Research Of A-site Modification Of Bismuth Pyrochlore Materials

A large amount of electronic circults such as varactor,phase shifter,filter,oscillater and so on are facilitated by tunable electronic devices.In the tunability technology of the device,the dielectric thin film varactor technology has a great application prospect in the communication field because of its fast response,low cost and easy integration.The core of tunable electronic components is tunable materials,so it is important to study new type of tunable materials and improve the performance of the existing tunable materials.Bi_1.5MgNb_1.5O₇?BMN?with cubic pyrochlore structure has attracted a large number of scholars'attention due to its moderate dielectric constant,extremely low dielectric loss and large dielectric tunability.In this paper,the change of the dielectric properties of the new material was studied by using different ions to replace Mg ions in the A-site of BMN materials.The loss mechanisms of BMN thin films were investigated and the BMN thin film varactor was carried out.The main contents and conclusions of this paper are as follows:1.The dielectric tunable mechanism of cubic pyrochlore was studied.The Cobalt,calcium and nickel ions were selected to replace Mg²⁺in the A-site of BMN.The Co-BMN,Ca-BMN and Ni-BMN ceramic chips and targets were prepared,and the structure and dielectric properties of the ceramic samples were analyzed.The results show that the new BMN material is still cubic pyrochlore structure,and the BMN material doped with 0.4%Ni has the best performance.The dielectric constant measured at 1 MHz is 141,and the dielectric loss is 0.0016.2.The loss mechanism of BMN materials were studied.The results showed that the intrinsic loss is the main source of dielectric loss.But beyond that,the local polarization loss and charge defect loss are also the sources of dielectric loss.With the increase of frequency,the proportion of charged defect loss is increasing.After A-doping,it is found that small ion radius has great influence on material defects.3.The influences of silicon substrate,sapphire substrate and substrate temperature on the dielectric properties of BMN films were studied.It was found that the dielectric properties of the films are best when the substrate is sapphire and the substrate temperature is 700?,with a dielectric constant of 101.2 and a dielectric loss of 0.0762.4.The micromachining process of the varactor is studied,and the BMN thin film varactor is fabricated by micro machining technology.