Capacitive pressure sensors have been widely studied and applied for their advantages such as high measurement sensitivity, wide pressure measurement range, low power consumption, robust structure, high overload characteristics, low fabrication cost, etc. The research on capacitive pressure sensors mainly focuses on improving the linearity of output characteristics and sensitivity. With this increasing research, touch mode capacitive pressure sensors (TMCPS) have been developed with better sensitivity and linearity than conventional planar electrodes.
The existing TMCPSs have constant touch point pressure (TPP) of different values. These TMCPSs operate in normal mode between zero pressure and TPP when external pressure is applied. The TPP of TMCPS has a direct effect on the effective operating pressure range, sensitivity and linearity of the device.
Rim Chang Sik, a researcher at the Institute of Semiconductor, has proposed a new structure of TMCPS with a spherical substrate electrode with TPP near zero, and investigated its characteristics.
The proposed TMCPS consists of an elastic diaphragm-top moving electrode that causes deformation under external pressure, and a curved bottom fixed electrode. The two electrodes are in touch before the external pressure is applied, and when the external pressure is applied, the upper moving diaphragm acts as a touch type, wrapping the bottom surface electrode from the beginning.
As the TTP of this device is near zero, it has a wider range of effective operating pressure, and its curved bottom surface provides better sensitivity and linearity than a planar CPS.