J. M. Li

Agency for Science, Technology and Research (A*STAR), Tumasik, Singapore

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Publications (40)29.69 Total impact

  • J. M. Li, H. X. Yang, K. G. Lim
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    ABSTRACT: Exothermal resistance measurement reveals that the phase transition of Ge2Sb2Te5 phase change memory (PCM) can take place far below the traditional crystallization temperature. The activation energy of nucleation is no longer a constant and highly dependent on applied electric fields. The field-dependent activation energy becomes much lower with higher applied field. Further, the field-dependent activation energy can be described by an exponential function of the applied fields. These findings provide physical fundamentals for analysis of nucleation switching mechanism of PCM. A switching model has been developed and the simulated current-voltage curve is in good agreement with the experimental measurement.
    Applied Physics Letters 06/2012; 100(26). · 3.52 Impact Factor
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    ABSTRACT: Thin films properties of amorphous TbFeCo were studied to determine its suitability for use in all optical magnetic recording. Ellipsometric techniques have been used to determine the optical properties of the films in the wavelength range of 350 to 800 nm. The effects of film thickness, Ar flow rate and presence of Ag under layer on magnetic properties were also investigated.
    Proc SPIE 06/2010;
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    ABSTRACT: This work presents a thermal analysis that explains experimental observation in all-optical magnetic recording (AOMR). An integrated model is used to describe thermal processes at different time scales in AOMR. The formation of magnetic marks is discussed and implemented by developing a simulator based on 3-dimensional finite element method (FEM). The simulator is able to carry out thermal analysis of the thin film media and is a useful tool for design of AOMR media structure, especially for the thermal sink layer.
    Proc SPIE 01/2010;
  • K. Eason, G. Vienne, J. M. Li
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    ABSTRACT: In this work, effective magnetic fields relevant to all-optical magnetic recording (AOMR) are analyzed considering, specifically, optically-induced spin-orbit (OSO) coupling and the Inverse Faraday Effect. Computing these fields with reasonable estimations of the required parameters, it is shown that OSO fields developed in typical rare earth alloys have a distribution with exterior rings of maximum amplitude in the perpendicular component, in contrast to the IFE field which has its maximum in the center. These observations may correlate to experimental observations that have revealed exterior rings in the recorded spots during the AOMR process.
    Proc SPIE 01/2010;
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    ABSTRACT: A multi-layer lateral PCM with N-doped Sb70Te30 was proposed and demonstrated. Both current sweep and pulse mode dynamic resistance test show that multi states exist in the device, which can be used for multi-level data storage. Simulation shows the working mechanism of multi-level and confirms the experiment results. More intermediate states can be realized by increasing the cycles of N-doped Sb70Te30 and ZnSSi02 deposited and by using different film thickness, which will be a promising solution to increase the data storage capacity for PCM largely.
    01/2010;
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    ABSTRACT: Phase change RAM (PCRAM) is one of the best candidates for the next-generation nonvolatile memory. Recently lateral PCRAM using a thin phase change bridge was proposed as a promising approach to achieve high density due to simpler fabrication process and lower RESET current. This paper proposes a new lateral PCRAM structure - edge contact lateral structure, together with a Sb7Te3-GeTe super-lattice-like (SLL) phase change medium to reduce the contact area, improve thermal confinement and hence reduce current. Its RESET current of 1.23 mA is less than that of normal lateral PCRAM with SLL (1.5 mA). It also shows good stability and resistance ratio after 105 overwriting cycles. Testing results are consistent with the simulation results.
    01/2009;
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    ABSTRACT: Super-resolution near-field optical disk is one of the solutions to overcome diffraction limit and achieve high density optical recording. In this paper, a structure of super-resolution near-field phase-change optical disk with a thin thermal shield layer behind the recording layer is proposed. The optical disks with the new structure were studied theoretically and experimentally. Thermal simulation shows that the thermal shield layer can reduce the phase change layer temperature, thus improve the thermal stability of the disks. The disks with this structure were fabricated and characterized. The experiment results are in good agreement with the simulation results.
    Proc SPIE 07/2007;
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    ABSTRACT: Investigation focuses on the local strain-stress field in the laser-beam-spot region in super resolution near-field structure. The three-dimensional finite element method is used to analyze the elastic thermal expansion in the readout process. The temperature distribution around the laser beam in a large laser power margin has been studied, and it may be related to the second phase transition. The investigation has revealed that the center of the laser beam is always ahead of the centers of the peak-temperature, peak-stress, and peak-strain regions so that the stress and strain are very different around the center of the laser beam. This may lead to the change of the optical properties. The super-resolution mechanism caused by the local thermal expansion is discussed.
    Japanese Journal of Applied Physics 07/2007; 46(7A):4148-. · 1.07 Impact Factor
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    ABSTRACT: An integrated analysis tool of optical system and media which combines system with media analysis of the discs is developed in this project. This software has been used to study the influence of disc tilt, cover layer thickness and scratches on high density recording, which show that it provides a powerful tool in practical applications.
    Proc SPIE 07/2007;
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    ABSTRACT: Understanding of the phase change in nano-scale, or so-called nano-phase change, and its related issues are important for its applications on both optical recording and phase change random access memory (PCRAM). Nano-phase change can be classified into thickness-dependent and structure dependent types. For PCRAM device performance, the film thickness-dependent thermal profile and materials' properties are the two important factors. In this work, the thickness dependence of nano-phase change for chalcogenide materials was studied by both simulation and experiments. A thermal model was built up to simulate the film thickness-dependent thermal profiles and its corresponding effects of line type PCRAM. The simulation results showed that the temperature profile, heating rate and cooling rate are strongly dependent on the thickness of phase change materials. Experiments had been conducted to investigate the thickness dependence of crystallization temperature for both nucleation-dominated and growth-dominated phase change material. It was found that the crystallization temperatures are function of the thickness for the both materials. Higher crystallization temperatures were obtained for thinner phase change films. The influence of above factors on the performance of PCRAM devices is discussed.
    Non-Volatile Memory Technology Symposium, 2006. NVMTS 2006. 7th Annual; 12/2006
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    ABSTRACT: An integrated software for analysis and design of PCRAM cells has been developed. The research focuses on the discussion on electric-thermal-mechanical analyses. The software involves in the materials, geometrical and layer structure design and electric pulse strategy. It aims to provide a powerful tool for structure optimization and failure analysis of PCRAM cells.
    Non-Volatile Memory Technology Symposium, 2006. NVMTS 2006. 7th Annual; 12/2006
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    ABSTRACT: 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 5 ns. 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.
    Applied Physics Letters 03/2006; 88(12):122114-122114-3. · 3.52 Impact Factor
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    ABSTRACT: Not Available
    Optical Data Storage Topical Meeting, 2006; 02/2006
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    ABSTRACT: Not Available
    Optical Data Storage Topical Meeting, 2006; 02/2006
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    ABSTRACT: The laser-beam spot size and track pitch of phase change optical disks are continuously decreasing. Hence any slight deformation in the disk will affect data storage performance efficiency. Thus said thermal deformation at high temperatures induced by laser irradiation becomes an important issue in optical disks. Thermal elastic deformation in blue-laser optical disks has been calculated by the finite element method (FEM). The associations of thermal deformation with disk structures and laser power have been investigated to supply methods to decrease thermal deformation. It was found that the peak temperature and peak deformation lies in different layers. Several methods of preventing deformation in blue-laser optical disks have been proposed. It was found that these methods can be used to optimize the structures of high density phase change optical disks.
    Japanese Journal of Applied Physics 01/2006; 45. · 1.07 Impact Factor
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    ABSTRACT: In this study, we focus on near-field characteristics and surface plasmon (SP) induced by uniform- and nonuniform-size Ag nanoparticles in the mask layers of super-resolution near-field structure (super-RENS). The finite-difference time-domain (FDTD) method is used to analyze scattering fields from the localized SPs of Ag nanoparticles. It has been found that the spatial extension of the evanescent field is very short along the thickness direction of the mask layers, and the three-dimensional coupling patterns of the evanescent fields from the nonuniform-size particles are the most irregular. The signal enhancement mechanism of a super-RENS disk is discussed.
    Japanese Journal of Applied Physics 01/2006; 45. · 1.07 Impact Factor
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    ABSTRACT: The mechanism of the aperture-type Blu-ray super-resolution near-field phase-change disk with a mask layer of Sb2Te3 was studied theoretically and experimentally. The thermal stability problem has been solved by developing a new thermal shield layer.
    Japanese Journal of Applied Physics 01/2006; 45:1385-1389. · 1.07 Impact Factor
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    ABSTRACT: The temperature dependences of phase-change random access memory (PCRAM) cells on different Ge-Sb-Te phase-change recording materials are studied and compared. A Ge2Sb2Te5 phase-change film has a larger resistance margin and a higher thermal stability than Ge1Sb2Te4 and Ge1Sb4Te7 films. The set resistance, reset resistance, resistance margin and threshold voltage of PCRAM cells decrease with increasing temperature. A Ge2Sb2Te5 PCRAM cell has a higher thermal stability of threshold voltage than Ge1Sb2Te4 and Ge1Sb4Te7 PCRAM cells.
    Japanese Journal of Applied Physics 01/2006; 45:3955-3958. · 1.07 Impact Factor
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    ABSTRACT: An initialization-free Blu-ray disc was proposed as a candidate for multispeed blue laser recording and successfully fabricated. Experiment results of the initialization-free Blu-ray disc showed that it had a multispeed blue laser recording capability with speeds of 1 to 3×. The crystallization acceleration effect caused by additional layers and the rapid cooling caused by the initialization-free disc structure were suggested as the physical mechanism of multispeed recording in an initialization-free Blu-ray disc.
    Japanese Journal of Applied Physics 01/2006; 45. · 1.07 Impact Factor
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    ABSTRACT: 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
    Non-Volatile Memory Technology Symposium, 2005; 12/2005