Ku-波段MEMS单刀双掷开关的设计与模拟

利用Ku-波段MEMS单刀单掷膜开关和成熟的微带线技术设计了一种Ku-波段MEMS单刀双掷膜开关.模拟结果为阈值电压19V左右,工作于Ku-波段(8～12)GHz,在中心频率15GHz处,导通开关的插入损耗为-0.15dB,截止开关的隔离度为-33dB,开关的回波损耗为-27dB.     

用于制备高机械可靠性RF MEMS开关的新型工艺

对介质桥串联接触式RF MEMS开关的制备工艺进行了研究.介绍了开关的结构,说明了采用常规制备工艺容易在桥膜上形成应力集中,严重影响开关的机械可靠性.通过改进工艺,提出了一种侧向钻蚀刻蚀介质桥膜下金属的方法,获得了平坦的介质桥膜.最后,给出了完整的开关制备流程.与常规工艺相比,新工艺避免了应力集中问题,提高了开关的机械可靠性,成品率从10%提高到了95%,工作寿命从1 000次提高到了2.5×107次.此外,在23.3 V的驱动电压下,开关插入损耗＜0.55 dB＠DC-10 GHz,隔离度＞53.2 dB＠DC-10 GHz.结果表明该工艺可满足无线通讯对MEMS开关成品率、寿命和微波性能的要求.     

低驱动电压两端固定"桥"式RF MEMS开关的研制

文中介绍了一低驱动电压接触式RF-MEMS开关,开关采取了两端固定的"桥式"结构,在桥与支撑点间采用折叠弯曲的铰链结构,而且紧靠中央信号线的旁边各有一个较大面积的电极,这些措施降低了开关的驱动电压.整个工艺采用表面微加工工艺.由实验测试可知:开关驱动电压11 V左右,与ANSYS模拟的值12 V基本一致,开关的S参数,在的范围内,插入损耗要小于-1 dB,在频段(≤5 GHz),开关的隔离度要优于-30 dB,在频段5～10 GHz,隔离度也要高于-20 dB.     

一种用于高机械可靠性RF MEMS开关制备的新型工艺

为提高介质桥串联接触式MEMS开关的工作寿命,本文改进了常规制备工艺,提出一种侧向钻蚀刻蚀介质桥膜下金属的方法,以获得平坦的介质桥膜,制备得到高机械可靠性的开关。与常规工艺相比,新工艺避免了应力集中问题,成品率从10％提高到了95％,工作寿命从1000次提高到了2500万次。在23.3V的驱动电压下,开关插入损耗 0.55dB＠DC-10GHz,隔离度 53.2dB＠DC-10GHz。     

Ku波段MEMS微波功率耦合器设计

针对现有的微波功率测量都基于热电偶和二极管等终端器件,功率信号在被检测后无法利用的问题,设计了一个基于微机电(MEMS)射频(RF)并联开关在Ku波段(12.4~18 GHz)应用的微波功率耦合器,包括等效电路、共面波导(CPW)匹配的设计和结构仿真。该耦合器是MEMS微波功率传感器的核心,它利用MEMS膜桥耦合CPW上的微波功率信号,大部分功率信号被检测后都能传至下级电路做进一步处理。为了减小反射损耗和获得宽频带响应,提出了两种优化方法,即凹槽调谐结构设计和补偿电容设计,经过优化设计后的Ku波段MEMS微波功率耦合器的回波损耗(S₁₁)和插入损耗(S₂₁)在中心频率15.2 GHz处分别达到了-42.90 dB和-0.15 dB,显示出耦合器的高隔离度和低损耗。同时在Ku波段,上述参数同中心频率点处的偏差分别为±6.41 dB和±0.04 dB,显示出其宽带特性。     

基于RF MEMS开关的4位分布式移相器的设计

RF MEMS移相器与传统移相器相比,具有低损耗、频带宽、微型化,同时与IC、MMIC电路易于集成等特点,文中设计一种Ka波段DMTL型RF MEMS移相器,采用了15个MEMS电容式并联开关,同时在MEMS开关中加入MIM电容,实现了4位相移。文中对Ka波段4位RF MEMS移相器进行设计与分析,通过MEMS开关的切换实现信号延迟通路,0~180°步进22.5°的相移功能。通过改变驱动电压从而调整MEMS桥的高度,仿真测得开关理论下压电压为18.9 V。仿真结果表明在中心频率31 GHz时,其插入损耗大于-2.2 d B,回波损耗小于-25 d B,相移误差在1.5°范围内,移相器具有较好的移相性能。     

Ku波段交直流分离的MEMS开关的模拟与设计

介绍了一种带直流驱动电极交直流分离的MEMS开关,研究了影响开关阈值电压的因素,运用缩腰设计、尺寸优化等方法降低开关的阈值电压,并将这种平膜开关与其他几种结构的膜开关进行比较.使用Coventor和HFSS软件模拟,设计的开关阈值电压小于20V,在Ku波段插入损耗低于0.1dB,反射损耗低于-25dB,谐振点隔离度高于40dB.     

基于共面波导的RF MEMS可调带阻滤波器

文中介绍了一种新型的RF MEMS可调帯阻滤波器。该滤波器是通过在共面波导地结构上刻蚀出缺陷地结构,形成基本谐振单元;再通过加入RF MEMS开关,实现可调滤波器。分析了滤波器的结构参数和RF MEMS开关与竖向槽的关系。可调帯阻滤波器制作在高阻硅(εr=11.9)基板上,厚度为460μm;表面金属材料为铝,厚度为2μm。该滤波器实现了14~18 GHz可调,可调范围约为30%;中心频点处对应的回波损耗大于-2 d B,插入损耗小于-35 d B;10 d B带宽大于8.6 GHz。     

片上集成MEMS射频滤波器

研究采用MEMS工艺技术制造可在硅集成电路片上集成的射频滤波器.MEMS工艺技术实现了高性能嵌入式螺管电感和金属-绝缘层-金属电容元件的集成制造.整个微加工制造工艺为低温工艺,可与CMOS集成电路工艺实现后端集成.基于此工艺,设计和实现了应用于5 GHz射频频段的微小化的片上集成滤波器,包括一种低通滤波器和一种带通滤波器.测试结果表明,5阶低通滤波器的 -1.5 dB 转折频率在5.3 GHz频率,从直流到5 GHz频率的插入损耗小于1.06 dB.实现的带通滤波器为两阶谐振耦合式,在中心频段5.3 GHz的最小插入损耗为4.3 dB,通带内的回波损耗大于13 dB.研究结果表明:该微加工技术适用于无源器件和滤波器电路的CMOS后端集成,适合高性能射频片上系统的应用.     

并联电容式RF MEMS开关的系统级设计与分析

针对传统设计方法分析RF MEMS开关的周期比较长的缺点,提出了一种基于静电控制的低压并联MEMS开关的系统级设计分析方法,实现了并联电容式RF MEMS开关的快速设计与优化分析。该方法采用Coventorware软件ARCHITECT模块搭建并联电容式RF MEMS开关系统级模型,分析了多物理耦合场下并联电容式RF MEMS开关的动态响应特性,得到位移和电压大小的对应关系曲线。仿真结果表明:系统级分析便于在不同层面上分析和解决问题,结合MEMS器件还可以做相关工艺设计版图分析,便于多次调整参数分析。     

Fundamental studies of Au contacts in MEMS RF switches

Microelectromechanical systems (MEMS) radio frequency (RF) switches hold great promise in a myriad of commercial, aerospace, and military applications. However, there is little understanding of the factors determining the performance and reliability of these devices. Fundamental studies of hot-switched gold (Au) contacts were conducted using a micro/nanoadhesion apparatus as a switch simulator. Experiments were conducted in a well defined air environment under precisely controlled operating conditions. Fundamental properties were connected to performance with an emphasis on the effects of contact force and electric current on contact resistance (R), microadhesion, and reliability/durability. Electric current had the most profound effect on switch performance. Observations at low current (1–10 A) include: (1) slightly higher R; (2) asperity creep; (3) high adhesion after rapid switching; (4) switch bouncing; and (5) reasonable durability. Conversely, observations at high current (1–10 mA) include: (1) slightly lower R; (2) melting; (3) no measurable adhesion; (4) less propensity for switch bouncing; (5) necking of contacts; and (6) poor reliability and durability due to switch shorting. Low current behavior was dominated by the propensity to form smooth surface contacts by hammering, which led to high van der Waals force. High current behavior was dominated by the formation of Au nanowires that bridge the contact during separation. Data suggest the presence of an adventitious film containing carbon and oxygen. Aging of the contacts in air was found to reduce adhesion.     

高 g值冲击下 MEMS器件可靠性研究

以基于SOI的MEMS开关器件为研究对象,建立了以SOI器件为基本结构的有限元分析模型,此次实验采取的是在SOI层上镀上一层Au,以便进行电路连接,并加载500～5000 g的惯性力进行有限元分析。经ANSYS有限元的分析,在500 g高惯性力的作用下,最容易产生金属层的脱落现象,造成MEMS器件的失效。通过这种方式对不同结构的MEMS开关器件进行有限元分析,限制其阀值加速度,减少由于惯性跌落试验而造成的实物破坏。     

基于可靠度仿真的MEMS加速度开关结构优化

基于MEMS加速度开关的结构与作用原理,利用ANSYS对悬臂梁进行有限元分析,获得在冲击载荷作用下悬臂梁的受力情况以及位移的大小; 采用蒙特卡罗方法产生伪随机数,模拟不同样本变量的随机分布情况,以解决试验样本不足的问题,对MEMS加速度开关的可靠度进行了分析计算; 采取改进结构以优化设计,降低开关的潜在危险和失效概率,提升可靠度。     

基于MEMS工艺的半导体电阻式气敏元件的研究

介绍了半导体电阻式气敏元件工作原理,设计了一种基于MEMS工艺的薄膜气敏元件结构,此结构以Si3N4/SiO2/Si3N4复合薄膜作为支撑隔热层,蜿蜒状多晶硅作为加热层,梳状Ag电极作为气敏薄膜信号电极,SiO2作为加热层与Ag电极的绝缘层,并在SiO2绝缘层上刻蚀通孔形成加热层与金属互连。该结构具有通用性,对不同气敏特性的材料均适用,且易于改进为组合结构或阵列结构。最后,对其工艺进行了阐述。     

Failure Mechanisms of Capacitive MEMS RF Switch Contacts

Microelectromechanical systems (MEMS) radio frequency (RF) switches hold great promise in a myriad of commercial, aerospace, and military applications. In particular, capacitive type switches with metal-to-dielectric contacts (typically Au- on-silicon nitride) are suitable for high frequency (≥10 GHz) applications. However, there is little fundamental understanding of the factors determining the performance and reliability of these devices. To address this void in understanding, we conducted fundamental studies of Au-on-Si₃N₄ contacts at various bias voltages using a micro/nanoadhesion apparatus as a switch simulator. The experiments were conducted in air at 45% relative humidity. The switch simulator allows us to measure fundamental parameters such as contact force and adhesion, which cannot be directly measured with actual MEMS switches. Adhesion was found to be the primary failure mechanism. Both a mechanical and electrical effect contributed to high adhesion. The mechanical effect is adhesion growth with cycling due to surface smoothening, which allows increased van der Waals interaction. The electrical effect on adhesion is due to electrostatic force associated with excess charge trapped in the dielectric, and was only observed at 40 V bias and above. The two effects are additive, but the electrical effect was not present until surfaces were worn smooth by cycling. Surface smoothening increases the electric field in the dielectric, which leads to trapped charge and higher adhesion. Excessive adhesion can explain decreased lifetime at high bias voltage previously reported with actual capacitive MEMS switches. Aging of open contacts in air was found to reduce adhesion. Surface analysis data show the presence and growth (in air) of an adventitious film containing carbon and oxygen. The adventitious film is responsible for aging related adhesion reduction by increasing surface separation and/or reducing surface energy. No junction growth and force relaxation with time were observed in capacitive switch contacts, as was previously observed with Au–Au contacts at low current in direct current MEMS switches.     

基于氧化锌纳米线的硅谐振式加速度计

设计制作了一种基于氧化锌纳米线的谐振式硅加速度计,该加速度计的敏感单元为由氧化锌纳米线横跨金属微电极组成的谐振器。采用介电电泳的方法组装了氧化锌纳米线,并利用FIB沉积Pt将氧化锌纳米线固定在微结构上以确保结构的可靠性。在加速度的作用下,质量块引起的惯性力通过支撑梁对纳米线施加应力,因此,在谐振条件下,纳米线谐振频率的变化反映了加速度的大小。谐振式加速度计的准数字输出能解决多数MEMS器件输出微弱信号检测难的问题。实验结果表明,加速度计的灵敏度随着纳米线的厚度的减小而急剧增加,选择500 nm厚度的纳米线作为理论分析,加速度计的灵敏度可达2.5 kHz/g以上。     

微机械光开关的应用及控制

本文以MEMS光开关为研究对象,详细介绍了MEMS的工作原理及其特点,并结合开发经验介绍用AT89C8252单片机、PLD和光传感器制成的光开关及与计算机之间的通信.     

基于阿基米德螺旋线的低g值微惯性开关

低g值惯性开关是一种对线加速度敏感并在施加的加速度作用下完成闭合的惯性装置。由于微小尺寸的限制,低g值(1-30 g)惯性开关只能设计为微质量块和低刚度支撑梁的结构。为了获得低刚度,设计了基于阿基米德螺旋线的平面螺旋梁结构。微开关由一个带触点的基座、一个惯性敏感单元以及框架和封盖组成。惯性敏感单元则由一个居中的质量块和支撑它的螺旋梁组成。在加速度作用下可动的质量块发生位移,与其下的触点接触,实现开关的闭合。惯性敏感单元采用有限元软件ANSYS进行分析,采用UV-LIGA工艺制作。进行了离心试验以获得低g值惯性开关的闭合门限。经3次测试,闭合门限值分别为21.22,21.39和21.20g,平均值为21.27g。测试结果表明,低g值惯性开关具有0.5g的闭合精度,多次测试重复性较好。     

The electrostatic-alloy bonding technique used in MEMS

Electrostatic-alloy bonding of silicon wafer with glass deposited by Au to form Si/Au-glass water, and bonding of Si/Au-glass with silicon wafer were researched during fabrication of pressure sensors. The silicon wafer and glass wafer with an Au film resistor were bonded by electrostatic bonding, and then Si-Au alloy bonding was formed by annealing at 400°C for 2 h. The air sealability of the cavity after bonding was finally tested using the N₂ filling method. The results indicate that large bond strength was obtained at the bonding interface. This process was used in fabricating a pressure sensor with a sandwich structure. The results indicate that the sensor presented better performances and that the bonding techniques can be used in MEMS packaging. __________ Translated from Journal of Harbin Institute of Technology, 2005, 37(1) (in Chinese)     

基于单片式微波集成电路的终端式MEMS微波功率传感器(英文)

提出了一种基于塞贝克效应的终端式MEMS微波功率传感器,该传感器的制作工艺与GaAs单片式微波集成电路(MMIC)工艺兼容.利用热电偶检测温度差,生成与微波功率成比例的直流电压,由GaAs/Au热电偶串联构成热堆.传感器将电功率转化为热,再间接测量热堆生成的直流电压.采用微机械加工技术,去除了器件底部的GaAs衬底,从而减小了热损耗和电磁损耗,提高了灵敏度.测试结果表明,在0～20 GHz内,HFSS模拟的S11＜-22 dB;测试输入功率为-20～20 dBm时,频率为0～20 GHz;在20 GHz时,灵敏度高于0.15 mV/mW;在整个频率范围内,回波损耗低于-26 dB.