Polymer bonding of GaN crystal layer on silicon substrate for micro mechanical resonator applications

A polymer bonding method of GaN crystal layer on silicon substrate is proposed for the integration of GaN micro electromechanical devices on silicon substrate. A GaN crystal layer is grown on a silicon wafer epitaxially with a buffer layer. Avoiding the influence of residual stress of the buffer layer on the GaN micro electromechanical devices, the GaN layer is transferred onto another silicon wafer by the polymer bonding method and the buffer layer is removed. The bonding method consists of two-step polymer process to prevent from breaking the bonded GaN thin layer by air bubbles. The polymer is patterned to generate air channels in the first polymer process so that the air bubbles are not remained after bonding the GaN/silicon wafer. The air channels are filled with another polymer in the second polymer process. Then, the silicon substrate of the GaN/silicon wafer is removed by silicon deep reactive ion etching, and the buffer layer for GaN crystal growth is also etched by fast atom beam of SF₆ plasma and Cl₂ reactive ion plasma. The bonded GaN layer is used for fabricating GaN micro mechanical resonators on silicon substrate by etching the polymers as sacrificial layer. The deformation of the freestanding resonator was minimized by removing the buffer layer. A cantilever resonator fabricated from GaN layer is excited by optical means and the basic characteristics are discussed.