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Journal ArticleDOI

Comparative study of various release methods for gold surface micromachining

01 Jan 2014-Journal of Micro-nanolithography Mems and Moems (International Society for Optics and Photonics)-Vol. 13, Iss: 1, pp 013005-013005
TL;DR: In this article, a comparison of dry and wet release methods for surface micromachining of metallic structures, such as RF MEMS switches, test structures, bridges, and cantilevers is presented.
Abstract: A comparison of dry and wet release methods for surface micromachining of metallic structures, such as RF MEMS switches, test structures, bridges, and cantilevers is presented. The dry release process is opti- mized by varying the concentration of O2 and CF4 plasma and RF power. The plasma ashing of the sacrificial layer typically results in damage to metallic structures or stress-related deformation due to rise in temperature (>80°C). A wet release process using critical point drying (CPD) has been investigated to realize gold-electro- plated structures with reduced residual stress. The CPD, being a low-temperature (31.1°C) process, is more suitable for compliant structures without any deformation. © 2014 Society of Photo-Optical Instrumentation Engineers (SPIE)
Citations
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Journal ArticleDOI
TL;DR: In this paper, a single-pole double-throw (SPDT) switch based on series capacitive configuration is proposed, and the critical process parameters are analyzed to improve the fabrication process.
Abstract: A compact radiofrequency (RF) MEMS single-pole double-throw (SPDT) switch based on series capacitive configuration is proposed. The critical process parameters are analyzed to improve the fabrication process. A technique of cold–hot thermal shock for lift-off method is explored. The residual stress in the structure is quantified by lancet test structures that come out to be 51 MPa. Effect of residual stress on actuation voltage is explored, which changes its value from 24 to 22 V. Resonance frequency and switching speed of the switch are 11 kHz and 44 μs, respectively, measured using laser Doppler vibrometer. Measured bandwidth of the SPDT switch is 20 GHz (5 to 25 GHz), which is verified with finite element method simulations in high frequency structure simulator© and an equivalent LCR circuit in advanced design system©. Insertion loss of the switch lies in −0.1 to −0.5 dB with isolation better than −20 dB for the above-mentioned bandwidth.

14 citations


Cites methods from "Comparative study of various releas..."

  • ...The final step of the fabrication process is the removal of sacrificial layer using critical point dryer (CPD).(16) During the implementation of fabrication processes, two major issues are encountered; unwanted flakes and poor adhesion of gold....

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Journal ArticleDOI
TL;DR: In this article, a single pole single throw (SPST) switch is developed without using any additional step, and the measured switching time of the switch is $1.8~\mu \text{s}$.
Abstract: RF MEMS ohmic switches are prone to stiction and contact degradation. In literature, bumps are made at the contact area to reduce stiction with additional fabrication steps. In this article, ohmic switch based on cantilever configuration is developed without using any additional step. The switch structure is modified to improve its mechanical parameters, such as pull-in voltage and switching speed. The measured switching time of the switch is $1.8~\mu \text{s}$ . A footprint of the developed single pole single throw (SPST) switch is 0.9 mm2. The insertion loss and isolation of the SPST switch are better than 0.8 and 20 dB, respectively. The switch has a wide bandwidth of 10 GHz (dc to 10 GHz). The switch has completed 725 million hot cycles at 1-dBm power.

13 citations


Cites methods or result from "Comparative study of various releas..."

  • ...However, a thin structural layer of the gold switch curled up due to stress [13]–[15], which results in a deviation from the simulated results....

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  • ...These molds are filled with 2-μm-thick electroplating followed by the removal of photoresist and etching of the seed layer [13]....

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Journal ArticleDOI
TL;DR: In this article, the effect of stress on pull-in voltage of a single-pole double-throw (SPDT) switch was analyzed using simulations and curve fitting. But the performance of the SPDT switch was not analyzed.
Abstract: RF MEMS switches are well known to exhibit performance superior to solid-state devices. However, electromechanical issues, such as repeatability and higher pull-in voltage, are a matter of concern. MEMS switches generally consist of metallic beams which curl up or down based on stresses in the structure. Stress-induced curling-up phenomenon, in such structures, increases the gap between the actuating electrode and the freely suspended metallic structure which in turn increases the pull-in voltage. This article focuses on simulations and curve fitting to analyze the effect of stress on pull-in voltage. The pull-in voltage of the switch is proportional to stress, and accordingly, its dependence on in-built stress and Young’s modulus is analyzed. In addition to mechanical analysis, RF response of the single pole double throw (SPDT) switch is discussed as a case study. Measured stress and pull-in voltage of the SPDT switch is 50 MPa and 16 V. In the presence of stress, the curled-up cantilever switch shows measured isolation better than 31 dB for dc to 10-GHz range.

11 citations


Cites methods from "Comparative study of various releas..."

  • ...6) The final step of the process is wet released using a critical point dryer (CPD) method as described in [11]....

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Journal ArticleDOI
TL;DR: In this article, the design, fabrication, and mechanical characterization of a compact-reduced stiction see-saw radio frequency MEMS switch is presented, which has a resonance frequency of 9.8 kHz with a corresponding switching speed of 46μs.
Abstract: The design, fabrication, and mechanical characterization of a compact-reduced stiction see-saw radio frequency MEMS switch are presented. The switch has a resonance frequency of 9.8 kHz with a corresponding switching speed of 46 μs. Use of a floating metal layer and optimal contact area ensures reduced stiction and smaller capacitive leakage. Overall size of the switch is 0.535 (0.50×1.070) mm2. Reduction in up-state capacitance also results in improvement in self-actuation voltage, insertion, and return loss. The optimized topology has improved the stiction and power handling of the switch.

11 citations

Journal ArticleDOI
TL;DR: In this article, an integrated approach for design, fabrication and encapsulation of RF MEMS switches in view of the optimal performance subsequent to packaging is described. But the authors focus on the bottom contact package (BCP), where the connection layout through silicon via holes is independent of the cavity geometry.
Abstract: The present paper describes an integrated approach for design, fabrication and encapsulation of RF MEMS switches in view of the optimal performance subsequent to packaging. 'Top and bottom contact' fabrication approaches are explored using different RF MEMS switch topologies. In the 'bottom contact package (BCP)' the packaging cap alignment is less critical as compared to the top contact packaging (TCP) approach where contact via is an integral part of the cap. In this case, the connection layout through silicon via holes is independent of the cavity geometry. For the devices under consideration, bulk etched silicon cavity height has been optimized to 50µm for optimal RF performance, e.g., isolation and insertion loss. Parasitic effects of top silicon cap are reduced by altering CPW impedance. Mechanical parameter damping is simulated for different cavity heights and found to be independent from cavity height after 20µ mo nwards.

6 citations

References
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Journal ArticleDOI
TL;DR: In this paper, a review on the problem of adhesion in microelectromechanical systems and the application of the principles and techniques of surface science to understand and manipulate, at the atomic level, the interfacial forces which are responsible for strong adhesion of microdevices are discussed.

275 citations

Journal ArticleDOI
TL;DR: In this paper, the progress made in plasma etching technologies is described from the viewpoint of requirements for the manufacturing of devices, and critical applications of RIE, isotropic etching, and plasma ashing/cleaning to form precisely controlled profiles of high-aspect-ratio contacts (HARC), gate stacks, and shallow trench isolation (STI) in the front end of line (FEOL) are described in detail.
Abstract: Plasma etching technologies such as reactive ion etching (RIE), isotropic etching, and ashing/plasma cleaning are the currently used booster technologies for manufacturing all silicon devices based on the scaling law. The needs-driven conversion from the wet etching process to the plasma/dry etching process is reviewed. The progress made in plasma etching technologies is described from the viewpoint of requirements for the manufacturing of devices. The critical applications of RIE, isotropic etching, and plasma ashing/cleaning to form precisely controlled profiles of high-aspect-ratio contacts (HARC), gate stacks, and shallow trench isolation (STI) in the front end of line (FEOL), and also to form precise via holes and trenches used in reliable Cu/low-k (low-dielectric-constant material) interconnects in the back end of line (BEOL) are described in detail. Some critical issues inherent to RIE processing, such as the RIE-lag effect, the notch phenomenon, and plasma-induced damage including charge-up damage are described. The basic reaction mechanisms of RIE and isotropic etching are discussed. Also, a procedure for designing the etching process, which is strongly dependent on the plasma reactor configuration, is proposed. For the more precise critical dimension (CD) control of the gate pattern for leading-edge devices, the advanced process control (APC) system is shown to be effective.

254 citations

Journal ArticleDOI
TL;DR: In this paper, the authors compared five different procedures commonly used to rinse and dry released microstructures: evaporation drying with deionized (DI) water or methanol, sublimation drying with t-butyl alcohol orp-dichlorobenzene, and supercritical drying with COz.
Abstract: Five different procedures commonly used to rinse and dry released microstructures are compared: evaporation drying with deionized (DI) water or methanol, sublimation drying with t-butyl alcohol orp-dichlorobenzene, and supercritical drying with COz. For objectivecomparison, identical test structures, made by the MCNC Multi-User EMS Processes (MUMPS), are used in evaluating the drying techniques. The test chips contain arrays of surface-micromachined polysilicon cantilevers (2 km thick, 2 pm gap from the substrate) with varying widths and lengths. Some beams feature dimples or tips to quantify their anti-stiction effect. This study reveals, for the first time, that the maximum beam length obtainable increases as the beam width increases for the cases of sublimation and supercritical dryin,, 0 opposite to the previously known case of evaporation drying. Both sublimation drying methods as well as supercritical drying rendered good results, releasing cantilevers up to 700 km in length without stiction. We also introduce a new setup that considerably improves the way sublimation is used to dry microstructures. 0 1998 Elsevier Science S.A.

120 citations


Additional excerpts

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Proceedings ArticleDOI
18 Aug 1999
TL;DR: In this paper, the authors reviewed the stiction problem for microelectromechanical systems, and the application of critical point drying for MEMS technology, and showed that the absence of surface tension in the supercritical phase of a fluid provides an excellent means to overcome stiction.
Abstract: A critical step in surface micromachining of microelectromechanical systems (MEMS) is the process that releases, cleans, and dries the flexible structures that are crucial to MEMS functionality. Standard release methods employed today can leave residue particles and can cause sticking because of surface tension. Aggressive design requirements, liquid processing, packaging, handling, transportation, and device operation etc., can contribute to device failure due to stiction. The use of supercritical carbon dioxide has been proven in various industries to achieve ultra-clean surfaces. Recent critical research studies by academia, research laboratories and industry have shown that supercritical carbon dioxide can be successfully used to alleviate the stiction problem and provide a clean and dry surface. The absence of surface tension in the supercritical phase of a fluid provides an excellent means to overcome stiction. The advantages of supercritical carbon dioxide include its relatively low critical temperature and pressure, its high diffusivity, low surface tension, and environmentally friendly (non-ozone depleting, non- hazardous). This paper reviews the stiction problem for MEMS, and the application of critical point drying for MEMS technology.

68 citations

Journal ArticleDOI
TL;DR: In this paper, a symmetric toggle switch (STS) is proposed for 8-14 GHz applications with low actuation voltage and high isolation, for high power and reliability applications in telecommunication.
Abstract: In this paper, we present a new type of rf MEMS switch with low actuation voltage and high isolation, for high rf power and reliability applications in telecommunication. ‘Symmetric toggle switch’ (STS) is based on push–pull mechanism and utilizes torsion springs and levers, placed symmetrically and transverse to CPW line. The switches designed for 8–14 GHz applications have analytically calculated and FEM simulated actuation voltages in the range of 8–10 V. The simulated insertion loss and isolation for the devices are 0.25 and 35 dB, respectively, at 10 GHz. The fabrication process and preliminary experimental results are also presented.

66 citations