Noise and Charge Discreteness as Ultimate Limit for the THz Operation of Ultra-Small Electronic Devices

With the aim of manufacturing faster electron devices, the industry has already entered into the nanoscale dimensions and Terahertz (THz) operating frequencies. Even neglecting all plasmonic dynamics in the contacts, the intrinsic discrete nature of the few electrons present simultaneously in the active region of nanometric devices can generate unavoidable fluctuations of the electrical current at THz frequencies. The consequences of this THz noise remind somehow unnoticed in the scientific community because its accurate study, which is simple with semiclassical models, requires unusual quantum transport formalisms capable of dealing with consecutive multi-time quantum measurements. In this work, a modeling of the electrical current at THz frequencies is introduced in terms of Bohmian trajectories. We explicitly simulate a double gate graphene transistor where the wave nature of electrons is given by the bispinor solution of the Dirac equation. We prove that this intrinsic THz noise increases unlimitedly when the volume of the active region decreases. We argue that the ultimate limit in the scaling strategy is determined by this fundamental and unavoidable THz noise.