Dielectric properties of epitaxial KNbO 3 ferroelectric thin films
- PDF / 129,064 Bytes
- 4 Pages / 612 x 792 pts (letter) Page_size
- 64 Downloads / 344 Views
The dielectric response of KNbO3 epitaxial ferroelectric thin films was measured as a function of bias, frequency, and temperature. Thin films with a thickness of 80 to 350 nm were deposited on spinel substrates by low-pressure metalorganic chemical vapor deposition. Bias dependence measurements showed hysteresis in the dielectric response. The dielectric constant decreased with bias, and the tunability was calculated to be between 35% and 42% for an applied field of 7 MV/cm. The frequency dependence of the dielectric constant followed a power law. A pronounced thickness effect was observed in the dielectric response, especially at the Curie temperature. With decreasing thickness, the dielectric constant and the loss tangent decreased. A diffuse ferroelectric phase transition was observed for films with a thickness less than 350 nm.
Ferroelectric materials are of interest for various applications because of their high permittivities and piezoelectric, pyroelectric, electrooptic, and nonlinear optical coefficients. Potassium niobate (KNbO3) is a particularly promising ferroelectric with its combination of relatively low dielectric constants (⑀1 155, ⑀2 ⳱ 44, and ⑀3 ⳱ 980) with extremely high electrooptic coefficients (r42 ⳱ 380 pm/V, r33 ⳱ 64 pm/V). This makes KNbO3 and its solid solution with KTaO3 very attractive for optoelectronic devices including high speed electrooptic switches, modulators, and frequency doublers.1–3 Because of the interest in this material for highfrequency, electrooptical devices, measurements of its dielectric properties have been performed on KNbO3 single crystals as well as pure and doped ceramics.4–8 Pressure-dependent changes in the low-frequency dielectric constant have been observed.9 Frequency dispersion has been observed and attributed to space charge effects and small atomic displacements within the ferroelectric phase.10,11 While the dielectric properties of KNbO3 single-crystal and bulk ceramics have been studied, little is known about these properties for epitaxial thin films despite their potential importance in waveguide structures.
a)
Present addresses: NSF Center for Advanced Materials and Smart Structures, North Carolina A&T State University, Dept. of Electrical Engineering, Greensboro, NC 27411; Materials Science Dept., North Carolina State University, Raleigh, NC 276957916. J. Mater. Res., Vol. 17, No. 2, Feb 2002
http://journals.cambridge.org
Downloaded: 10 Mar 2015
In this paper, we report on the frequency, bias, and temperature dependence of the dielectric constant for epitaxial thin films of KNbO3. Frequency response measurements indicate a power law dependence of the dielectric constant. A significant bias dependence of the dielectric constant was also observed. A pronounced thickness effect of the dielectric response was noted at high temperatures near the ferroelectric phase transition. KNbO3 films were grown by low-pressure metalorganic chemical vapor deposition at 800 °C as previously described.2 Niobium pentaethoxide {[NbOCH2(CH3)5]2} and rigorously purifi
Data Loading...
