Monolithic integration of Pb(Zr,Ti)O3 thin film based resonators using a complete dry microfabrication process

Monolithic fabrication of lead zirconate titanate [Pb(Zr,Ti)O₃ or PZT] based thin film resonant devices such as microcantilevers, Lamb wave and bulk acoustic wave resonators are demonstrated. High-performance PZT thin films with a thickness of 2.6 μm are prepared on a silicon on insulator wafer by a sputtering deposition process. A highly selective reactive ion etching process is employed for micro-patterning of PZT, platinum electrodes, and SiO₂ insulation layer. Self-actuation of the PZT microcantilevers is demonstrated and the frequency response is characterized using a laser Doppler vibrometer. The frequency response of the Lamb wave resonator is evaluated by measuring its transmission characteristic using a network analyzer. For a Lamb wave resonator with a length of 240 μm and an interdigital period of 80 μm, the 1st order and 2nd resonance frequencies are 15.3 and 41.8 MHz, respectively.     

Finite element analysis and experiments on a silicon membrane actuated by an epitaxial PZT thin film for localized-mass sensing applications

In this paper, we investigate the performance of a piezoelectric membrane actuated by an epitaxial piezoelectric Pb(Zr_0.2Ti_0.8)O₃ (PZT) thin film for localized-mass sensing applications. The fabrication and characterization of piezoelectric circular membranes based on epitaxial thin films prepared on a silicon wafer are presented. The dynamic behavior and mass sensing performance of the proposed structure are experimentally investigated and compared to numerical analyses. A 1500 μm diameter silicon membrane actuated by a 150 nm thick epitaxial PZT film exhibits a strong harmonic oscillation response with a high quality factor of 110-144 depending on the resonant mode at atmospheric pressure. Different aspects related to the effect of the mass position and of the resonant mode on the mass sensitivity as well as the minimum detectable mass are evaluated. The operation of the epitaxial PZT membrane as a mass sensor is determined by loading polystyrene microspheres. The mass sensitivity is a function of the mass position, which is the highest at the antinodal points. The epitaxial PZT membrane exhibits a mass sensitivity in the order of 10⁻¹² g/Hz with a minimum detectable mass of 5 ng. The results reveal that the mass sensor realized with the epitaxial PZT thin film, which is capable of generating a high actuating force, is a promising candidate for the development of high performance mass sensors. Such devices can be applied for various biological and chemical sensing applications.     

微型硅基弯曲板波器件

介绍了基于ZnO压电薄膜的微型弯曲板波(FPW)器件的设计与制作。为减小薄膜的应力,器件采用LTO/ZnO/LTO/Si3N4多层复合板结构,并采用直流磁控溅射工艺制备ZnO压电薄膜,在压电复合板结构上沉积两对叉指电极,分别用于Lamb波的激发和接收。X射线衍射分析表明,沉积的ZnO薄膜C轴高度择优;扫描电子显微镜分析表明,制备的ZnO薄膜平整、致密,晶粒生长呈现明显的柱状结构;通过分析制备的高次谐波体声波谐振器(HBAR)器件性能来间接检验ZnO压电薄膜的电学性能,HBAR器件的品质因子较高,表明薄膜有较好的压电性能。利用安捷伦E5071C网络分析仪检测FPW器件的频率响应,结果表明反对称A0模式Lamb波的实测中心频率与理论计算的频率结果基本一致。     

Sensing liquid density using resonant flexural plate wave devices with sol–gel PZT thin films

This study presents the design, fabrication and possible applications in liquid density sensing and biosensing of a flexure plate wave (FPW) resonator using sol–gel-derived lead zirconate titanate (PZT) thin films. The resonator has a two-port structure with a reflecting grating on a composite membrane of PZT and SiN_x. The design of the reflecting grating is derived from a SAW resonator model using COM theory to generate a sharp resonant peak. A comparison between the theoretical mass and the viscosity effects reveals the applications and the constraints of the proposed device in liquid sensing. Multiple coatings of sol–gel-derived PZT films are employed because of the cost advantage and the strong electromechanical coupling effect over other piezoelectric films. Issues of fabrication of the proposed material structure are addressed. Theoretical estimates of the mass and the viscosity effects are compared with the experimental values. The resonant frequency relates quite linearly to the density of low-viscosity liquids, revealing the feasibility of the proposed device. An erratum to this article can be found at     

Investigations on excitation and detection methods for Lamb wave sensors

Due to a high potential sensitivity, Lamb wave acoustic sensors have been studied for biochemical applications. Usually, Lamb waves are generated and detected using piezoelectric transducers. This technology involves bilayers structures and causes some problem of induced strain and temperature compensation. In this paper, we have investigated optical and electrostatic excitation methods. The optical excitation of Lamb waves is studied, and the main limitations of such an excitation method are pointed out. Theoretical as well as experimental studies are reported on electrostatic excitation of Lamb waves, and it is shown that this technique can be suitable for biosensors.     

含金属芯压电纤维传感Lamb波方向性研究

含金属芯压电纤维(MPF)是一种新型压电功能器件.阐述了基于小波变换的Lamb波能量因子计算原理,把MPF作为Lamb波传感器,分别采用幅值和小波变换能量因子的方法对MPF传感Lamb波的方向性进行了研究.研究结果表明:MPF对Lamb波的传感表现出很强的方向性.相比采用幅值表征的结果,采用能量因子进行传感方向性表征更...     

Membrane microcantilever arrays fabrication with PZT thin films for nanorange movement

Lead zirconate titanate (PZT) piezoelectric thin films have been prepared by sol-gel method to fabricate microcantilever arrays for nano-actuation with potential applications in the hard disk drives. In order to solve the silicon over-etching problem, which leads to a low production yield in the microcantilever fabrication process, a new fabrication process using DRIE etching of silicon from the front side of the silicon wafer has been developed. Silicon free membrane microcantilevers with PZT thin films of 1 μm in thickness have been successfully fabricated with almost 100% yield by this new process. Annealing temperature and time are critical to the preparation of the sol-gel PZT thin film. The fabrication process of microcantilever arrays in planar structure will be presented. Key issues on the fabrication of the cantilever are the compatible etching process of PZT thin film and the compensation of thin film stress in all layers to obtain a flat multi-layer structure.     

压电晶体传感器激励模型及其在结构健康监测中的应用

在结构健康监测系统中,基于应力波的结构损伤诊断技术是一种主动的局部损伤检测方法.压电晶体传感器作为激励部件可以在结构中引入高频应力波;其同裂纹等局部损伤发生相互作用将产生波动的能量耗散、波形反射以及波形干涉等现象.通过对附着在无约束金属板上的压电晶体传感器(PZT)激励模型的理论分析及有限元数值计算,说明PZT能有效地产生检测应力波,并可将其应用在结构局部损伤检测中.     

双压电结构乐甫波激发效率和液体传感的仿真

乐甫波器件适于液体检测,但在工程上经常因为激发效率较低而影响应用。与“压电基底-非压电薄膜”的单压电结构乐甫波器件相比,双压电结构的特点是薄膜也选用压电材料,以期增大器件整体的压电效应。在建立理论模型的基础上,通过空气中和液体检测时双压电结构乐甫波与声表面波、单压电结构乐甫波的机电耦合系数仿真并对比,表明对于某些压电基底和薄膜,双压电结构具有更高的乐甫波激发效率。并且,以液体介电常数检测为例,仿真结果还表明了双压电结构乐甫波比单压电结构具有更高的灵敏度。     

PZT压电薄膜在微传感器中的应用

锆钛酸铅压电材料(PZT)因具有优良的压电性能、热释电性能、铁电性能和介电性能而被广泛地应用在微电子机械系统(MEMS)中。基于微传感器,介绍了PZT薄膜,重点介绍了PZT薄膜在微传感器中的应用,并介绍了PZT薄膜微传感器的发展状况。     

Magnetic–acoustic–resonator sensors (MARS): a new sensing methodology

A new type of acoustic shear wave sensor fabricated from inexpensive glass and metal plates, in which the acoustic plate is remotely excited and detected with a radio frequency signal and a strong magnetic field, is described. This new acoustic plate resonance requires neither piezoelectric materials nor wire contacts, and is referred to as a magnetic–acoustic–resonator sensor or MARS device. This paper reports the concept of the MARS device and describes how shear wave resonances in aluminium and aluminium–glass composites are detected and verified. The effect of mass loading an aluminised glass plate demonstrates that MARS has Sauerbrey-like characteristics similar to the Quartz Crystal Microbalance (QCM). Prospects for liquid phase measurements are also indicated.     

基于圆形压电阵列的主动Lamb波损伤成像监测研究

对主动Lamb波结构健康监测中的压电阵列技术进行了研究。分析了传统的矩阵式压电阵列在应用中存在的问题,基于回声式原理研究设计了圆形压电阵列方法,分析了该方法的特点和信号采集过程,结合时间反转成像技术,实现对损伤的监测,实验结果表明:该方法能克服传统矩阵式压电阵列在应用中存在的监测范围、信号监测能力差异等问题,最后分析了圆形压电阵列还存在的问题。     

Modeling analysis of a triaxial microaccelerometer with piezoelectric thin-film sensing using energy method

This study applies energy method to derive the system modeling of a triaxial microaccelerometer that consists of a quadri-beam suspension, a seismic mass, and displacement transducers using piezoelectric thin films. Two suspension beams support both ends of the seismic mass, which is fabricated by anisotropic etching of silicon. An out-of-plane acceleration will result in a symmetric bend, and in-plane accelerations will produce asymmetric bend and torsion of the suspension beams. Two piezoelectric thin-film transducers are arranged at both ends of each suspension beam. Eight transducers in total are interconnected such that triaxial accelerations can be measured selectively. The structure stiffness of the suspension beams considers both the silicon beams and piezoelectric films by the use of the laminated beam theory. Therefore, the analytical model is applicable to the accelerometers with thick piezoelectric films. The model is based on the anisotropic material properties of Silicon and PZT and Euler’s beam equation with the assumptions that smaller strains and stresses are negligible. The analytical results of the resonant frequencies and sensor sensitivities to triaxial accelerations are presented and confirmed by finite element analysis.     

液体层-压电薄板中兰姆波对液体密度的声传感

叉指换能器在液体层 -压电薄板结构中可激发出兰姆波模式 ,兰姆波的相速度与液体介质的密度密切相关 ,并可反映出液体密度的变化。本文对液体层 -压电薄板结构中兰姆波的液体密度声传感过程进行了理论研究和数值分析 ,所得结果表明 ,用兰姆波对液体密度进行声传感是可行的。     

基于SAW器件的微间隙压力监测传感器

声表面波SAW(Surface Acoustic Wave)器件能进行无源无线通信,为微间隙等特殊环境下物理量的测量提供了新的解决思路.研究设计了一种基于声表面波延迟线的接触应力传感器.围绕微间隙环境,研究了声表面波器件的结构类型,并确定压力监测的技术方案;根据设计原理,设计一种新型声表面波传感器,并利用有限元分析法对压电基片进行应力仿真;将设计出的传感器进行实验测试并提出温度补偿.通过对声表面波传感器设计的探究,验证了利用声表面波传感器实现微间隙压力监测的可行性.     

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.     

Two-Port Electromechanical Model for Bulk-Piezoelectric Excitation of Surface Micromachined Beam Resonators

A small-signal model that describes the energy exchange between surface micromachined beams and bulk-lead zirconium titanate (PZT) actuators attached to the silicon substrate is presented. The model includes detection of acoustic waves launched from electrostatically actuated structures on the surface of the die, as well as their actuation by bulk waves generated by piezoelectric ceramics. The interaction is modeled via an empirical equivalent circuit, which is substantiated by experiments designed to extract the model parameters. The equivalent model is valid for cases where the beam resonance frequency is much smaller than the thickness mode resonance of the PZT/silicon stack. In this paper, the resonance frequency of the beams ranges between 200 and 300 kHz. As energy transfer between bulk-PZT and electrostatic actuated beam resonators must be reciprocal for small signals, this paper uses the extracted equivalent model to describe the physical sources of error that account for discrepancies in reciprocity.$hfill$[2008-0131]      

复合式微型能量采集器结构设计及关键技术

提出一种压电效应和电磁效应相结合的微型能量采集器,基础结构为压电换能器(PZT)基八悬臂梁、长有Au线圈质量块、铷铁硼(NdFeB)永磁体.利用有限元分析软件ANSYS对微结构建立模型,通过结构力学特性分析,得到所设计结构的一阶谐振频率为214.7 Hz,为后期测试提供指导意义.制定微机电系统(MEMS)加工工艺流程,利用L-Edit软件设计并绘制所需掩模版.利用溶胶-凝胶(sol-gel)技术制备厚度为3 529 nm的PZT压电厚膜,实现了其与基底Pt/Ti/SiO2/Si/SiO2的良好异质集成,完成微型能量采集器制造过程中关键一步.经介电性能测试,PZT厚膜具有双蝴蝶状的极化反转峰,体现出较高的介电性能和耐压强度.400 kV/cm驱动条件下,测得PZT厚膜的电滞回线,其剩余极化强度Pr为37.7 μC/cm2,矫顽场强为41.2kV/cm,表现出良好的铁电性能.     

MEMS压电-磁电复合式振动驱动微能源的设计

在单一效应的MEMS振动驱动微能源的基础上,提出了一种MEMS压电-磁电复合振动驱动微能源器件。该微能源由八悬臂梁-中心质量块结构和永磁铁两部分组成,环境振动使中心质量块振动,PZT压电敏感单元由于压电效应产生电势差;同时中心质量块上集成的高密度线圈切割磁感线产生感应电动势,将压电转换与磁电转换相结合把振动能转换为电能。建立了该结构的数学模型并用有限分析软件Ansys12.0对该器件进行力学特性分析,最后对加工出的微能源进行性能测试。测试结果表明,该微能源谐振频率为8 Hz,易与环境发生共振;在共振条件下,施加1 gn 的加速度,器件压电发电开路输出电压峰峰值达154 mV,磁电发电开路输出电压峰-峰值达8 mV,有望为无线传感网络节点提供稳定的能源。     

Thin-Film Piezoelectric Unimorph Actuator-Based Deformable Mirror With a Transferred Silicon Membrane

This paper describes a proof-of-concept deformable mirror (DM) technology, with a continuous single-crystal silicon membrane reflecting surface, based on$ PbZr _0.52 Ti_0.48 O _3$(PZT) unimorph membrane microactuators. A potential application for a terrestrial planet finder adaptive er is also discussed. The DM comprises a continuous, large-aperture, silicon membrane “transferred” onto a 20$,times,$20 piezoelectric unimorph actuator array. The actuator array was prepared on an electroded silicon substrate using chemical-solution-deposited 2-$mu m$-thick PZT films working in a$d _31$mode. The substrate was subsequently bulk-micromachined to create membrane structures with residual silicon acting as the passive layer in the actuator structure. A mathematical model simulated the membrane microactuator performance and aided in the optimization of membrane thicknesses and electrode geometries. Excellent agreement was obtained between the model and the experimental results. The resulting piezoelectric unimorph actuators with patterned PZT films produced large strokes at low voltages. A PZT unimorph actuator, 2.5 mm in diameter with optimized PZT/silicon thickness and design showed a deflection of 5.7$~mu m$at 20 V. A DM structure with a 20-$mu m$-thick silicon membrane mirror (50 mm$times,$50 mm area) supported by 400 PZT unimorph actuators was successfully fabricated and optically characterized. The measured maximum mirror deflection at 30 V was approximately 1$~mu m$. An assembled DM showed an operating frequency bandwidth of 30 kHz and an influence function of approximately 30%. 1738