Molecularly Thin Electrolyte for All Solid-State Nonvolatile Two-Dimensional Crystal Memory

Abstract

A molecularly thin electrolyte is developed to demonstrate a nonvolatile, solid-state, one-transistor (1T) memory based on an electric-double-layer (EDL) gated WSe2 field-effect transistor (FET). The custom-designed monolayer electrolyte consists of cobalt crown ether phthalocyanine and lithium ions, which are positioned by field-effect at either the surface of the WSe2 channel or an h-BN capping layer to achieve “1” or “0”, respectively. Bistability in the monolayer electrolyte memory is significantly improved by the h-BN cap with density functional theory (DFT) calculations showing enhanced trapping of Li+ near h-BN due to a ∼1.34 eV increase in the absolute value of the adsorption energy compared to vacuum. The threshold voltage shift between the two states corresponds to a change in charge density of ∼2.5 × 1012 cm–2, and an On/Off ratio exceeding 104 at a back gate voltage of 0 V. The On/Off ratio remains stable after 1000 cycles and the retention time for each state exceeds 6 h (max measured). When the write time approaches 1 ms, the On/Off ratio remains >102, showing that the monolayer electrolyte-gated FET can respond on time scales similar to existing flash memory. The data suggest that faster switching times and lower switching voltages could be feasible by top gating.

Ion-Locking in Solid Polymer Electrolytes for Reconfigurable Gateless Lateral Graphene p-n Junctions

“…The roughness of the channel surface was reduced from 1.32 ± 0.14 nm to 0.23 ± 0.02 nm after AFM cleaning, which is close to the surface roughness for freshly cleaved graphene on SiO 2 [36,51,55]. Note that the maximum current and mobility are not degraded after AFM cleaning -in accordance with our prior reports [33,56].…”

Electrolyte versus Dielectric Gating of Two-Dimensional Materials

“…43 Another alternative exploited monolayers of a crown ether complex, whose flexible nature enables changing the position of the ionic centers within the molecule by the electric field (Figure 4b). 44 A related approach employed ferrocene-based redox molecules adsorbed at monolayer MoS 2 surface, which were switched from a neutral to a positively charged state by the electrolyte top-gate, thus gating the MoS 2 (Figure 4c). 45 Light illumination was also employed as an additional "gate" to achieve higher on−off ratios in trilayer MoS 2 than a single dielectric gate.…”

“…The switching of the Fc-SH redox state, controlled by the electrolyte top-gate, acts as a voltage gate for the underlying MoS 2 . Reprinted with permission from ref (a), copyright 2018 American Chemical Society, ref (b), copyright 2019 American Chemical Society, and ref (c), copyright 2020 John Wiley and Sons.…”

Sub-3V, MHz-Class Electrolyte-Gated Transistors and Inverters

“…Thus, for typical EGTs with channel areas of ~1000 m 2 , and gel film thicknesses of ~1 m, Rp is on the order of 1 k, which is a large value. Less resistive, ultrathin gate electrolyte films are a clear goal for EGTs 36 .…”

“…In our view there are clear reasons why EGTs will not rival the speed of Si MOSFETs 2 (though perhaps not everyone agrees 38 ), but for envisioned applications of EGTs, gigahertz speeds do not appear necessary. As EGTs are being developed as physiological recording amplifiers 9,10 , and integrated into circuits 36,[39][40][41] and neural nets 4,11,13,14,16 , it is nevertheless important to establish the limits of performance that can be obtained by rational design. We note that there are other limitations to EGT performance like high dielectric loss tangents and quasi-static leak currents associated with electrolytes that are important for power consumption 2 , but these are not our focus here.…”