Gun-Tae Park

Measurement of piezoelectric coefficients of lead zirconate titanate thin films by strain-monitoring pneumatic loading method

A method to simultaneously measure the longitudinal (d33) and transverse (d31) piezoelectric coefficients of a lead zirconate titanate (PZT) thin film was developed. This system was based on the pneumatic loading method but was modified to monitor the radial strain when a pressurized gas was introduced into the chamber. The results of the bulk piezoelectric material measured by this system coincided with that measured by both the Berlincourt method and the resonance method. The effective d33 and the real d31 of the PZT thin film fabricated by the sol-gel multiple coating method, and poled at 300 kV/cm were 125 and −60 pC/N, respectively. The real d33 estimated upon considering the constraints by the silicon substrate was 180 pC/N.

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.

Effect of annealing atmosphere on domain structures and electromechanical properties of Pb(Zn1/3Nb2/3)O3-based ceramics

Annealing atmosphere effects on domain structures and electrical properties of Pb[(Zn1/3Nb2/3)0.5(Zr0.47Ti0.53)0.5]O3 (PZN–PZT) ferroelectric materials were investigated. The PZN–PZT specimens were annealed in argon, air, oxygen, and PbZrO3 atmospheres after being sintered at 1100 °C in air. The as-sintered specimens were composed of large plate-like domains. When the specimen was annealed in flowing oxygen atmosphere for 8 h at 960 °C, the domains were refined into fine twin-like domains; whereas when the specimen was annealed in argon atmosphere, the domains were modified into needle-like structures. These modifications to the domain structures have a strong effect on the electromechanical properties of this material. The formation and redistribution of lead and oxygen vacancies during thermal annealing were responsible for those variations in domain structures and electrical properties.

Orientation control of lead zirconate titanate film by combination of sol-gel and sputtering deposition

Highly oriented lead zirconate titanate (PZT) films were fabricated on a platinized silicon substrate using a combination of sol-gel and radio frequency (RF) magnetron sputtering deposition methods. A sol-gel derived PZT layer highly oriented to the (100) plane was deposited as a seed layer, and PZT with the same composition then was deposited on the seed layer by RF-magnetron sputtering. The film deposited on the seed layer showed a strong (100) preferred orientation, while the film deposited without the seed layer showed a (111) preferred orientation. Furthermore, a thick PZT film of up to 4 μm was able to be deposited without cracks by using the seed layer. The piezoelectric property of the (100) oriented film was much better than that of the (111) oriented film.

Study on velocity spread for axis-encircling electron beams generated by single magnetic cusp

The physical characteristics of an annular Pierce-type electron gun are investigated analytically. The electron gun is used in conjunction with a nonadiabatic magnetic reversal and adiabatic compression region to produce an axis-encircling beam. Typical magnetic field profiles that can generate zero velocity spreads are obtained from the analytical calculation, taking into account initial canonical angular momentum spreads at the cathode and the crossing of the beam trajectory and magnetic flux line before the magnetic cusp. Using this magnetic fields, a fairly low axial velocity spread of less than 1% is achieved by an electron trajectory program [W. B. Hermannsfeldt, Electron Trajectory Program (Stanford Linear Acceleration Center, Stanford, CA, 1979)], which agrees well with that by analytical estimation.

Orientation control of sol-gel-derived lead zirconate titanate film by addition of polyvinylpyrrolidone

Highly (100)and (111)-oriented lead zirconate titanate (PZT) films with a thickness of 350 nm were deposited on platinized Si substrates through a single spinning of a PZT sol containing polyvinylpyrrolidone (PVP) as an additive. The crystallographic orientation of the film was strongly influenced by pyrolysis conditions after spin coating. When the spin-coated sol was pyrolyzed at temperatures above 320 °C for relatively long periods of time (>5 min), (111)-oriented film was formed after annealing at 700 °C for 10 min. On the other hand, when the same sol was pyrolyzed at 320 °C for short periods of time (<5 min), the film was strongly oriented to the (100) direction after annealing. Organic residues derived from PVP decomposition acted as nucleation sites for the (100) oriented grains during annealing after the pyrolysis. The effective d33 of the (100)-oriented PZT film (100 pC/N) was much higher than that of the (111)-oriented film (62 pC/N) with the same thickness.

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.

Growth of highly (100) oriented lead zirconate titanate films on silicon and glass substrates using lanthanum nitrate as a buffer layer

Highly oriented lead zirconate titanate [Pb(Zr,Ti)O3; PZT] thin films were deposited on Pt∕Ti∕SiO2∕Si and glass substrates by the sol-gel method using lanthanum nitrate as a buffer layer. When the lanthanum nitrate buffer layer was annealed at temperatures between 450 and 550°C, the PZT layer coated onto this buffer layer showed strong (100) orientation. The film deposited on the buffer layer had this orientation, regardless of the other deposition conditions, such as the pyrolysis temperature, pyrolysis time, annealing temperature, and heating rate. The lanthanum nitrate buffer layer also acted as a very effective diffusion barrier against Pb–Si interdiffusion, thus allowing for the direct deposition of PZT films on Si, SiO2∕Si, and glass substrates. Using this buffer layer, highly oriented PZT film was fabricated stably and reproducibly, regardless of substrate material and the coating conditions. The nature of the lanthanum nitrate buffer layer and its role in the growth of the highly (100) oriented PZ...

Ferroelectric and piezoelectric properties of highly oriented Pb(Zr,Ti)O 3 film grown on Pt/Ti/SiO 2 /Si substrate using conductive lanthanum nickel nitrate buffer layer

The orientation and electrical properties of Pb(Zr,Ti)O3 thin films deposited on a Pt/Ti/SiO2/Si substrate using lanthanum nickel nitrate as a conductive buffer layer were analyzed. The lanthanum nickel nitrate buffer layer was not only electrically conductive but also effective in controlling the texture of the lead zirconate titanate (PZT) thin film. The role of the lanthanum nickel nitrate buffer layer and its effects on the orientation of the PZT thin film were analyzed by x-ray diffraction, electron beam back-scattered diffraction, and scanning electron microscopy. The annealed lanthanum nickel nitrate buffer layer was sufficiently conducting for use in longitudinal electrode configuration devices. The dielectric, ferroelectric, and piezoelectric properties of the highly (100) oriented PZT films grown with the lanthanum nickel nitrate buffer layer were measured and compared with those of (111) and (100) oriented PZT films deposited without a buffer layer.