Statistical spectroscopy of switching traps in deeply scaled vertical poly-Si channel for 3D memories

For future high density storage memories, 3D vertical poly-Si channel SONOS devices are emerging as the most prominent alternative because of the extreme reduction of cost per bit (1-3). This architecture, however, faces critical reliability issues related to the highly defective channel (4-5). For instance, we recently showed that discrete current drops and fluctuations (RTN) are clearly observed in the transfer characteristics (I_D vs. V_G) of these nanoscale vertical nFETs (Fig. 1). These instabilities were linked to single electron trapping/detrapping processes (6-7), which potentially may cause read errors during operation (4-5). The present paper therefore aims at characterizing these adverse switching traps to gain insight into their physical properties. A statistical comparison among different polysilicon channels is presented and benchmarked against monocrystalline planar nFETs. We reveal that a significant part of the switching traps reside in the poly-Si channel.