The fabrication of thin-film bulk acoustic wave resonators employing a ZnO/Si composite diaphragm structure using porous silicon layer etching

Thin-film bulk acoustic wave resonators (FBAR's) are used in monolithic mic rowave integrated circuits (MMIC's) for semiconductor devices, FBAR's are m ore attractive than surface acoustic wave resonators since they have the ad vantages of small size, low cost, and mass-production ability. In this lett er, an FEAR with an air-gap is fabricated by a surface micromachining techn ique which utilizes porous silicon layer (PSL) etching, This FEAR has a for ward reflection coefficient of -18.912 dB when the thickness of the ZnO thi n film measures 1 mu m, The EBAR is composed of a piezoelectric zinc oxide (ZnO) thin film and top and bottom electrode thin films of Au(1000 Angstrom )/Ni-Cr(50 Angstrom). The ZnO thin film is deposited by RF magnetron sputte ring, This fabrication process is compatible with conventional IC processes , thereby enabling the development of monolithic-integrated FBAR's on Si or GaAs substrates.