薄膜体声波谐振器(FBAR)谐振特性的模拟分析*

主要利用Mason等效电路模型对加入介质声损耗的薄膜体声波谐振器输入阻抗公式进行了推导,并利用该结果对薄膜体声波谐振器的谐振特性进行了模拟分析,分别就不同压电层材料和厚度以及不同电极材料和厚度对薄膜体声波谐振器谐振特性的影响进行了详细分析.结果表明,薄膜体声波谐振器谐振频率主要由压电材料和厚度决定但电极的影响也是很大的.在制作高频FBAR器件(5GHz以上)时,采用氮化铝作压电材料比用氧化锌作压电材料更合适.     

基于薄膜体声波谐振器的柔性有机挥发性气体传感器

本文制造了一种基于薄膜压电体声波谐振器的柔性有机挥发性（VOCs）气体传感器。通过转移印刷的方法,柔性体声波谐振器的电极与压电层采用的无机材料薄膜被从硅衬底上转移到超薄的聚酰亚胺基底上。该柔性谐振器的品质因数达到了1920,且在2.5 mm的弯曲半径下仅有相对于基频十万分之一左右的频率偏移。谐振器表现出了对于环己烷与乙醇气体良好的频率响应特性,且通过在器件表面修饰聚异丁烯（PIB）薄膜作为气体吸附材料,使得器件对于环己烷的响应提升了10倍以上。该柔性VOC气体传感器具有尺寸小,质量轻,机械柔性好的优点,在可穿戴环境检测设备,健康监测设备,食品变质检测的电子标签等领域有着广泛的应用前景。     

基于ADS下FBAR的设计与仿真

现代无线通信技术推进了高频元件的相关发展,微纳技术的迅速发展和新型功能材料的出现以及压电薄膜制备技术的日益成熟使高性能频率控制器件的微型化成为可能。本文主要通过对FBAR的结构以及原理做介绍,设计出一款上下0.3 um厚的钼材料电极,1 um ALN压电薄膜和2.5 um的二氧化硅衬底的空气隙型薄膜体声波谐振器,采用MBVD模型对其进行理论推导,并在ADS软件下搭建电路仿真,得到S参数曲线,进而算出有效机电耦合系数为3.65%、串、并联谐振因子分别为1579.33和555.02,有效机电耦合系数与品质因数Q值得乘积最高可以达到57.65。数据表明该FBAR性能较好,其带宽较大,插入损耗较低,达到了FBAR设计的标准。     

薄膜体声波谐振器的FDTD数值分析

提出了基于时域有限差分方法对薄膜体声波谐振器进行数值分析的新方法。利用时域有限差分法理论对压电材料的控制方程,牛顿方程和电学方程在空间和时间进行了离散化,通过得到的差分方程直接得出了声场传播的时域数值解。使用该数值方法对薄膜体声波谐振器的电学特性阻抗进行了分析,并将结果与一维Mason模型的解析解进行了比较验证。     

薄膜体声波谐振器（FBAR）滤波器研究

薄膜体声波谐振器（FBAR）滤波器具有小尺寸、高频、宽频带、高功率容量等特点，符合5G通信系统对射频滤波器的要求，因而成为射频滤波器的研究热点。本文对FBAR滤波器的结构原理、电路拓扑形式、关键材料和空腔结构方案四个方面进行了综合阐述与研究。首先介绍了FBAR的基本结构、描述了其工作原理，并指出用于衡量性能优劣的两个关键参数——有效压电耦合系数keff2和品质因数Q。然后概括了FBAR滤波器的电路拓扑形式，并分析了Ladder形式、Lattice形式和Ladder-Lattice组合形式三种电路拓扑形式的特点。随后研究了FBAR滤波器的关键材料——压电材料与电极材料，并进行了性能特性的比较。其次总结了FBAR的空腔工艺制备方案，重点关注硅反面刻蚀型与空气隙型两大类，并给出了对比与讨论。最后对FBAR滤波器的进一步发展做出了展望。     

射频反应溅射制备AlN薄膜的研究

高次模薄膜体声波谐振器(HBAR)具有简单的半导体工艺特性和良好的高频特性能,在分析HBAR结构和工作模式的基础上,用MBVD模型在ADS上仿真设计了2 GHz谐振频率间隔20 MHz的HBAR,实验采用掩模合射频溅射制备了这种HBAR,实测谐振频率间隔22 MHz,与理论接近,显示了较好的频率特性,实验同时制备了的高C轴取向的AlN薄膜.     

基于ELC谐振器的湿度传感器

LC谐振式湿度传感器因无源无线,可极大拓展传感器应用范围,已成为湿度传感器的研究热点之一.将超常媒质(metamaterials)应用在谐振器的结构选择上,解决了传统LC谐振式传感器尺寸过大,灵敏度较低的问题.湿度传感器由电耦合LC谐振器(ELC谐振器)和聚乙烯醇(PVA)敏感薄膜构成.首先利用电磁仿真软件,分析ELC谐振器主要结构参数对谐振特性的影响,设计和制作谐振频率为2.45 GHz的谐振器,品质因数达到302.然后通过滴涂法将制备好的感湿材料聚乙烯醇溶液涂敷在ELC谐振器表面制作湿度传感器,并进行了湿度敏感测试.实验结果显示:ELC谐振器在全频段内磁导率均为正,在频段2.19 GHz~2.98 GHz内介电常数为负,具有超常媒质特性;湿度传感器在相对湿度35% RH~88% RH范围内,谐振频率共偏移69.875 M,且在83%~88% RH湿度范围内感湿灵敏度η达到71.5 MHz/% RH.研究表明ELC谐振器因超常媒质特性实现了结构小型化,且由于品质因数较高改善了湿度灵敏度.     

电容式微超声传感器的电极参数优化设计

建立了电容式微超声传感器(cMUT)的有限元模型,通过对模型进行静电-结构耦合仿真分析,研究了金属电极的结构参数包括电极面积、电极厚度、电极材料以及电极相对与薄膜的位置等参数的变化对传感器性能的影响.分析了电极参数与传感器吸合电压,静态电容,机电转换比以及机电耦合系数的关系,最后得到了优化的电极结构参数,即金属电极面积为传感器振动薄膜面积的一半时,传感器具有较低的吸合电压和较大带宽值及机电耦合系数.     

LLC谐振变换器的扩展描述函数法建模

给出了LLC谐振变换器的等效电路,基于扩展描述函数法建立了该等效电路的小信号模型、得到了LLC变换器的稳态解及其直流电压增益特性。借助PSpice仿真软件得到了该变换器在不同开关频率和不同电路参数下输出变量对控制变量的频率特性曲线。分析了开关频率、输入电压、占空比、品质因数和负载等主要参数对频率特性的影响。所作的工作对变换器参数的优化设计、闭环控制及动态性能设计具有指导意义。     

薄膜热电极尺寸效应分析及试验研究

薄膜型热电极作为薄膜热电偶结构的核心部位,其尺寸设计对热电偶功能及性能的实现起着重要作用;文章研究了热电偶电极薄膜的尺寸效应,建立了薄膜热电偶热电及热传导机理数学模型,分析了热电极尺寸对热电偶静态及动态特性的影响,设计并制作了不同尺寸规格热电极的薄膜热电偶,对热电极的尺寸效应物理性能开展了试验研究,试验结果表明热电偶电极薄膜厚度与动态响应时间呈正相关,长度、宽度、面积等尺寸参数对热电偶特性无明显影响,为薄膜热电偶电极尺寸设计提供了理论基础与工程依据。     

新型体声波传感器读出电路的实验验证

为了实验验证此前通过仿真验证的基于六端口反射计的新型BAW传感器读出电路的方案的可行性,本文制作了新型BAW传感器读出电路并对其进行了测试.以串联谐振频率约为1.5 GHz的薄膜体声波谐振器(FBAR)为待测器件(DUT),设计、制作了一种能够满足该FBAR谐振频率测量带宽(1.3 GHz~1.7 GHz)要求的PCB上微带六端口网络和检波器,配合射频信号发生器和示波器,获得了模拟DUT(50ΩSMA匹配负载)的反射系数-频率(Γ-f)曲线测量结果.与矢量网络分析仪(VNA)的测量结果进行了对比,两者吻合较好,实验验证了"基于六端口反射计的BAW传感器读出电路"可用于FBAR谐振频率的测量.本文工作对实用化BAW传感器的研制和片上矢量网络分析仪(VNA-on-Chip)的设计都有借鉴意义.     

Highly sensitive mass sensor using film bulk acoustic resonator

Film bulk acoustic resonators (FBAR) have recently been adopted as alternatives to surface acoustic wave (SAW) in high frequency devices, due to their inherent advantages, such as low insertion loss, high power handling capability and small size. FBAR device can also be one of the standard components as mass sensor applications. FBAR sensors have high sensitivity, good linearity, low hysteresis and wide adaptability. In this study, a highly sensitive mass sensor using film bulk acoustic resonator was developed. The device structure of FBAR is simulated and designed by the Mason model, and fabricated using micro electromechanical systems (MEMS) processes. The fabricated FBAR sensor exhibits a resonant frequency of 2442.188 MHz, measured using an HP8720 network analyzer and a CASCADE probe station. Experimental results indicate that the mass loading effects agree with the simulated ones. Results of this study demonstrate that the sensitivity of the device can be achieved as high as 3654 Hz cm²/ng.     

Comparison of FBAR and QCM-D sensitivity dependence on adlayer thickness and viscosity

Unlike the quartz crystal microbalance, which has been used extensively for the analysis of biochemical interactions, only few measurements with biochemical adsorbent have been done with film bulk acoustic resonators (FBAR). In this paper, the FBAR behaviour on exposure to a lipid vesicle solution and the formation of a polyelectrolyte multilayer structure is investigated and compared with the results obtained with the quartz crystal microbalance. Differences in the resonator response were found between the two techniques and depending on the resonators resonance frequency ranging from the MHz to the GHz regime. As an explanation, we suggest that the penetration depth and the influence on viscoelastic properties, which are both known to be frequency dependent, cause the variations in the results. As a consequence, the higher operating resonance frequencies of the FBAR increase the sensitivity to changes in the viscoelasticity of the adsorbent and also decrease the sensing length of the device.     

Thin-film electro-acoustic sensors based on AlN and its alloys: possibilities and limitations

Sputter deposited aluminum nitride (AlN) thin films have played a central role for the successful development of the thin film electro-acoustic technology. The development has been primarily driven by one device—the thin film bulk acoustic resonator, with its primary use for high frequency filter applications for the telecom industry. Recently, increased piezoelectric properties in AlN through the alloying with scandium nitride have been identified both experimentally and theoretically. This opens up new possibilities for the thin film electro-acoustic technology. Here expectations and discussions are presented on acoustic FBAR sensor performance when based on AlN as well as on such AlN alloys to identify possible benefits and limitations. Inhere, the distinction is made between direct and in-direct (acoustic) use of the piezoelectric effect for sensor applications. These two approaches are described and compared in view of their advantages and possibilities. Especially, the indirect (or acoustic) use is identified as interesting for its versatility and good exploitation of the thin film technology to obtain highly sensitive sensor transducers. It is pointed out that the indirect approach can well be obtained internally in the piezoelectric material structure. Original calculations are presented to support the discussion.     

Electrical Frequency Tuning of Film Bulk Acoustic Resonator

This paper describes the design, fabrication, and measurement of an electrically tunable film bulk acoustic resonator (FBAR) that is formed by integrating FBAR with an electrostatic microelectromechanical systems actuator. Around 1.47% tuning of the series resonant frequency ( Deltaf cong 22.5 MHz) at 1.5 GHz is experimentally obtained with an electrostatic actuation voltage of 7 V. This is the highest frequency tuning reported for FBAR operating at above 1 GHz without any extra power consumption. Two integration approaches of FBAR and air-gap capacitor are presented and compared, in terms of fabrication process and Q factor. The approach that minimizes any possible energy loss in the acoustic wave propagation path shows a quality factor (160-304) significantly higher than the one having a capacitor right on top surface of the FBAR's piezoelectric film. Furthermore, we have characterized the electrical tuning of FBAR through piezoelectric stiffening due to an applied DC electric field and report a linear frequency shift of about -8 ppm/V at 3.4 GHz.     

FBAR传感器信号检测与处理电路研究

设计并制作了薄膜体声波谐振器(FBAR)的生化传感器信号检测与处理电路,该电路采用混频器,把高频信号混频到低频信号,降低了信号的处理难度,并以Cyclone FPGA为核心控制器,完成对采样数据的处理和存储,并实现了实时传输等功能。利用该电路对双工器进行了初步测试,结果表明,谐振频率与网络分析仪所测结果一致。     

A new model of on‐chip inductors on ferrite film using KB‐FDSMN neural network

A new model of on‐chip planar inductors on ferrite film is developed by virtue of the knowledge‐based frequency‐dependent space‐mapping neural network (KB‐FDSMN). A modified π‐equivalent circuit is used to construct the KB‐FDSMN model for improving reliability in the model generalization. This new model makes use of empirical formulas to quickly estimate some circuit parameters for reducing the number of independent variables, whereas a three‐layer neural network is trained for the desirable accuracy and used to compute the rest of circuit parameters. This new approach provides an efficient scheme to model the on‐chip magnetic film inductors. In comparison with the conventional neural network model and the standalone modified π‐equivalent model, this new KB‐FDSMN model can map the input–output relationships with fewer hidden neurons yet better accuracy and higher reliability in the model generalization. © 2010 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2010.     

FBAR-on-diaphragm type electro-acoustic resonant micro-accelerometer: a theoretical study

We presented a theoretical study of the performance of a novel FBAR-on-diaphragm sensor-head structure for the FBAR-based electro-acoustic resonant micro-accelerometer. This structure overcomes disadvantages in the FBAR-beam structure for its limited cantilever beam thickness, and deficiencies in the embedded-FBAR structure for its complex micro-fabrication process. Its elastic diaphragm is made of silicon dioxide (SiO₂)/silicon nitride (Si₃N₄) bilayer film, which is not only more susceptible to the IC compatible integration process for the Si-based microstructure and the FBAR, but also improves sensitivity and temperature stability of the BAW accelerometer. FBAR-on-diaphragm type BAW accelerometer integrates the acceleration sensing structure, i.e., the SiO₂/Si₃N₄ bilayer diaphragm and the Si proof-mass, with the AlN FBAR electro-acoustic transducer. Preliminary performance analysis on FBAR-on-diaphragm type BAW accelerometer suggests that the FBAR-on-diaphragm structure is feasible. We obtained modal frequencies of the FBAR-on-diaphragm structure and stress distribution of the diaphragm under 0–100 g acceleration loads through the finite element modal analysis and static simulation, Applying the calculated maximum stress to the piezoelectric film in FBAR for qualitative analysis, and combining the dependency of elastic coefficient on stress in the Wurtzite AlN film calculated with the first-principle method, we roughly predicted the maximum elastic coefficient variation in the Wurtzite AlN film under different acceleration load. With the help of the RF simulation software ADS, we changed the longitudinal wave velocity corresponding to the elastic constants with variant acceleration loads. By comparing the resulted resonant frequencies of the sensor head without and with different acceleration loads, we qualitatively characterized its frequency shift and sensitivity. In our study, we gave further analysis of the simulation results. It reveals that the first-order modal frequency of the SiO₂/Si₃N₄ circular diaphragm is quite far away from the higher ones, which means less cross modal coupling. It also reveals that under the acceleration load, its resonant frequency with a quite linear acceleration–frequency shift characteristic will up-shift with the sensitivity of several KHz/g.     

The effects of temperature, relative humidity and reducing gases on the ultraviolet response of ZnO based film bulk acoustic-wave resonator

This study investigated the influence of temperature, relative humidity and reducing gases on the ultraviolet (UV) response of ZnO based film bulk acoustic-wave resonator (FBAR). As temperature increased, the UV response of the FBAR degraded. This was attributed to the softening of the ZnO film with increasing temperature. Water molecules can replace adsorbed oxygen on the ZnO surface. At high relative humidity, more oxygen was replaced by water. In this way, the density of the ZnO film increased and less oxygen was left on the surface to be desorbed by UV, both of which contributed to a lower UV response. Reducing gases, such as acetone, can react with the surface adsorbed oxygen and reduce the density of the ZnO film, resulting in UV response degradation.     

基于薄膜体声波谐振器的免疫球蛋白传感器制备

研制了一种基于薄膜体声波谐振器（ FBAR）的生物免疫球蛋白传感器,该FBAR采用AlN作为压电层,3对Ti/W金属层作为布拉格声学反射层,工作频率为2.047 GHz,回波损耗为－32 dB。利用自组装膜法修饰顶部金电极敏感区域。测试了免疫球蛋白G抗体和抗原的特异性结合前后传感器的指标变化。结果得到传感器的Q值和灵敏度分别达到846,3.38 kHz·cm2/ng,远高于广泛使用的石英晶体微天平（ QCM）,具有广阔的应用前景。