Efficient thermal annealing methods for performance improvement of SMR-Type FBAR devices

Abstract

There have been a number of researches to integrate RF devices into a one-chip because the higher performance generally can be achieved by realizing a system with lower power consumption, better signal integrity, and smaller size. Recently, due to the considerable progress in microelectronics technology, most of the RF components such as power amplifier and mixer can be highly integrated. However, the RF filter is a main obstacle to prevent completion of a one-chip transceiver and thus it has been used only as a single off-chip component for wireless mobile systems. In this point of view, film bulk acoustic resonator (FBAR) can be a good candidate to integrate the RF filter with other RF components because materials and processing techniques used for FBAR device fabrication are very compatible with Si and GaAs wafer processing. Since FBAR filter is composed of more than two series/parallel FBARs, the most important issue for an excellent filter is to maximize the performance of FBAR itself. Therefore, in this thesis, thermal annealing treatments on FBAR devices were investigated to improve the resonance characteristics. Thermal annealing is a heat treatment wherein the microstructure of a material is altered, causing changes in its properties such as strength and hardness. This treatment has been widely used in the semiconductor fabrication. Typically annealing results in softening of the metal through removal of crystal defects and the internal stresses which they cause. FBAR is composed of many layers of different materials. Especially SMR-type FBAR has more layers than back-etched or air-gap type FBARs. Accordingly some researchers have performed thermal annealing processes on SMR-type FBAR devices to improve the resonance characteristics by eliminating imperfect microstructures and adhesions in FBAR devices. Those thermal treatments were named Bragg reflector-annealing, thermal treatment on only acoustic Bragg reflectors and post-annealing, annealing ...