High-isolation CPW MEMS shunt switches. 2. Design

For pt.1 see ibid., vol.48, no.6, p.1045-1052 (2000). In this paper, the second of two parts, the equivalent RLC model of the shunt switch is used in the design of tuned two- and four-bridge “cross” switches from 10 to 40 GHz. The cross switch attained an insertion loss of less than 0.3-0.6 dB, a return loss below -20 dB from 22 to 38 GHz in the up state, and a down-state isolation of 45-50 dB with only 1.5 pF of down-state capacitance (C_d). Also, an X-band microelectromechanical system (MEMS) switch with an insertion loss of less than 0.2 dB and an isolation of 35 dB is presented. This is done by inductively tuning the LC series resonance of the shunt switch. The MEMS bridge height is 1.5-2.5 μm, resulting in a pull-down voltage of 15-25 V. Application areas are in low-loss high-isolation communication and radar     

High-isolation CPW MEMS shunt switches. 1. Modeling

This paper, the first of two parts, presents an electromagnetic model for membrane microelectromechanical systems (MEMS) shunt switches for microwave/millimeter-wave applications. The up-state capacitance can be accurately modeled using three-dimensional static solvers, and full-wave solvers are used to predict the current distribution and inductance of the switch. The loss in the up-state position is equivalent to the coplanar waveguide line loss and is 0.01-0.02 dB at 10-30 GHz for a 2-μm-thick Au MEMS shunt switch. It is seen that the capacitance, inductance, and series resistance can be accurately extracted from DC-40 GHz S-parameter measurements. It is also shown that dramatic increase in the down-state isolation (20⁺ dB) can be achieved with the choice of the correct LC series resonant frequency of the switch. In part 2 of this paper, the equivalent capacitor-inductor-resistor model is used in the design of tuned high isolation switches at 10 and 30 GHz     

高隔离度S波段MEMS膜桥开关

常规的 MEMS膜桥开关在 1 0 GHz以上频段才具有低插损、高隔离度 (>2 0 d B)的优点。文中介绍了一种应用于微波低频段—— S波段的高隔离 MEMS膜桥开关 ,给出了开关的设计与优化方法 ,建立了开关的等效电路模型。通过双膜桥结构、选择高介电常数的介质膜、微电感结构膜桥这些措施 ,达到提高开关隔离度的目的。利用 HFSS软件仿真的结果表明 ,该开关在微波低频段 (3～ 6GHz)有着很好的隔离性能。开关样品在片测试的电性能指标 :插损 <0 .3 d B,隔离度 >40 d B,驱动电压 <2 0 V     

MEMS switches

Microelectromechanical system (MEMS) microswitches are receiving increasing attention, particularly in the RF community. Low power consumption, low insertion loss, high isolation, excellent linearity, and the ability to be integrated with other electronics all make microswitches an attractive alternative to other mechanical and solid-state switches. This article features a newly developed, surface micromachined, electrostatically actuated direct metal-to-metal microswitch which can be used in applications from dc through microwave.     

MEMS optical switches

Leveraging MEMS's inherent advantages such as the batch fabrication technique, small size, integrability, and scalability, MEMS is positioned to become the dominant technology in optical crossconnect switches. MEMS optical switches with complex movable 3D mechanical structures, micro-actuators, and micro-optics can be monolithically integrated on the same substrate by using the matured fabrication process of the integrated circuit industry. In this article we report various popular actuating mechanisms and switch architectures of MEMS optical switches. The basics of surface and bulk micromachining techniques used to fabricate MEMS devices are reviewed. Examples of 2D and 3D approaches to MEMS optical switches are described. The pros and cons of the two approaches are analyzed. In the short term, MEMS-based optical switches seem to have captivated the attention of both the industry and academia. However, there are challenges that threaten the long-term survival of this technology. The problems that remain to be fully addressed are discussed     

发展中的RF MEMS开关技术

射频MEMS开关是用MEMS技术形成的新的电路元件,与传统的半导体开关器件相比具有插入损耗低、隔离度大、线性度好等优点,将对现有雷达和通信中RF结构产生重大的影响。介绍了射频MEMS开关的工作原理、优化设计,分析了可靠性问题,举例说明了射频MEMS开关的应用,指出了其发展所面临的问题。     

双膜桥微波MEMS开关

介绍了一种双膜桥微波MEMS开关 ,给出了开关的设计与优化方法 ,建立了开关的仿真模型 ,使用硅表面微机械工艺制造了双膜桥开关样品 ,其主要结构为硅衬底上制作CPW金属传输线电极和介质层 ,然后制作具有微电感结构的金属膜桥 ,提高了开关隔离度。利用HFSS软件仿真的结果表明 ,该开关在微波低频段 (3～ 6GHz)有着很好的隔离性能。研制的开关样品在片测试的电性能指标为 :插损小于 0 .3dB ,隔离度大于 4 0dB ,驱动电压小于 2 4V。     

双膜桥微波MEMS开关

介绍了一种双膜桥微波MEMS开关，给出了开关的设计与优化方法，建立了开关的仿真模型，使用硅表面微机械工艺制造了双膜桥开关样品，其主要结构为硅衬底上制作CPW金属传输线电极和介质层，然后制作具有微电感结构的金属膜桥，提高了开关隔离度。利用HFSS软件仿真的结果表明，该开关在微波低频段(3～6GHz)有着很好的隔离性能。研制的开关样品在片测试的电性能指标为：插损小于0．3dB，隔离度大于40dB，驱动电压小于24V。     

发展中的RF MEM5开关技术

射频MEMS开关是用MEMS技术形成的新的电路元件,与传统的半导体开关器件相比具有插入损耗低、隔离度大、线性度好等优点,将对现有雷达和通信中RF结构产生重大的影响.介绍了射频MEMS开关的工作原理、优化设计,分析了可靠性问题,举例说明了射频MEMS开关的应用,指出了其发展所面临的问题.     

W-band CPW RF MEMS circuits on quartz substrates

This paper presents W-band coplanar waveguide RF microelectromechanical system (MEMS) capacitive shunt switches with very low insertion loss (-0.2 to -0.5 dB) and high-isolation (/spl les/ -30 dB) over the entire W-band frequency range. It is shown that full-wave electromagnetic modeling using Sonnet can predict the performance of RF MEMS switches up to 120 GHz. Also presented are W-band 0/spl deg//90/spl deg/ and 0/spl deg//180/spl deg/ switched-line phase shifters with very good insertion loss (1.75 dB/bit at 90 GHz) and a wide bandwidth of operation (75-100 GHz). These circuits are the first demonstration of RF MEMS digital-type phase shifters at W-band frequencies and they outperform their solid-state counterparts by a large margin.     

基于砷化镓衬底的RF MEMS膜开关

射频微机械开关由于其优越的高频特性在微波和毫米波电路中表现出巨大的应用前景。但是目前的微机械开关都是制作在硅基衬底上的，难于与后面的高频砷化镓处理电路相集成。本文介绍了基于砷化镓衬底的RFMEMS膜开关，着重介绍了开关的工作原理、制作过程和测试结果。     

基于砷化镓衬底的RF MEMS膜开关

射频微机械开关由于其优越的高频特性在微波和毫米波电路中表现出巨大的应用前景。但是目前的微机械开关都是制作在硅基衬底上的 ,难于与后面的高频砷化镓处理电路相集成。本文介绍了基于砷化镓衬底的RFMEMS膜开关 ,着重介绍了开关的工作原理、制作过程和测试结果     

Inline capacitive and DC-contact MEMS shunt switches

This paper presents inline capacitive MEMS shunt switches suitable for X/K-band and Ka/V-band applications. The inline switch allows for a low- or high-inductance connection to the ground plane without changing the mechanical characteristics of the MEMS bridge. Excellent isolation and loss are achieved with this design, and the performance is very similar to the standard capacitive MEMS shunt switch. Also, a new metal-to-metal contact MEMS shunt switch is presented. A novel pull-down electrode is used which applies the electrostatic force at the same location as the metal-to-metal contact area. A contact resistance of 0.15-0.35 Ω is repeatable, and results in an isolation of -40 dB at 0.1-3 GHz. The measured isolation is still better than -20 dB at 40 GHz. The application areas are in high-isolation/low-loss switches for telecommunication and radar systems     

Hybrid ring coupler for W-band MMIC applications using MEMS technology

The hybrid ring coupler was designed and fabricated on a GaAs substrate using surface micromachining techniques, which adopted dielectric-supported air-gapped microstrip line (DAML) structure. The fabrication process of DAML is compatible with the standard monolithic microwave integrated circuit (MMIC) techniques, and the hybrid ring coupler can be simply integrated into a plane-structural MMIC. The fabricated hybrid ring coupler shows wideband characteristics of the coupling loss of 3.57 /spl plusmn/ 0.22dB and the transmission loss of 3.80 /spl plusmn/ 0.08dB across the measured frequency range of 85 to 105GHz. The isolation characteristics and output phase differences are -34dB and 180/spl plusmn/1/spl deg/, at 94GHz, respectively.     

Compact single-pole six-throw switch using centre-anchor MEMS switches

A single-pole six-throw switch based on centre-anchor MEMS switches is presented. It has a chip size of 1 mm/sup 2/ and shows isolation of -48 dB and insertion loss of -0.5 dB between P1 and P4 at 6 GHz. Also, to evaluate the RF performance, the SP6T switch has been modelled using a structure-based /spl pi/ small-signal model.     

Free-space fiber-optic switches based on MEMS vertical torsionmirrors

This paper reports on the design, fabrication, and performance of a novel MEMS (micro-electro-mechanical-system) fiber-optic switch based on surface-micromachined vertical torsion mirrors. The vertical torsion mirror itself can be used as a 1×2 or an ON-OFF switch. A 2×2 MEMS fiber-optic switch with four vertical torsion mirrors has also been fabricated. The switching voltage is measured to be 80 V for switching angles of 45°. We have achieved a switching time of less than 400 μs (fall time) and an optical insertion loss of 1.25 dB for single-mode fibers. In addition, a bulk-micromachined silicon submount has been developed to package the switch with microball lenses and multimode fibers with passive alignment. With the micromachined switch chip and the hybrid-packaging scheme, the size, weight, and potentially the cost of the fiber-optic switches can be dramatically reduced     

Contact physics of gold microcontacts for MEMS switches

This work presents a study of gold metallic contacts regarding contact resistance, heat dissipation, and surface damage in the normal-force regime of tens to hundreds of μN, which is typical of the contact forces from microactuation. The purpose of this work is to present the micromechanical switch designer with practical information on gold contact phenomena in this force regime, as most work in micrometallic contacts has focused on contact forces greater than 1 mN. Results indicate actuation forces of several hundred μN are required for reliable fully metallic contacts, with resistance and current carrying ability primarily dependent on morphology, thermal management, and nm-depth material properties of the contact electrodes     

Modeling of dielectric charging in electrostatic MEMS switches

The most important failure mechanism for electrostatic MEMS switches is dielectric charging, which contributes to a significant reduction of the device lifetime. In this study the correlation between the dielectric properties and the switch lifetime is evaluated. The conduction mechanism and trapping kinetics for two types of PECVD SiN_x are determined by I–V sweeps and constant-current injections from Metal–Insulator–Metal (MIM) capacitors. This type of procedure is used as a basis for modeling the charge build-up in a switch. Despite significant differences between the dielectrics, in terms of leakage current and trapping properties, the numerical model of charge build-up fits well with experimental data. We conclude that the switch lifetime can be correlated with the trapping properties of the dielectric itself.     

Gamma radiation effects on RF MEMS capacitive switches

Dielectric-based RF MEMS capacitive switches were fabricated and characterized for their response to dielectric charging, thermal storage and cycling and to total dose gamma irradiations. The evolution of the switch electromechanical and RF characteristics (actuation and releasing voltages, insertion losses, isolation) were evaluated as a function of the applied stress (temperature or total ionizing dose). It is indicated that the thermal stress has a relatively minor impact on the switches (the switches remained functional with nearly the same electrical properties). Under our particular test conditions, C(V) and S-parameters measurements show that gamma radiation has low to moderate effects on the components behavior.     

Performance of RF MEMS switches at low temperatures

The actuation voltage of microelectromechanical system (MEMS) metal switches was investigated at temperatures ranging from 10 to 290 K. The investigation shows a 50% increase in the actuation voltage at low temperature. A comparison has been made using a published model and showed similar increment of actuation voltage at low temperature