Ultra-thin parylene films as gate insulators in nanoscale field-effect transistors

Abstract

The growth and characterization of nanowires (NW) has inspired tremendous research efforts in a broad range of disciplines. The development of self-assembled NW growth enables the fabrication of defect-free single crystal nanowires. High-mobility III-V semiconductor nanowires have shown particular promise as channels in high-performance field effect transistors (FET). This work helps to advance the development and understanding of NWFET devices by introducing a new gate insulator, new device fabrication methods, and by studying quantum transport effects in new nanostructures: (i) Gate oxides cause a high density of charge traps at the nanowire surface. This reduces transistor performance in NWFETs. In this work, we introduce the organic polymer parylene as a new gate insulator. Using parylene will enable the incorporation of semiconductor surface passivation layers that have been shown to reduce charge trapping and enhance transistor performance. We built a custom chemical-vapor deposition system specifically designed to grow ultra-thin parylene films that can conformally coat single nanowires. Oxygen plasma etching in combination with lithographic methods were used to pattern the parylene thin films and create fully functional wrap-gated NWFETs that exhibit performance on par with oxide-insulated devices. (ii) The gate needs to fully wrap around the nanowire to maximize NWFET performance. In this work, we introduce a fabrication method that allows for the fabrication of multiple independent wrap gates on the same nanowire without additional processing steps. This method was used to create a logic gate and a common-source transistor pair, each on a single nanowire. We introduce a second fabrication method that significantly enhances the control over the gate-segment length, which allows for the creation of shorter wrap gates. (iii) Low-temperature measurements were conducted to advance the understanding of quantum transport phenomena in nanoscale III-V FETs. We report transport features in a GaAs nanowire that we attribute to one-dimensional conductance quantization. We also present the measurements on InAs nano membranes, a novel nanostructure grown by selective area epitaxy. These exhibit signatures attributed to magnetoconductance fluctuations, weak localization/antilocalization and Shubnikov-de Haas oscillations.