Enhancing the Resistive Switching Performance in a Physically Transient Memristor by Doping ${\mathrm{Mo}\mathrm{S}}_2$ Quantum Dots

Resistive random-access memory has attracted tremendous attention and numerous investigations as a promising next-generation nonvolatile memory device to address the physical limits of flash memory. Particularly, physically transient resistive switching memory is intensively researched for its degradable and environmentally friendly characteristics. Zinc oxide ($\mathrm{Zn}\mathrm{O}$), as a low-cost biocompatible and biodegradable material, has been widely used in the dielectric layer, yet many previous studies on $\mathrm{Zn}\mathrm{O}$-based memory devices show unsatisfactory switching properties. In this work, ${\mathrm{Mo}\mathrm{S}}_2$ quantum dots (QDs) are added between the $\mathrm{W}$ bottom electrode and $\mathrm{Zn}\mathrm{O}$ insulator by spin coating ($\mathrm{W}/{\mathrm{Mo}\mathrm{S}}_2$ QD$/\mathrm{Zn}\mathrm{O}/\mathrm{Ag}$) to improve its resistive switching behavior. The modified device exhibits distinctly better properties, including more-uniform switching parameters (low- and high-resistance states, $V_{\mathrm{set}}$, $V_{\mathrm{reset}}$), ultralow threshold voltages, and steady retention. Moreover, we transfer the device onto polyvinyl alcohol substrate, making it fully degradable, and it is completely dissolved in phosphate-buffered solution after 40 min. These results indicate that the ${\mathrm{Mo}\mathrm{S}}_2$ QD–optimized transient resistive switching memory shows great potential in green electronics, implantable biomedical devices, and secure information-storage applications.

Figure 1

(a) Schematic diagram of the structure of $\mathrm{W}/{\mathrm{Mo}\mathrm{S}}_2$ QD$/\mathrm{Zn}\mathrm{O}/\mathrm{Ag}$ device. (b) Cross-section SEM image of the device. (c) AFM image of ${\mathrm{Mo}\mathrm{S}}_2$ QDs spin coated on the $\mathrm{W}$ bottom electrode. (d) AFM scanning result along the straight line in (c). (e) TEM image of ${\mathrm{Mo}\mathrm{S}}_2$ QDs. (f) TEM image of ${\mathrm{Mo}\mathrm{S}}_2$ QDs on a smaller scale. Inset is the particle diameter distribution of ${\mathrm{Mo}\mathrm{S}}_2$ QDs.

Figure 2

I-V characteristics of the $\mathrm{W}/\mathrm{Zn}\mathrm{O}/\mathrm{Ag}$ device (a) without ${\mathrm{Mo}\mathrm{S}}_2$ QDs and (b) with ${\mathrm{Mo}\mathrm{S}}_2$ QDs. (c) Statistical cumulative probabilities of V_set and V_reset and (d) LRS and HRS of the two devices of 50 cycles. (e) Endurance performance and (f) retention performance of the two devices with a read voltage of 0.1 V.

Figure 3

Double-logarithmic plots of I-V curves in HRS and LRS from different devices and their linear fittings. (a) HRS and (b) LRS from device 1. (c) HRS and (d) LRS from device 2. (e) HRS and (f) LRS from device 3. (g) I-V curve of $\mathrm{W}/\mathrm{Zn}\mathrm{O}/\mathrm{W}$ device.

Figure 4

Schematic diagram of RS mechanism in our memory devices: (a) Oxidation of $\mathrm{Ag}$ to ${\mathrm{Ag}}^{+}$ at $\mathrm{Ag}/\mathrm{Zn}\mathrm{O}$ interface. (b) Migration of ${\mathrm{Ag}}^{+}$ ions and reduction reaction at the bottom electrode. (c) Formation of $\mathrm{Ag}$ conductive filament. (d) Rupture of $\mathrm{Ag}$ conductive filament under a reverse voltage. (e) Schematic diagram of $\mathrm{Ag}$ filament growth in device without ${\mathrm{Mo}\mathrm{S}}_2$ QDs. (f) Schematic diagram of $\mathrm{Ag}$ filament growth in device with ${\mathrm{Mo}\mathrm{S}}_2$ QDs. (g) Electric field simulation with matlab in $\mathrm{Zn}\mathrm{O}$ layer from 0 to 1 V around a ${\mathrm{Mo}\mathrm{S}}_2$ quantum dot and equipotential lines are also illustrated.

Figure 5

(a) I-V characteristics of the $\mathrm{W}/{\mathrm{Mo}\mathrm{S}}_2$ QD$/\mathrm{Zn}\mathrm{O}/\mathrm{Ag}$ device on PVA substrate. Fully transient property of the device on PVA substrate. (b) Device transferred onto PVA substrate. (c) Image of the device immersed in PBS at room temperature after 1 min, (d) 5 min, (e) 10 min, (f) 20 min, and (g) 40 min.