[Truncated abstract] The salient feature of next generation infrared (IR) on-chip integrated sensors is likely to be sensitivity in a narrow wavelength band that is tuneable over a selected range of the IR spectrum. It is proposed that this can be achieved by the integration of present-day HgCdTe IR detectors with thin-film based microelectro- mechanical systems (MEMS) optical mirror technology. Narrow-band sensitivity is obtained by optical resonance phenomena within a Fabry-Perot (FP) cavity, that is created by two Bragg reflectors and is monolithically integrated with an HgCdTe IR detector. Electrostatic actuation of the thin-film membrane supported Bragg reflector is the means of providing wavelength discrimination of the incident IR photons which, for example, could be used for target discrimination or detection of various chemical/biological species via identification of narrow spectral features . . . The outcomes from this thesis have been incorporated into a monolithic integrated technology comprising low-temperature MEMS and HgCdTe IR detector technology. The integrated technology has been shown to be viable, and successful prototypes have been fabricated. Structural properties of the SiNx, SiOx, and Ge layers encompassed in the suspended IR reflector have allowed for IR photon detection in a narrow wavelength band with full-width at halfmaximum of ∼100nm that is tunable over a wavelength range from 2.2 to 1.85μm using a maximum tuning voltage of only 7.5V. Although the thesis objectives have been focused on a specific application related to multi-spectral IR detection technology as a demonstration vehicle, the findings of this thesis are directly applicable to any MEMS technologies that are to be merged with temperaturesensitive substrates/materials.