We have developed an interdigited electrode structure for applying a static electric field to a ferroelectric thin film, which enables nearly full transmission of a perpendicularly polarized terahertz wave. This approach has been used to determine the electric field dependence of the complex permittivity of a SrTiO3 thin film on a sapphire substrate up to about 2THz employing time-domain terahertz spectroscopy. We have demonstrated up to 10% variation of the film permittivity at 300GHz at room temperature induced by an applied electric field of 100kV∕cm. No dielectric dispersion is observed between 1MHz and about 500GHz. The field-induced changes are attributed to soft mode hardening.

The nonlinear microwave properties of ferroelectric SrTiO 3 thin films are characterized via complex analysis of the intermodulation distortion ͑IMD͒ signals up to high microwave power. The measurements reveal an unusual dependence of the IMD signals on the input power, which indicates the presence of two different nonlinear properties being responsible for the generation of IMD, i.e., the nonlinear permittivity and conductivity at low and high rf power levels, respectively. The IMD signal strength cannot be explained in terms of the classical description based on a Taylor expansion of the nonlinear parameter. In contrast, simulations of the frequency spectra using more appropriate descriptions of two nonlinear parameters yield an excellent agreement between theory and experiment, and, thus, demonstrate that the IMD experiments together with the simulation might provide further insight into the mechanism of nonlinear behavior of these materials. © 2004 American Institute of Physics. ͓DOI: 10.1063/1.1751223͔The rapid development of microwave applications in a broad variety of technologies ͑e.g., communication, radar, anti-collision systems, etc.͒ has triggered a strong demand for frequency-tunable resonators and filters operating in the GHz regime. Thin films of ferroelectrics provide high relative permittivity , which can be modified by a dc electric field. Therefore, these materials can be utilized in tunable capacitors for electronic devices. In contrast to bulk dielectrics, they can be integrated into small complex thin film devices and, for instance, be used in combination with perovskite superconductors of extremely low rf losses. However, up to the present a few problems inherent to these materials have to be solved. One of those is given by the nonlinear behavior of at high levels of microwave power. The latter effect has not attracted too much interest up to now. However, in the case of device integration and miniaturization, the tunable elements can be exposed to large rf power and, thus, nonlinear effects might become important.In this letter we will focus on the nonlinear dielectric properties of ferroelectric thin films. The nonlinear dielectric properties are analyzed by measurements of third ͑and higher͒ order intermodulation distortion ͑IMD͒ signals on SrTiO 3 ͑STO͒ thin film varactors. The experimental results are compared with theoretical predictions based on Taylor expansions of the nonlinear permittivity and numerical simulations.The STO films ͑thickness of 400 nm͒ are grown on CeO 2 -buffered r-cut sapphire via on-axis magnetron rf sputtering technique. The structural orientation of STO strongly depends on gas pressure and substrate temperature during deposition. At low process pressure and temperature, STO growths predominantly ͑110͒ oriented, at higher temperature T H Ͼ840°C additionally ͑111͒-oriented STO is observed and leads to a relaxation of the film. The relative permittivity and losses of the films are shown in Fig. 1; the temperature dependence and absolute values are comparable to ...

No abstract

The nonlinear microwave properties of ferroelectric SrTiO 3 thin films are characterized via complex analysis of the intermodulation distortion ͑IMD͒ signals up to high microwave power. The measurements reveal an unusual dependence of the IMD signals on the input power, which indicates the presence of two different nonlinear properties being responsible for the generation of IMD, i.e., the nonlinear permittivity and conductivity at low and high rf power levels, respectively. The IMD signal strength cannot be explained in terms of the classical description based on a Taylor expansion of the nonlinear parameter. In contrast, simulations of the frequency spectra using more appropriate descriptions of two nonlinear parameters yield an excellent agreement between theory and experiment, and, thus, demonstrate that the IMD experiments together with the simulation might provide further insight into the mechanism of nonlinear behavior of these materials. © 2004 American Institute of Physics. ͓DOI: 10.1063/1.1751223͔The rapid development of microwave applications in a broad variety of technologies ͑e.g., communication, radar, anti-collision systems, etc.͒ has triggered a strong demand for frequency-tunable resonators and filters operating in the GHz regime. Thin films of ferroelectrics provide high relative permittivity , which can be modified by a dc electric field. Therefore, these materials can be utilized in tunable capacitors for electronic devices. In contrast to bulk dielectrics, they can be integrated into small complex thin film devices and, for instance, be used in combination with perovskite superconductors of extremely low rf losses. However, up to the present a few problems inherent to these materials have to be solved. One of those is given by the nonlinear behavior of at high levels of microwave power. The latter effect has not attracted too much interest up to now. However, in the case of device integration and miniaturization, the tunable elements can be exposed to large rf power and, thus, nonlinear effects might become important.In this letter we will focus on the nonlinear dielectric properties of ferroelectric thin films. The nonlinear dielectric properties are analyzed by measurements of third ͑and higher͒ order intermodulation distortion ͑IMD͒ signals on SrTiO 3 ͑STO͒ thin film varactors. The experimental results are compared with theoretical predictions based on Taylor expansions of the nonlinear permittivity and numerical simulations.The STO films ͑thickness of 400 nm͒ are grown on CeO 2 -buffered r-cut sapphire via on-axis magnetron rf sputtering technique. The structural orientation of STO strongly depends on gas pressure and substrate temperature during deposition. At low process pressure and temperature, STO growths predominantly ͑110͒ oriented, at higher temperature T H Ͼ840°C additionally ͑111͒-oriented STO is observed and leads to a relaxation of the film. The relative permittivity and losses of the films are shown in Fig. 1; the temperature dependence and absolute values are comparable to ...

No abstract