Thermal Effects of Platinum Bottom Electrodes on PZT Sputtered Thin Films Used in MEMS Devices

Abstract

For an optimum performance of MEMS devices such as microactuators and microsensors based on piezoelectric thin films a Si/Ti/Pt bottom electrode is widely used. This study shows temperature dependence of surface morphology of both platinum bottom electrode and piezoelectric lead titanate zirconate (PZT) thin films. Ti (10 nm) and Pt (100 nm) thin films were deposited on silicon substrate by thermal evaporation and electron beam, respectively, without vacuum breaking. After annealing treatment, the Pt film exhibited (111) preferred orientation. Finally a 0.8 micron thick PZT (54/46) films were deposited by r.f. magnetron sputtering at room temperature in pure Ar followed by a conventional post annealing treatment on silicon substrate. The XRD measurements have shown the perovskite structure of PZT films with (100) preferred orientation growth. The roughness of platinum film measured by AFM test showed the continuous smoothness of platinum surface for different annealing temperatures. The SEM test results demonstrated that irrespective of the annealing temperature increases, recrystallization of platinum and nano-size holes on Pt surface occurred. The latter caused the acceleration of out-diffusion titanium atoms through Pt layer and reach to the other side of surface. The surface state of Pt thin film is very important as it could strongly influence the PZT surface morphology so the existence of bubbles and depression on PZT surface are increased with both recrystallization of Pt grains and nano-size holes on Pt film surface when the annealing temperature increased.