The electrical switching behavior of GeTe-based phase change memory devices is characterized by time resolved experiments. SET pulses with a duration of less than 16 ns are shown to crystallize the material. Depending on the resistance of the RESET state, the minimum SET pulse duration can even be reduced down to 1 ns. This finding is attributed to the increasing impact of crystal growth upon decreasing switchable volume. Using GeTe or materials with similar crystal growth velocities, hence promises nonvolatile phase change memories with dynamic random access memorylike switching speeds.

We discuss novel multi-level write algorithms for phase change memory which produce highly optimized resistance distributions in a minimum number of program cycles. Using a novel integration scheme, a test array at 4bits/cell and a 32kb memory page at 2bits/cell are experimentally demonstrated. Introduction Phase change memory (PCM) is widely considered to be a potential next-generation non-volatile solid-state memory [1-3]. In addition to its superior write speed compared to 0.2pm -flash, PCM offers a large signal margin between its -crystalline and amorphous states. This wide dynamic range Fig. 2: TEM image of phase-change element (PCE), with underlying also opens the door for multi-level cells (MLC). In this paper, TiN heater on top of W contact. The phase-change material and the we explore MLC write algorithms for up to 16 levels in small o T test arrays, and then demonstrate a 4-level, 32kbit page being overln Tiner are coNnected ubinEs thr a via.part of an experimental memory chip. transferred into the TiN layer using RIB. After strip, oxide isolation is deposited and planarized, exposing the top of the Integration Scheme pillar electrode. The Ge2Sb2Te5 and TiN top electrode layers The memory cell consists of a pillar-heater phase change are then deposited, patterned into islands and encapsulated element (PCE) in series with an access nMOSFET (180nm with dielectric. Top contacts and metallization lines are CMOS technology). As shown in Fig. 1, the 50nm bottom formed using a standard Cu damascene process. Fig. 2 shows electrode heater is fabricated in a subtractive process from a a TEM cross-section of the finished pillar-heater PCE. 75nm thick TiN layer directly deposited over the W contacts.

An ultra-thin phase-change bridge (PCB) memory cell, implemented with doped GeSb, is shown with <100µA RESET current. The device concept provides for simplified scaling to small crosssectional area (60nm 2 ) through ultra-thin (3nm) films; the doped GeSb phase-change material offers the potential for both fast crystallization and good data retention.

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We have studied the coupling of a classic ridge waveguide with a two-dimensional photonic crystal (PC) waveguide, using finite-difference time-domain calculations. The ridge waveguide exhibits only a weak refractive-index confinement of light, as it is commonly used in buried-heterostructure or ridge-waveguide lasers. The light is coupled to a PC waveguide that consists of one missing row along the ?K direction in a triangular lattice of air cylinders in AlGaAs. We compare various designs for PC tapers with that of a classic taper and for butt coupling. The calculation yields high coupling efficiency that exceeds 80% for a 2.5-microm-long PC taper. In addition, the dependence of the efficiency on the PC air-fill factor and on alignment tolerances is analyzed.

We propose carbon as new resistive memory material for non-volatile memories and compare three allotropes of carbon, namely carbon nanotubes, graphene-like conductive carbon and insulating carbon for their possible application as resistance-change material in high density non-volatile memories. Repetitive high-speed switching and the potential for multi-level programming have been successfully demonstrated.

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We demonstrate a two-dimensional photonic crystal defect laser diode based on a coupled cavity waveguide. The laser cavity is formed by 40 coupled hexagonal defect microcavities in a triangular lattice of air cylinders, which are etched into an InGaAsP/InP laser structure. The coupling of the individual cavity modes creates minibands within the photonic band gap. Stable single-mode lasing occurs on the first miniband mode with the lowest group velocity with side mode suppression greater than 40 dB. The lasers emit up to 2.6 mW at a 1.53 μm wavelength under continuous-wave operation at room temperature.