Design Of Micromirror Research Articles

Design and Fabrication Method of a Large-Size Electromagnetic MEMS Two-Dimensional Scanning Micromirror

Design and Fabrication Method of a Large-Size Electromagnetic MEMS Two-Dimensional Scanning Micromirror

Design and fabrication of non-resonant PZT MEMS micromirror with buried piezoresistors for closed loop position control

This paper reports on a 1D PZT micromirror integrated with buried piezoresistors for quasi-static feedback position control. The piezoresistors located along or below the PZT actuators could achieve the sensitivity as high as 3.1 mV/°, which was two orders of magnitude higher than the traditional ones located at the torsion springs (8.2 μV/°). This increased the signal-to-noise ratio by 2 orders of magnitude, which could enable the accurate position control. The response of the longitudinal sensors along the beams had a fast settling time less than 1 ms. The average position error was 0.975%, which was much better than that from the conventional shear stress sensor on the torsion bar of 3.1%.

Shock Destructive Reliability Analysis of Electromagnetic MEMS Micromirror for Automotive LiDAR

Light Detection and Ranging (LiDAR) devices are preferred sensors in the field of automatic and intelligent driving. LiDAR based on Micro-Electro-Mechanical Systems (MEMS) micromirrors has gained vital attention owing to the advantages of MEMS devices. In a harsh environment, the shock reliability of micromirrors has significantly constrained automotive applications, but such studies are rarely reported. In this work, the shock destructive reliability of electromagnetic MEMS micromirror in the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$z$ </tex-math></inline-formula> -direction is investigated to accelerate the commercialization of MEMS-LiDAR. The drop fall tests cover from 100 to 800 g in the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$z$ </tex-math></inline-formula> -direction, and the fracture emerges at the shock level of around 700 g. To comprehensively explore the factors of shock destructive reliability, finite element and dynamic models are completed. Finite element analysis is employed to investigate the stress distribution under shock loads, and the fracture is located at the position of maximum stress. The dynamic response and peak stress with shock pulses are explored numerically by the established dynamic model. The calculated results demonstrate that the response reaches a peak when the frequency of shock is the same as the natural frequency of micromirror. The results of peak stress with varied shock levels can be utilized to quickly predict the shock resistance. This work provides a deep insight into the optimization for the design of MEMS micromirror, which may promote the applications of MEMS-based LiDAR in autonomous driving. [2021-0200]

Design of electrostatic actuated MEMS biaxial scanning micro-mirror with serpentine structure

In this paper, the design and simulation fabrication of MEMS biaxial scanning parallel plate type micromirror with serpentine beams is described as having different folded beam dimensions. This scanning micro-mirror is an optical device used to steers and reflects incident light along with 1-D and 2-D with an angular rotation by 1° scan angle i.e. displacement of ∼43 µm of the mirror. It is applicable in coherence tomography, light projection, non-linear optics, optical switch, confocal microscopes, LiDAR etc. Electrostatic actuation in 2-D scanning micromirrors has a gimbal configuration and work on the principle of electrostatic forces between pairs of movable and fixed electrodes. However, a larger mirror dimension (∼5mm) results in a large electrodes gap which further requires a higher driving voltage to achieve the desired scan angle. To reduce the driving voltage, the straight torsion springs which connect the mirror to the gimbal are replaced by serpentine structures. The effects of pull-in voltage and resonant frequency in the order of 1 KHz straight torsion and serpentine beam on MEMS micromirror having a dimension of 5000 μm were studied.

Design and Development of a Double-Bridge Micromirror With Bending and Twisting Cantilevers for Multiobject Spectroscopy

This article presents the design, development, and characterization of a double-bridge electrostatically actuated micromirror for multiobject spectroscopy (MOS). The proposed structure is an improvement over single-bridge micromirrors in terms of aperture size, pull-in voltage, degrees of freedom, and fill factor. The two-axis symmetric rotation mechanism of the proposed micromirror is achieved by bending and twisting action of the suspended cantilevers which is contrary to the twisting cantilevers of a conventional one-axis torsional micromirror. The placement of anchor and cantilevers under the mirror plate results in a high fill factor when arranged in a 2-D array. The analytical modeling, design optimization, and static and dynamic analysis are done using finite-element method (FEM) in Coventorware. An optimized design is fabricated using a simple approach of surface micromachining and electroplating. For a micromirror of size $200\,\,\mu \text{m}\,\,\times 200\,\,\mu \text{m}$ and the actuation gap of $2.5~\mu \text{m}$ , the device exhibits a tilt angle of 1.5° at a pull-in voltage of 23.1 V, a switching time of $38~\mu \text{s}$ , and the resonance frequency of 35.23 kHz. A ${3} \times {3}$ array of the micromirror is demonstrated with a fill factor of more than 95%. The deflection range can be increased by simply increasing the thickness of the sacrificial layer and without any major process modification.

Vacuum packaged electromagnetic 2D scanning micromirror

We herein present the design, fabrication, and wafer-level packaging of an electromagnetic biaxial scanning micromirror. The vacuum packaging of the micromirror was implemented by anodically bonding the glass cap wafer to both sides of the silicon substrate with the micromirror. The measured quality factor of the vacuum packaged micromirror is 1923.2 for the horizontal scan, whereas that of the device in the air is 649.6. The maximum optical scan angle of the vacuum packaged micromirror is 24.19° at 155 mApp and 11.9 kHz for the horizontal scan, and 7.1° at 204.7 mApp and 60 Hz for the vertical scan. The estimated vacuum level of the package is 1.65 ± 0.85 Torr.

Design and simulation of a MEMS analog micro-mirror with improved rotation angle

This paper presents design and simulation of a MEMS analog torsional micro-mirror with improved rotation angle. The working range and consequently the rotation angle limitation of electrostatically actuated torsional micro-mirror due to pull-in instability are solved. Pedestal and suspension beams are presented to achieve electrostatically actuated torsional micro-mirror with extended working range. In the electrostatically actuated torsional micro-mirror, increasing the applied voltage decreases the equivalent stiffness of the structure and leads the system to an unstable condition by undergoing to a saddle node bifurcation. In the proposed structure to eliminate pull-in instability and increase the rotation angle range, mechanical stiffness of the structure is increased by adding a pedestal and locating auxiliary fixed-free beams in the free ends of the micro-mirror. The governing equations in relation to the proposed structure are derived. To verify, the numerical results are compared with simulated results.

Fabrication of mems devices – a scanning micro mirror case study

This paper presents the working principle, design, and fabrication of a silicon-based scanning micromirror with a new type of action mechanism as an example of MEMS (Micro-Electro-Mechanical Systems). Micromirrors can be found in barcode readers as well as micro-projectors, optical coherence tomography, or spectrometers’ adjustable filters. The fabrication process of the device prompted us to describe and discuss the problems related to the manufacture of MEMS. The article starts with some terminology and a brief introduction to the field of microsystems. Afterwards, the concept of a new scanning micromirror is explained. The device is operated by two pairs of thermal bimorphs. A special design enables to maintain a constant distance from the center of the mirror to the light source during the scanning process. The device was implemented in a one degree-of-freedom micromirror and a two degree-of-freedom micromirror. The fabrication process of both types is described. For each case, a different type of substrate was used. The first type of substrate was a standard silicon wafer; the second one, SOI (Silicon-On-Insulator). The process with the first one was complicated and caused many problems. Replacing this substrate with SOI solved some of the issues, but did not prevent new ones from arising. Nevertheless, the SOI substrate produces much better results and it is preferable to manufacture this type of MEMS devices.

A micromirror with CNTs hinge fabricated by the integration of CNTs film into a MEMS actuator

This paper reports a robust fabrication process to integrate carbon nanotubes (CNTs) film into a micro electromechanical systems actuator by the design and fabrication of a silicon micromirror supported by CNTs hinges. Vertically aligned single wall carbon nanotubes forest film was synthesized by water-assisted chemical vapor deposition. CNTs film was then condensed, manually maneuvered and patterned by EB lithography to form a flexible hinge of a mirror. The mirror is actuated by a electrostatic angular vertical comb actuator and the performance had been characterized. The mirror could be driven by a low voltage with a rotate angle of 1.5° and a response frequency of 500 Hz.

Design and Simulation of a MEMS Torsional Micromirror

In this paper, we designed an electrostatic driving MEMS torsional micromirror. The operation principle of the torsional micromirror is analyzed. Based on the analysis, a set of optimized design parameters of the micromirror is suggested. The design optimization of the micromirror is also performed with MathCAD software. At last an ANSYS simulation is achieved in the paper, which proves that the micromirror can provide a maximum workable torsional angle rotation of ±0.55º with corresponding driving voltage of 17.5V.

Design of a MEMS micromirror actuated by electrostatic repulsive force

A microelectromechanical system (MEMS) micromirror actuated by electrostatic repulsive force is demonstrated. The design is based on the principle that an asymmetric electric field produced by special layout of the electrodes can generate a repulsive force, which moves the mirror surface upwards. The factors affecting the magnitude of the driving force of the micromirror actuator are analyzed by FEA. The prototype is fabricated using a commercial available surface micromachining process and successfully tested using a Zygo NewView7300 interferometer. The displacement of the micromirror reaches 1.2μm at 60V.

Compact Low-Voltage Operation Micromirror Based on High-Vacuum Seal Technology Using Metal Can

In this paper, we present the design, fabrication, and vacuum package of an electrostatic comb-drive resonant micromirror. The micromirror having a high resonant frequency suitable for a laser scanning display was fabricated using a silicon-on-insulator (SOI) wafer. An individual die which was an array of four micromirrors with a total size of 5.5 × 5.5 mm2 was diced from the SOI wafer by dry etching. The die was packaged in a transistor-outline-8 metal can with a window in a vacuum-packaging machine at a pressure of 10-4 Pa. To evacuate the residual gases generated after the package process, a nonevaporable getter was used in the metal can. The resonant frequencies of the fabricated micromirrors were 13 and 25 kHz, respectively. An optical rotation angle of about 10° was achieved at a low driving voltage of 5 V. Due to the decrease of air-friction loss, the operation voltage decreased by a factor of 32 compared with the voltage operated at atmospheric pressure. The operation pressure in the vacuum package was evaluated to be about 0.7 Pa from the amplitude and quality factor of the mirror oscillation. Moreover, several properties, such as the surface profile of the micromirror, were evaluated before and after the packaging. The durability of the packaged mirror was tested at temperatures of up to 75°C. The theoretical explanations about air friction were also described.

FE modeling of stress and deflection of PZT actuated micro-mirror: Effect of crystal anisotropy

Abstract In this paper, we present finite element (FE) modeling of thermomechanical stress and deflection of lead zirconate titanate (PZT) actuated micro-mirror taking material anisotropy into account. Including silicon anisotropy in thermomechanical FE simulation resulted in 5% lower stresses and 9% higher deflections than those obtained for isotropic properties of silicon. Piezoelectric simulation with anisotropic properties of both silicon and PZT material has shown lower stresses and higher deflections compared to those obtained with isotropic properties of materials. The thickness of silicon substrate in the diaphragm region has also shown to have a significant influence on the deflection of micro-mirror. The deflection was found to increase dramatically to 133 mrad with the complete removal of silicon substrate. FE modeling taking materials anisotropy into account has proved to serve as an indispensable tool to realize an optimal design of micro-mirror.

Modeling, Design, Fabrication, and Demonstration of a Digital Micromirror With Interdigitated Cantilevers

We present the modeling, design, fabrication, and measurement results of a novel digital micromirror based on a new actuator called interdigitated cantilevers. In contrast to conventional micromirrors that rotate through the twisting actuation of a hinge, this micromirror has a symmetric bidirectional rotation through a bending actuation of interdigitated cantilevers hidden under a mirror plate. For the static and dynamic characteristics of the proposed micromirror, analytical models were developed first on the basis of the Euler-Bernoulli beam equation, as well as both distributed and lumped-parameter models. The results of the developed analytical models are in good agreement with those of a finite-element-method (FEM) simulation, having just a 10% deviation. On the basis of these analytical models, we successfully designed, fabricated, and evaluated a micromirror with a mirror size of 16 mum times 16 mum. The fabricated micromirror has a mechanical rotation angle of plusmn10deg, a pull-in voltage of 54 V, a resonant frequency of 350 kHz, and a switching response time of 17 mus. The measurement results compare favorably with those of analytical models and FEM simulations, with deviations of less than 15% and 10%, respectively.

Reliability Based Design Optimization of MEMS Considering Pull-In

The increased use of micro-electro-mechanical systems (MEMS) as key components for actuation and sensing purposes in novel devices and systems emphasizes the need for optimal design methods. Stochastic variations in manufacturing and operational conditions must be considered in order to meet performance goals. This study proposes a reliability based design optimization methodology for the design of geometrically complex electrostatically actuated MEMS. The first order reliability method is used for reliability analysis of fully-coupled electrostatic-mechanical problems. A general methodology for predicting the instability phenomenon of pull-in and incorporating it into an automatic optimization process is proposed and verified with analytical and experimental results. The potential of this methodology is illustrated with the design of an analog micromirror.

用于激光二极管抽运固体激光器热畸变补偿的MEMS微变形镜设计

用于激光二极管抽运固体激光器热畸变补偿的MEMS微变形镜设计

A low-drift, open-loop controlled, single crystalline silicon micromirror with floating field-limiting shields

This paper describes the design, fabrication and testing of a one-axis micromirror in order to suppress the electric charging problem related to its actuation. The electrostatically-actuated torsional micromirror is of the parallel-plate type. Since the dielectric around the electrodes below the mirror plates is highly exposed, we installed gold shields in the floating state around the electrodes, so as to cover the exposed dielectric surface. The gold shields played a leading role in limiting the electric field between the electrodes. This effect was characterized and the tilting angle stability was measured by observing the micromirror performance with and without the floating field-limiting shields. Drift measurements of these two types of micromirrors were made using a position-sensing detector (PSD). The micromirror with the field-limiting shields, namely micromirror type A, showed a tilting angle drift of 0.005° at 83% of the pull-in voltage, while a tilting angle drift of 0.5° was measured at the same percentage of the pull-in voltage for the micromirror without the field-limiting shields, namely micromirror type B. At 97.7% of the pull-in voltage, the pull-in phenomenon occurred after 220 s for micromirror type B due to the charging effect. On the other hand, micromirror type A showed no pull-in phenomena with elapsed time at a bias of 97.7% of the pull-in voltage due to the resolution of the charging effect.

Study of a deformable micro-mirror based on PZT films

This paper presents the design and fabrication of a novel deformable micro-mirror which is mainly composed of a silicon-based lead zirconate titanate (PbZr53Ti47O3, PZT) film using an inexpensive, simple and reliable sol?gel method. In accordance with the converse piezoelectric effect, deformation of the new micro-mirror, with the structure , can be achieved by changing the thickness of the PZT film by controlling the applied voltage. The new micro-mirror has the advantage of small size, light weight and fast response time over a conventional one based on the bimetal thermal effect or electrostatic force principle. An x-ray diffraction pattern of the fabricated PZT film was obtained and the deformation of the PZT thickness was tested with a digital interferometer. Experiments demonstrated that a micro-mirror made from the structure of PZT film could alter the thickness of the film and be practicably used in an adaptive optical system.

Electromagnetic Two-Dimensional Scanner Using Radial Magnetic Field

In this paper, we present the design, fabrication, and measurement results of a two-dimensional electromagnetic scanning micromirror actuated by radial magnetic field. The scanner is realized by combining a gimbaled single-crystal-silicon micromirror with a single turn electroplated metal coil, with a concentric permanent magnet assembly composed of two concentric permanent magnets and an iron yoke. The proposed scanner utilizes the radial magnetic field rather than using a lateral magnetic field oriented 45° to the horizontal and vertical scan axes to achieve a biaxial magnetic actuation. The single turn coil fabricated with electroplated copper achieves a nominal resistance of 1.2Ω. A two-dimensional scanner with mirror size of 1.5mm in diameter was fabricated. Maximum optical scan angle of 8.8° in horizontal direction and 8.3° in vertical direction were achieved. Forced actuation of the gimbal at 60 Hz and resonant actuation of the micromirror at 19.1-19.7kHz provide slow vertical scan and fast horizontal scan, respectively. The proposed scanner can be used in raster scanning laser display systems and other scanner applications.

An electrostatic scanning micromirror with diaphragm mirror plate and diamond-shaped reinforcement frame

We present the design, fabrication and measurement results of a comb-driven electrostatic scanning micromirror. Instead of a conventional micromirror having uniform thickness across the entire reflective surface, a diaphragm mirror plate supported by an array of diamond-shaped frame structures is fabricated monolithically. The fabrication process is a simple sequence of silicon deep etch processes on both sides of the silicon-on-insulator (SOI) substrate without the substrate bonding process. The micromirror is fabricated on the device layer of the substrate. The mirror plate undergoes a rotational motion by an electrostatic force between the movable comb electrodes connected to the micromirror and stationary comb electrode formed on the handle wafer. A scanning micromirror with a 10 µm thick diaphragm mirror plate, having a planar dimension of 1.5 × 1.5 mm2, supported by an array of 110 µm thick rhombic support frames, was fabricated and tested. A mechanical deflection angle of 8.5° at a resonance frequency of 19.55 kHz and a pressure of 7 mTorr was obtained. A prototype of the raster scanning laser projection display system was developed using the fabricated micromirror as the horizontal scanner and a galvanomirror as the vertical scanner, respectively.