【作者】 张翼；

【导师】 鲍景富；

【作者基本信息】 电子科技大学 ， 电路与系统， 2020， 博士

【摘要】 近年来,在电子器件不断小型化、集成化的趋势下,微机电系统(Micro-Electro-Mechanical system,MEMS)技术以其体积小、功耗低、与集成电路工艺相兼容的优势,展现出了广阔的应用前景。RF(Radio Frequency,射频)MEMS可动器件作为可重构网络中核心器件,由于其优异的性能及在组件层面广泛的应用,成为近年来研究的热点和难点。这其中,MEMS开关因其低插损、高隔离度、极高的线性度和高功率处理能力,在整个RF系统中广泛被用于信号路由及控制(衰减、相移等)。而MEMS谐振器则在RF系统中广泛被用作频率参考及选择元件,二者作为RF MEMS可动器件的代表,对其核心电气特征参数展开研究具有十分重要的意义。对于RF MEMS开关而言,其驱动电压的高低直接影响器件的功耗水平,而高功耗是移动通信设备所无法接受的。并且高驱动电压需要为器件配置额外的变压电路,降低器件的集成兼容性,故而驱动电压对于RF MEMS开关而言至关重要。而品质因数作为谐振器的核心参数,具有高品质因数的谐振器能够改善其所构成振荡器的相位噪声性能,为其组成的滤波器提供更低的插入损耗及更好的频率选择性,对于传感器而言,品质因数越高则传感器更为灵敏。此外,由于谐振器封装过程中不可避免地引入了馈通电容,因此寄生容性馈通对于微机电谐振器而言亦是不容忽视的关键参数,并且寄生馈通也是当谐振器作为液体传感器时决定其品质因数及传输特性的关键指标。有鉴于此,本文重点研究了射频微机电开关的驱动电压以及射频微机电谐振器的品质因数和寄生馈通。本论文的主要研究工作内容有:1.对射频微机电开关驱动电压问题进行深入研究,提出了一款石墨烯复合开关梁和一款基于应力补偿机制开关梁结构,同普通单一金属材料开关梁相比,所提出复合结构开关梁可以通过有效地降低梁结构的残余应力以降低弹性系数,进而降低开关驱动电压。通过对薄膜材料进行研究,提出并制备了石墨烯夹层低应力薄膜,在此基础之上成功制备了以石墨烯夹层薄膜作为梁结构材料的低驱动电压高可靠性微机电开关。设计以氮化硅为结构层的开关梁结构,利用应力补偿原理减少开关梁所受残余应力,对射频微机电开关制备工艺进行研究,优化了开关梁牺牲层反应离子刻蚀工艺参数,给出了相应的工艺改进方案,制备了所提出的基于应力补偿机制的射频微机电开关,并对其驱动电压进行测试。2.为提高微机电谐振器品质因数这一核心参数,对TPoS(硅上压电薄膜)谐振器能量损耗机制进行了研究。提出了两款TPoS谐振器,对谐振器支撑梁结构进行改进。同未进行改进的原型谐振器相比,改进后谐振器可以有效降低锚点损耗,实现谐振器品质因数的提升。第一款TPoS谐振器通过在支撑梁部分增加反射块结构并在锚点部分采用T型梁构造对耗散能量进行反射,其中反射块结构基于布拉格反射机制,利用多层周期性排列高、低等效声阻抗材料层以反射能量,达到降低锚点损耗提升品质因数的作用。第二款TPoS谐振器基于两级隔振理论对支撑梁结构进行改进,在支撑梁上设计口字分支结构作为隔振结构,将部分由谐振体通过支撑梁耗散至锚点的声能约束在悬浮口字分支结构中,减少了谐振器的锚点损耗,进而提升了品质因数。3.针对微机电谐振器在封装过程中或用于液体传感器时引入较大寄生容性馈通的问题,对TPoS谐振器进行研究。利用工作在偶数阶侧向伸缩模态下TPoS谐振器的压电特性,设计双叉指电极结构,通过引入差分输入、输出结构使TPoS谐振器实现单器件全差分配置,以此实现TPoS谐振器的共模抑制和差模放大,最后基于这种共模和差模特性提出一款基于全差分配置的双叉指电极结构TPoS谐振器,该谐振器具有良好的共模抑制和差模放大能力。通过对该谐振器不同输入、输出配置下传输特性进行测试,验证了全差分配置下所提出谐振器对插入损耗的提升及对寄生馈通的抑制作用。综上所述,本文针对RF MEMS开关及谐振器这两款可动RF MEMS器件中的代表性器件进行了研究,分别针对各自关键性能参数,即开关的驱动电压、谐振器的品质因数及寄生馈通,提出了相应的改进方法。论文将理论与实验相结合,从理论探索、仿真分析、测试验证等多方面对所提出改进方法进行了系统的研究,从而实现了所针对性能参数的提升。更多还原

【Abstract】 With the trend of miniaturization and integration of electronic devices,micro-electro-mechanical system(MEMS)technology is showing a vast prospect for application.MEMS is featured with the advantages of small size,low power consumption and compatibility with integrated circuit technology.RF MEMS movable device is the core of reconfigurable network.It has become a hot and chanllenging research topic in recent years due to its excellent performance and wide application at the component level.With the properties of low insertion loss,high isolation,high linearity and high power processing capability,MEMS switches are widely used in signal routing and control(attenuation,phase shift,etc.)in the whole RF system.MEMS resonators are widely used as frequency reference and selection components in RF system.Therefore,both MEMS switches and MEMS resonators are considered as representatives of RF MEMS movable devices.Deep study to the core electrical characteristic parameters of the devices takes important significance in RF system.For the RF MEMS switch,driving voltage produces impact to the power efficiency.High power consumption is unacceptable for mobile communication devices.Besides,high driving voltage requires additional transformer circuit,which will reduce the device compatibility.Consequently,the driving voltage is extremely important for the RF MEMS switch.For the resonator,quality factor is the core parameter.Resonator with high quality factor can help oscillator getting better phase noise performance.Besides,it also helps filter get lower insertion loss and better frequency selectivity.In sensors,the high quality factor corresponds to the accurate sensitivity.In addition,due to the inevitable introduction of feedthrough capacitor in the process of resonator packaging,parasitic capacitive feedthrough is also a key parameter for MEMS resonators.Moreover,the parasitic feedthrough is also a key index which determins the quality factor and transmission characteristics when the resonator is used as a liquid sensor.For this reason,this dissertation focuses on the driving voltage of RF MEMS switch,the quality factor and parasitic feedthrough of RF MEMS resonator.The main contents of this dissertation are as follow:1.The driving voltage of RF MEMS switch is studied deeply.A graphene composite switch beam structure and another switch beam based on stress compensation mechanism are proposed.Compared with the ordinary single metal switch beam,proposed multi-layer composite switch beam can effectively reduce the residual stress of the beam structure to lower the elastic coefficient,resulting in the reduce on switch pull-down voltage.The switch beam structure design use silicon nitride as the structure layer.Residual stress of the switch beam is reduced by the principle of stress compensation.The fabrication process of RF MEMS switch is also studied.The reactive ion etching parameter of the switch sacrificial layer is optimized with the corresponding process optimization scheme provided.The RF MEMS switch based on the stress compensation mechanism is fabricated and driving voltage is tested.Based on the study of thin film materials,the graphene sandwich low stress thin film was proposed and fabricated.Based on the process,the low driving voltage and high reliability MEMS switch with graphene sandwich film as beam structure material is successfully fabricated.2.In order to improve the quality factor of MEMS resonator,the energy loss mechanism of TPoS(Thin-film Piezoelectric-on-Silicon)resonator has been researched.Two TPoS resonators are proposed.By improving the supporting beam structure of the resonator,proposed resonator effectively reduces the anchor loss and improves the quality factor of the resonator,comparing with the original resonator without improving the supporting beam.The first TPoS resonator reflectes the dissipative energy by adding reflection block structure in the supporting beam and adopting T-shaped beam structure on the anchor part of the supporting beam.Based on Bragg reflection mechanism,the reflection block structure has utilized multi-layer periodic arrangement of high and low effective acoustic impedance material layers to reflect energy,achieving the goal of reducing the anchor loss and improving the quality factor.The second TPoS resonator is designed to improve the support beam structure based on the two-stage vibration isolation theory.The suspension frame structure is designed on the support beam as the vibration isolation structure.Part of the acoustic energy dissipated from the resonant body to the anchor part through the support beam can be constrained within the suspension frame structure,which reduces the anchor loss of the resonator and improves the quality factor.3.In order to solve the problem of large parasitic capacitive feedthrough in the process of packaging of MEMS resonators or in liquid sensor applications,this dissertation has studied the suppression of parasitic feedthrough in TPoS resonators.Based on the piezoelectric characteristics of TPoS resonator working in even order width extensional mode,a dual interdigital electrodes structure is designed.By introducing differential input and output structure,TPoS resonator can realize the fully-differential configuration by single device to realize the common mode suppression and differential mode amplification of TPoS resonator.Based on this common mode and differential mode,a TPoS resonator with double interdigital electrode structure based on fully-differential configuration is proposed.This resonator possesses good common mode suppression and differential mode amplification.After test in transmission characteristics of the resonator in different input and output configurations,experimental results show that insertion loss has been improved,and parasitic feedthrough has been suppressed in fully differential configuration.To sum up,this dissertation has studied the RF MEMS switches and resonators,which are representative devices of the movable RF MEMS equipment.Corresponding improvement methods are proposed according to the key performance parameters,that is,the driving voltage of the switch,quality factor and the parasitic capacitive feedthrough of the resonator.The theory and experiment are taken into combination in this dissertation.The improved methods are systematically studied from theoretical exploration,simulation analysis,test verification and other aspects to achieve the improvement of performance parameters.更多还原