Improvement of Operation Characteristics for MONOS Charge Trapping Flash Memory with SiGe Buried Channel

We propose and investigate a novel metal/SiO_2/Si_3N_4/SiO_2/SiGe charge trapping flash memory structure (named as MONOS), utilizing SiGe as the buried channel. The fabricated memory device demonstrates excellent program-erasable characteristics attributed to the fact that more carriers are generated by the smaller bandgap of SiGe during program/erase operations. A flat-band voltage shift 2.8 V can be obtained by programming at +11 V for 100 μs. Meanwhile, the memory device exhibits a large memory window of \sim7.17 V under \pm12 V sweeping voltage, and a negligible charge loss of 18% after 10^4 s' retention. In addition, the leakage current density is lower than 2.52\times10^-7 A\cdotcm^-2 below a gate breakdown voltage of 12.5 V. Investigation of leakage current-voltage indicates that the Schottky emission is the predominant conduction mechanisms for leakage current. These desirable characteristics are ascribed to the higher trap density of the Si_3N_4 charge trapping layer and the better quality of the interface between the SiO_2 tunneling layer and the SiGe buried channel. Therefore, the application of the SiGe buried channel is very promising to construct 3D charge trapping NAND flash devices with improved operation characteristics.