Imprinting micro- and nanostructures on non-planar surfaces has gained prominence in various fields such as optoelectronics, photonics and biomedical implants. It has been implemented for applications such as optical sensor arrays and optical fibers. Nanoimprint lithography (NIL) is a low cost, high resolution nanofabrication process. In this work, soft UV-NIL process is used in which a flexible stamp is used which makes it ideal for imprinting on curved surfaces such as plano-convex lens. However, the substrate to stamp positioning for successful transfer of patterns is crucial and needs to be addressed. The Nanopositioning and Nanomeasuring machine (NPMM), developed in the Collaborative Research Center (of the German Research Foundation) of TU Ilmenau, provides a unique solution to the challenges of positioning and alignment. Therefore, a UV-LED assisted small scale NIL-setup was designed, developed and integrated into the NPMM and it was further realized for carrying out fabrication of micro- and nanostructures on silicon chips and planoconvex lenses. In addition to scanning electron microscopy (SEM) and atomic force microscopy (AFM) characterization, the structures were further characterized using a focus sensor. The utilized focus sensor is an optical sensor developed at the Institute for Process Measurement and Sensor Technology of TU Ilmenau. It was observed that the imprinted structures were of considerably good fidelity. Thus, a distinctive integrated imprinting process for flat and non-flat surfaces was developed and implemented.
Microsystems for autonomous limit monitoring can be used for triggering maintenance and thus help to reduce costs. We present a fully integrated passive microsystem for binary counting of off-limit conditions. The mechanical design and a mechanical characterization of the system fabricated using SOI (silicon-on-insulator) technology are shown. The binary counting mechanism is realized by utilizing mechanical coupling elements between bit elements. The mechanical energy needed for switching the first bit to the state "high" was found to be 0.1 μJ by moving the entrance 37 μm and applying a force of up to 8.2 mN. 0.36 μJ was determined for switching the bit back to the state "low" by applying a 69 μm distance and a force of up to 10.2 mN. The system needs input energy for counting only, not for storing the counter value.<p> </p> Expanding the design to up to ten bit elements would offer a passive microsensor able to detect 1023 off-limit conditions. A mechanical binary microcounter is presented that does not require electrical energy supply. It is suitable for counting any physical event that can be converted into an adequate force-travel-characteristic.
In a novel hyperspectral imaging concept based on confocal chromatic microscopy, a pinhole array (matrix of pinholes) has to be scanned across an intermediate image plane to capture the full object plane. In this paper a two-axis stepping microdrive is presented for the pinhole array (6×7.5×0.2 mm<sup>3</sup> of glass, weight 20 mg), featuring a 10 μm step size and a 200 μm displacement range in each direction. With the two-axis stepwise actuation of the pinhole array, the imaged area of the object plane is increased from 7% (fixed pinhole array) up to 89% with actuated array. The two-axis positioning is implemented with a three-axis inchworm motion driven by electrostatic forces. A combination of horizontal and vertical electrostatic actuators are arranged to achieve a precise in-plane actuation of the pinhole array. The microdrive is fabricated with established MEMS technologies and features a size about 1 cm<sup>2</sup> with 1 mm thickness. The microdrive is capable to position the pinhole array over the displacement range. The array size enables a 1:1 optical imaging on an 8 mm diagonal size CCD. The presented stepping microdrive outperforms existing microsystem solutions with a combination of high payload, large step size, displacement range, and the large optical aperture. Furthermore, the device concept enables the positioning of milligram weights with a highly integrated microsystem.
We present tunable lenses based on aluminum nitride membranes. The achievable tuning range in the refractive power is 0 to 25 dpt with an external pressure load of ≤20 kPa . The lenses are manufactured using MOEMS technology. For 500-nm-thick membranes with a diameter of 3 mm, a spherical deflection profile is found. The system provides good long-term stability showing no creep or hysteresis. A model for the refractive power versus applied pressure is derived and validated experimentally. Based on this model, design guidelines are discussed. One essential parameter is the residual stress of the aluminum nitride layer that can be controlled during deposition.
We present an integrated beam scanning system without moving mechanical parts. The device based on the thermooptical effect. In combination with a silicon oxynitrid waveguide and a planar integrated lens we use thin film heaters for thermooptical deflection of a guided mode close to the edge of an integrated optical chip. This leads to a deflection at the collimation optic consisting of a planar lens. We show thermal simulation for the optimization of the heater position. The result of the thermal simulation is combined with BPM simulation to evaluate the change of the mode position during heating. First deflection measurements of the system are shown.
We introduce sputtered aluminum nitride thin films for tunable micro-optics. During lens fabrication, AlN is deposited on a silicon substrate. Silicon is structured by using DRIE, which allows fabrication of circular, rectangular and irregular membrane shapes. In this contribution, we present the design, fabrication and characterization of AlN membranes for tunable cylindrical lenses. An optimized “dogbone” membrane is presented, which deflects cylindrically and has a small footprint. Compared to conventional rectangular membranes the optically useful area is doubled. The load deflection characteristic is investigated and basic relations between the refractive power and applied pressure are found. The relation can be used for tailoring the membrane properties, i.e. their residual stress, for a specific application. According to this calculation, a refractive power of 25 dpt with a lens aperture of 3x3 mm<sup>2</sup> is achieved for 12 kPa of applied pressure. The cylindrical deflection of the “dogbone” membrane is measured. The maximum shape difference in measured to be 270 nm.
Although a lot of micromechanical mirror devices are already available, there is still a lack of devices for measurement applications with large reflective plains and static deflection in the range of <-10° to >10° in analog mode. In our approach, aluminum nitride (AlN) deposited by reactive sputtering is used as torsional spring material. In contrast to crystalline and amorphous materials such as silicon or silica, the nanocrystallinity of AlN inhibits the propagation of cracks. Material tests show high mechanical strength and linear elastic behavior. Fatigue of the hinges couldn’t be observed so far. Those material attributes enable the fabrication of thin and compliant springs. Aside from the geometric parameters, spring stiffness can be tuned by the mechanical film stress during deposition. To reach highly dynamic mirror deflection, electrostatic actuation is used. Measurement results show an analog mechanical deflection range of ±11.7°. Using the pull-in, a digital rotation angle of about ±21° is achieved. These results match well with simulations. The mirror plain is stiffened by a bulk silicon layer. The samples have a mirror plate of 1.2 x 1.0 mm<sup>2</sup>suspended by 20 or 30 μm wide, 350 μm long and 0.4 μm thin stacked AlN (300 nm) /Al (100 nm) torsional springs.
A microlens suitable for integration with photonic elements on the same substrate is presented. It is fabricated utilizing
planar standard technologies such as UV lithography, ICP-CVD and Deep Reactive Ion Etching. For reaching an optical
3D functionality with 2 D structuring methods a variation of the refractive index during the layer deposition process in
the vertical direction is used. For the horizontal direction, parallel to the substrate, the shape of etched side walls
determines the focus. This procedure allows the independent control of light propagation in two perpendicular directions
with planar technologies. To demonstrate the potential of the technology, optical elements for the collimation of fiber-based
light sources are presented.
The integration of RFID tags into packages offers the opportunity to combine logistic advantages of the technology with
monitoring different parameters from inside the package at the same time. An essential demand for enhanced product
safety especially in pharmacy or food industry is the monitoring of the time-temperature-integral. Thus, completely
passive time-temperature-integrators (TTI) requiring no battery, microprocessor nor data logging devices are developed.
TTI representing the sterilization process inside an autoclave system is a demanding challenge: a temperature of at least
120 °C have to be maintained over 45 minutes to assure that no unwanted organism remains. Due to increased
temperature, the viscosity of a fluid changes and thus the speed of the fluid inside the channel increases. The filled length
of the channel represents the time temperature integral affecting the system.
Measurements as well as simulations allow drawing conclusions about the influence of the geometrical parameters of the
system and provide the possibility of adaptation.
Thus a completely passive sensor element for monitoring an integral parameter with waiving of external electrical power
supply and data processing technology is demonstrated. Furthermore, it is shown how to adjust the specific TTI
parameters of the sensor to different applications and needs by modifying the geometrical parameters of the system.
This article presents a new approach for airborne particle generation for optical tweezers. The used element is a 500 nm
thin aluminum nitride membrane with an integrated heating element. Thus the membrane works as thermo-mechanical
actor. The membrane device is characterized concerning their mechanical and thermal behavior. Successful airborne
particle generation is demonstrated with 10 μm silicon dioxide spheres. They are lifted up some 10th of μm from the
membrane surface. The development and test of this device serves as starting point for experiments with optical tweezers
This work aims for utilizing human ocular motion for the self-sufficient power supply of a minimally invasive
implantable monitoring system for intraocular pressure (IOP). With a proven piezoelectric functionality (d<sub>33</sub>>5 pm/V),
nanocrystalline thin films of aluminum nitride (AlN) provide a good capability for micromechanical energy harvesting
(EH) in medical applications. Many d<sub>31</sub>-mode microcantilever architectures are poorly suited for human-induced EH:
Resonant mass-spring-damper systems are tested under high, narrow-band excitation frequencies. However, human
motions, e.g. vibrations of eyeballs are marked by their low frequency, unpredictable, mainly aperiodic and time-varying
signature. Different vibration types and directions are 3-dimensionally superimposed. Saccadic eye movements are
favorable for inertial microgenerators because of their high dynamic loading (ω≤1000°/s). Our generator concept
(symmetric active/active-parallel-bimorph cantilever) enables a high structural compliance by maximizing the
piezoactive volume at very low cantilever thicknesses (<1 μm). An increased length and seismic mass enable an
effective excitation by low-level aperiodic vibrations such as saccadic acceleration impulses. Analytic calculations and
FEA-simulations investigate the potential distribution and transient response of different bimorph structures (length 200-
1000 μm, width 20-200 μm) on broadband vibrations. First released monomorph and bimorph structures show very low
resonant frequencies and an adequate robustness.
Step-structured thermo-mechanical actuators based on aluminum nitride (AlN) thin films and their application in
refractive beam steering are investigated. The actuators will tilt a suspended plate and deform a liquid surface to realize a
micro-prism. Arrays of tunable micro-prisms will increase the resolution of compound eye systems. A numerical
actuator description is presented and the beam geometry is investigated, considering achievable tilt angles and actuator
linearity. For an accurate design, the coefficient of thermal expansion (CTE) of AlN is determined, while measuring the
bow of a coated silicon substrate at different temperatures. For a temperature difference of 300 K, the results show a
maximum tilt angle of 7.1 °, which is independent of actuator length. Furthermore, the fabrication process is introduced
and the nano-crystalline structure of AlN at facets, which are caused by pre-structured substrates, is investigated.
We present design and realization concepts for thin compound eye cameras with enhanced optical functionality. The
systems are based on facets with individually tunable focus lengths and viewing angles for scanning of the object space.
The active lens elements are made of aluminum nitride (AlN)/nanocrystalline diamond (NCD) membranes. This material
system allows slow thermally actuated elements with a large deformation range as well as fast piezoelectric elements
with a smaller deformation range. Due to the extreme mechanical stability of these materials, we are able to realize
microoptical components with optimum surface qualities as well as an excellent long-term stability.
We use facets of microlenses with 1 mm in diameter and a tunable focusing power to compensate for the focus shift for
different viewing angles during the scanning procedure. The beam deflection for scanning is realized either by laterally
shifting spherical elements or by a tunable microprism with reduced aberrations. For both actuators we present a design,
fabrication concept and first experimental results.