Electron injection in tunneling-oxide-less charge-trap flash memories

This paper presents a physics-based technology computer-aided design framework for electron trapping in tunneling-oxide-less Al2O3/Si3N4 (AN) charge-trap devices and its extension to Al2O3/Si3N4/SiO2 (ANO) stacks. Unlike conventional ANO devices with a SiO2 tunneling oxide, AN devices place the Si3N4 layer in direct contact with the poly-Si channel, requiring a different electron injection model. The model combines Fowler–Nordheim tunneling through Si3N4 with direct channel-to-nitride injection caused by the tunneling-oxide-less gate stack. These two mechanisms are represented using shallow and deep trap-energy levels in the nitride layer. The trap energy Et, trap density Nt, tunneling effective mass m*, and spatial distribution are calibrated by matching simulated programming transients and ID–VG characteristics to measurements from fabricated AN devices. The measurement-calibrated framework accurately predicts the threshold-voltage shift ΔVth and trapped-electron distributions as functions of programming voltage and temperature. It also clarifies how Et, Nt, m*, and the spatial distribution determine the trapping rate, stored charge, and trapping location. Using the same nitride trap parameters, the model is applied to ANO devices with different tunneling-oxide thicknesses and accurately predicts their trapped-electron density distribution and ΔVth characteristics. These results establish tunneling-oxide-less AN devices as effective platforms for extracting intrinsic nitride trap parameters applicable to conventional ANO flash stacks and more complex tunneling-stack designs.