PT03. Piezoelectric actuator renaissance

Summary form only given. I will discuss five key trends in this paper for providing the future perspectives; “Performance to Reliability”, “Hard to Soft”, “Macro to Nano”, “Homo to Hetero” and “Single to Multi-functional”. First in the materials trend, the worldwide toxicity regulation is accelerating the development of Pb-free piezoelectrics for replacing the conventional PZTs. Second, high power piezoelectrics with low loss have become a central research topic from the energy-efficiency improvement viewpoint; that is to say, “real (strain magnitude) to imaginary performance (heat generation reduction)”. Third, we are facing the revival polymer era after `80s because of their elastically soft superiority. Larger, thinner, lighter and mechanically flexible human interfaces are the current necessity in the portable electronic devices, leading to the development in elastically soft displays, electronic circuits, and speakers/microphones. Polymeric and polymer-ceramic composite piezoelectrics are reviving and commercialized. PZN-PT or PMN-PT single crystals became focused due to the rubber-like-soft piezo-ceramic strain after 25 years of the discovery. In the MEMS/NEMS area, piezo MEMS is one of the miniaturization targets for integrating the piezo-actuators in a micro-scale devices, aiming at bio/medical applications for maintaining the human health. “Homo to hetero” structure change is also a recent research trend: Stress-gradient in terms of space in a dielectric material exhibits piezoelectric-equivalent sensing capability (i.e., “flexoelectricity”), while electric-field gradient in terms of space in a semiconductive piezoelectric can exhibit bimorph-equivalent flextensional deformation (“monomorph”). New functions can be realized by coupling two effects. Magnetoelectric devices (i.e., voltage is generated by applying magnetic field) were developed by laminating magnetostrictiveTerfenol-D and piezoelectric PZT materials, and photostriction was demonstrated by coupling photovoltaic and piezoelectric effects in PLZT. In the application area, the global regime for “ecological sustainability” particularly accelerated new developments in ultrasonic disposal technology of hazardous materials, diesel injection valves for air pollution, and piezoelectric renewable energy harvesting systems.