Germanium resistors for RF MEMS based microsystems

This paper introduces the use of germanium as resistive material in RF MicroElectroMechanical (MEMS) devices. Integrated resistors are indeed highly required into RF MEMS components, in order to prevent any RF signal leakage in the bias lines and also to be compatible with ICs. Germanium material presents strong advantages compared to others. It is widely used in microtechnologies, notably as an important semi-conductor in SiGe transistors as well as sacrificial or structural layers and also mask layer in various processes (Si micromachining especially). But it also presents a very high resistivity value. This property is particularly interesting in the elaboration of integrated resistors for RF components, as it assures miniaturized resistors in total agreement with electromagnetic requirements. Its compatibility as resistive material in MEMS has been carried out. Its integration in an entire MEMS process has been fruitfully achieved and led to the successful demonstration and validation of integrated Ge resistors into serial RF MEMS variable capacitors or switches, without any RF perturbations.     

RF MEMS,BST, and GaAs varactor system‐level response in complex modulation systems

This article presents the response of RF microelectromechanical systems (RF MEMS), barium strontium titanate (BST), and gallium arsenide (GaAs)‐based tunable filters and reconfigurable matching networks to a wideband code‐division‐multiple‐access signal centered at 1.95 GHz. The RF MEMS tunable filter and impedance tuner result in very low intermodulation distortion and spectral regrowth compared to their BST and GaAs counterparts. The linearity of the BST and GaAs tunable networks improves considerably by using a series combination of BST and GaAs varactors, but the RF MEMS‐based networks still show the best linearity of all three technologies. Also, it is shown that the reconfigurable networks, tuned with capacitive RF MEMS can handle up to 1 W of RF power with no self‐actuation. © 2007 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2008.     

Accurate Simulation of RF MEMS VCO performance including phase noise

A new coupled circuit and electrostatic/mechanical simulator (COSMO) is presented for the design of low phase noise radio frequency (RF) microelectromechanical systems (MEMS) voltage-controlled oscillators (VCOs). The numerical solution of device level equations is used to accurately compute the capacitance of a MEMS capacitor. This coupled with a circuit simulator facilitates the simulation of circuits incorporating MEMS capacitors. In addition, the noise from the MEMS capacitor is combined with a nonlinear circuit-level noise analysis to determine the phase noise of RF MEMS VCO. Simulations of two different MEMS VCO architectures show good agreement with experimentally observed behavior.     

Chip-level integration of RF MEMS on-chip inductors using UV-LIGA technique

This paper presents a chip-level integration of radio-frequency (RF) microelectromechanical systems (MEMS) air-suspended circular spiral on-chip inductors onto MOSIS RF circuit chips of LNA and VCO using a multi-layer UV-LIGA technique including SU-8 UV lithography and copper electroplating. A high frequency simulation package, HFSS, was used to determine the layout of MEMS on-chip inductors with inductance values close to the target inductance values required for the RF circuit chips within the range of 10%. All MEMS on-chip inductors were successfully fabricated using a contrast enhancement method for 50 μm air suspension without any physical deformations. High frequency measurement and modeling of the integrated inductors revealed relatively high quality factors over 10 and self-resonant frequencies more than 15 GHz for a 1.44 nH source inductor and a 3.14 nH drain inductor on low resistivity silicon substrates (0.014 Ω cm). The post-IC integration of RF MEMS on-chip inductors onto RF circuit chips at a chip scale using a multi-layer UV-LIGA technique along with high frequency measurement and modeling demonstrated in this work will open up new avenues with the wider integration feasibility of MEMS on-chip inductors in RF applications for cost-effective prototype applications in small laboratories and businesses.     

A Self-Aligned Fabrication Process for Capacitive Fixed-Fixed Beam RF MEMS Components

A self-aligned fabrication process for capacitive fixed-fixed beam RF microelectromechanical system (MEMS) components is disclosed. It enables the scaling of the critical dimensions and reduces the number of processing steps by 40% compared with a conventional RF MEMS fabrication process. RF MEMS varactors with beam lengths of 30 are demonstrated by using the self-aligned fabrication process, and the performance of a four-by-four RF MEMS varactor bank is discussed as well. At 20 GHz, the measured capacitance values range between 180.5 and 199.2 fF. The measured capacitance ratio is 1.15 when a driving voltage of 35 V is applied, and the measured loaded -factor ranges between 14.5 and 10.8. The measured cold-switched power handling is 200 mW.     

Skin-Effect Self-Heating in Air-Suspended RF MEMS Transmission-Line Structures

Air-suspension of transmission-line structures using microelectromechanical systems (MEMS) technology provides the effective means to suppress substrate losses for radio-frequency (RF) signals. However, heating of these lines augmented by skin effects can be a major concern for RF MEMS reliability. To understand this phenomenon, a thermal energy transport model is developed in a simple analytical form. The model accounts for skin effects that cause Joule heating to be localized near the surface of the RF transmission line. Here, the model is validated through experimental data by measuring the temperature rise in an air-suspended MEMS coplanar waveguide (CPW). For this measurement, a new experimental methodology is also developed allowing direct current (dc) electrical resistance thermometry to be adopted in an RF setup. The modeling and experimental work presented in this paper allow us to provide design rules for preventing thermal and structural failures unique to the RF operation of suspended MEMS transmission-line components. For example, increasing the thickness from 1 to 3 mum for a typical transmission line design enhances power handling from 5 to 125 W at 20 GHz, 3.3 to 80 W at 50 GHz, and 2.3 to 56 W at 100 GHz (a 25-fold increase in RF power handling)     

Design and process considerations for fabricating RF MEMS switches on printed circuit boards

Design considerations and process development for fabricating radio frequency microelectromechanical systems (RF MEMS) switches on microwave laminate printed circuit boards (PCBs) are presented in details in this work. Two key processes, high-density inductively coupled plasma chemical vapor deposition (HDICP CVD) for low-temperature silicon nitride deposition, and compressive molding planarization (COMP) have been developed for fabricating RF MEMS switches on PCB. The effects of process conditions of HDICP CVD on low-temperature nitride film are fully characterized for its use in RF MEMS switches on PCB. Not only can COMP planarize the surface of the photoresist for lithographic patterning over topologically complex surfaces, but also simultaneously create a membrane relief pattern on the surface of a MEMS structure. Several membrane-type capacitive switches have been fabricated showing excellent RF performance and dynamic responses similar to those on semiconductor substrates. This technology promises the potential of enabling further monolithic integration of switches with other RF components, such as antennas, microwave monolithic integrated circuits (MMICs), phase shifters, tunable filters, and transmission lines on the same PCBs reducing the losses due to impedance mismatching from components/system assembly and simplifies the design of the whole RF system. [1416].     

RF MEMS Sequentially Reconfigurable Sierpinski Antenna on a Flexible Organic Substrate With Novel DC-Biasing Technique

Devices and systems that use RF microelectromechanical systems (RF MEMS) switching elements typically use one switch topology. The switch is designed to meet all of the performance criteria. However, this can be limiting for highly dynamic applications that require a great deal of reconfigurability. In this paper, three sets of RF MEMS switches with different actuation voltages are used to sequentially activate and deactivate parts of a multiband Sierpinski fractal antenna. The implementation of such a concept allows for direct actuation of the electrostatic MEMS switches through the RF signal feed, therefore eliminating the need for individual switch dc bias lines. This reconfigurable antenna was fabricated on liquid crystal polymer substrate and operates at several different frequencies between 2.4 and 18 GHz while maintaining its radiation characteristics. It is the first integrated RF MEMS reconfigurable antenna on a flexible organic polymer substrate for multiband antenna applications. Simulation and measurement results are presented in this paper to validate the proposed concept.[2007-0013]     

RF MEMS在微波器件中的小型化应用

文章首先阐述了微电子机械系统(MEMS)技术的基本概念、工艺流程及发展概况;其次,介绍了RF MEMS技术在射频系统中的应用及RF MEMS器件在功耗、体积、质量、性能和成本上的优势;最后重点介绍了RF MEMS技术应用,包括RF MEMS开关、移相器、谐振器和滤波器等典型微波元器件,分析其结构特征、发展现状和相对于传统器件的性能优势,在此基础上展望RF MEMS技术应用前景。     

Schottky Barrier Contact-Based RF MEMS Switch

This paper presents the design, fabrication, and measurement results for a novel Schottky barrier contact-based radio frequency (RF) microelectromechanical systems (MEMS) switch. This Schottky barrier contact allows one not only to operate the RF MEMS switch in a traditional capacitive mode when it is reverse biased but also conduct current in a forward biased state. Forward biasing the switch recombines trapped charges, thus extending the lifetime of the switch. This paper intimately combines MEMS processing with solid-state electronics to produce a truly unique RF device.$hfill$[2008-0097]      

Design and consideration of wafer level micropackaging for distributed RF MEMS phase shifters

A novel packaging structure which is performed using wafer level micropackaging on the thin silicon substrate as the distributed RF MEMS phase shifters wafer with vertical feedthrough is presented. The influences of proposed structure on RF performances of distributed RF MEMS phase shifters are investigated using microwave studio (CST). Simulation results show that the insertion loss (S₂₁) and return loss (S₁₁) of packaged MEMS phase shifters are −0.4–1.84 dB and under −10 dB at 1–50 GHz, respectively. Especially, the phase shifts have well linear relation at the range 1–48 GHz. At the same time, this indicated that the proposed pacakaging structure for the RF MEMS phase shifter can provide the maximum amount of linear phase shift with the minimum amount of insertion loss and return loss of less than −10 dB.     

串联电容式RF MEMS开关设计与制造研究

介绍了一种串联电容式RF MEMS开关的设计与制造。所设计的串联电容式RF MEMS开关利用薄膜淀积中产生的内应力使MEMS桥膜向上发生翘曲,从而提高所设计的开关的隔离度,克服了串联电容式RF MEMS开关通常只有在1GHz以下才能获得较高隔离度的缺点。其工艺与并联电容式RF MEMS开关完全相同,解决了并联电容式RF MEMS开关不能应用于低频段(<10GHz)的问题。其插入损耗为-0.88dB@3GHz,在6GHz以上,插入损耗为-0.5dB;隔离度为-33.5dB@900MHz、-24dB@3GH和-20dB@5GHz,适合于3~5GHz频段的应用。     

悬臂梁接触式RF MEMS开关的关键工艺研究

采用厚度为2μm的Au制作成共平面波导（CPW）、聚酰亚胺作为牺牲层、PECVD法淀积Si3N4薄膜作为悬臂梁,制作成悬臂梁接触式RF MEMS开关。着重对开关的关键工艺-CPV的Au剥离工艺和悬臂梁制作工艺进行研究,讨论了工艺中存在的问题及其解决方法。通过实验获得较佳的工艺参数,并制作出驱动电压为12-20V的悬臂梁接触式RF MEMS开关。     

A low loss and power efficient micro-electro-thermally actuated RF MEMS switch for low power and low loss applications

Microsystem Technologies - A novel laterally and micro-electro-thermally actuated RF MEMS switch is presented in this paper. Despite many RF MEMS switches requiring continuous actuation voltage to...     

Layered axial force coupled membrane based metal contact single-pole quad-throw RF MEMS switch: design,RF performance and mechanical modeling

Microsystem Technologies - RF MEMS is a perfect candidate to replace the conventional switches used for microwave frequency. Most of the RF MEMS switches developed generally concentrate on...     

A W‐band RF‐MEMS switched LNA in a 70 nm mHEMT process

This work presents a monolithic integrated reconfigurable active circuit consisting of a W‐band RF micro‐electro‐mechanical‐systems (MEMS) Dicke switch network and a wideband low‐noise amplifier (LNA) realized in a 70 nm gallium arsenide (GaAs) metamorphic high electron mobility transistor process technology. The RF‐MEMS LNA has a measured gain of 10.2–15.6 dB and 1.3–8.2 dB at 79–96 GHz when the Dicke switch is switched ON and OFF, respectively. Compared with the three‐stage LNA used in this design the measured in‐band noise figure (NF) of MEMS switched LNA is minimum 1.6 dB higher. To the authors’ knowledge, the experimental results represent a first time demonstration of a W‐band MEMS switched LNA monolithic microwave integrated circuit (MMIC) in a GaAs foundry process with a minimum NF of 5 dB. The proposed novel integration of such MEMS switched MMICs can enable more cost‐effective ways to realize high‐performance single‐chip mm‐wave reconfigurable radiometer front‐ends for space and security applications, for example. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:639–646, 2015.     

A novel DMTL capacitive switch with electrostatic actuation MAM capacitors

A novel DMTL capacitive switch with electrostatic actuation metal–air–metal (MAM) capacitors is presented. The top board of MAM capacitors will be pulled down together with the switch bridge. It has higher isolation in down-state than DMTL capacitive switch and has lower insert loss and higher self-actuation RF power comparing with MEMS shunt capacitive switch. Two of the novel DMTL capacitive switches are designed for high isolation and high self-actuation RF power, respectively. The calculated result shows that both of the two novel switches have lower insert loss than the MEMS shunt capacitive switch. The self-actuation RF power of them are 4 and 2.4 times that of MEMS shunt capacitive switch, respectively, at the cost of ?6.23 and ?3.54?dB reduction in isolation (30?GHz).     

介质层充电对电容式RF MEMS 开关的影响

电容式RF MEMS开关介质层电荷累积被认为是导致开关失效的主要原因.基于电容式RF MEMS开关工作过程中电场强度的变化,分析讨论了累积电荷的来源,并推导出相应的计算公式.对于随机性较大的界面极化问题,根据理论计算公式,提出从工艺上减小极化现象发生的解决方案.在讨论影响介质层电荷注入各种因素及相互之间关系的基础上,建立了基于电荷累积的开关寿命预测模型.     

RF MEMS压控振荡器的研制及相位噪声特性研究

利用RF MEMS可变电容作为频率调节元件,制备了中心频率为2 GHz的MEMS VCO器件.RF MEMS可变电容采用凹型结构,其控制极板与电容极板分离,并采用表面微机械工艺制造,在2 GHz时的Q值最高约为38.462.MEMS VCO的测试结果表明,偏离2.007 GHz的载波频率100kHz处的单边带相位噪声为-107 dBc/Hz,此相位噪声性能优于他们与90年代末国外同频率器件.并与采用GaAs超突变结变容二极管的VCO器件进行了比较,说明由于集成了RF MEMS可变电容,使得在RF MEMS可变电容的机械谐振频率近端时,MEMS VCO的相位噪声特性发生了改变.     

Low temperature epoxy bonding for RF MEMS capacitive switch

Packaging is one of the most critical tasks for MEMS devices. Unlike solid state devices, MEMS structures involves moving structures which needs to be protected from outer environment ensuring free movement of the structure. In the present paper, inverted silicon cavity is used for capping the MEMS devices. However, in case of RF MEMS, silicon cavity would add parasitics and affects its electrical performance. Enclosing the MEMS structure, its mechanical response will also alter. The electrical as well as mechanical characteristics of the RF MEMS switch are analyzed using finite element method simulations. The electrical response of the fabricated switch after packaging is compared with unpackaged device.