Tunable Dynamic Capacitance Arising from Coulomb Blockade in a 2D Nanoclusters Assembly

Abstract

Radio-frequency devices such as voltage controlled oscillators (VCOs) or mixers are present in a wide variety of applications from general public electronics or telecoms to military radars. They mainly rely on variable capacitors to either tune their operating frequency or modulate their impedance. In the quest for performance and low power consumption, downscaling has been the main answer from the CMOS industry. However, this strategy will reach its limit reaching the nanometer scale. Hence, alternative ways such as the Micro ElectroMechanical Systems (MEMS) have been sought for. This paper is interested in a way Coulomb blockade of electrons in a distribution of metallic clusters embedded in the dielectric of a capacitor can be used to design a voltage controlled tunable capacitor. A layer of nanoparticles is embedded in a capacitor in tunnelling range from the flrst electrode in the Coulomb blockade transport regime. The flrst insulating layer is thin enough to make tunnel phenomenon possible on the contrary to the second one which is too thick and prevents tunnelling. The whole structure is biased via a DC source controlling the onset of Coulomb blockade according to their position in the size distribution. A small AC signal leads to a charging-discharging process of the clusters related to the total dynamic capacitance of the system. The multi-layer system is grown by sputtering. We present the model, numerical simulations and validating experiences with variable capacitors using insulating materials such as alumina or MgO.