Abstract
A kind of devices Pt/Ag/ZnO:Li/Pt/Ti with high resistive switching behaviors were prepared on a SiO2/Si substrate by using magnetron sputtering method and mask technology, composed of a bottom electrode (BE) of Pt/Ti, a resistive switching layer of ZnO:Li thin film and a top electrode (TE) of Pt/Ag. To determine the crystal lattice structure and the Li-doped concentration in the resulted ZnO thin films, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) tests were carried out. Resistive switching behaviors of the devices with different thicknesses of Li-doped ZnO thin films were studied at different set and reset voltages based on analog and digital resistive switching characteristics. At room temperature, the fabricated devices represent stable bipolar resistive switching behaviors with a low set voltage, a high switching current ratio and a long retention up to 104 s. In addition, the device can sustain an excellent endurance more than 103 cycles at an applied pulse voltage. The mechanism on how the thicknesses of the Li-doped ZnO thin films affect the resistive switching behaviors was investigated by installing conduction mechanism models. This study provides a new strategy for fabricating the resistive random access memory (ReRAM) device used in practice.
Highlights
To the best knowledge, the resistive random access memory (ReRAM) has been considered as a promising candidate for generation nonvolatile memory (NVM) devices [1], due to their relatively excellent properties including small threshold voltage [2], low power consumption, fast switching speed [3], simple structure design and high storage density [4], etc
The main fabrication process of the proposed devices is shown in Figure 1a. (1) cleaning a silicon wafer substrate with orientation by using standard cleaning method, growing oxide layer on the surface of the silicon wafer by thermal oxidation method to form a 200 nm thickness SiO2 layer; (2) depositing Ti thin films as adhesion layer on the SiO2 /Si substrate based on a direct current radio frequency (RF) magnetron sputtering method using a pure Ti target, and depositing Pt thin films above the resulted Ti thin films by repeating the above magnetron sputtering method
To obtain the bottom electrode (BE); (3) sputtering resistive switching layer by RF magnetron sputtering method using two ceramic targets, i.e., a pure ZnO and Li-doped ZnO; (4) using a metal mask method to depositing Ag on the surface of ZnO thin films, and a Pt layer with thickness of 200 nm was deposited on the Ag thin films in order to protect the top electrode (TE) from oxidation, where the sputtering Ti, Ag and Pt were carried out in atmosphere of argon (47 sccm) with RF power of 100 W and pressure of
Summary
The resistive random access memory (ReRAM) has been considered as a promising candidate for generation nonvolatile memory (NVM) devices [1], due to their relatively excellent properties including small threshold voltage [2], low power consumption, fast switching speed [3], simple structure design and high storage density [4], etc. The resistive switching behaviors have been reported in a lot of materials, such as complex oxides [5,6], organics [7] and binary metal oxides [8,9,10], etc. The binary metal oxides have been common materials for fabricating ReRAM attributing to their simple preparing process, compatibility with integrated circuit processes, and easy to dope [11], etc. The fabrication of the metal oxide memristors mainly concentrates in ZrO2 [12], TiO2 [13], NiO [14], HfO2 [15] and ZnO [16], etc
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