Micro-opto-electro-mechanical Systems Research Articles

Parallel Optical Profilometry Assisted Conception of an Opto-Electronic Illuminator Using a VCSEL and Diffractive Optics

Micro-opto electromechanical systems are of growing importance in the development of new miniaturised projection, imaging and detection technologies. Because of the increasing complexity of construction involving layers of microelectronics, optoelectronics and micro-optics, di erent types of defects can appear that need to be understood and controlled in order for the miniaturised system to operate correctly within the given speci cations. We have recently developed a miniaturised structured light (micro-opto electromechanical systems) projector consisting of a multilayer sandwich made of a rst layer of 3 bars of 12 VCSEL laser sources, a second layer of Fresnel collimating lenses (di ractive optical elements) and a third layer of Fourier di ractive optical elements to produce the structured light pattern. The main defects that had to be controlled were alignment errors, the rst ones being between the emitting surface and the collimating lenses and the second one concerning the lateral alignment of the photomasks used to produce the 4 levels of the Fourier elements. We demonstrate how 3D geometrical shape characterization of the emitting structures and di ractive optical elements surface structures using coherence scanning interferometry played a major role in the conception and fabrication of a prototype micro-optoelectromechanical projection system to understand the source of the alignment errors and to minimise them.

MOEMS Vibration Sensor for Advanced Low-frequency Applications with pm Resolution

Abstract The majority of MEMS vibration sensors requires relatively high resonance frequencies of several kilohertz to avoid mechanical contact of moving parts such as electrode plates. In contrast to that, our hybrid micro-opto-electro- mechanical system (MOEMS) enables sensor applications at low frequencies. This work describes a distinct MOEMS featuring extremely low resonance frequencies of below 200 Hz. It is operated ambient air without closed loop feed- back, extensive electronics and cooling. Due to the soft suspension of the micro-mechanical sub-system the funda- mental limit, the Brownian noise floor, is reached. The resulting noise equivalent displacement for frequencies above the resonance is 1.9 pm/ √Hz, which is equivalent to 0.29 μg/ √Hz below the resonance. We describe the design space for sensors with further enhanced sensitivity and resonance frequencies far below 100 Hz.

GaN nanostructuring for the fabrication of thin membranes and emerging applications

We present a review of technological methods developed in recent years for the purpose of gallium nitride nanostructuring, with the main focus on fabrication of thin GaN membranes. In particular, we report on traditional methods of wet etching undercutting for membrane manufacturing, technologies applied for the fabrication of photonic crystal structures based on GaN nanomembranes, double side processing, and surface charge lithography. Prospects of membrane applications in photonic devices, sensors, and microoptoelectromechanical and nanoelectromechanical systems are discussed, taking into account the advantageous piezoelectric, optical, and mechanical properties of GaN and related III-V nitride materials.

Digital micromirror device as a diffractive reconfigurable optical switch for telecommunication

Digital micromirror devices (DMDs) by their high-switching speed, stability, and repeatability are promising devices for fast, reconfigurable telecommunication switches. However, their binary mirror orientation is an issue for conventional redirection of a large number of incoming ports to a similarly large number of output fibers, like with analog micro-opto electro-mechanical systems. We are presenting here the use of the DMD as a diffraction-based optical switch, where Fourier diffraction patterns are used to steer the incoming beams to any output configuration. Fourier diffraction patterns are computer-generated holograms that structure the incoming light into any shape in the output plane. This way, the light from any fiber can be redirected to any position in the output plane. The incoming light can also be split to any positions in the output plane. This technique has the potential to make an “any-to-any,” true nonblocking, optical switch with high-port count, solving some of the problems of the present technology.

Large area and broadband semi-reflective Bragg mirror membrane manufactured by PECVD

Non-absorbing beam splitters integrated on silicon are desirable for various micro-opto electro mechanical systems (MOEMS) devices. In this paper, we demonstrate the manufacturing with a 100% yield of dielectric membranes having a diameter up to 5.9 mm and an approximately 50% reflectivity in the 570–900 nm wavelength range. The membranes are made from a stack of up to 12 alternating SiNx and SiO2 plasma enhanced chemical vapor deposition (PECVD) films deposited and annealed on silicon. Backside micromachining of the silicon wafer by deep reactive ion etching followed by XeF2 etching is used to release the membranes. Annealing effects on stress variation and hydrogen bonding in PECVD single films and multilayers were investigated in detail to get a multilayer stack with controlled tensile stress. Optical measurements of the reflectivity, flatness and vibrations of these membranes show that they are suitable for use in MOEMS devices working in the visible-near infrared range.

Optical propagation and refraction in silicon complementary metal–oxide–semiconductor structures at 750 nm: toward on-chip optical links and microphotonic systems

This paper analyzes the optical propagation and refraction phenomena in various complementary metal–oxide–semiconductor (CMOS) structures at 750 nm wavelength. Operation at these wavelengths offers the potential realizations of small microphotonic systems and micro-opto-electro-mechanical systems (MOEMS) in CMOS integrated circuitry, since Si-based optical sources, waveguides, and silicon (Si) detectors can all be integrated on a single chip. It could also increase the optical coupling efficiencies to external optical fibers. With the help of Monte Carlo and RSoft BeamPROP simulations, we demonstrate achievements with regard to optimizing vertical emission, focusing, refraction, splitting and wave guiding in 0.35 to 1.2 μm CMOS technology at 750 nm wavelength. The material properties, refractive indices, and thicknesses of various CMOS over-layers were incorporated in the simulations and analyses. The analyses show that both Si nitride and Si oxi-nitride offer good viability for developing such waveguides. Effective single-mode wave-guiding with calculated loss characteristics of 0.65 dB⋅cm −1 , with modal dispersion characteristics of less than 0.2 ps⋅cm −1 and with a bandwidth-length product of higher than 100 GHz-cm seems possible. A first iteration realization of an optical link is demonstrated, utilizing specially designed avalanche-based Si-LEDs and a specially designed first iteration CMOS waveguide. Potential applications of avalanche-based Si LEDs into microphotonic systems and MOEMS are furthermore proposed and highlighted.

Microassembly process to fabricate a microoptoelectromechanical systems scanning mirror with angular vertical comb electrodes

We present a simple microassembly technology that easily realizes angular vertical combs for a microoptoelectromechanical systems scanner. The scanner is composed of a device section with comb electrodes and a tilting section with four tapered pillars. During the microassembly process, two tilting pillars push down the levers so that the comb electrodes connected with the micromirror are tilted; the other two alignment pillars fit into the alignment holes of the device section, which is fabricated via a deep reactive ion etching process of a silicon-on-insulator wafer. The tilting section is fabricated through a series of anisotropic wet etching of a (100) silicon wafer and patterning processes of SU-8, which is robust enough to ensure repeatability of the initial tilted angles of the movable comb electrodes. The pull-in investigation function is analyzed through a numerical estimation to obtain a large scan angle with stable behavior. The fabricated microscanner shows an optical scan angle of up to 4.23 deg at 90 V in the static mode and stable actuation of up to 11.3 deg at a resonant frequency of 2.87 kHz. The roughness of the mirror surface is less than 10 nm, which will have a negligible effect on imaging quality. The initial tilted angles in the microassembly process showed high repeatability within 10% error.

MOEMS uniaxial accelerometer based on EpoClad/EpoCore photoresists with built-in fiber clamp

In this paper, a novel polymer MOEMS (micro-opto-electro-mechanical systems) accelerometer is reported. Low cost, photopatternable epoxies, EpoClad and EpoCore, are lithographically patterned through a 2 masks process to form this accelerometer in a simple and robust fabrication process. EpoClad is used for the cladding layer and EpoCore for the waveguides, fiber optic clamps and the seismic mass. Fiber optic clamping structures are presented that can be fabricated without extra process steps, and still assure both in-plane and out-of-plane clamping. The acceleration sensing principle is based on light intensity modulation by the seismic mass's position. A laser diode light source and a photodiode, connected to the sensor core through optical fibers, are used to extract the intensity variation as a function of acceleration. A vibration test was conducted to evaluate the performance of this MOEMS accelerometer.

Research of MOEMS Pressure Sensor

In recent years, with the development of optical communication by leaps and bounds, promote the Micro-opto-electro-mechanical system (MOEMS) development. As a new technology, the MOEMS have been widely used in optical communication, optical switching, data storage, optical sensing and etc.. Compared with the traditional pressure sensors, the optical pressure sensor based on MOEMS has some unique advantages. In this paper, the structures, operation principles and fabrication processes of various MOEMS pressure sensors are described mainly. Finally, the structure and Key technology of a MOEMS pressure sensor array is presented in brief.

垂直梳齿驱动的大尺寸MOEMS扫描镜

A Micro-opto Electro-mechanical System(MOEMS) scanning mirror with a large size,large torsional angles and a low driving voltage actuated by a vertical comb driver was proposed.The working principle of the vertical comb driver was analyzed and its fabrication process was discussed.By using a bulk micromaching process technology combined with a silicon-silicon bonding process,a vertical comb driver actuated MOEMS scanning mirror was fabricated.The fabricated scanning mirror has a size of 3 mm×2 mm,and a resonant frequency of 1.32 kHz.The test results show that the mirror has a high quality optical surface and the RMS of surface roughness is only 8.64 nm.When the driving voltage is set to be 95 V,the maximum rotation angle of the mirror is 2.4°.Furthermore,the tested turn-on responding time and turn-off responding time for the mirror are 1.887 ms and 4.418 ms,respectively.

Robust Precision Position Detection With an Optical MEMS Hybrid Device

For vibration and displacement sensors, robustness is one of the key requirements. Optical measurement concepts are among the most promising possibilities to achieve it. The presented microoptoelectromechanical system sensor modulates a light flux by means of two congruently placed aperture gratings: one etched into a seismic mass and the other fixed to the sensor package. Commercially available LED and photodetector components at the top and bottom of the sandwich structure generate and detect this modulated light flux and allow for a cost-effective implementation. The prototype used for experimental verification is actuated by inertial forces and exhibits a high sensitivity of 0.85 mV/nm for displacements of the seismic mass and a corresponding noise level of about 14 pm/√Hz. This sensitivity and noise level can be further improved, paving the way for small, lightweight, robust, and high-precision displacement sensors for a large variety of applications.

Improved micro-optoelectromechanical systems deformable mirror forin vivooptical microscopy

Micro-optoelectromechanical systems (MOEMS) deformable mirrors are being developed for focus control in miniature optical systems including endoscopic microscopes and small form-factor camera lenses. A new process is described to create membrane mirrors made from the photoset polymer SU-8. The SU-8 also serves as the adhesive layer for wafer bonding, resulting in a simple, low cost fabrication process. The process details and the optical properties of the resulting focus control mirrors, which have a diameter of 2 mm, a stroke in excess of 8 μm and very low residual aberration, are described. Multiple actuation electrodes allow active control of more than 1.4 μm peak-to-peak of wavefront spherical aberration. The MOEMS mirror is demonstrated in a confocal microscope in which it provides focus control during capture of in vivo images.

Design and process test of a novel MOEMS accelerometer based on Raman—Nath diffraction

A novel micro-opto-electro-mechanical system (MOEMS) accelerometer based on Raman—Nath diffraction is presented. It mainly consists of an FPW delay line oscillator and optical strip waveguides. The fundamental theories and principles of the device are introduced briefly. A flexural plate-wave delay-line oscillator is designed to work as an acousto-optic (AO) shifter, which has a Klein—Cook parameter of 0.38. Single-mode optical strip waveguides of 2 μm in width and thicknesses of 0.6 μm are designed by using the effective index method for light transmission. The Ey00 mode waveguide polarizers are designed to ensure the consistency of the light polarization in the waveguides. The fabrication process, based on (100) oriented, 450-μm-thick silicon wafers is proposed in detail, and some difficulties in the process are discussed carefully. At last, a series of process tests are undertaken to solve the proposed problems. The results indicate that the proposed design and fabrication process of the device is dependable and realizable.

Theoretical analysis and concept demonstration of a novel MOEMS accelerometer based on Raman—Nath diffraction

The design and simulation of a novel microoptoelectromechanical system (MOEMS) accelerometer based on Raman—Nath diffraction are presented. The device is planned to be fabricated by microelectromechanical system technology and has a different sensing principle than the other reported MOEMS accelerometers. The fundamental theories and principles of the device are discussed in detail, a 3D finite element simulation of the flexural plate wave delay line oscillator is provided, and the operation frequency around 40 MHz is calculated. Finally, a lecture experiment is performed to demonstrate the feasibility of the device. This novel accelerometer is proposed to have the advantages of high sensitivity and anti-radiation, and has great potential for various applications.

Micro-optoelectromechanical systems for space-based instruments

Micro-optoelectromechanical systems for space-based instruments

Polymer MOEMS Accelerometer

In this paper, a novel polymer MOEMS (Micro-Opto-Electro-Mechanical Systems) accelerometer is reported on. Low cost, photopatternable epoxies, EpoClad and EpoCore, are UV exposed by lithography to form this accelerometer in a simple and robust fabrication process. The EpoClad is used for the cladding layer and EpoCore for the waveguides, fiber optic clamps and the seismic mass. The acceleration sensing principle is based on light intensity modulation by the reflection of seismic mass’ position. A laser diode light source and a photodiode, connected to the sensor core through optical fibers, are used to extract the intensity variation as a function of acceleration. A vibration test of this MOEMS accelerometer yields a measured sensitivity of 1.5 mV/g.

Research of Micro-Accelerometer Based on MOEMS

Micro-Opto-Electro-Mechanical System (MOEMS) has the advantages of small size, light weight, little energy consumption, high reliability, high-volume production and so on. Micro-sensor is a new generation of sensor being developed, improved and expanded, and it will have a huge effect on the measurement area of still adopted traditional sensors. The characteristics and MOEMS manufacturing technologies are introduced. The concept and advantages of micro-sensors are described. The working principle of micro-accelerometer is analyzed.Micro-accelerometer will play an increasingly key role in the new monitoring and control equipments.Pole coupling is the key issue of micro-accelerometer to be resolved, but the rapid developing signal processing technology can provide new solutions to it.

Assembly of 3D micro‐components: a review of recent research

PurposeThe purpose of this paper is to review recent developments in micro‐scale assembly technologies, primarily in the context of microsystems based on three‐dimensional (3D) micro‐electromechanical systems (MEMS) and micro‐opto‐electromechanical systems (MOEMS) technologies.Design/methodology/approachFollowing a brief introduction, this paper first discusses the problems associated with the assembly of micro‐components and then considers the role of robots and self‐assembly technologies. This is followed by a brief summary and conclusion.FindingsExperimental robotic systems have been developed and used for the assembly of a wide range of MEMS and MOEMS components. Various self‐assembly technologies offer prospects for massively parallel microassembly but have yet to achieve the success of the robotic approach. Some work has sought to combine the best feature of both approaches but as yet, no technologies have been developed that can rapidly, accurately and cost‐effectively assemble micro‐components into hybrid 3D MEMS/MOEMS devices in a true production environment.Originality/valueThis paper provides a detailed review of recent progress in the robotic and self‐assembly of micro‐components.

Fabrication of sloped sidewalls by inductively coupled plasma etching for silicon micro-optic structures

Current work on deep-reactive ion etching has primarily focused on creating vertical sidewalls for microelectromechanical system and electronics applications. For micro-optical and micro-optoelectromechanical system structures control of the sidewall angles other than vertical is as important as the ultimate depth. In this work, we investigate the control of sidewall profiles using an inductively coupled plasma technique. The material systems being investigated on blanket samples are silicon and silicon dioxide with CF4, CHF3, and SF6 chemistries. Micro-optic structures are created by photolithography and CHF3 gas has been explored to achieve a wide range of etch rates, smooth etch profiles, and sidewall angles. The etch profiles are characterized by scanning electron microscopy.

Wafer-Level Heterogeneous Integration for MOEMS, MEMS, and NEMS

Wafer-level heterogeneous integration technologies for microoptoelectromechanical systems (MOEMS), microelectromechanical systems (MEMS), and nanoelectromechanical systems (NEMS) enable the combination of dissimilar classes of materials and components into single systems. Thus, high-performance materials and subsystems can be combined in ways that would otherwise not be possible, and thereby forming complex and highly integrated micro- or nanosystems. Examples include the integration of high-performance optical, electrical or mechanical materials such as monocrystalline silicon, graphene or III-V materials with integrated electronic circuits. In this paper the state-of-the-art of wafer-level heterogeneous integration technologies suitable for MOEMS, MEMS, and NEMS devices are reviewed. Various heterogeneous MOEMS, MEMS, and NEMS devices that have been described in literature are presented.