Touch Mode Capacitive Pressure Sensor for Passive Tire Monitoring System

Abstract

Passive Tire Monitoring System (PTMS) enables to detect pressure, temperature and ID number of each tire. And it also can warn drivers about low pressure or flat tires. In our proposal, the sensors to detect tire pressure are implanted in each tire. Therefore, they must have a robust structure enough to withstand against an overload pressure that is applied during curing process of tires, as well as a high sensitivity and its good linearity in their operating range. Touch Mode Capacitive Pressure Sensor(1) seems to be suitable for this system, because it has some advantages such as near linear output, strong endurance against overload pressure and a robust structure compared with other conventional pressure sensors. The purpose of this study is to improve the minimum burst pressure of the Touch Mode Capacitive Pressure Sensors in the high volume production. As a result of observation with AFM and TEM, we found that some etch-pits, which are produced in etching process of the diaphragm of the sensors, make the diaphragm weak. Consequently, we could optimize the etching conditions, and obtain the sensors of which the minimum burst pressure is 3.5MPa and more at a high yield rate. Keywords : Touch Mode Capacitive Pressure Sensor, Passive Tire Monitoring System, burst pressure, etch-pits. © 2003, The Institute of Electrical Engineers of Japan. All rights reserved.