Long Shibing

Resistive switching characteristics of Ti/ZrO2/Pt RRAM device

In this paper, the bipolar resistive switching characteristic is reported in Ti/ZrO2/Pt resistive switching memory devices. The dominant mechanism of resistive switching is the formation and rupture of the conductive filament composed of oxygen vacancies. The conduction mechanisms for low and high resistance states are dominated by the ohmic conduction and the trap-controlled space charge limited current (SCLC) mechanism, respectively. The effect of a set compliance current on the switching parameters is also studied: the low resistance and reset current are linearly dependent on the set compliance current in the log—log scale coordinate; and the set and reset voltage increase slightly with the increase of the set compliance current. A series circuit model is proposed to explain the effect of the set compliance current on the resistive switching behaviors.

Resistivity measurements of self-assembled epitaxially grown erbium silicide nanowires

Single orientation epitaxial erbium silicide (ErSi2) nanowires (NWs) were fabricated by laser ablation and a post-annealing process on the Si (110) surface. The average width of the NWs is 10 nm and the maximum length is more than 10 µm. The resistivity of the NWs was measured at room temperature using two methods: AFM probe measurement and direct electrodes deposited by FIB. It was demonstrated that the resistivities of the NWs were ten times that of the ErSi2 film material. The experimental data were compared with theoretical predictions for the strong size effect to the erbium silicide NW resistivity.

CMOS Compatible Nonvolatile Memory Devices Based on SiO2/Cu/SiO2 Multilayer Films *

We systematically investigate the resistive switching characteristics of SiO2 films with a Cu/SiO2/Cu/SiO2/Pt multilayer structure. The device exhibits good resistive switching performances, including a high ON/OFF resistance ratio (>103), good retention characteristic (>104s), satisfactory switching endurance (>200 cycles), a fast programming speed (<100 ns) and a high device yield (~100%). Considering these results, SiO2-based memories have highly promising applications for nonvolatile memory devices.

Unipolar resistive switching of Au+-implanted ZrO2 films

The resistive switching characteristics of Au+-implanted ZrO2 films are investigated. The Au/Cr/Au+-implanted-ZrO2/n+-Si sandwiched structure exhibits reproducible unipolar resistive switching behavior. After 200 write-read-erase-read cycles, the resistance ratio between the high and low resistance states is more than 180 at a readout bias of 0.7 V. Additionally, the Au/Cr/Au+-implanted-ZrO2/n+-Si structure shows good retention characteristics and nearly 100% device yield. The unipolar resistive switching behavior is due to changes in the film conductivity related to the formation and rupture of conducting filamentary paths, which consist of implanted Au ions.

Effect of Pulse and dc Formation on the Performance of One-Transistor and One-Resistor Resistance Random Access Memory Devices

We investigate the effect of the formation process under pulse and dc modes on the performance of one transistor and one resistor (1T1R) resistance random access memory (RRAM) device. All the devices are operated under the same test conditions, except for the initial formation process with different modes. Based on the statistical results, the high resistance state (HRS) under the dc forming mode shows a lower value with better distribution compared with that under the pulse mode. One of the possible reasons for such a phenomenon originates from different properties of conductive filament (CF) formed in the resistive switching layer under two different modes. For the dc forming mode, the formed filament is thought to be continuous, which is hard to be ruptured, resulting in a lower HRS. However, in the case of pulse forming, the filament is discontinuous where the transport mechanism is governed by hopping. The low resistance state (LRS) can be easily changed by removing a few trapping states from the conducting path. Hence, a higher HRS is thus observed. However, the HRS resistance is highly dependent on the length of the gap opened. A slight variation of the gap length will cause wide dispersion of resistance.

Charge storage characteristics of hydrogenated nanocrystalline silicon film prepared by rapid thermal annealing

The early stages of hydrogenated nanocrystalline silicon (nc-Si:H) films deposited by plasma-enhanced chemical vapour deposition were characterized by atomic force microscopy. To increase the density of nanocrystals in the nc-Si:H films, the films were annealed by rapid thermal annealing (RTA) at different temperatures and then analysed by Raman spectroscopy. It was found that the recrystallization process of the film was optimal at around 1000°C. The effects of different RTA conditions on charge storage were characterized by capacitance–voltage measurement. Experimental results show that nc-Si:H films obtained by RTA have good charge storage characteristics for nonvolatile memory.

Modeling and simulation development of electron beam resist based on cellular automata

Abstract This paper presents a robust Cellular Automata model which predicts the two dimensional development profile as a function of development time, exposure dose and electron beam resist type. The main advantage of CA model is that they exhibit high efficiency and accuracy when handling arbitrarily complex system. In the CA method, A resist is represented by an array of discrete cells that reside in a crystalline lattice. Development of the resist is represented by removal and of individual cell according to development rules. During development, the decision to remove or retain a particular cell is based on the link status of its lattice neighbors according to cell-removal rules, The link status is categorized by number of neighboring cells and their relative positions. The modeling approach also uses Monte-Carlo simulation of electron scattering and energy dissipation and a simple development rate versus dose model for the resist. An absolute quantitative evaluation of the simulation accuracy is made based on resist exposure-development measurement and comparisons with SEM micrographs of experimental profiles of PMMA, SAL601 and ZEP520.The comparisons show good quantitative agreement and indicate the model based on CA can be used as a quantitative processing aid. Simulation results illustrate the importance of resist, beam and dose.

Ordered InAs quantum dots with controllable periods grown on stripe-patterned GaAs substrates

GaAs (001) substrates are patterned by electron beam lithography and wet chemical etching to control the nucleation of InAs quantum dots (QDs). InAs dots are grown on the stripe-patterned substrates by solid source molecular beam epitaxy, A thick buffer layer is deposited on the strip pattern before the deposition of InAs. To enhance the surface diffusion length of the In atoms, InAs is deposited with low growth rate and low As pressure. The AFM images show that distinct one-dimensionally ordered InAs QDs with homogeneous size distribution are created, and the QDs preferentially nucleate along the trench. With the increasing amount of deposited InAs and the spacing of the trenches, a number of QDs are formed beside the trenches. The distribution of additional QDs is long-range ordered, always along the trenchs rather than across the spacing regions.