Since research on piezoelectric thin films started in the beginning of 1990, interest in the piezoelectric property of thin films has been growing rapidly. Particularly many researchers are working on this for MEMS (Micro Electro Mechanical System) applications.
Extensive studies are being carried out on the piezoelectric thin films, especially those based on the PZT system. This is due to relatively simple process of fabrication and high piezoelectric coefficient of PZT. There are a lot of applications using piezoelectric thin films. For example, MEMS, microactuator, microsensor, memory device like FeRAM, optical device and IR detector. Specially, the ferroelectric thin film actuator for optical applications is one of the most promising candidates for the up-coming commerization.
The piezoelectric coefficient is one of the most important parameters in the development of MEMS incorporationg piezoelectric thin films. For simple process of operating, we are trying to reduce poling processes which are currently requisite to operate piezoelectric thin films. For this, we must study on intrinsic piezoelectricity. Some piezoelectric thin films show $d_{33}$ without poling process. These are found only in thin films. For bulk PZT, specimens without poling do not show $d_{33}$. The reason why some piezoelectric thin films shows $d_{33}$ without poling process can be explained by preferred orientation or curie temperature.
Using this built-in piezoelectricity, we can obtain similar property without poling, so this is a highly desired property for thin film application. If we know the origin of built-in piezoelectricity and develop the way to form built-in piezoelectricity artificially, we can have great advantage.
Lead Zirconate Titanate$( Pb(Zr,Ti)O_3)$ thin films have been prepared on a bottom electrode, $LSCO(La_{0.5}Sr_{0.5}CoO_3)$, which can be one of the most fundamental parameters of PZT thin films by DC reactive sputtering and PLD(Pulsed Laser Deposition). The piezoelectric properties of PZT thin film have been measured by our pneumatic loading method. Even though the piezoelectric property of thin films is a crucial factor in the MEMS and thin film devices, very few reports have been provided in the last decade. We have examined the effects of LSCO electrode, poling and annealing conditions on microstructural properties and electrical properties of PZT thin films, especially piezoelectric property and P-E characteristics.
PZT thin films on LSCO deposited by DC reactive sputtering showed highly preferred (001) and (002) orientation. Highly preferred PZT thin films showed good piezoelectric coefficients. Annealing and poling improved $d_{33}$. After 650℃ annealing, SEM showed denser structure. It could be one of factors which contributed to the improvement of $d_{33}$. PZT thin film on LSCO after 650℃ annealing shows the best piezoelectric property. Particularly it had very good $d_{33}$ without poling process. Therefore, this property will be very useful for MEMS applications because it does not need poling process.
PZT thin films deposited on LSCO electrode by Pulsed Laser Deposition. 500mTorr Oxygen working pressure, 26kV voltage and 10Hz laser frequency were optimal conditions to deposit PZT by PLD. PZT thin films on LSCO deposited by PLD showed (001),(110),(002) orientations and intrinsic piezoelectricity as well. PZT thin films after reverse poling showed the highest piezoelectric coefficient. Until now few investigatins carried out in the respect of poling directions. Therefore to obtain the best performance of piezoelectric devices, we must study poling direction more deeply.
