Thermal Conductivity Sensor with Isolating Membrane Holes

Abstract

In this paper we present a thermal conductivity gas sensor with improved sensitivity by adding holes in the thin-film membrane. A numerical model is created and validated against the reference CMOS MEMS thermal conductivity sensor. The numerical model is used to investigate the advantages of having isolating holes through the membrane, located on either side of the heating resistor. These holes increase robustness and minimise catastrophic failure caused by pressure difference whilst simultaneously increasing sensitivity by enhancing convective interaction. The electro-thermal efficiency is shown to increase by 16% whilst the sensitivity to measuring percentage CO2 increases by 39.2%. It is also shown that increasing the width of the holes does not have significant effect on these sensitivities; thus, small holes can be incorporated, leaving room for multiple resistors across the membrane for different measuring techniques. This paper serves as proof that membrane holes can be used to optimise thermal conductivity sensors and will serve as a reference when these designs are fabricated and tested, leading to a new low-power, high-sensitivity gas sensor.