An Investigation on Efficient Acoustic Energy Reflection of Flexible Film Bulk Acoustic Resonators

This paper investigates the issues on acoustic energy reflection of flexible film bulk acoustic resonators(FBARs). The flexible FBAR was fabricated with an air cavity in the polymer substrate, which endowed the resonator with efficient acoustic reflection and high electrical performance. The acoustic wave propagation and reflection in FBAR were first analyzed by Mason model, and then flexible FBARs of 2.66 GHz series resonance in different configurations were fabricated. To validate efficient acoustic reflection of flexible resonators, FBARs were transferred onto different polymer substrates without air cavities. Experimental results indicate that efficient acoustic reflection can be efficiently predicted by Mason model. Flexible FBARs with air cavities exhibit a higher figure of merit(FOM). Our demonstration provides a feasible solution to flexible MEMS devices with highly efficient acoustic reflection(i.e. energy preserving) and free-moving cavities, achieving both high flexibility and high electrical performance.

A new model for film bulk acoustic wave resonators

Based on cavity resonance and sandwich composite plate （3D） theoretical model for frequency dispersion characterization theory, this paper presents a universal three-dimensional and displacement profile shapes of the film bulk acoustic resonator （FBARs）. This model provides results of FBAR excited thickness-extensional and flexure modes, and the result of frequency dispersion is proposed in which the thicknesses and impedance of the electrodes and the piezoelectric material are taken into consideration; its further simplification shows good agreement with the modified Butterworth-Van-Dyke （MBVD） model. The displacement profile reflects the vibration stress distribution of electrode shapes and the lateral resonance effect, which depends on the axis ratio of the electrode shapes a/b. The results are consistent with the 3D finite element method modeling and laser interferometry measurement in general.

Active control scheme for improving mass resolution of film bulk acoustic resonators

High mass resolution of sensors based on film bulk acoustic resonators （FBARs） is required for the detection of small molecules with the low concentration. An active control scheme is presented to improve the mass resolution of the FBAR sen- sors by adding a feedback voltage onto the driving voltage between two electrodes of the FBAR sensors, The feedback voltage is obtained by giving a constant gain and a constant phase shift to the current on the electrodes of the FBAR sensors. The acoustic energy produced by the feedback voltage partly compensates the acoustic energy loss due to the material damping and the acoustic scattering, and thus improves the quality factor and the mass resolution of the FBAR sensors. An explicit expression relating to the impedance and the frequency for an FBAR sensor with the active control is derived based on the continuum theory by neglecting the influence of the electrodes. Numerical simulations show that the impedance of the FBAR sensor strongly depends on the gain and the phase shift of the feedback voltage, and the mass resolution of the FBAR sensor can greatly be improved when the appropriate gain and the phase shift of the feedback voltage are used. The active control scheme also provides an effective solution to improve the resolution of the quartz crystal microbalance （QCM）.

Tunable Ba_(0.5) Sr_(0.5) TiO_3 film bulk acoustic resonators using SiO_2 /Mo Bragg reflectors

Tunable and switchable Ba 0.5 Sr 0.5 TiO 3 film bulk acoustic resonators（FBARs） based on SiO 2 /Mo Bragg reflectors are explored,which can withstand high temperature for the deposition of Ba x Sr 1 x TiO 3（BST） films at 800 C.The dc bias-dependent resonance may be attributed to the piezoelectricity of the BST film induced by an electrostrictive effect.The series resonant frequency is strongly dc bias-dependent and shifts downwards with dc bias increasing,while the parallel resonant frequency is only weakly dc bias-dependent and slightly shifts upwards at low dc bias（ 45 V） while downwards at higher dc bias.The calculated relative tunability of shifts at series resonance frequency is around 2.3% and the electromechanical coupling coefficient is up to approximately 8.09% at 60-V dc bias,which can be comparable to AlN FBARs.This suggests that a high-quality tunable BST FBAR device can be achieved through the use of molybdenum（Mo） as the high acoustic impedance layer in a Bragg reflector,which not only provides excellent acoustic isolation from the substrate,but also improves the crystallinity of BST films withstanding higher deposition temperature.

微型FBAR器件性能优化设计

利用有限元仿真软件建立了薄膜体声波谐振器模型,研究了不同谐振面积(3600~10000μm^(2))条件下,电极形状(矩形、梯形、圆形和正五边形)及变迹角(30°、36°、40°和45°)对寄生谐振的影响,得到史密斯阻抗曲线和不圆度值,讨论了阶梯负载结构对横向声波泄露的抑制作用。仿真结果表明,电极形状为非正五边形,变迹角为40°时,对寄生谐振的抑制效果最好;在谐振面积为3600μm^(2)时,其不圆度为6.45%,与谐振面积为10000μm^(2)时矩形电极相当。设计的电极阶梯负载结构提升了并联谐振点处的品质因数,当电极横向尺寸为60μm时,二阶电极负载结构的品质因数为1378,比无电极负载结构的品质因数高10.07%。

薄膜体声波谐振器FBAR技术在滤波器的应用研究及其专利数据分析

本文简单介绍了薄膜体声波谐振器FBAR的具体结构、工作原理以及FBAR技术的应用,重点介绍了FBAR技术在滤波器的应用及其工作原理,梳理了常见的几种FBAR滤波器结构,最后通过检索分析,从多个角度对FBAR技术在滤波器应用领域的专利申请进行专利分析,为后续企业在该应用领域进行专利布局提供一定的参考价值。

Development and Analysis of an RF Film Bulk Acoustic Resonator

A high-Q diaphragm-structure film bulk acoustic resonator （FBAR） with a flat support diaphragm, made of Si3 N4/SiOz/Si3 N4 composite films ,is proposed. The N/O/N composite diaphragm overcomes the wrinkling in the released support diaphragm caused by the residual stress of a single Si3N4 or SiO2 diaphragm. ZnO piezoelectric film deposited employing a DC reactive magnetron sputtering method is used as the piezoelectric material for the FBAR device. The XRD 0- 20 scan indicates that the ZnO film has the preferred c-axis orientation growth,implying good piezoelectric properties. The S parameter measurement shows that there＇ are three primary resonances in the frequency range from 0.4 to 2.6GHz. The series resonant frequency,parallel resonant frequency, Kett^2, and quality factors of the three resonances are calculated. The third one,with a frequency of about 2.4GHz,has the highest quality factor about 500. Thus,it is expected to be a candidate to form a 2.4GHz low-phase-noise oscillator.

High Q,high frequency,high overtone bulk acoustic resonator with ZnO films

Bulk acoustic wave resonators with piezoelectric films have been widely explored for the small size and high quality factor （Q） at GHz. This paper describes a high overtone bulk acoustic resonator （HBAR） based on AI/ZnO/AI sandwich layers and c-axis sapphire substrate. ZnO film with high quality c-axis orientation has been obtained using DC magnetron sputtering. The fabricated HBAR presents high Q at the multiple resonances from a 0.5-4.0 GHz wide band with a total size （including the contact pads） of 0.6 mm×0.3 mm×0.4 mm, The device exhibits the best acoustic coupling at around 2.4 GHz, which agrees with the simulation results based on the one-dimensional Mason equivalent circuit model. The HBAR also demonstrates Q values of 30 000, 25 000, and 6500 at 1.49, 2.43, and 3.40 GHz, respectively. It is indicated that the HBAR has potential applications for the low phase noise high frequency oscillator or microwave signal source.

FBAR电极和压电薄膜制备工艺研究

薄膜体声波谐振器(FBAR)制备工艺中,压电薄膜及金属电极的质量和形貌直接影响了器件的性能如品质因数、插入损耗及带宽等。研究了决定FBAR性能的关键工艺,包括Mo电极的刻蚀、AlN压电薄膜的溅射和腐蚀,从而实现高质量电极及压电薄膜结构。同步调节光刻胶掩膜侧壁角度和刻蚀选择比,得到了平缓的底电极侧壁角度,实现了有利于AlN溅射连续性的底电极形貌,通过调节溅射工艺中N_(2)流量组分和温度等参数得到高质量的AlN薄膜,对比不同质量分数和温度的腐蚀溶液对AlN腐蚀工艺的影响,对AlN腐蚀不净及钻蚀问题进行分析,得到最佳的AlN腐蚀条件。最终工艺优化后制备出的FBAR经测试具有良好的滤波器特性,该研究对FBAR制备工艺和性能的提升具有借鉴意义。

Preparation of AlN thin films for film bulk acoustic resonator application by radio frequency sputtering

Aluminum nitride （AlN） thin films with high c-axis orientation have been prepared on a glass substrate with an Al bottom electrode by radio frequency （RF） reactive magnetron sputtering. Based on the analysis of Berg＇s hysteresis model, the improved sputtering system is realized without a hysteresis effect. A new control method for rapidly depositing highly c-axis oriented AlN thin films is proposed. The N2 concentration could be controlled by observing the changes in cathode voltage, to realize the optimum processing condition where the target could be fixed stably in the transition region, and both stoichiometric film composition and a high deposition rate could be obtained. Under a 500 W RF power of a target with a 6 cm diameter, a substrate temperature of 450 ℃, a target-substrate distance of 60 mm and a N2 concentration of 25%, AlN thin film with preferential （002） orientation was deposited at 2.3 μm/h which is a much higher rate than previously achieved. Through X-ray diffraction （XRD） analysis, the full width at half maximum （FWHM） of AlN （002） was shown to be about 0.28°, which shows the good crystallinity and crystal orientation of AlN thin film. With other parameters held constant, any increase or decrease in N2 concentration results in an increase in the FWHM of AlN.

大于3 GHz超宽带FBAR滤波器结构设计与仿真

该文提出了一种获得相对带宽约为70.61%的基于氮化铝薄膜的超宽带薄膜体声波谐振器(FBAR)滤波器的设计方法,即在中心频率为6.5 GHz下滤波器的带宽为4.835 GHz。仿真分析表明,通过串并联电感的方式,并在电感端串并联电容,可消除因增加电感而带来的谐波谐振点干扰对带通的影响,实现了FBAR滤波器的超宽带。该工作开辟了设计和制作带宽超过3 GHz的超宽带体声波滤波器的新途径。

基于掺钪氮化铝FBAR的滤波器设计研究

设计了一款工作在2.11~2.18 GHz频段的薄膜体声波滤波器。基于有限元仿真研究了掺钪氮化铝(AlScN)的薄膜体声波谐振器,并分析了掺钪对谐振器性能的影响。提出了边缘凸起结构的优化设计方案,改善了谐振器的有效机电耦合系数和品质因数。利用Modified Butterworth-van Dyke(MBVD)等效电学模型对FBAR滤波器进行仿真研究,并将所设计的7层内置螺旋电感与滤波器电路进行协同仿真,优化后的FBAR滤波器在2.11~2.18 GHz频段的插入损耗<2 dB,带外抑制>40 dB。

Portable FBAR based E-nose for cold chain real-time bananas shelf time detection

Being cheap,nondestructive,and easy to use,gas sensors play important roles in the food industry.However,most gas sensors are suitable more for laboratory-quality fast testing rather than for cold-chain continuous and cumulative testing.Also,an ideal electronic nose(E-nose)in a cold chain should be stable to its surroundings and remain highly accurate and portable.In this work,a portable film bulk acoustic resonator(FBAR)-based E-nose was built for real-time measurement of banana shelf time.The sensor chamber to contain the portable circuit of the E-nose is as small as a smartphone,and by introducing an air-tight FBAR as a reference,the E-nose can avoid most of the drift caused by surroundings.With the help of porous layer by layer(LBL)coating of the FBAR,the sensitivity of the E-nose is 5 ppm to ethylene and 0.5 ppm to isoamyl acetate and isoamyl butyrate,while the detection range is large enough to cover a relative humidity of 0.8.In this regard,the E-nose can easily discriminate between yellow bananas with green necks and entirely yellow bananas while allowing the bananas to maintain their biological activities in their normal storage state,thereby showing the possibility of real-time shelf time detection.This portable FBAR-based E-nose has a large testing scale,high sensitivity,good humidity tolerance,and low frequency drift to its surroundings,thereby meeting the needs of cold-chain usage.

框架结构对薄膜体声波谐振器性能提升的研究

本文研究了框架结构(Frame)对薄膜体声波谐振器(Film Bulk Acoustic Resonator,FBAR)提升性能的作用,从两种Frame结构对体声波能量的反射匹配基础理论出发,针对其功能特点,以实验的方式确定了低频和高频多组框架微结构的组合,对多组FBAR进行了版图绘制以及光刻流片,最终通过片上测试得到了所有分组的谐振器性能.对测试得到的性能进行了分组统计筛选,从测试结果来看,经过优选之后的Frame结构分组无论是对低频还是高频FBAR谐振器都具有提升性能的作用.对低频(1.7 GHz附近)FBAR来说,并联谐振品质因数可以提升1000以上.对高频(5.5 GHz附近)FBAR来说,并联谐振品质因数可以提升300以上.对横向寄生模式较强的高频FBAR,优选的Frame结构可以提升谐振器的横向寄生模式抑制,使串联谐振频率之下的阻抗相位波动减少5°以上.

背腔刻蚀型横向激励薄膜体声波谐振器制备技术研究

随着移动通信技术的快速发展,薄膜体声波滤波器逐渐向高频和大带宽方向发展。该文研究了POI(LiNbO_(3)/SiO_(2)/Si)基片上背腔刻蚀型横向激励薄膜体声波谐振器制作工艺,通过研究POI基IDT光刻、背腔硅刻蚀等工艺,确定了IDT层曝光量和背腔刻蚀等关键工艺参数。研制出的背腔刻蚀型横向激励薄膜体声波谐振器,其谐振频率为4565 MHz,反谐振频率为5035 MHz,机电耦合系数为20.86%。此制备工艺对研究高频、大带宽薄膜体声波滤波器具有重要的参考意义。

窄带FBAR带通滤波器设计

由薄膜体声波谐振器构成的滤波器,其带宽受压电材料机电耦合系数的影响,较难实现窄带滤波器设计。使用ADS射频仿真软件设计了一种通带为1.18～1.20 GHz的窄带薄膜体声波滤波器,分别通过比较增加无源电容元件、改变串并联谐振器面积比、在压电振荡堆内增加一层非压电层和采用两个中心频率不同的薄膜体声波滤波器串联这四种方法,得出窄带薄膜体声波滤波器的优化设计方案。设计得到的滤波器突破了压电材料本身机电耦合系数限定的带宽值,实现了窄带要求,并且带外抑制以及带内插损等设计指标均满足要求。

薄膜声体波谐振器(FBAR)的研究进展

综述了国内外FBAR技术的研究现状和进展。分析了基于空气腔和布拉格反射层两种主流FBAR的结构、工作原理和建模方法。阐述了适用于FBAR的压电薄膜材料、电极材料以及布拉格反射层材料的选择。并介绍了作为FBAR主要应用的射频滤波器和双工器的拓扑结构和设计方法,以及制备FBAR器件时需克服的关键技术等问题。

X波段FBAR用AlN薄膜制备研究

采用中频磁控溅射法,在硅基上制备了X波段薄膜体声波谐振器(FBAR)滤波器用AlN压电薄膜。对AlN薄膜进行了分析表征,结果表明,AlN压电薄膜具有良好的(002)面择优取向,摇摆曲线半峰宽为2.21°,膜厚均匀性优于0.5%,薄膜应力为-5.02 MPa,应力可在张应力和压应力间进行调节。将该AlN薄膜制备工艺应用于FBAR器件的制作,研制出X波段FBAR器件,谐振频率为9.09 GHz,插入损耗为-0.38 dB。

S波段网格型FBAR滤波器的研制

介绍了一种单端口,端口阻抗为50Ω的S波段宽带薄膜体声波谐振器（FBAR）滤波器,该滤波器采用网格型结构的FBAR滤波器芯片级联巴伦芯片实现。对宽带FBAR滤波器芯片的设计过程、工艺实现过程进行了说明。采用0.35μm Ga As工艺实现了3~8 GHz频率范围的巴伦芯片,在FBAR滤波器芯片的中心频率处,幅度不平衡度为0.53 d B,相位不平衡度为0.55°。制备的FBAR滤波器通带频率范围为3 100~3 400 MHz,1 d B带宽约为369 MHz,在2 660 MHz和3 840 MHz处带外抑制分别为45.6 d Bc和41.3 d Bc,尺寸仅为12 mm×7 mm×2.9 mm。将实测结果与仿真结果进行了对比,两者一致性很好。

密封空气型FBAR温度传感器

薄膜体声波谐振器(FBAR)是性能优良的压电换能器。通过在体硅刻蚀型FBAR背面密封空气的方法制作了密封空气型FBAR,研究了密封空气型FBAR用作温度传感器的可行性。实验结果表明,在20～100℃的温度范围内,密封空气型FBAR温度传感器的并联谐振频率随温度线性变化,且具有很好的稳定性与可靠性。