and has all the available specification of the original four point probe - just with more functionality and a slightly higher cost.
Soft-tipped vs Hard-Tipped Probes
Another issue faced by thin films researchers is how to measure the sheet resistance of organic conductor layers, very thin films and other delicate samples without damaging the layers. Therefore the four point probe comes with a choice of probe tip.
The Four Point Probe is compatible with two different head designs: soft-tipped probes or hard-tipped probes.
The soft-tipped probes reduce any potential damaging delicate thin films with rounded tips and a larger surface area with a radius of 0.24 mm. The soft-tipped probes are mounted on springs, so that they retract into the probe head after making contact with the sample. This design spreads the downward force into a uniform force of 60 grams across the four pins. These soft tips are also gold plated to increase conductivity.
The sharped-tipped probes are more like traditional probes you'd find in a probe station. The sharp-tipped four-point probe head is designed for materials with naturally forming oxide layers and has a tip diameter of 0.08 mm. The sharp tipped probes can peirce through oxide layers, directly contacting materials like silicon. The nickel-plated tungsten carbide probes can apply a maximum force of 197.43 gf to pierce the insulating layer for reliable sample measurements.
| Soft-Tipped Probes | Hard-Tipped Probes | |
|---|---|---|
| Radius | 0.24 mm | 0.08 mm |
| Force Applied | 60 gram-force | 197 gram-force |
| Suitable for | Organic films, very thin films, delicate samples | Materials that form oxide layers, silicon |
| Not ideal for | Materials that form oxide layers, silicon | Organic films, very thin films, delicate samples |
If you are unsure of which head you need, or you work with both organic and inorganic layers, you can interchange the heads on the four point probe easily. This will give you the maximum measurement type range, giving you loads of flexibility in your experiments.
Four-Point Probe
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How to Measure Sheet Resistance using a Four-Point Probe
The most common technique used for measuring sheet resistance (surface resistance) is the four-probe method. This technique involves using four equally spaced, co-linear probes to make electrical contact with the material. Most four-point probes available commercially use sharp needles as probes. These can scratch or pierce delicate materials often used in thin film electronic devices. This can make it difficult to take accurate sheet resistance measurements, and result in the thin film becoming unusable.
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How to Replace the Four-Point Probe Head
To change the head on on your four-point probe, follow these specific steps: Unfasten the screws attaching the probe head to the unit.
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