Rethinking the Characterization of Nanoscale Field‐Effect Transistors: A Universal Approach

• Published in: Small (Weinheim an der Bergstrasse, Germany) Vol. 16; no. 22; pp. e1907321 - n/a
• Main Authors: Byrne, Kristopher, Shik, Alexander, Wisniewski, David, Ruda, Harry E.
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 01.06.2020
• Subjects: Capacitance; carrier concentration; Carrier density; carrier mobility; carrier transport model; Charge transport; electrical characterization; Field effect transistors; Mathematical models; Nanotechnology; Parameters; quantum capacitance; Resistance; Semiconductor devices; Threshold voltage; Transistors; Transport equations; Transport properties; carrier concentration; carrier mobility; nanotechnology; quantum capacitance; electrical characterization; field-effect transistors; carrier transport model
• ISSN: 1613-6810; 1613-6829
• DOI: 10.1002/smll.201907321

Standard methods for calculating transport parameters in nanoscale field‐effect transistors (FETs), namely carrier concentration and mobility, require a linear connection between the gate voltage and channel conductance; however, this is often not the case. One reason often overlooked is that shifts in chemical and electric potential can partially compensate each other, commonly referred to as quantum capacitance. In nanoscale FETs, capacitance is often unmeasurable and an analytical formula is required, which assumes the conducting channel as metallic and common methods of determining threshold voltage no longer couple properly into transport equations. As present and future FET structures become smaller and have increased channel‐gate coupling, this issue will render standard methods impossible to use. This work discusses the validity of common methods of characterization for nanoscale FETs, develops a universal model to determine transport properties by only measuring the threshold voltage of an FET and presents a new parameter to easily classify FETs as either quantum capacitance‐limited or metallic approximated charge transport. Also considered in this work is electrical hysteresis from trap states and, in combination with the proposed universal model, novel techniques are introduced to measure and remove the errors associated with these effects often ignored in literature. The influence of quantum capacitance on deviation from the metallic capacitance model (C/C0) for experimental data from literature as a function of a universal parameter β is presented. This introduces a quantum capacitance‐limited transport regime (shaded blue), where the metallic approximation is invalid (shaded red). Inset: β dependence on density of states for different capacitive couplings (surface area to capacitance S/C0).