Jeongmin Oh

Correlation between strain and dielectric properties in ZrTiO4 thin films

Single-phase paraelectric ZrTiO4 thin films were synthesized at various temperatures using direct-current magnetron reactive sputtering. The dielectric constants (e) and dielectric losses (tan δ) of as-deposited and annealed films were measured in the 100 kHz range using a Pt upper electrode and a phosphorous-doped Si (100) bottom electrode. Data showed that as the deposition temperature increased, the dielectric losses decreased, while the dielectric constants did not change much. Similar trends for dielectric losses were observed after annealing at 800 °C. These results of dielectric losses correlated well with strains in ZrTiO4 thin films, analyzed from x-ray diffraction peak widths at various scattering angles.

Effect of microstructures on the microwave dielectric properties of ZrTiO4 thin films

To obtain various paraelectric ZrTiO4 thin-film microstructures, the films were synthesized at different deposition temperatures using rf magnetron sputtering. Both the dielectric losses (tan δ) and dielectric constants (e) of the ZrTiO4 thin films were measured up to 6 GHz using a circular-patch capacitor geometry. The films showed enhanced crystallinity with increasing deposition temperature, as determined from the x-ray diffraction peak widths at various scattering vectors. The microwave dielectric losses correlated very well with the level of crystallinity or strain, while the dielectric constants did not alter significantly.

Dielectric Properties and Strain Analysis in Paraelectric ZrTiO4 Thin Films Deposited by DC Magnetron Sputtering

The dielectric constants and dielectric losses of ZrTiO4 thin films deposited by DC magnetron reactive sputtering were investigated. The paraelectric properties were measured in the 100 kHz range, and compared with an equivalent circuit model. As the deposition temperature increased (up to 600°C), the dielectric losses (tan δ) decreased (down to 0.017±0.007), while the dielectric constants (e) were in the range of 35±7. Post annealing at 800°C in oxygen for 2 h reduced tan δ down to 0.005±0.001, higher than those of well-sintered bulk ZrTiO4. The systematic trend of tan δ as a function of deposition temperature and post annealing showed good correlations with strains in ZrTiO4 thin films deduced from the broadening of X-ray diffraction peak.

Influence of the Microstructures on the Dielectric Properties of ZrTiO4 Thin Films at Microwave-Frequency Range

The dielectric properties of paraelectric ZrTiO4 thin films were investigated in the microwave-frequency range. The dielectric losses (tan δ) and dielectric constants (e) were successfully measured up to ~ 5 GHz using a circular-patch capacitor geometry. The effects of the microstructures on the dielectric properties were also investigated. The ZrTiO4 films were deposited at different temperatures and RF power densities to vary the film microstructures. As the deposition temperature and RF power density were increased, the film crystallinity was enhanced and dielectric losses decreased. The microwave dielectric losses correlated very well with the level of local strain and unit-cell dilation, while the dielectric constants did not alter significantly.

Crystallinity Dependence of Microwave Dielectric Properties in (Ba,Sr)TiO3 Thin Films.

The dielectric properties of (Ba0.43Sr0.57)TiO3 (BST) thin films were investigated in the microwave-frequency range. The dielectric losses (tan δ) and dielectric constants (e) were successfully measured up to ~6 GHz using a circular-patch capacitor geometry. The deposition temperatures were varied from room temperature to 750°C to investigate the effects of crystallinity on the dielectric properties. As the film crystallinity was enhanced, the dielectric losses increased from 0.0024±0.0018 at room-temperature to 0.0102±0.0017 at 750°C deposition. The dielectric constants varied from 10.29±0.02 to 243±1 in the same deposition-temperature range. Raman spectroscopy showed that the increase in dielectric losses of the BST thin films was correlated with the growth of microscopic polar regions induced by symmetry-breaking defects. Because the sizes of these regions are proportional to the dielectric constants of host lattices (crystallinity), dielectric losses increase with the deposition temperatures.

Microwave dielectric relaxation of the polycrystalline (Ba,Sr)TiO3 thin films

The microwave dielectric properties of the (Ba,Sr)TiO3 thin films annealed at various oxygen pressures ranging from 5to500mTorr were investigated over the frequency range 0.5–5GHz using a circular-patch capacitor geometry. The dielectric constant (e) followed Curie–von Schweidler relaxation in the microwave-frequency range, and the degree of relaxation corresponded qualitatively with the measured dielectric loss (tanδ). As the oxygen pressure varied, the dielectric loss had a maximum value of ∼0.03 at 100mTorr, and its behavior was correlated with the Raman strength of the polar modes.

Effect of crystallinity on the dielectric loss of sputter-deposited (Ba,Sr)TiO 3 thin films in the microwave range

The crystallinity dependence of the microwave dielectric losses in (Ba,Sr)TiO 3 thin films was investigated. The sputter-deposition temperatures were altered to vary the level of thin-film crystallinity on a Pt/Si substrate. The dielectric losses (tan ) were measured up to 6 GHz without parasitic (stray) effects by using a circular-patch capacitor geometry and an equivalent-circuit model. The microwave dielectric losses increased from 0.0024 ± 0.0018 to 0.0102 ± 0.0017 with increasing crystallinity. These deteriorated dielectric losses showed a good correlation with the symmetry-breaking defects, as confirmed by Raman spectra at approximately 760 cm �1 , inducing microscopic polar regions above the Curie temperature of the bulk (Ba0.43Sr0.57)TiO3.