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 cut-off frequency f_T and the maximum oscillation frequency f_max. f_T is defined as the frequency f were the current gain |h₂₁| gets 0 dB. The current gain can be calculated from the measured S­parameters by [36]:
 

.

(8)

 
If |h₂₁| [dB] is positive in the whole measured frequency range |h₂₁| [dB]is linearly extrapolated to zero versus log(f) with a slope of 20dB/dec. f_max is defined as the frequency at which the unilateral gain MUG gets zero. MUG can be obtained from S­parameters by [36]:
 

.

(9)

 

• 3.2 Small Signal Equivalent Circuit Parameter Extraction
• 3.3 Determination of Capacitances by Quasi Static Approximation

   
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