Based on the micro-electronics fabrication process, Micro-Opto-Electro-Mechanical Systems (MOEMS) are under study in order to be integrated in next-generation astronomical instruments for ground-based and space telescopes. Their main advantages are their compactness, scalability, specific task customization using elementary building blocks, and remote control. At Laboratoire d’Astrophysique de Marseille, we are engaged since several years in the design, realization and characterization of programmable slit masks for multi-object spectroscopy and micro-deformable mirrors for wavefront correction. First prototypes have been developed and show results matching with the requirements.
A System-in-Package (SiP) concept for the 3D-integration of a Single Wall Carbon Nanotube (SWCNT) resonator with its CMOS driving electronics is presented. The key element of this advanced SiP is the monolithic 3D-integration of the MEMS with the CMOS electronics using Through Silicon Vias (TSVs) on an SOI wafer. This SiP includes: A glass cap vacuum-sealed to the main wafer using an eutectic bonding process: a low leak rate of 2.7 10-9 mbar•l/s was obtained; Platinum-TSVs, compatible with the SWCNT growth and release process; The TSVs were developed in a “via first” process and characterized at high-temperature — up to 850 °C. An ohmic contact between the Pt-metallization and the SOI silicon device layer was obtained; The driving CMOS electronic device is assembled to the MEMS using an Au stud bump technology. Keywords: System-in-Package (SiP), vacuum packaging, eutectic bonding, “via-first” TSVs, high-temperature platinum interconnects, ohmic contacts, Au-stud bumps assembly, CMOS electronics.
With the rising need for microfabricated chip-scale atomic clocks to enable high precision timekeeping in portable applications, there has been active interest in developing miniature (<few cm3), chip-scale alkali vapor lamps, since vapor plasma discharge sources are currently the standard for optical pumping in double-resonance clocks. We reported in 2012 a first microfabricated chip-scale Rubidium dielectric barrier discharge lamp. The device’s preliminary results indicated its high potential for optical pumping applications and wafer-scale batch fabrication. The chip-scale plasma light sources were observed to be robust with no obvious performance change after thousands of plasma ignitions, and with no electrode erosion from plasma discharges since the electrodes are external. However, as atomic clocks have strict lamp performance requirements including less than 0.1% sub-second optical power fluctuations, power consumption less than 20 mW and a device lifetime of at least several years, it is important to understand the long-term reliability of these Rb planar mini-lamps, and identify the operating conditions where these devices can be most reliable and stable. In this paper, we report on the reliability of such microfabricated lamps including a continuous several month run of the lamp where the optical power, electrical power consumption and temperature stability were continuously monitored. We also report on the effects of temperature, rf-power and the lamp-drive parasitics on the optical power stability and discuss steps that could be taken to further improve the device’s performance and reliability.
Multi-object spectroscopy (MOS) is a powerful tool for space and ground-based telescopes for the study of the formation
and evolution of galaxies. This technique requires a programmable slit mask for astronomical object selection.
We are engaged in a European development of micromirror arrays (MMA) for generating reflective slit masks in future
MOS, called MIRA. The 100 x 200 μm2 micromirrors are electrostatically tilted providing a precise angle. The main
requirements are cryogenic environment capabilities, precise and uniform tilt angle over the whole device, uniformity of
the mirror voltage-tilt hysteresis and a low mirror deformation.
A first MMA with single-crystal silicon micromirrors was successfully designed, fabricated and tested. A new generation
of micromirror arrays composed of 2048 micromirrors (32 x 64) and modelled for individual addressing were fabricated
using fusion and eutectic wafer-level bonding. These micromirrors without coating show a peak-to-valley deformation
less than 10 nm, a tilt angle of 24° for an actuation voltage of 130 V. Individual addressing capability of each mirror has
been demonstrated using a line-column algorithm based on an optimized voltage-tilt hysteresis. Devices are currently
packaged, wire-bonded and integrated to a dedicated electronics to demonstrate the individual actuation of all
micromirrors on an array. An operational test of this large array with gold coated mirrors has been done at cryogenic
temperature (162 K): the micromirrors were actuated successfully before, during and after the cryogenic experiment. The
micromirror surface deformation was measured at cryo and is below 30 nm peak-to-valley.
A novel technology is presented for arrays of vertical flaps as optically modulating elements which are actuated
electrostatically to horizontal position at low voltages of 30-50V. One application is a reflective display exhibiting
a contrast ratio of 1:95. We will also show a) shutters for transmissive devices in an array configuration and
b) switchable gratings. A large variety of flap geometries are fabricated such as flat reflective, grating, lens or
grid shape. Poly-Si refill of thin high aspect-ratio trenches followed of dry etching of the surrounding material is
used to fabricate the flaps suspended by torsion beams.
We show a laser beam shaping device made of a deformable continuous reflective membrane fabricated over a scanning
stage. The combination of two actuator schemes enables shaping and smoothing of a laser beam with a unique compact
device. It is designed to shape an input laser beam into a flat top or Gaussian intensity profile, to support high optical load
and to potentially reduce speckle contrast. One single electrode is needed to deform the whole membrane into multiple
sub-reflecting concave elements. The scanning stage is used simultaneously to smooth out the remaining interference
patterns. The fabrication process is based on SOI wafer and parylene refilling to enable the fabrication of a 100 % fill
factor 5 by 5 mm2 deformable membrane. Applications for such device are laser machining and laser display.
Multi-object spectroscopy (MOS) allows measuring infrared spectra of faint astronomical objects that provides
information on the evolution of the Universe. MOS requires a slit mask for object selection at the focal plane of the
telescope. We are developing MEMS-based programmable reflective slit masks composed of 2048 individually
addressable micromirrors. Each micromirror measures 100 × 200 μm2 and is electrostatically tilted by a precise angle of
at least 20°. The main requirements for these arrays are precise and uniform tilt angle over the whole device, uniformity
of the mirror electromechanical behavior, a flat mirror deformation and individual addressing capability of each mirror.
This capability of our array is achieved using a line-column algorithm based on an optimized tilt angle/voltage hysteresis
of the electrostatic actuator.
Micromirror arrays composed of 2048 micromirrors (32 × 64) and modeled for individual addressing were fabricated
using fusion and eutectic wafer-level bonding. These micromirrors without coating demonstrated a peak-to-valley
deformation less than 8 nm and a tilt angle of 24° for an actuation voltage of 130 V. A first experiment of the linecolumn
algorithm was demonstrated by actuating individually 2 × 2 micromirrors.
In order, to avoid spoiling of the optical source by the thermal emission of the instrument, the micromirror array has to
work in a cryogenic environment. Therefore, these devices were characterized in a cryogenic environment at -111°C and
several lines of micromirrors were tilted successfully under these conditions.
We report on the advances towards the design and fabrication of a system consisting of two 10mm mirrors, one actuated magnetically and the other electrostatically. The system will be used for beam steering. The maximum resonant frequencies and deflection angle of each of the actuators will be reviewed and compared.
Shaping light with microtechnology components has been possible for many years. The Texas Instruments digital
micromirror device (DMD) and all types of adaptive optics systems are very sophisticated tools, well established and
widely used. Here we present, however, two very dedicated systems, where one is an extremely simple MEMS-based
tunable diffuser, while the second device is complex micromirror array with new capabilities for femtosecond laser pulse
shaping. Showing the two systems right next to each other demonstrates the vast options and versatility of MOEMS for
shaping light in the space and time domain.
A new kind of MEMS reflective display is being developed having high contrast and reflectivity, better than on printed
paper. The system is based on novel vertical flaps, which can be electrostatically turned by 90° to horizontal position.
After fabrication, the poly-silicon flaps are vertical to the wafer surface and on the top suspended by torsion beams. In
this state the pixel is black, incoming ambient light passes by the flaps and is absorbed by an underlying absorptive layer.
When the flaps are turned to horizontal position light is reflected back and the pixel gets white. A self-aligning four
masks bulk microfabrication process is employed, which uses poly-silicon filling of high aspect-ratio cavities. Parylene
was also employed as flap material. Thanks to auto stress-compensation the flaps are not deformed due to intrinsic
stresses. Low actuation voltages down to 20V can be achieved.
Multi-object spectroscopy is a powerful tool for space and ground-based telescopes for the study of the formation of
galaxies. This technique requires a programmable slit mask for astronomical object selection. We are developing
MEMS-based programmable reflective slit masks for multi-object spectroscopy that consist of micromirror arrays on
which each micromirror of size 100 x 200 μm2 is electrostatically tilted providing a precise angle. The main requirements
for these arrays are cryogenic environment capabilities, precise and uniform tilt angle over the whole device, uniformity
of the mirror voltage-tilt hysteresis and a low mirror deformation. A first generation of MEMS-based programmable
reflective slit masks composed of 5 x 5 micromirrors was tested in cryogenic conditions at 92 K. Then, first prototypes of
large arrays were microfabricated and characterized, but the reliability of these arrays had to be improved. To increase
the reliability of these devices, a third generation of micromirror arrays composed of 64 x 32 micromirrors is under
development. This generation was especially designed for individual actuation of each mirror, applying a line-column
algorithm based on the voltage-tilt hysteresis of the actuator. The fabrication process was optimized and is now based on
multiple wafer level bonding steps. Microfabricated devices have micromirror with a peak-to-valley deformation less
than 3 nm. The mirrors can be tilted at 20° by an actuation voltage lower than 100 V. First experiments showed that our
micromirrors are well suited for the line-column addressing of each micromirror.
An all polymeric colorimetric gas sensor with its associated electronics for ammonia (NH3) detection targeting low-cost
and low-power applications is presented. The gas sensitive layer was inkjet printed on a plastic foil. The use of the foil
directly as optical waveguide simplified the fabrication, made the device more cost effective and compatible with large
scale fabrication techniques, such as roll to roll processes. Concentrations of 500 ppb of NH3 in nitrogen with 50% of RH
were measured with a power consumption of about 868 μW in an optical pulsed mode of operation. Such sensors foresee
applications in the field of wireless systems, for environmental and safety monitoring.
The fabrication of the planar sensor was based on low temperature processing. The waveguide was made of PEN or PET
foil and covered with an ammonia sensitive layer deposited by inkjet printing, which offered a proper and localized
deposition of the film. The influence of the substrate temperature and its surface pretreatment were investigated to
achieve the optimum deposition parameters for the printed fluid. To improve the light coupling from the light source
(LED) to the detectors (photodiodes), polymeric micro-mirrors were patterned in an epoxy resin.
With the printing of the colorimetric film and additive patterning of polymeric micro-mirrors on plastic foil, a major step
was achieved towards the implementation of full plastic selective gas sensors. The combination with printed OLED and
PPD would further lead to an integrated all polymeric optical transducer on plastic foil fully compatible with printed
electronics processes.
We are developing MEMS-based programmable reflective slit masks for future generation infrared multi-object
spectroscopy (MOS) for space and ground-based telescopes. These devices are composed of monocrystalline silicon
micromirrors of size 200 × 100 um2 which can be tilted by electrostatic actuation yielding a tilt-angle of 20°. An
electromechanical clamping mechanism has been demonstrated providing uniform tilt-angle within one arc minute
precision over the whole array (5 × 5 micromirrors). Slit masks of different sizes have been produced; the largest one
measures 25 × 22 mm2 and is composed of 20'000 micromirrors. Thanks to the architecture and the fabrication process
of these slit masks; the micromirror peak-to-valley deformation (PTV) is uniform over the device and was measured
being below 10 nm for uncoated micromirror. A slit mask of size 5 × 5 micromirrors was successfully tested in cryogenic
conditions at 92 K; the micromirrors were actuated before, during and after the cryogenic experiment. To achieve for the
large arrays a better fabrication yield and a higher reliability, the architecture, the process flow, the assembly and the
electronics are being optimized. Optical characterizations as well as experiments of the large devices are underway.
We present our evaluation of a compact laser system made of a 795 nm VCSEL locked to the Rubidium absorption line
of a micro-fabricated absorption cell. The spectrum of the VCSEL was characterised, including its RIN, FM noise and
line-width. We optimised the signal-to-noise ratio and determined the frequency shifts versus the cell temperature and
the incident optical power. The frequency stability of the laser (Allan deviation) was measured using a high-resolution
wavemeter and an ECDL-based reference. Our results show that a fractional instability of ≤ 10-9 may be reached at any
timescale between 1 and 100'000 s. The MEMS cell was realised by dispensing the Rubidium in a glass-Silicon preform
which was then, sealed by anodic bonding. The overall thickness of the reference cell is 1.5 mm. No buffer gas was
added. The potential applications of this compact and low-consumption system range from optical interferometers to
basic laser spectroscopy. It is particularly attractive for mobile and space instruments where stable and accurate
wavelength references are needed.
We present a dynamic laser beam shaper based on MEMS technology. We show a prototype of a dynamic diffuser made
of single crystal silicon. A linearly deformable silicon micromembrane is used to diffuse a laser beam in one dimension.
Resonance frequencies of the membrane can range from 1 kHz to 20 kHz. Mode shapes of the deformable mirror are
excited using magnetic actuation. Diffusing angle can be tuned by adjusting the driving current in the membrane. We
measured a diffusing angle of 1° for an applied current of 40 mA. The aluminum coated mirror can handle 140 W/cm2 of
visible to infrared optical power. Application to smooth out interference pattern generated by a static diffuser is shown.
We show the first results of a linear 100-micromirror array capable of modulating the phase and amplitude of the spectral
components of femtosecond lasers. Using MEMS-based reflective systems has the advantage of utilizing coatings tailored
to the laser wavelength range. The innovative features of our device include a novel rotational, vertical comb-drive actuator
and an X-shaped, laterally reinforced spring that prevents lateral snap-in while providing flexibility in the two degrees of
freedom of each mirror, namely piston and tilt. The packaging utilizes high-density fine-pitch wire-bonding for on-chip
and chip-to-PCB connectivity. For the first deployment, UV-shaped pulses will be produced to coherently control the
dynamics of biomolecules.
Multi-object spectroscopy (MOS) is a powerful tool for space and ground-based telescopes for studying the formation of
galaxies. This technique requires a programmable slit mask for astronomical object selection. A first sample of MEMS-based
programmable reflective slit masks with elements of size 200×100 μm2 has been successfully tested in cryogenic
conditions at 92 K. Devices of larger size were microfabricated, the largest chip measures 25×22 mm2 and is composed
of 200×100 electrostatic actuated micromirrors. These devices are composed of two chips: the electrode chip and the
mirror chip, which are processed separately and assembled consecutively. The mirror chip is bonded on top of the
electrode chip and microfabricated pillars on the electrode chip provide the necessary spacing between the two parts. A
process flow utilizing refilling techniques based on borophosphosilicate glass (BPSG) deposition and reflow was
developed. Programmable reflective slit masks based on this fabrication process were microfabricated and characterized.
These devices exhibit a micromirror deformation of 11 nm peak-to-valley and an actuation voltage of 145 V for a tilt
angle of 9°. Preparation of samples for MOS experiments are underway.
We present a dynamic laser beam shaper based on MEMS technology. We show a prototype of a dynamic diffuser made
of single crystal silicon. A linearly deformable silicon micromembrane is used to diffuse a laser beam in one dimension.
Resonance frequencies of the membrane can range from 1 kHz to 100 kHz. Diffusing angle can be tuned by adjusting the
driving voltage. We measured a diffusing angle of 0.16° for an actuation voltage of 20 V.
Next-generation infra-red astronomical instrumentation for space and ground-based telescopes requires MOEMS-based
programmable slit masks for multi-object spectroscopy (MOS) which has to work in cryogenic environment. A first
prototype of micromirror arrays (MMA) of 5×5 single-crystal silicon micromirrors was successfully designed,
fabricated and tested. 100×200 μm2 micromirrors can be tilted by electrostatic actuation yielding 20° mechanical tiltangle.
The MMA were successfully actuated before, during and after cryogenic cooling, below 100 K. A MMA is
composed of two different chips fabricated on silicon on insulator (SOI) wafers: the mirror chip and the electrode chip.
The array was obtained by assembling these two chips. For the assembly step of large array (100×200 micromirrors) we
needed high precision alignment as well as the suppression of manual handling. Therefore we developed a technique of
assembly for such devices and we designed and fabricated a dedicated XYZ tip/tilt stage. This stage allows aligning the
electrodes towards the micromirrors with a micrometer precision. Large MMA of 100×200 micromirrors, measuring
22 mm×25 mm, for large field of view were microfabricated and assembled using the above setup. No additional
deformations were observed due to the assembly step. The peak to valley (PTV) deformation of the micromirrors was
found to be 14 nm PTV. The first actuation tests were carried out.
We are developing a linear array of micromirrors designed for optical, femtosecond laser pulse shaping. It is a bulkmicromachined
device, capable of retarding or diminishing certain laser frequencies in order to perform phase and amplitude modulation within a frequency band spanning the UV to the near-infrared. The design consists of a linear array of mirrors fixed on either side by springs. They feature two degrees of freedom: Out-of-plane motion for phase shifting and
rotational motion for binary amplitude modulation, both realized using vertical comb drives. The first applications will include femtosecond discrimination experiments on biomolecules.
We are developing single-crystalline silicon micromirror arrays (MMA) for future generation infrared multiobject
spectroscopy (IR MOS). The micromirrors are 100μm × 200μm in size and can be tilted by electrostatic actuation
yielding a tilt-angle of 20°. Arrays of 5x5 micromirrors were gold-coated and tested at below 100K. The coated and
uncoated micromirrors are optically flat (peak-to-valley deformation < λ/20 for λ > 1μm) at room temperature
and in cryogenic environment. Successful actuation has been done at room temperature and at temperatures
below 100K. Large arrays of 200x100 micromirrors are being fabricated and an actuation scheme for extremely
large arrays has been developed.
We report on micromirror arrays being developed for use as
reflective slit masks in multiobject spectrographs for astronomical applications.
The micromirrors are etched in bulk single crystal silicon,
whereas cantilever-type suspension is realized by surface micromachining.
One micromirror element is 100200 m in size. A system of multiple
landing beams is developed, which electrostatically clamps the mirror
at a well-defined tilt angle when actuated. The mechanical tilt angle
obtained is 20 deg at a pull-in voltage of 90 V. Measurements with an
optical profiler show that the tilt angle of the actuated mirror is stable with
a precision of one arc minute over a range of 15 V. This electrostatic
clamping system provides uniform tilt angle over the whole array: the
maximum deviation measured between any two mirrors is as low as one
arc minute. The surface quality of the mirrors in the actuated state is
better than 10 nm peak-to-valley and the local roughness is around 1-nm
rms. Cryogenic testing shows that the micromirror device is functional at
temperatures below 100 K.
Next generation of infra-red astronomical instrumentation for space telescopes as well as ground-based extremely large
telescopes requires MOEMS devices with remote control capability and cryogenic operation, including programmable
multi-slit masks for multi-object spectroscopy (MOS).
For the complete testing of these devices, we have developed in parallel and coupled a high-resolution Twyman-Green
interferometer and a cryogenic-chamber for full surface and operation characterization. The interferometer exhibits a
nanometer accuracy by using phase-shifting technique and low-coherence source. The cryogenic-chamber has a
pressure as low as 10e-6 mbar and is able to cool down to 60K. Specific interfaces minimizing stresses for vacuum and
cryo have been set.
Within the framework of the European program on Smart Focal Planes, micro-mirrors have been selected for generating
MOEMS-based slit masks. A first 5×5 micro-mirror array (MMA) with 100×200μm2 mirrors was successfully
fabricated using a combination of bulk and surface silicon micromachining. They show a mechanical tilting angle of
20° at a driving voltage below 100V, with excellent surface quality and uniform tilt-angle. The mirrors could be
successfully actuated before, during and after cryogenic cooling. The surface quality of the gold coated micro-mirrors at
room temperature and below 100K, when they are actuated, shows a slight increase of the deformation from 35nm
peak-to-valley to 50nm peak-to-valley, due to CTE mismatch between silicon and gold layer. This small deformation is
still well within the requirement for MOS application.
Refractive, diffractive and reflective micro-optical elements for laser beam shaping and homogenizing have been manufactured and tested. The presented multifunctional optical elements are used for shaping arbitrary laser beam profiles into a variety of geometries like, a homogeneous spot array or line pattern, a laser light sheet or flat-top intensity profiles. The resulting profiles are strongly influenced by the beam properties of the laser and by diffraction and interference effects at the micro-optical elements. We present general design rules for beam shaping and homogenizing. We demonstrate the application of such multifunctional micro-optical elements for a variety of applications from micro-laser machining to laser diagnostic systems.
We are developing micromirror arrays (MMA) for future generation infrared multiobject spectroscopy (MOS)
requiring cryogenic environment. So far we successfully realized small arrays of 5×5 single-crystalline silicon
micromirrors. The 100μm ×200μm micromirrors show excellent surface quality and can be tilted by electrostatic
actuation yielding 20° mechanical tilt-angle. An electromechanical locking mechanism has been demonstrated
that provides uniform tilt-angle within one arc minute precision over the whole array. Infrared MOS requires
cryogenic environment and coated mirrors, silicon being transparent in the infrared. We report on the influence
of the reflective coating on the mirror quality and on the characterization of the MMA in cryogenic environment.
A Veeco/Wyko optical profiler was used to measure the flatness of uncoated and coated mirrors. The uncoated
and unactuated micromirrors showed a peak-to-valley deformation (PTV) of below 10nm. An evaporated 10nm
chrome/50nm gold coating on the mirror increased the PTV to 35nm; by depositing the same layers on both
sides of the mirrors the PTV was reduced down to 17nm. Cryogenic characterization was carried out on a
custom built interferometric characterization bench onto which a cryogenic chamber was mounted. The chamber
pressure was at 10e-6 mbar and the temperature measured right next to the micromirror device was 86K. The
micromirrors could be actuated before, during and after cryogenic testing. The PTV of the chrome/gold coated
mirrors increased from 35nm to 50nm, still remaining in the requirements of < lambda/20 for lambda=1μm.
Devices based on SOI technology are subject to bow due to residual stress induced by the buried oxide. We have
designed and fabricated a compact tunable piston tip-tilt mirror device in which the shape and the arrangement of the
suspension beams result in both a reduced stress in the suspension beams and an optically flat mirror. The piston tip-tilt
mirror is characterized by an accurate vertical displacement of up to 18 &mgr;m @ 80 V with good repeatability, and a tip-tilt
of up to 2 mrad @ 50 V.
We report on micromirror arrays being developed for the use as reflective slit mask in Multi Object Spectrographs
for astronomical applications. The micromirrors are etched in bulk single crystal silicon whereas the cantilever
type suspension is realized by surface micromachining. One micromirror element is 100μm x 200μm in size. The
micromirrors are actuated electrostatically by electrodes located on a second chip. The use of silicon on insulator
(SOI) wafers for both mirror and electrode chip ensures thermal compatibility for cryogenic operation. A system
of multiple landing beams has been developed, which passively locks the mirror at a well defined tilt angle when
actuated. The mechanical tilt angle obtained is 20o at a pull-in voltage of 90V. Measurements with an optical
profiler showed that the tilt angle of the actuated and locked mirror is stable with a precision of one arc minute
over a range of 15V. This locking system makes the tilt angle merely independent from process variations across
the wafer and thus provides uniform tilt angle over the whole array. The precision on tilt angle from mirror to
mirror measured is one arc minute. The surface quality of the mirrors in actuated state is better than 10nm
peak-to-valley and the local roughness is around 1nm RMS.
KEYWORDS: Micromirrors, Mirrors, Astronomical imaging, Molybdenum, Electrodes, James Webb Space Telescope, Space telescopes, Spectrographs, Telescopes, Microopto electromechanical systems
Next generation MOS for space as well as ground-based instruments, including NIRSpec for JWST, require a
programmable multi-slit mask. A promising solution is the use of MOEMS-based devices such as micromirror arrays
(MMA) or micro-shutter arrays (MSA). Both configurations allow remote control of the multi-slit configuration in real
time. Engaged in the design studies for NIRSpec, we have developed different tools for the modelling and the
characterization of these devices. Since, we have continued our studies with commercial TI MMA and we show that in
a 20° ON-OFF configuration, the 3000 contrast requirement is fulfilled for any F# of 8m-class telescopes as well as
future ELT's.
Within the framework of the JRA on Smart Focal Planes, micro-mirrors have been selected in order to get a first
demonstrator of a European MOEMS-based slit mask. We have fixed several key parameters: one micromirror per
astronomical object, high optical contrast of at least 3000, tilting angle of 20°, fill factor of more than 90%, size of a
micro-element around 100 × 200 μm2, driving voltage below 100V. The MMA would also work in a wide range of
temperature down to cryogenic temperatures.
Based on these parameters, we have designed a new MMA architecture, using a combination of bulk and surface
micromachining. A first small test array of micro-mirrors was successfully fabricated and shows the desired mechanical
tilting angle of 20° at a driving voltage of about 100V. Preliminary measurements show a surface quality better than
lambda/20. Assembly of small test arrays with their electrode chips and design of larger arrays are under way.
Devices based on SOI technology are subject to bow due to residual stress induced by the buried oxide. We have designed and fabricated a compact tunable piston tip-tilt mirror device in which the shape and the arrangement of the suspension beams result in both a reduced stress in the suspension beams and an optically flat mirror. The piston tip-tilt mirror is characterized by an accurate vertical displacement of up to 18 μm @ 80 V with good repeatability, and a tip-tilt of up to 2 mrad @ 50 V.
A 2D MEMS platform for a microlens scanner application is reported. The platform is fabricated on an SOI wafer with 50 μm thick device layer. Entire device is defined with a single etching step on the same layer. Through four S-shaped beams, the device is capable of producing nonlinear 2D motion from linear 1D translation of two pairs of comb actuator sets. The device has a clear aperture of 2mm by 2mm, which is hallowed from the backside for micro-optics assembly. In this paper, a numerical device model and its
validation via experimental characterization results are presented. Integration of the micro-optical components with the stage is also discussed. Additionally, a new driving scheme to minimize the settling time of the device in DC operation is explored.
Programmable multi-slit masks are required for next generation Multi-Object Spectrograph (MOS) for space as well as for ground-based instruments. A promising solution is the use of MOEMS devices such as micromirror arrays (MMA) or micro-shutter arrays (MSA), which both allow the remote control of the multi-slit configuration in real time. In the present work we developed and microfabricated a novel micro mirror array suited for this application. The requirements are: high contrast, optically flat (λ/20) mirrors in operation, high fill factor, uniform tilt angle over the whole array and low actuation voltage. In order to fulfill these requirements we use a combination of bulk and surface micromachining in silicon. The mirrors are actuated electrostatically by a separate electrode chip. The mirrors are defined by deep reactive ion etching in the 10μm thick device layer of a silicon-on-insulator (SOI) wafer, whereas the suspension of the mirrors is defined by a patterned poly-silicon layer hidden on the backside of the mirrors. The mirror size is 100 x 200 μm2 and the dimensions of a typical cantilever suspension are 100 x 5 x 0.6 μm3. On a separate SOI wafer the electrodes and the spacers are processed by using a self aligned delayed mask process. The first results on the mirror chips show that the micromirrors can easily achieve the desired mechanical tilt angle of more than 20° associated with a good surface quality, which is necessary for a high contrast spectroscopy.
The second generation circular digital variable optical attenuator (CDVOA) with an effective area of 1500 μm diameter has been designed and fabricated based on SOI technology. C-band incoming Gaussian light can be reflected to an outgoing fiber from a shiny circular area, which is divided into sectors that can be individually tilted and addressed electrostatically to achieve variable light attenuation. Using a delay mask process, each movable component i) has an underlying ridge frame to maintain flatness, ii) is suspended by two micro beams at a bridge structure that connects to a handle where aluminum electrode is located underneath, and iii) is separated by wall structures at the handle area to reduce crosstalk from adjacent electrodes. Critical fabrication processes including the mirror and chip release are performed using a HF vapor phase etcher. Fluidic pressure and chip-dicing shocks are avoided. Initial results show that a mirror sector suspended by two 345 μm long beams with a cross-section of about 5×5 μm2 can be tilted to 2.8° at about 18 V driving voltage. Initial interferometric measurement gives estimated individual mirror flatness after metallic reflective coating to be about λ/15. The assembled chips are ready for further testing and characterization.
We report on an angle-tunable oblique incidence resonant grating filter that can be used to drop individual channels from the C-band for incident TE-polarized light. For tuning purpose, the filter is glued onto a tiltable platform of a MEMS device. Continues scanning of the platform allows to monitor channel presence and power. The reflected wavelength is tuned by changing the angle of incidence of the resonant grating filter, which is composed of two thin films with a grating pattern on top of it. The first layer on a glass substrate acts as a waveguide, and the second layer separates the waveguide from the grating. The grating has been patterned by holographic recording and dry etching. The filter works over a wavelength range of 1520-1580 nm and its response has a Lorentian shape with 0.5 nm FWHM peak width. The MEMS part is based on SOI technology and is processed in only two DRIE steps. The platform measures 2 x 2 mm2 with a through-hole of 1.6 x 1.8 mm2 for light transmission. Two arrays of combs attached to the platform as well as a set of four static combs are used to electrostatically incline the platform by ± 4° with a driving voltage of about 60 V.
We report on a 4x4 optical matrix switch for telecom application. It consists of a 4x4 array of vertical mirrors that have the same pitch as the fibers of commercially available fiber ribbons (250 μm). This compact design enables a parallel assembly to optical components, which simplifies the time consuming and costly process for switches with larger pitch. Additionally, a small pitch leads to a short optical coupling length, which facilitates the integration of a suitable collimation system. However there are physical limitations for optical MEMS in conjunction with assembled micro-optics. The optical beam exiting a collimator diverges, the divergence angle is indirectly proportional to the beam waist and the coupling length increases quadratically. Our calculations show that for a pitch of 250 µm a mirror height of 100 μm is optimal. The mirrors are monolithically etched onto a platform etched during a previous step. No assembly of the mirrors to the actuators is needed. Alignment structures for the optical components are etched during the same step as the mirrors, which lead to self aligned structures. The platform is supported by 150 μm long torsion beams with sub-micron diameter. The electrostatic actuation voltage is given by a separate chip. The mirror moves out of the optical path when the platform is actuated and goes to the switching state if no voltage is applied. The first prototypes have been actuated at 200 V, which agrees with a CoventorWare simulation used for designing the device. Light was successfully switched with a 4x4 OXC. An 8x8 OXC is shown and electrostatically characterized.
We present a lamellar grating interferometer realized with MEMS technology. It is used as time-scanning Fourier transform spectrometer. The motion is carried out by an electrostatic comb drive actuator fabricated by silicon micromachining, particularly by silicon-on-insulator technology. We have measured the spectrum of an extended white light source with a resolution of 1.2 nm at a wavelength of 436 nm, and of 13 nm at 1544 nm. The wavelength accuracy is better than 0.5 nm and the inspected wavelength range extends from 380 nm to 1700 nm. The optical path difference maximum is 226 μm and is limited by the mechanical instability of the actuator. The dimension of the device is 7 mm x 8 mm x 0.5 mm. The device includes two individual lamellar grating spectrometers operated by the same actuator, allowing the immediate calibration of the optical path difference.
We present several devices using different spectroscopic concepts. First, we show the successive steps and improvements in connection with the Michelson interferometer which we have already realized, in particular the use of fibers to bring in and collimate the light. A possible method to obtain micro-optical elements that are suitable for integration on the interferometer chip is proposed. Then, we present a lamellar grating interferometer, an array of commutable slits to realize a Hadamard transformer, and a movable curved diffraction grating. All of these devices have been realized by silicon micro-machining, more particularly with silicon-on-insulator (SOI) technology.
Thin-film Pt nano interdigitated electrodes realized by combining e-beam lithography and standard photolithography are presented. The resulting nano-IDAs have an active area of 76 μm × 100 μm, an electrode pitch of 785 nm and a gap of 250 nm. The initial results show that this technology is well adapted for the realization of sub-micrometer metallic structures.
In this paper, the development of a 1X4 micro optical switch utilizing electrostatic actuation and vertical silicon mirrors was reported. This device was fabricated from silicon-on-insulator (SOI) wafer using a bulk micromachining process, which allowed the fabrication of vertical mirrors and U-grooves through deep reactive ion etching (DRIE) of silicon. A few process steps were required in the fabrication. Moreover, the device was patterned in a single lithographic step. A relatively high yield (up to 70%) was achieved during the microfabrication due to this compact process flow. More importantly, the footprint was less than 13mm2. To verify the design, the stress/strain distribution around the actuator was examined using FEM simulation. The relationship between driving voltage and mirror displacement derived from simulation agreed well with the measurement. Tapered lensed singlemode fiber were assembled into U-grooves and positioned passively by fiber stopper. The device was then packaged and pigtailed. Characterization on the mechanical and optical performance of this device show the promising characteristics of this 1×4 optical switch for use in optical networks.
The microtribometer fabricated is designed to observe the wear of removable flat silicon test inserts, coated with thin film layers such as DLC and moving in an oscillating manner relatively to each other. For observing the low wear of DLC layers in a reasonable amount of time, high oscillating speed is essential and can be achieved by reducing the mass in motion. The silicon microtribometer reaches oscillating frequencies of 10 Hz while applying a normal force on the test inserts up to 9.6 N, the maximal displacement amplitude being 1.5 mm. The two silicon main parts of the microtribometer guide test inserts along one direction in a back and forth motion while avoiding any side friction, the actuation being done by an external linear motor. For such application crystalline silicon presents, compare to other materials, the advantage of the invariance of its behavior over time.
Silicon has been widely used as the material of choice for the fabrication of MEMS I MST devices. The compatibility of MEMS manufacturing equipment with standard IC equipment presents one ofthe main reasons for this choice. However, over the past years, we have seen new equipment dedicated to MEMS fabrication enter the market place. One such example is the Deep Reactive Ion Etcher, which is capable of vertically etching silicon at a rate of several microns per minute. This type of equipment, now available from several vendors, has revolutionized the MEMS fabrication capabilities and has opened the door to a whole new family of MEMS devices [1].
In this paper, we report the development of a new 1X4 micro optical switching device which utilizes electrostatic actuation and vertical silicon mirrors. This device is fabricated using a bulk micromachining process, which allows the fabrication of vertical mirrors and U-grooves through deep reactive ion etching (DRIE) of silicon. A limited number of process steps are required in the fabrication. Moreover, the device is patterned in a single lithographic step. A relatively high yield (up to 70%) is achieved during the microfabrication due to this compact process flow. More importantly, a small footprint (<13mm2 in die size) is realized. A single mode fiber with a tapered end is placed into a U-groove and positioned passively by a fiber stopper, prior to adhesive bonding with a silicon substrate and a glass cover. Preliminary characterization on the mechanical and optical performance of this device has been carried out, which reveals the promising characteristics of this 1X4 optical switch for use in optical networks.
A high-speed Ta-Si-N gas microvalve has been designed, fabricated and characterized. Ta-Si-N has a unique combination of electrical and mechanical properties suitable for robust high performance MEMS devices. The valve reported here represents the first working MEMS device integrating a sputtered Ta-Si-N layer, for use at differential pressures greater than 2 bar and capable of achieving controlled flow-rates under pulse width modulation (PWM). Previously reported, electrostatically actuated microvalves (3,4,5) were limited to operating pressures less than 200 mbar, and their switching behavior was not studied. The valve is based on a surface micromachined Ta-Si-N membrane that closes a deep reactive ion etched hole. The valve was optimized to achieve a low actuation voltage and fast commutation. This study focuses on the characterization of the switching behavior of the valve membrane and its influence on the flow-rate.
We present the design and characterization of a new 4 X 4 switch based on the previously developed 2 X 2 fiber switch. The switching principle uses plasma etched vertical mirrors that can be moved in and out of two pairs of optical fibers with the integrated electrostatic actuator. The 4 X 4 switch is built by connecting 16 individual 2 X 2 switches in a common package (100 X 50 X 35 mm). Instead of integrating the 16 switch elements on the same chip, we preferred assembling the switches by fusion splicing. The insertion loss is less than 1.8 dB for each state.
The continuous progress in micro- and nano-system technologies has allowed the successful development of many innovative products in process control, environmental monitoring, healthcare, automotive and aerospace as well as information processing systems. In this paper on overview will be given of current progress in micro- and nanofabrication process technologies, such as deep reactive ion etching, micro-electro discharge machining, thick photoresistant processing and plating. The availibility of these micro- and nanofabrication processes will be illustrated with examples of new generations of silicon-based sensors, actuators and Microsystems with a particular emphasis on real applications of these components and systems.
We present a miniaturized Fourier transform (FT) spectrometer based on silicon micromachined. The FTS is a Michelson interferometer with one scanning mirror. The motion of the mirror is carried out by a n electrostatic comb drive actuator. The mirror displacement is 39 micrometers and its reproducibility is +/- 13 nm, which leads to a resolution better than 10 nm in the visible wavelength range. A new design of this chip has been realized in order to integrate an input fiber, a collimating lens system as well as a beam splitting plate. This new design allows to undertake spectroscopy with white light. The limitation of light collimation and the effect of the size of the source have been studied by numerical simulations.
The continuous progress in micro- and nano-system technologies has allowed the successful development of many innovative products in process control, environmental monitoring, healthcare, automotive and aerospace as well as information processing systems. In this paper on overview will be given of current progress in micro- and nanofabrication process technologies, such as deep reactive ion etching, micro-electro discharge machining, thick photoresistant processing and plating. The availibility of these micro- and nanofabrication processes will be illustrated with examples of new generations of silicon-based sensors, actuators and Microsystems with a particular emphasis on real applications of these components and systems.
KEYWORDS: Silicon, Actuators, Sensors, Field effect transistors, Gas sensors, Microfabrication, Atomic force microscopy, Deep reactive ion etching, Switches, Microsystems
The continuous progress in micro- and nano-system technologies has allowed the successful development of many innovative products in process control, environmental monitoring, healthcare, automotive and aerospace as well as information processing systems. In this paper on overview will be given of current progress in micro- and nanofabrication process technologies, such as deep reactive ion etching, micro-electro discharge machining, thick photoresistant processing and plating. The availibility of these micro- and nanofabrication processes will be illustrated with examples of new generations of silicon-based sensors, actuators and Microsystems with a particular emphasis on real applications of these components and systems.
The continuous progress in micro- and nano-system technologies has allowed the successful development of many innovative products in process control, environmental monitoring, healthcare, automotive and aerospace as well as information processing systems. In this paper on overview will be given of current progress in micro- and nanofabrication process technologies, such as deep reactive ion etching, micro-electro discharge machining, thick photoresistant processing and plating. The availibility of these micro- and nanofabrication processes will be illustrated with examples of new generations of silicon-based sensors, actuators and Microsystems with a particular emphasis on real applications of these components and systems.
KEYWORDS: Silicon, Actuators, Sensors, Field effect transistors, Gas sensors, Microfabrication, Deep reactive ion etching, Semiconducting wafers, Atomic force microscopy, Switches
The continuous progress in micro- and nano-system technologies has allowed the successful development of many innovative products in process control, environmental monitoring, healthcare, automotive and aerospace as well as information processing systems. In this paper on overview will be given of current progress in micro- and nanofabrication process technologies, such as deep reactive ion etching, micro-electro discharge machining, thick photoresistant processing and plating. The availibility of these micro- and nanofabrication processes will be illustrated with examples of new generations of silicon-based sensors, actuators and Microsystems with a particular emphasis on real applications of these components and systems.
KEYWORDS: Silicon, Actuators, Sensors, Field effect transistors, Gas sensors, Microfabrication, Deep reactive ion etching, Semiconducting wafers, Atomic force microscopy, Microsystems
The continuous progress in micro- and nano-system technologies has allowed the successful development of many innovative products in process control, environmental monitoring, healthcare, automotive and aerospace as well as information processing systems. In this paper on overview will be given of current progress in micro- and nanofabrication process technologies, such as deep reactive ion etching, micro-electro discharge machining, thick photoresistant processing and plating. The availibility of these micro- and nanofabrication processes will be illustrated with examples of new generations of silicon-based sensors, actuators and Microsystems with a particular emphasis on real applications of these components and systems.
Optical MEMS is a challenging new field that combines micro- optics with micro-mechanics in order to build compact systems. In this paper we present a miniaturized Fourier transform spectrometer (FTS) fabricated on silicon. The FTS is a Michelson interferometer with one scanning mirror. The motion of the mirror is carried out by a new type of electrostatic comb drive actuator. The mirror is designed to be linear with respect to the applied voltage. Experimentally, we have measured a mirror displacement of 38.5 micrometer corresponding to a maximum optical path difference of 77 micrometer. The applied voltage was plus or minus 10 V and the non-linearity of the driving system is plus or minus 0.25 micrometer. A method is presented to correct the spectrum in order to get rid of the non-linearity. The measured resolution of the spectrometer after the phase correction is 16 nm at a wavelength of 633 nm.
Accurate dosing of liquids in sub-microliter quantities requires a precise measurement of the dispensed quantities. This paper describes applications of a micro flow sensor based on the differential pressure measurement across a fluid restriction. The small size and high accuracy of the flow sensor are very attractive for the integration into sophisticated instrumentation. The use of well-developed hybrid assembly technologies allows for extreme miniaturization and high-density parallel measurements in multi-channel application.
Giovanni Fiaccabrino, Peter van der Wal, Nico de Rooij, Milena Koudelka-Hep, Marylou Tercier, Cecile Belmont-Hebert, Jacques Buffle, Fabio Confalonieri, Guiliano Riccardi, Flavio Graziotin
In order to meet the stringent demands of natural and waste waters monitoring for artifact-free data, an increasing effort is directed towards developing on-line and in-situ measuring schemes. In this context, the development of microfabricated electrochemical detectors for stripping analysis of trace metals has attracted particular attention. In this paper we report on the fabrication and analytical performance of a microfabricated electrode for direct Square Wave Anodic Stripping Voltammetry analyses of trace metals in natural waters. It is based on a mercury-plated thin-film Ir microdisk array covered by a layer of an antifouling gel. To facilitate the control of the gel deposition and to improve its mechanical stability, a polymeric containment ring has been formed around the array. The sensor is then integrated within a complete Voltammetric In situ Profiling analytical system.
With advances in micromachining and the consequent growing sophistication of microstructures, emphasis is increasingly being laid on the design and realization of complete microsystems. In this paper we show some possible combinations of micromachining technologies to build microsystems for applications in photonics, nanoscience, bio-electrochemical systems and micromechanics. The common point of such a large range of devices is their fabrication technology, which has developed from the basic integrated circuit techniques into a wide spectrum of specific micromachining technologies. This article gives an overview of established and newer microfabrication technologies and their application to the construction of some chosen microsystems.
The fabrication and characterization of a microfabricated, fexural plate, acoustic wave delay line is presented for use in the physical translation of fluids and/or biological cells. The device consists of dual interdigitated transducers patterned on a thin film composite membrane of silicon nitride, platinum, and sol gel derived piezoelectric ceramic (PZT). The acoustic properties of the device are presented along with preliminary applications to mechanical transport and liquid delivery systems. Improved acoustic signals and improved mass transport are achieved with PZT over present fexural plate wave devices employing ZnO as the piezoelectric material.
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