Design and performance analysis of MEMS capacitive pressure sensor array for measurement of heart rate

Abstract

In this paper, a diaphragm based MEMS capacitive pressure sensor array in conjunction with signal conditioning circuitry is designed for measuring Heart Rate (HR) of human being. In order to measure the heart rate, an array of capacitive sensors are mounted on wrist in such a way that the radial artery blood flow during contraction and expansion of the heart, impinges on the sensor diaphragms. Due to blood flow in the wrist artery, the designed circular diaphragm of the sensor is being deflected and thus induces a corresponding change in the original capacitance value. A proposed schematic of the system to measure the change in capacitance consists of signal conditioning circuitry along with the sensors. The structure of the sensor consists of parallel plates having 1.5 micron air gap in between. This change in capacitance is detected by a CMOS based capacitance-to-voltage converter which is designed as a precision interface with the sensor array. The designed MEMS sensor has a Poly Silicon diaphragm and is capable of identifying HR (60–100 bpm) which corresponds to a specific change in absolute pressure from 10 to 100 kPa for 5 micron thick diaphragm with 3600 µm area. The design of the sensor along with its fabrication steps and characteristics analysis are performed in FEM based simulation software.