【作者】 李侃；

【导师】 王德苗； 金浩；

【作者基本信息】 浙江大学 ， 物理电子学， 2011， 博士

【摘要】 作为一种新颖的射频MEMS器件,薄膜体声波谐振器(FBAR)近年来在无线通信领域取得了巨大的商业成功。与此同时,FBAR在微质量生物传感领域的应用,正成为下一个研究热点。与传统的质量传感器——石英晶体微天平(QCM)相比,FBAR具有谐振频率高、质量灵敏度高、体积小、可集成等优点。本论文主要从FBAR传感器的四个方面进行了研究：对双模式FBAR的理论分析与建模、压电薄膜A1N的制备、FBAR原型器件的制备与测试以及FBAR在质量传感器上的应用模型,主要取得了以下成果：1.研究了基于c轴倾斜取向压电薄膜的厚度场激励双模式FBAR的谐振机理和振动模式,并建立了双模式复合FBAR的电学阻抗解析表达式,提出了双模式复合FBAR的改进型Mason等效电路模型。研究结果表明：A1N压电薄膜的压电参数、机电耦合系数、体声波速以及振动模式等随晶体的c轴倾斜角度0增大呈周期性变化,理想FBAR中存在为纵波和剪切波双模式,当θ=0°或66.5°时,理想FBAR中仅存在纵波模式；当c轴倾斜角度0=47.6°或90°时,理想FBAR中仅存在剪切波模式；当θ为0°、34.4°时,可分别获得最大的纵波机电耦合系数和剪切波机电耦合系数。2.在反应溅射模型基础上,深入研究了择优取向A1N压电薄膜的制备技术,优化了工艺方法,实现了高速沉积择优取向A1N薄膜。通过理论分析和实验研究表明,增大系统抽速、采用磁控溅射技术减小靶面有效溅射面积等可以减弱以至消除反应溅射系统中的迟滞效应；N2浓度过高或过低时都不利于A1N择优取向生长,当N2浓度为25%时最有利于A1N薄膜的择优取向生长。论文提出并实现了消除反应溅射过程中的迟滞现象、将靶稳定控制在金属态与中毒态之间的过渡态、并实现快速沉积择优取向A1N薄膜的优化工艺方法。该方法在优化的工艺条件下,A1N(002)衍射峰半高宽为0.28°,薄膜沉积速率为2.1μm/h。同时实现了c轴倾斜取向生长A1N薄膜,倾斜角度为22°,成膜速率为1.85μm/h。这一成果已被SCI收录,具有重要应用价值。3.提出并制备了Al/W全金属膜系布拉格反射层结构,这种新颖的膜系申请了二项发明专利。使用探针台和矢量网络分析仪测得基于5层Al/W反射层的固态装备型FBAR谐振频率为2.25GHz, Q值为170,此结构具有金属薄膜之间结合力好、热应力小、器件结构简单可靠、热容量大、沉积速率快等优点。此外,还制备了基于SiO2/W布拉格反射层的固态装备型FBAR。4.制备出了硅反面刻蚀结构的FBAR原型器件,包括厚度场激励的纵波模式FBAR和侧向场激励的剪切模式FBAR。使用探针台和矢量网络分析仪测得纵波模式FBAR的谐振频率为1.03GHz, Q值达到1350；剪切模式FBAR的谐振频率为1.4GHz, Q值为370。5探讨了双模式FBAR微质量传感器,建立了这种微质量传感器模型,理论研究表明：对于均匀质量负载、在压电薄膜的不同c轴倾斜角度下、纵波和剪切模式FBAR的质量灵敏度SL(θ)、Ss(θ)分别为-1403cm2/g～-1366cm2/g、-1344cm2/g～-1309cm2/g;对于相同的质量负载,不同c轴倾斜角度的FBAR传感器的质量灵敏度与FBAR的机电耦合系数有关。建立了双模式FBAR质量传感器的有限元模型,利用ANSYS软件分别仿真分析了质量负载的沉积位置改变时纵波和剪切模式FBAR传感器的谐振特性,结果表明：当质量块位于FBAR的中心位置时,传感器的质量响应度最大,纵波和剪切FBAR传感器的质量响应度分别为-8150kHz/ng、-7500kHz/ng;当质量块距离FBAR中心位置越远时,FBAR的质量响应度越小,且剪切模式FBAR的质量响应度变化更快。更多还原

【Abstract】 As a novel type RF MEMS device, thin film bulk acoustic resonator (FBAR) has in the last two decades made tremendous advances and has already been successfully commercialized, primarily driven by filter applications for telecom industry. At the same time, the development of FBAR sensors has paved the way for a second major application of FBAR technology, and therefore is becoming the next hotspot. Compared wih the traditional mass sensor, Quartz Crystal Microbalance (QCM), FBAR sensors have the advantages of high resonant frequency, high mass sensitivity, small size, CMOS-compatibility.We mainly studied the four aspects of FBAR sensor: the theory analysis and modeling of dual-mode FBAR, preparation of AlN piezoelectric thin film, FBAR prototype device fabrication and testing, and modeling of FBAR mass sensor. The main results of this dissertation are listed as follows:1. Resonant mechanism and vibration mode of thickness excited dual-mode FBAR based on AlN with tilted c-axis orientation was researched. The electrical impedance expression and the improved Mason equivalent circuit model of dual-mode complex FBAR were presented. It was found that piezoelectric parameters, electromechanical coupling coefficient, bulk acoustic wave velocity and vibration mode of AlN films depend on the tilt angle 0. It showed that pure longitudinal modes occur at 0°nd 66.5°, pure shear modes occur at 47.6°nd 90°, and both modes occur at the other angles. The maximum electromechanical coupling coefficient of longitudinal and shear modes appear atθ=0°nd 34.4°, respectively.2. Based on the reactive sputtering modeling, fabrication process of AlN films with preferred oriented and high deposition rate was studied. Theoretical analysis and experimental results showed that increasing the system pumping speed, using magnetron sputtering technique etc. may weaken or even eliminate the hysteresis effect of reactive sputtering process; neither too high nor too small N2 concentration benefits orientation of AlN and at the N2 concentration of 25%, AlN thin film has the most favorable orientation. Finally, in the optimized process, FWHM of AlN (002) diffraction peak is 0.28°, and the deposition rate is 2.1μm/h. A reactive sputtering process for growing AlN thin films with a c-axis inclination of 22°has also been developed and the deposition rate is 1.85μm/h.3. A new Al/W all-metal Bragg reflector structure was proposed and fabricated. AlN based solidly mounted resonator (SMR) utilizing 5-layer Al/W Bragg reflector was fabricated and measured, using the probe station and vector network analyzer. The device has a resonance frequency of around 2.25GHz and a Q value of around 170. This structure has a good adhesion between metal film, small thermal stress, large heat capacity, fast deposition rate, etc and has been applied for patents. Besides, AlN based SMR using SiO2/W Bragg reflector was also fabricated.4. Back-etched FBAR prototype devices were prepared, including thickness field excited longitudinal mode FBAR and lateral field excited shear mode FBAR. The longitudinal mode FBAR has a resonance frequency of 1.03GHz and a Q value of around 1350, while the shear mode FBAR has a resonance frequency of 1.4GHz and a O value of 370.5. A dual-mode FBAR mass sensor model was established and the results showed that the mass sensitivity of longitudinal mode FBAR SL(θ) and shear mode FBAR Ss(θ) with different inclination are -1403cm2/g～-1366cm2/g and -1344 cm2/g～-1309 cm2/g, respectively. The mass sensitivity of FBAR sensor with a certain tiled angle depends on the electromechanical coupling coefficient. The finite element model of FBAR mass sensor was established. Both longitudinal and shear mode FBAR sensors’ resonance characteristics were analyzed using ANSYS software. The results showed that the sensors of both modes have the maximum mass responsibility when the mass load located at the center of FBAR; the mass response of longitudinal and shear mode FBAR are -8150kHz/ng,-7500kHz/ng respectively. The farther the mass load deposits from the center, the lower of the FBAR sensor’s response and the response changes faster in the shear mode FBAR sensor than in the longitude mode.更多还原