Physical Review B

International Technology Roadmap for Semiconductors 2003の要求清浄度について － シリコンウエハ表面と雰囲気環境に要求される清浄度, 分析方法の現状について －

Materials whose optical properties can be reconfigured are crucial for photonic applications such as optical memories. Phase-change materials offer such utility and here recent progress is reviewed. Phase-change materials (PCMs) provide a unique combination of properties. On transformation from the amorphous to crystalline state, their optical properties change drastically. Short optical or electrical pulses can be utilized to switch between these states, making PCMs attractive for photonic applications. We review recent developments in PCMs and evaluate the potential for all-photonic memories. Towards this goal, the progress and existing challenges to realize waveguides with stepwise adjustable transmission are presented. Colour-rendering and nanopixel displays form another interesting application. Finally, nanophotonic applications based on plasmonic nanostructures are introduced. They provide reconfigurable, non-volatile functionality enabling manipulation and control of light. Requirements and perspectives to successfully implement PCMs in emerging areas of photonics are discussed.

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Phase-change materials for non-volatile photonic applications

IEEE transactions on computer-aided design of integrated circuits and systems : a publication of the IEEE Circuits and Systems Society

The phase-shifting mask consists of a normal transmission mask that has been coated with a transparent layer patterned to ensure that the optical phases of nearest apertures are opposite. Destructive interference between waves from adjacent apertures cancels some diffraction effects and increases the spatial resolution with which such patterns can be projected. A simple theory predicts a near doubling of resolution for illumination with partial incoherence σ < 0.3, and substantial improvements in resolution for σ < 0.7. Initial results obtained with a phase-shifting mask patterned with typical device structures by electron-beam lithography and exposed using a Mann 4800 10× tool reveals a 40-percent increase in usuable resolution with some structures printed at a resolution of 1000 lines/mm. Phase-shifting mask structures can be used to facilitate proximity printing with larger gaps between mask and wafer. Theory indicates that the increase in resolution is accompanied by a minimal decrease in depth of focus. Thus the phase-shifting mask may be the most desirable device for enhancing optical lithography resolution in the VLSI/VHSIC era.

Improving resolution in photolithography with a phase-shifting mask

A wideband noise-cancelling low-noise amplifier (LNA) without the use of inductors is designed for low-voltage and low-power applications. Based on the common-gate-common-source (CG-CS) topology, a new approach employing local negative feedback is introduced between the parallel CG and CS stages. The moderate gain at the source of the cascode transistor in the CS stage is utilized to boost the transconductance of the CG transistor. This leads to an LNA with higher gain and lower noise figure (NF) compared with the conventional CG-CS LNA, particularly under low power and voltage constraints. By adjusting the local open-loop gain, the NF can be optimized by distributing the power consumption among transistors and resistors based on their contribution to the NF. The optimal value of the local open-loop gain can be obtained by taking into account the effect of phase shift at high frequency. The linearity is improved by employing two types of distortion-cancelling techniques. Fabricated in a 0.13-μm RF CMOS process, the LNA achieves a voltage gain of 19 dB and an NF of 2.8-3.4 dB over a 3-dB bandwidth of 0.2-3.8 GHz. It consumes 5.7 mA from a 1-V supply and occupies an active area of only 0.025 mm2.

A Wideband Inductorless LNA With Local Feedback and Noise Cancelling for Low-Power Low-Voltage Applications

Three-dimensional (3D) integration and multi-level cell (MLC) are two attractive technologies to achieve ultra-high density for mass storage applications. In this work, a three-layer 3D vertical AlOδ/Ta2O5-x/TaOy resistive random access memories were fabricated and characterized. The vertical cells in three layers show good uniformity and high performance (e.g. >1000X HRS/LRS windows, >1010 endurance cycles, >104 s retention times at 125°C). Meanwhile, four level MLC is demonstrated with two operation strategies, current controlled scheme (CCS) and voltage controlled scheme (VCS). The switching mechanism of 3D vertical RRAM cells is studied based on temperature-dependent transport characteristics. Furthermore, the applicability of CCS and VCS in 3D vertical RRAM array is compared using resistor network circuit simulation.

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Study of Multi-level Characteristics for 3D Vertical Resistive Switching Memory

In this letter, the conduction and switching mechanisms of Al/AlOx/WOx/W bilayer resistive random access memory devices are investigated. Five stable resistance states were achieved through current compliance control. For each resistance state, I-V characteristics at different temperatures were measured. Conduction mechanisms are found to vary with resistance states. At low resistance levels, devices show ohmic conduction with metallic behavior. Conduction at medium resistance levels is due to electron hopping. The carrier transport at high resistance levels is governed by Schottky emission. Based on the resistance-dependent transport characteristics, an oxygen migration model is proposed to explain the switching mechanism between different resistance states.

Study of conduction and switching mechanisms in Al/AlOx/WOx/W resistive switching memory for multilevel applications

In this Letter, a comprehensive analysis of how the metallic behavior transition to hopping was presented by studying the transport mechanisms of low resistance states (LRS) in Ta2O5−x/TaOy resistive switching devices at very low temperatures. Three types of conduction behaviors were reported through temperature-dependent measurements ranging from 5 K to 250 K. Memory cells at low LRS show metallic behavior due to the formation of metallic filament. The temperature dependence of resistance at medium LRS exhibits an interesting phenomenon that a positive temperature coefficient transfers into a negative one at temperature of 20 K. Detailed analysis reveals that this phenomenon is caused by the coexistence of extended and localized states, with metallic conduction at higher temperatures and variable-range hopping at lower temperatures. Carrier transport at high LRS is dominated by electrons hopping conduction with nearest-neighboring hopping conduction changing into variable-range hopping as temperature dec...

Metallic to hopping conduction transition in Ta2O5−x/TaOy resistive switching device

A scalable industry-oriented, 24-element "2-/spl pi/" compact circuit model for on-chip RF CMOS spiral inductors is presented. It has a good accuracy up to self-resonant frequency (SRF). Two levels of modeling approaches are provided, which are: 1) the fixed model, which extracts the values of circuit elements directly from the measured S-parameters of a given device, achieving high accuracy, but no scalability and 2) the scalable model, in which circuit elements are related to the geometry (i.e., layout) through a set of formulas with model parameters calibrated upon a few testing devices. The synthesis procedure is also discussed, which includes the scalable model and a SPICE simulator as the evaluation method within the iteration loop.

Zhiping Yu

Papers

A Wideband Inductorless LNA With Local Feedback and Noise Cancelling for Low-Power Low-Voltage Applications

Study of Multi-level Characteristics for 3D Vertical Resistive Switching Memory

Study of conduction and switching mechanisms in Al/AlOx/WOx/W resistive switching memory for multilevel applications

Metallic to hopping conduction transition in Ta2O5−x/TaOy resistive switching device

Scalable compact circuit model and synthesis for RF CMOS spiral inductors