Flash memory based on MoTe₂/boron nitride/graphene semi-floating gate heterostructure with non-volatile and dynamically tunable polarity

Atomically thin two-dimensional (2D) materials are promising candidates to develop flash memories with premium performances as compared to conventional bulk materials, because of their ultra-thin thickness and highly tunable electrical properties. So far, most of the reported 2D material based flash memories work in the uni-polar mode, which usually further integrate additional local gate to achieve bi-polar function. However, such approach is volatile, meaning that the gate bias has to be applied persistently to maintain the polarity change and thus increases the power consumption. Here, we report a bi-polar memory based on MoTe₂/h-BN/graphene semi-floating gate (SFG) heterostructure, which has non-volatile and dynamically tunable polarity. The SFG configuration has the channel layer of MoTe₂ and dielectric layer of h-BN half-stacked on the floating gate layer of graphene. The off-graphene half of the MoTe₂ channel can be tuned between n-type and p-type by simultaneously applying ultraviolet (UV) illumination and electrical field through the back gate, which maintains this polarity after the removal of both stimuli. As a result, the SFG memory can work in the non-volatile bi-polar mode, with a on/off ratio of ~ 100 and switching speed of 1 ms. On the other hand, the on-graphene half of the MoTe₂ channel remains n-type under UV illumination and electrical bias, so that the MoTe₂ full floating gate memory maintains n-type, which implements the integration of both n- and p-type memories in a single 2D heterostructure. This capability provides great flexibility for memory devices adapting in various emerging applications.