H. X. Guo

The Resistive Switching Mechanism of Ag / SrTiO3 / Pt Memory Cells

Reproducible and reliable bipolar resistive switching was obtained from Ag/SrTiO 3 (STO)/Pt memory cells. The current-voltage characteristic of the Ag/STO/Pt cells with a positive voltage applied to the Pt electrode and the results of X-ray photoelectron spectroscopy imply that the electrochemical reaction and the diffusion of Ag + ions play a critical role in the resistive switching effect. The temperature dependence of the on-state resistance, combined with the time dependence of the on- and off-state resistances under a constant voltage, provides further evidence that the resistive switching mechanism should be ascribed to the formation and dissolution of the metallic Ag nanofilaments.

Resistive switching devices based on nanocrystalline solid electrolyte (AgI)0.5(AgPO3)0.5

Resistive switching devices with a sandwich structure Ag∕(AgI)0.5(AgPO3)0.5∕Pt were fabricated on silicon(001) wafer by using the pulsed laser deposition method and the focused ion beam nanofabrication technique. (AgI)0.5(AgPO3)0.5 films deposited at room temperature show a nanocrystal structure and the composition of the films was identified by using x-ray photoelectron spectroscopy. The current-voltage characteristics of the Ag∕(AgI)0.5(AgPO3)0.5∕Pt memory units show good switching behaviors. The ratio of the conductance between the “ON” state (high conductance) and the “off” state (low conductance) reaches 1×106. The ON and OFF states can be effectively written, read, and erased up to 4×105 scanning cycles by using a set of voltage pulses with an amplitude less than 3V. It also could be observed that the time for the writing and erasing operations could be less than 150ns. The switching mechanism of the Ag∕(AgI)0.5(AgPO3)0.5∕Pt memory devices was ascribed to the possible formation and dissolution of Ag...

The growth of metallic nanofilaments in resistive switching memory devices based on solid electrolytes

Memory cells with sandwich structure based on solid electrolytes Ag30S2P14O42, called ASP, were fabricated on Pt/Ti/Si(001) wafers by using pulsed laser deposition and focused ion beam nanofabrication technique. The current-voltage characteristic of the ASP memory units shows satisfactory switching behaviors. The switching of the devices was explained by the formation and rupture of Ag nanofilaments with the help of bipolar electrical pulses. A simplified model was proposed to describe the growth of the Ag nanofilaments. It was shown that the effective cross section area of the Ag nanofilaments increased at initial stage, then decreased after reaching a maximum until the top and bottom electrodes were connected.

Bipolar resistive switching performance of the nonvolatile memory cells based on (AgI)0.2(Ag2MoO4)0.8 solid electrolyte films

Resistive switching memory cells with polycrystalline (AgI)0.2(Ag2MoO4)0.8 (AIMO) solid electrolyte films as storage medium were fabricated on SiO2/Pt/Ti/Si substrates by using pulse laser deposition technique and focused ion beam lithography. X-ray diffraction, scanning electron microscopy, and energy dispersive x-ray analysis have been employed to investigate the structure, the surface morphology, and the composition of AIMO thin films. The Ag/AIMO/Pt memory cells with sandwich structure exhibit stable, reproducible, and reliable resistive switching characteristics. The ratio of resistance between high resistance states and low resistance states can reach ∼105. Moreover, the low resistance is ∼500 Ω at a compliance current of 0.5 mA, which is favorable to reduce the power dissipation of the entire circuit. The switching-on mechanism has been discussed and the metallic conduction characteristic has also been verified. The fast response speed and the good retention properties further indicate that polycry...

The thermal stability and electrical properties of LaErO3 films as high-k gate dielectrics

Lanthanum erbium oxide thin films have been deposited on an Si (1 0 0) wafer by using the pulsed laser deposition technique. The thermal and electrical properties of LaErO3 films were investigated by x-ray diffraction, x-ray photoelectron spectroscopy and high resolution transmission electron microscopy. Capacitance measurements reveal good C–V curves with an equivalent oxide thickness of 1.4 nm and little hysteresis. Transmission electron microscopic images reveal that the 6.5 nm LaErO3 film shows a thin interfacial layer even after being annealed in N2 at 700 °C for 30 s. X-ray photoelectron spectroscopic spectra indicate that little SiO2 was formed at the interface during the deposition of LaErO3 films. The measured thermal and electrical properties of the thin film suggest that the LaErO3 film should be a promising candidate for future high-k gate dielectrics.

Band alignments and improved leakage properties of (La2O3)0.5(SiO2)0.5/SiO2/GaN stacks for high-temperature metal-oxide-semiconductor field-effect transistor applications

The band alignments of (La2O3)0.5(SiO2)0.5(LSO)/GaN and LSO/SiO2/GaN gate dielectric stacks were investigated comparatively by using x-ray photoelectron spectroscopy. The valence band offsets for LSO/GaN stack and LSO/SiO2/GaN stack are 0.88 and 1.69 eV, respectively, while the corresponding conduction band offsets are found to be 1.40 and 1.83 eV, respectively. Measurements of the leakage current density as function of temperature revealed that the LSO/SiO2/GaN stack has much lower leakage current density than that of the LSO/GaN stack, especially at high temperature. It is concluded that the presence of a SiO2 buffer layer increases band offsets and reduces the leakage current density effectively.

Effect of NH3 and N2 annealing on the interfacial and electrical characteristics of La2O3 films grown on fully depleted SiGe-on-insulator substrates

The interfacial structure and the electrical properties of pulsed laser deposition derived La2O3 ultra-thin films on fully depleted SiGe-on-insulator (FD SGOI) substrates before and after post-annealing in NH3 and N2, respectively, have been investigated comparatively. The results from high-resolution transmission electron microscopy and x-ray photoelectron spectroscopic revealed that interface reactions take place after the NH3 and N2 annealing process, but, as compared with the N2 annealing process, the NH3 annealing process can effectively decrease the thickness of the interfacial layer and incorporate more nitrogen at the dielectric/SiGe interface, resulting in smaller equivalent oxide thickness. The La2O3 capacitors annealed in NH3 show good capacitance–voltage characteristics with negligible hysteresis, smaller interface trap density and lower gate-leakage current density in comparison with those of capacitors annealed in N2. It is demonstrated that the NH3 annealing process can be a promising technology in improving the quality of high-k dielectric on FD SGOI substrates.

Monte Carlo simulation of the percolation in Ag30Ge17Se53 amorphous electrolyte films

Monte Carlo simulations using a dielectrophoresis model were performed to investigate the microstructural evolution and the conductance change of an Ag30Ge17Se53 electrolyte film clapped by a Ag active electrode, at which a positive bias was applied, and a Pt inert electrode. It has been revealed that driven by the electrical field Ag ions were injected into the electrolyte from the Ag electrode to form conductive particles, thereafter, the particles align themselves in nanowires connecting Ag electrode and Pt electrode and leading to an electrical percolation. It is responsible for the resistive switching of the system. The transmission electron microscopic observations and resistive measurement results are in good agreement with the results of simulations.

Modulation of the band offsets between La2Hf2O7 and fully depleted SiGe on insulator by NH3 treatment

Band alignments of La2Hf2O7 (LHO) films grown on fully depleted SiGe on insulator (FD SGOI) substrates have been investigated by x-ray photoelectron technique. The valence and conduction band offsets for LHO/FD SGOI systems are determined to be 3.25 and 1.49 eV, respectively. Such asymmetric band alignment can be modulated to be quite symmetric by the surface nitridation of FD SGOI using NH3 treatment. The impact of NH3-treatment temperature on band offsets is also investigated.