Fei Zhuge

Nonvolatile resistive switching in graphene oxide thin films

Reliable and reproducible resistive switching behaviors were observed in graphene oxide (GO) thin films prepared by the vacuum filtration method. The Cu/GO/Pt structure showed an on/off ratio of about 20, a retention time of more than 104 s, and switching threshold voltages of less than 1 V. The switching effect could be understood by considering the desorption/absorption of oxygen-related groups on the GO sheets as well as the diffusion of the top electrodes. Our experiments indicate that GO is potentially useful for future nonvolatile memory applications.

Resistance switching in polycrystalline BiFeO3 thin films

We report resistance switching effects in polycrystalline pure BiFeO3 films prepared by a sol-gel method. By current-voltage and conductive atomic force microscope (c-AFM) measurements, resistance switching effects are observed in BiFeO3 films annealed at and above 650 °C. A fresh sample can be transformed into a low-resistive state by applying a high positive voltage without forming process and then be switched to a high-resistive state by applying a negative voltage. Both c-AFM and retention results suggest that the redistribution of oxygen vacancies in grain boundaries could play a key role on the resistance switching in the polycrystalline pure BiFeO3 films.

Effect of top electrodes on photovoltaic properties of polycrystalline BiFeO3 based thin film capacitors

We investigated capacitors based on polycrystalline narrow-band-gap BiFeO(3) (BFO) thin films with different top electrodes. The photovoltaic response for the capacitor with a Sn-doped In(2)O(3) (ITO) top electrode is about 25 times higher than that with a Au top electrode, which indicates that the electrode plays a key role in determining the photovoltaic response of ferroelectric thin film capacitors, as simulated by Qin et al (2009 Appl. Phys. Lett. 95 22912). The light-to-electricity photovoltaic efficiency for the ITO/polycrystalline BFO/Pt capacitor can reach 0.125%. Furthermore, under incident light of 450 µW cm(-2) and zero bias, the corresponding photocurrent varies from 0.2 to 200 pA, that is, almost a 1000-fold photoconductivity enhancement. Our experiments suggest that polycrystalline BFO films are promising materials for application in photo-sensitive and energy-related devices.

Nonvolatile resistive switching memory based on amorphous carbon

Resistive memory effect has been found in carbon nanostructure-based devices by Standley et al. [Nano Lett. 8, 3345 (2008)]. Compared to nanostructures, hydrogenated amorphous carbon (a-C:H) has much more controllable preparation processes. Study on a-C:H-based memory is of great significance to applications of carbon-based electronic devices. We observed nonvolatile resistance memory behaviors in metal/a-C:H/Pt structures with device yield 90%, ON/OFF ratio >100, and retention time >105 s. Detailed analysis indicates that the resistive switching originates from the formation/rupture of metal filaments due to the diffusion of the top electrodes under a bias voltage.

Mechanism for resistive switching in an oxide-based electrochemical metallization memory

A comparison of the asymmetric OFF-state current-voltage characteristics between Cu/ZnO/Pt and Cu/ZnO/Al-doped ZnO (AZO) electrochemical metallization memory (ECM) cells demonstrates that the Cu filament rupture and rejuvenation occur at the ZnO/Pt (or AZO) interface, i.e., the cathodic interface. Therefore, the filament is most likely to have a conical shape, with wider and narrower diameters formed at the anodic and cathodic interfaces, respectively. It is inferred that the filament growth starts at the anode surface and stops at the cathode surface. Our results indicate that oxide-based ECM cells strongly differ from sulfide- and selenide-based ones in the resistive switching mechanism. VC 2012 American Institute of Physics.

Nonvolatile resistive switching in metal/La-doped BiFeO3/Pt sandwiches

The resistive switching (RS) characteristics of a Bi(0.95)La(0.05)FeO(3) (La-BFO) film sandwiched between a Pt bottom electrode and top electrodes (TEs) made of Al, Ag, Cu, and Au have been studied. Devices with TEs made of Ag and Cu showed stable bipolar RS behaviors, whereas those with TEs made of Al and Au exhibited unstable bipolar RS. The Ag/La-BFO/Pt structure showed an on/off ratio of 10(2), a retention time > 10(5) s, and programming voltages < 1 V. The RS effect can be attributed to the formation/rupture of nanoscale metal filaments due to the diffusion of the TEs under a bias voltage. The maximum current before the reset process (on-to-off switching) was found to increase linearly with the current compliance applied during the set process (off-to-on switching).

Nonvolatile bistable resistive switching in a new polyimide bearing 9-phenyl-9H-carbazole pendant

A new polyimide bearing the functional pendant 9-phenyl-9H-carbazole moieties, poly[2,2-(4,4′-di(N-benzyloxycarbazole)-3,3′-biphenylene)propane-hexafluoroisopropylidenediphthalimide] (6F-BAHP-PC PI), has been designed as a functional material for resistance memory devices. The ITO/6F-BAHP-PC PI/Ag memory device exhibits nonvolatile resistive switching (RS) with a high ON/OFF ratio (>106), long retention time (>6 × 104 s), good endurance, and low power consumption (∼100 μW). In situconductive atomic force microscopy measurements show that the RS of 6F-BAHP-PC PI originates from the formation/rupture of nanoscale conducting filaments.

Improvement of reproducible resistance switching in polycrystalline tungsten oxide films by in situ oxygen annealing

The electric-field-induced resistance switching in polycrystalline tungsten oxide films was investigated. Compared with the as-deposited film, the film annealed in an oxygen atmosphere shows a more stable switching behavior, a higher low-to-high resistance ratio, and a better endurance and retention. Based on the x-ray photoemission spectroscopy analysis, the resistance switching was attributed to the change in the interfacial barrier potential, due to the electron trapping/detrapping in the surface states, and the switching improvement was attributed to the decrease in the surface density of states. The present work suggests a possible approach controlling the resistance switching property by surface modification.

Structural, Chemical, Optical, and Electrical Evolution of SnOx Films Deposited by Reactive rf Magnetron Sputtering

In this paper, SnO(x) films were produced by reactive radio frequency magnetron sputtering under various oxygen partial pressure (P(O)) in conjunction with a thermal annealing at 200 °C afterwards. The obtained SnO(x) films were systematically studied by means of various techniques, including X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, spectroscopic ellipsometry, and Hall-effect measurement. The structural, chemical, and electrical evolution of the SnO(x) films was found to experience three stages: polycrystalline SnO phase dominated section with p-type conduction at P(O) ≤ 9.9%; amorphous SnO(2) phase dominated area at P(O) ≥ 12.3%, exhibiting n-type characteristics; and conductivity dilemma area in between the above mentioned sections, featuring the coexistence of SnO and SnO(2) phases with compatible and opposite contribution to the conductivity. The polycrystalline to amorphous film structure transition was ascribed to the enhanced crystallization temperature due to the perturbed structural disorder by incorporating Sn(4+) into the SnO matrix. The inversion from p-type to n-type conduction with P(O) variation is believed to result from the competition between the donor and acceptor generation process, i.e., the n-type behavior would be present if the donor effect is overwhelming, and vice versa. In addition, with increasing P(O), the refractive index decreased from 3.0 to 1.8 and the band gaps increased from 1.5 to 3.5 eV, respectively.

Ambipolar inverters using SnO thin-film transistors with balanced electron and hole mobilities

Ambipolar thin film transistors have attracted increasing research interests due to their promising applications in complementary logic circuits and the dissipative charge transporting devices. Here, we report the fabrication of an ambipolar transistor using tin mono-oxide (SnO) as a channel, which possesses balanced electron and hole field-effect mobilities. A complementary metal oxide semiconductor-like inverter using the SnO dual operation transistors is demonstrated with a maximum gain up to 30 and long-term air stability. Such logic device configuration would simplify the circuit design and fabrication process, offering more opportunities for designing and constructing oxide-based logic circuits.