Scanning Micromirror Research Articles

Design and investigation of dual-axis electrostatic driving MEMS scanning micromirror

Design and investigation of dual-axis electrostatic driving MEMS scanning micromirror

Driving Principle and Stability Analysis of Vertical Comb-Drive Actuator for Scanning Micromirrors.

We have developed a manufacturing process for micromirrors based on microelectromechanical systems (MEMS) technology. The process involves designing an electrostatic vertically comb-driven actuator and utilizing a self-alignment process to produce a height difference between the movable comb structure and the fixed comb structure of the micromirror. To improve the stability of the micromirror, we propose four instability models in micromirror operation with the quasi-static driving principle and structure of the micromirror considered, which can provide a basic guarantee for the performance of vertical comb actuators. This analysis pinpoints factors leading to instability, including the left and right gap of the movable comb, the torsion beams of the micromirror, and the comb-to-beams distance. Ultimately, the voltages at which device failure occurs can be determined. We successfully fabricated a one-dimensional micromirror featuring a 0.8 mm mirror diameter and a 30 μm device layer thickness. The height difference between the movable and fixed comb structures was 10 μm. The micromirror was able to achieve a static mechanical angle of 2.25° with 60 V@DC. Stable operation was observed at voltages below 60 V, in close agreement with the theoretical calculations and simulations. At the driving voltage of 80 V, we observed the longitudinal displacement movement of the comb fingers. Furthermore, at a voltage of 129 V, comb adhesion occurred, resulting in device failure. This failure voltage corresponds to the lateral torsional failure voltage.

Online Iterative Optimization for Angle Tracking of Electromagnetic Scanning Micro-Mirror With Unmatched Interference and Hysteresis

Online Iterative Optimization for Angle Tracking of Electromagnetic Scanning Micro-Mirror With Unmatched Interference and Hysteresis

Piezoelectric 1D MEMS scanning micromirror fabricated with bulk PZT laminated on stainless steel plate

In this research, a piezoelectric metal scanning micromirror with a large reflective surface area is presented. Unlike conventional scanning micromirrors fabricated with single-crystal silicon, stainless steel plate is used as the structural layer material. Two distinct device models, varying in cantilever and connector geometry, were conceptualized and experimentally assessed. These fabricated devices utilized the strain induced in bulk PZT (lead zirconate titanate) plates affixed to the cantilevers on opposing sides of the reflective surface. A 5 mm-diameter gold-coated silicon mirror plate served as the reflective surface. We evaluated the performance of two bulk PZT plates, PZT-5H and PZT-8. Our experimental results reveal that model #1, driven by PZT-5H with a sinusoidal input voltage of 200 Vpp, achieved a maximum optical scan angle of 26°, while model #2 exhibited a more substantial maximum scan angle of 44°. The average resonant frequency of the PZT-5H samples was 1264 Hz for model #1 and 995 Hz for model #2. These findings underscore the viability of stainless steel plates as a robust structural layer for piezoelectric scanning micromirrors. The proposed design holds potential for integration into a 3D LiDAR system when combined with an additional slow vertical scanner.

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

A robust lateral shift free (LSF) electrothermal micromirror with flexible multimorph beams

Electrothermal bimorph-based scanning micromirrors typically employ standard silicon dioxide (SiO2) as the electrothermal isolation material. However, due to the brittle nature of SiO2, such micromirrors may be incapable to survive even slight collisions, which greatly limits their application range. To improve the robustness of electrothermal micromirrors, a polymer material is incorporated and partially replaces SiO2 as the electrothermal isolation and anchor material. In particular, photosensitive polyimide (PSPI) is used, which also simplifies the fabrication process. Here, PSPI-based electrothermal micromirrors have been designed, fabricated, and tested. The PSPI-type micromirrors achieved an optical scan angle of ±19.6° and a vertical displacement of 370 μm at only 4 Vdc. With a mirror aperture size of 1 mm × 1 mm, the PSPI-type micromirrors survived over 200 g accelerations from either vertical or lateral directions in impact experiments. In the drop test, the PSPI-type micromirrors survived falls to a hard floor from heights up to 21 cm. In the standard frequency sweeping vibration test, the PSPI-type micromirrors survived 21 g and 29 g acceleration in the vertical and lateral vibrations, respectively. In all these tests, the PSPI-type micromirrors demonstrated at least 4 times better robustness than SiO2-type micromirrors fabricated in the same batch.

Pixelated vertical-cavity surface-emitting laser arrays from colloidal quantum dot films

Pixelated arrays of vertical-cavity surface-emitting lasers from colloidal quantum dot thin films have been demonstrated. CdSe/ZnCdS core/shell structured colloidal quantum dots have been used as laser gain medium. 10 pairs of alternating layers between GaN and nanoporous GaN consisted highly reflective distributed Bragg reflectors, exhibiting more than 99% of reflectivity in the spectral range of 600 nm–650 nm. Close-packed colloidal quantum dot solid thin films were sandwiched between the two GaN/nanoporous GaN distributed Bragg reflectors to achieve well-defined lasing outputs under pulsed optical excitation with the lasing threshold as low as 11.0 μJ/cm2. The resulting CQD-VCSEL devices exhibited a lasing output power of 1.5 μW and a conversion efficiency of 11.4%. Finally, a two-axis scanning micro-mirror was used to complete the 25 (5 by 5) pixelated laser arrays system.

Super-twisting Sliding Mode Control Based on Electrostatic MEMS Micromirror Scanning

In this paper, a Super-twisting sliding-mode control method based on a nonlinear interference observer is proposed for the external perturbation of MEMS micromirrors during beam scanning. Developing a physical model of electrostatic MEMS micromirror, the Super-twisting sliding-mode control algorithm based on nonlinear interference observer is applied to the electrostatically driven MEMS scanning micromirror with side electrodes, with the demonstration on stability of the control system by Lyapunov theory. The method effectively improves the anti-disturbance performance of the system. The simulation results show that the Super-twisting sliding mode control method based on nonlinear disturbance observer can effectively enhance the disturbance inhibition of the system.

Development of an Optoelectronic Integrated Sensor for a MEMS Mirror-Based Active Structured Light System.

Micro-electro-mechanical system (MEMS) scanning micromirrors are playing an increasingly important role in active structured light systems. However, the initial phase error of the structured light generated by a scanning micromirror seriously affects the accuracy of the corresponding system. This paper reports an optoelectronic integrated sensor with high irradiance responsivity and high linearity that can be used to correct the phase error of the micromirror. The optoelectronic integrated sensor consists of a large-area photodetector (PD) and a receiving circuit, including a post amplifier, an operational amplifier, a bandgap reference, and a reference current circuit. The optoelectronic sensor chip is fabricated in a 180 nm CMOS process. Experimental results show that with a 5 V power supply, the optoelectronic sensor has an irradiance responsivity of 100 mV/(μW/cm2) and a -3 dB bandwidth of 2 kHz. The minimal detectable light power is about 19.4 nW, which satisfies the requirements of many active structured light systems. Through testing, the application of the chip effectively reduces the phase error of the micromirror to 2.5%.

Electromagnetic 2D scanning micromirror fabricated with 3D printed polymer parts for LiDAR applications

In this research, an omnidirectional scanning micromirror fabricated using a three-dimensional (3D) printing process and manual assembly is presented. The core part of the scanning micromirror is printed with photocurable resin using vat polymerization based on digital light processing. Externally fabricated 6mm-diameter aluminum-coated silicon mirror plate, self-supported coils, and permanent magnets were assembled with the printed part to provide a reflective surface and electromagnetic actuation. Two types of devices with different spring shapes were designed and tested. Modal analyses were performed for each model with different magnet combinations in the design phase. To optimize the 3D printing process, resin mixtures with various mixing ratios were tested. An optical scan angle of 8.98° has been obtained for model #1 printed with an ABS-like resin at 309 Hz and an input current of 0.2 A rms . For model #2 printed with a 9:1 mixture of ABS-like resin and B9R-2-Black resin, an optical scan angle of 6.04° at 356 Hz an input current of 0.2 A rms has been obtained. Spiral scan patterns with various modulation depths were generated using model #1. • An omnidirectional scanning micromirror fabricated using a 3D printing process • Core part of the device is printed with vat polymerization using DLP • Resin mixtures with various mixing ratios were tested to optimize the fabrication • Two types of devices with different spring geometries were designed and tested

A Model Independent Control Scheme for Electromagnetic Scanning Micromirrors

Due to the existence of hysteresis and unmeasured electromagnetic torque, it is not easy to establish an accurate model of an electromagnetic scanning micromirror (ESMM) system. Therefore, the use of model-based angle control strategies limits the large-scale application of ESMM chips in industrial manufacturing. In this article, a model independent control (MIC) method is proposed to control the deflection angle of ESMM, which can avoid the modeling process and facilitate the large-scale industrial application of ESMM chips. In the proposed approach, the controller design is not based on mathematical model of the micromirror but just using the measured input and output of the ESMM. To predict the behavior of ESMM with hysteresis, a model-free predictor based on the measured system I/O data is proposed. After that, an online model-free nonsmooth optimization algorithm is developed to search for the optimal control solution. Then, the stability of the MIC system is analyzed. At the end, the performance of the proposed method is verified through simulation and experimental results.

Online Optimization Control With Predictive Gradient Descent for MEMS Micro-Mirrors

In this article, an online optimization control scheme is proposed for the angle control of MEMS scanning micromirror actuated via electromagnetic method. In order to avoid complicated process of building precise model of the MEMS micromirror, a control structure not relying on precise model is developed. In this structure, a simplified linear dynamic model is used to describe the basic dynamic behavior of the micromirror. Then, a model error compensation mechanism is introduced to compensate for the model uncertainty caused by unmodeled dynamics and nonlinear factors, such as hysteresis. Moreover, a predictive gradient descent based optimization mechanism is proposed to compensate the effect of time-delay and speed up the convergence of online optimization process. Then, the stability analysis of the proposed control system is implemented. Finally, the proposed control scheme is applied to the angle control of electromagnetically driven scanning micromirror and the corresponding experimental results are presented.

Electromagnetic omnidirectional scanning micromirror with multi jet fusion printed structures for smart factory applications

This paper presents a new omnidirectional scanning micromirror fabricated with a multi jet fusion three-dimensional (3D) printing process. The proposed electromagnetically actuated wobbling scanner has an aluminum-coated 6 mm-diameter mirror supported by quadpod springs and magnets for actuation. The analytic model for optimizing the driving coil is presented and compared with the finite element analysis results. The core part of the structural layer is fabricated by the 3D printing process and assembled with a separately fabricated reflective surface, permanent magnets, and coils. Three different combinations of magnets are tested to improve the optical scan angle of the device and provide a wider field of view (FOV). The one-dimensional (1D) horizontal (H) scan angle of 15.2° is obtained at 415 Hz, and 14.5° is obtained at the vertical (V) scan mode at 406 Hz. The applied current at both scan modes is less than 100 mA rms . The two-dimensional (2D) scan capability is also analyzed by generating the Lissajous, circular, and spiral scan patterns. For the spiral scan, a 2D FOV of 8° is achieved with the driving frequency of 400 Hz and the phase difference of 120°, which is equivalent to the FOV of 360° × 4°, the vertical angular resolution of 0.01°, and frame rate of 1 fps for light detection and ranging (LiDAR) system optics. The amplitude modulation depth and frequency are 100% and 1 Hz, respectively. The developed device can potentially be utilized in various LiDAR applications for the smart factory. • A 6 mm-diameter omnidirectional scanning micromirror has been fabricated by multi jet fusion 3D printing. • Operation principle of the scanner has been analyzed and spiral scan pattern with 8° field-of-view has been generated. • Surface morphology and characteristics of the MJF fabricated device have been analyzed. • Tested various 2D scan capabilities, including of Lissajous, circle, and spiral scan.

Design and Fabrication of Silicon-Blazed Gratings for Near-Infrared Scanning Grating Micromirror

Blazed gratings are the critical dispersion elements in spectral analysis instruments, whose performance depends on structural parameters and topography of the grating groove. In this paper, high diffraction efficiency silicon-blazed grating working at 800–2500 nm has been designed and fabricated. By diffraction theory analysis and simulation optimization based on the accurate boundary integral equation method, the blaze angle and grating constant are determined to be 8.8° and 4 μm, respectively. The diffraction efficiency is greater than 33.23% in the spectral range of 800–2500 nm and reach the maximum value of 85.62% at the blaze wavelength of 1180 nm. The effect of platform and fillet on diffraction efficiency is analyzed, and the formation rule and elimination method of the platform are studied. The blazed gratings are fabricated by anisotropic wet etching process using tilted (111) silicon substrate. The platform is minished by controlling etching time and oxidation sharpening process. The fillet radius of the fabricated grating is 50 nm, the blaze angle is 7.4°, and the surface roughness is 0.477 nm. Finally, the blazed grating is integrated in scanning micromirror to form scanning grating micromirror by MEMS fabrication technology, which can realize both optical splitting and scanning. The testing results show that the scanning grating micromirror has high diffraction efficiency in the spectral range of 810–2500 nm for the potential near-infrared spectrometer application.

Static High Voltage Actuation of Piezoelectric AlN and AlScN Based Scanning Micromirrors

Piezoelectric micromirrors with aluminum nitride (AlN) and aluminum scandium nitride (Al0.68Sc0.32N) are presented and compared regarding their static deflection. Two chip designs with 2 × 3 mm2 (Design 1) and 4 × 6 mm2 (Design 2) footprint with 600 nm AlN or 2000 nm Al0.68Sc0.32N as piezoelectric transducer material are investigated. The chip with Design 1 and Al0.68Sc0.32N has a resonance frequency of 1.8 kHz and a static scan angle of 38.4° at 400 V DC was measured. Design 2 has its resonance at 2.1 kHz. The maximum static scan angle is 55.6° at 220 V DC, which is the maximum deflection measurable with the experimental setup. The static deflection per electric field is increased by a factor of 10, due to the optimization of the design and the research and development of high-performance piezoelectric transducer materials with large piezoelectric coefficient and high electrical breakthrough voltage.

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.

Micromachined two-axis water-immersible scanning mirror using torsional and bending hinges

We report a two-axis water-immersible microscanning mirror using torsional and bending biaxially oriented polyethylene terephthalate hinges. Two different designs based on a four- or single-coil electromagnetic actuator are investigated. A micromachining-based fabrication process is developed to enable high patterning resolution and alignment accuracy and to reduce the amount of manual assembly. With a torsional hinge, the fast axis has a resonance frequency of 300 to 500 Hz in air and 200 to 400 Hz in water. With a bending hinge, the slow axis has a resonance frequency of 60 to 70 Hz in air and 20 to 40 Hz in water. 2D B-scan and 3D volumetric ultrasound microscopy are demonstrated using the hybrid-hinge scanning mirror. The ability of scanning the slow axis at DC or very low frequencies allows a dense raster scanning pattern to be formed for improving both the imaging resolution and field of view.

Improvement and Optimization of Electromagnetic Integrated Scanning Micromirror.

In this paper, the effect of driving system on working performance of electromagnetic integrated scanning micromirror (ISM) is studied. To further improve the optimization design of the electromagnetic ISM, the detailed theoretical analysis, simulation analysis, and experimental test are carried out, respectively. By changing the force form and external magnetic field of the device, the mechanical scanning angle, driving voltage, and resonant frequency of the electromagnetic ISM will be changed accordingly, and then the change of the working performance of the ISM is explored. Through the optimization analysis and comparative test, the optimal design scheme of driving system is obtained, and the effect of driving system on the working performance of the electromagnetic ISM is verified. The experimental results show that by optimizing the structure of the driving system, the mechanical scanning angle of the electromagnetic ISM is increased by about 20%, and the driving voltage is decreased about 10% observably, and the working performance of the electromagnetic ISM is significantly improved. The research results have important significance and practical application value for the extended application of the electromagnetic ISM in the field of optical detection.

Real-time variable field-of-view scanning of LiDAR by controlling the drive voltage of MEMS micromirror

As the new generation of 3D imaging Lidar is being more and more miniaturized, low-cost and high-precision, micro-electromechanical systems(MEMS) are being considered as core components due to their unique characteristics. In practice, according to the distance of the measured objects, it is necessary to change the field-of-view scanning in real-time to achieve the best imaging effect. In this paper, we attempt to establish a nonlinear dynamic model of the MEMS scanning micromirror, and thereby determine the nonlinear relationship between the driving voltage and the scanning angle. The field-of-view scanning in the range of 0–40° can be achieved by controlling the drive voltage of the MEMS scanning micromirror.

Low Power Electromagnetic Scanning Micromirror for LiDAR System

In this article, a low power and compact scanning micromirror for LiDAR (light detection and ranging) system is designed, fabricated, and characterized. A 5 mm-diameter scanning micromirror is electromagnetically actuated with multi-turn copper winding formed on the gimbal and magnet assembly formed under the silicon substrate. A unique magnetic circuit that generates an asymmetric radial magnetic field has been designed and analyzed. A series-connected double spring-mass system consisting of a gimbal and a mirror plate has been used to amplify the deflection angle. An analytic model of the system has been developed and verified with finite element analysis. Also, a reinforcement rim structure is utilized to reduce the dynamic deformation of the reflective surface down to 19.3 nm <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rms</sub> . An optical scan angle of 30 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sup> is obtained at 690 Hz, 17.4 mA <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rms</sub> input, and corresponding power consumption is 7.8 mW <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rms</sub> . A prototype scanning system with 180 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sup> x 30 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sup> field-of-view has been demonstrated with fabricated scanning micromirror as the vertical scanner. The proposed approach provides a simple and compact design for a large diameter scanning micromirror, which can potentially be utilized in various LiDAR applications.