Low-temperature anodic bonding of silicon and crystal quartz wafers for MEMS application

Conventional fabrication of MEMS devices based on the quartz consists of a high tech processing of the very crystal with electrodes and subsequent manual assembling to the package. The limitation of the manual assembling could be eliminated through integration of the processing and packaging in a single high-tech process by means of silicon/crystal quartz bonding. New integrated technology would be able to create devices with new capabilities unobtainable with outdated technology. Low-temperature anodic bonding of silicon and quartz wafer appears to be the most promising method for elaboration of the unified technology. In this work, strong bonding of Si- and crystal quartz wafers close to the mechanical strength of the initial materials has been achieved as result of low-temperature annealing in electric field under pre-activation of crystal surfaces by oxygen plasma. Tensile test shows a disruptive stress of the samples at about 35 MPa. High bonding strength is associated with electric field applied during the annealing process. Similar bonding strength has been achieved for a pair of crystal quartz and structured silicon wafer with preetched micro cavities. Strong low-temperature bonding, including the bonding with pre-etched cavities, could be a key element of new technology of MEMS devices and provide new opportunities for miniaturization of sensors based on crystal quartz.