3.1 DC and RF Measurements
The DC and RF characteristics of fabricated HEMTs are determined by
measuring the voltages and currents on the three terminals and 2port
Sparameters. One of the most important figures of merit are the current
gain cutoff frequency f_{T} and the maximum oscillation
frequency f_{max}. f_{T} is defined as the
frequency f were the current gain h_{21} gets 0
dB. The current gain can be calculated from the measured Sparameters
by [36]:
. 
(8)

. 
(9)

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Helmut Brech 19980311