Fig. 1. (Color online) The schematic and characterization of the QNV memory. (a) The linearly varied density of states DOS(E), super-exponentially decreased electron density n(E) with the energy of Gr Dirac material, and the cut-off of electron injection from Gr Dirac material to channel over the bulk barrier ϕ_B. The orange dashed line in n(E) represents the Boltzmann distribution. (b) The schematic structure of the QNV memory in which MoS₂ serves as the channel, Gr-hBN servers as the semi-blocking layer, and WSe₂ serves as the floating gate. (c) The false-colored optical microscope image of the device. The scale bar is 5 μm. (d) The Raman spectra of monolayer Gr and multilayer MoS₂ and WSe₂ were measured by using a 532 nm solid-state laser. (e) The double sweep transfer characteristic of the QNV memory under V_DS = 0.5 V. A large I_on/I_off exceeding 10⁴ is achieved when reading at V_G = 0 V. The inset is the full measurement range (V_G varying from –2 to 2 V) of transfer characteristics on a logarithmic scale.

Fig. 2. (Color online) The symmetric ultrafast programming and erasing operation of the QNV memory. (a) The initial state is state-1 and the 5 V gate voltage pulse with different pulse widths is applied for the programming operation. After that, the reading operation is carried out at V_G = 0 V and V_DS = 0.5 V. (b) The initial state is state-0 after applying a positive gate voltage pulse for programming and the –5 V gate voltage pulse with different pulse width is applied for the erasing operation. After that the reading operation is carried out at V_G = 0 V and V_DS = 0.5 V. (c) The current state after the programming and erasing operations with different pulse width gate voltage pulse (the pulse amplitude is fixed 5 V). The data points of the current state are the mean value of the sampling points produced while monitoring the channel current 5 s after the programming/erasing operation. (d) The endurance of the device for 100 cycles of the programming/erasing pulse, demonstrating that no performance degradation was observed.

Fig. 3. (Color online) The data retention ability of the QNV memory. (a) The retention characteristic of the memory after the programming operation with different gate pulse widths (the pulse amplitude is fixed 5 V). (b) The relationship between the state-0 output current and program pulse width for different wait times. (c) The comparison of the refresh time of our device with the other QNV memory devices^{[1, 18–20]} under different pulse widths.

Fig. 4. (Color online) The schematic illustrations of the band diagrams and charges transport in the QNV memory at different operation modes: (a) program, (b) read-0, (c) erase, and (d) read-1. The blue balls and arrows represent the electrons and electron flow direction, respectively. The approximate electron affinities of MoS₂ and WSe₂ are 4.0–4.2, 3.5–4.0 eV respectively, and the work function of monolayer Gr is ~4.3 eV.