薄膜体声波谐振器的力敏特性研究（英文）

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。     

微机械谐振式加速度计的研究现状及发展趋势

微机械谐振式加速度计(MMRA)是通过检测加速度施加前后谐振器谐振频率变化实现对加速度检测的。该传感器具有频率信号输出、稳定性好、灵敏度高、精度高等优点,己成为MEMS传感器的重要发展方向之一。详细讨论了微机械谐振式加速度计设计中的关键技术,难点及对应解决方案、发展趋势。其中,关键技术包括机械结构、激励与检测方式以及谐振器刚度改变方式。分析了谐振器的三种机械结构以及微杠杆工艺误差造成的不对称性;根据谐振器材料的压电特性,可将MMRA分为压电MMRA和非压电MMRA,压电MMRA的激励与检测方式都是压电激励/压电检测,非压电MMRA主要为静电激励/电容检测;讨论了轴向应力和静电刚度这两种谐振器刚度改变方式的原理和适用范围。微机械谐振式加速度计主要存在四个技术难点:机械耦合、温度特性、工艺误差、组装与封装,并针对这四点给出了相应的解决方案。集成,静电刚度,新材料,多轴以及更高的性能指标将是今后微机械谐振式加速度计的主要发展趋势。     

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。     

具有二氧化硅温度补偿层的薄膜体声波谐振器的建模与分析（英）

薄膜体声波谐振器(FBAR)的谐振频率会受到外界环境温度的影响而产生漂移,对于FBAR滤波器而言,这种温度-频率漂移特性会导致其中心频率、插入损耗、带内纹波等性能发生变化,降低其在电学应用中的可靠性。应用ANSYS有限元分析软件,对一个典型Mo-AlN-Mo三层结构的FBAR进行了温度-频率漂移特性的仿真,得到其在［－50 ℃, 150 ℃］温度范围内的频率温度系数(TCF)约为－3510－6/℃。在FBAR叠层薄膜结构中添加了一层具有正温度系数的二氧化硅温度补偿层,分析了该补偿层厚度对FBAR的温度-频率漂移特性、谐振频率和机电耦合特性的影响。设计了具有一层二氧化硅温度补偿层的FBAR叠层,由Mo/AlN/SiO2/Mo多层薄膜构成,仿真得到其频率温度系数为0.87210－6/℃;与没有温度补偿层的FBAR相比,温度稳定性得以显著改善。关键词: Abstract: Key words:     

体声波力传感器灵敏度的微分-综合分析法

为了分析基于应力/应变效应的体声波(BAW)力传感器的敏感机理、准确计算其灵敏度,提出了一种用于BAW力传感器灵敏度分析的微分-综合分析法。该方法借鉴了微积分的原理,在Mason等效电路模型中将一个完整的BAW谐振器替换为多个谐振器微元的并联,从而将谐振器有源区面积A上应力/应变场的有限元计算结果与压电薄膜材料的力学特性、谐振器微元的电声学特性关联起来;最后,在射频电路仿真软件中进行等效电路的综合,得到整个BAW谐振器在应力/应变场作用下的阻抗特性曲线及其串/并联谐振频率。当BAW谐振器微元的划分足够细密时,获得的灵敏度分析结果将足够精确。为了论证该方法的原理,给出了一个直观的校核案例。以一个嵌入式FBAR结构的四梁BAW加速度计表头为例,介绍了该方法用于BAW力传感器灵敏度分析的详细过程。虽然案例中只讨论了一种应力/应变型BAW力传感器的单一力敏机理,但该方法具有普适性。并且,当谐振器微元小到接近其压电材料晶格的尺度时,就能与压电薄膜的力-声-电特性的第一性原理计算结果关联起来,实现从微观材料特性到介观器件物理的多尺度计算。     

体声波力传感器灵敏度的微分-综合分析法

为了分析基于应力/应变效应的体声波(BAW)力传感器的敏感机理、准确计算其灵敏度,提出了一种用于BAW力传感器灵敏度分析的微分-综合分析法。该方法借鉴了微积分的原理,在Mason等效电路模型中将一个完整的BAW谐振器替换为多个谐振器微元的并联,从而将谐振器有源区面积A上应力/应变场的有限元计算结果与压电薄膜材料的力学特性、谐振器微元的电声学特性关联起来;最后,在射频电路仿真软件中进行等效电路的综合,得到整个BAW谐振器在应力/应变场作用下的阻抗特性曲线及其串/并联谐振频率。当BAW谐振器微元的划分足够细密时,获得的灵敏度分析结果将足够精确。为了论证该方法的原理,给出了一个直观的校核案例。以一个嵌入式FBAR结构的四梁BAW加速度计表头为例,介绍了该方法用于BAW力传感器灵敏度分析的详细过程。虽然案例中只讨论了一种应力/应变型BAW力传感器的单一力敏机理,但该方法具有普适性。并且,当谐振器微元小到接近其压电材料晶格的尺度时,就能与压电薄膜的力-声-电特性的第一性原理计算结果关联起来,实现从微观材料特性到介观器件物理的多尺度计算。     

具有二氧化硅温度补偿层的薄膜体声波谐振器的建模与分析(英文)

薄膜体声波谐振器(FBAR)的谐振频率会受到外界环境温度的影响而产生漂移,对于FBAR滤波器而言,这种温度-频率漂移特性会导致其中心频率、插入损耗、带内纹波等性能发生变化,降低其在电学应用中的可靠性。应用ANSYS有限元分析软件,对一个典型Mo-AlN-Mo三层结构的FBAR进行了温度-频率漂移特性的仿真,得到其在[-50℃,150℃]温度范围内的频率温度系数(TCF)约为-35×10-6/℃。在FBAR叠层薄膜结构中添加了一层具有正温度系数的二氧化硅温度补偿层,分析了该补偿层厚度对FBAR的温度-频率漂移特性、谐振频率和机电耦合特性的影响。设计了具有一层二氧化硅温度补偿层的FBAR叠层,由Mo/AlN/SiO2/Mo多层薄膜构成,仿真得到其频率温度系数为0.872×10-6/℃;与没有温度补偿层的FBAR相比,温度稳定性得以显著改善。     

ZnO薄膜硅微压电矢量水听器

提出了一种基于ZnO压电薄膜的硅微压电矢量水听器,其核心部件是利用微电子机械系统(MEMS)技术制作的悬臂梁结构压电加速度计。由近似解析和有限元分析,得出加速度计的灵敏度和谐振频率,并在此基础上对其进行了优化设计。研制了MEMS压电加速度计,并装配后构成MEMS矢量水听器。测试结果表明:加速度灵敏度在20~1,200 Hz范围内约为0.83 mV/(m/s2)。经过液柱法测量,在1 kHz时,MEMS矢量水听器等效声压灵敏度为-229.5 dB (ref.1V/μPa),比同类型压阻式MEMS矢量水听器的灵敏度高17 dB以上。      

用于矢量水听器的低频高灵敏度层合梁加速度传感器

压电加速度传感器是同振型矢量水听器的核心部件。为了满足低频高灵敏度矢量水听器的应用需求,提出并研究一种具有层合梁结构的低频高灵敏度加速度传感器。结合弹性力学和压电方程推导层合梁加速度传感器的加速度灵敏度解析解表达式,通过有限元仿真对层合梁加速度传感器尺寸进行优化,给出优化后的尺寸范围。从优化的尺寸范围中选取两种不同尺寸进行加速度传感器振动特性的仿真分析及实物制作(其中压电材料为PZT-5)与性能测试。仿真与测试结果均表明,相比已有的同尺寸金属梁加速度传感器,层合梁加速度传感器可以有效降低谐振频率并提升加速度灵敏度。当压电层厚度为0.5 mm时,加速度灵敏度最大提升3.9 dB,谐振频率下降23%。测试结果与理论分析相符。      

碳纳米管/聚二甲基硅氧烷复合薄膜的制备及力敏特性研究

针对传感器的敏感单元发展需求,提出了一种碳纳米管复合材料.该材料是以碳纳米管作为填充粒子,结合聚二甲基硅氧烷(PDMS)有机基体,采用超声共混方法制备的一种新型传感器敏感元件.详细分析研究了复合材料的制备工艺参数,以及在不同工艺参数下该复合材料的力敏特性.扫描电镜测试表明碳纳米管在PDMS中分散均匀且镶嵌良好.通过对不同体积分数的碳纳米管与PDMS复合材料进行电学性能测试,研究薄膜的"力-电阻"和"力-电容"耦合性能,测试了薄膜结构的力敏效应.计算得到复合薄膜材料的压阻灵敏度因子达到40,压电容灵敏度因子达到70.实验研究表明,通过改变碳纳米管与PDMS的比例,可以很好地调节其电子输运特性以及电阻和电容的应力敏感特性,可以为该类型的力敏材料在不同的力敏传感技术领域提供新的研究思路.     

Fabrication of piezoelectric AlN thin film for FBARs

This paper focuses on the fabrication of film bulk acoustic-wave resonator (FBAR) comprising an aluminum nitride (AlN) piezoelectric thin film sandwiched between two metal electrodes and located on a silicon substrate with a low-stress silicon nitride (Si₃N₄) support membrane for high frequency wireless applications, and analyzes the optimization of the thin AlN film deposition parameters on Mo electrodes using the reactive RF magnetron sputter system. Several critical parameters of the sputtering process such as RF power and Ar/N₂ flow rate ratio were studied to clarify their effects on different electrodes characteristics of the AlN films. The experiment indicated that the process for Mo electrode was easier compared with that of the Pt/Ti or Au/Cr bi-layer electrode as it entailed only one photo resist and metal deposition step. Besides, Pt/Ti or Au/Cr electrodes reduced the resonance frequency due to their high mass density and low bulk acoustic velocity. Compared with the case of the Al bottom electrode, there is no evident amorphous layer between the Mo bottom electrode and the deposited AlN film. The characteristics of the FBAR devices depend not only upon the thickness and quality of the AlN film, but also upon the thickness of the top electrode and the materials used. The results indicate that decreasing the thickness of either the AlN film or the top electrode increases the resonance frequency. This suggests the potential of tuning the performance of the FBAR device by carefully controlling AlN film thickness. Besides, increasing either the thickness of the AlN film or higher RF power has improved a stronger c-axis orientation and tended to promote a narrower rocking curve full-width at half-maximum (FWHM), but increased both the grain size and the surface roughness. An FBAR device fabricated under optimal AlN deposition parameters has demonstrated the effective electromechanical coupling coefficient (k _eff²) and the quality factor (Q _{f x} ) are about 1.5% and 332, respectively.     

Two-step sputtered ZnO piezoelectric films for film bulk acoustic resonators

This study investigates high-performance ZnO piezoelectric films used for thin film bulk acoustic resonators (TFBAR). The ZnO piezoelectric film was deposited on a Pt/Ti electrode using an RF magnetron sputter by a two-step method at room temperature. The Pt/Ti electrode was deposited by a DC sputtering system, on which, ZnO piezoelectric films were deposited in one step and in two steps to minimize roughness in the first step and produce the preferred orientation in the second. Both field-emission scanning electron microscopy (FESEM) and atom force microscopy (AFM) revealed that ZnO piezoelectric film deposited by two-step sputtering exhibited favorable characteristics, such as a rigidly precise surface structure with surface roughness of 7.37 nm, even better than in one-step sputtering. Examining the ZnO thin film by X-ray diffraction (XRD) showed a much higher c-axis-preferring orientation than in one-step sputtering. The reflection coefficient of the resonator device was measured using an HP8720 network analyzer. The frequency response of the FBAR device exhibited a return loss of -25 dB at a resonant frequency of 2212 MHz with a high coupling coefficient of 6.7%. PACS 68.55.Jk; 43.35.Ns; 81.15.-z     

基于MgxZn1−xO薄膜固体装配型体声波谐振器

本文研制了一种基于磁控溅射掺镁氧化锌(Mg_xZn_(1-x)O)压电薄膜的S波段固体装配型体声波谐振器(SMR-FBAR)。相比传统的氧化锌(ZnO)薄膜,Mg_xZn_(1-x)O具有高纵波声速,高电阻率优点,而且Mg原子以替位或填隙的方式进入晶格,没有改变ZnO的铅锌矿结构。通过优化磁控溅射参数的方法,获得了c轴方向生长良好的Mg_xZn_(1-x)O薄膜,并成功制得了串联谐振频率以及并联谐振频率分别在2.416 GHz和2.456 GHz的谐振器,测得其有效机电耦合系数为4.081%,回波损耗(S11)为-23.89 d B。这种SMR机械强度高、可靠性高、尺寸小,具有可立体集成到CMOS芯片表面的优势。     

Analysis of force-frequency effect of piezoelectric circular resonators strained by edge angular-sector stresses

Summary A theoretical analysis of force-frequency effect of two opposite loads distributed over an angular part of the crystal edge is performed in the case of a piezoelectric resonator or sensor. Stresses are determined at the centre of the crystal and the subsequent frequency shift is calculated. Applying the obtained results, the location and angular width of holders are determined for an AT-cut. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

Fabrication and analysis of ZnO thin film bulk acoustic resonators

This study employs RF magnetron sputter technique to deposit high C-axis preferred orientation ZnO thin film on silicon substrate, which is then used as the piezoelectric thin film for a thin film bulk acoustic resonator (FBAR). Electrical properties of the FBAR component were investigated by sputtering a ZnO thin film on various bottom electrode materials, as well as varying sputter power, sputter pressure, substrate temperature, argon and oxygen flow rate ratio, so that structural parameters of each layer were changed. The experimental results show that when sputter power is 200 W, sputter pressure is 10 mTorr, substrate temperature is 300 °C, and argon to oxygen ratio is 4:6, the ZnO thin film has high C-axis preferred orientation. The FBAR component made in this experiment show that different bottom electrode materials have great impact on components. In the experiment, the Pt bottom electrode resonant frequency was clearly lower than the Mo bottom electrode resonant frequency, because Pt has higher mass density and lower acoustic wave rate. The component resonant frequency will decrease as ZnO thin film thickness increases; when top electrode thickness is higher, its resonant frequency also drops, due to top electrode mass loading effect and increased acoustic wave path. Therefore, ZnO thin film and top/bottom electrode thickness can be fine-tuned according to the required resonant frequency.     

Biosensing of biophysical characterization by metal-aluminum nitride-metal capacitor

Aluminum nitride thin films were fabricated as stress biosensors for biosensing cell attachment. The features and capacitance of AlN films following cell culture were detected via leakage current density and biocompatibility testing. Analytical results demonstrate that the failure of the capacitors produced slit-like microvoids to form on the AlN film, following cell differentiation and proliferation. Slit-like microvoids incurred substantial current leaking of the cell cultured-capacitor, even at a low breakdown voltage. Stress variation during cell differentiation and proliferation were responsible for the formation of microvoids and the low breakdown voltage. The stress produced lattice distortion of the AlN film, resulting in a piezoelectric effect on the AlN film surface. Results of this study demonstrate that the piezoelectric AlN film is highly promising as a biosensing film.     

ZnO-based film bulk acoustic resonator devices on a specially designed Bragg reflector

In this paper, we studied ZnO-based film bulk acoustic resonator (FBAR) device fabricated on a specially designed multilayered Bragg reflector part. Very thin chromium adhesion layers (0.03 μm thick) were additionally deposited to improve the quality of the Bragg reflector and some thermal treatments were performed to improve the resonant characteristics of the FBAR device. At the operating frequency of ∼2.7 GHz, excellent resonant characteristics were observed in terms of return loss and quality factor, and effective electromechanical coupling coefficient.     

Structural and mechanical characteristics of (1 0 3) AlN thin films prepared by radio frequency magnetron sputtering

The (1 0 3)-oriented aluminum nitride (AlN) thin film is an attractive piezoelectric material for the applications in surface acoustic wave and film bulk acoustic wave resonator devices. In this work, we repot structural and mechanical characteristics of (1 0 3) AlN thin films deposited onto (1 0 0) Si substrates with radio frequency magnetron sputtering at different sputtering powers at 150, 250, and 350 W. Comparisons were made on their crystalline structures with X-ray diffraction, surface morphologies with atomic force microscopy, mechanical properties with nanoindentation, and tribological responses with nanoscratch. Results indicate that for the sputtering power of 350 W, a high-quality (1 0 3) AlN thin film, whose hardness is 18.91 ± 1.03 GPa and Young's modulus is 242.26 ± 8.92 GPa, was obtained with the most compact surface condition.