Channel Engineering for Nanotransistors in a Semiempirical Quantum Transport Model

Abstract

Abstract:One major concern of channel engineering in nanotransistors is the coupling of the conduction channel to the source/drain contacts. In a number of previous publications, we have developed a semiempirical quantum model in quantitative agreement with three series of experimental transistors. On the basis of this model, an overlap parameter 0 ≤ C ≤ 1 can be defined as a criterion for the quality of the contact-to-channel coupling: A high level of C means good matching between the wave functions in the source/drain and in the conduction channel associated with a low contact-to-channel reflection. We show that a high level of C leads to a high saturation current in the ON-state and a large slope of the transfer characteristic in the OFF-state. Furthermore, relevant for future device miniaturization, we analyze the contribution of the tunneling current to the total drain current. It is seen for a device with a gate length of 26 nm that for all gate voltages, the share of the tunneling current becomes small for small drain voltages. With increasing drain voltage, the contribution of the tunneling current grows considerably showing Fowler-Nordheim oscillations. In the ON-state, the classically allowed current remains dominant for large drain voltages. In the OFF-state, the tunneling current becomes dominant.

A One-Dimensional Effective Model for Nanotransistors in Landauer–Büttiker Formalism

“…[1,2] we give a detailed derivation of all relevant formulas necessary to construct a one-dimensional effective model for a nanotransistor described in Refs. [6][7][8]. In this model, quantum transport in nano-FETs can be described quantitatively.…”

“…(compare with Equation (1) of Ref. [8]). Here we neglected in the wave function overlap the energy dependence, C 11 (E xy ) → CΘ(E xy ) and introduced the valley degeneracy of N ch v = 2 in the n-type conduction channel.…”

“…In a series of papers [1][2][3][4][5][6][7][8], we developed a compact transistor model in which quantum transport in a variety of industrial nano-FETs could be described quantitatively [6][7][8]. Our compact transistor model allows for the extraction of important device parameters as the effective height of the source-drain barrier of the transistor, device heating, and the overlap between the wave functions in the contacts and in the electron channel thus describing the quality of the coupling between conduction channel and contacts.…”

“…Moreover, the existence of the discrete representation of the R-matrix in the eigenbasis of the Wigner-Eisenbud functions (see Equation 22) allows for the systematic construction of the one-dimensional effective transistor model used in Refs. [6][7][8] as will be described in Sections 5-8.…”

“…V L (x) = −eU D x/L (linear decrease of the drain voltage) and E V 0 .The parameter V 0 is interpretable as the effective height of the source-drain barrier. The parameters V 0 and C as well as T are adjusted to experiments in Refs [6][7][8]…”