New pulsed measurement setup for GaN and GaAs FETs characterization

Abstract

A new setup is proposed for the measurement of current–voltage pulsed characteristics of electron devices. The main advantages of the system consist in: shorter pulse widths through generation in a 50-Ω environment, simple average current monitoring through separation of the direct and alternate current paths, setting of average voltage values independently of pulse amplitudes and duty cycle, and stability of the setup guaranteed by wide-band dissipative terminations. The system is used for the characterization of dispersive effects due to carrier energy traps and thermal phenomena in GaAs and GaN on SiC field effect transistors. The basic differences between the two technologies are highlighted in the paper.

A Double-Pulse Technique for the Dynamic I/V Characterization of GaN FETs

“…4 (top). Remarkable differences between the two sets of curves as well as anomalous current slope changes at the quiescent drain voltages are observed, as already noticed in [3], [4]. The two I/V characteristics are measured again by using the proposed double-pulse technique, by realizing and through the pre-pulses.…”

“…Unfortunately, this behavior undermines the basic principle of standard pulsed measurement procedures, since some portions of the pulsed I/V characteristic are not obtained in the presence of a constant amount of trapped charges. As it has been shown in [4], due to this reason anomalous slope changes are observed in the pulsed I/V characteristics and drops in the dc Manuscript current absorbed from power supply are well evident in the operative regions affected by trap-state variations. It is also worth noting that a dependence of the trapping state on the peak values of voltages [2], is coherent with the less-than-expected output power observed in GaN-based power amplifiers at increasing drain voltages [5].…”

“…To this aim, a recently presented setup for pulsed I/V measurements in a environment [4] is customized in order to implement the proposed characterization technique. Bias voltages are applied at the gate and drain ports through the dc-feed path of commercial bias networks , while incident pulsed waves are injected into the ac-coupled ports.…”

“…Typical pulse widths and duty cycles, adopted for GaAs-and GaN-based FETs, are below and 1%, respectively [1]. However, as known in literature [2]- [4], the time constants associated with charge trapping effects in GaN FETs seem to show an asymmetry between charge capture (fast, in the order of a few ns) and release (much slower than typical pulse widths). Unfortunately, this behavior undermines the basic principle of standard pulsed measurement procedures, since some portions of the pulsed I/V characteristic are not obtained in the presence of a constant amount of trapped charges.…”

“…Since the device can be forced in a thermal and trapping state close to the one involved in its operation within a power amplifier (or any other large-signal application), the I/V sets obtained are expected to provide an accurate description of the device behavior under periodic steady-state operation at microwave frequencies. Although the proposed technique is theoretically suitable to be implemented in standard pulsed I/V measurement setups, which are based on voltage pulses, here it is developed and tested by customizing a setup [4] based on the generation of periodic pulsed waveforms in a environment. The customization involves a reshaping of the ac components of the pulsed excitation, with the aim of presetting the same trap-state before sampling the incident and reflected drain travelling waves during the actual peaks of the gate and drain incident pulsed waves.…”