Wafer bonding processes based on RTP (Rapid Thermal Processing) have been demonstrated for MEMS (Microelectromechanical Systems) packaging applications, including hermetic sealing and vacuum encapsulations. Both RTP aluminum-to-glass and aluminum-to-nitride bonding systems have been achieved and characterized with accelerated and reliability experiments and analyses. As proof-of-concept demonstrations, a post-packaging frequency turning process using PLD (Pulsed Laser Deposition) and a miniaturized microbial fuel cell for micro power generation are also presented.

Aluminum-to-glass RTP bonding is demonstrated at 990°C for 2 seconds and the packaged cavities have been tested under both IPA (Isopropanol Alcohol) gross leakage and autoclave harsh environment tests. The activation energy of the aluminum-to-glass bonding system is experimentally characterized as 3.5eV. In the aluminum-to-nitride bonding experiments, the optimized process parameters are found at 750°C for 10 seconds and the activation energy is characterized as 2.5eV. X-ray diffraction (XRD) spectrum confirms the diffusion bonding process as no new compound is identified at the bonding interface. Accelerated tests have been conducted at 130°C, 2.7 atm and 100% RH for 864 hours on packaged MEMS cavities and the statistical failure data are collected and analyzed using the Maximum Likelihood Estimator. Results show that, with 90% confidence, the mean-time-to-failure (MTTF) is estimated as 0.017 years (149 hours) under an accelerated condition (130°C. 2.7atm and 100% RH) on a sealing area of 1000 x 1000 μm² with sealing ring width of 150 μm and aluminum solder thickness of 4 μm. Furthermore, vacuum packaging of surface-micromachined, comb-shape resonators has been demonstrated by aluminum-to-nitride RTP bonding. The quality factor was measured as 1800 ± 200 corresponding to a pressure about 200mTorr inside the package. A long-term stability monitoring has been carried out for 37 weeks and an accelerated test in harsh environment has been conducted for 24 hours. Both tests show quality factor remain stable.

Post-packaging frequency tuning of microresonators by using PLD is demonstrated after the RTP packaging process. A pulsed laser(6 nano-second. 532nm and 0.6mJ) is used to deposit thin film metals on top of the resonator surface. The controllability and a maximum natural frequency change of −18.1% have been accomplished experimentally. Finally, a miniaturized microbial fuel cell is realized using microorganisms (Saccharomyces cerevisiae) to catalyze glucose and generate electricity at 300 mV with the assistance of a proton-exchange membrane.