New ultrahigh-speed device concepts: from THz nanoplasma devices to glass-like electronics for neuromorphic computation

There is a never-ending push for electronic systems to provide faster operation speeds, higher energy efficiencies, and higher power capabilities at smaller scales. These requirements are apparent in different areas of electronics, from radiofrequency (RF) to logic and power electronic systems. For instance, a faster operation would result in communication links with higher capacities, logic circuits with higher processing speeds, and more compact power converters. Metal-oxide-semiconductor (MOS), as the main platform for electronics so far, has enabled a variety of functional devices with applications in our everyday lives. The speed, power delivery, energy consumption, and size of MOS-based devices, however, are constrained by fundamental properties of semiconductor materials. For example, the trade-off between electron density and mobility limits the current density of semiconducting channels, resulting in a power-frequency trade-off in active devices, and the thermionic subthreshold-slope limit imposed by Boltzmann–Tyranny constrains their minimum supply voltage and ultimately their power consumption. Besides the intrinsic properties of materials, the interfaces (e.g. metal-semiconductor junctions) in classic devices also limit the performance of electronics. For example, the contact resistance of metal-semiconductor tunneling junctions severely constrain the high-frequency performance of diodes and transistors in the millimeter and sub-millimeter bands, and short-channel effects in MOS-based devices restrict downscaling of transistors, which hinders the extreme integration in logic circuits. This thesis tackles some of the most fundamental challenges in different areas of electronics, with a focus on high-speed devices. The first part of the thesis is dedicated to high-speed radiofrequency electronics, where two new device concepts are proposed: electronic metadevices and nanoplasma switches. Electronic metadevices operate based on collective and controllable electromagnetic interactions in deep-subwavelength scales, as an alternative to controlling the flow of electrons. The proposed devices overcome some the theoretical limits in classical electronic devices such as diodes and transistors. Electronic switches realized based on this new concept enable achieving very high cutoff frequency figure-of-merit (FOM) exceeding 10 THz, very low losses with ultra-small contact resistances below 20 ℩ ÎŒm, and large breakdown voltages over 30 V, extending state-of-the-art by two orders of magnitude. Based on this new device concept, two-port and three-port ultrahigh-speed modulators operating in the THz band are demonstrated. In the second chapter, the common drawback of power-frequency trade-off in semiconductor devices which ultimately leads to the terahertz gap, is tackled by proposing ultrafast nanoplasma devices – new electronic switches operating based on plasma formation in nano-gaps. Nanoplasma switches offer current densities over 300 A mm−1 and switching speeds over 10 V ps−1. A compact nanoplasma-based terahertz source capable of generating peak powers above 1 W at 300 GHz is demonstrated. This new concept sets the stage for the future ultrafast electronics with applications in terahertz sources and modulators, relying only on a single metal layer. Nanoplasma devices are compatible with any kind of electronic platforms, from CMOS and III-V to flexible electronics. High-speed logic electronics is concerned in the second part of