Resistive properties of CuInS₂ quantum dots regulated by niobium-doped lead zirconate titanate ferroelectric films

Abstract

As a new type of non-volatile memory, quantum dot resistive random access memory (RRAM) has attracted much attention for its easy preparation, fast responding time, high storage density, and smaller device size. CuInS₂ quantum dot (CuInS₂ QD) is a kind of excellent resistive functional material with abundant electron capture sites, high optical absorption coefficient, and high carrier mobility. In this work, CuInS₂ QDs/Nb:Pb (Zr_0.52Ti_0.48)O₃ (PNZT) films are prepared by spin-coating CuInS₂ QDs on PNZT films. The results show that the resistive properties of CuInS₂ QDs RRAMs can be effectively improved by introducing PNZT films and can be controlled by changing the polarization direction. The CuInS₂ QDs/PNZT film in the negative polarization state promotes the interfacial electrons to enter into the PNZT film, which will reduce the height of the interfacial barrier and the thickness of the interfacial depletion region. And it will reduce the resistance of the composite film at the low resistance state (LRS). Compared with the switching voltage and resistive switching ratio of the pure CuInS₂ QDs film (10³), the switching voltage of the device decreases to –4.1/3.4 V and the resistive switching ratio increases to 10⁶. Furthermore, it maintains good stability in the 10³ cycle durability test. In contrast, the CuInS₂ QDs/PNZT film interface has a larger barrier height and depletion-layer thickness when the PNZT is in the positive polarization state, which increases the resistance of the composite film in the LRS state. As a result, the switching voltage of the device increases to –6.4/5.7 V with a resistive switching ratio of 10⁴. The resistive properties of the CuInS₂ QDs/PNZT film can be tuned by changing the polarization direction, as the polarization direction of the PNZT changes the interfacial energy band structure and affects the conduction mechanism. This work reveals the feasibility of using ferroelectric thin films to improve the resistive properties of quantum dots RRAMs and thus providing an approach to further developing RRAMs.