AlN薄膜腔声谐振器的制备及性能研究

采用体硅微细加工工艺制备了基于AlN压电材料的薄膜腔声谐振器，研究了器件结构中谐振区形状和面积对谐振器性能的影响。以X射线衍射仪、扫描电镜表征了AlN压电薄膜的结构及形貌，高频网络分析仪表征谐振器频率特性。测试结果表明，谐振器所用AlN压电薄膜具有C轴择优取向及良好的柱状晶结构；器件频率特性良好，谐振频率达1．759GHz，机电耦合系数3．75％，品质因数79．5。通过研究不同谐振区形状、面积谐振器的性能，明确了结构因素对器件频率特性的影响，分析了其中的机制。     

固贴式薄膜体声波谐振器性能受压电材料的影响分析

利用Math CAD软件对固贴式薄膜体声波谐振器(SMR-FBAR)器件建立数学模型进行仿真,分析了不同压电薄膜材料和厚度,不同电极材料和厚度对FBAR器件谐振特性的影响。采用射频磁控溅射方法制备氮化铝(AlN)薄膜,利用扫描探针显微镜中的压电力显微镜(PFM)模块对AlN薄膜的压电性能进行了测试。得到主要结论为:复合FBAR的谐振频率因为增加了电极厚度因素相比理想FBAR的谐振频率偏低;压电材料的机电耦合系数对器件带宽起决定性作用,器件的机电耦合系数正比于材料的机电耦合系数;AlN具有较高的压电系数,可以有效提升器件性能,增大带宽,适合作为压电薄膜材料;采用小尺寸压电薄膜和电极厚度有益于提高器件的频率。     

电极和基片对高次谐波体声波谐振器参数的影响

1.引言 产生高稳定频率控制信号的器件通常要求在谐振模式上具有高Q值.常用的器件有晶体器件,表面声波器件和微波谐振器件等,但是这些器件常常不能满足应用所要求的性能,有的不能在高频工作,或者Q值达不到所需的要求.高次谐波体声波谐振器(HBAR)是由高Q值的非压电基片、压电薄膜和两个电极构成,压电薄膜作为换能器在基片中激发声波,一定激发频率下会在基片里形成驻波,从而导致整个HBAR器件产生谐振.HBAR在谐振模式有高Q值,并且可以在高频下工作,Q-频率的乘积能超过1014,所以HBAR在频率控制和频率选择方面具有十分优越的性能[1].     

应用于体声波谐振器的ZnO薄膜结构和电学特性

采用直流磁控溅射的方法制备了ZnO压电薄膜,并在双面抛光的熔融石英基片上制备了高次谐波体声波谐振器.x射线衍射结果显示ZnO压电薄膜C轴择优取向明显,衍射峰半高宽为0.1624°,显示出较好的结晶质量;扫描电镜分析观察到ZnO垂直于基片表面的柱形晶粒结构和较平滑的薄膜表面.体声波器件的电学测试结果显示器件具有很好的多模谐振特性,说明ZnO压电薄膜很好地激发出了厚度方向的纵声波,可应用于体声波器件和声表面波器件中.另外采用间接的方法得到ZnO压电薄膜在870MHz时的介电常数约为5.24,介电损耗因子为1.07,进一步减小介电损耗因子,可以提高器件的Q值.     

基于微机电系统的薄膜体声波谐振器技术

随着我国无线通讯的飞速发展,通讯器件的微型化、低功耗、低成本、高性能与集成化等越来越受人们关注。基于微机电系统的薄膜体声波谐振器技术是实现系统低功耗与微型化的重要技术,薄膜体声波谐振器具有体积小、频率高、换能效率高等诸多优势。为了对基于微机电系统的薄膜体声波谐振器有一个更深层次的认识,文章阐述了薄膜体声波谐振器的基本结构与工作原理,并分析了薄膜体声波谐振器及技术的应用与发展趋势。     

初应力对压电薄膜体声波谐振器厚度拉伸模态谐振特性的影响

本文研究了初应力对压电薄膜体声波谐振器（FBAR）厚度拉伸模态谐振特性的影响。利用含初应力压电材料的压电弹性基本方程,推导出理想FBAR在正弦激励电压作用下的振动方程。然后根据边界条件,求出问题的解。得到了串联和并联谐振频率,并给出了具体的数值算例,讨论了初应力对谐振频率、带宽和有效机电耦合系数的影响。所得结果对于提高和改善FBAR的性能有参考意义。     

固贴式薄膜体声波谐振器用材料体系研究进展

固贴式薄膜体声波谐振器(SMR-FBAR)技术是近年来电子工业领域里的突破性技术,具有2GHz以上的工作频率、极高的的品质因子及良好的机械稳定性等众多的优异特性.基于其独特的优越性,固贴式薄膜体声波谐振器成为了科研工作者们关心的热点,并在第三代无线通信系统中已得到广泛应用,例如作为基本单元用来制作滤波器、双工器和振荡器等第三代无线通信系统中的频率选择器件.器件选用的材料体系是决定器件性能的关键因素.本文以器件结构为线索,综述了固贴式薄膜体声波谐振器用材料体系的研究进展,包括压电薄膜(氮化铝、氧化锌等)、高/低声阻抗材料以及电极薄膜,讨论了材料性能和器件性能的关系,并对材料体系下一步的研究方向进行了展望。     

薄膜体声波谐振器的研究进展

薄膜体声波滤波器作为一种发展高频滤波器的全新解决方案,比声表面波滤波器(SAWF)、陶瓷介质滤波器具有更高的Q值,低的损耗和在高频时具备更高的功率承受能力.介绍了薄膜体声波谐振器的研究历史和研究概况,薄膜体声波谐振器的原理和3种典型结构,具体阐述了薄膜体声波谐振器的关键技术及其材料体系的要求.     

2.4GHz射频薄膜体声波谐振器的研制

提出了基于ZnO压电薄膜多层结构的2.4GHz射频薄膜体声波谐振器,并进行了研究.采用修正后的Mason等效电路模型对器件的谐振特性进行了分析和模拟.给出了采用MEMS工艺制备器件的工艺流程,并利用射频网络分析仪对实验器件进行了测试.利用多点数值拟合的方法消除射频测试中引入的寄生分布参数,提取出器件的实际参数:器件的串联谐振频率fs和并联谐振频率fp分别为2.3714GHz和2.3772GHz,相应的有效机电耦合系数为0.598%;串联谐振频率处和并联谐振频率处的Q值分别为500.3和425.5,f·Q值乘积达到1.2×1012.该谐振器器件的有效直径为200μm,样品实际尺寸为1.2mm×1.2mm×0.3mm,可用来制备体积小、高性能和低相噪的射频振荡器.     

薄膜体声波滤波器的材料、设计及应用

薄膜体声波谐振器及滤波器具有工作频率高、工艺简单、尺寸小、易于集成等优点,成为目前应用于高频通信前置滤波器的首选.系统介绍了用于薄膜体声波谐振器的几种主要材料(AlN、ZnO、PZT)的具体特点、制备工艺及薄膜体声波谐振器与滤波器的结构、设计及其应用.     

哑铃形热声谐振器的谐振频率

热声自激振荡模态取决于声学谐振器结构形式和特征尺度。级联型热声热机依靠哑铃形谐振器来调制所需要的局部高阻抗行波声场,谐振管通常由几段不同横截面的管段组成。哑铃形热声谐振器的谐振频率由共鸣腔容积、谐振管截面和长度共同决定。根据哑铃形谐振器不同截面管段内的声传播规律、共鸣腔声学边界条件以及管段间的声压和体积流率连续条件,利用行波叠加的方法,建立均匀管模型、变截面模型和热声网络模型,得到了系统谐振频率随共鸣腔容积变化和谐振管特征尺寸变化的规律。系统谐振频率的变化将引起最佳听音点的位置的移动,进一步起到调节回热器声阻抗的作用。实际热声热机实验研究中,通过改变谐振器特征尺度或结构形式调节系统的谐振频率,也是热声热机调试过程中实现自激振荡的主要手段。     

Resonator/Oscillator response to liquid loading

The resonant frequency of a thickness-shear mode resonator operated in contact with a fluid was measured with a network analyzer and with an oscillator circuit. The network analyzer measures changes in the device's intrinsic resonant frequency, which varies linearly with (ρη)(1/2), where ρ and η are liquid density and viscosity, respectively. The resonator/oscillator combination, however, responds differently to liquid loading than the resonator alone. By applying the operating constraints of the oscillator to an equivalent-circuit model for the liquid-loaded resonator, the response of the resonator/oscillator pair can be determined. By properly tuning the resonator/oscillator pair, the dynamic range of the response can be extended and made more linear, closely tracking the response of the resonator alone. This allows the system to measure higher viscosity and higher density liquids with greater accuracy.     

The AlN based solidly mounted resonators consisted of the all-metal conductive acoustic Bragg reflectors

The AlN based solidly mounted resonators utilizing the all-metal conductive Bragg reflectors have been demonstrated. The devices with different reflectors of Mo/Ti, W/Ti and AlN/Mo pairs have been fabricated and the frequency responses have been compared. The bottom electrode is incorporated into the conductive Bragg reflector, thereby reducing the parasitic resistance and the damping of the acoustic energy. The experimental results reveal that Mo/Ti and W/Ti reflectors exhibit excellent properties of frequency selection and clamping the acoustic wave. The devices show the distinct resonant phenomenon near 2.4 GHz with the excellent suppression of the shear mode and the sidelobe mode. Compared to the conventional device consisted of AlN/Mo reflector, the devices consisted of the conductive reflectors demonstrate the higher resonance frequency and obviously improved performance.     

Estimation of quartz resonator Q and other figures of merit by an energy sink method

An important determinant of the quality factor Q of a quartz resonator is the loss of energy from the electrode area to the base via the mountings. The acoustical characteristics of the plate resonator are changed when the plate is mounted onto a base substrate. The base substrate affects the frequency spectra of the plate resonator. A resonator with a high Q may not have a similarly high Q when mounted on a base. Hence, the base is an energy sink and the Q will be affected by the shape and size of this base. A lower bound Q will be obtained if the base is a semi-infinite base since it will absorb all acoustical energies radiated from the resonator. A scaled boundary finite element method is employed to model a semi-infinite base. The frequency spectra of the quartz resonator with and without the base are presented. In addition to the loss of energy via the base, there are other factors which affect the resonator Q, such as, for example, material dissipation, and damping at the interfaces of quartz and electrodes. The energy dissipation due to material damping increases with the resonant frequency and the reduction of resonator size; hence material damping becomes important in the current and future miniaturized resonators operating at very high frequencies. An energy sink model along with material dissipation would provide realistic Q, motional capacitance, motional resistance, and other figures of merit useful for designing resonators. The model could be used for evaluating resonator and mountings designs of microelectromechanical systems and miniaturized devices. The effect of the mountings, and plate and electrode geometries on the resonator Q and other electrical parameters are presented for AT-cut quartz resonators. Model results from the energy sink method were compared with experimental results and were found to be good.     

Electrical actuation and readout in a nanoelectromechanical resonator based on a laterally suspended zinc oxide nanowire

In this paper, we present experimental results describing enhanced readout of the vibratory response of a doubly clamped zinc oxide (ZnO) nanowire employing a purely electrical actuation and detection scheme. The measured response suggests that the piezoelectric and semiconducting properties of ZnO effectively enhance the motional current for electromechanical transduction. For a doubly clamped ZnO nanowire resonator with radius ~10 nm and length ~1.91 μm, a resonant frequency around 21.4 MHz is observed with a quality factor (Q) of ~358 in vacuum. A comparison with the Q obtained in air (~242) shows that these nano-scale devices may be operated in fluid as viscous damping is less significant at these length scales. Additionally, the suspended nanowire bridges show field effect transistor (FET) characteristics when the underlying silicon substrate is used as a gate electrode or using a lithographically patterned in-plane gate electrode. Moreover, the Young's modulus of ZnO nanowires is extracted from a static bending test performed on a nanowire cantilever using an AFM and the value is compared to that obtained from resonant frequency measurements of electrically addressed clamped–clamped beam nanowire resonators.     

Nonlinear response of ferromagnetic film resonator under conditions of nonlinear damping of magnetization oscillations

Nonlinear response of a tangentially magnetized ferromagnetic film resonator has been experimentally studied under the conditions where the nonlinear effects in the resonator are related to four-wave parametric processes. It is shown that an increase in the microwave power supplied to the resonator leads to a nonlinear shift of the eigenfrequencies and broadening of the resonant absorption peaks. The latter phenomenon is related to the nonlinear damping of magnetization in the resonator. It is established that the nonlinear shift of the frequency is thresholdless, while the nonlinear damping has a threshold, the appearance of which also leads to limitation of the nonlinear shift of the resonator frequency.     

Acoustic Wave Flow Sensor Using Quartz Thickness Shear Mode Resonator

A quartz thickness shear mode (TSM) bulk acoustic wave resonator was used for in situ and real-time detection of liquid flow rate in this study. A special flow chamber made of 2 parallel acrylic plates was designed for flow measurement. The flow chamber has a rectangular flow channel, 2 flow reservoirs for stabilizing the fluid flow, a sensor mounting port for resonator holding, one inlet port, and one outlet port for pipe connection. A 5-MHz TSM quartz resonator was edge-bonded to the sensor mounting port with one side exposed to the flowing liquid and other side exposed to air. The electrical impedance spectra of the quartz resonator at different volumetric flow rate conditions were measured by an impedance analyzer for the extraction of the resonant frequency through a data-fitting method. The fundamental, 3rd, 5th, 7th, and 9th resonant frequency shifts were found to be around 920, 3572, 5947, 8228, and 10 300 Hz for flow rate variation from 0 to 3000 mL/min, which had a corresponding Reynolds number change from 0 to 822. The resonant frequency shifts of different modes are found to be quadratic with flow rate, which is attributed to the nonlinear effect of quartz resonator due to the effective normal pressure imposing on the resonator sensor by the flowing fluid. The results indicate that quartz TSM resonators can be used for flow sensors with characteristics of simplicity, fast response, and good repeatability.     

微机械谐振子单端口电容检测方法研究

针对微机械谐振子电容信号难以检测的问题,本文采用基于频域分离的单端口静电激励／电容检测方案,并配合以隔离变压器应用技术。这种检测方式时域连续,除此,单端口检测既简化了谐振器结构,又避免了双端口检测中激励信号与检测信号存在耦合干扰的问题。实验结果表明：所设计的方案可以有效观测到梁的谐振现象并解算出谐振子的振动信息,为下一步实现单端口谐振子的闭环奠定了基础。     

Micromachined thin film plate acoustic resonators utilizing the lowest order symmetric lamb wave mode

Thin film integrated circuits compatible resonant structures using the lowest order symmetric Lamb wave propagating in thin aluminum nitride (AlN) film membranes have been studied. The 2-mum thick, highly c-oriented AlN piezoelectric films have been grown on silicon by pulsed, direct-current magnetron reactive sputter deposition. The films were deposited at room temperature and had typical full-width, half-maximum value of the rocking curve of about 2 degrees. Thin film plate acoustic resonators were designed and micromachined using low resolution photolithography and deep silicon etching. Plate waves, having a 12-mum wavelength, were excited by means of both interdigital (IDT) and longitudinal wave transducers using lateral field excitation (LW-LFE), and reflected by periodical aluminum-strip gratings deposited on top of the membrane. The existence of a frequency stopband and strong grating reflectivity have been theoretically predicted and experimentally observed. One-port resonator designs having varying cavity lengths and transducer topology were fabricated and characterized. A quality factor exceeding 3000 has been demonstrated at frequencies of about 885 MHz. The IDT based film plate acoustic resonators (FPAR) technology proved to be preferable when lower costs and higher Qs are pursued. The LW-LFE-based FPAR technology offers higher excitation efficiency at costs comparable to that of the thin film bulk acoustic wave resonator (FBAR) technology     

Detecting and evaluating the signals of wirelessly interrogational passive SAW resonator sensors

The wireless sensing signal of a passive surface acoustic wave (SAW) resonator sensor is the response of the SAW resonator in a passive circuit to wireless radio frequency interrogation. The response is produced only in the case that the interrogation covers the operational frequency band of the resonator. The wireless response is transient and can only be detectable in a proximity after switching off the interrogation. Due to the fact that, while used as a sensor, the resonant frequency of the resonator is related to and varying with the measurand, the interrogation to a passive SAW resonator sensor has to trace and follow the correspondent variation of the frequency band of the device. The energy evaluation of the response is applied to detect the availability of the sensing response and is used as a feedback argument to roughly localize the operational frequency range of the sensor. A modified frequency estimation is employed to estimate the sensing characteristic frequency in the transient wireless sensing signal with a low signal-to-noise ratio. The estimation is used to further adjust the interrogation frequency to follow the frequency variation of the sensor until the response becomes optimal. The evaluation of signal energy along with the statistical quantity of frequency estimation gives a reference for the confidence of the estimated frequency.