P.K. Tan

Phase change random access memory cell with superlattice-like structure

A superlattice-like structure (SLL) incorporating two nonpromising phase change materials was applied to phase change random access memory (PCRAM) cell. A properly designed SLL structure could balance both the phase change speed and stability of a PCRAM. Moreover, SLL PCRAM cells exhibited lower programming current and fast working time of 5ns. The main reason for the excellent performances is due to the much lower thermal conductivity of the SLL material compared to that of bulk materials. The thermal conductivity of eight SLL layers cycle was found to be smaller than 30% of that of single layer material.

Nonvolatile phase change memory nanocell fabrication by femtosecond laser writing assisted with near-field optical microscopy

The phase change memory cells were developed by using a combination system of a femtosecond laser with near-field scanning optical microscopy. The memory cells with feature size varying from 800nm down to 90nm were achieved. The cell functional performances were tested, and the scalability of the programming current as a function of the memory cell features was investigated. The optical near-field distance which is one of the critical factors to achieve high resolution nanostructures was studied experimentally with the consideration of the whole fabrication process for functional devices. The Bethe-Bouwkamp model was employed to study the effects of the optical near-field distance to the nanostructure geometry. The programming current of 0.8mA was observed for the memory nanocell at a feature size of 90nm.

Super-resolution near-field optical disk with an additional localized surface plasmon coupling layer

A structure of super-resolution near-field phase-change optical disk with localized surface plasmon coupling effect is proposed. A localized surface plasmon coupling layer (LSPCL) was introduced to form a coupled localized surface plasmons (CLSP) with the mask layer. Recording marks as small as 31 and 36 nm were observed in two structures, which were both much smaller than the smallest mark of 56 nm observed from the conventional one without LSPCL. CLSP not only can reduce mark size but it can also improve carrier-to-noise ratio of recording marks. The thermal stability of the disk was also studied.

Superlattice-like structure for phase change optical recording

In order to increase the crystallization speed and data transfer rate (DTR), a superlattice-like structure (SLL) was applied to the recording layer of phase change optical disks. Unlike the conventional phase change layer, the recording layer with the SLL structure consisted of alternating thin layers of two different phase change materials, i.e., GeTe and Sb2Te3. Although neither GeTe nor Sb2Te3 could be used as a phase change layer material for practical applications, present experimental results revealed that the phase change optical disk with the SLL structure demonstrated an excellent recording property that could meet practical recording requirements. X-ray photoelectron spectroscopy was employed to confirm that the SLL structure could be preserved after many times of melting and quenching. Dynamic properties of the optical recording disk with the SLL structure were investigated with a 1 T pulse duration of 8 ns and a constant linear velocity of 19 m/s. A clear eye pattern was observed. The carrier-...

Investigations on nonvolatile and nonrotational phase change random access memory

In this work, phase change random access memory (PCRAM) was studied theoretically and experimentally. Phase change materials were deposited and their physical parameters were measured. A simulation and design software for PCRAM was developed based on multidisciplinary theories including electrodynamics, thermal conduction, crystallization kinetics and numerical computations. By introducing physical models of PCRAM elements, a general macromodel of the phase change random access memory (PCRAM) elements for HSPICE-based computer simulator is proposed. PCRAM array were designed, fabricated, and tested by using a self built tester. Also, near field optical scan microscope incorporated with fs laser was used to fabricate nano scale PCRAM cells

Thermal modelling and simulation of non-volatile and non-rotating phase change memory cell

A thermal analysis of chalcogenide random access memory (C-RAM) cell, a non-rotational nonvolatile phase change memory cell, was conducted. A three-dimensional finite-element method was used in the simulation of C-RAM cell. The thermal effect generated by applying an electric pulse was calculated and analyzed. The dependence of its thermal performances due to electrical and geometrical variations was also investigated. Temperature performances including temperature profiles and history, the heating and cooling rates, and heat flow characteristics were obtained and analyzed.

Method and physical mechanism of initialization-free phase-change optical recording

A new method of initialization-free phase-change (PC) optical recording was proposed based on the crystallization kinetics of PC media. It was suggested that two special additional layers could be added to the disk to form a new disk structure for the initialization-free function. The physical mechanism of initialization-free PC optical recording was discussed. A model was proposed to explain the initialization-free method which combined the surface crystallization induced by the additional layer and the temperature change during the sputtering process. The simulation results of the initialization-free disk showed only a slight influence of the initialization-free structure on the writing/erasing properties of the PC recording layer. Experimental results verified the feasibility of the initialization-free method for PC optical recording.

Study of geometric effect on phase change random access memory

In this paper, phase change random access memory (PCRAM) devices with two different geometric configurations were studied. The geometry effect on device functionalities in terms of thermal and electrical properties has been analyzed by simulation and experiments. Based on 0.35mum technology, 128 bits PCRAM array integrating with CMOS as the selection device were fabricated. The two types of PCRAM cells were implemented and characterized. The simulation results showed that both the bottom electrode and phase change layer geometry and the size of the interface between the phase change material and the bottom electrode were the determinant factors to the temperature profile and heat distribution. Both simulation and experimental results show that PCRAM device with type II structure required lower current to start phase change from crystalline state to amorphous state. However, it required a larger current to be fully RESET. A model was proposed in this paper to discuss this phenomenon

Surface roughening of recording media and readout performance of phase-change optical disk

Scaling characteristics of the surface roughening of the phase-change optical media have been investigated. Studies have shown that the variation-correlation function of the surface profile of recording media follows an asymptotic power law. The influence of the film surfaces with different roughness on the readout performance of the optical media has been investigated based on a scalar diffraction model. The results show that only one roughness parameter cannot reflect the responding readout properties of a phase-change optical disk such as signal noise and jitter due to the surface roughening. Fractal Brownian motion is applied to simulate the scaling characteristics of the surface roughening. Influence of the surface roughening with different Hurst exponents on the readout performance of the optical media has been studied. Results of the numerical calculation from both simulated and physical surfaces of the phase-change media show that the surface roughening with a lower Hurst exponent will cause a hig...

Multi-Speed Blu-ray Disc with Superlattice-like Structure

In this paper, the superlattice-like structure is proposed as a candidate for multi-speed blu-ray disc, the materials in superlattice-like recording layer are studied and the multi-speed recording properties of superlattice-like blu-ray discs are demonstrated