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. 2017 Jan 26;10(2):110.
doi: 10.3390/ma10020110.

Open-Source Automated Mapping Four-Point Probe

Handy Chandra  1 , Spencer W Allen  2 , Shane W Oberloier  3 , Nupur Bihari  4 , Jephias Gwamuri  5 , Joshua M Pearce  6   7
Affiliations

Open-Source Automated Mapping Four-Point Probe

Handy Chandra et al. Materials (Basel). .

Abstract

Scientists have begun using self-replicating rapid prototyper (RepRap) 3-D printers to manufacture open source digital designs of scientific equipment. This approach is refined here to develop a novel instrument capable of performing automated large-area four-point probe measurements. The designs for conversion of a RepRap 3-D printer to a 2-D open source four-point probe (OS4PP) measurement device are detailed for the mechanical and electrical systems. Free and open source software and firmware are developed to operate the tool. The OS4PP was validated against a wide range of discrete resistors and indium tin oxide (ITO) samples of different thicknesses both pre- and post-annealing. The OS4PP was then compared to two commercial proprietary systems. Results of resistors from 10 to 1 MΩ show errors of less than 1% for the OS4PP. The 3-D mapping of sheet resistance of ITO samples successfully demonstrated the automated capability to measure non-uniformities in large-area samples. The results indicate that all measured values are within the same order of magnitude when compared to two proprietary measurement systems. In conclusion, the OS4PP system, which costs less than 70% of manual proprietary systems, is comparable electrically while offering automated 100 micron positional accuracy for measuring sheet resistance over larger areas.

Keywords: 3-D platform; ITO; TCO; conductivity; four-point probe; indium tin oxide; libre hardware; open source hardware; sheet resistance; transparent conducting oxide.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
Measurement process flowchart.
Figure 2
Figure 2
Printed four-point probe holder showing mounted four-point probe head.
Figure 3
Figure 3
OpenSCAD images showing: (a) Probe holder top part; (b) Carriage part x-axis mount.
Figure 4
Figure 4
3-D printer bed fixed with springs and a pair of printed specimen clips (white).
Figure 5
Figure 5
Current source circuit.
Figure 6
Figure 6
Parasitic resistance and leakage of current source circuit.
Figure 7
Figure 7
Instrumentation amplifier circuit.
Figure 8
Figure 8
Assembled open source printed circuit board for four-point probe measurements.
Figure 9
Figure 9
The graphical user interface (GUI) for open source four-point probe (OS4PP) software.
Figure 10
Figure 10
Discrete resistor measurement circuit.
Figure 11
Figure 11
Modified 3-D printer with custom measurement circuit for OS4PP measurements.
Figure 12
Figure 12
Comparison of measurement results on discrete resistor.
Figure 13
Figure 13
Results of automated sheet resistance measurement (Ω/sq) using OS4PP: (a) Reference sample; (b) 50 nm ITO annealed 10 min; (c) 50 nm ITO annealed 20 min; (d) 50 nm ITO annealed 30 min.
See this image and copyright information in PMC

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