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Vacuum-controlled wafer-level packaging for micromechanical devices

A vacuum-controlled wafer-level packaging process for micromechanical devices was developed. The process includes a thick titanium deposition process and a vacuum anodic bonding process which is performed in argon ambient unlike conventional process which is carried out in nitrogen ambient. Because the thick getter film absorbs most of oxygen molecules released during the bonding, but does not absorb argon at all, the vacuum level in the package is controlled by only adjusting argon pressure. To estimate the vacuum level, a quality factor is obtained from the frequency response of the packaged device. When the devices are packaged in argon ambient at a pressure of 5 × 10−2 Torr, the average value of the quality factors is about 5000. This shows that the vacuum levels of the packaged devices are almost same as the initial argon setting pressure, considering the correlation between the quality factor and the vacuum level which is investigated by a preliminary experiment. The vacuum-level controllability of the proposed vacuum packaging process was verified repeatedly under other ambient pressure conditions. Durability testing was done more than 1000 h, but no significant variation in the quality factor was observed.