SiGe/Si heterojunction drain transistor for faster 3D NAND flash memory erase

Some 3D NAND flash memory technologies utilize the phenomenon of Gate Induced Drain Leakage (GIDL) for erase operation. As the number of memory cells stacked in a 3D NAND string increases, larger GIDL current is needed to maintain the same erase speed. In this work, the use of silicon-germanium (SiGe), which has a smaller band-gap energy compared to silicon (Si), is proposed to augment GIDL current through enhanced band-to-band tunneling. TCAD simulation confirms that, when the heavily doped drain and a portion of the undoped channel region of the drain transistor comprise SiGe, both GIDL current and erase speed are enhanced significantly, while maintaining the same off-state current in inhibit mode operation.