In the present work, the role of bimaterial microcantilever (MC) physical dimensions on its photothermal sensitivity, response time and noise characteristics are studied. Laser induced deflection in Al/Si MCs with varying Width/Length (W/L) ratio between 0.07 and 0.6 (at a constant thickness of ~2 µm) was studied using an AFM head, by sequentially exposing them to a UV laser source (wavelength ~406 nm) at a constant incident laser power of 2.5 mW. While the absorbed power and incident flux sensitivities were found to decrease with increasing W/L ratio, response time was found to improve. These results are explained on the basis of simultaneous decrease in effective stiffness and thermal conductance of MCs with reducing W/L ratio. Noise equivalent power, counter intuitively, did not improve with reducing dimensions, instead it was found to be at its optimum value (566 pW/Hz) for W/L ratio ~0.3 and is explained on the basis of variation in MC stiffness and Q-factor with MC dimensions.