Multilayer Organic Multichip Module Implementing Hybrid Microelectromechanical Systems

We present the design and development of an organic package that is compatible with fully released RF microelectromechanical systems (MEMS). The multilayer organic package consists of a liquid-crystal polymer film to provide near hermetic cavities for MEMS. The stack is further built up using organic thin-film polyimide. To demonstrate the organic package, we have designed and implemented a 2-bit true-time delay X-band phase shifter using commercially available microelectromechanical switches. The packaged phase shifter has a measured insertion loss of 2.45 plusmn 0.12 dB/bit at 10 GHz. The worst case phase variation of the phase shifter at 10 GHz is measured to less than 5deg. We have also conducted temperature cycling (-65degC to 150degC) and 85/85 to qualify the packaging structures.     

Fabrication and accelerated hermeticity testing of an on-wafer package for RF MEMS

A hermetic silicon micromachined on-wafer dc-to-40-GHz packaging scheme for RF microelectromechanical systems (MEMS) switches is presented. The designed on-wafer package has a deembedded insertion loss of 0.03 dB per transition up to 40 GHz (a total measured loss of 0.3 dB including a 2.7-mm-long through line) and a return loss below -18dB up to 40 GHz. The hermeticity of the packaged is tested using an autoclave chamber with accelerated conditions of 130/spl deg/C, 2.7 atm of pressure, and 100% relative humidity. The fabrication process is designed so as to be completely compatible with the MEMS switch process, hence, allowing the parallel fabrication of all the components on a single wafer. The on-wafer proposed packaging approach requires no external wiring to achieve signal propagation and, thus, it has the potential for lower loss and better performance at higher frequencies.     

A Novel Wafer-Level Hermetic Packaging for MEMS Devices

Some emerging microelectromechanical systems (MEMS) devices such as high-performance inertial sensors and high-speed actuators must be operated in a high vacuum and in order to create this vacuum environment, specific packaging is required. To satisfy this demand, this paper presents a novel method for hermetic and near-vacuum packaging of MEMS devices. We use wafer-level bonding technology to combine with vacuum packaging, simultaneously. For this packaging solution, the wafers with air-guided micro-through-holes were placed on a custom-built design housed in a vacuum chamber maintained at a low-pressure environment of sub-10 mtorr. Packaging structure is then sealed by solder ball reflow process with the lower heating temperature of 300degC to fill up micro-through-hole. Experimental results shown the hermetical packaging technique using solder sealing is adapted to the wafer-level microfabrication process for MEMS devices and can achieve better yield and performance. Thus, this technique is very useful for many applications with high performance and low packaging cost can be obtained due to wafer-level processing.     

射频MEMS封装技术

MEMS在射频(RF)应用领域表现出的低功耗、低损耗和高数据率的优越特性为RF无线通信系统及其微小型化提供新的技术手段。在产品设计的初期阶段,RF MEMS封装的设计考虑是降低成本、提高产品合格率的有效途径。我们主要针对当前RF MEMS器件与电路设计制造中突出的问题——封装技术进行研究,指出封装在产品设计中的重要地位和技术实现方法,特别介绍了计算机仿真在RF MEMS器件与电路封装中的作用。     

Moisture Lifetime Testing of RF MEMS Switches Packaged in Liquid Crystal Polymer

This paper presents for the first time the effects of moisture on radio frequency microelectromechanical systems (MEMS) switches packaged entirely inside a flexible, organic polymer [namely, liquid crystal polymer (LCP)]. Moisture tests were administered at 100degC and 100% relative humidity to evaluate long-term exposures and at 85degC and 85% relative humidity to evaluate short-term exposures. The effect of the moisture was quantified by before and after S-parameter measurements, by a weight gain analysis, and by visual inspection. Both global and localized bonding techniques were investigated to compare the best-case scenario to a more practical case. The effects of an 18 mum thick copper layer on both sides of the package were studied as well as the size of the bonding contact area. It was found that many packages that passed the Military Standard 883 G, Method 1014.12 for seal quality were unable to provide adequate protection from moisture. This indicates that the requirements for MEMS devices is more rigorous than the Military Standard. This standard is commonly quoted in literature as a metric for qualifying polymer packaging techniques. This paper demonstrates the necessity for proper testing of MEMS devices in a moist environment. It has been determined that for the bonding methods presented in this paper, an LCP packaged MEMS switch could potentially survive 7-10 h in jungle conditions, 5-7 weeks in ambient conditions, or 1.4-1.8 years in desert conditions.     

静电式RF MEMS开关的可靠性

MEMS开关是最常见的RF MEMS控制元件,是RF结构中一个关键的MEMS器件。长期可靠性是目前制约MEMS开关商业化进程中的一个主要问题。主要综述了静电式RF MEMS开关可靠性的新进展。欧姆式开关通常由于黏附或接触电阻的增大而失效,电容式开关的主要失效机理则与电介质层的充电有关。接触材料的选择是决定欧姆开关可靠性最重要的一个因素,"主动断开/被动接触"MEMS开关适用于软金属材料欧姆接触的可靠性要求。改善电容式开关可靠性的途径是改善介电层、优化驱动电压波形等以减小介质层的充电。     

The package integration of RF-MEMS switch and control IC for wireless applications

The integration of microelectromechanical systems (MEMS) switch and control integrated circuit (IC) in a single package was developed for use in next-generation portable wireless systems. This packaged radio-frequency (RF) MEMS switch exhibits an insertion loss under -0.4 dB, and isolation greater than -45 dB. This MEMS switch technology has significantly better RF characteristics than conventional PIN diodes or field effect transistor (FET) switches and consumes less power. The RF MEMS switch chip has been integrated with a high voltage charge pump plus control logic chips into a single package to accommodate the low voltage requirements in portable wireless applications. This paper discusses the package assembly process and critical parameters for integration of MEMS devices and bi-complementary metal oxide semiconductor (CMOS) control integrated circuit (IC) into a single package.     

Three-dimensional interconnect for multilayer module packages with selectively anodised aluminium substrate

It is reported that 3-D interconnects fabricated with a selectively anodised aluminium process for a multilayer module package can be used to evaluate high-frequency performance. The proposed method of fabricating vertical interconnects is easier and more cost-effective than other RF MEMS processes. To transfer RF signals vertically, coaxial hermetic seal vias with characteristic 50 Omega impedances and embedded anodised aluminium vias with a solder ball attachment and flip-chip bonding were used. The optimised interconnect structure demonstrated RF characteristics with an insertion loss of less than 1.55 OmegadB and a return loss of less than 12.25 OmegadB over a broad bandwidth ranging from 0.1 to 10 OmegaGHz. Experimental results suggest that the developed technology, which is based on selectively anodised aluminium, can be applied to new 3-D packaging solutions.     

RFMEMS开关及其抗连续波烧毁功率的测试与分析

MEMS开关的功率能力是MEMS开关使用中必须考虑的一个指标,本文测试了我所研制的RFMEMS开关的抗连续波烧毁功率性能,其抗连续波烧毁功率达到35.1dBm。解剖分析了烧毁样品,对功率烧毁机理进行了进一步的讨论。     

低压驱动RF MEMS开关设计与模拟

RF MEMS开关存在驱动电压高、开关时间长等问题,利用ANSYS对电容式开关加以改进,设计扭转臂杠杆与打孔电容膜相结合的新型开关。通过静电耦合与模态分析的仿真,可以在理论上改善RF MEMS开关的射频性能,并有工艺的可行性。     

Thermal solutions for discrete and wafer-level RF MEMS switch packages

In discrete radio frequency (RF) microelectromechanical systems (MEMS) packages, MEMS devices were fabricated on silicon or gallium arsenide (GaAs) chips. The chips were then attached to substrates with die attach materials. In wafer-level MEMS packages, the switches were manufactured directly on substrates. For both types of packages, when the switches close, a contact resistance of approximately 1 /spl Omega/ exists at the contact area. As a result, during switch operations, a considerable amount of heat is generated in the minuscule contact area. The power density at the contact area could be up to 1000 times higher than that of typical power amplifiers. The high power density may overheat the contact area, therefore affect switch performance and jeopardize long-term switch reliabilities. In this paper, thermal analysis has been performed to study the heat dissipation at the switch contact area. The goal is to control the "hot spots" and lower the maximum junction temperature at the contact area. A variety of chip materials, including Silicon, GaAs have been evaluated for the discrete packages. For each chip material, the effect of die attach materials has been considered. For the wafer-level packages, various substrate materials, such as ceramic, glass, and low-temperature cofired ceramic (LTCC) have been studied. Thermal experiments have been conducted to measure the temperature at the contact area and its vicinity as a function of dc and RF powers. Several solutions in material selection and package configurations have been explored to enable the use of MEMS with chips or substrates with relatively poor thermal conductivity. For discrete MEMS packages, placing the die inside a copper cavity on the substrate provides significant heat dissipation. For wafer-level packages, thin diamond coatings on the substrate could reduce the hot-spot temperature considerably.     

Fully integrated electrothermal multidomain modeling of RF MEMS switches

RF MEMS switches have demonstrated excellent performance. However, before such switches can be fully implemented, they must demonstrate high reliability and robust power-handling capability. Numerical simulation is a vital part of design to meet these goals. This paper demonstrates a fully integrated electrothermal model of an RF MEMS switch which solves for RF current and switch temperature. The results show that the beam temperature increases with either higher input power or increased frequency. The simulation data are used to predict switch failure due to temperature-related creep and self pull-in over a wide range of operating frequency (0.1-40 GHz) and power input (0-10 W). Self pull-in is found to be the dominant failure mechanism for an example geometry.     

Reliability testing of flexible printed circuit-based RF MEMS capacitive switches

In this paper, reliability results of a novel type of electrostatically actuated RF MEMS capacitive switches developed by our group are discussed. The test setup used for reliability testing consists of the capacitive MEMS switch under test connected in series with a resistor. A specified actuation waveform is applied to the switch and the voltage waveform across the resistor is continuously recorded. The recorded waveform aids in identifying short, open, or stiction failure of the switch. Further, the waveform recorded can be analyzed to study the degradation, reliability, and lifetime characteristics of the switch. The proposed method has been used to study the reliability, failure, and hold-down test characteristics of flexible circuit-based RF MEMS switches. Reliability testing up to 75 million operations has been carried out for flexible circuit-based RF MEMS switches.     

Application of Au-Sn eutectic bonding in hermetic radio-frequency microelectromechanical system wafer level packaging

Development of packaging is one of the critical issues toward realizing commercialization of radio-frequency-microelectromechanical system (RF-MEMS) devices. The RF-MEMS package should be designed to have small size, hermetic protection, good RF performance, and high reliability. In addition, packaging should be conducted at sufficiently low temperature. In this paper, a low-temperature hermetic wafer level packaging scheme for the RF-MEMS devices is presented. For hermetic sealing, Au-Sn eutectic bonding technology at temperatures below 300°C is used. Au-Sn multilayer metallization with a square loop of 70 μm in width is performed. The electrical feed-through is achieved by the vertical through-hole via filling with electroplated Cu. The size of the MEMS package is 1 mm × 1 mm × 700 μm. The shear strength and hermeticity of the package satisfies the requirements of MIL-STD-883F. Any organic gases or contamination are not observed inside the package. The total insertion loss for the packaging is 0.075 dB at 2 GHz. Furthermore, the robustness of the package is demonstrated by observing no performance degradation and physical damage of the package after several reliability tests.     

微波电路的MEMS天关进展

开关是微波信号变换的关键元件,和传统的半导体开关相比,射频微机电系统（RF MEMS）开关具有优良的高频特性和固有的重量轻、尺寸小、低功耗等优点,而且其制作工艺和传统的CMOS工艺相兼容。本文较为详细地了串联悬臂梁开关、并联悬臂梁开关和膜开关的工作原理及典型的性能参数。由于其优越的微小特性,MEMS开关已在许多电路和系统中,包括微波前端电路、数字电容器组和移相网络中得到应用。     

RF MEMS开关的设计分析

针对具有低损耗、高隔离度性能的微机电系统(Micro-Electro-Mechanical System,MEMS)开关,介绍了串联DC式和并联电容式的开关结构模型,并对并联电容式MEMS开关的工作原理、等效电路模型和制造工艺流程进行了描述,利用其模型研究了开关的微波传输性能,设计了一款电容耦合式开关并进行了仿真。由仿真结果可得,开关"开态"时的插入损耗在40 GHz以内优于-0.3 dB;开关"关态"时的隔离度在20～40 GHz相对较宽的频带内优于-20 dB。     

埋置型叠层微系统封装技术

包含微机电系统(MEMS)混合元器件的埋置型叠层封装,此封装工艺为目前用于微电子封装的挠曲基板上芯片(COF)工艺的衍生物。COF是一种高性能、多芯片封装工艺技术,在此封装中把芯片包入模塑塑料基板中,通过在元器件上形成的薄膜结构构成互连。研究的激光融除工艺能够使所选择的COF叠层区域有效融除,而对封装的MEMS器件影响最小。对用于标准的COF工艺的融除程序进行分析和特征描述,以便设计一种新的对裸露的MEMS器件热损坏的潜在性最小的程序。COF/MEMS封装技术非常适合于诸如微光学及无线射频器件等很多微系统封装的应用。     

Design and Development of a Package Using LCP for RF/Microwave MEMS Switches

We present the development of an ultrahigh moisture-resistant enclosure for RF microelectromechanical system (MEMS) switches using liquid-crystal polymer (LCP). A cavity formed in LCP has been laminated, at low temperature, onto a silicon MEMS switch to create a package. The LCP-cap package has an insertion loss of less than 0.2 dB at X-band. E595 outgas tests demonstrate that the LCP material is suitable for constructing reliable packages without interfering with the operation of the MEMS switch. The package also passes Method 1014, MIL-STD-883 gross leak, and fine leak hermeticity tests     

An embedded overlay concept for microsystems packaging

An embedded overlay concept for packaging hybrid components containing microelectromechanical systems (MEMS) is described. This packaging process is a derivative of the chip-on-flex (COF) process currently used for microelectronics packaging. COF is a high performance, multichip packaging technology in which die are encased in a molded plastic substrate and interconnects are made via a thin-film structure formed over the components. A laser ablation process has been developed which enables selected areas of the COF overlay to be efficiently ablated with minimal impact to the packaged MEMS devices. Analysis and characterization of the ablation procedures used in the standard COF process was performed to design a new procedure which minimized the potential for heat damage to exposed MEMS devices. The COF/MEMS packaging technology is well-suited for many microsystem packaging applications such as micro-optics and radio frequency (RF) devices.     

埋置型叠层微系统封装技术

包含微机电系统(MEMS)混合元器件的埋置型叠层封装,此封装工艺为目前用于微电子封装的挠曲基板上芯片(COF)工艺的衍生物.COF是一种高性能、多芯片封装工艺技术,在此封装中把芯片包入模塑塑料基板中,通过在元器件上形成的薄膜结构构成互连.研究的激光融除工艺能够使所选择的COF叠层区域有效融除,而对封装的MEMS器件影响...