Ag-doped ZnO thin films have been fabricated by pulsed laser deposition. Thermal analysis and X-ray photoelectron spectroscopy (XPS) were systematically investigated to verify the doping mechanism of Ag doped ZnO thin film depending on deposition temperature. The fabricated p-type Ag doped ZnO films shows the hole concentration in the range from 4.9x10<sup>16</sup> to 6.0x10<sup>17</sup> cm<sup>-3</sup>.
Lead-based ferroelectric thin films offer a wide variety of applications in dielectric, piezoelectric, pyroelectric, electro-optic, and memory devices. Among many applications, Pb-based thin films are suitable for increasing the integration of DRAM due to high relative dielectric constant. Thin films of PLT(28) Pb<SUB>0.72</SUB>La<SUB>0.28</SUB>Ti<SUB>0.93</SUB>O<SUB>3</SUB>) have been deposited on Pt/Ti/SiO2/Si substrates in situ by a laser ablation. We have systematically investigated the effect of deposition temperatures on the crystal structures and the electrical property of the films. The temperature has been varied from 500 degree(s)C to 700 degree(s)C. The crystal structures and the electrical properties of the thin films have been observed to strongly depend on the deposition temperature by C-V measurement, scanning electron microscopy, and X-ray diffraction method.
Surface modification of YBa<SUB>2</SUB>Cu<SUB>3</SUB>O<SUB>7-x</SUB> (YBCO) target in the process of pulsed laser deposition was systematically investigated by Scanning Electron Microscopy (SEM). We observed that the size of cones formed on YBCO target by pulsed laser became larger with increasing the laser energy density. The image of SEM shows the difference of cone formations at the boundary and at the center of the ablated area on the target surface. This nonuniform modification of the ablated area is supposed to be mainly due to Gaussian profile of the laser beam and the difference of thermal conductivities of the ablated area. To eliminate cones, we have used the method of rotating the target by 180 degree(s) to shot the same number of laser beams on the same spot from opposing angles. Experimental results of losing the directionality and changing the shape of cones formed on YBCO target surface by laser beams incident on the same spot from opposing angles are obtained. These results are mainly due to altering irradiation geometry because cones develop only under unidirectional laser beam. Raman spectroscopy illustrates that the target phase is less degraded by the laser beams incident from opposing angles than the laser beams incident from one direction.
C-axis oriented superconducting YBCO thin films on Hastelloy (Ni-Cr-Mo alloys) with yttria-stabilized zirconia (YSZ) buffer layers were fabricated by in situ pulsed laser deposition in a multitarget processing chamber. Generally, it is difficult to make films on flexible metallic substrates due to inherent interdiffusion problems between metallic substrates and superconducting overlayers. To overcome this difficulty, it is necessary to use YSZ buffer layers since it will not only limit the interdiffusion process but also minimize the surface microcrack formation due to smaller mismatch between the film and the substrate. In order to enhance the crystallinity and the transport properties of YBCO films on metallic substrates, YSZ buffer layers were grown at various temperatures different with the deposition temperature to grow YBCO films. On YSZ buffer layer grown at higher temperature than that for YBCO film, the YBCO thin film was found to be textured with c-axis orientation by x-ray diffraction and had a high zero- resistance critical temperature of 85 K. Critical current density for this film at 77 K was 4.7 X J/cm<SUP>2</SUP>.
We have fabricated YBa<SUB>2</SUB>Cu<SUB>3</SUB>O<SUB>7-(delta</SUB> ) (YBCO) superconducting line resonator and tunable line resonator on ferroelectric Sr<SUB>0.5</SUB>Ba<SUB>0.5</SUB>TiO<SUB>3</SUB> (SBTO) buffered MgO(100) substrate and discussed the frequency shift mechanism of superconductor as a function of temperature and bias voltage, respectively. The resonators were designed using superconducting YBCO epitaxial thin films. Optimized resonator shown the resonant frequency of 10 GHz at 77 K. The YBCO films were grown in situ by pulsed laser deposition technique at 750 degree(s)C and oxygen partial pressure of 200 mTorr. The resonators have linear microstrip line separated by a gap of 5 micrometers and 0.5 mm, respectively. A gap is intentionally introduced to generate mainly a capacitive series reactance. The equivalence circuit of line resonator is a II network consisted of three capacitances. As the series capacitance C<SUB>12</SUB> of SBTO ferroelectric thin films was changed by a bias voltage applied on the strip conductors including the gap, resonance frequency was shifted about 20 MHz from the unbiased center frequency of 10 GHz. The variation of resonance peak could be explained by a serial capacitance model. To find a central frequency mechanism depending on temperature, we fit the raw data using f(T)/f(10 K) and simple power law model. The shifting of the resonant frequencies due to temperature was fit to a two-fluid model, BCS theory and empirical formula. Also the surface impedance of superconducting YBCO films as a function of temperature at 10 GHz has been estimated by a transmission line method.
We have designed the microstrip-type multipole (7-pole and 9-pole) lowpass filters consisting of both transmission lines and open stubs. The filters were fabricated on high temperature superconducting (HTS) YBa<SUB>2</SUB>Cu<SUB>3</SUB>O<SUB>7-(delta</SUB> ) (YBCO) thin films grown on MgO(100) substrates by pulsed laser deposition. For 7-pole lowpass filter, the measured insertion losses were within 0.5 dB, and up to 8 GHz the passband shows very flat with ripples of less than 0.05 dB. For 9-pole filter, we observed the insertion loss of 5.0 dB and the ripples of 0.64 dB. The skirt became steep and the off-band rejection increased large as the number of poles increases.
A new bandpass filter design is presented which uses arbitrary image impedance of the superconducting thin film coupled lines. In order to investigate the performance of different superconducting bandpass filters with different image impedances, we have selected and designed 4-pole Chebyshev 50 (Omega) and 75 (Omega) coupled line superconducting bandpass filters which have the same passband of 11.7 approximately 12.4 GHz. The measured result of the 75 (Omega) coupled line superconducting bandpass filter agrees with the result of the 50 (Omega) coupled line superconducting bandpass filter. The technique used in this paper to change the filter structure is particularly attractive because of its application to improve the power-handling ability of superconducting passive device and its possibility to reduce the size of superconducting thin film microwave device which has the limitation of superconducting thin film size.
The microstrip filters, such as multipole lowpass filter and multipole bandpass filter, have been designed, fabricated, and characterized. The YBa<SUB>2</SUB>Cu<SUB>3</SUB>O<SUB>7-(delta</SUB> ) (YBCO) epitaxial thin films on MgO substrates were grown in situ at 760 degree(s)C by pulsed laser deposition. The design of filters in a microstrip configuration and their microwave responses were simulated by microwave design simulator, respectively. The filter patterns on the laser ablated YBCO/MgO film were generated using conventional photolithography and ECR-etching process. The performance of filters was measured as a function of temperature and frequency. Microwave loss properties were superior for the filters patterned from HTS films to the filters fabricated from Au-metal films of the same dimensions.
Epitaxial YBa<SUB>2</SUB>Cu<SUB>3</SUB>O<SUB>7-x</SUB> (YBCO) superconducting thin films have been grown on (100) MgO substrates by pulsed laser deposition. The characterization of YBCO superconducting thin films grown on MgO under the optimized condition has been performed with x-ray diffraction (XRD), Atomic Force Microscopy (AFM), magnetic property measurement in SQUID magnetometer and resistivity measurement. The fabrication and characterization of dual mode disc resonators (DMDRs) have been discussed with superconducting thin films grown under optimized deposition conditions.