MOS memory with double-layer high-? tunnel oxide Al2O3/HfO2 and ZnO charge trapping layer

In this work, the effect of using a double layer of high-κ tunnel oxides Al₂O₃/HfO₂ instead of a single layer Al₂O₃ in MOS memory with ZnO charge trapping layer is studied. A memory effect due to charging in the ZnO layer is observed using high frequency C-V measurements. The shift of the threshold voltage (Vt) obtained from the hysteresis measurements at 10/-10 V program/erase voltage is around 3.3 V with single layer tunnel oxide while 7 V with the double layer tunnel oxide with same total oxide thickness. In addition, the memory structures show long retention times (>10 years) which make them promising for applications in non-volatile memory devices. Moreover, the results highlight that tunnel band engineering can be used to further reduce the operating voltage and equivalent oxide thickness of future memory devices without sacrificing the memory performance.