Norshakila Haris

Design and characterisations of double-channel GaAs pHEMT Schottky diodes based on vertically stacked MMICs for a receiver protection limiter

A microwave receiver protection limiter circuit has been designed, fabricated and tested using vertically stacked GaAs MMIC technology. The limiter circuit with a dimension of 2.5 × 1.3 mm2 is formed by using double-channel AlGaAs/InGaAs pseudomorphic HEMT (pHEMT) Schottky diodes integrated with a low-loss V-shaped coplanar waveguide multilayer structure. The electrical parameter characteristics of the pHEMT Schottky diodes are presented including the C–V profile showing the presence of a double channel in the device layer structure. This unique feature can also be seen from the double-peak responses of the electron density as a function of the device layer width, which represent the high electron concentration at two different 2-DEG layers of the structure. An equivalent circuit model of pHEMT Schottky diodes is demonstrated showing good agreement with the measurement results. At zero-bias condition, the devices show high performance in diode detector applications with voltage sensitivities of more than 89 mV μW−1 at 10 GHz and at least 5.4 mV μW−1 at 35 GHz. The measurement results of the limiter circuit demonstrated the blocking of input power signals greater than 20 dBm input power at 3 GHz. To the best of our knowledge this is the first demonstration of the use of pHEMT Schottky diodes in microwave power limiter applications.