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.