Optimisation of performance for platinum nanowires as sub-wavelength bolometers

Electronic properties and sensitivity of metallic bolometers were studied as a function of thin-film thickness in the active area. Our devices are made of platinum and chromium, with an active area of lateral dimensions 1 mu m by 300 nm. The thickness of the metallic film was varied between 3.3 nm and 82.3 nm. Temperature coefficient of resistance and resisitvity were characterized, and are respectively increasing and decreasing with the thickness increasing. A threshold thickness of 40 nm is revealed where both parameters reach a constant value. Responsivity and detectivity were evaluated, unveiling the importance of 1/f noise. Responsivity reaches a maximum value of 2x10(5) V.W-1 for bolometers with a 7.5 nm thickness. Detectivity keeps a constant value of 1x10(8) cmHz(1/2)/W for samples thicker than 40 nm, before dropping considerably as the thickness is decreased. This loss in detectivity is believed to be due to the prominence of 1/f noise in such thin samples.