Coherence between gate- and drain-current fluctuations in MESFET´s and MODFET´s biased in the ohmic region

The gate and drain current fluctuations and their coherence have been investigated on MESFETs from NEC and RTC and on MODFETs from NEC, Fujitsu, and Sony. In the frequency range of 10 Hz to 100 kHz the observed spectra show mainly 1/f and generation-recombination noise. Some devices show a complete absence of coherence in that frequency range. Other devices show a coherence as high as 0.55 at low frequencies and a drop at higher frequencies. Some devices show a very low coherence level which increased above a characteristic frequency. The proposed model explains the experimentally observed trends and their physical meaning. The coherence measurement can be used as an additional diagnostic tool for MESFET and MODFET reliability studies