IMPROVED SRTIO3 MULTILAYERS FOR MICROWAVE APPLICATION - GROWTH AND PROPERTIES

Au/SrTiO3 (STO), AU/YBa2CU3O7-x (YBCO)/STO, Au/STO/CeO2/STO, and Au/ST O/MgO/STO multilayer structures on LaAlO3 substrates have been fabrica ted. Their properties are investigated at 1 MHz and at microwave frequ encies (40 MHz-40 GHz) as a function of applied voltage, and in the te mperature range between 20 and 300 K. The STO thin films showed compar atively high values of dielectric constant (up to 1800 at 50 K) with l ow measured film losses, tan delta<0.005, (limit of the measurement se tup), at 20 GHz and 20 K, indicating their applicability for microwave devices. The dielectric constant is shown to be independent of freque ncy to at least 40 GHz, while the losses exhibit no or weak frequency dependence. Relaxation of the STO film in oxygen atmosphere before dep osition of YBCO is shown to reduce interactions between the YBCO and S TO films. After an ''ex situ'' high-temperature (900 degrees C) treatm ent in flowing oxygen a reduction of the STO dielectric constant as we ll as tan delta has been observed. Using cerium dioxide as a sublayer in a multilayer STO structure gives rise to an additional (110) STO pe ak. Substituting the CeO2 layer with a MgO layer drastically reduces t his peak, but the lattice distortion increases, with increased dielect ric constant and higher controllability as a result. Multilayers with eight intermediate oxygen relaxations during the STO film deposition s howed the lowest losses and highest dielectric constant with 25% tunab ility of the effective dielectric constant at 20 K and with an applied electric field of 19 kV/cm. (C) 1998 American Institute of Physics.