Nonlinear nanoelectronic devices operating at room temperature

Abstract

Innovative nanoelectronic device concepts that are beyond the scaling limits of silicon technology can have applications in future generation computations and communications, medical and security imaging, radio astronomy, etc. In particular, these devices may achieve a very high speed well beyond those of the conventional semiconductor devices. A variety of novel devices have recently been proposed including the ballistic rectifier and self-switching device (SSD). Compared with conventional rectifying diodes, both devices are based on entirely new working principles since they do not require any p-n junction or barrier structures. As a result, zero threshold voltage can be achieved, eliminating the need for a bias circuit. The planar nature of these devices means that the electrodes are placed side by side rather than on top of each other, which greatly reduces the parasitic capacitance and enables THz (1 THz = 1,000 GHz) speeds at room temperature. Despite previous work on the novel device working principles and high-speed operation, the devices have only been fabricated using conventional semiconductors. Furthermore, the research on their noise properties is so far very limited even though the device noise figures are almost as important as the speed when used as THz detectors. Manchester is the birthplace of graphene and both novel nanodevices have single-layered architecture, which is ideally-suited to use graphene as the active layer. Since the device speed generally scales with the carrier mobility, graphene based ballistic rectifiers and SSDs are expected to operate at THz frequencies. In this work, both mechanically exfoliated graphene flakes and chemical-vapour deposited graphene films have been used to fabricate the nanodevices for the first time. Their DC and radio-frequency performance have been characterised. Properties of graphene are strongly influenced by its immediate surroundings including any adsorbed molecules, interaction with the supporting substrate due to its large surface to volume ratio. Here, back-gate voltage induced hysteresis of electrical transport under normal atmospheric conditions is systematically investigated. Time-domain DC measurement and short pulse characterisation technique were employed to develop the understanding of such mechanisms, which will help to improve the stability and the reliability of graphene device properties.Finally, the noise properties of the ballistic rectifier were studied. Both thermal noise and flicker noise have been characterised. The findings have been discussed in the context of the mobility fluctuation based Hooge's empirical relation. A physical model was also constructed on the noise of a narrow constriction, and the obtained analytical expression may be applicable to a wide range of nanodevices that consist of point-contact-like structures.

Date of Award	1 Aug 2014
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Aimin Song (Supervisor)