Electrical and electromechanical properties of ferroelectric thin films for microelectromechanical applications

Ferroelectric thin films have various potential applications in electronic devices. This thesis investigated the dielectric, electrical and electromechanical properties of lead based ferroelectric thin films and their potential applications in microelectronic and micromechanical devices, such as nonvolatile random access memories, dynamic random access memories, and microactuators.; Dielectric and ferroelectric properties of thin films in the lead zirconate-lead titanate (PZT) solid solution have been studied. X-ray diffraction and ESEM in situ study on the sol/gel thin film growth process revealed that the ferroelectric thin films crystallized rapidly and that rapid thermal processing could improve the quality of the films. Ferroelectric relaxor composition of lead magnesium niobate-lead titanate (PMN-PT) thin films were also successfully fabricated by the sol/gel technique. Thin films with composition 90PMN10PT had dielectric constant as high as 6300 at room temperature which is the highest value that has been reported in ferroelectric thin films.; Electrical conduction and dielectric breakdown mechanism of these films have been studied. Dielectric breakdown field was as high as 2 MV/cm and leakage current was as low as 10{dollar}sp{lcub}-9{rcub}{dollar} A/cm{dollar}sp2{dollar} in PZT thin films. Interfacial layers between the electrodes and ferroelectric thin films played an important role in electrical properties at high frequencies.; Piezoelectric and electrostrictive properties of ferroelectric thin films were studied systematically first time. According to the characteristics of field induced strain, the films can be divided into three groups: normal ferroelectric type (PZT), ferroelectric relaxor type (90PMN10PT), and antiferroelectric type (PLSZT); each of them has its own advantages for micromechanical device applications. PZT (52/48) thin films has a large piezoelectric coefficient: d{dollar}sb{lcub}33{rcub}{dollar} is 215 (pC/N) at d.c. bias field of 75 kV/cm; d{dollar}sb{lcub}31{rcub}{dollar} is -100 (pC/N). Electromechanical coupling factor k{dollar}sb{lcub}rm eff{rcub}{dollar} was in the range of 0.15-0.49. The field induced piezoelectricity in 90PMN10PT thin films is tunable by d.c. bias field, d{dollar}sb{lcub}33{rcub}{dollar} coefficients vary from 27 (pC/N) to 256 (pC/N). Electrostrictive coefficients were {dollar}rm Msb{lcub}11{rcub} = 3.5times 10sp{lcub}-16{rcub} msp2/Vsp2{dollar} and {dollar}rm Qsb{lcub}11{rcub} = 1.2times 10sp{lcub}-2{rcub} msp2/Csp2{dollar} respectively. The piezoelectric characteristics of antiferroelectric thin films (PLSZT) was also controlled by electric fields. The largest piezoelectric coefficient d{dollar}sb{lcub}rm 33{rcub}{dollar} is about 200 (pC/N) and this value can be enhanced 35 times near a resonant frequency.; Finally, a cantilever type microactuator was designed, and the calculated parameters showed that the ferroelectric thin film actuator has great promise.