A MEMS SLM with an array of 64×64 pixels, each 120 μm ×120 μm in size, with 98% fill-factor, has been developed.
Each reflector in the array is capable of 5 μm of stroke, and ±4° tip and tilt. From a prototype array, 14 contiguous pixels
have been independently wired-out to off-chip drive electronics. These 14 pixels have been demonstrated to be effective in
an off-the-shelf AO system (with requisite modifications to suit the SLM). For a low-order static aberration, the measured
Strehl ratio has been improved from 0.069 to 0.861, a factor of 12 improvement.
The rapid commercialization and long-term reliability of optical MEMS is greatly facilitated by a Design-for-Reliability mindset, relying on an interdependent development framework simultaneously optimizing design, materials choices, processing, reliability, subsystem design, and packaging. Even with the best mechanical design, the electrical design and packaging choices of these devices has a large impact both on performance (e.g., speed and stability) and on reliability (e.g., corrosion and dielectric or gas breakdown). In this paper we discuss the reliability and performance of two-axis MEMS micromirrors and present several design, processing and packaging steps that were needed to achieve open-loop drift-free operation and mean-time-to-failure in excess of 2000 years. In particular the relationship between leakage currents and the accumulation of quasi-static charge in dielectrics are discussed, along with several techniques to mitigate charging and the associated drift in electrostatically actuated or sensed MEMS devices. Two key parameters are shown to be the electrode geometry and the conductivity of the dielectric. Electrical breakdown in sub-micron gaps is presented as a function of packaging gas and electrode spacing. We discuss the trade-offs involved in choosing gap geometries, dielectric properties, and packaging solutions. Finally galvanic corrosion of poly-silicon in HF release etch baths is discussed along with techniques to minimize this corrosion.
Flavio Pardo, Vladimir Aksyuk, Susanne Arney, H. Bair, Nagesh Basavanhally, David Bishop, Gregory Bogart, Cristian Bolle, J. Bower, Dustin Carr, H. Chan, Raymond Cirelli, E. Ferry, Robert Frahm, Arman Gasparyan, John Gates, C. Randy Giles, L. Gomez, Suresh Goyal, Dennis Greywall, Martin Haueis, R. Keller, Jungsang Kim, Fred Klemens, Paul Kolodner, Avi Kornblit, T. Kroupenkine, Warren Lai, Victor Lifton, Jian Liu, Yee Low, William Mansfield, Dan Marom, John Miner, David Neilson, Mark Paczkowski, C. Pai, A. Ramirez, David Ramsey, S. Rogers, Roland Ryf, Ronald Scotti, Herbert Shea, M. Simon, H. Soh, Hong Tang, J. Taylor, K. Teffeau, Joseph Vuillemin, J. Weld
As telecom networks increase in complexity there is a need for systems capable of manage numerous optical signals. Many of the channel-manipulation functions can be done more effectively in the optical domain. MEMS devices are especially well suited for this functions since they can offer large number of degrees of freedom in a limited space, thus providing high levels of optical integration.
We have designed, fabricated and tested optical MEMS devices at the core of Optical Cross Connects, WDM spectrum equalizers and Optical Add-Drop multiplexors based on different fabrication technologies such as polySi surface micromachining, single crystal SOI and combination of both. We show specific examples of these devices, discussing design trade-offs, fabrication requirements and optical performance in each case.
Optical Micro-Electro-Mechanical Systems (Optical MEMS, or MOEMS) comprise a disruptive technology whose application to telecommunications networks is transforming the horizon for lightwave systems. The influences of materials systems, processing subtleties, and reliability requirements on design flexibility, functionality and commercialization of MOEMS are complex. A tight inter-dependent feedback loop between Component/ Subsystem/ System Design, Fabrication, Packaging, Manufacturing and Reliability is described as a strategy for building reliability into emerging MOEMS products while accelerating their development into commercial offerings.
The PolytecTM laser Doppler vibrometer was used to characterize the dynamics mechanical reliability and lifetimes of surface-micromachined self-assembling MEMS tilting mirrors. The mechanical modes of micromirror can be identified and corresponding resonance frequencies measured. It was found, for certain experimental conditions, that micromirror operation simulating contact between poly-Si surfaces may result in device lifetime reduction due to stiction at the point of contact. The appropriate modifications in device design eliminate the effect of stiction on device lifetime. Moreover, for up to 109 mechanical cycles completed no friction-related device degradation has been observed. In controlled dry ambient at room temperature, micromirrors have been able to complete about 2x1010 switching operations without signs of mechanical degradation. The results validate the robustness and long term mechanical ability of evaluated micromirror devices.
We present a full factorial study of the effect of relative humidity and voltage on the oxidation of surface-micromachined poly-silicon wiring and electrodes. Our system consists of 500 nm thick poly-Si wires and electrodes insulated from the substrate wafer by 600 nm of Si-rch SixNy, fabricated using a surface-micromachinging process. In dry ambients, oxidation or damage to the bottom poly-Si layer (the Poly0 layer) in MicroElectroMechanical Systems (MEMS) devices occurs so slowly that little can be learned in a timely manner, even when stressing the electrodes at electric fields close to dielectric breakdown. We observe however that in ambient with elevated relative humidity the Poly0 wires and electrodes anodically oxidize within a short period of time when operated at moderately large voltages. Only the most positively biased poly-Si structures oxidize, and we describe the anodic oxidation and association volume expansion as a function of a number of accelerating factors including relative humidity and voltage. A threshold is observed in relative humidity bot not in voltage.
This course will provide attendees with a basic working knowledge of how to design MEMS for reliability. The course will concentrate on MEMS design, reliability physics, MEMS-specific fundamental reliability phenomena and failure modes, and accelerated testing protocols. Practical and useful examples from various arenas of MEMS application will be provided.
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