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Abstract
Threshold voltages of sub-10 nm double gate (DG) MOSFET have been analyzed for doping concentration, including thermionic and tunneling currents. Threshold voltage shifts is inevitable for channel length of sub-10 nm even though DGOSFETs are developed to reduce short channel effects (SCEs). Since subthreshold current is greatly consisted of tunneling current in the region of sub-10 nm, increase of subthreshold current due to tunneling shows severe SCEs. Influence of doping concentration on threshold voltages is investigated in this paper. To obtain subthreshold current consisted of thermionic and tunneling current, potential distribution is derived from Poisson's equation with analytical series form. As a result, subthreshold currents are changed due to deviation of potential distribution changed by doping concentration, and threshold voltages is changed by subthreshold current. Threshold voltage is significantly changed for doping concentration of 1019/cm3 above, and shifts of threshold voltage are increased with reduction of channel length. Threshold voltage shifts are significantly occurred in the region of high doping concentration with increase of oxide thickness.
Keywords: Double gate, Threshold voltage, doping concentration, tunneling current
1. Introduction
The development of an integrated circuit (IC) can be due to development of discrete transistors. A transistor is an active element that is responsible for driving an IC and determines the operating characteristics of IC. The refinement of transistor is inevitable to maximize the efficiency of the transistor. Reducing the size of a transistor results not only in increasing the operating speed but also in the reduction of the power consumption, which has the greatest influence on the improvement of integration degree. Particularly, the reduction of the power consumption needs to reduce subthreshold current. As the subthreshold current increases, it exhibits various short channel effects (SCEs) such as a degradation of subthreshold swing and threshold voltage shift in subthreshold region. Conventional CMOSFETs have many problems in miniaturization by sub-10 nm unit because of increase of SCEs [1]. To solve these problems, the transistor developed is a double gate (DG) MOSFET. DGMOSFET is a device that doubles capability to control the carrier flow in the channel by fabricating the gate above and below the channel [2-4].
The subthreshold current consists of a thermionic current and a tunneling current. If the channel length is reduced...