A new type of low noise uncooled microbolometer has been designed and fabricated. The sensor uses the low-noise properties of mechanical resonators (NEMS). As the temperature increases due to infrared absorption, the torsional Young’s modulus of mechanical parts decreases, modifying thereby the resonance frequency. Residual strains change also due to thermal expansion of layers, contributing also to the temperature coefficient of frequency (TCF). We compared the performances of various devices designed with different thermal isolation to identify the best devices for infrared detection and to assess the theoretical performance of such sensors. Results from FEM simulations of TCF for different designs are finally provided and confronted to experimental data.