Study And Design Of Phase Shifters Using BST Ferroelectric Thin Film

With the development of aviation and space technology and the needs of the military, the phase array's radar has developed quickly. It is urgent to develop a phase shifter which has high speed and precision of phase shift, low insert loss, large capacity of power, small bulk, little weight, low cost, high reliability. Ferroelectric phase shifter can meet these requirements well and has attracted more and more focus. BST Ferroelectric films, which have many merits such as high Dielectric constants, high tunability and low loss, are considered as the optimum choice to prepare ferroelectric phase shifters.In this thesis, millimeter-wave thin film dielectric phase shifter was investigated, which has significantly potential application in T/R module of phased array radar. The requirements to the properties of Ferroelectric thin film applied to dielectric phase shifter were analyzed. The property ,structure and preparing technique of BST thin film were investigated .Ba_xSr_1-xTiO₃ (BST) film is prepared used Sol-gel technique. The film is smooth, has no cracks and of good properties. After the analysis of some structures commonly used in dielectric phase shifters, according to the theory of microwave planar transmission lines, A CPW-type ferroelectric thin film dielectric phase shifter was designed, The phase shifter was a coplanar waveguide (CPW) transmission line with two substrates of BST/MgO structure. Considering characteristic of the device, the phase shifter was simulated with the high frequency structure simulator (HFSS), which is commercial software based on finite element method. We study the rule how the structure parameters affect the insert loss and phase shift of the device and how the dielectric properties of BST thin films do. These parameters were optimized to improve the performance of the phase shifter.Finally the layout of the BST thin film phase shifter was designed.The results show: the phase shifter had a figure of merit (FOM) of 53.56°/dB. Structure parameters of the CPW have great influence on the performance of the phase shifter. Widening the signal line width of the CPW line can reduces the insert loss of the phase shifter, but reduces the phase shift also. It is similar to the gap width of the CPW. Ticker BST film can obtain larger phase shift, but the insert loss is higher too. The dielectric properties of BST thin films are also important factors which affect the performance of the phase shifter. To obtain good performance, lower Dielectric constants (usually less than 500) and lower loss tangent is expected. The higher the...