LiNbO3声表面波特性及其应用

LiNbO3因其优异的压电性能和声表面波特性被广泛应用于声表面波器件中.着重介绍LiNbO3的压电性能、声表面性能及其薄膜制备技术,对通过不同制备工艺生长出的LiNbO3薄膜的质量和声表面波性能进行了比较,并简要介绍了LiNbO3在声表面波领域应用的新进展.     

声表面波器件的研究进展

声表面波器件作为一种新型的电子器件，近年来引起了人们极大的关注，在科学研究领域有了较大的进展，在现代无线通讯领域的应用范围日趋广泛。本简述了目前国际上出现的声表面波器件的制备方法、性能研究及其应用，展望了其今后的发展趋势。     

声表面波天平检测卫星污染

通过对声波表面天平历史发展、声波天平传感器类型、声表面波器件、声表面波传感器原理和特点的阐述,讨论了其在空间监测卫星污染的可行性,通过对该项技术的深入研究后表明,声表面波技术可应用在污染敏感卫星的微量监测领域。该项技术在空间环境监测方面具有广泛的应用前景。     

声表面波在AlN/GaN中的传播特性分析

从矩阵方法的基本原理出发,结合AlN/GaN结构的机械和电学边界条件,推导出用于求解声表面波在AlN/GaN结构中的相速的行列式方程.通过求解该行列式方程,分析了声表面波在AlN/GaN结构中的传播特性,包括声表面波相速和机电耦合系数随频率、AlN的膜厚和c轴取向的变化规律.AlN/GaN结构减弱了GaN中施主杂质的影响,使该结构更适合于声表面波器件的应用,AlN和GaN作为半导体压电材料,其AlN/GaN结构便于与其它电路集成化,有利于减小器件的尺寸,增强声表面波器件的功能.     

基于COMSOL的声表面波器件仿真

声表面波器件在通信、传感、射频识别等领域有着广泛的应用.以有限元方法为基础,利用有限元软件COMSOL对声表面波器件进行了仿真.从器件的模型建立入手,按由浅入深的顺序对无电极压电基片、压电基片表面沉积叉指换能器、叉指换能器表面溅射薄膜、薄膜上负载液体的4种结构进行了仿真分析.仿真研究表明:叉指换能器的电极效应会产生正、反特征频率,并且两种频率都随着叉指电极的敷金比与高度增加而向低频偏移;薄膜厚度的增加同样会导致器件频率向低频变化;当器件负载液体用于液体密度检测时,可通过器件频率变化对液体密度的灵敏程度来对薄膜厚度进行优化.其研究结果可以为声表面波器件的设计制作提供依据.     

金刚石声表面波器件的研究与进展

高频无线通讯系统的迅速发展推动了对高频声表面波 (SAW)器件需求的不断增大。金刚石具有最高的声速和许多优于其他材料的特性 ,因此金刚石声表面波器件受到了越来越多的关注。本文介绍了金刚石声表面波器件的构成、制备方法 ,讨论了金刚石声表面波器件近年来国际上的研究进展 ,包括理论研究与实验进展的概况 ,并讨论了金刚石声表面波器件的未来发展趋势     

金刚石声表面波器件的研究与进展

高频无线通讯系统的迅速发展推动了对高频声表面波(SAW)器件需求的不断增大。金刚石具有最高的声速和许多优于其他材料的特性，因此金刚石声表面波器件受到了越来越多的关注。本文介绍了金刚石声表面波器件的构成、制备方法，讨论了金刚石声表面波器件近年来国际上的研究进展，包括理论研究与实验进展的概况，并讨论了金刚石声表面波器件的未来发展趋势。     

声表面波单电子输运器件的频率响应研究

为减少样品盒的电磁效应对声表面波单电子输运的影响,需要优化器件的样品盒结构.我们用全波法模拟不同样品盒的声表面波单电子输运器件的频率响应,同时测试该频率响应.模拟结果与测试结果较为一致.二者表明,电磁馈通效应对声表面波单电子输运器件的频率响应影响显著.通过适当改进器件的样品盒可以较有效地抑制电磁馈通效应.这将有助于提高量子化声电电流的精度.     

Chirp变换频谱分析仪的设计及其数字部分的实现

太赫兹频谱分析仪应用技术中,Chirp变换频谱分析应用了声表面波滤波器件,能够保障中频、分辨率等参数,满足深空探测领域对稳定性和功耗的严格要求。但目前国内的Chirp变换频谱分析仪只能处理400 MHz带宽的输入信号,不能完全满足应用需要。为了提高带宽,本文围绕1 GHz带宽声表面波滤波器件,利用直接数字频率合成技术产生与其匹配的2 GHz带宽的线性调频信号,设计了带宽为1 GHz,中心频率为3. 2 GHz的频谱分析仪,并对数字部分进行了实现和结果分析验证。     

中高频声表面波关键材料与应用研究

随着第三代通讯技术的发展,声表面波(SAW)器件的使用频率不断提高,从最初的数MHz发展到现在的数GHz,如应用于1.9GHz的个人通讯服务系统,2.4GHz的无线局域网络系统及高于5GHz无线多端发送系统。这些高频应用系统的不断发展显著增大了高频声表面波器件的市场需求以及对相关材料与器件研究的兴趣。介绍近年来在中高频声表面波材料与应用方面所作的一些研究工作,主要进展有:(1)采用纳米级金属(Ti、Zr、Ni)过渡层,并通过适量添加Mo等微合金元素,研制出多种具有高抗电迁移和功率耐受性的叉指换能器材料,制备的滤波器频率达到2.4GHz;(2)成功解决Si、金刚石、ZnO、Al多层材料间声匹配问题,获得可用于高频声表面波器件制作的高品质材料,ZnO薄膜具有高度C轴取向(类单晶结构),制作得器件频率达3GHz。(3)将藕合模(COM)和镜像耦合理论成功应用于多层复合膜声表面波器件的设计,发展出具有自主知识产权的设计平台和相关软件;(4)针对高频声表亚200纳米密集叉指换能器和毫米级汇流条同时曝光的挑战,发展了一种新的分层分剂量进行临近效应修正电子束直写技术,制备出线宽达0.2μm的声表面波器件(中心频率为3～4G...     

Platinum and palladium high-temperature transducers on langasite

There is a pressing need for the fabrication of surface acoustic wave (SAW) devices capable of operating in harsh environments, at elevated temperature and pressure, or under high-power conditions. These SAW devices operate as frequency-control elements, signal-processing filters, and pressure, temperature, and gas sensors. Applications include gas and oil wells, high-power duplexers in communication systems, and automobile and aerospace combustion engines. Under these high-temperature and power-operating conditions, which can reach several hundred degrees Centigrade, the typically fabricated aluminum (A1) thin film interdigital transducer (IDT) fails due to electro and stress migration. This work reports on high temperature SAW transducers that have been designed, fabricated, and tested on langasite (LGS) piezoelectric substrates. Platinum (Pt) and palladium (Pd) (melting points at 1769 degrees C and 1554.9 degrees C, respectively) have been used as thin metallic films for the SAW IDTs fabricated. Zirconium (Zr) was originally used as an adhesion layer on the fabricated SAW transducers to avoid migration into the Pt or Pd metallic films. The piezoelectric LGS crystal, used as the substrate upon which the SAW devices were fabricated, does not exhibit any phase transition up to its melting point at 1470 degrees C. A radio frequency (RF) test and characterization system capable of withstanding 1000 degrees C has been designed and constructed. The LGS SAW devices with Pt and Pd electrodes and the test system have been exposed to temperatures in the range of 250 degrees C to 750 degrees C over periods up to 6 weeks, with the SAW devices showing a reduced degradation better than 7 dB in the magnitude of transmission coefficient, /S21/, with respect to room temperature. These results qualify the Pt and Pd LGS SAW IDTs fabricated for the above listed modern applications in harsh environments.     

Theoretical Studies on the SAW Properties of LGS at High-Temperature in Optimal Cuts

Surface acoustic wave (SAW) devices play a significant role in signal processing, frequency control and sensing applications. In general, they cannot operate at elevated temperature. The new crystal of langasite provides possibility for surface acoustic wave devices applied at high temperature. This paper studies the SAW properties of single and doubly rotated cuts of LGS at high temperature. The calculated SAW properties of LGS are analyzed in space with aid of contour plots, and two promising SAW orientation regions at high temperature are presented. For some typical cuts and propagating directions within the two optimal regions, their SAW characteristics vs temperature are discussed. Based on the experimental evidence in some literatures, the reliability of calculated results is verified.     

SAW oscillator frequency stability at high temperatures

A broad overview of various factors affecting the frequency stability of surface-acoustic-wave (SAW) resonators is given. Two major causes of rapid degradation in the long-term frequency stability are the presence of a chromium interface between aluminum and quartz, and moderate to high drive levels in SAW devices with pure aluminum fingers, resulting in metal migration in the region of high thin-film stresses. On the other hand, devices with copper-doped aluminum electrodes maintained excellent long-term stability, even when operating at 175 degrees C and at moderately high drive levels. Experimental data on both the long-term and short-term frequency stabilities of SAW devices at 25 degrees C and 175 degrees C for moderate to high drive levels are presented. Results obtained for the frequency stabilities of SAW devices with pure aluminum and copper-doped aluminum electrodes are compared. It is shown that the short-term frequency stability of SAW devices with copper-doped aluminum electrodes is a few parts in 10(10), even at 175 degrees C and for moderately large drive levels. Overall, the best short-term frequency stability is found to be for a gate time of 0.1 s.     

Growth of A1N piezoelectric film on diamond for high-frequency surface acoustic wave devices

Diamond films are very desirable for application to SAW devices because of their high acoustic wave velocity, which allows the extending of the frequency limit of operation at a given interdigital transducer line-width resolution. Use of high-quality AIN as the piezoelectric layer in conjunction with diamond is also desirable because of its high SAW velocity--the highest among all piezoelectric materials--together with its excellent electrical, mechanical, and chemical properties. The problems arising in the growth of A1N films on diamond have prevented, until now, the use of this combination of materials. In this paper we present recent results on the growth of highly oriented, low-stressed A1N films on diamond. SAW propagation on A1N/diamond has been theoretically investigated together with electromechanical coupling for both the Rayleigh and the Sezawa modes. The theoretical calculations show that high SAW velocities are achievable with good coupling efficiencies. Under proper conditions very large piezoelectric couplings are predicted--k2 = 2.2 and 4% for the Rayleigh and the Sezawa wave, respectively--comparable to those observed in strongly piezoelectric single crystals such as LiNbO3, but with SAW velocities approximately two-fold higher. Experiments performed on A1N/diamond/Si SAW test devices have shown good agreement between experimental results and theoretical predictions and demonstrate the feasibility of SAW devices based on this technology.     

Applicability of LiNbO3, langasite and GaPO4 in high temperature SAW sensors operating at radio frequencies

The applicability of LiNbO3, langasite and GaPO4 for use as crystal substrates in high temperature surface acoustic wave (SAW) sensors operating at radio frequencies was investigated. Material properties were determined by the use of SAW test devices processed with conventional lithography. On GaPO4, predominantly surface defects limit the accessible frequencies to values of 1 GHz. Langasite SAW devices could be operated up to 3 GHz; however, high acoustic losses of 20 dB/micros were observed. On LiNbO3, the acoustic losses measured up to 3.5 GHz are one order of magnitude less. Hence, SAW sensors capable of wireless interrogation were designed and processed on YZ-cut LiNbO3. The devices could be successfully operated in the industrial-scientific-medical (ISM) band from 2.40 to 2.4835 GHz up to 400 degrees C.     

Numerical analysis of wave generation and propagation in a focused surface acoustic wave device for potential microfluidics applications

We develop a 3-D finite element model of a focused surface acoustic wave (F-SAW) device based on LiNbO/sub 3/to analyze the wave generation and propagation characteristics for devices operating at MHz frequencies with varying applied input voltages. We compare the F-SAW device to a conventional SAW device with similar substrate dimensions and transducer finger periodicity. SAW devices with concentrically shaped focused interdigital transducer fingers (F-IDTs) are found to excite waves with high intensity and high beam-width compression ratio, confined to a small localized area. F-SAW devices are more sensitive to amplitude variations at regions close to the focal point than conventional SAW devices having uniform IDT configuration. We compute F-SAW induced streaming forces and velocity fields by applying a successive approximation technique to the Navier-Stokes equation (Nyborg's theory). The maximum streaming force obtained at the focal point varies as the square of the applied input voltage. Computed streaming velocities at the focal point in F-SAW devices are at least an order of magnitude higher than those in conventional SAW devices. Simulated frequency response indicates higher insertion losses in F-SAW devices than in conventional devices, reflecting their greater utility as actuators than as sensors. Our simulation findings suggest that F-SAW devices can be utilized effectively for actuation in microfluidic applications involving diffusion limited transport processes.     

Organic vapor sensors based on SAW resonator and organic films

The majority of investigations of SAW devices used as chemical sensors are based on delay line oscillators. However, SAW resonator oscillator offers some advantages over the SAW delay line oscillator for its higher stability. In the incipient stage of fabricating gas sensors based upon SAW resonator, taking detection of organic vapor as an example, the analysis method that combines the SAW theory with organic film technology has been adopted to give an intensive insight into the responses of two-port SAW resonator coated with LB-film and cast-film after exposure to organic vapors.     

A surface acoustic wave biosensor concept with low flow cell volumes for label-free detection

Special surface acoustic wave (SAW) devices using horizontally polarized surface shear waves can be operated in water. They allow an easy detection of molecules with biological relevance (e.g., proteins) via direct detection of the adsorbed mass. The transducer structures of conventional SAW devices are usually connected to the electronics by bond wires. In consequence, flow cell volumes can hardly be designed smaller than 50 microL. A new type of SAW device that is coupled capacitively with the electronics enables the reduction of flow cell volumes down to 60 nL, which decreases sample consumption and reduces the length of the measurement cycles down to a few minutes. To create an immunosensor, the SAW devices first are coated with a thin parylene layer for creating a sensor surface that is chemically homogeneous. Then OptoDex, a dextran containing both photoactive and functional groups is immobilized photochemically. Finally, antibodies are coupled via conventional EDC/NHS chemistry. The technique has been used to monitor urease binding at anti-urease-coated SAW devices in real time and with good resolution. Because of the simple sensor handling and the economical sample use, the new SAW device is particularly suitable for the design of an array.     

Chemical sensor based on surface acoustic wave resonator using Langmuir-Blodgett film

A one-port surface acoustic wave (SAW) resonators incorporating Langmuir-Blodgett (LB) films has been investigated. SAW sensors are one potential applications of SAW devices. Most of the work reported on SAW sensor concerns delay lines. In this paper we characterize the mass loading effects of one-port resonators by depositing successive monolayers of LB films onto the surface. A 90 MHz SAW gas-phase sensor has been fabricated on an ST cut quartz substrate, and one-port resonator configurations have been used as the sensing element. Ultra thin monolayers of arachidic acid and arachidic acid ethyl ester have been deposited using the LB method. The resonant frequencies and the Q values have been measured as sensor response. Experimental results show that the Q values and the resonant frequencies of the one-port SAW resonator vary with film mass loading on the SAW device surface.