Researches On Key Technologies Of SPM-based Ultra-High-Density Data Storage

Traditional magnetic storage, optical storage and semiconductor storage have their own physical limitations because of the superparamagnetic effect, diffraction and minimum lithography element size. Scanning probe microscopy (SPM) based data storage technology is an ideal high-density data storage technology, which can break through the physical limitations of the traditional storage technology. But low data rate and short probe lifetime are the problems faced nowadays. This dissertation applies piezoelectric material, lead zirconate titanate (PZT), into SPM technology, brings up the novel "thermo-piezoelectric-mechanical" method for data storage and describes its mechanism in detail.Piezoelectric cantilevers array is the key part in the storage system for "thermo-piezoelectric-mechanical" storage. In this dissertation, a novel piezoelectric cantilever probe with low stiffness and high resonance frequency was structural designed by decreasing its geometric dimensions. A multi-layered cantilever with non-rectangle and unequal sections is abstracted as the mechanics model of the probe. By theoretical analysis, the spring constant and the resonance frequency of the cantilever probe was calculated as 4 N/m and 245 kHz respectively. The microheater integrated on the free end of the cantilever is the main object of thermal analysis. The results show that heat dissipation is mainly by conduction along the cantilever body to the substrate, partly by conduction into air, while convection and radiation could be neglected.Data writing process is the interaction between tip and storage medium. Based on the material properties of polymethyl methacrylate (PMMA) and data writing mechanism, a six-stepped model was set up to describe the whole data writing process. This model includes mechanical contact analysis, thermal conduction analysis, viscoelasticity analysis and tracing of moving interface integrated with volume of fluid analysis. The result of numerical simulation for the single data pit writing process shows that under the thermal and mechanical loading, a 50nm depth center-depressed and more than 10nm peripheral-heaved data pit was formed. The pilling up around the pit is caused by extruding fluid status media instead of thermal expanding.The research of data reading out is concentrated on the piezoelectric charge sensitivity. The charge sensitivity could be better through the following ways: increasing the thickness of the elastic layer of the cantilever, peeling off part of passivation layer and applying DC bias to PZT. The probe structure and data reading out process were also optimized.Some experimental researches were executed on the fabrication and preparation for the key structures and main materials involved in the storage system. Anisotropic wet etching was used to fabricate single-crystalline silicon tip, which has an aspect ratio of 1.56 and curvature radius of less than 50nm. Spin coating was used to prepare 200nm-thick PMMA thin film, which roughness is less than 2nm of Ra value. Plasma enhanced chemical vapor deposition (PECVD) was used to prepare low-stressed silicon nitride thin films and amorphous silicon thin films.All above research results show that besides high storage density, "thermo-piezoelectric-mechanical" storage has higher data access rate, longer probe lifetime and lower power consumption. This storage method could resolve the problems of low data rate and short probe lifetime and promote the utilization of ultra-high-density data storage technology.