Study Of Design And Process Of BST Ferroelectric Films Based Phase Shifter

The ferroelectric films based shifter for phase array antenna was a new phase shifterbased on the ferroelectric thin film coplanar waveguide structure. It was one of the hotspotsto military institutions and research organizations all over the world for its high reliability,anti-radiation, low drive power, small size and low cost. In this paper, the primary studywas about the phase shifters’ theory, design and process, which focused on the basic theoryand analysis method of coplanar waveguide phase shifter, the effect of interdigital on phaseshifters, and the preparation process of ferroelectric thin film and so on.Based on the transmission line theoretical models and quasi-static field method, thisexperiment analyzed the parameter characteristics of coplanar waveguide structurerespectively, simultaneously combining these two theories and the interdigital capacitordecomposition model, then came up with the simplified computational model for a lowerfrequency. This simplified theory can help to design the phase shifter with periodicinterdigital structure and the approximate structure. HFSS software was used to simulatethe coplanar waveguide structures with interdigital capacitor. The simulation results showedthat more interdigital, the more increasing in the high frequency of insertion loss and returnloss. While it will speed up the rate of periodical changes, so the phase angle can changerapidly, this was conducive to achieve a larger shift for phase shifter. Simulation resultsobtained different actual effective dielectric constant of interdigital structure model, and thecalculation verified the simplified calculating theoretical model, which stated that therewere a direct linear relationship between the interdigital capacitor structure and phaseshifter phase angle variation.This experiment prepared the BST target and BST films separately by solid statereaction and RF magnetron sputtering. After analyzing the thin films sample, a greatrelationship between the BST phase and pressure was found. The BTO and STOdouble-target sputtering at the same time need to adjust the sputtering power of BTO andSTO respectively, in order to control the film barium strontium ratio. Through the XRDanalysis, it could be drawn that the double-target co-sputtering method could prepare various components BST thin films, in the case of process parameters controllability.The phase shifter unit structure could be prepared through semiconductor process. Theactual lithography experiment identified test parameters which was suitable to thisexperiment’s large-scale of irregular substrate lithography: AZ5214E photoresists,500rpmspin coating for15seconds,4000rpm spin coating for30seconds; pre-baked120seconds at97℃; exposure80seconds; postbake120seconds at112℃; pan-exposure110seconds;developing49seconds. Under different process parameters sputtering the copper electrode,its process parameters were identified approximately: low air pressure, the suitable airpressure was about1Pa; the substrate temperature should not be too high or low, it wouldbetter be at about120℃; Copper sputtering power over much would effect on theprecipitation,60~100W may be the appropriate scope.