A Research On The Application Of Microware Thin-Film Dielectric Materials

With the development of wireless communication,the integration,miniaturization,high stability and low cost of communication equipment become the main development trend of microwave RF devices.The trend makes the microwave dielectric thin film material have wider application prospect than the corresponding ceramic material.This paper focuses on the application of two kinds of microwave dielectric thin films with adjustable performance and low loss character in microwave RF devices.Firstly,barium strontium titanate(Ba1-xSrxTiO3,BST)ferroelectric thin films can be widely used in microwave tunable devices because of their high tunability and low dielectric loss.Secondly,silicon nitride(SiNx)dielectric thin film can be widely used in power semiconductor devices because of extremely low dielectric loss,high resistivity,high density,high chemical stability and so on.So this paper mainly focus on the fabrication of a tunable bandpass filter based on BST ferroelectric thin films and SiNx thin film MIM(metal-insulator-metal)capacitors used for power amplifier matching circuit.The research contents and main results are as follows:1.BST thin films are deposited on a single-crystal sapphire substrate by using radio frequency magnetron sputtering.We find out suitable annealing temperature and rising and cooling rates to release interface stress in order to obtain dense and uniform structure of BST thin films.2.BST thin films MIM capacitors are fabricated by a photolithography process,and their dielectric properties are measured.The results show that the dielectric properties of BST thin films deposited by RF magnetron sputtering are well,and the loss is less than 2%,and the dielectric tunability of BST film can reach to 50% under the bias of 40 V.3.BST thin film capacitors as tunable components could be used to design a fifth-order combline tunable microstrip bandpass filter based on the previous design experience on microwave devices.At last,we can accomplish the fabrication of the designed filter by coating,lithography process and thickening the top electrode.The bandpass filter can achieved 13.6% tunability under the application of 30 V bias.4.This paper gives detailed introducation that the power amplifier classification and main performance indexes,and analyzes the design of the broadband power amplifier.According to its working frequency range requirements,we select TriQuint,TGF2023-2-02 power amplier tube core and analyzed it by ADS(Advanced Design System)simulation design.With the consideration of circuit size,bandwidth and the adjustable properties of impedance finally use the microstrip line and lumped elements mixed matching.5.According to the electrical performance requirements of the distributed capacitance used for the power matching circuit,we explore to fabricate SiNx thin-film MIM capacitor through the Plasma Enhanced Chemical Vapor Deposition(PECVD)method and the dry etching process.Then the corresponding electrical properties of the SiNx thin film capacitors are tested.