Laterally-Trapped-Charge Profiling Based on the Extraction of the Flat-Band Voltage by Using the Optical Substrate Current in Charge Trapping Flash Memory Cells

摘要

A novel extraction method for the locally-trapped-charge profiling combined with a new local Hatband voltage (V_(FB)) extraction under optical excitation is proposed. Under optical illumination in metal-oxide-semiconductor field effect transistors (MOSFETs), the substrate current (I_(sub,photo)) is abruptly increased at V_(FB) due to a sudden increase in the excess carrier diffusion current. In nitride read-only memory (NROM)-type charge trapping flash (CTF) memory cells, there are multi-step responses in optical substrate current (I_(sub,photo))-gate voltage(V_G) curves because V_(FB) is varied along the channel by the laterally non-uniform profile of electrons trapped in the nitride storage layer. We analyzed the mechanism of I_(sub,photo) and verified it by using integrated systems engineering technology computer aided design (ISE TCAD) simulations. The height of the step is shown to be related to the programmed region and the width is shown to be related to the density of trapped charges. Using this novel method, we investigated laterally-trapped-charge profiling in CTF memory cells.