Nanophotonic Crystal Waveguide With Embedded Piezoresistor on MEMS Cantilever for Sensing Application

Abstract

Micro-Electro-Mechanical-System (MEMS) cantilevers are sensitive to minute changes in environmental parameters. MEMS cantilevers possess a single readout transduction mechanism like stress to frequency, resistive and capacitive changes. Here, we demonstrate a novel dual readout MEMS cantilever for sensing applications with high optical and resistive sensitivities. The proposed work focuses on the design, fabrication and characterization of an L-shaped 2D photonic crystals (PhC) waveguide piezoresistive MEMS cantilever and its use in a sensor platform. We integrated a 2D PhC waveguide on top of the cantilever along with a piezoresistor element embedded within the cantilever and attained a synergistic combination of both optical and resistive sensing. When the cantilever deflects in the ‘Z’ direction, it is perceived that it leads to stress in the cantilever and the corresponding change in resistance and the optical property is measured. Thus, a unique L-shaped cantilever is designed for reliable coupling of the light inside the 2D PhC waveguide using optical fiber. An orthogonal measurement setup is developed to demonstrate the cantilevers dual readout feature. We achieved excellent piezoresistive and optical sensitivities of ~0.0072 (( $\Delta \text{R}$ /R)/ $\mu \text{m}$ ), and ~0.046 (( $\Delta \text{P}$ /P)/ $\mu \text{m}$ ), respectively. The fabricated cantilever is tested with the VOC and measurements show that it provides two distinct signatures i.e., $\Delta \text{R}$ /R and $\Delta \text{P}$ /P for the same target analyte. Therefore, the miniaturized MEMS cantilever is unique because of its dual readout feature and it can be vital in high detection accuracy applications.