A modified sol-gel process for lead zirconate titanate (PZT) thin film deposition has been presented to overcome the problems of film cracking, short-circuiting and diffusion of PZT to substrate. In the modified sol-gel process, we pattern the pyrolyzed PZT thin film by wet etching before every treatment of post-annealing for crystallization. The modification brings two advantages: film cracking is eliminated due to the reduction of internal stress; PZT diffusion to substrate is avoided due to removing PZT film from the areas without Pt buffer layer before high-temperature post-annealing treatment. The modified sol-gel process is applied to fabrication of piezoelectric cantilever, which includes sputtering and patterning top and bottom electrodes, depositing PZT layer by the modified sol-gel process and releasing cantilever structure by a double side deep reaction ion etching process. After the fabrication, performances of PZT thin film such as hysteresis loop upon polarization and X-ray diffraction pattern are evaluated. Finally, resonant frequency is measured for the fabricated piezoelectric cantilever to verify its self-exited capability for future applications as micro sensors or actuators. These experimental results indicate that the modified sol-gel process for PZT deposition can greatly improve quality and yield rate of the fabrication of piezoelectric devices without causing any adverse effect.
Dynamic testing of micro devices by lead zirconate titanate (PZT) base excitation is presented in this work. Followed with a brief discussion of base excitation principle, the suitability of piezoelectric plate for high bandwidth vibration excitation is revealed. To compare the dynamic testing results based on this method, a 1.21mm (L) by 0.52mm (W) PZT micro cantilever with self-exciting capability is designed and fabricated by a sol-gel process. The fabricated PZT micro cantilever beam is then attached to a 10mm by 10mm by 1 mm piezoelectric plate (PI piezoceramic). A Polytech scanning laser Doppler vibrometer (SLDV) system is used to measure the resonance frequencies and corresponding modal shapes of the micro cantilever beam under the piezoelectric plate base excitation and the PZT micro cantilever self-excitation, respectively. It is found that piezoelectric plate base excitation would be more powerful than self excitation to stimulate the mode shapes of a micro device under testing.
TiNi films were deposited on silicon by co-sputtering TiNi target and a separate Ti target at a temperature of 450°C. Results from differential scanning calorimeter, in-situ X-ray diffraction and curvature measurement revealed clearly martensitic transformation upon heating and cooling. Two types of TiNi/Si optical micromirror structures with a Si mirror cap (20 micron thick) and TiNi/Si actuation beams were designed and fabricated. For the first design, three elbow shaped Si beams with TiNi electrodes were used as the arms to actuate the mirror. In the second design, a V-shaped cantilever based on TiNi/Si bimorph beams was used as the actuation mechanism for micromirror. TiNi electrodes were patterned and wet-etched in a solutions of HF:HNO3:H2O (1:1:20) with an etch rate of 0.6 μm/min. The TiNi/Si microbeams were flat at room temperature, and bent up with applying voltage in TiNi electrodes (due to phase transformation and shape memory effect), thus causing the changes in angles of micromirror.
Piezoelectric micro devices based on lead zirconate titanate (PZT) thin film have received considerable attention because of their wide potential in nanotechnology, biosensors and microelectromechanical systems. Thin film cracking, device short-circuiting and substrate surface degrading are commonly encountered problems for PZT micro device fabrication using chemical solution deposition (or CSD) process. These problems often lead to an extreme low yield (<10%) of fabrication and hinder the integration of piezoelectric components into micro-electromechanical systems. In this work, a new manufacturing method for PZT micro devices is developed for the first time to avoid all these problems. Unlike other modified PZT sol-gel processes, in our process pyrolysised PZT thin film is patterned by wet etching before (rather than after) the high temperature sintering treatment. This new process can tremendously reduce the cracking of thin film and eradicate the diffusion of PZT to those substrate surfaces without Pt buffer layer. The effectiveness of the process is proved by 1) the 100% fabrication yield of a number of PZT micro cantilevers, bridges and platforms, 2) the complete elimination of contaminated surfaces by PZT diffusion.
Electrostrictive actuators are a relatively new development in the field of smart material actuators. However, a major deficiency of electrostrictive actuators is their limitation of motion accuracy due to inherent non-linearity and hysteresis. This paper presents a new iterative learning control approach to improve the positioning/tracking accuracy of electrostrictive actuators. In this scheme, the iterative gain is not fixed but variable according to previous trial result and the nominal input/output relationship of the electrostrictive actuator. The convergence to the desired position/trajectory is theoretically proved. The effectiveness ofthis control scheme is experimentally demonstrated through actual positioning and tracking control ofa stacked electrostrictive actuator. The results show that using this variable gain iterative learning control scheme, not only can the stability of precision positioning be obviously improved, but also precise and non-delay tracking can be achieved.