This PDF file contains the front matter associated with SPIE Proceedings Volume 11697, including the Title Page, Copyright Information, and Table of Contents.

Welcome and Introduction to SPIE Photonics West OPTO conference 11697: MOEMS and Miniaturized Systems XX

Wavefront shaping is of main interest in the field of Adaptive Optics for Astronomy, wide-field imaging in Microscopy and live cells/tissues imaging in Biology. We propose an innovative technology for a new type of membrane deformable mirror, made by coupling a reflective polymeric membrane with a monolithic non-pixelated photoconductive substrate. The device is called continuous photocontrolled deformable mirror (PCDM), actuated by sending a light flux with given shape and intensity distribution, on the back side of the photoconductor, opposite to the reflective side. Unlike the other actuation mechanisms, this allows to obtain a continuous actuation field, without the typical segmented actuators pattern. Furthermore, it leads to a strong simplification to the driving electronics, for example by eliminating hundreds of cables used for the deformation control. Fundamental is the role played by the photo-excitation dynamics of the photoconductive material, in fact the deformation is obtained through the electrostatic pressure exerted by the photo-generated charge carriers, on the thin reflective membrane. We have developed a device with a single crystalline semiconductor photoconductor wafer, either Silicon or Cadmium Sulfide. The actuation is controlled by a light pattern modulated by a DMD (Digital Micromirror Device) chip, generating a reprogrammable actuator pattern projected on the photoconductor. In order to test the performance of the PCDM, we are addressing two deformation regimes: static behavior and dynamical response. We are then able to measure the response with light actuation, as the influence function matrix with respect to the number of projected virtual actuators; the response with frequency, including response time, resonance frequency, with respect to the different applied patterns, and with respect to the number of virtual actuators; finally, the response in open/close loop.

In this work, 2D piezoelectrically driven MEMS circular scanners have been designed, fabricated and tested. These mirrors own large optical apertures of 7 mm, 10 mm and 20 mm for good beam shapes. Also HR-coating layers for 515 nm and 1050 nm reaching up to 99.99% reflexion and 0.1% transmission were applied onto the mirror surface for the suitability of high power laser, where the wavelengths were specified according to the laser source development demands. Based on piezoelectric position sensing elements integrated on the MEMS mirrors a closed-loop control was developed. In this paper the design efforts, realizing circular-scanning and eliminating non-linearity during mode superposition, and fabrication efforts will be reported. Characterization results focusing on mechanical behaviors, position sensing signal, HR-coating will be also important parts of this work.

In the field of raster scanning projectors, linear micromirrors used for image scan along the vertical axis are driven by a sawtooth waveform, whose frequency is related to image refresh rate (typically 60-120 Hz). Such driving profile with a fast retrace (10% of the period) excites the fundamental resonant mode, stimulating unwanted ringing of the tilt angle that worsens image quality, requiring a compensation. Open-loop solutions based on pre-distortion of the driving profile require accurate calibration of the device and do not offer enough versatility among different micromirrors. Embedded position sensors enable implementation of closed-loop techniques: this work presents an innovative linear control strategy for mirrors with piezoresistive position sensing, which allows to achieve accurate tracking of the control signal while suppressing resonance. The concept is based on a control approach: the goal is to damp the mirror quality factor, while achieving accurate tracking, within few tens of m◦ , and compensate for mechanical non-linearities by nulling the error between angle and control signal. An analog implementation is studied on a theoretical basis, to determine the fundamental limit in terms of tracking accuracy and noise. Then, a more versatile design is presented, where the controllers are implemented digitally to cover a wide range of mirror parameters. Analytical/behavioral simulations show the capability to achieve accuracy within 20°m . Experimental testing on an analog implementation of the resonance damping loop proves the validity of the approach.

MEMS micromirror is playing more important roles in various applications. To increase the detection range and field-ofview (FOV), bigger aperture size with larger rotation angle (θ_opt⋅D) is always preferred. However, it comes with the cost of worse collimation performance due to larger dynamic deformation. A backside rib support design can be added to the mirror which can reduce dynamic deformation while keeping rotational inertia of moment low. Meanwhile, integrated piezoelectric actuator can be adopted to provide large driving force and to increase the rotation angle. In this paper, we demonstrate a MEMS micromirror actuated by integrated PZT thin film, with a large aperture size of 12mm×18mm and resonant frequency of 1.65 kHz can achieve 4.8° optical angle under 20 V_pp driving voltage. Design rules are deduced from the theoretical analysis to improve the performance of piezoelectric-actuated MEMS mirror.

Piezoelectric thin films have gained attention as key materials for the actuation of micro devices since they provide high drive forces compared to others actuation mechanisms. One of the most challenging application field is the design of quasistatic MEMS scanners, in which is difficult to have a high torsional angle and large reflective area while maintaining a good device robustness. In this work a monoaxial, quasi-static MEMS mirror with PZT actuation will be presented, surpassing the limitations found in the state-of-the-art solutions. The mirror has a large reflective area in the visible spectrum (4x3mm with aluminum coating) and the half mechanical opening angle is of 9deg (corresponding to a field of view of 36deg) with a relatively low actuation voltage (40V). To enable the mirror control, a diffused piezoresistive sensor in a Wheatstone bridge configuration is integrated in the technology platform. The innovative mirror design guarantees high resonant frequencies of the torsional mode (>500Hz) and higher spurious modes (>2.5kHz), which allow a quasistatic actuation for the typical display refresh rates (up to 120Hz). The high frequencies of the translational spurious modes guarantee a high robustness against shocks and vibrations, which makes this mirror suitable for consumer or automotive products. In this paper it will be described the working principle of the patented MEMS design, the manufacturing process, the FEM simulations and the experimental findings obtained on fabricated samples.

Although external cavity diode lasers have become firmly established for their excellent properties for species detection, they have severe limitations in terms of high acquisition rates. In this paper, we present our new ECDL design based on a resonantly driven MEMS scanner. By using the MEMS technology, a defined frequency range can be tuned extremely fast and without mode-hops. This allows scanning frequencies in the high kHz range to be achieved. The results of the characterization of the spectral properties of the MEMS-based system and its use for rapid detection of trace gases are presented.

In this paper, we report a new two-axis micro scanning mirror (WIMSM) using torsional and bending BoPET (biaxially-oriented polyethylene terephthalate) hinges. With a torsional hinge, the fast axis has a resonance frequency of 265 Hz in air and 172 Hz in water. With a torsional hinge, the fast axis has a resonance frequency of 265 Hz in air and 172 Hz in water. With a bending hinge, the slow axis has a resonance frequency less than 1 Hz. When the two axes are driven at their resonance frequencies, a dense raster scanning pattern with a maximal scanning range is obtained. For demonstration, 3D volumetric ultrasound microscopy in water is conducted with the new WIMSM.

Spectroscopy-based gas sensing has occupied a significant role in environmental, industrial and healthcare applications. Two specific concerns of the technology are miniaturization and portability, while maintaining the device performance. The mid-infrared strong absorption characteristics of different gases can offer the required detection limits when used with multi-pass gas cells due to longer interaction lengths. These cells raise the need for wide-spectral range angle-tolerant mirror designs compatible with micromachining technologies. In this work, we investigate the use of silicon-based gold coated deeply-etched optical MEMS mirrors and show that the grain nature of the deposited metal leads to degraded mirror. We study the effect of the grain-to-volume ratio of the gold mirror structure and present a method to boost the mirror performance by using a hybrid wideband insulator-metal-insulator (IMI) plasmonic structure. Different insulators were investigated with different layer thicknesses, taking into consideration the grain nature of the layers. A mirror reflectivity that is about 98% with 10% bandwidth of about 3.1 μm and wide angles of incidence of 0°–70° is obtained. The wide angle feature enables the use of the structure as a curved mirror in multi-pass gas cells used in infrared spectroscopic applications.

MEMS Mirrors provide a great way to spatially scan light and is being used for a wide range of applications such as raster scanning RGB light for Display Engines or scanning infra-red light for depth cameras (3D sensing) by using structured light or Time of Flight (TOF) techniques. Yet, in some cases it is required to deploy multiple MEMS Mirrors that ought to work in tandem, such as implementing a Display Engine for a binocular HMD (Head Mount Display, AR/VR/MR) generating two images, one per eye. In such a case, it is necessary to synchronize the movement of the MEMS mirrors, so that the images that are presented to the viewer, would create a homogenous and consistent image. Another possible use case is to increase the Field Of View, such as for an Automotive Lidar application, so that each Scanning Engine with a mounted MEMS Mirror would cover a subset of the scanned scene, yet collectively would provide an increased scanned FOV. The scanning of each segment by one Scanning Engine would be done sequentially and in a synchronized manner with the other Scanning Engines. This paper will present a viable synchronization mechanism for two main types of MEMS Mirror: Resonant Mirror and Quasi Static Mirrors. The paper will discuss the challenges and considerations of the System Clock, Master / Slave modes, overcoming jitter and noise and modeling by simulations the expected results. Additionally, the paper will present the actual results of such system implementation as a result of this work.

The wish for higher-level advanced driver assistance systems requires infrared based ranging systems like LiDAR provided that it offers high speed, wide field-of-view, small size and especially low cost. The only way to combine these attributes is the use of cost-efficient and mass-producible MEMS scanners suitable for automotive applications. In this work we present a wide-angle LiDAR demonstrator for short range applications based on a single resonantly operated MEMS, a single laser and single light detector. The MEMS mirror is capable of tilting ± 45° mechanically and thus enabling a large field-of-view of up to 180°. The incorporated mirror plate has an elliptical shape of 2 mm x 4 mm in size and the overall volume of the MEMS device is less than 0.7 cm³. Low-power microcontroller based closed-loop electronics is used to keep the very high Q device within its resonance frequency range at all times enabling high scan rates of more than 3000 scans per second and accurate position detection better than 0.1°. Both automotive suitability and high energy efficiency is achieved by hermetic wafer-level sealing under vacuum as well as internal piezoelectric drive and sense structures. The demonstrated wide-angle scanning LiDAR further consists of a 905 nm eye-safe pulse laser source operating at up to 200 kHz with an optical peak output power of 30 W as well as a one-dimensional SPAD based detector with 2x192 channels. Together this leads to high density and high resolution point clouds using just a single laser, detector and MEMS scanner.

In this work, 2D MEMS quasi-static mirrors based on piezoelectric, non-ferroelectric AlScN/AlN actuators with three different mirror plates (diameters of 2 mm, 5 mm and 10 mm) using a design and manufacturing platform will be reported. While the AlN/AlScN driving actuators ensure high linearity and large tilting angles, the multiple-waferbonding technique via glass fritting enables 3D construction of the MEMS mirrors and hermetic sealing. Even though there is no request on vacuum package for quasi-static driving, hermitic sealing on wafer level with appropriate interior pressure level within the sealing improves the mechanical robustness of the MEMS components and protects them from the particles and humidity from the environment. Since the main design concept was adopted from the previous work and adapted for different aperture sizes, this paper will focus on reporting further simulation results on mechanical behaviors, especially shock survivability under very harsh environment, the technology efforts and results of utilizing such a design and manufacturing platform for AlScN/AlN driven MEMS mirrors.

This paper presents a full system, based on two dedicated ASICs, to drive and control a resonant piezoelectric micromirror. The driving ASIC, exploiting the essentially capacitive-like pseudo-differential behavior of the micro-mirror, implements an innovative and efficient energy recovery topology. With only two additional external capacitors, C·V² ·f load power consumption can be reduced by a theoretical factor 6. It works up to 40V driving voltage, providing two trapezoidal signals in phase opposition up to 65kHz driving frequency in order to be compatible with most of the micromirror devices. Driving signal amplitude can be adjusted at 15 bits resolution through a novel low-frequency noise free circuit for opening angle control (OAC), briefly described. Classical resistive Wheatstone bridge, designed close to the rotational springs, provides a voltage signal representative of the micro-mirror position. Sensing ASIC is aimed to bias the bridge and read the output voltage extracting high-resolution data for mirror resonance frequency control. A new circuital solution allows to compensate for resistive bridge sensitivity variations in temperature without any additional sensor on the mirror. The two ASICs have been diffused in BCD 0.18mm process at 3.3V voltage supply, preliminary step for a full integration of driving and sensing parts. Silicon results show that driver is effectively able to reduce load power consumption by a factor > 5 with only 2.5mW additional consumption at 40V and 25kHz driving signal, on top of integrated Boost converter efficiency. Control algorithms, based on sensing data, allow to keep stable resonance frequency providing 7mdegRMS mechanical accuracy over ±15deg opening angle.

Light detection and ranging (LIDAR) is one of solutions to extract 3D depth image of objects. Especially, as fabrication process of silicon image sensor has been progressed, amplitude-modulated continuous wave (AMCW) time-of-flight (ToF) cameras have been widely used due to their relatively cheap price and high measurement accuracy. However, to estimate ToF, reflected laser signal should be sequentially demodulated using optoelectronic device such as demodulation pixel, which induces relatively long integration and processing times. Additionally, due to the limitation of demodulation contrast and optical fill factor of demodulation pixel, depth measurement accuracy is also limited. To cope with such shortcomings of conventional ToF cameras, a novel AMCW method based on parallel phase-demodulation and related scanning LIDAR prototype are demonstrated in this paper. This scanning AMCW LIDAR prototype has enabled scanning object in extremely short integration time with adaptable field of view (FoV) and resolution to extract precise 3D depth images.

This work aimed to create a beam steering system based on a resonant micromirror with a control drive and sense modules implemented with low-voltage electronics and piezoelectric actuation and sensing. Solution's optimization goal was to create scalable architecture with minimal power consumption and reduce an overall MOEMS system size. We applied a direct digital control methodology for resonant piezoelectric elements by designing a level-translating electronics to directly interface actuator and sense elements with MAX1000 FPGA development board. This implementation merged control and measurement loops into VLSI design operating in the FPGA. The system behavior studied with 2D-scanning mirrors featuring an in-house piezoelectric MEMS-platform with AIN patterned actuation and sensing elements by measuring the generated laser reflection and pattern cross-correlating it with electrical signals. The developed MOEMS system provides the means for 2D optical scanning with a 1.8V logic level drive. Characterization results presented, study a mirror reflection pattern correlation with optical signals, and implemented control methods enabled frequency control with feedback in all operating conditions. The mirror feedback loop in the time domain provides reliable phase delay and oscillation period information. The calibrated look-up table post-processing module leverages this information and calculates the mirror's angular position at a given moment in time. The direct digital interface with a resonant piezoelectric mirror can deliver controllable beam steering in a single-supply, low-voltage, and high integration environment. The digital control loop allows for measurement and adjustment on a cycle-to-cycle basis, enabling further algorithm development for advanced functions like cross-sensor compensation, safety, and sensor fusion.

In this study, we propose and demonstrate a reflex optical phased array (OPA) chip, represents the most advanced optical scanning component of the third-generation LiDAR, and it has competitive advantages. The result showed the two-dimensional control of free-space optical fields at a wavelength of 1,550 nm at a 100 kHz modulation speed, which used dielectric thin film of SiN with an electro-optic response, realizing programmable space-variant control of optical wavefronts in a 32 × 4 pixel array at high speed. The 2D beam steering around a 30° × 2.5° field of view with the beam widths of 1.0° × 0.6°. We will provide custom solid-state LiDARs to clients, and these LiDARs will be more cost-effective than the commercial LiDAR products and will become more receptive by the autonomous vehicle market.

We report a new optofluidic transmissive wavefront modulator optimized for gravity-neutral performance and miniaturized dimensions. The modulator is optimized for compensating gravity-induced aberrations by simulating its behavior with various design configurations. Miniaturization was achieved by a novel method for liquid filling and sealing of the modulator. Key elements of the new interface are intra-substrate channels fabricated by a selective laser-induced etching process. The modulator has a final thickness of 750 µm and can be operated in any orientation without significant loss of modulation quality.

A thermal emitter fabricated on complementary metal-oxide-semiconductor (CMOS)-compatible facilities is a key component for low-cost mid-infrared gas sensing. While conventional thermal emitters have broad spectrum and wide emission angle, which limit the sensing performance. In this work, a microelectromechanical system (MEMS)-based thermal emitter with photonic crystal has been designed and fabricated using CMOS-compatible technology. The photonic crystal enables the emission wavelength selectivity within mid-infrared regime. By engineering photonic crystal dimension, the emission enhancement wavelength can be matched to the fingerprint wavelength of chemical gas for efficient chemical gas sensing purpose.

We present the optical and electrical properties of AlN-based and 12% doped ScAlN-based pyroelectric detectors fabricated on 8-inch wafers respectively. Both AlN and ScAlN materials are deposited at a temperature of ~200^oC, making them potential candidates for CMOS compatible MEMS pyroelectric detectors. FTIR spectroscopy is used to measure the absorption of these pyroelectric detectors over the wavelength range of ~2–14 μm and the results show absorption improvement up to ~75% for ScAlN-based pyroelectric detectors compared to that of AlN-based pyroelectric detectors at the wavelength of 4.26 μm where CO₂ gas absorption of IR radiation is anticipated. Higher output current (~3-fold increase) is also observed from ScAlN-based pyroelectric detectors. Other than pyroelectric coefficient that contributes to improved performance for ScAlN-based pyroelectric detectors, we believe that absorptivity of the device also plays a major role in the performance of pyroelectric IR detectors. The results obtained from the study of the electrical and optical properties of AlN-based and ScAlN-based CMOS compatible MEMS pyroelectric detectors will bring forth potential applications of these detectors onto multi-functional integrable and monolithic platforms.

Hyperspectral imaging and fluorescence sensing are widely used technologies in many applications in biomedical sciences. The key component in such techniques is the wavelength optical tunable filter that covers a wide range of excitation and emission spectrums of fluorophores. The detection sensitivity and specificity are highly dependent on the spectral filtering method’s characteristics and performance. Acousto-optic tunable filters (AOTF) and liquid crystal tunable filters (LCTF) are widely used spectral filtering methods for microscopy systems. Due to the complexity of these filters’ structures, they lack the integrability in miniaturized systems. Miniaturization allows portability, lower cost due to the possibility of mass production along with small amounts of samples and reagents needed to perform the analysis. Herein, we introduce a plasmonic tunable optical filter based on hybrid dielectric and plasmonic thin films of TiO₂, SiO₂ and Ag respectively, with a tunable air gap. The simplicity of the structure fabrication allows its integrability in lab-on-chip systems. The gap thickness can be changed by a micro-actuator, which translates to a tunable range of central wavelengths that exceeds 300 nm covering several types of fluorophores’ excitation and emission ranges. The peak's maximum transmittance is above 70% for all colors, and can even be up to 85% for some colors, with a rejection band over the rest of the visible range. The same filter structure could be tuned to cover different bands in the visible range by changing the film's thicknesses and materials.

We present the concept and detailed design of a Smart Slit Assembly for next generation spectrometers, and we experimentally demonstrate operation of an individual 221 μm × 111 μm smart slit channel employing a MEMS actuated shutter to continuously modulate the intensity of the optical input signal. The MEMS actuated shutter is fabricated in a 211 μm thick device layer of a Silicon-On-Insulator wafer by Deep Reactive Ion Etching. Electrostatic comb drive actuators allow an absolute displacement of 52 μm at 74 V, resulting in a continuously tunable shutter efficiency of up to 99.97% at an operating wavelength of 532 nm.

Smart Glasses, a subcategory of Head Mounted Display devices, are getting popular in the recent years, offering a convenient way to add information in addition to what the wearer see. Designers are seeking ways to build a Display Engine that can meet the targeted image performance (such as resolution, filed of view) yet keeping the total device size and weight as low as possible. This paper presents an innovative Display Engine based on Laser Beam Scanning (LBS) and outlines the main building blocks that were design and prototyped. It presents the use of MEMS Micro Mirrors (Resonant mirror and Linear mirror) and a newly developed RGB laser light source that integrates the three laser diodes into a single package. This paper outlines the opto-mechanical design considerations, beam and spot size analysis, the driving electronics, mirror and color control loops, the procedures and steps to assemble and calibrate the optical engine and finally presents the achieved results of this work.

The detection and identification of molecular gases are of high relevance in many applications within healthcare, production monitoring and safety as well as environmental monitoring. One of the major difficulties of trace gas analysis is due to the bulky and expensive systems, what excludes both mobile and handheld use. For this purpose we present our new system based on the Quartz Enhanced PhotoAcoustic Spectroscopy (QEPAS), which can provide the required properties for gas analysis. We have developed a compact detection unit where DFB laser, collimation optics and QTF are integrated in a 14-pin butterfly housing. Therefore an optimization of the DFB laser chips will be presented too. The results show, that the laser diodes not only provide excellent performance, but also allow a detection limit for the greenhouse gas methane and carbon dioxide in the ppm range.

The development of devices that are based on MEMS-on-CMOS technology becomes increasingly time-consuming since System-on-a-Chip (SoC) solutions for highly integrated and miniaturized devices are approaching smaller feature sizes. In order to reduce the development costs and shorten the time-to-market periods, the combination of commercially available CMOS processes from foundries with the subsequent processing in a dedicated MEMS facility is beneficial. This concept offers the possibility to separate the different technological requirements of conventional CMOS manufacturing and MEMS actor processing, which may follow different design rules and process specifications. As a representative of the dedicated MEMS foundries, Fraunhofer IPMS performs surface micromachining on 200 mm wafers for a variety of MEMS devices, in particular for spatial light modulators (SLM). Over the past decade, much experience was gained in development activities for customer specific applications like micro mirror arrays. In this paper, we will discuss essential requirements and upcoming challenges for the monolithic integration of surface micro-machined optical MEMS on foundry-fabricated CMOS backplanes, as conventional (i-Line) lithography is approaching patterning limits. We will present approaches of tuning the planarization of the CMOS chip surface to achieve an excellent mirror array flatness with CMOS compatible inorganic sacrificial layer techniques. Concepts like Mix&Match lithography for achieving high overlay accuracy and the litho stitching technique for the patterning of large chips will be reviewed and a brief outline of our roadmap for the implementation of DUV lithography will be presented.

We review our recent work on compact and low power silicon photonic components based on microelectromechanical systems (MEMS) and implemented in imec’s iSiPP50G foundry platform. Large scale reconfigurability is attractive for emerging applications such as photonic accelerators for AI workloads. However, the large power consumption and footprint of current components prohibits scaling to large circuits. Silicon MEMS offer 10000x lower power consumption, a small footprint, and excellent mechanics. We show phase shifters, couplers, and wavelength filters . The devices have small footprints of a few tens of micrometers per side, low insertion losses of the order of 0.1 dB and time constants of the order of 1 µs.

We present a new concept of spectroscopic sensor based on optomechanical transduction. The optomechanical interaction induces a strong dependence of the mechanical properties of a membrane on the optical losses induced by the absorption of an intra-cavity gas. Optically quantifying the variation of these parameters allows us to measure the gas concentration. The system is analysed theoretically and numerically with FEM simulation to estimate the responsivity. Fiber Bragg Grating based Extrinsic Fiber Fabry-Pérot cavity of various types as well as integrated mid-infrared cavities with highly reflective Bragg multilayers mirrors and silicon or stoichiometric silicon nitride membrane are studied.

Polarized Fourier transform infrared FTIR spectroscopy has been used extensively to monitor orientation for polymer quality control and optimized the mechanical properties. In the manufacturing process, using an in-line portable spectrometer would be a great advantage providing near real-time feedback during polymer production processes including temperature, and drawing/stretching. The goal is to let the chains within a polymer disentangle and become more systematic/oriented with predictable properties. In this work, we present a measurement technique using microelectromechanical system (MEMS) based polarization controlled Fourier transform spectrometer in the extended near-infrared used to monitor the polymer quality. The spectrometer is operating in the wavelength range of 1300 nm to 2600 nm (about 3846 cm^-1 to 7692 cm^-1) with a spectral resolution of 66 cm^-1. The polarized-FTIR data were collected for a commercial plastic CD sleeve with thickness of about 1 mm in transmission mode. An ultra-broadband wire grid linear polarizer is used, inserted in the light path and rotated 360º in steps 10º. The polarizer orientation is kept in the same position for both background and sample measurements. The dichroic ratios of different absorption bands have been determined with the polarizer oriented parallel and perpendicular to a reference direction. The orientation quality of the polymer can be detected from the dichroic ratio with dichroic ratio equals to one representing an isotropic material. Comparison with a benchtop device is conducted showing good agreement. The presented solution paves the way for a low-cost and portable device for on-line polymer quality control.

MEMS mirrors are used in projection systems based on Laser Beam Scanning LBS and hence they are involved in applications as Augmented Reality Headset and LiDAR. Characterization of the electro-mechanical behavior of MEMS structures plays an important role in the following control strategy definition and system integration. A mono-axial resonant PZT actuated MEMS mirror is addressed and the characteristics of the mechanical structure is investigated by measuring the frequency response of the functional and the main spurious vibrational modes. In addition, a dedicated analysis on the nonlinear behavior is performed Calibration stations with camera sensors are used for optical and electrical analyses while vibrometric and stroboscopic measurement techniques are employed for detecting micrometric movements of the structure. A piezoresistive sensor with Wheatstone bridge configuration is built on board of the MEMS mirror for tracking mirror position during actuation. The combined effects of the functional and spurious modes on the sensor frequency response are evaluated and compared with the MEMS mirror model. In this work, a full characterization on the electro-mechanical parameters of a resonant mono-axial PZT actuated MEMS mirror is presented and a detailed comparison between collected data and model prediction is reported.

The architecture used for driving linear micromirrors in raster scanning systems is typically composed of digital circuits, responsible for generating a sawtooth-like reference signal synchronized to the fast axis, and analog circuits responsible of driving the device. Bridging the two domains is the D/A converter, typically clocked in the MHz range, whose noise sources and distortion affect the accuracy of the scan line. With typical refresh rates in the order of 60 Hz, simulating transistor-level implementations requires up to days for a few operating cycles (i.e. 1.7 cycles/day). This drives the need for accurate models of the dominant noise sources and their impact on scan accuracy, able to achieve verification times compatible with typical design flow timelines. The architecture of this work is composed of a sigma-delta based current-steering D/A converter, which is modelled analytically and behaviorally with its white and flicker noise sources and non-idealities. Each current generator is modelled independently to capture time-variant effects. The developed model can accurately predict noise both from Cadence simulations and experimental measurements, while also reducing simulation times by three orders of magnitude (i.e. 5.7 cycles/minute). The model thus allows to optimize the design and quickly verify the possibility to achieve a tilt-angle rms noise within 1 m◦ in open-loop driving conditions. Experimental results also show a significant distortion, which is not predicted by the model: as hypotheses on its root causes are formulated, the model will enable their investigation within reasonable times.

Miniaturizing optical resonators on-chip offers employing them in lab-on-chip sensing devices, which achieves portability, lower price, and only finger prick sample sizes. However, the chip microfabrication limitation may impose some challenges. Taking the Fabry-Pérot cavity, the mirrors ideally should have curved shape in 3D to match the lightbeam wave front to achieve good light confinement inside the resonator. But as 3D curvature is challenging to fabricate on-chip, straight mirrors are usually used instead with short cavity lengths to avoid high diffraction loss with the beams’ multiple trips between the 2 mirrors. The short length limits the sample space between the mirrors, so it can’t accommodate large samples such as some types of biological cells. In previous work, the curvature is divided on 2 plans by using cylindrical mirrors for the horizontal plan confinement, and a fiber-rod-lens for the vertical plan confinement. That scheme achieved good light stability; but the curved mirrors produced side peaks as higher order resonance modes, which put limitation on the sensor range. In this work, a novel design is introduced to overcome this limitation by using straight mirrors instead of curved ones, and use an upright cylindrical lens to confine the light in the transverse direction before the cavity. The novel structure is designed by analytical modeling, and verified by numerical simulations. The cavity lengths are typically of tens of micrometers and can reach hundreds, allowing the fluidic channel to hold large test samples. The chip is fabricated in silicon, then fiber-rod-lenses are simply added post-fabrication.

In this paper, a new design of an electrothermal micromirror integrated with piezoresistive sensors is proposed. The micromirror is composed of four electrothermal bimorph actuators and four piezoresistive position sensors. In order to reduce the influence of temperature on piezoresistance, silicon dioxide can be used to thermally isolate the piezoresistive sensors from the silicon substrate. The optimized micromirror has a square mirror plate of 1800 * 1800 μm² and a footprint of 4040 * 4040 μm² , leading to a fill factor of 20%. The simulation results show that the optical fields of view of the micromirror are about 7° in the tilt and tip directions and the maximum piston displacement is close to 600 μm. The simulation results also show that the sensitivity and resolution of the piezoresistive sensors under a 3 V bias voltage are 2.88 mV/° and 0.4 μrad for the tip-tilt motion, respectively, and 0.056 mV/μm and 1.2 nm for the piston motion, respectively.