Low temperature quartz-to-silicon bonding for SAW applications

A new process for the fabrication of piezoelectric quartz thin films on silicon is investigated. With this process, new silicon-implemented acoustic wave delay lines for sensor applications can be realized. An acoustic-wave delay-line consists of two interdigital thin film metal transducers (IDTs) fabricated on a piezoelectric crystal. In order to realize acoustic-wave devices on (nonpiezoelectric) silicon, the use of piezoelectric thin films such as zinc oxide, aluminum nitride or PZT has been reported. However, these films often exhibit stress, aging, pinholes, or poor reproducibility which affects the performance of the device. The bonding of piezoelectric quartz (with its known and fixed mechanical and piezoelectric properties) to silicon improves the performance of silicon-implemented acoustic-wave devices. The process used, consists of a wet chemical treatment after which the wafers are prebonded at room temperature. Annealing at 140 degrees C for 3 hours yields a sufficient high bond strength.