Quantitative and predictive model of reading current variability in deeply scaled vertical poly-Si channel for 3D memories

Abstract

3D vertical poly-Si channel SONOS devices are emerging as the most prominent alternative for the 10nm nonvolatile memory technology node and beyond (1–2) provided that a significant drive current I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">READ</inf> is delivered at a fixed reading gate voltage V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">READ</inf> . Recently, we showed the discrete drops observed in the transfer characteristic (I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</inf> vs. V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</inf> ) of 3D transistors (Fig. 1) are linked to single electron trapping in the highly defective poly-Si channel (3). This effect, in addition to low poly-Si mobility, results in low drain current measured in poly-Si channel transistors (4). As an immediate consequence, a large drain current I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</inf> variability is observed in such deeply scaled devices (Fig. 1a). In order to develop a correct model predicting this I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</inf> variability, both i) the charging component and ii) the intrinsic g <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</inf> -variability have to be separately characterized and physically understood to be afterwards correctly combined. The present abstract therefore aims at developing the methodology to predict the I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</inf> distribution at fixed reading gate voltage V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">READ</inf> by physical understanding of both effects: electron trapping and transconductance variations.