Two-axis MEMS Research Articles

Study on the influence of manufacturing tolerance of the spring beam on the sensitivity of the two-axis MEMS accelerometer

Study on the influence of manufacturing tolerance of the spring beam on the sensitivity of the two-axis MEMS accelerometer

Water-Immersible MEMS Mirror with a Large Optical Aperture.

This paper presents a two-axis AlScN-based water-immersible MEMS mirror fabricated in an 8-inch MEMS process. Compared with other studies, this device has a larger optical aperture 10 mm in diameter. The resonant frequencies of the device are 1011 Hz in air and 342 Hz in water. The scanning angle reaches ±5° and ±2° at resonant frequencies in air and water, respectively. The cavitation phenomenon is observed when the device is operating in water, which leads the device to electrical failure. To address this issue, a device with reduced resonant frequencies-246 Hz and 152 Hz in air and water-is characterized, through which the bubbles can be effectively prohibited. This MEMS mirror could potentially be used in ultrasound and photoacoustic microscopy applications.

A MEMS Mirror-Based Confocal Laser Endomicroscope with Image Distortion Correction

Scanning MEMS mirrors can extend confocal laser microscopy into endoscopic applications, but the practical use of MEMS mirror-based confocal endomicroscopy is hindered partially by various image distortions such as barrel, fan-shaped and nonlinear distortions. In this work, the nonlinear scanning behaviors of an electrothermal MEMS mirror are analyzed and incorporated into an optical scanning model that takes all these three types of distortions into account. The model generates a 2D spatial mapping that can be applied to correct all of the image distortions in one step without a calibration board. To experimentally validate this method, a confocal laser endomicroscope employing a two-axis scanning electrothermal MEMS micromirror is designed and constructed, and confocal fluorescence images of a patterned micro-structure are obtained with the MEMS endomicroscope. The results show that the overall image distortion is reduced by at least one order of magnitude in the length direction.

AlScN Piezoelectric MEMS Mirrors with Large Field of View for LiDAR Application.

This paper presents AlScN piezoelectric two-axis MEMS mirrors with gimbal-less and gimbaled designs fabricated in a CMOS-compatible manner. Integrated piezoelectric sensors provided feedback signals of the actual mirror positions. The mirror with a diameter of 1.5 mm possessed adjustable optical tilt angles of up to 22.6° @ 30 V, with a high resonance frequency of about 8.2 kHz, while the 3 mm mirror reached 48.5° @ 41 V. The mirror with the gimbaled structure exhibited an excellent field of view and good mechanical decoupling. Additionally, a significant improvement in mirror scanning performance was observed in a vacuum (4 Pa), proving that the optical field of view was magnified by more than a factor of 10.

Three-beam Doppler optical coherence tomography using a facet prism telescope and MEMS mirror for improved transversal resolution

An improved three-beam Doppler optical coherence tomography system was developed. It utilizes a custom-made three-facet prism telescope to improve the transversal resolution at the sample. Furthermore, a two-axis gimbal-less MEMS mirror is used to minimize off-pivot beam movement at the pupil of the eye, enabling circular scanning for in vivo retinal measurements. We demonstrate the system’s abilities for in vitro circular scanning to measure absolute flow and to reconstruct the full velocity vector on a bifurcation flow phantom. Moreover, in vivo retinal measurements using circular scanning around vessel bifurcations of healthy human volunteers were performed. Measurements of the absolute mean flow and its orientation are in good agreement with the expected values for in vitro measurements. For in vivo measurements, the in- and outflow of blood for retinal vessel bifurcations show an excellent agreement, demonstrating the reliability of the technique.

Correction of image distortions in endoscopic optical coherence tomography based on two-axis scanning MEMS mirrors

A two-axis scanning microelectromechanical (MEMS) mirror enables an optical coherence tomography (OCT) system to perform three-dimensional endoscopic imaging due to its fast scan speed and small size. However, the radial scan from the MEMS mirror causes various distortions in OCT images, namely spherical, fan-shaped and keystone distortions. In this paper, a new method is proposed to correct all of three distortions presented in OCT systems based on two-axis MEMS scanning mirrors. The spherical distortion is corrected first by directly manipulating the original spectral interferograms in the phase domain, followed by Fourier transform and three-dimensional geometrical transformation for correcting the other two types of distortions. OCT imaging experiments on a paper with square ink printed arrays and a glass tube filled with milk have been used to validate the proposed method. Distortions in OCT images of flat or curved surfaces can all be effectively removed.

Two-axis MEMS scanner with transfer-printed high-reflectivity, broadband monolithic silicon photonic crystal mirrors

We present a two-axis electrostatic MEMS scanner with high-reflectivity monolithic single-crystal-silicon photonic crystal (PC) mirrors suitable for applications in harsh environments. The reflective surfaces of the MEMS scanner are transfer-printed PC mirrors with low polarization dependence, low angular dependence, and reflectivity over 85% in the wavelength range of 1490nm~1505nm and above 90% over the wavelength band of 1550~1570nm. In static mode, the scanner has total scan range of 10.2° on one rotation axis and 7.8° on the other. Dynamic operation on resonance increase the scan range to 21° at 608Hz around the outer rotation axis and 9.5° at 1.73kHz about the inner rotation axis.

A novel two-axis MEMS scanning mirror with a PZT actuator for laser scanning projection

This study presents a novel design for a two-axis scanning device driven by lead-zirconate-titanate (PZT) ceramic. The proposed device consists of a scanning mirror and a Y-shaped piezoelectric actuator. The scanning mirror was fabricated using an MEMS process involving three masks. Experimental results show that the fast and slow frequencies at resonance are 25.0 kHz and 0.56 kHz, respectively. The optical scanning angles are 27.6° and 39.9°. The power consumption of the device is 13.4 mW at a driving voltage of 10 V. This study also develops a laser projection module integrated with the scanning device. The module can project a 2-D image at a resolution of 640 x 480.

MEMS Gyro Aided Calibration of Electronic Compass

In this paper, an MEMS gyro aided on line calibration algorithm for electronic compass is presented. This electronic compass module consists of a three-axis AMR sensor, a two-axis MEMS tilt sensor and a one-axis MEMS gyro. The automatic calibration method requires to rotate the electronic compass two full 360-degree revolution. In this rotation procedure, magnetic field data, attitude data and angular rate data are recorded. Based on recorded magnetic field data and attitude data, raw heading data is calculated. This raw heading data is verified by angular rate output of MEMS gyro. Results of experiment show that the accuracy of calibrated compass is better than 0.5 deg and MEMS gyro aided on line calibration algorithm is effective for electronic compass.

Miniature endoscopic optical coherence tomography probe employing a two-axis microelectromechanical scanning mirror with through-silicon vias

We present the design and experimental results of a new MEMS-based endoscopic optical coherence tomography (OCT) probe. The uniqueness of this miniature OCT imaging probe is a two-axis MEMS mirror with through-silicon vias (TSVs) for interconnecting. The TSV interconnection enables ultracompact probe design, successfully reducing the probe size to only 2.6 mm in diameter. The MEMS mirror is actuated by an electrothermal actuator that is capable of scanning ± 16° at only 3.6 V DC. Two-dimensional and three-dimensional OCT images of microspheres embedded in PDMS and acute rat brain tissue have been obtained with this miniature probe in a time-domain OCT system.

Two-axis MEMS angular rate sensor with magnetoelectric feedback torques in excitation and measurement channels

The design of a two-axis micromechanical angular rate sensor based on a vibrating gyroscope of R-R type is presented in this paper. The gyroscope is built with the use of “sandwich” scheme, which uses the magnetoelectric exciter of torsional oscillations of a silicon sensitive element, two feedback loops on measurement channels consisting of capacitive pickoffs, amplifiers and magnetoelectric torquers (MT). Design features of the device provide its operability in gas-filled chamber at atmospheric pressure. Digital systems designed for the resonance tuning of the device and the maintenance of constant amplitude of angular rate of pendulum oscillations are described. The systems compensating the device zero bias and generating the output signals based on the microcontroller are also considered. The reasons for occurrence of gyroscope zero bias, connected with manufacturing defects of torsional pendulum elastic suspension and magnetic systems, are analyzed, and recommendations are given for their compensation by using such procedures as adjusting magnetic system of the exciter of torsional oscillations, modifying the elastic elements and introducing a compensating signal in a feedback loop. The results of calculating an elastic micromechanical system, modeling a gyroscope motion are presented in the paper at various ways of forming a feedback loop, as well as results from experimental research of the micromechanical angular rate sensor under development.

A Bidirectional Two-Axis Electrostatic MEMS Positioning System

We report on the design, fabrication, and testing of a bidirectional two-axis MEMS positioning system that is used to move a stage. Sandia National Laboratories' MEMS foundry process was utilized for the fabrication of the device; this process incorporates five layers of polysilicon and four sacrificial layers of silicon dioxide. The positioning assembly consists of a pin and slotted-arm arrangement, wherein the pin is constrained between the slotted arms and the positioning of the pin is achieved by identical electrostatic drives on both axes. The electrostatic drives consist of a comb drive interfaced with a compliant-mechanism-based distance multiplier. The stage is connected to a cantilever arm extending from the positioning pin. The crosstalk between the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</i> - and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Y</i> -axes was less than 0.3 ¿m through displacements of ~30 ¿m in both <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</i> - and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Y</i> -directions. The displacement shows a quadratic relationship with the applied voltage.

External linearisation of a MEMS electrothermal scanner with application in a confocal microscope

A compensatory mapping (CM) technique for external linearisation of a MEMS electrothermally actuated optical scanner is reported. Each individual axis of a two-axis MEMS scanner was linearised by the CM technique, and the scanner was then incorporated into a confocal optical microscope configuration. Cross-talk in the scanner when both axes are driven simultaneously, and arising when a drive signal to one axis of the scanner produces a mechanical response in the orthogonal scan axis, was subsequently compensated for by using a look-up-table optimised using a random search algorithm.

Experimental characterization of two-axis MEMS scanners with hidden radial vertical combdrive actuators and cross-bar spring structures

In this paper, we perform the experimental characterization of two-axis MEMS scanners driven by radial vertical combdrive actuators. The dc scan ranges are limited by the pull-in effect. Each scanner utilizes a cross-bar spring structure to achieve two rotational degrees of freedom (DOFs) without employing any gimbal. Both the actuators and torsion springs are hidden underneath the mirror to obtain a small form factor. The devices are fabricated by a five-layer polysilicon surface micromachining process (SUMMiT-V). Devices with different combinations of parameter values are experimentally characterized and compared.

First principles jitter characterization of two-axis MEMS mirrors

Recently developed MEMS micromirror technology provides an opportunity to replace macroscale actuators for laser beamsteering in lidar and free-space optical communication systems. Precision modeling of mirror pointing and its dynamics are critical to the design of MEMS beamsteerers. Beam jitter ultimately limits MEMS mirror pointing, with consequences for bit error rate and overall optical system performance. Sources of jitter are platform vibration, control voltage noise, and Brownian motion noise. This work relates the random jitter of the mirror facet to its originating sources via a multidimensional first-order Taylor expansion of a first-principles-derived analytic expression for the actuating torque. The input torque, consisting of deterministic and stochastic components, is related to the 2-D jitter through a pair of coupled damped harmonic oscillator differential equations. The linearized 2-D jitter model for the mirror is simulated using Matlab, while the full nonlinear torque model was simulated using Simulink. The work describes an experimental setup and methodology that is used to make precise micromirror measurements. Experimental measurements are in agreement with the jitter model, i.e., the linearized model is able to predict mirror facet jitter based on the measured power spectral densities for the sources of jitter.

Linearization of a two-axis MEMS scanner driven by vertical comb-drive actuators

A driving scheme using a pair of differential voltages (Vx, Vy) over a bias voltage is proposed to linearize the dc characteristic (angle versus voltage) of a two-axis MEMS scanner. The micromirror has a gimbal-less structure and is driven by vertical comb-drive actuators in conjunction with a leverage mechanism. At an optimal bias voltage of 53 V, a linear optical scan range of ±3.2° is achieved experimentally in both the x and y directions with the differential voltages ranging from −10 V to + 10 V.

Single fiber confocal microscope with a two-axis gimbaled MEMS scanner for cellular imaging

We present a single fiber reflectance confocal microscope with a two dimensional MEMS gimbaled scanner. Achieved lateral and axial resolutions are 0.82 mum and 13 mum, respectively. The field of view is 140 x 100 mum at 8 frames/second. Images and videos of cell phantoms and tissue are presented with sub-cellular resolution.

A high port-count wavelength-selective switch using a large scan-angle, high fill-factor, two-axis MEMS scanner array

We present a high-port-count (scalable to 1 times 32) wavelength-selective switch (WSS) using a large scan-angle, high fill-factor, two-axis analog micromirror array in conjunction with a densely packed two-dimensional array of fiber collimators. A partially populated (1 times 9) WSS exhibits a fiber-to-fiber insertion loss of 5.57 plusmn 1.4 dB and an extinction ratio of 51 plusmn 11 dB. The channel spacing is 100 GHz

Scanning Micromirrors Fabricated by an SOI/SOI Wafer-Bonding Process

MEMS scanning micromirrors have been proposed to steer a modulated laser beam in order to establish secure optical links between rapidly moving platforms. An SOI/SOI wafer-bonding process has been developed to fabricate scanning micromirrors using lateral actuation. The process is an extension of established SOI technology and can be used to fabricate stacked high-aspect-ratio structures with well-controlled thicknesses. Fabricated one-axis micromirrors scan up to 21.8/spl deg/ optically under a dc actuation voltage of 75.0 V, and have a resonant frequency of 3.6 kHz. Fabricated two-axis micromirrors scan up to 15.9/spl deg/ optically on the inner axis at 71.8 V and 13.2/spl deg/ on the outer axis at 71.2 V. The micromirrors are observed to be quite durable and resistant to shocks. Torsional beams with T-shaped cross sections are introduced to replace rectangular torsional beams in two-axis MEMS micromirrors, in order to reduce the cross-coupling between the two axial rotations. Fabricated bidirectional two-axis micromirrors scan up to /spl plusmn/7/spl deg/ on the outer-axis and from -3/spl deg/ to 7/spl deg/ on the inner-axis under dc actuation.