Epitaxial growth and planar dielectric properties of compositionally graded (Ba1−xSrx)TiO3 thin films prepared by pulsed-laser deposition

Abstract

We have heteroepitaxially deposited compositionally graded (Ba1−xSrx)TiO3 (BST) thin films with increasing x from 0.0 to 0.25 on (100)-oriented MgO substrates using pulsed-laser deposition. The compositional gradients along the depth in the graded films were characterized by Rutherford backscattering spectroscopy. By using surface interdigital electrodes, the planar dielectric response of epitaxial graded BST films was measured as a function of frequency, temperature, and dc applied voltage. At room temperature, the dielectric constant of the graded BST film was about 450 with a dielectric loss, tan δ of 0.007 at 100 kHz. Measurements varying the dc bias voltage showed hysteresis of the dielectric response and a tunability of 25% at an applied electric field of 80 kV/cm. The graded BST films undergo a diffuse phase transition with a broad and flat profile of the capacitance versus temperature. Such behavior of the dielectric response in graded BST films is attributed to the presence of the compositional and/or residual strain gradients in the epitaxial graded films. With such a graded structure, it is possible to a build a dielectric thin-film capacitor with a low-temperature dependence of the capacitor over a broad temperature regime.

Graded ferroelectric capacitors with robust temperature characteristics

“…In tunable filters, for instance, this would be unacceptable since the resonant frequency varies directly with changes in the dielectric constant. 7 Currently, only few materials satisfy the stringent requirements of low losses and temperature stability in cellular base stations and handheld devices. These materials are in the low to medium dielectric constant range.…”

Challenges and opportunities for multi-functional oxide thin films for voltage tunable radio frequency/microwave components

“…Similar studies of compositionally graded thin films with different composites of BST and using different deposition techniques, such as PLD 140 and RF sputtering, 141 are also available in the open literature.…”

“…BST thin films with extreme temperature insensitivity have been demonstrated recently, [135][136][137][138][139][140][141][142] by conceiving a material design which controls the magnitude and the sign of the temperature coefficient of capacitance (TCC) of the BST thin film material in a parallel plate varactor device configuration. In particular, a very successful material design consisted of a compositionally stratified BST multi-layer heterostructure material design whereby the Ba/Sr ratios range from 60/40 to 90/10 within the thin film heterostructure.…”

Dielectric properties of compositionally graded Ba1–xSrxTiO3 thin films described by the transverse‐field Ising model

“…Many experimental studies have been published concerning compositionally graded ferroelectric structures [13][14][15][16][17], but only a few theoretical reports can be found in the literature [18]. Prior theoretical works on CGMs have mainly focused on the origin of the abnormal polarization offset; few studies have concentrated on the dielectric properties.…”

“…There have been several experimental reports on the dielectric properties of compositionally graded BST. Zhu et al [13] measured the planar dielectric response of epitaxial graded BST films as a function of frequency, temperature, and applied dc voltage. A broad and flat profile of dielectric constant versus temperature was observed, which could be attributed to the presence of the compositional and strain gradients in the system.…”