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Measuring the Voltage Coefficient of Resistance on Integrated Circuit Resistors

IP.com Disclosure Number: IPCOM000087593D
Original Publication Date: 1977-Feb-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 3 page(s) / 42K

Publishing Venue

IBM

Related People

Bergeron, DL: AUTHOR [+2]

Abstract

When making resistors, either by diffusion or ion-implantation in semiconductor material, the resistor body is always isolated from the background of the semiconductor by a PN junction. This PN junction has a depletion region associated with it, which in turn is dependent on the impurity doping levels in the background (usually N epi) and in the resistor body, as well as the voltage bias impressed across the resistor and resistor-background junction. Fig. 1 shows the typical bias condition with the associated depletion region.

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Measuring the Voltage Coefficient of Resistance on Integrated Circuit Resistors

When making resistors, either by diffusion or ion-implantation in semiconductor material, the resistor body is always isolated from the background of the semiconductor by a PN junction. This PN junction has a depletion region associated with it, which in turn is dependent on the impurity doping levels in the background (usually N epi) and in the resistor body, as well as the voltage bias impressed across the resistor and resistor-background junction. Fig. 1 shows the typical bias condition with the associated depletion region.

As the voltage biases, either across the resistor or between resistor and background change, the depletion region boundaries move in or out (higher or lower biases) of the resistor body causing the resistance to change. This change is called the voltage coefficient of resistance (VCR) and is a parameter which must be considered in the overall resistor value, especially in precision circuits.

In the development of precision resistors, it is found that accurate measurement of the VCR is difficult since the VCR is on the order of a few thousand parts per million (ppm) per volt. The normal method is to measure the resistor at two different voltage levels (current through resistor is measured) and calculate the VCR from the following relation: VCR Identical to R(v2) - R(v1) over R(v1) Divide by V(2) - V(1) ppm/volt.

Two limitations make this method inaccurate. The first limitation is that changing the voltage (and hence current) changes the power dissipated in the resistor and, hence, the temperature is also changed giving rise to an additional change in the measured resistance. Secondly, the calculated VCR depends on the small difference in two large measured values. For a resistor with a VCR of 1000 ppm/v, an instrument accuracy of 0.001% is required to determine VCR with an accuracy of 10% for a 1 volt change in bias.

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