1Key Laboratory of Microelectronics Devices & Integrated Technology, Institute of Microelectronics, Chinese Academy of Sciences, Beijing 100029 2University of Chinese Academy of Sciences, Beijing 100049
Abstract:We propose and investigate a novel metal/SiO$_{2}$/Si$_{3}$N$_{4}$/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 $\sim$7.17 V under $\pm$12 V sweeping voltage, and a negligible charge loss of 18% after 10$^{4}$ s' retention. In addition, the leakage current density is lower than $2.52\times10^{-7}$ A$\cdot$cm$^{-2}$ 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$_{3}$N$_{4}$ 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.