Solution-processed black phosphorus nanoflakes for integrating nonvolatile resistive random access memory and the mechanism unveiled

Abstract

In this study, we demonstrated the integration of black phosphorus (BP) nanoflakes in a resistive random access memory (RRAM) with a facile and complementary metal-oxide-semiconductor-compatible process. The solution-processed BP nanoflakes embedded in polystyrene (PS) as an active layer were sandwiched between aluminum electrodes (Al/BP:PS/Al). The device shows a figure of merit with typical bipolar behavior and forming-free characteristics as well as excellent memory performances such as nonvolatile, low operation voltage (1.75 V) and high ON/OFF ratio (>102) as well as the long retention time (>1500 s). The improved device performances were attributed to the formation of effective trap sites from the hybrid structure of the active layer (BP:PS), especially the BP nanoflakes and the partly oxidized species (PxOy). Moreover, the extrinsic aluminum oxide layer was observed after the device operation. The mechanism of switching behavior was further unveiled through the carrier transport models, which confirms the conductive mechanisms of space-charge-limited current and Ohmic conductance at high resistance state (HRS) and low resistance state, respectively. Additionally, in the high electric field at HRS, the transfer curve was well fitted with the Poole–Frenkel emission model, which could be attributed to the formation of the aluminum oxide layer. Accordingly, both the trapping/de-trapping of carriers and the formation/rupture of conductive filaments were introduced as transport mechanisms in our devices. Although the partial PxOy species on BP were inevitable during the liquid phase exfoliation process, which was regarded as the disadvantages for various applications, it turns to a key point for improving performances in memory devices. The proposed approach to integrating BP nanoflakes in the active layer of the RRAM device could pave the way for next-generation memory devices.

Black Phosphorus Nanosheet/Melamine Cyanurate Assemblies as Functional Active Layers for Artificial Synapse Memristors

“…By using Au as the electrodes, an oxidation−reduction (redox) reaction could be eliminated at the interface between the electrode and MCA− BP active layer, where a redox reaction is commonly observed in BP-based resistive random-access memory (RRAM) by using Al electrodes followed the formation of the amorphous aluminum oxide layer (AlO x ). 45 For the memristor, the active layer is composed of the MCA supramolecules incorporating BP nanosheets (Figure 4c), while the TS selector could be achieved by inserting an additional pure MCA layer as a tunneling barrier (Figure 4d). The optical microscopy of devices with crossbar structure in a memristor and their corresponding SEM and AFM images are provided in the Supporting Information (Figure S3).…”

“…Thanks to the flexibility of stacking varied layers of the two-terminal sandwiched structure, we study the memristor (Au/MCA–BP/Au) and the TS selector (Au/MCA–BP/MCA/Au) by using our 2D-layered composite film self-assembly by BP nanosheets and MCA supramolecules. By using Au as the electrodes, an oxidation–reduction (redox) reaction could be eliminated at the interface between the electrode and MCA–BP active layer, where a redox reaction is commonly observed in BP-based resistive random-access memory (RRAM) by using Al electrodes followed the formation of the amorphous aluminum oxide layer (AlO x ) . For the memristor, the active layer is composed of the MCA supramolecules incorporating BP nanosheets (Figure c), while the TS selector could be achieved by inserting an additional pure MCA layer as a tunneling barrier (Figure d).…”

“…Likewise, the electric pulse also stimulates the paths of the proton to exhibit potentiation and depression, emulating the strengthening and weakening of synapses in the nervous system, respectively. More importantly, the high reliability of the devices can be supported by the stable structure of supramolecules even under charge transport through hydrogen bond networks, which is flexible for the arising three different processes, including the vibrational motion dynamics of the hydrogen bonds, the proton transfer reactions, and the forming and breaking of hydrogen bonds . Furthermore, the elapsed time of three processes ranges from femtoseconds to picoseconds, where the time scale is much shorter than that of the molecular transition at the order of a microsecond.…”

“…Therefore, the combination of BP and supramolecules with hydrogen bond network could be worth exploring the resistive switching devices. Also, BP-based memristor has been studied because of the features of a tunable bandgap and the native phosphorus oxide (P x O y ), providing versatile properties on memristors such as light-controlled memories. − In nanodevice applications, 2D materials are promising candidates for emerging devices with extraordinary features, not only the transistor scaling but also new architectures such as in-memory computing to the future technology with power-performance-area (PPA) benefit. ,− Nowadays, neuromorphic computing with the directly implemented logic and memory blocks provides a platform to overcome the von Neumann bottleneck, achieving high performance and low power consumption on the development of artificial neural networks. − The memristors with analog resistive properties have shown the promise to mimic synaptic reconfiguration, and the memristor crossbar arrays have revealed capability for energy-efficient neuromorphic computing, where the sneak-path current can be significantly suppressed by stacking selectors. − …”

In Situ Cleaning and Fluorination of Black Phosphorus for Enhanced Performance of Transistors with High Stability

“…Among the 2D family, 2D semiconductors with well-controlled Fermi levels, which are tunable by electrostatic fields, are promising candidates for next-generation nanoelectronics. For instance, 2D transition-metal dichalcogenides (TMDs) have exhibited various electronic applications with high performances due to their mature synthesis technologies, such as wafer-scale and quality controllable procedures. − Currently, noble metal dichalcogenides (such as PtS 2 and PtSe 2 ), , few-layer black phosphorus (BP), and InSe have attracted intensive attention for nanoelectronics applications due to their desirable characteristics, including suitable band gap and high mobility. − Additionally, BP has a widely tunable direct band gap that allows it to be an ideal material in optoelectronics. − …”