Aize Hao

Ag-NPs doping enhanced resistive switching performance and induced changes in magnetic properties of NiFe2O4 thin films

Ag-NPs doped NiFe2O4 (NFO) thin films have been synthesized by the chemical solution deposition method. The effect of Ag-NPs incorporation on the resistive switching (RS) properties of NFO films with different doping concentrations in the range of 0 to 1.0% Ag was investigated. Results show that Ag-NPs doped NFO based memory devices perform resistive switching with much better uniformity and repeatability in switching cycles, and have excellent reliability at an appropriate Ag-NPs doping concentration (i.e. 0.5%) instead of very low and high doping concentrations (i.e. un-doped NFO film, 0.2% and 1.0% Ag). On the basis of analyses performed on current–voltage characteristics and their temperature dependence, it was found that the carrier transport occurred through the conducting filaments in the low resistance state with ohmic conduction, and in the high resistance state with Schottky emission. In addition, the temperature dependence of the resistance and magnetic behavior at HRS and LRS revealed that the physical origin of the RS mechanism, which involves the formation and rupture of the conducting paths, consists of oxygen vacancies and Ag atoms. Ag-NPs doping-induced changes in the saturation magnetization, associated with resistive switching, have been ascribed to variations in the oxygen vacancy concentration. The excellent endurance properties (>103 cycles), data retention (of >105 s at 298 and 358 K), and good cycle-to-cycle uniformity are observed in 0.5% Ag-NPs doped NFO-based memory devices.

Coexistence of unipolar and bipolar resistive switching behaviors in NiFe2O4 thin film devices by doping Ag nanoparticles

The coexistence of unipolar and bipolar resistive switching (RS) behaviors of Ag-nanoparticles (Ag-NPs) doped NiFe2O4 (NFO) based memory devices was investigated. The switching voltages of required operations in the unipolar mode were smaller than those in the bipolar mode, while ON/OFF resistance levels of both modes were identical. Ag-NPs doped NFO based devices could switch between the unipolar and bipolar modes just by preferring the polarity of RESET voltage. Besides, the necessity of identical compliance current during the SET process of unipolar and bipolar modes provided an additional advantage of simplicity in device operation. Performance characteristics and cycle-to-cycle uniformity (>103 cycles) in unipolar operation were considerably better than those in bipolar mode (>102 cycles) at 25 °C. Moreover, good endurance (>600 cycles) at 200 °C was observed in unipolar mode and excellent nondestructive retention characteristics were obtained on memory cells at 125 °C and 200 °C. On the basis of tem...

Coexistence of unipolar and bipolar switching in nanocrystalline spinel ferrite ZnFe2O4 thin films synthesized by sol-gel method

In this letter, we report the coexistence of unipolar and bipolar switching in a solution-based nanocrystalline spinel ferrite ZnFe2O4 thin film prepared by the sol-gel method. It is seen that the Au/ZnFe2O4/Pt device could be activated between unipolar and bipolar switching modes just by choosing RESET-voltage polarity. Conversions between unipolar to bipolar switching modes are reversible and controllable. The results show that the SET-voltage of unipolar switching is smaller than that of bipolar switching, while memory windows (ON/OFF ratio) are identical. Furthermore, filaments are induced by the migration of oxygen vacancies (VOs), which are responsible for reducing variations in SET voltages of unipolar switching. By analyzing the current transport conduction mechanism, the electrode-limited Schottky emission mechanism is dominated in the high field region. Temperature dependence of low and high resistance states indicates that conductive filaments are composed of VOs and metallic Zn atoms, involving Joule heating and electrochemical redox reaction effects. Investigation on coexisting both unipolar and bipolar switching modes in a single Au/ZnFe2O4/Pt memory cell would open a pathway for spinel ferrite based low-cost nonvolatile memory.In this letter, we report the coexistence of unipolar and bipolar switching in a solution-based nanocrystalline spinel ferrite ZnFe2O4 thin film prepared by the sol-gel method. It is seen that the Au/ZnFe2O4/Pt device could be activated between unipolar and bipolar switching modes just by choosing RESET-voltage polarity. Conversions between unipolar to bipolar switching modes are reversible and controllable. The results show that the SET-voltage of unipolar switching is smaller than that of bipolar switching, while memory windows (ON/OFF ratio) are identical. Furthermore, filaments are induced by the migration of oxygen vacancies (VOs), which are responsible for reducing variations in SET voltages of unipolar switching. By analyzing the current transport conduction mechanism, the electrode-limited Schottky emission mechanism is dominated in the high field region. Temperature dependence of low and high resistance states indicates that conductive filaments are composed of VOs and metallic Zn atoms, involvin...

Narrowing the band gap to enhance the resistive switching properties of Pr3+-doped ZnO thin films by Cd-ion doping

Pr3+/Cd2+ co-doped ZnO hexagonal structure thin films with c-axis preferred orientation were deposited on Pt/Ti/SiO2/Si substrates using a chemical solution deposition method, and the effect of Cd-ion doping on the resistive switching properties of Zn0.97−xPr0.03CdxO thin films (x = 0, 0.02, 0.04, and 0.06) has been investigated. The results showed that Cd-doping improved the resistive switching properties of the Pt/Zn0.97−xPr0.03CdxO/Pt devices. The resistive switching devices exhibited good endurance, long retention, and uniform switching voltages. The resistive switching characteristics also show a good temperature stability beneficial for further device applications. The I–V characteristics and their temperature dependence analysis indicated that the conduction mechanism was ohmic conduction behavior for the low resistance state and at low voltage region for the high resistance state, whereas the conduction mechanism at relatively higher voltage for the high resistance state is trap-controlled space charge limited current. The resistive switching process has been explained using a conductive filament-related formation/rupture mechanism considering the thermal effects and the migration of oxygen vacancies. The reasons for the improvement of resistive switching performance through Cd ion doping, were attributed to the decrease of the band gap and the control of oxygen vacancies.