高次谐波体声波谐振器的机械品质因数

机械品质因数Q_M是高次谐波体声波谐振器(High-overtone Bulk Acoustic Resonator,HBAR)一个关键的特性参数。首次较系统地研究了Q_M随构成HBAR的3个组成部分(基底、压电薄膜和电极)的结构参数(厚度)和性能参数(特性阻抗与机械衰减因子)的变化规律。在谐振频率附近,将HBAR的分布参数等效电路简化为集总参数等效电路,首次用解析表达式给出它们的变化规律,分析了Q_M在给定频率最近谐振点的变化情况。结果表明,固定压电层厚度,Q_M随基底厚度的连续增加略呈振荡(非单调)上升,当基底厚度很大时趋于基底材料的机械品质因数;固定基底厚度,Q_M随压电层厚度的连续增加呈波浪式下降;选择低损耗的蓝宝石或YAG作为基底可以获得较大的Q_M值;电极的损耗必须考虑,它会降低Q_M值;与Au电极相比,具有较低损耗的A1电极选择适当厚度可以获得较高的Q_M值;此外,Q_M随频率的增加呈下降趋势。上述的结果为HBAR的优化设计提供了相应的理论依据。根据我们对K_eff²的研究,Q_M与K_eff²的变化规律往往是相悖的,因此在设计HBAR时要在这两者作适当的权衡。     

高次谐波体声波谐振器谐振频率分布研究

基于由谐振频率分布提取压电薄膜参数的方法,研究影响高次谐波体声波谐振器(HBAR)谐振频率分布的因素。对多种HBAR进行模拟计算,模拟结果显示,变化基片对薄膜的声阻抗比值会引起并联谐振频率间隔的分布和有效机电耦合系数的分布改变;当薄膜的基模在高频时,改变电极对薄膜的声阻抗比值和电极厚度会引起谐振频率分布改变。这些结果表明,通过调整影响谐振频率分布的因素能使谐振频率变化,进而得到在特定的频率上产生谐振。     

高次谐波体声波谐振器机械品质因数的测量*

高次谐波体声波谐振器(HBAR)具有高的机械品质因数(Q_M)和多模谐振谱特性,其在频率控制系统中具有重要应用。对制备的Al/Zn O/Au/Sapphire结构HBAR器件进行了Q_M的测定,从实际的测试系统出发,给出了它的等效电路,通过一系列分析处理得到了Q_M随频率的变化曲线。结果表明,Q_M随频率增加逐渐减小。     

基于ZnO薄膜的高次谐波体声波谐振器的研究

基于ZnO作压电层和蓝宝石作基底的高次谐波体声波谐振器(HBAR),采用不同电极材料和溅射方法进行优化。优化选定镀铬-金/氧化锌/铬-金/蓝宝石结构。对制备的器件进行了测试分析,结果显示,具有多模谐振特性的HBAR器件在2.87GHz Q值达到43000。根据一维Mason等效电路模型,HBAR器件还进行了理论仿真,结果表明理论结果与实测值基本一致。     

高次谐波体声波谐振器机械品质因数的谐振谱特性

高次谐波体声波谐振器(High-overtone Bulk Acoustic Resonator,HBAR)是由基底、压电薄膜及上下电极所组成的器件,它具有高的品质因数Q和多模谐振频谱特性.从给出HBAR的谐振谱出发,以各层的结构(厚度)和材料特性(特性阻抗和机械衰减因子)为参数,系统研究了机械品质因数Q_M的谐振谱特性。Q_M随基底或压电薄膜的厚度变化表现为一系列对应不同阶数的曲线。在给定频率下,Q_M随基底厚度的增加振荡上升,且最终趋于基底材料的机械品质因数,而其随压电薄膜厚度的增加呈波浪式下降。对于给定结构的HBAR,Q_M随频率(阶数)的增加呈波浪式下降。此外,考虑电极的厚度对Q_M的变化规律影响不大。为了获得较大的Q_M,应选择Al/AlN/Al/Sapphire或YAG结构的HBAR,且基底要较厚,压电薄膜和电极厚度要适中。     

薄膜体声波谐振器的力敏特性研究

薄膜体声波谐振器(FBAR)力传感器作为一种新型的谐振式传感器,力敏特性是其设计原理。以FBAR微加速度计为例研究了工作在纵波模式,采用具有纤锌矿结构的AlN作为压电薄膜的FBAR,施加应力载荷后,其弹性常数改变导致FBAR谐振频率偏移的力敏特性。首先,采用有限元(FEA)静力学仿真,得到惯性力载荷作用下集成在硅微悬臂梁上的压电薄膜的应力分布;选取最大应力值作为载荷,基于第一性原理计算纤锌矿AlN的弹性系数与应力的关系式,预测惯性力载荷作用下AlN弹性系数的最大变化量。其次,采用谐响应分析,对比空载和不同惯性力载荷作用下FBAR微加速度计的谐振频率和偏移特性,预测FBAR微加速度计的加速度-谐振频率偏移特性。最后仿真分析得到：惯性力载荷作用下,FBAR微加速度计的谐振频率向高频偏移,灵敏度约为数kHz/g;其加速度增量-谐振频率偏移特性曲线具有良好的线性度。     

薄膜体声波谐振器的力敏特性研究

薄膜体声波谐振器(FBAR)力传感器作为一种新型的谐振式传感器,力敏特性是其设计原理。以FBAR微加速度计为例研究了工作在纵波模式,采用具有纤锌矿结构的AlN作为压电薄膜的FBAR,施加应力载荷后,其弹性常数改变导致FBAR谐振频率偏移的力敏特性。首先,采用有限元(FEA)静力学仿真,得到惯性力载荷作用下集成在硅微悬臂梁上的压电薄膜的应力分布;选取最大应力值作为载荷,基于第一性原理计算纤锌矿AlN的弹性系数与应力的关系式,预测惯性力载荷作用下AlN弹性系数的最大变化量。其次,采用谐响应分析,对比空载和不同惯性力载荷作用下FBAR微加速度计的谐振频率和偏移特性,预测FBAR微加速度计的加速度-谐振频率偏移特性。最后仿真分析得到:惯性力载荷作用下,FBAR微加速度计的谐振频率向高频偏移,灵敏度约为数kHz/g;其加速度增量-谐振频率偏移特性曲线具有良好的线性度。     

薄膜体声波谐振器的伽马辐照敏感机理分析

实验证明薄膜体声波谐振器(FBAR)用于检测伽马辐照是可行的,但未对敏感机理进行深入研究。针对这一问题,根据两种不同的FBAR结构,提出了不同机理来解释FBAR在伽马辐照下谐振频率偏移的原因。其中结构一FBAR为四层叠层结构（金属层-压电层-氧化层-金属层）,伽马辐照之后,会在辐照敏感层(氧化层)形成一个电压,相当于给压电层施加了一个直流电压,从而使谐振频率发生偏移;结构二与结构一不同的是,结构二FBAR在氧化层和压电层之间有一半导体层,辐照之后在氧化层中形成的电压改变了半导体的表面势,使半导体空间电荷层电容发生改变,从而改变谐振频率。通过仿真得到两种不同机理的结果,并与相关文献的测试结果对比,发现频率偏移的趋势和频率偏移量的数量级是相同的,因此提出来的两种机理是可行的。     

薄膜体声波谐振器性能模型参数的提取方法

薄膜体声波谐振器(FBAR)性能模型包含两个关系式：一个是FBAR有效机电耦合系数与其形状因子(面积与周长之比)的关系式,另一个是FBAR品质因数与其形状因子的关系式。前一个关系式中的参数为FBAR边缘区域的等效宽度,后一个关系式中的参数为表征FBAR横向声能泄漏的因子。为使性能模型用于不同膜层结构、材料及制备工艺的FBAR,建立FBAR性能模型参数的提取流程。以一种5层复合结构的FBAR为例,在同一晶片上,制备多个不同形状因子的FBAR。针对其中一个五边形FBAR,在ADS软件中通过Mason电路模型仿真得到其性能值(有效机电耦合系数和品质因数);再使用矢量网络分析仪和射频探针台实测其性能值。将仿真与实测得到的性能值代入FBAR性能模型,解算出这两个参数。确定参数之后,使用FBAR性能模型预测同一晶片上其它不同性能因子FBAR的有效机电耦合系数和品质因数,预测值的相对误差在3%之内,验证了该参数提取流程的有效性。     

薄膜体声波谐振器的伽马辐照敏感机理分析

实验证明薄膜体声波谐振器(FBAR)用于检测伽马辐照是可行的,但未对敏感机理进行深入研究。针对这一问题,根据两种不同的FBAR结构,提出了不同机理来解释FBAR在伽马辐照下谐振频率偏移的原因。其中结构一FBAR为四层叠层结构（金属层-压电层-氧化层-金属层）,伽马辐照之后,会在辐照敏感层(氧化层)形成一个电压,相当于给压电层施加了一个直流电压,从而使谐振频率发生偏移;结构二与结构一不同的是,结构二FBAR在氧化层和压电层之间有一半导体层,辐照之后在氧化层中形成的电压改变了半导体的表面势,使半导体空间电荷层电容发生改变,从而改变谐振频率。通过仿真得到两种不同机理的结果,并与相关文献的测试结果对比,发现频率偏移的趋势和频率偏移量的数量级是相同的,因此提出来的两种机理是可行的。     

Effective electromechanical coupling coefficient of high-overtone bulk acoustic resonator

A high-overtone bulk acoustic resonator(HEAR) is composed of a substrate,a piezoelectric film and upper and lower electrodes,the influences of their structure parameter(thickness) and performance parameter(characteristic impedance) on effective electromechanical coupling coefficient K_(eff)~2 are investigated systematically.The relationship between K_(eff)~2 and these parameters is obtained by a lumped parameter equivalent circuit instead of distributed parameter equivalent circuit near the resonant frequency,and K_(eff)~2 at the resonance frequency closest to the given frequency is analyzed.The results show that K_(eff)~2 declines rapidly and oscillatorily with the continuous increase of the substrate thickness when the piezoelectric film thickness is fixed,and decreases inversely proportion to the thickness when the substrate thickness is greater than a certain value.With the ratio of the characteristic impedance of the substrate to the piezoelectric layer increasing,the maximum of K_(eff)~2 obtained from the variation curve of K_(eff)~2 with the continuous increase of the piezoelectric film thickness decreases rapidly before reaching the minimum value,and later increases slowly.Fused silica with low impedance is appropriate as the substrate of HBAR to get a larger K_(eff)~2.Compared with Al electrode,Au electrode can obtain larger K_(eff)~2 when the appropriate electrode thickness is selected.The revealed laws above mentioned provide the theoretical basis for optimizing parameters of HBAR.     

Mechanical quality factor of high-overtone bulk acoustic resonator

Mechanical quality factor Qm is a key characteristic parameter of High-overtone bulk acoustic resonator(HBAR). The effects of structure parameter(thickness) and perfor?mance parameters(characteristic impedance and mechanical attenuation factor) of substrate,piezoelectric film and electrode constituting HBAR on Qm are carried out. The relationships between Qm and these parameters are obtained by a lumped parameter equivalent circuit instead of distributed parameter equivalent circuit near the resonance frequency, and the an?alytical expressions oi Qm are given. The results show that Qm increases non-monotonically with the continuous increase of the substrate thickness for HBAR with certain piezoelectric film thickness, and it approaches to the substrate material mechanical quality factor as the substrate thickness is large. Qm decreases wavily with the continuous increase of the piezoelectric film thickness for HBAR with certain substrate thickness. Sapphire and YAG with low mechanical loss are appropriate as the substrate to get a larger Qm- The electrode loss must be considered since it can reduce Qm- Compared with Au electrode, A1 electrode with lower loss can obtain higher Qm when the appropriate electrode thickness is selected. In addition, Qm decreases with the increase of frequency. These results provide the theoretical basis for optimizing the parameters of HBAR and show that trade-oflFs between Qm and must be considered in the design because their changes are often inconsistent.     

Electrode effects on general modes in high-overtone bulk acoustic resonators

Generally, in theoretical calculations of high-overtone bulk acoustic resonators (HBAR), metal electrode effects were always ignored. However, the acoustical impedance, thickness and loss of the electrodes affect practically the performances of HBAR operating at high-frequency. For very high-frequency cases, the thickness of the metal electrode is always on the same order of that of the piezo-film and the electrode effects on modes cannot be negligible. In this paper, based on the resonance frequency spectra and Butterworth Van Dyke equivalent circuit of HBAR, the effects of the material, loss, and thickness of the electrodes on the figure of merit, effective electromechanical coupling factor, quality factor, etc. are analyzed. It is demonstrated that the performance of HBAR can also be optimized by using the electrodes with proper impedance, loss and thickness.     

Parameter characterization of high-overtone bulk acoustic resonators by resonant spectrum method

Effects of electrode on high-overtone bulk acoustic resonator (HBAR) spectra are analyzed by numerical simulation. The figure of merit (FOM), the effective electromechanical coupling factor, k(eff)(2)(m), and the quality factor Q(s) of the unique mode are discussed based on the resonance spectra of the HBAR. It is demonstrated that electrodes with proper acoustic impedance and thickness could improve the performance of the HBAR, or degrade the performance if the electrodes are not properly chosen.     

Incredible negative values of effective electromechanical coupling coefficient for surface acoustic waves in piezoelectrics

The extraordinary case of increase in velocity of surface acoustic waves (SAW) caused by electrical shorting of the surface of the superstrong piezoelectric crystal potassium niobate, KNbO3, is numerically found. The explanation of this effect is based on considering SAWs as coupled Rayleigh and Bleustein-Gulyaev modes. A general procedure of approximate decoupling of the modes is suggested for piezoelectric crystals of arbitrary anisotropy. The effect under study takes place when the phase velocity of uncoupled sagittally polarized Rayleigh waves is intermediate between the phase velocities of uncoupled shear-horizontal Bleustein Gulyaev waves at the free and metallized surfaces. In this case, the metallization of the surface by an infinitely thin layer may cause a crossover of the velocity curves of the uncoupled waves. The presence of the mode coupling results in splitting of the curves with transition from one uncoupled branch to the other. This transition is responsible for the increase in SAW velocity, which appears to be greater than its common decrease produced by electrical shorting of the substrate surface.