Role of Plastic Encapsulant on the RF Performance of the GaN Based HEMT Amplifier

This paper presents design, realization and plastic encapsulation of the GaN HEMT die for high power applications. Design & realization of GaN discrete HEMT die based high-power amplifier is carried out to evaluate the performance of the module using selected encapsulant material. The power amplifier is designed at S-band frequencies with 5-watt output power to meet aerospace system requirements. The optimum values of the circuit elements are simulated in standard software. Large signal simulations have showed an output power of 37.4 dBm with 18 dB gain at 2.2 GHz. The simulated input and output return losses are 15 dB and 9 dB respectively. The simulated design is implemented using hybrid microwave integrated circuit (HMIC) approach. The amplifier is realized using thin film processes and packaging techniques. The discrete GaN HEMT die is assembled in a package with Cu-W base to meet reliability requirements of the aerospace system. The realized power amplifier module is characterized initially without encapsulant for small and large signal measurements. The fabricated power amplifier achieved 15 dB small signal gain with 37 dBm output power and 50% PAE across the band 2.1-2.4 GHz. The simulated and measured results of the designed amplifier are comparable. Later plastic encapsulation is performed and module is characterized. GaN HEMT die is encapsulated using dam & fill technology using manual dispensing method. The plastic encapsulation has not degraded the performance of the module and meeting the aerospace system specifications.