The function of the 4-point probe is to measure up the resistivity of any semiconductor material. It have the right to measure either mass or slim film specimen, every of which is composed of a various expression. The derivation will certainly be presented in this tutorial.

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The 4-point probe setup provided in the EECS 143 instructional lab is composed of four equally spaced tungsten steel tips v finite radius. Each reminder is supported by springs top top the other finish to minimization sample damage during probing. The four metal tips are part of an auto-mechanical phase which travel up and also down throughout measurements. A high impedance current resource is offered to supply present through the outer two probes; a voltmeter procedures the voltage throughout the inner 2 probes (See figure 1) to recognize the sample resistivity. Typical probe spacing s ~ 1 mm.

Figure 1. Schematic the 4-point probe configuration

2. Concept

Bulk SampleIn our derivations because that this section, we assume the the steel tip is infinitesimal and also samples space semi-infinite in lateral dimension. For bulk samples where the sample thickness t >> s, the probe spacing, we assume a spherical protrusion of existing emanating native the external probe tips. The differential resistance is:

We bring out the integration in between the inside probe tips (where the voltage is measured):

where probe spacing is uniformly s. Because of the superposition of present at the external two tips, R = V/2I. Thus, us arrive at the expression for mass resistivity:

Thin SheetFor a an extremely thin great (thickness t

3. Operation Procedures

The following steps must be take away in the following sequence:

Turn on the voltmeter, set the setting to DC and also voltage selection to 200 mV.Place wafer ~ above the probe stage.Flip the toggle switch located atop the probe station from “NEUTRAL” come “DOWN”.Watch the probe casing reduced until the probes stabilize top top the wafer.Return the toggle move of the probe station to the “NEUTRAL” position.Turn top top the current resource by transforming the black color switch “S1” come the “ON” position.Set the existing to the preferred level, and also proceed v measuring the voltage across the inner 2 probes. Map the wafer.When measure up is finished, shut off the current source by transforming the switch “S1” come the “OFF” position.Flip the probe terminal toggle move from “NEUTRAL” to “UP”.Wait till the probe casing is every the means up, then set the toggle switch ago to “NEUTRAL”.Turn turn off voltmeter.

James Chan, feather 1994

The original page have the right to be discovered here: http://www-inst.eecs.berkeley.edu/~ee143/fa10/lab/four_point_probe.pdf

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