Optical microactuation in piezoceramics

Optically/electrically operable flexible film microactuators that can offer up to two orders high efficiency of photonic to mechanical conversion compared to ceramic actuators are conceptualized. A polarized ceramic wafer of non- centrosymmetric perovskite ferroelectric ABO₃ compounds, such as lead lanthanum zirconate titanate (PLZT), when exposed to an illumination (approximately 350 to 400 nm wavelength) close to the bandgap energy, can generate a large photovoltage (approximately 1.0 kV/mm) across its length, and by the inverse piezoelectric effect cause the piezoceramic wafer to deflect in the direction away from the illumination. The optical actuation effect in piezoceramic wafers is investigated as a function of thickness, composition, and surface roughness. Such flexible microactuators would enable a new generation of micro- electro-mechanical and micro-opto-mechanical systems where the actuation will not be restricted by the clamping effect due to the rigid substrate as in the current silicon based micromachined structures. To deposit the piezoceramic film directly onto a flexible substrate, the substrate must have high temperature stability, high strength (Young's Modulus approximately 4.9 X 10¹⁰ N/m²), a close match of thermal coefficients of expansion with the piezoceramic film, and a tailorable crystal orientation in order to provide a desired template for growth of oriented PLZT. This paper also presents a comparison of a variety of flexible substrate films and fibers and our recent results on polybenzoxazole (PBO), a polymeric candidate for a flexible high temperature substrate. Variation of the properties of PBO as a function of temperature are also presented.