Optical Microelectromechanical Systems Research Articles

A Proposal to Enhance High-Frequency Optical MEMS Accelerometer Sensitivity Based on a One-Dimensional Photonic Crystal Wavelength Modulation System

In this article, a novel optical microelectromechanical systems (MEMS) accelerometer sensor based on a one-dimensional photonic crystals wavelength modulation system is proposed with a focus on optimizing the sensitivity of the high-frequency device. The proposed accelerometer consists of a sensitive optical system and a high-frequency mechanical structure, which have been studied by rigorous coupled wave analysis (RCWA) and finite element analysis (FEA). A very large bandwidth, excellent sensitivity to optical sensing and considerable resolution of the high-frequency device of the proposed sensor provide several attractive performance aspects. Through a rigorous theoretical argument, the following results are demonstrated: a photonic band gap (PBG) from 1.1 to 2.8 $\mu $ m, a bandwidth from 0 to 20 kHz, an optical system sensitivity of to 3.38, and an accelerometer sensitivity of 2.06 nm/g, with a measurement range of ± 217 g and a resolution of 4.850 mg. In view of these optimized performances, the proposed MEMS accelerometer can be used for all kinds of high frequency applications.

Measurement of water content in heavy oil with cavity resonator

The study of optical microcavity sensors in current micro optical electromechanical systems (MOEMS) devices is an important research direction in this field. In this study, a surface plasmon optical waveguide structure with MIM (Metal Insulator Metal), semi-circular resonator, and T-shaped resonator was examined. The effects of the coupling distance, the geometrical size of the T-shaped cavity and its asymmetry, and the radius of the semi-circular cavity on the Fano resonance spectrum were analyzed numerically. The sensitivity of the refractive index sensor was up to1066.67nm/RIU. The detection of the water content of the heavy oil found that the Fano resonance line shifted to the short-wave direction as the volume percentage of the contained water increased. The volume percentage resolution of the sensor's heavy oil water content could be as low as2.05×10-9. The proposed structure can overcome the shortcomings of common refractive index sensors and therefore has great application prospects in chemical and biological sensing.

Design, simulation, and fabrication of three-dimensional microsystem components using grayscale photolithography

Grayscale lithography is a widely known but underutilized microfabrication technique for creating three-dimensional (3-D) microstructures in photoresist. One of the hurdles for its widespread use is that developing the grayscale photolithography masks can be time-consuming and costly since it often requires an iterative process, especially for complex geometries. We discuss the use of PROLITH, a lithography simulation tool, to predict 3-D photoresist profiles from grayscale mask designs. Several examples of optical microsystems and microelectromechanical systems where PROLITH was used to validate the mask design prior to implementation in the microfabrication process are presented. In all examples, PROLITH was able to accurately and quantitatively predict resist profiles, which reduced both design time and the number of trial photomasks, effectively reducing the cost of component fabrication.

The electronic transport characteristics in wide band-gap nitrogen vacancy diamond/Si hetero-structure using Raman spectrum

Abstract The negative charged nitrogen vacancy center in diamond is ideal sensitive detectors for quantum measure applications. Raman active phonon and inelastic light scattering in face-centered cubic diamond/Si(1 0 0) films were primarily studies by Raman spectra in various scattering configurations and NV concentration. The fabricated diamond (1 0 0) thin films were successfully epitaxial grown on Si(1 0 0) substrate using MPCVD. The Raman scattering spectrum of diamond/Si(1 0 0) hetero-structure with different thickness nanostructure is present to investigate spin orbital transport dynamics of phase transition. Diamond hetero-junction experiments were carried out at different conditions such as temperature range of 15–300 K and concentration of NV. The results show a strong peak at 1332 cm−1 of D mode indicates the E2g of diamond, as well as the peak 1550 cm−1 of a broad band F2g symmetry G mode which corresponds to the nano-diamond. The disordered graphitic carbon is formed by disordered SP2 hybridization. The 1132 cm−1 and 1480 cm−1 are corresponding with hydrogen bonding within film grain boundaries. The transfer of diamond sp2 content extracted from C C peak and converted to the sp3 spin related effect. The diamond/Si(1 0 0) PDOS indicated the spin-related couple of SP3, and p and d orbital hybridization. The research leads to a better understanding of the Raman active spectra and inelastic light scattering of diamond/Si(1 0 0) films and offers guidelines for better orbital hybridization material design in deep ultra-violet photo-sensor, gyroscopes, field effect transistors (FET) using diamond hetero-structure and high-k oxide gate structure, magnetometer, thermometer, and optical switching micro-electromechanical system (MEMS) devices.

Sense high refractive index sensitivity with bragg grating and MIM nanocavity

The study of optical microcavity sensors in current micro optical electro mechanical systems (MOEMS) devices is an important research direction in this field. This study investigates a new type of nanocavity temperature sensor based on the S-shaped metal-insulator-metal (MIM) and Bragg grating. The analysis of the original sensor model shows that the resonance wavelength of the proposed grating's reflection spectrum shifts to the long-wave direction with the change of refractive index. The value of the high refractive index sensitivity is 1960 nm/RIU, which is obtained near the Bragg resonance wavelength of 1950 nm, and the figure of merit (FOM) is 14.6. The structure is further optimized by adding nanocavity in the middle of the S-shaped MIM Bragg grating. Results show that the refractive index sensitivity is basically unchanged, but the corresponding FOM is 27.7, showing an improvement of 89.7%. The temperature sensor sensitivity is as high as 4.95 nm/°C, and the reflection spectrum resonance wavelength of the proposed grating shifts to the short-wave direction as the temperature changes. High sensitivity can be obtained when the Bragg resonance wavelength is long. Moreover, the Bragg wavelength has a good linear relationship with external physical parameters, such as refractive index and temperature. The findings of this study have certain theoretical and practical values in realizing high-precision, anti-harsh environment, and multi-sensor integrated MOEMS devices.

Optical MEMS accelerometer sensor relying on a micro‐ring resonator and an elliptical disk

Here, a novel optical micro-electro-mechanical systems (MEMS) accelerometer sensor based on a micro-ring resonator and an elliptical disk is proposed. The designed optical MEMS accelerometer is then analysed to obtain its functional characteristics. The proposed optical MEMS sensor presents an optical sensitivity of 0.0025 nm/g, a mechanical sensitivity of 1.56 nm/g, a linear measurement range of ±22 g, a first resonance frequency of 13.02 kHz, and a footprint of 34 μm × 50 μm. Furthermore, the achieved functional characteristics of the proposed accelerometer are compared to several recent contributions in the related field. According to this comparison study, the present optical MEMS accelerometer can be a suitable device for many applications ranging from consumer electronics to inertial measurement units.

Design Guidelines for MEMS Optical Accelerometer based on Dependence of Sensitivities on Diaphragm Dimensions

This work deals in specifying the design considerations while constructing a Micro Electro Mechanical Systems (MEMS) optical accelerometer working on capacitive sensing technique. Sensitivity is one of the most demanded characteristics of any sensor. The sensor considered is a MEMS capacitive accelerometer in which both displacement and capacitance are the primary sensing characteristics. This differential capacitive accelerometer causes change in displacement due to applied acceleration and further produces change in capacitance. So, the main focus in this work is to improve or select the suitable diaphragm dimensions of the differential capacitor in order to get optimal capacitive and displacement sensitivity. This is done for an Optical MEMS (MOEMS) based sensor where slight change has a large-scale impact. The electrical signal is converted to optical by adding an Optical Interferometer. Mach–Zehnder Interferometer (MZI) is used to carry out the intensity modulation which also gives protection in inflammable surroundings. This makes the system suitable for working in high temperature regions.

MEMS-in-the-lens architecture for a miniature high-NA laser scanning microscope

Laser scanning microscopes can be miniaturized for in vivo imaging by substituting optical microelectromechanical system (MEMS) devices in place of larger components. The emergence of multifunctional active optical devices can support further miniaturization beyond direct component replacement because those active devices enable diffraction-limited performance using simpler optical system designs. In this paper, we propose a catadioptric microscope objective lens that features an integrated MEMS device for performing biaxial scanning, axial focus adjustment, and control of spherical aberration. The MEMS-in-the-lens architecture incorporates a reflective MEMS scanner between a low-numerical-aperture back lens group and an aplanatic hyperhemisphere front refractive element to support high-numerical-aperture imaging. We implemented this new optical system using a recently developed hybrid polymer/silicon MEMS three-dimensional scan mirror that features an annular aperture that allows it to be coaxially aligned within the objective lens without the need for a beam splitter. The optical performance of the active catadioptric system is simulated and imaging of hard targets and human cheek cells is demonstrated with a confocal microscope that is based on the new objective lens design.

Tunable surface wrinkling on shape memory polymers with application in smart micromirror

Surfaces with tunable topological features enable important applications, such as optical devices, precision metrology, adhesion, and wetting. In this study, we demonstrate a facile method to fabricate and control the surface morphologies by combining thin film wrinkling and thermal expansion. This approach utilizes self-assembled surface wrinkling induced by shape recovery of shape memory polymers (SMPs) and localized thermal expansion caused by Joule heating. Recovering the prestrain in the SMP substrate induces global wrinkling of the thin film on the substrate. Joule heating in the SMP by a heating wire embedded in the substrate induces thermal expansion of the substrate in a localized area, which leads to the disappearance of the wrinkling pattern. This effect is reversed when heating is stopped, leading to reversible and repeatable tuning of the surface morphology in a controllable localized surface region. With metal coating, the SMP surface can be switched from specular to diffuse reflectance in response to external Joule heating. Finally, we demonstrate a smart micromirror device with its diffuse reflectance tunable between 13.5% and 81.9% in the visible light region. This approach provides a method to modulate surface diffusivity by controlling its surface morphologies, with potential applications in optical display and optical microelectromechanical systems devices.

An Optical MEMS Acoustic Sensor Based on Grating Interferometer.

Acoustic detection is of great significance because of its wide applications. This paper reports a Micro-Electro-Mechanical System (MEMS) acoustic sensor based on grating interferometer. In the MEMS structure, a diaphragm and a micro-grating made up the interference cavity. A short-cavity structure was designed and fabricated to reduce the impact of temperature on the cavity length in order to improve its stability against environment temperature variations. Besides this, through holes were designed in the substrate of the grating to reduce the air damping of the short-cavity structure. A silicon diaphragm with a 16.919 µm deep cavity and 2.4 µm period grating were fabricated by an improved MEMS process. The fabricated sensor chip was packaged on a conditioning circuit with a laser diode and a photodetector for acoustic detection. The output voltage signal in response to an acoustic wave is of high quality. The sensitivity of the acoustic sensor is up to −15.14 dB re 1 V/Pa @ 1 kHz. The output signal of the high-stability acoustic sensor almost unchanged as the environment temperature ranged from 5 °C to 55 °C.

Modal analysis of TE and TM excitations in a metallic slotted micromirror

In this work, we present a modal analysis for a metallic slit, where closed-form expressions for the slotted micromirror electric field coupling coefficient and transmittance are derived for both TE and TM polarizations. This can be handy in the design of optical microelectromechanical systems devices and their applications, where the metallic slit is analyzed by solving the eigenfunction problem. The modes excited inside the metallized slotted micromirrors (slit inner structure) are approximated to be the same modes excited inside a parallel plate waveguide structure for TE and TM excitations. The parallel plate waveguide representing the inner walls of the slotted micromirror is assumed to be infinite in the vertical direction. The transmittance of the micromirror with a vertical slit has been calculated for both TE and TM polarizations based on Gaussian beam excitation. Finite-difference time-domain simulation is carried out for the slotted micromirror transmittance, and the results are compared to the modal analysis predictions. A noticeable conformity has been observed.

Maskless X-Ray Lithography Based on Microoptical Electromechanical Systems and Microfocus X-Ray Tubes

The main advantages and problems of maskless X-ray lithography (MXRL) are discussed. Consideration is given to two concepts of lithography in which the chip of a microoptical electromechanical system (MOEMS) of micromirrors and a microfocus X-ray tube chip with a “breakthrough” thin-film target are used as dynamic masks. Each of them can occupy its own niche in a research area or in the mass production of microchips. A description of the project of a MXRL facility (demonstrator of technologies), which is based on the concept of MOEMS, developed at the Institute for Physics of Microstructures, Russian Academy of Sciences, is presented for the first time.

2-D MEMS Scanner for Handheld Multispectral Dual-Axis Confocal Microscopes

We describe a 2-D microelectromechanical systems (MEMS) scanner for a handheld multispectral confocal microscope for early detection and diagnosis of cervical cancer. This paper is an expansion of work originally reported in the Proceedings of IEEE International Conference on Optical MEMS and Nanophotonics 2012. The MEMS scanner and fabrication process has been designed to improve performance for the dual-axis confocal microscopy architecture. Dual-axis confocal microscopy achieves comparable transverse and depth resolution to high numerical aperture (NA) single-axis confocal microscopy but achieves longer working distance by utilizing low-NA optics. The MEMS scanner has an inner gimbal design with torsional flexures separated from the reflectors to reduce light loss and oxide-free outer axis torsional flexures by utilizing poly vias for electrical access to the inner gimbal electrodes. The devices are large-scale batch fabricated using a double layer silicon-on-insulator (SOI) process and predice postreleasing of dies. The scanner has electrostatic optical deflection angles of 2° for the single-sided inner axis at 75 V and ±3° for the outer axis at 120 V. The device has resonance frequencies of ~2.48 kHz and ~348 Hz for the inner and outer axis torsional modes, respectively. Reflectance and fluorescence images with 650 μm × 800 μm field of view are demonstrated at 15 frames/s. The transverse (axial) resolutions are 4.78 μm (6.2 μm), 5.77 μm (6.2 μm), and 7.45 μm (5.6 μm) for wavelengths of 561, 662, and 781 nm, respectively.

Noise suppression of a micro-grating accelerometer based on the dual modulation method

The micro-grating accelerometer, as a representative micro-optical electromechanical system accelerometer, is studied widely on account of the advantages of small size and high-resolution performance. The extreme accuracy of the micro-grating accelerometer is restricted mainly by the noise floor. In order to improve the performance of the micro-grating accelerometer, a dual modulation method is proposed, which is combined with intensity modulation and phase modulation. The intensity modulation can move the signal to a high frequency, and the light source noise is suppressed perfectly by combining phase modulation. The dual modulation method is verified by constructing the micro-grating accelerometer prototype. Based on the two conditions above, the impact of 1/f noise is diminished. By comparison, the fluctuation of the system at 0.01 g (1 g=9.8 m/s2) is reduced by about 3 dB, which is in line with expectations. The power spectral density image shows that the system noise floor reaches −50 dB with a decrease of about 10 dB. We hope that the low-noise micro-grating accelerometer will be used generally in the future.

Design, Optimization, and Realization of a High-Performance MOEMS Accelerometer From a Double-Device-Layer SOI Wafer

An ultrasensitive single-axis out-of-plane micro optical electro mechanical system (MOEMS) accelerometer with a relatively low cross-axis sensitivity based on a designated micromachined sensing structure and grating interferometry cavity is proposed. While seeking to achieve high performances, we investigated and optimized the design of the mechanical structure, with tensile stress in the flexure close to the ultimate yield strength of monocrystalline silicon. Expressions for acceleration-displacement sensitivity are given and compared with the results of finite-element-method simulations. The highly symmetric accelerometer was fabricated through a particular fabrication process on a specific double-device-layer silicon-oninsulate wafer. The acceleration-displacement sensitivity of the optimal sensing structure, as obtained from static acceleration measurement, was 158.20 μm/g and outperforms its previously reported counterparts. Experimental results revealed that the MOEMS accelerometer with an optimal design achieved an acceleration sensitivity of 2485 V/g with a resonant frequency of 34.5 Hz and a noise level of 185.8 ng/(Hz) <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sup> , corresponding to a resolution of 1 μg, as well as a cross-axis sensitivity of 3.48%/0.1 g, which is one order smaller than the conventional one. The proposed design may pave the way for the applications that require extremely high sensitivity, low cross-axis sensitivity, and comparatively low-frequency response, such as seismology and microgravity detection.

An Optical MEMS Accelerometer Based on a Two-Dimensional Photonic Crystal Add-Drop Filter

In this paper, a novel optical microelectromechanical systems accelerometer sensor is proposed by using a two-dimensional photonic crystal add-drop filter which is relied on a wavelength modulation approach. The proposed optical sensing system consists of a laser diode light source, tunable add-drop filter based on ring resonator principal, photo-detector, and integrated waveguides. Simulation results show that the functional characteristics of the proposed sensor are as follows: mechanical sensitivity of 1.6 nm/g, linear measurement range of $-$ 156 to 156 g, optical sensitivity of 0.0756 nm/g, and first resonance frequency of 12.9 kHz. These functional characteristics make it very interesting in a wide spectrum of applications, ranging from consumer electronics to automotive and inertial navigation.

In-Plane Optical Beam Collimation Using a Three-Dimensional Curved MEMS Mirror

The collimation of free-space light propagating in-plane with respect to the substrate is an important performance factor in optical microelectromechanical systems (MEMS). This is usually carried out by integrating micro lenses into the system, which increases the cost of fabrication/assembly in addition to limiting the wavelength working range of the system imposed by the dispersion characteristic of the lenses. In this work we demonstrate optical fiber light collimation using a silicon micromachined three-dimensional curved mirror. Sensitivity to micromachining and fiber alignment tolerance is shown to be low enough by restricting the ratio between the mirror focal length and the optical beam Rayleigh range below 5. The three-dimensional curvature of the mirror is designed to be astigmatic and controlled by a process combining deep, reactive ion etching and isotropic etching of silicon. The effect of the micromachining surface roughness on the collimated beam profile is investigated using a Fourier optics approach for different values of root-mean-squared (RMS) roughness and correlation length. The isotropic etching step of the structure is characterized and optimized for the optical-grade surface requirement. The experimental optical results show a beam-waist ratio of about 4.25 and a corresponding 12-dB improvement in diffraction loss, in good agreement with theory. This type of micromirror can be monolithically integrated into lensless microoptoelectromechanical systems (MOEMS), improving their performance in many different applications.

Micro-Hole Drilling on Glass Substrates—A Review

Glass micromachining is currently becoming essential for the fabrication of micro-devices, including micro- optical-electro-mechanical-systems (MOEMS), miniaturized total analysis systems (μTAS) and microfluidic devices for biosensing. Moreover, glass is radio frequency (RF) transparent, making it an excellent material for sensor and energy transmission devices. Advancements are constantly being made in this field, yet machining smooth through-glass vias (TGVs) with high aspect ratio remains challenging due to poor glass machinability. As TGVs are required for several micro-devices, intensive research is being carried out on numerous glass micromachining technologies. This paper reviews established and emerging technologies for glass micro-hole drilling, describing their principles of operation and characteristics, and their advantages and disadvantages. These technologies are sorted into four machining categories: mechanical, thermal, chemical, and hybrid machining (which combines several machining methods). Achieved features by these methods are summarized in a table and presented in two graphs. We believe that this paper will be a valuable resource for researchers working in the field of glass micromachining as it provides a comprehensive review of the different glass micromachining technologies. It will be a useful guide for advancing these techniques and establishing new hybrid ones, especially since this is the first broad review in this field.

Demodulation of an optical fiber MEMS pressure sensor based on single bandpass microwave photonic filter.

In this paper, a demodulation method for optic fiber micro-electromechanical systems (MEMS) extrinsic Fabry-Perot interferometer (EFPI) pressure sensor exploiting microwave photonics filter technique is firstly proposed and experimentally demonstrated. A single bandpass microwave photonic filter (MPF) which mainly consists of a spectrum-sliced light source, a pressurized optical fiber MEMS EFPI, a phase modulator (PM) and a length of dispersion compensating fiber (DCF) is demonstrated. The frequency response of the filter with respect to the pressure is studied. By detecting the resonance frequency shifts of the MPF, the pressure can be determined. The theoretical and experimental results show that the proposed EFPI pressure demodulation method has a higher resolution and higher speed than traditional methods based on optical spectrum analysis. The sensitivity of the sensor is measured to be as high as 86 MHz/MPa in the range of 0-4Mpa. Moreover, the sensitivity can be easily adjusted.

Suppression of span in sealed microcavity Fabry–Perot pressure sensors

Optical microelectromechanical system pressure sensors working on the principle of extrinsic Fabry–Perot (FP) interferometer are designed and fabricated for pressure range of 1-bar absolute. Anodic bonding of silicon with glass is performed under atmospheric pressure to form FP cavity. This process results in entrapment of gas in the sealed microcavity. The effect of trapped gas is investigated on sensor characteristics. A closed-loop solution is derived for the deflection of the diaphragm of a sealed microcavity pressure sensor. Phenomenon of “suppression of span” is brought out. The sensors are tested using white light interferometry technique. The residual pressure of the trapped gas is estimated from the experiments. The developed model has been used to estimate the deflection sensitivity of the free diaphragm and the extent of suppression of span after bonding.