Sensitivity Improvement of Micro-diaphragm Deflection for Pulse Pressure Detection

Abstract

Cardiovascular diseases are one of the leading causes of death. Globally, they underlie the death of one third of the world’s population. The main cause of cardiovascular diseases is atherosclerosis which makes arteries less elastic (called ‘‘hardening of the arteries” or ‘‘arterial stiffness’’). The optical Micro Electro Mechanical System (MEMS) pressure sensor has shown its potential in the diagnosis of arterial stiffness that can be conducted by detecting the pulse pressure in the radial artery. In this paper, we attempt to improve the sensitivity of micro-diaphragm deflection in optical Micro-electromechanical System (MEMS) sensors as applied to pulse pressure detection, thus aiming to determine the safety of a person’s measured pulse of cardiovascular disease. The deflection sensitivity improvement was evidenced using Finite Element Analysis ANSYS software. Corrugation for periphery-clamped silicon nitride (Si3N4) micro-diaphragm based on the variation of the diaphragm thickness (td) and some corrugation factors such as the corrugation angle (β) and the corrugation depth (hc) was implemented to reduce bending and tensile stresses which limit the micro-diaphragm deflection sensitivity. This was supported by calculating the von Mises stress. Analytic results show agreement with ANSYS software simulation with a static response of 1.27 μm maximum deflection under applied pressure of 300 mmHg in the case of the corrugated micro-diaphragm, compared to a 0.32 μm maximum deflection in the case of a flat micro-diaphragm, and for the same applied pressure, a maximum deflection sensitivity of 4.23 × 10−3 μm/mmHg for the corrugated micro-diaphragm compared to 1.07 × 10−3 μm/mmHg for the flat one, and the reduction of micro-diaphragm bending and initial tensile stresses exhibited by maximum equivalent stress (von Mises stress) of 159.99 MPa for the corrugated compared to 175.9 MPa for the flat one. Therefore, the implementation of corrugation presents the chance to control mechanical deflection sensitivity and compared to the film deposition process control it is often an easier way.