Gallium Nitride Micromechanical Lateral Bulk-mode Resonators for GHz Radio Frequency Applications

Description

As a material, Gallium Nitride (GaN) has been a hot research topic for its unique electronic and optoelectronic properties. The main consumer markets for GaN optoelectronics include laser diodes and energy-saving light emitting diodes (LEDs). GaN-power-devices promise highly-energy-efficient power conversion. Radio-frequency (RF) GaN electronics are now applied in wireless data transmission, and telecoms in future. Its unique material properties fulfill a niche unreached by silicon-based electronics; currently still the most popular material just before GaN. In contrast to the progress made in GaN optoelectronics and electronics, the potential of this material’s excellent electro-mechanical properties remain largely untapped.Over the last 15 years, there has been sizeable research on realizing mechanically vibrating components (called resonators) fabricated in Silicon for integration with Silicon integrated circuits. Resonators form the heart-beat of almost every electronic product. The technology has matured to a point today where a number of spin-offs have taken off in the past 6 years. In comparison, research activity in electromechanical GaN resonators has been fairly recent and at lower frequencies (~MHz). Given GaN’s favored position in RF electronics, there is impending need to investigate methods and the underlying science for realizing mechanical resonators in GaN atGHzrange.The research objective of this proposal is to investigate and implement GaN micromechanical lateral-mode resonators working at 1GHz; not achieved to date. High frequency generally comes at a cost of performance: reduced Q and larger motional resistance. The 1GHz GaN resonators in this proposal will be marked by Q >1000 and motional resistance <1kW. For the first time, this proposal will demonstrate a 1GHz narrow-band GaN mechanical filter with insertion loss better than -10dB.In collaboration withProf Kevin Chen (HKUST), a process will be created to fabricate the proposed devices. Lateral-bulk-modes, instead of commonly used flexural-modes, will be employed to obtain the required Q’s at 1GHz. Motional resistance will be reduced through a combination of device design, process enhancements, and novel applications of transduction methods. This includes unique implementation of a resonant-body-HEMT in a lateral-bulk-mode resonator to provide active electromechanical gain. These are planned for fundamental mode operation first before advancing to higher-order overtones to reach 1GHz. Finally, the overtone-resonators will be cascaded to realize a 1GHz narrowband filter.Based on initial assessments derived analytically and by simulation, we are confident that the proposed targets are realistically achievable. The expected results will be research milestone of significant impact both scientifically and commercially.