Optimization of a VOC Sensor with a Bilayered Diaphragm Using FBAR as Strain Sensing Elements

Abstract

Film bulk acoustic resonators (FBARs) are widely applied in mass bio-sensing and pressure sensors, owing to their extreme sensitivity and integration ability, and ability to miniaturize circuits. A volatile organic compound (VOC) sensor with a polymer-coated diaphragm, using FBARs as a strain sensing element is proposed and optimized. This vapor sensor is based on organic vapor-induced changes of mechanical deformation of the micro-diaphragm. The four FBARs are located at the edge of the bi-layer diaphragm comprising silicon nitride and silicon oxide for strain extraction. In this work, the strain distribution of the FBAR area under vapor loads is obtained using the finite element analysis (FEA) and the response frequency changes of the FBARs under vapor loads are obtained based on both the first-principle methods to deduce the elastic coefficient variation of aluminum nitride film in FBARs under the bending stresses and the Mason equivalent circuit model of the sensor using ADS software. Finally, optimizations are performed on both the bilayered diaphragm structure and sensing film. The diaphragm with a 0.7 μm silicon nitride layer and a 0.5 μm silicon oxide layer are considered to be the optimized design. The optimal coverage area of the sensing film for the diaphragm is around 0.8.

Carbon Nanostructure Embedded Novel Sensor Implementation for Detection of Aromatic Volatile Organic Compounds: An Organized Review

“…The presence of π-electron conjugation results in high charge transfer in carbon-based materials . Generally, the detection of VOCs is governed by their interaction with carbon-based materials by diffusion and sensed by the active center of carbon-based materials, − microgravimetric sensors, − and resistive sensors. − When a molecule species interacts with the sidewalls of carbon-based or any semiconductor materials during gas detection, changes in conductance , (due to charge transfer or mobility change) or capacitance (from inherent or induced dipole moments) occur. − The interaction between the VOCs and carbon-based compounds (rGO, CNTs, and CDs) depends strongly on the architecture and design of the composites or materials which may have a larger contact area, thus allowing greater sensitivity. The CNT has two variables, SWCNT and MWCNT.…”

Design and Optimization of a BAW Microphone Sensor

“…Because the pure SiO 2 diaphragm suffers from buckling and wrinkling issues due to its internal compressive stress, a 1 µm Si 3 N 4 layer should be further deposited to counteract membrane internal stress. However, our previous research results show that the resonant frequency of FBAR decreases rapidly with the increase in the Si 3 N 4 thickness; owing to the high operation frequency that is beneficial in obtaining high sensitivity, the thinner thickness of the Si 3 N 4 is better [18]. Considering that the Si 3 N 4 support film has no side effects on the impedance characteristics of the FBAR, the thinnest thickness is preliminarily determined as 0.2 µm.…”

Performance Evaluation of Energy-Autonomous Sensors Using Power-Harvesting Beacons for Environmental Monitoring in Internet of Things (IoT)

“…These are also the places where air quality is a major concern because of the presence of high concentrations of gaseous pollutants such as NO 2 , NO, SO 2 , CO that are harmful to humans and whose values have to be monitored and kept below established limits. Volatile organic compounds (VOCs) are also significant environment pollutants and are a threat to human health because they consist of toxic chemicals that can cause irritations, headaches or can even damage the central nervous system [ 19 , 20 ].…”