Study On The Preparation And Properties Of Zn Doped BMT Thin Film

The medium permittivity dielectric materials with stable frequency temperaturecoefficient have been widely used in mobile phones, satellite communications,phased array radar and other fields as microwave resonator. In order to meet theincreasing miniaturization and integration of electronic product design requirements,thin film materials are the key point. Microwave dielectric films are gaining moreand more attention and research, for its highly integrated, low loss, easy coupling,etc. Because of the high Q×f value in microwave frequency, Ba(Mg1/3Ta2/3)O3is aimportant material in the communications industry, as dielectric resonators (DRS)and wave filters.In this paper, we prepare the BMT thin films by the aqueous solution-gel method,which using water as the solvent, by adding citric acid and ammonium to complexingions. It’s a quite cheap and environmental friendly method. Through adjusting the pHvalue and the molar ratio of metal:citric acid, we can get a stable BMT precursorsolution. By dipping a little ethanolamine with the ratio M:ETA=1:1, the BMTprecursor solution has a good wettability to the substrate and easily spreading film.Studies have shown that Ta precursor solution calcinated at800℃can get Ta2O5witha pure orthorhombic structure; BMT precursor solution calcinated at600℃for2hcan get BMT with a pure cubic perovskite structure.We have studied the heat treatment of BMT thin film and the effect of theZn-doping BMT thin films. Pre-annealing the BMT film at650℃for2min is aneffective way to reduce the holes, which organics can be totally burned down and thefilm is in the nucleation state. The growing of the films grains can not full with theroom which is left by the organics, so the holes in the films can not be avoided. Wecould get the well grown crystal grains with less holes by annealing thin films at750℃, at the same time we could get the relatively good performance. The Zn ionssubstituted the Mg positions in the lattice, which could expand the unit cell, then thedielectric constant could be increased. The amount of the Zn-doped should be exactlycontrolled.With a little Zn-doped(x=0.2), the surface of thin films are more smooth.More Zn-doped BMT thin films will get cracks. The dielectric constant of thin films is mainly determined by the crystal structure. Under the premise of fully grown grains,morphology of the film plays a dominant role in the dielectric loss. The best overallperformance of the thin film component is got by x=0.2, with a properties:BMT(x=0.0): εr=23.5, Q×f=250GHz(2.5GHz), τε=900ppm/℃; BMZT(x=0.2):εr=24.3, Q×f=1800GHz(1.8GHz), τε=300ppm/℃. Ba([Mg0.8Zn0.2]1/3Ta2/3)O3(x=0.2)film has a higher Q×f and lowerτεthan BMT film. Thermal stress and the presence ofholes greatly restrict the performance of the thin film.