Crystallographic and dielectric properties of highly oriented BaTiO3 films: Influence of oxygen pressure utilized during pulsed laser deposition

Abstract

The crystal structure of BaTiO 3 thin films grown by pulsed laser deposition on MgO substrates was found to be strongly influenced by the oxygen pressure used during growth. Low pressures produced epitaxial films with highly strained out-of-plane lattice parameter c compared to inplane parameter a, while increasing oxygen pressure resulted in the ratio c/a<1 with a concomitant increase in polycrystallinity. The dielectric properties varied with changing crystal structure reaching a maximum permittivity value in films near the minimum point of tetragonal distortion and exhibiting relaxor-like behavior in c/a<1 films close to this point. Hysteresis observed in dielectric tuning loops pointed to the presence of the ferroelectric phase in all films at room temperature. As a result of high electric field poling treatment at 300°C, the tunability generally increased and initially symmetric tuning curves became asymmetric. The tuning curve in c/a<1 samples became nearly linear, supporting the premise of polarization reorientation with changing deposition condition. Phase transitions to the paraelectric phase were highly suppressed and shifted upwards in temperature from the bulk transition temperature of 130 to ∼250°C in strongly c-oriented films. Moderate shifts in oxygen working pressure were demonstrated to produce films with very different properties thereby offering convenient means for strain engineering and control of preferred crystal orientation and polarization direction of highly oriented BTO films.

Orientation Dependent Dielectric Characteristics of Nanocrystalline Pb(ZrxTi1-x)O3Films with Inter Digital Electrodes

“…Dielectric maximum moved toward higher temperatures in 150 nm film as the frequency changed from 100 Hz to 1 kHz and in 200 nm film as the frequency increased from 100 Hz to 10 kHz. Same kind of frequency dependence was also found in highly oriented BaTiO 3 thin films [17]. This temperature shift towards higher temperatures as a function of frequency might be an indication of relaxor behaviour [18,19].…”

Optical properties of BaTiO3 thin films: Influence of oxygen pressure utilized during pulsed laser deposition

“…The crystal phase could not be determined conclusively, and this can potentially explain the deviation between birefringence and crystal distortion values in films deposited at 25 and 30 mTorr oxygen pressures. The shift from epitaxial film to polycrystalline structure was also suggested by atomic force microscope (AFM) studies as reported in [7]. The surfaces of the samples deposited at low oxygen pressures (1.5 and 10 mTorr) had RMS roughness of less than 1 nm.…”

“…The out-ofplane lattice parameters were calculated from θ−2θ patterns (Rigagu RU 300) while in-plane parameters were determined from (202)/(220) non parallel-to-surface planes (Bruker D8 equipment) together with θ−2θ scan results. Further information on the XRD analysis and surface morphology studies are provided in ref [7]. A Si x N y striploaded waveguide design was chosen for the Mach-Zehnder modulator waveguides, allowing for the use of easily patterned materials for the guiding structure rather than having to pattern the BTO layer itself.…”

Dielectric and Tunability Properties of Nanostructured Nd-modified Pb(ZrxTi1-x)O3Thin Films up to Microwave Frequencies

“…Dielectric maximum around ∼420 • C also moved towards higher temperatures with frequency from 100 Hz to 10 kHz. Same kind of relaxor-type dependence was also found in our previous studies on nanocrystalline PNZT films [12], as well as on highly oriented BaTiO 3 [13], and in (Pb 0.5 Ba 0.5 )ZrO 3 thin films studied by Hao et al [14]. The 150-nm-film, for comparison, showed typical diffusive phase transition with one dielectric relaxation maximum around ∼390 • C, and the transition of the 50-nm-film was already strongly suppressed due to high residual compressive stress state.…”