Single Chip-Based Nano-Optomechanical Accelerometer Based on Subwavelength Grating Pair and Rotated Serpentine Springs

Abstract

Optical coupling between subwavelength grating pairs allows for the precise measurement of lateral or vertical displacement of grating elements and gives rise to different types of displacement and inertial sensors. In this paper, we demonstrate a design for a nano-optomechanical accelerometer based on a subwavelength grating pair that can be easily fabricated by a single Silicon-on-insulator (SOI) chip. The parameters of the subwavelength grating pair-based optical readout, including period, duty cycle, thickness of grating and metal film, and the distance of the air gap, were optimized by combining a genetic algorithm and rigorous coupled wavelength analysis (RCWA) to obtain the optimal sensitivity to the displacement of suspended grating element and the acceleration. A corresponding mechanical design was also completed to meet the highly sensitive acceleration measurement requirement while considering the mechanical cross-axis sensitivity, dynamic range, bandwidth, and fabrication feasibility. This device was verified by both RCWA and finite-different-time-domain methods, and a tolerance analysis was also completed to confirm that it is able to achieve the extremely high optical displacement sensitivity of 1.8%/nm, acceleration-displacement sensitivity of 1.56 nm/mg, and acceleration measurement sensitivity of more than 2.5%/mg, which is almost one order of magnitude higher than any reported counterparts. This work enables a single SOI-based high performance accelerometer, and provides a theoretical basis and fabrication guides for the design.

Micromachined Accelerometers with Sub-µg/√Hz Noise Floor: A Review

“…Lu et al [ 77 ] (2017) at Zhejiang University developed an optical MEMS accelerometer, similar to the design of the Sandia National Laboratory [ 73 ], by measuring the acceleration through the change of the interference pattern produced by two gratings, as shown in Figure 16 . One grating was suspended above the proof mass and the other was on the surface of the proof mass to form a cavity between the two gratings [ 78 , 79 , 80 ]. With light illuminated on the top grating by a laser source, part of the light was transmitted to the bottom grating and reflected to produce an interference pattern, which was detected by a photodiode.…”

Fabrication of Vertical MEMS Actuator with Hollow Square Electrode for SPR Sensing Applications

“…To support the actuator plate, various types of springs such as crab-leg spring [ 21 ], clamped-clamped spring [ 22 ], folded-beam spring [ 23 ], and serpentine spring [ 24 ] have been designed and used in MEMS actuators. Among them, we used the serpentine spring for the design of the vertical MEMS actuator, because it can provide larger vertical deflection due to a low vertical direction spring constant per the unit area [ 25 ]. In case of the glass substrate, the hollow square electrode has been proposed for SPR sensor application (see Figure 2 b).…”

Review of micromachined optical accelerometers: from m<i>g</i> to sub-μ<i>g</i>

“…But one should take into account that these sensors are still limited in applications in terms of their demanding requirements for working environment (cryogenic or vacuum) and micromachining design and process. There are still several demonstrations of practical MOEMS accelerometers based on surface plasmon coupling by means of nanocavity or nanostructure, such as the designs proposed by Rogers 157 , Feng 158 , and Lu 159 , etc. However, the performance is not perfectly correlated to the physical picture.…”