Jae-Wung Lee

Piezoelectric and ferroelectric properties of 1-μm-thick lead zirconate titanate film fabricated by a double-spin-coating process

Lead zirconate titanate (PZT) films were deposited on platinized silicon substrates by spin coating using PZT sols containing polyvinylpyrrolidone (PVP) as an additive. Single-layered 1-μm-thick PZT films with 60∕40 composition were fabricated using two successive spin coatings followed by a single heat treatment step. The crack formation was effectively suppressed by the presence of nanosized pores which were generated during the heat treatment. The film has a preferred orientation corresponding to the (100) crystallographic direction. The ferroelectric and piezoelectric properties of the specimen were comparable to those of a film with same composition and thickness but prepared by the conventional sol-gel procedure.

Enhanced ferroelectric properties of Pb(Zr,Ti)O3 films by inducing permanent compressive stress

This study examined the effects of permanent residual compressive stress on the ferroelectric properties of PbZrxTi1−xO3 (PZT) films that was induced during cooling after annealing. PZT films were deposited on the tensile side of elastically bent silicon substrates by rf magnetron sputtering using a single oxide target. Compressive stress was induced on the film by removing the substrate from the holder immediately after annealing. The compressive stress effectively compensated for the inherent tensile stress that had developed during cooling. The ferroelectric properties were enhanced markedly by the induced stress; the remnant polarization and the saturation polarization increased by 35% and 24%, respectively, while the coercive field did not change much. Contrary to the ferroelectric properties, the dielectric properties decreased slightly by the stress.

Effects of lanthanum nitrate buffer layer on the orientation and piezoelectric property of Pb(Zr, Ti)O3 thick film

Highly oriented Pb(Zr,Ti)O3 (PZT) films were deposited on Pt/Ti/SiO2/Si substrates by the sol-gel method using lanthanum nitrate as a buffer layer. When the lanthanum nitrate buffer layer was heat treated at temperatures between 450 and 550 °C, the PZT layer coated onto this buffer layer showed a strong (100) preferred orientation. Regardless of the other deposition conditions, such as the pyrolysis temperature, pyrolysis time, annealing temperature and heating rate, the film deposited on the buffer layer had this orientation. Thick films were also fabricated using the sol-gel multi-coating method, and the (100) texture was found to be maintained up to a thickness of 10 m. The ferroelectric hysteresis and piezoelectric coefficient (d33) of highly oriented PZT thick films were characterized, and the (100) oriented PZT film showed higher piezoelectric property than the (111) oriented film.

Thick Pb(Zr,Ti)O3 film without substrate

In order to fabricate thick PbZrxTi1−xO3 (PZT) films for microelectromechanical system applications, the authors introduce a concept of freestanding film without a substrate. PZT films with a thickness of up to 20μm were deposited on a very thin Pt layer without a substrate by the rf-magnetron sputtering method using a single oxide target. The Pt layer (thickness <1μm) was obtained by sputtering the Pt on a Si substrate with a carbon layer between them, and subsequently removing the carbon layer by oxidation in air at 400°C. Piezoelectric properties of the film were comparable to those of bulk PZT as a result of the removal of clamping effect of the substrate.

Thick Pb(Zr,Ti)O 3 films fabricated by inducing residual compressive stress during the annealing process

The effects of residual stress induced during the annealing process on the microstructural evolution and electrical properties of Pb(Zr,Ti)O3 (PZT) films were investigated. PZT films were deposited on platinized silicon substrates by the radio frequency magnetron sputtering method using a single oxide target. Compressive stress was induced in the film by bending the silicon substrate during sputtering using a specially designed substrate holder and subsequently annealing the film without the holder. Without the residual stress, the PZT film was severely cracked when it was thicker than 2 m due to the thermal expansion mismatch between the PZT and the Si substrate. On the other hand, when the residual stress was applied, no cracks were detected in the film for thicknesses of up to 4 m. The suppression of crack formation was attributed to the residual compressive stress that compensated for the tensile stress generated during and/or after the annealing process. The electrical properties of the PZT film with the residual stress were improved compared to those of the PZT film without the residual stress.