Optical MEMS switching technology has attracted attention in managing data flow due to its compactness and
robustness. It allows hundreds of optical channels to be switched by micro-mirrors with very low power consumption.
Furthermore, the ability to switch signals independent of data rates, formats, wavelengths and protocols is advantageous
in many real world environments such as internet peering exchanges, undersea cable landing locations and data centers.
All of these applications require a highly reliable and stable switching system. Dielectric isolation has a huge impact on
major failure modes of capacitive MEMS devices such as breakdown and charging. This issue becomes more
challenging in electrostatic MEMS optical switches since they usually operate at relatively high voltages. The charges
trapped in this dielectric layer could cause interference in the electric field, resulting in erratic responses of the steering
mirrors and instability of pointing accuracy over temperature and time, which greatly degrades the system performance.
Aiming at reducing charging and preventing high voltage breakdown, a dielectric charging guard has been developed by
using an oxide "fence" with extended breakdown path length that is shielded by conductive sidewalls of the silicon
interposer. In this paper, the reliability tests as well as the performance impact to the optical switch will be presented,
including characterizations of breakdown voltage, leakage current, and charging verses temperature. The test results
demonstrate highly repeatable switching accuracy of micro-mirrors with very low drift at varied temperature. Failures
induced by fabrication will also be discussed.
growth of data and video transport networks. All-optical switching eliminates the need for optical-electrical conversion
offering the ability to switch optical signals transparently: independent of data rates, formats and wavelength. It also
provides network operators much needed automation capabilities to create, monitor and protect optical light paths. To
further accelerate the market penetration, it is necessary to identify a path to reduce the manufacturing cost significantly
as well as enhance the overall system performance, uniformity and reliability. Currently, most MEMS optical switches
are assembled through die level flip-chip bonding with either epoxies or solder bumps. This is due to the alignment
accuracy requirements of the switch assembly, defect matching of individual die, and cost of the individual components.
In this paper, a wafer level assembly approach is reported based on silicon fusion bonding which aims to reduce the
packaging time, defect count and cost through volume production. This approach is successfully demonstrated by the
integration of two 6-inch wafers: a mirror array wafer and a "snap-guard" wafer, which provides a mechanical structure
on top of the micromirror to prevent electrostatic snap-down. The direct silicon-to-silicon bond eliminates the CTEmismatch
and stress issues caused by non-silicon bonding agents. Results from a completed integrated switch assembly
will be presented, which demonstrates the reliability and uniformity of some key parameters of this MEMS optical
A high-stroke micromirror array was designed, modeled, fabricated and tested. Each pixel in the 4×4 array consists of a
self-aligned vertical comb drive actuator that has had a single-crystal silicon mirror successfully bonded to it. Two
different bonding technologies were used, photoresist bonding and fusion bonding. The results of each of these bonding
methods will be presented. Analytical models combined with CoventorWare<sup>R</sup> simulations were used to design these
elements that would move up to 10 microns in piston motion with 200V applied. Devices were fabricated according to
this design and difference measurements performed with a white-light interferometer demonstrated a displacement of
0.18 microns with 200V applied. Further investigation revealed that fabrication process inaccuracy led to significantly
stiffer mechanical springs in the fabricated devices. The increased stiffness of the springs was shown to account for the
reduced displacement that was observed.
A high-stroke micro-actuator array was designed, modeled, fabricated and tested. Each pixel in the 4x4 array consists of a self-aligned vertical comb drive actuator. This micro-actuator array was designed to become the foundation of a micro-mirror array that will be used as a deformable mirror for adaptive optics applications. Analytical models combined with CoventorWare<sup>(R)</sup> simulations were used to design actuators that would move up to 10 microns in piston motion with 100V applied. Devices were fabricated according to this design and testing of these devices demonstrated an actuator displacement of 1.4 microns with 200V applied. Further investigation revealed that fabrication process inaccuracy led to significantly stiffer mechanical springs in the fabricated devices. The increased stiffness of the springs was shown to account for the reduced displacement of the actuators relative to the design.
The National Science Foundation Center for Adaptive Optics (CfAO) is coordinating a program for the development of spatial light modulators suitable for adaptive optics applications based on micro-optoelectromechanical systems (MOEMS) technology. This collaborative program is being conducted by researchers at several partner institutions including the Berkeley Sensor & Actuator Center, Boston Micromachines, Boston University, Lucent Technologies, the Jet Propulsion Laboratory, and Lawrence Livermore National Laboratory. The goal of this program is to produce MEMS spatial light modulators with several thousand actuators that can be used for high-resolution wavefront control applications that would benefit from low device cost, small system size, and low power requirements. The two primary applications targeted by the CfAO are astronomy and vision science. In this paper, we present an overview of the CfAO MEMS development plan along with details of the current program status.
Direct detection of photons emitted or reflected by an extrasolar planet is an extremely difficult but extremely exciting application of adaptive optics. Typical contrast levels for an extrasolar planet would be 10<SUP>9</SUP> - Jupiter is a billion times fainter than the sun. Current adaptive optics systems can only achieve contrast levels of 10<SUP>6</SUP>, but so-called extreme adaptive optics systems with 10<SUP>4</SUP> -10<SUP>5</SUP> degrees of freedom could potentially detect extrasolar planets. We explore the scaling laws defining the performance of these systems, first set out by Angel (1994), and derive a different definition of an optimal system. Our sensitivity predictions are somewhat more pessimistic than the original paper, due largely to slow decorrelation timescales for some noise sources, though choosing to site an ExAO system at a location with exceptional r<SUB>0</SUB> (e.g. Mauna Kea) can offset this. We also explore the effects of segment aberrations in a Keck-like telescope on ExAO; although the effects are significant, they can be mitigated through Lyot coronagraphy.
The NSF Center for Adaptive Optics (CfAO) is coordinating a five to ten year program for the development of MEMS-based spatial light modulators suitable for adaptive optics applications. Participants in this multi-disciplinary program include several partner institutions and research collaborators. The goal of this program is to produce MEMS spatial light modulators with several thousand actuators that can be used for high-resolution wavefront control applications and would benefit from low device cost, small system size, and low power requirements. We present an overview of the CfAO MEMS development plan along with details of the current program status. Piston mirror array devices that satisfy minimum application requirements have been developed, and work is continuing to enhance the piston devices, add tip-tilt functionality, extend actuator stroke, create a large array addressing platform, and develop new coating processes.