Extrinsic scaling effects on the dielectric response of ferroelectric thin films

Abstract

Articles you may be interested inThe effect of stress on the dielectric and tunable properties of barium stannate titanate thin films Appl. Phys. Lett. 94, 052902 (2009); 10.1063/1.3073743 Barium titanate nanocrystals and nanocrystal thin films: Synthesis, ferroelectricity, and dielectric properties J. Appl. Phys. 100, 034316 (2006); 10.1063/1.2218765 Combined effect of thickness and stress on ferroelectric behavior of thin BaTiO 3 films J. Appl. Phys. 93, 2855 (2003); 10.1063/1.1540225Diffuse phase transitions, electrical conduction, and low temperature dielectric properties of sol-gel derived ferroelectric barium titanate thin films Pyroelectric Ba 0.8 Sr 0.2 TiO 3 thin films derived from a 0.05 M solution precursor by sol-gel processing Scaling effects in polycrystalline ferroelectric thin films were investigated by preparing barium titanate in a manner that maintained constant composition and film thickness while allowing systematically increased grain size and crystalline coherence. The average grain dimensions ranged from 60 to 110 nm, and temperature dependence of permittivity analysis revealed diffuse phase transitions in all cases. Maximum permittivity values ranged from 380 to 2040 for the smallest to largest sizes, respectively. Dielectric hysteresis is evident at room temperature for all materials, indicating stability of the ferroelectric phase. Comparison of permittivity values at high electric fields indicates that the intrinsic dielectric response is identical and microstructural artifacts likely have a minimal influence on film properties across the sample series. Permittivity values, however, are substantially smaller than those reported for bulk material with similar grain dimensions. X-ray line broadening measurements were taken for the grain size series at the Cornell High Energy Synchrotron Source ͑CHESS͒, which revealed coherent scattering dimensions substantially smaller than the microscopy-determined grain size. Collectively these data sets suggest that permittivity values are influenced not only by grain size but also by the mosaic structure existing within each grain, and that thin film thermal budgets, which are several hundred degrees lower than used for bulk processing, are responsible for reduced crystalline coherence, and likely the origin of degraded electromechanical response in thin film ferroelectrics.

Thin fim barium strontium titanate capacitors for tunable RF frond-end applications

“…The measured data in Figure 6.4 shows the shift of the Curie temperature with decreasing Ba content and is consistent with the work of others [84,86,149]. The lower ε r compared with bulk ceramics and the broad Curie maximum is attributed to the grain sizes and interfacial layers for thin film capacitors, which are for all compositions in the order of 20-30 nm, e.g., compared to the much larger grain size differences in [149] of 1 µm, 1.5 µm and 10 µm for sintered (at much higher CHARACTERIZATION AND OPTIMIZATION temperatures) BaTiO 3 hot-pressed ceramics.…”

“…Identical measurement observations were encountered by J.F. Ihlefeld et al [84] and by I.P. Koutsaroff et al [145].…”

“…The data reported in [84] show that barium titanate ceramics and thin films with small grain sizes < 700 nm result in capacitors with reduced relative permittivities and reduced temperature dependence of the relative permittivity. The grain size can be influenced not only by the annealing or postannealing temperature, but also by the composition.…”

“…The properties of poly-crystalline thin and thick films differ from those of single crystalline films [23,25]. Typically, the transition between the ferroelectric and paraelectric phase is smeared out against the temperature due to local variations in stress, orientation, and additional defects such as grain boundaries [82][83][84], and compositional variations.…”

“…Measurements carried out by J.F. Ihlefeld et al [84] on BaT iO 3 films, deposited by chemical solution deposition and annealed between 700-900 • C, shows that the grain size and ε r increases with annealing temperature.…”