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和表面波器件相比,薄膜体声波谐振(FBAR)器件重量轻、尺寸小、成本低而且能够处理的功率大.因此,FBAR技术被认为是能够满足现代移动通信系统滤波要求的最有竞争力的技术.对FBAR器件进行模拟的方案中,Butterworth-van Dyke(BVD)模型被广泛应用,但是它不可能被用于分析FBAR的复杂结构.为了准确模拟FBAR器件,必须用到数值方法,如有限元法(FEM)或者时域有限差分(FDTD)法.本文中,FDTD法被用于对薄膜体声波谐振进行二维分析.压电方程和牛顿方程在时间域和空间域中通过中间有限差分进行离散化.完全匹配层(PML)边界条件被用于实现两侧的吸收边界.在空气-铝和空气-氮化铝界面上,自由边界条件在FDTD方案中得以实现.另外,在铝-氮化铝内部边界附近,通过对材料常数取两侧的平均值的方式,实现了连续边界条件,保证了数值计算的稳定性.一款静电场模拟软件ANSOFT Maxwell 2D被用于计算电场强度的分布.当FBAR被外加电压驱动,而电压为时间的正弦函数时,FBAR的输出电流可以表示为一系列正弦函数之和.这些正弦函数中包含了顺态解和稳态解.找出稳态解,就可以计算响应工作频率时的FBAR阻抗特性.文中给出了在不同电极厚度如0.2μm、0.3μm、0.4μm、0.5μm和0.6μm情况下阻抗特性的计算结果.由于能陷效应,基频谐振强度随着电极厚度从0.2μm增加到0.4μm逐渐增强.可是,当电极厚度增加到0.5μm谐振强度又开始减弱.这个现象可以归因于电极的质量负载效应.质量负载会降低谐振强度.通过模拟结果,当氮化铝膜厚度在3μm时,最佳电极厚度应该在0.4μm.我们利用FDTD法对FBAR进行了二维分析.模拟结果显示,FDTD法是分析各种FBAR结构的有力工具.
Compared with surface wave devices, FBAR devices are light weight, small size, low cost and capable of handling large amounts of power. Therefore, FBAR technology is considered to be the most competitive to meet the filter requirements of modern mobile communication systems Butterworth-van Dyke (BVD) model is widely used in the simulation of FBAR devices, but it can not be used to analyze the complex structure of FBAR.In order to accurately simulate the FBAR device, we must use numerical methods such as Finite Element Method (FEM) or Finite-Difference Time-Domain (FDTD) method. In this paper, the FDTD method is used for two-dimensional analysis of bulk acoustic resonance. The piezoelectric and Newton equations pass the intermediate finite The discretization is discretized.The PML boundary conditions are used to achieve the absorption boundaries on both sides.Free boundary conditions are achieved in the FDTD scheme at the air-aluminum and air-aluminum nitride interfaces.In addition, - aluminum nitride near the internal boundary, by means of taking the average of both sides of the material constant means to achieve a continuous boundary conditions to ensure the stability of numerical calculations.A electrostatic field simulation software ANSOFT Maxwell 2D is used To calculate the distribution of electric field strength, the output current of the FBAR can be expressed as the sum of a series of sinusoidal functions when the FBAR is driven by an applied voltage and the voltage is a sinusoidal function of time.These sine functions include both the forward solution and the steady-state solution By finding the steady state solution, we can calculate the FBAR impedance response in response to the operating frequency. The calculation results for the impedance characteristics at different electrode thicknesses such as 0.2μm, 0.3μm, 0.4μm, 0.5μm and 0.6μm are given. The fundamental resonance frequency increases gradually from 0.2μm to 0.4μm due to the trap effect, however, the resonance intensity begins to decrease when the electrode thickness increases to 0.5μm, which can be attributed to the mass loading effect of the electrodes. The mass load will reduce the resonance strength.According to simulation results, when the thickness of aluminum nitride film is 3μm, the optimal thickness of electrode should be 0.4μm.We used FDTD method to do two-dimensional analysis of FBAR.The simulation results show that FDTD method A powerful tool for various FBAR structures.