Resonant-typed microscanners based on a silicon diaphragm and actuated by PZT was designed and fabricated on purpose to improve the deformed microstructure while resonating at high frequency. In order to yield large actuating force, hybrid PZT deposition process: sol-gel method and laser ablation was developed to manufacture thick PZT films with well-crystallized perovskite phase for the applications of microscanners. In our previous study, a sol-gel derived PZT was used due to the high film quality, large deposition area and easy composition control. However, to make a thick and crack-free PZT film, several times of coating and thermal treatment is not only time consumption, but increases the risk of contamination and leads the complicated problem of thermal residual stress. In this paper, the hybrid-derived PZT film with thickness of 3 μm was prepared with simplified steps and reduced processing time. Regarding to the performance of microscanners, 1D scan motion with straight patterns and scan angle of 8±1° has been demonstrated, while resonating with 7 Vp at resonance frequency (2325 Hz). The 2D scan pattern with area of (8±1°)×(5±1°) and less deformed edged was also obtained successfully due to the improvement of the silicon-based flat mirror surface.
To prepare lead zirconate titanate (Pb(ZrxTi1-x)O3): PZT) thin films at a higher deposition rate and a lower substrate temperature, the PZT films were fabricated by a hybrid process of sol-gel technique and pulsed laser ablation deposition. First, one layer of PZT (about 0.12-0.14 μm) was coated on Si/SiO2/Ti/Pt substrate by sol-gel process. Then PZT film was deposited at a rate of 0.7 μm/hr by pulsed excimer laser-ablation on the substrate with one sol-gel derived PZT seed layer. A target of Pb(Zr0.52Ti0.48)O3 with 20 wt% excess PbO was used. The substrate temperature was about 500 °C. The film fabricated by the hybrid process showed the perovskite PZT phase without pyrochlore phase. The dielectric constant measured at 1 kHz was approximately 1580. The saturation polarization, remnant polarization and coercive field of 0.8 μm thick film were about 46.6 μC/cm2, 24.5 μC/cm2 and 36.4 kV/cm, respectively. The residual stresses in the thin film stacks were measured by the changes in the radius of curvature of the wafer. A relatively lower tensile stress (approximately 33 MPa) was obtained compared to the sol-gel derived PZT film. Therefore, the PZT films with good electrical and mechanical properties can be fabricated by using the hybrid process of the sol-gel technique and laser ablation.
This paper reports the structural properties of lead zirconate titanate system formed in pulsed laser ablation deposition method. X-ray diffraction and scanning electron microscope was used for surface and the crystalline structure observation. The target material is prepared in conventional solid state reaction method using oxide powder. Formed lead zirconate titanate film has amorphous structure in as-deposited condition. Post-annealing treatment between 600 degree(s)C and 900 degree(s)C was carried out after deposition. Perovskite structure was formed on the Pt/Ti/SiO2/Si substrate after annealing treatment in all cases. The formed film has flat surface and homogeneous structure observed by scanning electron microscope.
Lead zirconate titanate (PZT) has been used in microsystems because of its high piezoelectric properties. We have succeeded in developing a beam and mirror scanner actuated by sol-gel deposited PZT ([Pb(Zr,Ti)O3] thin films as in our previous work. However, the problem of residual stress, which was observed in all fabricated devices, has not been solved yet. In this study, we developed a scanner actuated by double layered PZT to compensate for the residual stress and gain greater actuation force. The PZT layer was prepared by the sol-gel technique. The crystal orientation of the PZT films showed a strong (111)texture, which was reported to have good dielectric and ferroelectric properties in our previous work. The devices were fabricated through thin film depositions, lithography, dry plasma etching, and ICP releasing processes. By comparing with the conventional single layer PZT structure, the residual stress can be reduced in the double layered PZT structure. For a one dimensional bimorph beam scanner, an optical scanning angle of approximately 45- degree was obtained at a resonant frequency of 4.25 kHz, which is much larger than the one actuated by a single layered PZT unimorph beam scanner.
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