It has long been recognized in the design of micromirror-based optical systems that balancing static flatness of the mirror surface through structural design with the system’s mechanical dynamic response is challenging. Although a variety of mass reduction approaches have been presented in the literature to address this performance trade, there has been little quantifiable comparison reported. In this work, different mass reduction approaches, some unique to the work, are quantifiably compared with solid plate thinning in both curvature and mass using commercial finite element simulation of a specific square silicon-on-insulator–based micromirror geometry. Other important considerations for micromirror surfaces, including surface profile and smoothness, are also discussed. Fabrication of one of these geometries, a two-dimensional tessellated square pattern, was performed in the presence of a 400-μm-tall central post structure using a simple single mask process. Limited experimental curvature measurements of fabricated samples are shown to correspond well with properly characterized simulation results and indicate ∼67% improvement in radius of curvature in comparison to a solid plate design of equivalent mass.
There are numerous applications for micromirror arrays seen in our everyday lives. From flat screen televisions and
computer monitors, found in nearly every home and office, to advanced military weapon systems and space vehicles,
each application bringing with it a unique set of requirements. The microelectromechanical systems (MEMS) industry
has researched many ways micromirror actuation can be accomplished and the different constraints on performance each
design brings with it. This paper investigates a new “zipper” approach to electrostatically driven micromirrors with the
intent of improving duel plane beam steering by coupling large deflection angles, over 30°, and a fast switching speed.
To accomplish this, an extreme initial deflection is needed which can be reached using high stress bimorph beams.
Currently this requires long beams and high voltage for the electrostatic pull in or slower electrothermal switching. The
idea for this “zipper” approach is to stack multiple beams of a much shorter length and allow for the deflection of each
beam to be added together in order to reach the required initial deflection height. This design requires much less pull-in
voltage because the pull-in of one short beam will in turn reduce the height of the all subsequent beams, making it much
easier to actuate. Using modeling and simulation software to characterize operations characteristics, different bimorph
cantilever beam configurations are explored in order to optimize the design. These simulations show that this new
“zipper” approach increases initial deflection as additional beams are added to the assembly without increasing the
actuation voltage.
This paper discusses research being conducted on aluminum nitride (AlN) as a pyroelectric material for use in detecting
applications. AlN is being investigated because of its high pyroelectric coefficient, thermal stability, and high Curie
temperature. In order to determine suitability of the pyroelectric properties of AlN for use as a detector, testing of several
devices was conducted. These devices were fabricated using microelectromechanical systems (MEMS) fabrication
processes; the devices were also designed to allow for voltage and current measurements. The deposited AlN films used
were 150 nm – 300 nm in thickness. Thin-films were used to rapidly increase the temperature response after the thermal
stimulus was applied to the pyroelectric material. This is important because the pyroelectric effect is directly
proportional to the rate of temperature change. The design used was a face-electrode bridge that provides thermal
isolation which minimizes heat loss to the substrate, thereby increasing operation frequency of the pyroelectric device. A
thermal stimulus was applied to the pyroelectric material and the response was measured across the electrodes. A
thermal imaging camera was used to monitor the changes in temperature. Throughout the testing process, the annealing
temperatures, type of layers, and thicknesses were also varied. These changes resulted in improved MEMS designs,
which were fabricated to obtain an optimal design configuration for achieving a high pyroelectric response. A
pyroelectric voltage response of 38.9 mVp-p was measured without filtering, 12.45 mVp-p was measured in the infrared
(IR) region using a Si filter, and 6.38 mVp-p was measured in the short wavelength IR region using a long pass filter. The
results showed that AlN’s pyroelectric properties can be used in detecting applications.
Carbon nanotubes (CNTs) have many unique properties ideal for field emission such as narrow diameters, high aspect
ratios, high temperature stability, good conductivity, and structural strength. A gated array is preferable to a diode type
array due to the lower extraction voltages and reduced screening effects. An inexpensive fabrication process has been
developed using self-assembling nanosphere lithography for sub-micron gate dimensions of a CNT field emission array.
The array fabrication process consists of a silicon wafer with a 20 nm titanium diffusion barrier followed by 10 nm
nickel catalyst layer covered with 1-2 μm of silicon dioxide.
Self-assembling polystyrene spheres are deposited in a
monolayer across the substrate to create the gate mask. The diameter of the spheres is reduced to the desired gate
dimensions using an oxygen plasma ash. The gate metal is then deposited via evaporation. The gate openings are created through
lift-off facilitated by dissolving the polystyrene spheres in an ultrasonic acetone bath. Reactive ion etching is used to remove the silicon dioxide and expose the nickel catalyst layer for CNT synthesis within the gate openings. The process is demonstrated for both 1 μm and 500 nm diameter polystyrene spheres for gate dimensions and gate pitch of 500 nm and 250 nm respectively. The resulting array is analyzed using a scanning electron microscope. Further development of the polystyrene monolayer deposition method is necessary to decrease defects in the monolayer structure. Future work will investigate the reduction of gate dimensions to 20 - 50 nm to facilitate a single CNT per gate array.
Our investigation addresses the modeling, design and fabrication of artificial structures, commonly called metamaterials.
Metamaterials enable electromagnetic properties which do not naturally exist from basic structural symmetry. This
investigation focuses on the modeling, fabrication and testing of metamaterials at terahertz wavelengths. This research
utilizes a foundry fabrication process called PolyMUMPs to construct the metamaterial array. The PolyMUMPS process
is commonly used for MEMS devices and consists of three polysilicon and two silicon dioxide layers. An array of split
ring resonators consisting of the polysilicon and silicon dioxide layers was constructed. The split ring resonators are an
important aspect to the metamaterial because they allow us to take advantage of structural properties such as scaling,
resonant frequency response, and magnetic flux. The metamaterial structure obtains its symmetry from the etching
process used to isolate the individual patterns. The "as-built" figure of merit (FOM) is defined as the ratio of the real
component to the imaginary component of the refractive index. By comparing the analytical and FEM models to identify
key limitations of the FOM structures, this investigation will point out manufacturing limitations that can be adjusted to
improve the FOM. By gaining a higher ratio to the FOM, this improves the overall performance of the metamaterial
structure at the selected wavelength. Through the understanding obtained from the modeling data and actual
manufacturing comparison, changes to key parameters which limit the FOM can lead to metamaterial array
improvements and ultimately to better components suitable for terahertz applications.
Microelectromechanical systems (MEMS) are an important enabling technology for reducing electronic component
geometries and device power consumption. An example of MEMS technology, used in radio frequency (RF) circuits and
systems, is the microswitch. Although the operation of microswitches is relatively simple, they are plagued by poor
reliability - they must operate over 100 billion cycles. Improvements in the mechanical design of the microswitch have
helped to increase their reliability but further improvements are necessary. To accomplish this, research needs to be
conducted on the actual contact surfaces for investigation of the mechanical, thermal and electrical phenomena that
affect reliability. The focus of this paper is the development of a unique high lifecycle test fixture capable of the
simultaneous measurement of contact resistance and contact force. By incorporating a high resonance force sensor, cycle
rates reaching 3kHz will be achieved enabling researchers to conduct a wide range of reliability studies. The fixture will
be isolated from vibrations and will be housed in a dry-box enclosure to minimize contamination. The test fixture will be
automated with control and data acquisition instrumentation to optimize data collection and test repeatability. It is
predicted that this new test fixture will provide the potential for significant work to be done to improve the reliability of
MEMS microswitches. Several tests were conducted using components of the new test fixture. Preliminary results
indicate the feasibility and support the need for the continuing development of this new test fixture.
Physical vapor deposited nickel catalyst layers of 10, 50, 100, 200, 350, and 500 angstroms were granulated using hydrogen plasma for varying times to determine an effective carbon nanotube (CNT) growth process using microwave plasma enhanced CVD (MPECVD). Nickel was deposited via sputtering or evaporation. The catalyst granule size, density, and resulting CNTs were analyzed. Sputtered nickel of 50 angstroms with 5 minutes of hydrogen plasma pretreatment resulted in the most effective CNT growth.
In order to meet the goals of the Department of Defense (DoD) for smaller and more accurate weapons, numerous
projects are currently investigating the miniaturization of weapons and munition fuze components. One of these
efforts is to characterize the performance of small detonators. The velocity of the flyer, the key component
needed to initiate a detonation sequence, can be measured using a photonic Doppler velocimeter (PDV). The
purpose of this research was to develop a microelectromechanical system (MEMS) device that would act as an
optimal retroreflective surface for the PDV. Two MEMS solutions were explored: one using the PolyMUMPsTM
fabrication process and one in-house fabrication design using silicon on insulator (SOI) wafers. The in-house
design consisted of an array of corner reflectors created using an SOI wafer. Each corner reflector consisted of
three separate mirror plates which were self-assembled by photoresist pad hinges. When heated to a critical
temperature (typically 140-160 °C), the photoresist pads melted and the resulting surface tension caused each
mirror to rotate into place. The resulting array of corner reflectors was then coated with a thin layer of gold to
increase reflectivity. Despite the successful assembly of a PolyMUMPsTM corner reflector, assembling an array of
these reflectors was found to be unfeasible. Although the SOI corner reflector design was completed, these devices
were not fabricated in time for testing during this research. However, the bidirectional reflectance distribution
function (BRDF) and optical cross section (OCS) of commercially available retroreflective tapes were measured.
These results can be used as a baseline comparison for future testing of a fabricated SOI corner reflector array.
Coded aperture imaging (CAI) has been used in both the astronomical and medical communities for years due to its
ability to image light at short wavelengths and thus replacing conventional lenses. Where CAI is limited, adaptive coded
aperture imaging (ACAI) can recover what is lost. The use of photonic micro-electro-mechanical-systems (MEMS) for
creating adaptive coded apertures has been gaining momentum since 2007. Successful implementation of micro-shutter
technologies would potentially enable the use of adaptive coded aperture imaging and non-imaging systems in current
and future military surveillance and intelligence programs. In this effort, a prototype of MEMS microshutters has been
designed and fabricated onto a 3 mm x 3 mm square of silicon substrate using the PolyMUMPSTM process. This
prototype is a line-drivable array using thin flaps of polysilicon to cover and uncover an 8 x 8 array of 20 μm apertures.
A characterization of the micro-shutters to include mechanical, electrical and optical properties is provided. This
prototype, its actuation scheme, and other designs for individual microshutters have been modeled and studied for
feasibility purposes. In addition, microshutters fabricated from an Al-Au alloy on a quartz wafer were optically tested
and characterized with a 632 nm HeNe laser.
This paper discusses our investigation into artificial structures called metamaterials. Metamaterials make it
possible to achieve electromagnetic properties not existing in nature. The investigation focuses on the modeling,
fabrication and testing of metamaterials at optical frequencies. The main purpose of this research is to identify a method
to fabricate the artificial structures. We identify limitations in the fabrication process which are used to build the
metamaterials. Measured reflectance data from fabricated devices is then compared with modeled data to identify
limitations affecting the "as-built" figure of merit (FOM). Understanding the parameters which limit the FOM will lead
to device fabrication improvements and ultimately to components suitable for optical applications such as optical
surveillance systems.
This experiment explores the manufacturability of controllable Micro-electromechanical (MEMS) mirrors to direct
optical signals. Design includes four separate mirrors which independently control vertical displacement,
horizontal displacement, vertical pitch and horizontal pitch. Such devices could be used for a variety of applications
but were specifically intended for future use in communications between optical based circuits residing on
separate chips. Prototype devices were built in PolyMUMPs to test the feasibility of this process for applications
such as this, including a full outgoing beam path with mirror orientations and actuation designs to accomplish
this. Several elements of this outgoing beam path were successful and those which needed improvement indicate
a high probability of success with limited trials needed. Improvement recommendations on currently successful
design elements which could still be improved within the scope of PolyMUMPs have been identified. Originally
intended only to direct the outgoing beam, this design could be used on the incoming path as well. Such a
design would ensure that the receiving device only requires a target location and not that a specific incoming
vector be obtained. This would thus comprise all the elements needed for a prototype proof of concept device to
be built. More sophisticated fabrication processes could provide drastic improvements to both transmission and
reception beam paths and potentially allow for a variety of more sophisticated designs to improve compactness,
controllability, tighten tolerances on moving parts, increase mirror quality, and improved productivity of large
quantities of devices.
We investigated the effects of hydrogen pretreatment on nickel catalyst of different thicknesses and deposition
methods on a silicon substrate and how it will affect the growth of carbon nanotubes using microwave plasma
enhanced chemical vapor deposition (MPECVD). Nickel catalyst of 10, 50, 100, 200, 350 and 500 Å thickness
was treated with hydrogen flowing at 135 standard cubic centimeter per minute (sccm), substrate temperature
of 400 °C, microwave power of 400 W, and pressure of 20 torr. The treated catalyst granule size and density was
determined optically through scanning electron microscope (SEM) images and atomic force microscope (AFM)
measurements. We found that sputtered catalyst needs a longer pretreatment than evaporated catalyst. As
expected, the pretreatment time must be increased as the catalyst thickness increases to get granule sizes and
densities favorable for carbon nanotube (CNT) growth. CNT growth took place with a hydrogen flow of 120
sccm, methane flow of 15 sccm, substrate temperature of 650 °C, microwave power of 1000 W and a pressure
of 20 torr. We determined the catalyst can be over treated causing catalyst conglomeration that result in poor
CNT growth.
This paper will investigate a novel thermally actuated micro-shutter design for micro-optical-electro-mechanical system
(MOEMS) applications. The use of actuators in optical systems has improved with new developments in micro-electromechanical
systems (MEMS) designs for use as components in optical systems. Thermal actuators provide a novel
approach to scaling MOEMS to reduce size, weight and power of optical systems. Through the investigation of an
aluminum electro-thermal actuator, we developed an in-house fabrication method which operates at less than one volt to
aid in reducing the size, weight, and power of the optical system. This paper discusses several challenges and
opportunities that may arise from the fabrication of thermally actuated micro-shutter designs which can help improve the
actuator's uniformity, reproducibility, and reliability. In addition, we discuss the characterization of the thermal actuator
micro-shutter to include mechanical, electrical and optical properties. The "switching" speed of the thermal actuator will
also be assessed from a scaling perspective to determine usability.
This paper will investigate micro-shutter developments for IR applications. By demonstrating a interrupter mechanism
MEMS design, we will show how to implement a micro-shutter technology to enable adaptive coded aperture imaging
and non-imaging systems. The use of Photonic MEMS for creating adaptive coded apertures, for surveillance systems,
has been gaining momentum since 2007 1,2. Through the investigation of the interrupter mechanism 3,4, we will
demonstrate a novel approach for IR applications. This paper discusses challenges and opportunities that may arise from
the fabrication of a MEMS interrupter mechanism. We discuss the characterization of the micro-shutter to include
mechanical, electrical and IR properties. The "open and close" speeds of the micro-shutter device will also be assessed
from a scaling perspective to determine usability through modeling and simulation.
This paper will investigate a novel agile-pitch diffraction grating array design and phenomenology, for micro-shutter
Photonic MEMS technologies, to enable adaptive coded aperture imaging and non-imaging systems. The use of Photonic
MEMS for creating adaptive coded apertures, for surveillance systems, has been gaining momentum since 2007 1,2. The
use of the agile-pitch diffraction grating has also been used previously to perform beam-dispersion which is a critical
step in imaging processing 3. Through the investigation of new diffraction grating approaches, we hope to show a
reconfigurable capability for agile beam steering for adaptive coded apertures surveillance imaging and non-imaging
systems. This paper discusses challenges and opportunities that may arise from in-house fabrication of agile-pitch
diffraction grating array micro-shutter designs which may prevent and/or improve structural uniformity, reproducibility,
& reliability. This paper will also discuss characterization of the micro-shutters to include mechanical, electrical and
optical properties. The "open and shut" speeds of the micro-shutter device will also be assessed from a scaling
perspective to determine usability.
This paper will investigate micro-shutter MEMS "fabrication techniques" and processes to identify opportunities and
barriers for successful implementation of micro-shutter technologies to enable adaptive coded aperture imaging and nonimaging
systems. The use of photonic MEMS for creating adaptive coded apertures has been gaining momentum since
2007. Both Industry-based1, 2 and University-based3 studies have demonstrated their unique solutions for implementing
MEMS-based micro-shutter technologies; however, there are many unique and novel MEMS-based "fabrication and
characterization" processes and solutions that will be considered herein as we explore micro-shutter technologies. This
paper discusses challenges and opportunities that may arise from in-house fabrication of MEMS which may prevent
and/or improve structural uniformity, reproducibility, & reliability. This paper will also discuss characterization of the
micro-shutters to include mechanical, electrical and optical properties. The "open and close" speeds of the micro-shutter
device will also be assessed from a scaling perspective to determine usability.
We report the influence of bonding temperature on SU-8 to SU-8 bonding and report fabrication of a hybrid microelectromechanical-tunable filter (MEM-TF) using SU-8 bond pads. We demonstrate use of 2-µm-thick 50×50-µm2 SU-8 bond pads to attach 4.92-µm-thick 250×250-µm2 Al0.4Ga0.6As-GaAs distributed Bragg reflectors (DBR) to polysilicon MUMPs® piston actuators. Advantages of this process include compatibility with hydrofluoric-acid-release chemistry, low-temperature/low-pressure bonding, simple bond-pad photolithography, 57% flip-bonded DBR yield, and 30% electrostatically actuatable hybrid MEM-TF yield.
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