Scaling properties of gold nanocluster chemiresistor sensors

The effect of geometric scaling on the performance of metal-insulator metal-ensemble (MIME) chemiresistors based on gold nanoclusters is investigated. The ultrasmall size of the nanoclusters is shown to enable extreme scaling of the sensors with reductions in area of at least a factor of 104 over conventional MIME devices. If the operating voltage is held constant, the absolute sensitivity of the devices is found to remain essentially unchanged by the geometric scaling. Interestingly, this occurs despite the fact that contact resistance appears to play a significant role in the smallest devices. The detection limit of the sensors is set by a signal-to-noise ratio, and because 1/f noise tends to dominate, reduction in sensor size raises the noise floor, leading to a degradation in the detection limit. Because of the importance of the 1/f noise, optimal performance will be obtained by operating the sensors under ac conditions with filtering. Despite the degradation in performance that results from scaling, nanocluster-based chemiresistors of reduced size can still be advantageous because of the possibility of achieving vapor-sensing systems of substantially reduced size, power, complexity, and cost, as well as new applications, e.g., for sensor arrays.