Research On Growth And Device Processing Of Ferroelectric Thin Films

In this paper, growth of the important ferroelectric films, including strontium barium titanate (BST), strontium barium niobate (SBN) and lead zirconate titanate (PZT), and fabrication of the relevant devices were reviewed. For BST material, the Sol-Gel growth mechanism of Ba0.7Sr0.3TiO3 (BST30) thin film was studied. The crystal phase, cross-sectional micro structure and surface morphology results indicated that the orientation and thickness of MgO buffer layer can mainly affect the microstructure of BST30 film. By measuring the optical (the refractive index and thickness fitting process) and electrical properties (measurement ofⅠ-Ⅴcurve), the action of MgO buffer layer on the character of BST30 film was also estimated. For SBN material, the Sr0.75Ba0.25Nb2O6 (SBN75) thin films were deposited on silicon substrate with MgO (100) and TiN (100) buffer layer by radio-frequency magnetron sputtering technique. By introducing a 900℃annealed SBN self-buffer layer before SBN75 deposition, the highly c-axis orientation of SBN75 thin film can be obtained on MgO buffer layer. The mechanism was studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The composition analysis showed that the SBN75 films had target-film composition transfer and the TiN buffer layer was partially oxidized during SBN growth. Moreover, the conditions for SBN/MgO/Si treated as waveguide structure were also determined by calculating the refractive index of each layer and penetration depth of MgO buffer layer. For PZT material, two types of unimorph actuator arrays were fabricated based on the excellent d31 and d33 piezoelectric properties of Sol-Gel derived Pb(Zr0.52Ti0.48)O3 (PZT52) thin film. The actuator arrays utilized diaphragm structures, in which the PZT52 layers were driven by interdigitated electrodes (IDT-mode) and parallel plate electrodes (d31-mode), respectively. Test results showed that both piezoelectric diaphragms had good dynamic and static performance, which can generate considerable deflections (>2μm) at low voltage (0～15V). Moreover, the intrinsic strain conditions shaping the deflection profiles for the diaphragm actuators were evaluated with finite element method (FEM). The clamped parallel plate configuration without a diaphragm was also characterized to estimate the thermal effects in actuators under DC applied voltage.Through the above studies, we have mastered the process of fabricating high-quality ferroelectric thin films and MEMS devices, which lays a good foundation of further research in the filed of Ferroelectric-Silicon Microelectronics Integrated Systems (FSMIS).