Measurements of Nonlinear Dielectric Constants of Pb(Zr,Ti)O₃ Thin Films Using a Dynamic Measuring Method

Abstract

The nonlinear dielectric constants of Pb(Zr,Ti)O3 (PZT) thin films were studied using a dynamic measuring method. The 111-oriented PZT thin films with various Zr/Ti ratios were deposited on platinum-coated silicon substrates using a sol–gel method. The ε333 of the films increased with the Zr concentration in the tetragonal region and reached a maximum value of 280 aF/V close to the morphotropic phase boundary (Zr/Ti= 52/48). This measured value is 400 times larger than that of LiTaO3 single crystals.

Material Design Strategy for Enhancement of Readback Signal Intensity in Ferroelectric Probe Data Storage

“…where f p and E p are the frequency and the intensity of the ac bias field, respectively, and linear permittivity. (C s + C st )/C s is a calibration factor related to the stray capacitance [7]. The linear relationship between m f and E p was confirmed for this experiment, as shown in Fig.…”

“…On the other hand, we must pay attention to some tradeoff relationship when |χ (2) | is increased in accordance with such a concept. According to (7), an increase in P s is effective to enhance |χ (2) |. However, even in PbTiO 3 , which has the largest P s in typical ferroelectrics known to date, P s is approximately 100 μC/cm 2 [13], and it seems to be difficult to obtain a novel ferroelectric material that has a much larger P s than this.…”

“…Equation ( 15) has a complicated form, unlike (7). This formula may give a peculiar impression because this formula allows χ (2) to be positive when the absolute value of the second term is larger than that of the first term, while the experimentally obtained χ (2) is always negative [14], [15].…”

“…This material is also advantageous to study intrinsic nonlinear permittivity because high-quality single crystals are available. In contrast, in measurements of thin films or ceramics, the measured signal often contains extrinsic nonlinear permittivity derived from grains and domain boundaries in addition to intrinsic nonlinear permittivity [7], [16]. The readout speed is associated with intrinsic nonlinear permittivity because it determines the polarity of each written bit.…”

“…Thus, in FPDS, the polarization direction is detected in an indirect way using the nonlinear dielectric response while paying attention to the switching of the sign of nonlinear permittivity ε 333 depending on the polarization direction in noncentrosymmetric materials. However, practically sufficient readback signal intensity has not yet been obtained, because ε 333 of the existing recording media is extremely small [7].…”