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微机电系统和集成电路中常用的热氧化SiO2是各向同性材料,研究了其在单轴应力场中介电常数的变化规律。依据介质在自由和束缚两种边界条件下受到单轴应力作用产生的应变不同,从电动力学基本关系出发推导了各向同性电介质两种边界下的介电电致伸缩系数计算公式,表明介电电致伸缩系数是与电介质的初始介电常数、杨氏模量和泊松比有关的常数。计算得到热氧化SiO2薄膜在自由和束缚条件下的介电电致伸缩系数M12分别为-0.143×10-21和-0.269×10-21 m2/V2。搭建了基于三维微动台的微位移加载系统,测量了在单轴应力下微悬臂梁SiO2薄膜电容的变化,测量得到热氧化SiO2薄膜的M12为(-0.19±0.01)×10-21 m2/V2,表明实际SiO2薄膜介质层的边界条件处于自由和束缚之间。
The thermal oxidation of SiO2, which is commonly used in MEMS and integrated circuits, is an isotropic material. The variation of dielectric constant in uniaxial stress field is studied. According to the difference of the strain caused by the uniaxial stress of the medium under both the free and bound boundary conditions, the formula of the dielectric electrostrictive coefficient under two kinds of isotropic dielectric boundaries is deduced from the basic electrokinetic relationship, which shows that the dielectric The electrostrictive coefficient is a constant related to the initial dielectric constant, Young’s modulus and Poisson’s ratio of the dielectric. The calculated dielectric electrostrictive coefficient M12 of the thermally-oxidized SiO2 film under free and restrained conditions is -0.143 × 10-21 and -0.269 × 10-21 m2 / V2, respectively. The micro-displacement loading system based on three-dimensional micro-motion stage was set up to measure the capacitance of SiO2 thin film under uniaxial stress. The measured M12 of thermal oxidation SiO2 film was (-0.19 ± 0.01) × 10-21 m2 / V2, indicating that the boundary conditions of the actual SiO2 thin film dielectric layer are between free and bound.