Pulsed I(V) Characterization
Pulse testing is essential for measuring devices with charge storage and thermal dependencies, and for tests outside the safe operating area (SOA). Applications include characterization of microwave transistors, MESFETs, HEMTs, and testing radar system components.The arbitrary pulsed semiconductor parameter analyser system (APSPA) implements fast, accurate pulse testing of microwave transistors, MMICs, and MOSFETs.
Dispersion
Dispersion in microwave devices is a well known phenomenon. Pulsed measurement of transistor characteristics avoids dispersion to give a true picture of high-frequency behavior. Conventional semiconductor analysers are not designed to do this.Flexible pulsed testing of device characteristics is key to the analysis and understanding of dispersion. It is necessary to measurement bias dependence and time-domain behavior. Characteristics can be measured about different quiescent bias points, exposing thermal and charge dependencies.
Dispersion in the drain characteristics of a microwave MESFET is shown in this overlay of two measurements. The pulsed-bias measurement (o) made after 200ns steps from the bias at (x) is markedly different from the conventional dc measurement (-).The conventional DC characteristics look good but can be misleading. The effect of heating and change in trapping state of the device is different for every point in the dc characteristic.
The pulse characteristics present the behavior for the heating and trap state of the bias point of the pulse measurement. These are isodynamic because the temperature and trap state is constant. A true isodynamic characteristic is therefore the response to microwave frequencies.
Time Evolution Characteristics of Pulse Timing
Is the measured characteristic isodynamic?
The only way to tell is to examine the characteristics over a range of frequencies or pulse timings. The idea is to observe the change in characteristics as the device bias point is changed. A typical measurement is shown in the following figure: