Direct comparison of the electrical properties in metal/oxide/nitride/oxide/silicon and metal/aluminum oxide/nitride/oxide/silicon capacitors with equivalent oxide thicknesses

We examine the electrical properties of metal/oxide/nitride/oxide/silicon (MONOS) capacitors with two different blocking oxides, SiO₂ and Al₂O₃, under the influence of the same electric field. The thickness of the Al₂O₃ layer is set to 150 Å, which is electrically equivalent to a thickness of the SiO₂ layer of 65 Å, in the MONOS structure for this purpose. The capacitor with the Al₂O₃ blocking layer shows a larger capacitance-voltage memory window of 8.6 V, lower program voltage of 7 V, faster program/erase speeds of 10 ms/1 μs, lower leakage current of 100 pA and longer data retention than the one with the SiO₂ blocking layer does. These improvements are attributed to the suppression of the carrier transport to the gate electrode afforded by the use of an Al₂O₃ blocking layer physically thicker than the SiO₂ one, as well as the effective charge-trapping by Al₂O₃ at the deep energy levels in the nitride layer.