Resistances of tenths of ohms to several ohms in transmission lines have been measured in laboratory systems from the power supply to the device under test (DUT). High-current semiconductor devices may draw currents of several amps. In cases such as these, the voltage drop in the transmission lines may rise up to several volts. In order to properly characterize the DUT, the losses in the transmission line and the voltage drop across the line must be measured and accounted for. A procedure for measuring the transmission line resistances is described. Once these values are known, it is necessary to apply a transform to the raw measured data in order to determine the actual voltages on the device of interest. A simple MATLAB code for determining the DUT current and voltage behavior is presented when the raw IV data and the transmission line resistances are known.

A three-port device, such as a bipolar junction transistor (BJT), a metal oxide semiconductor field effect transistor (MOSFET), or a high electron mobility transistor (HEMT), when measured on-wafer, may be measured using two separate power lines with ground-signal-ground (GSG) on-wafer probes. Each power supply has two resistances associated with transmission line losses. These are the resistance before the DUT, which will be called the power resistance (RP), and the resistance after the DUT, which will be called the common resistance (RC). Each port is identified by number. In this system, Port 1 is normally used to bias the gate on the DUT, and Port 2 is normally used to bias the drain on the DUT.

The first measurement is made by shorting the probe on Port 1. The second measurement is made by shorting the probe on Port 2. The third measurement is made by landing the probes on a through standard, like the kind typically used in a thru-reflect-line (TRL) s-parameter calibration. The final measurement is made by landing both probes on a solid metallic standard.

There is a non-trivial difference between the measured IV characteristics and the actual IV characteristics of the DUT. This is especially true in the linear (ohmic) region of device operation.

This work was done by Benjamin D. Huebschman of the Army Research Laboratory. For more information, download the Technical Support Package (free white paper) at www.defensetechbriefs.com/tsp under the Electronics/Computers category. ARL-0104