A novel dual-channel 3D NAND flash featuring both N-channel and P-channel NAND characteristics for bit-alterable Flash memory and a new opportunity in sensing the stored charge in the WL space

摘要

This work proposes a novel dual-channel 3D NAND Flash that exhibits both n-channel and p-channel NAND characteristics. The NAND is junction-free without dopant inside the array. Unlike the conventional 3D NAND, the drain side near SSL is N+ doped junction, while source side near GSL is P+ junction. A positive pass-gate read voltage (Vpass, r) induces n-type virtual source/drain for the center WL's, giving an n-channel behavior. On the other hand, a negative Vpass, r induces p-type virtual source/drain, giving the p-channel behavior. Both n- and p-channel reads produce excellent Id-Vg characteristics with very small leakage current. The advantage of this device is that the carrier source of both +FN programming and -FN erasing can be readily provided by either N+ drain or P+ source, respectively, without waiting for the GIDL generated minority carrier for the floating-body 3D NAND. This gives a much faster +/- FN speed than conventional 3D NAND. Moreover, both +FN and -FN can find suitable inhibit method, enabling a novel bit-alterable Flash memory. We have successfully compared, for the first time, two sensing methods (n- and p-channel read) and identified the trapped charge in the space between WL's. This not only provides characterization of charge lateral profile but also a new opportunity to create another storage node (in WL space) inside the array.