Pyroelectric infrared sensors utilize interfacial polymer bonding, thick porous silica layer and Si3N4 thin film as conventional methods of reducing heat sinking with substrate. The thick polymer and porous silica layers cause additional enhancement in thermal time constant (τD) as well thermal mass (Cth) of pyroelectric sensor which reduces the rate of temperature change (dT/dt) and limits responsivity at lower frequencies. The SiO2 thin layer posses lower heat conductivity than Si3N4 thin films and often used in Si bulk micromachining as etch barrier. This paper proposes use of micromachined SiO2 thin membrane as thermal insulation layer in bulk micromachined pyroelectric infrared sensor. The study is supported by the comparative radiation heat transfer, finite element analysis and the practical thermal measurements on fabricated pyroelectric infrared sensor using non destructive thermal imaging method. © 2017, Springer-Verlag GmbH Germany.