Polymer Waveguide Co-integration with
Microelectromechanical Systems (MEMS) for Integrated
Optical Metrology
K. S. Brown, B. J. Taylor, J. M. Dawson and L. A. Hornak
Microelectronic Systems Research Center
Dept. of Computer Science and Electrical Engineering
West Virginia University
Morgantown, WV 26506-6109
e-mail: lahmsrc. wvu. edu
ABSTRACT
The merging of Microelectromechanical (MEM) devices and optics to create Microoptoelectromechanical
(MOEM) systems provides opportunity to create new devices and to expand the functionality and applications
of MEMS technology. Planar optical waveguide co-integration with surface micromachined (SMM) structures and
inclusion of diffractive optical systems within 3-D MEMS chip stack architectures have the potential to enable integrated optical test, metrology, and state feedback functions for complex MEM systems. This paper presents the
results of research developing a fabrication process for co-integrating polymer optical waveguides with prefabricated
MEMS devices. Multimode air superstrate rectangular optical waveguides have been fabricated using Ultradel optical polyimides over unreleased MEMS dice fabricated using the MultiUser MEMS Process Service (MUMPS) SMM
process. These structures serve as the basic building block for exploration of guided wave integrated optical metrology functions for MEMS. Specially designed "split-comb" linear resonator devices enabling coupling of waveguide
output to the resonator stage for position measurement are one class of a set of prototype vIEMS function MUMPS
testbeds under development for both guidance and evaluation of waveguide and free-space TOM efforts. Recently
initiated work analytically and experimentally evaluating through-wafer free-space micro-optical systems for TOM
will also be outlined.'
Keywords: MEMS, metrology, MOEMS, optical metrology, optical polymers, optical waveguides, polymer waveguides.
1 Introduction
Tntegration of micro-optical, microelectromechanical (MEM) and microelectronic systems offers significant promise
for achieving the microoptoelectromechanical (MOEM) system functionality necessary to meet the performance
needs of a number of emerging display, sensing, communications, and control applications[1}. Merging of micro-
electronics with MEMS via direct integration or hybrid techniques is well established for signal acquisition and
processing{2J . Recent achievement of free-space micro-optical structures in MEMS represent the critical initial
development of a set of basic optical elements from which more complicated micro-optical functions can be constructed. Already, this emerging "tool set" for MEMS system researchers includes an extensive set of bulk and
surface micromachined (SMM) micro-optical components supporting free-space optical beam manipulation such as
integrated scanners, micromirrors arrays, filters, and 3-D micro-optics{3, 4, 5, 6, 7, 8] . Relative to these efforts, the
cointegration of optical waveguide and planar micro-optical components directly with the SMM MEMS environment
1This work is sponsored in part by the NSF, MIPS Division, through a National Young Investigator Award.
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SPIE Vol. 3276. 0277-786X/98/$1O.OO
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Optical Distribution Plane
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Local Sensing Network
(a.)
(h.)
Figure 1: Illustration of Integrated Optical Metrologv (IOM) for MEMS using (a) planar optical waveguide H-tree
global IOVPr distribution with local detection. and (b) folded diffractive optics distribution plane and through—wafer
tralmsmmlission to MEMS devices.
has receive(i significantly less attention. Routine insertion of optical waveguides and planar micro—optical elements
into MEMS components has the potential to
• enable "mixed-mode" MOEM components drawing upon integrated guided wave and free-space functions to
support self contained MOEM systems.
• enable optical I/O to MEMS compatible with fiber ribbon arrays and other emerging advanced optical and
microelectronic packaging.
• enable integrated optics to becone a standard design element and tool for the MEMS systems designer (e.g.
for sensing or feedback control) allowing the routing and distribution of light throughout a MEMS die.
Among the critical areas for which the designers of emerging MEI\IS systems may most benefit from the
availability of a \IE\IS compatible planar vaveguide and micro-optics technology are in the related areas of microstructure metrologv and control. Due to the micron to submicron range of typical MEMS structure movements.
optical techniques have emerged as the dominant approach for achieiving highly accurate positional nieasuremerits
independent of the MEMS structure and its actuation rnechanism[9]. Typically, stroboscopic. amplitude based. or
interferometric optical techniques using canmera. bulk optics. or optical fiber probe setups have been used during
wafer or (lie-level test with a conventional semiconductor device probe station to evaluate and characterize the
impulse response or kinematic behavior of MEMS[1O. 11. 12]. The information yielded by these important techniques has proven essential to the understanding of the detailed behavior of micromechanical structures which is so
necessary for their effective control. \Vhile the open-loop control enabled b the information obtained from external
optical characterization adequately addresses the control needs of a limited set of MEMS applications, as with any
mechanical system. closed-loop feedback control which relies upon continuous accurate knowledge of the state (e.g.
position) of the system provides the highest degree of design flexibility and enables application of basic optimal
control techniques. Continuous "in situ' optical monitoring of the positional state of a MEMS structure decoupled
from the method of actuation using planar integrated optical waveguides and/or micro-optics to deliver and recollect
an optical wavefront which has interacted with the micromechanical structure opens the door to integrated optical
metrologv (TOM) for \IEMS test and control. As complex systems emerge based on large arrays of actuators, the
ability to densely route optical waveguides within the integrated array or micro-optically probe the array over its
area from a plane parallel to a MEMS die wthin a 3-D chip stack offers the opportunity to sense actuator states
and optically feed back this information for local and global array control. Figure 1 illustrates planar waveguide
and free-space diffractive optics approaches for achieving IOM.
113
The implied extensive cointegration of optical waveguide and micro-optical components necessary for MEMS
integrated optical metrology must be achieved in a way which retains the full potential of MEMS and their supporting
microelectronics while at the same time achieving efficient performance of the optical elements when they are placed
in the MEMS environment[13]. The MCNC Multi-User MEMS Process Service (MUMPS) 5MM process represents a
broadly accepted, mature baseline MEMS foundary process with which compatibility must be assured. The issue of
process compatibility facing the cointegration of integrated optics with MEMS strongly parallels the ongoing efforts
which have emerged over the last 10 to 15 years mapping integrated optics for optical interconnections into the
well entrenched and rapidly evolving VLSI and MCM environments[14, 15, 16] . Lessons learned and methodologies,
materials, and processes used in achieving integrated optical interconnects within microelectronic systems offer an
important starting point in the definition of a set of guided wave and planar microoptic processes compatible with
5MM MEMS. The IOM approaches illustrated in Figure 1 reflect the two major thrusts in optical interconnect
R&D, cointegrated optical waveguide and planar diffractive/through-wafer networks. Of most critical importance,
sharing in the learning curve for optical interconnects can in parallel assure compatibility with the microelectronic
environment within which intelligent MEMS must be embedded{17].
This paper describes research recently initiated leveraging the knowledge base developed by the optical interconnect research community to analytically and experimentally explore both polymer guided wave and planar
free-space micro-optical approaches for achieving fully process compatible, integrated optical metrology and state
feedback within MEMS. Current experimental efforts will be described which focus on cointegration of polyimide
multimode waveguides within surface micromachined (5MM) component prototype function testbeds fabricated
using the MCNC MUMPS foundary. In addition, efforts now beginning to analytically and experimentally evaluate through-wafer micro-optical systems within these testbeds for achieving TOM within 3-D chip stack MEMS
architectures will also be discussed.
2 IOM Studies
Prior and ongoing research on optical interconnections within microelectronic systems provides a strong base of
information on optical microelements, optical routing functions, and technologies driven by the need both for
low cost and for compatibility with an existing substrate with microfabricated elements and devices{15]. This
information base is viewed as particularly relevant in the evaluation of the compatibility of technologies and optical
devices for MEMS cointegration. Techniques for the implementation of optical interconnections at low levels of
advanced microelectronic systems such as the chip-to-chip level within multichip modules are particularly relevant
the MEMS applications considered here[16J. Such interconnections have focused on polymer materials[18, 19, 20,
21]. High efficiency, single-mode folded diffractive (holographic) elements on glass plates placed above the MCM
substrate have also been extensively studied for this application, in this case often using inorganic optical element
materials[22]. Both of these approaches have received significant attention by the 01 community due to their
potential to be benignly added to the microelectronic environment, in many cases solely via post processing rather
than by insertion of nonstandard processing steps early in established foundary processes. Based on this knowledge
base, the two technologies of polymer integrated waveguides and diffractive micro-optics were selected as the focus
of this research and serve as the means to achieve and evaluate integrated optical metrology for MEMS. Selection
of these specific technologies provides two strongly complimentary directions to the metrology research allowing
exploration of techniques for monitoring of structures both from within the MEMS plane and perpendicular to
it. Due to the established status of the MUMPS foundary 5MM process at MCNC, and its wide availability and
accessibility to other researchers and MEMS systems developers, this surface micromachining process will serve as
the baseline MEMS technology with which compatibility will be sought.
114
2.1 Polymer Optical Waveguide Cointegration
The key requirements for successful waveguide technology co-integration with MEMS mirror those which have
resulted in emphasis on polymer optics for optical interconnections. Both applications favor waveguide implementation through low-temperature post-processing of nearly completed devices for low cost, acceptable performance,
and compatibility with the VLSI/MCM technologies. Compatibility with MCM substrates shares with the MEMS
compatibility issue the appearance of substantial surface topography, potentially interfering with successful cointegration of the optical elements. Thick planarizing opt:ical films (5 - 1Otm thick) supporting multimode waveguide
fabrication not only reduce the impact of underlying topography, but also facilitate coupling to external multimode
polymer (e.g. Dupont Polyguide) or silica fiber arrays.
Despite the similarities with optical interconnections on MCMs which favor the use of polymers, the far more
aggressive and sensitive surface structures resulting from the micromachining processes used for MEMS impose
distinct challenges and constraints (as well as offering new potential opportunities by using mechanical elements as
part of the optical system) for integrated polymer waveguide and optical element cointegration with MEMS. Issues
of residual topography at the waveguiding layer are a primary representative concern in the 5MM environment. Step
sizes of multiple microns can be present in SMM devices between the last polysilicon or metal layers and the low-stress
nitride in contact with the silicon substrate. For waveguide co-integration with MEMS, the significance of strain in
the optical polymer extends beyond the optical characteristics and adhesion issues of concern in interconnects. The
application, design, and fabrication of optical polymer waveguides and optical elements within MEMS must ensure
their addition is effectively benign from a mechanical standpoint.
2.1.1 Waveguide Fabrication Process
Research has focused on the use of commercially available fiourinated optical polyimides, in combination with
existing inorganic thin films (e.g. oxides, poly) in the SMM environment, to serve as the optical polymer materials
for development of a polymer integrated optical waveguide cointegration process. Emphasis has thus far been on
definition of a fabrication process for multimode rectangular optical waveguides given their status as a generic optical
element with which a variety of amplitude modulation based TOM approaches may be explored. Heavily multimode
guides can achieve dense in-plane waveguide routing using reflecting corners while showing the least sensitivity to
film thickness variations arising from MEMS feature topography during film spin application.
Multimode integrated optical waveguides have been successfully fabricated using the AMOCO family of Ultradel polyimides on both full wafer and individual die substrates. The Ultradel family of polyimides features two
fluorinated polymer formulations, Ultradel 9020 and 9120, for fabrication of polymer guided wave components. At
632 nm, n9o2o 1.5479 and n9120 = 1.5620 enabling Ultradel 9020 and 9120 to serve as the substrate/cladding and
waveguide core, respectively. Figure 2(a) shows the the process flow for fabrication of the air cladding rectangular
optical waveguides shown in Figure 2(b). Prior to spin application of the Ultradel 9020 low index layer which will
serve as the lower substrate optical buffer layer for the waveguide, a series of cleaning and dehydration bake steps and
adhesion promoter is first applied to the substrate. Using a single spin application, a thickness of 4.5 im is typically
used for this 9020 optical buffer layer, although buffer layer thicknesses greater than 5 ,um are readily obtainable
with multiple spin applications. Adjustment of this layer thickness necessary for vertical alignment of waveguiding
structures with microstructures is readily achievable via the spin application process. Following softbake, the sample
is then exposed with G-line UV radiation through a bead removal mask and the bead region on the edge of the wafer
or die removed during spray development. This step assures good mask-film contact and enhances the quality of the
pattern transfer in the 9120 polyimide during its subsequent exposure which will define the rectangular waveguiding
regions. After hardbake of the substrate 9020 polyimide layer, the Ultradel 9120 polymer is spun on and softbaked.
A waveguiding layer thickness of 2 ,am has thus far been used although a range of thicknesses are obtainable similar
to the 9010 material. The 9120 layer is then patterned with a G-line UV exposure and subsequent spin development
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Sample Prep
Dehydration Bake
Adhesion Promoter Application
Si or MUMPS nitride
or PSG substrate
Spincast Ultradel 9020 Polyimide
Softbake, Expose Bead Mask,
Develop, Hardbake
4.5 Rm
4'
optical buffer layer (9020)
substrate
Spincast Ultradel 9120 Polyimide
Softbake, Expose Waveguide Mask
Develop, Hardbake
2
I
core
I
waveguide core layer (9120)
optical buffer layer (9020)
(b)
substrate
(a)
Figure 2: Polyimide air superstrate optical waveguide fabrication process.
to form the high index waveguiding layer. The process is completed with a final hardbake. Waveguides have been
fabricated and tested at 632 nm over a variety of widths from 5 m guides to 100 m. Figure 2(b) shows arrays of
5
waveguides on 20 jim centers fabricated on a featureless silicon wafer.
As indicated in Figure 4 discussed below, the process described above has been used to successfully fabricate
multimode waveguide IOM I/O structures over unreleased SMM split comb MEMS devices on MUMPS dice. These
initial studies have not yet attempted to functionally combine the waveguides with the MEMS buthave established
the ability to post process MUMPs die and combine with them the polymer waveguide process established for
featureless wafers. Issues which remain for this prerelease waveguide cointegration approach is adaptation of the
wet etch release process to assure microstructure release without significant undercutting of the waveguiding layer. A
second cointegration approach under investigation features initiation of the polyimide waveguide fabrication process
directly on the MUMPS nitride layer after a selective area PSG reactive ion etch to establish the region in which
the waveguiding structure will be placed followed by a standard HF release.
The process shown in Figure 2(a) can serve as a foundation from which other waveguide geometries appropriate
to specific IOM implementations can be realized including ridge, buried ridge, and buried rectangular guides[13.
The air superstrate rectangular waveguide process described above, with the addition of a final spuncast 9010 layer
to serve as a superstrate cladding for the waveguide, will yield a buried rectangular guide geometry capable of
supporting single mode operation given correct choice of optical waveguide crossection dimensions. Single mode
waveguides, while posing a microfabrication challenge in the topographic MEMS environment, offer the potential
m
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MEM Structure
transmission
Polv
nitride
AR film
A
probe
A.
.jIA'
beamretu beam
polished die hack
MEMS Device Plane
I
MEMS die
diffractive elements
on die back
to Optics Plane
optical input
optical output
Figure 3: Through—wafer optical architecture supporting IOM.
to realize phase sensitive. interferometric TOM. To date. single mode vaveguides have not been explored as a part
of this work in favor of free-space diffractive optical approaches for achieving interferometric TOM discussed below.
2.2
Diffractive Optics Processing/Packaging for IOM
As illustrated in Figure 1. the diffractive optics approaches to TOM borrowed from optical interconnect research are
nonintrusive to the plane of the MEMS structures in the same way that optical interconnects implemented with
diffractive micro—optics are benign to the microelectronic circuit planes with winch they communicate. However.
while diffractive optical approaches achieve this necessary system constraint, they strongly impact the integrated
microsvsteni postprocessing and packaging. necessitating 3-D die or wafer stacks, wafer/die backside processing.
and increased assembly aligmunent precision. Therefore, while fabrication processes for realization of the necessary
(liffractive optical elements is clearly needed. the focus of experimental efforts now being initiated will naturally lay
with the configuration of elements and planes necessary to construct a micro—optical s stem to aclueve the desired
IO\l function.
2.2.1 Through-Wafer Micro-Optical Systems
Emphasis in this research is on the T/O stage of the micro-optical systems from which the optical beam is launched
towards and collected from the MEMS component for IOM. Systems divide into two major catagories. those from
which the incident light is distributed and incident upon the structure to be sensed from above the MEMS plane
and those which probe the MEMS plane from beneath it via transmission through the MEMS silicon substrate
(Figure 1(h)). Both these micro-optical systems have their foundation in folded and 3-D diffractive optical interconnect ions for achieving massively parallel vertical connectivity between planes of microelectronics. The outcome of
this research establishing TOM based on these approaches within prototype function testbeds described below lays
the groundwork for establishing the ability to individually poll the positional state of large arrays of MEM structures without perturbing either the MEMS array or the medium which the MEMS sense or actuate. Through-wafer
techniques arc especially interesting for this reason and are receiving primary attention in this work. \Vhen optical
wavelengths beyond the band edge of silicon (1.1im wavelength or longer) are used. the silicon wafer is essentially
transparemmt enabling transmission directly through the silicon. Using diffractive optical elements either on separate
substrates beneath or aligned on the back of the target wafer, optical radiation can be focused through the target
wafer to points on its top side as illustrated in Figure 1(b). This technique was first proposed and experimentally
evaluated for optical interconnects in 3-D wafer-level svstems[23. 24. 25]. Figure 3 illustrates the approach for
monitoring the state of a microstructure on the upper surface of a die with an optical probe beam incident from
beneath the die.
Among the issues arising from this approach are the reflection loss incurred as a result of the large index
difference between air and silicon/polysilicon (n = 3.45 at 1.3im) and the need for use of back side polished wafers.
For the MEMS testbeds summarized below to be used in diffractive optical IOM evaluations, unreleased MUMPS
die will have their backs chemomechanically polished. The nitride layer, which is an integral part of the MUMPS
process, serves as a near optimal antireflection coating on the device side of the transmission path at a wavelength
of 1.3im for Si. This large index difference between air and polysilicon will prove beneficial for collection of a return
signal from poly members. Design alteration to the MEMS will be kept to a minimum but necessarily include
transmission windows in the poly ground plane for through-wafer TOM and potentially polishing of the final poly
layer prior to structural release as well as additional metallization for reflectivity enhancement.
2.2.2 Diffractive Elements
Elements will predominantly be designed and fabricated as binary, single level phase gratings with multiple phase
gratings used only on an as-needed basis. The relative simplicity of binary elements is favored over the increased
complexity and optical efficiency of multilevel phase gratings (which require a two mask process with multiple phase
film etch steps) given the focus of this research on the initial definition of TOM micro-optical systems. Subsequent
in-depth development of TOM systems resulting from this research may appropriately draw more extensively on
optimal, higher efficiency diffractive components. Microelements apart from the MEMS die will be fabricated
on transparent glass substrates directly in the glass substrate surface using standard microlithographic methods.
Elements fabricated on the MEMS die will draw upon the photodefined polyimide microstructures discussed above
to form diffractive elements, such as fresnel phase plates, on the back of unreleased MEMS die which will be
chemomechanically polished after being received back from MUMPS. These elements will be used to evaluate the
suitability for through-wafer optical techniques for potentially massively parallel TOM originating from micro-optical
transmission beneath the active MEMS plane surface.
3 IOM Prototype Function Testbeds
Using well established MEMS structures as representative device testbeds, the cointegrated polymer waveguide
processes and diffractive optical approaches described above will be used to establish guided-wave structures and
micro-optical systems for achieving TOM functions. These testbeds also serve the important role of providing
both guidance and evaluation of optical polymer processes and diffractive optical system design and development.
Intensity modulation based positional encoding will be favored for its simplicity, using existing and/or additional
patterned MEMS features to provide intensity modulation of optical signals delivered to and sensed from the
structure by either integrated waveguides or diffractive optics. Significantly more complex coherent techniques
utilizing interference to obtain high precision positional accuracy will primarily be explored in the prototype function
testbeds using diffractive optical systems. MEMS structures to be used as TOM testbeds and the metrology issues
to be explored using them include the following.
.
Drive Linear Motion Testbed Linear comb resonators are among the best established and most used
5MM devices. Figure 4(a) shows a split comb drive design which is among the structures under study for
linear comb resonator guided wave TOM. The split comb allows the placement of an optical waveguide near the
translational stage. The multimode waveguide design shown in Figure 4(a) utilizes a polymer substrate layer
and relies upon variation in the reflected power coupled back into the waveguide input which is subsequently
split and collected at the output. Figure 4(b) shows an unreleased split comb device fabricated using MUMPS.
Comb
The linear comb device shown is one of a set of split comb devices on the die with a range of resonant frequencies
and split comb gaps for waveguide placement. The polyimide multimode waveguide T/O structure shown is
fabricated using the process shown in Figure 2 directly over the unreleased PSG layers. The input and
output branches are 12 ,um which merge through reflecting corners to the center waveguide which is 24 pm
118
optical
input
PSGor
anchored
I
poly
comb
I_______________
nitride
Li
multimode
wave2uide
V
V
\ patterned
polymer
substrate
layer
V
optical
output
anchored
poly
comb
(a.)
I
actuated
poiv plate
(b.)
.0
1
(c.)
gear
patterned polymer
substrate layer
Figure 4: Integrated Optical Metrology (TOM) testbeds. Split comb linear motion testbed with multimode polymer
waveguides (a). Polvimide waveguides fabricated on an unreleased split comb linear resonator (b). Planar wavguide
IOM within rotational testbed (c).
in width. As discussed above. waveguide cointegration studies currently focus on wet etch or prepolvmer
process selective area PSG etch techniques to achieve device release and complete waveguide cointegration.
Critical areas for evaluation using this IOM testbed include the placement constraints on waveguide layout
given MEMS topology, the influence of waveguide endface profile control, the reflectivity of the poly member
arid resulting return signal to noise ratio, and the ability to sense and distinguish undesirable (e.g. torsional)
modes. The vertical probing of linear comb devices enabled by diffractive optics may be especially effective in
this regard.
As illustrated in Figure 3. an offset through-wafer probe of a MEMS structure through a transmission window
in the pol 0 ground plane can also potentially be used for TOM of translational motion. Probe beam placement
near the translating stage edge may be used for simple chopper modulation of the return beam by lateral stage
motion. Rotational motion of the stage which changes the gap in the optical cavity formed between the poly
stage and nitride window can provide an effective means to coherently measure such motion in this structure
where it is undesired as well as other devices in which it is sought (i.e. torsional mirrors). A central issue to
119
be resolved experimentally for this coherent metrology approach is the optical quality of the underside of the
poly layers. In contrast to the top side of poly which requires polishing for optical flatness, the expectation
is that the initial nucleation surface of the poly on the deposited oxide may more closely approximate a more
optically flat surface.
.
Torsional/Vertical Motion Testbed Electrostatically deflected surfaces capable of undergoing a torsional rotation or purely vertical deflection from the surface of the MEMS wafer have already been employed in a number
of applications including digital video displays and phase conformable adaptive optical surfaces. The primary
focus of this functional testbed will be evaluation of through-wafer free-space interferometric approaches for
TOM of this class of stuctures. In adaptive optics applications, phase changes in the wavefront reflected from
the top surface of a MEMS array offer feedback through the optical system of the positional state of the microdeflector array. Application of this same principle through the substrate of the MEMS using through-wafer
propagation offers a means to obtain positional information on the state of large MEMS arrays in nonoptical
applications. Testbeds will utilize electrostatically deflected plates actuated about a torsional member and
vertical deflection achieved through stretching of suspended serpentine springs. Critical issues parallel those
detailed above for coherent sensing of nonideal modes in linear actuators.
.
Gear/Motor Rotary Motion Testbeds Rotary structures in electrostatic motors or microgear and microturbine
elements such as those found in electrostatic engines or micropumps represent another fundamental set of
MEMS elements. Optical metrology studies completed using bulk optical techniques have firmly established
the need for feedback of the rotational state of these elements and have suggested the merit of integrated
approaches such as shown in Figure 4(d)[1O}. Figure 4(c) shows a gear with waveguide input and outputs
positioned so as to give two output signals in quadrature as suggested in [10]. This approach is representative
of the set of guided wave rotational TOM techniques which will be evaluated. Diffractive free-space IOM
within the rotary testbeds, such as a gear encoder using a similar through-wafer configuration to that shown
in Figure 3, will explore both amplitude-based and coherent approaches similar to those described for the linear
comb above. Testbed MEMS will include established gear and electrostatic motor designs. Critical areas for
testbed evaluation for the TOM of rotational motion are rotational state determination and the ability to
identify nonideal behavior (e.g. sup, wobble, etc.).
3.1 Testbed Evaluations of IOM for MEMS Control
A primary goal of the testbed work is to provide a foundation for studies evaluating the role of TOM in MEMS control.
For a subset of the MEMS testbeds for which cointegrated guided wave and free-space micro-optical approaches have
been determined to yield adequate system state information, a simple feedback control system will be implemented
to demonstrate TOM application to MEMS control. Following the completion of basic MEMS system identification,
a control system will be designed and implemented through use of an optical detection, control, and actuation circuit
external to the MEMS testbed die. This control testbed will use the same test setup employed in the collection of
optical metrology data from the integrated optical system while driving the MEMS structure.
3.2 Summary
Research recently initiated leveraging advances in optical polymer waveguides and diffractive optics driven by optical
interconnection and packaging research to realize techniques for Tntegrated Optical Metrology (TOM) within MEMS
has been presented. Efforts focusing on achieving and evaluating TOM within prototype MEMS function testbeds
using planar polymer optical waveguide co-integration with surface micromachined structures and through-wafer
diffractive optical systems within 3-D MEMS chip stack architectures were outlined. Development of a fabrication
process for co-integration of polyimide multimode air superstrate rectangular optical waveguides with unreleased
120
MEMS dice fabricated using the MUMPS surface micromachining process were also detailed. While the optical
metrology application is serving to drive and focus research efforts within specific MEMS prototype function testbeds,
in a larger sense, the research's impact extends to all MEMS applications for which guided wave and planar microoptics hold potential. This research seeks not only the specific goal of realizing MEMS integrated optical metrology
through successful cointegration of polymer waveguides and planar free-space micro-optics within the MEMS 5MM
environment, but also the broader goal of establishing these, as well as a richer set of integrated optical technologies
as part of the growing toolset of micro-optical components available to MEMS researchers and systems designers.
4 References
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(1995).
[13] Hornak, "Polymer Integrated Optics: Enabling technology for Micro-Electro-Mechanical Systems," in Proc
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{ 14j Goodman, Leonberger, Kung and Athale, "Optical interconnection for VLSI systems," Proc. IEEE, vol. 72,
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[15] Tewksbury and Hornak, "Optical clock distribution in electronic systems," Journal of VLSI Signal Processing,
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121
[16 Tewksbury and Hornak, "Multichip Modules: A platform for optical interconnections within microelectronic
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