Study On Mechanism Of Ultra-High-Density Data Storage Based On AFM And Chalcogenide Phase-Change Materials

With the rocketing development of technologies of the Internet, multimedia video,high speed computer etc, people have been in urgent need of the more higher speed and density data storage. But traditional magnetic storage, optical storage and semiconductor storage have their own physical limitations because of the superparamagnetic effect, diffraction and minimum lithography element size, so it is very difficult to further improved the data storage density. The data storage with the aid of scanning probe microscopy (SPM) can record the nano scale information, so it is expected to be a next generation ultra-high-density storage technology. For the above-mentioned reasons, the dissertation introduced the GeSb2Te4 film into the SPM technology, which is a kind of chalcogenide materials widespread used in optical storage, and provided a novel method of ultra high density storage technology based on the effect of thermoelectricity, and described its mechanism in detail, the main work includes four aspects as follows:The dissertation analyzed the mechanism of phase change in chalcogenide materials and the principle of information storage using such materials, and established the basic scheme of SPM storage based on the phase change films and the atomic force microscopy(AFM) technology, and elaborated the writing, erasing and readout data process. As well as, a phase change storage device based on SPM is also established in the lab, which can be used to carry out some storage experiments.On this base, a direct and convenient method for preparing GeSb2Te4 film by the RF magnetron sputtering has been developed, simultaneously, the optimum producing process and parameters were explored through experimentation and comparison with surface topography of films. Then, X-ray diffraction(XRD), transmission electron microscopy(TEM) and inductive coupled plasma emission spectrometer(ICP) were carried out to analyze the composition, interior structures and state of the GeSb2Te4 films. The results indicated that the deposited GeSb2Te4 film was amorphous, but with the increment of annealing temperature, two-stage process of phase transition was discovered, the first stage was transformation between the amorphous phase and the crystalline phase with fcc structure, and the other is the fcc-hex phase transition. The Johnson-Mehl-Avrami-Kolmogorov(JMAK) kinetics was optimized combining classical nucleation theory. The incubation time and crystallite cluster size was predicted based correlation equation in order to know the GeSb2Te4 films were suitable for use the storage medium or not.Differential Scanning Calorimetry(DSC) was carried out to analyze the thermo-physical parameters and structure on different annealing temperatures and heating rate, and achieved the crystallization temperature and glass transition temperature of different heating rate. The resistivity of films after annealing treatment were measured by four--probe method, it is showed that the resistivity of as-deposited films was far larger than the fcc and hex crystal structure. Besides, the dissertation also studied comprehensive research on the?-?characteristics and the activation energy of films. Mechanical properties of GeSbTe films, including hardness, elastic modulus, adhesive and force friction, were investigated by TriboIndenter nanomechanical test system, and the effect of sputtering parameters, thickness, roughness and relative humidity on mechanical properties of films was taken into account simultaneously. Experimental results showed that quality of the surface of GeSb2Te4film will affect the hardness and elastic modulus. The effect on the adhesion and friction between the tip and GeSb2Te4 film increased with a rise of relative humidity. Moreover, the influence of sputtering power and annealing temperature on residual stress also were studied by ADC2000 stress test instrument.Based on the principle of the data storage using phase change medium and probe, this dissertation established the thermoelectricity coupled model and the memory structure model using for finite element analysis(FEA). The COMSOL Multiphysics, a multi-physical coupling field FEA software, was used to simulated the process of writing and erasing information. In order to conclude the appropriate voltage parameters, different amplitude and width pulse was applied to calculate the temperature field changes of phase change storage medium. Besides, the probe and conductive layer parameters, including electric conductivity, thermal conductivity, probe diameter and so on, influencing on the temperature field of films were evaluated too. All these provided the strong support for further improving the storage structure in subsequent research work. These results are expected to be useful for the design of ultra high-density data storage, and of significance for establishing a framework of theory of novel data storage technology.