Based On Srtio ₃ Optimal Design Of Voltage - Controlled Capacitor Band - Pass Filter

SrTiO₃(STO) thin films exhibit a large electric field dependence of dielectric permittivity. The microwave surface resistance of YBa2Cu3O7-x (YBCO) is much lower than that of the normal conductor. The typical value of Rs for YBCO epitaxial thin film is smaller than 1 m? at 10 GHz and 77K. High quality epitaxial STO/YBCO multilayers can be fabricated due to their similar crystal structure and small lattice parameters mismatch. The filter made from STO/YBCO thin films shows high tunable speed, low microwave loss and high power handling capability. So STO/YBCO multilayers have attracted much interests for electronically tunable filter in the last decade.In the dissertation, high quality STO/YBCO multilayers were prepared on MgO and LaAlO3 substrates by pulsed laser deposition ( PLD ). The XRD results showed that STO/YBCO multilayers are well-crystallized and highly (001) oriented. AFM images indicated that the surfaces of STO/YBCO thin films are smooth and homogeneous (RMS=3.82 nm). Parallel capacitors and interdigital capacitors (IDC) were fabricated to measureεr and tanδof the STO layers as a function of external DC electric filed. At 10 KHz and 77 K, the tunability of parallel capacitor and interdigital capacitor are 68 % and 28%, respectively.The models of multilayer microstrip and multilayer substrate interdigital capacitor were set up, parameters of IDC were also abstracted from the simulated results in the dissertation. In addition, a 3-pole tunable combline passband filter based on Chebyshev lowpass prototype was designed and optimized. The simulated results showed that the central frequency of the filter was tuned from 1.25 GHz to 1.43 GHz , the tunability is 13.5%, when the value of IDC changes from 1.72 pF to 1.26 pF. While insertion loss is smaller than 1dB, return loss is lower than 13 dB, passband ripple is about 0.25 dB and the attenuation out of passband is higher than 45 dB at f0±150 MHz.