【作者】 李丽；

【导师】 赵正平； 杨瑞霞；

【作者基本信息】 河北工业大学 ， 微电子学与固体电子学， 2006， 博士

【摘要】 近年来，随着无线通信系统的飞速发展，对低相位噪声压控振荡器(VCO)的需求也同益增加。VCO的调谐能力通常由可变电容来实现，要获得低相位噪声，需要高Q值的片上可变电容。然而，利用标准的集成电路工艺实现高Q值的片上可变电容是非常困难的。因此，现在的VCO器件通常采用片外分立的PN结变容二极管，这样不仅增加了系统的面积，而且存在封装复杂、功耗高以及成本高等缺点。因此，迫切需要能与VCO电路单片集成的高Q值的可变电容。 本论文采用全波电磁场仿真软件对凹型结构RF MEMS可变电容的结构参数进行了优化，优化目标为可变电容在2GHz时Q值最高。并对寄生电容量进行了讨论，在此基础上，得出了可变电容的单端口等效电路模型。根据优化后的结构，采用有限元分析软件得到了吸合电压及一阶谐振频率。 对平行板结构RF MEMS可变电容的运动过程进行了非线性分析。采用迭代方法对其动力学方程进行了求解，建立了动力学模型。并对空气压膜阻尼以及外加电压对运动的影响进行了详细讨论。首次发现了在RF MEMS可变电容存在的双稳态现象，并对此现象出现的原因进行了说明。把双稳态的特性应用于研究可变电容的调节范围，在理论上预言了调节范围大于50％的状态是存在的。 在RF MEMS开关加工工艺基础上，提出了适合凹型结构RF MEMS可变电容的表面微机械工艺流程，并进行了流片验证，其Q值为目前国内报道的最高数值，并且制造工艺与标准的集成电路工艺兼容，易于实现片上集成。 对振荡器中的两种相位噪声模型：线性时不变模型和线性时变模型进行了系统分析和概括。并对RF MEMS可变电容引起的机械热噪声进行了讨论，提出了以可变电容响应时间最短作为标准，优化阻尼孔数目，降低相位噪声的方法。对MEMS VCO电路的相位噪声进行了讨论，得出了与文献一致的结论，即当频偏位于可变电容的机械谐振频率近端时，电路中起主要作用的相位噪声是RF MEMS可变电容的机械热噪声，而频偏较大时，起主要作用的是电热噪声。 将凹型结构的RF MEMS可变电容与微波薄膜混合集成电路工艺制造的电路键合在一起，制备了国内第一个微波MEMS VCO器件。其单边带相位噪声性能优于90年代末国外同频率器件。谐波抑制以及杂波抑制性能优于采用变容管的VCO器件。更多还原

【Abstract】 In recent years, increased demand for wireless communication systems motivates a growing interest in low phase noise voltage controlled oscillator (VCO). The tunability of VCO is normally provided by a variable capacitor. Achieving low phase noise requires a high-Q on-chip variable capacitor. However, it is very difficult to realize a high-Q on-chip variable capacitor by standard integrated circuit (IC) process. Hence, current VCO is often implemented by an external PN junction varactor. The off-chip device not only increases final system area, but also increases package complexity, power consumption and cost. Therefore, a high-Q on-chip variable capacitor is needed stringently which can be integrated monolithically with VCO circuit.The quality factor of concave shape RF MEMS variable capacitor is optimized by full-wave electromagnetic field simulation software, and the goal of optimization is to receive the highest quality factor at the frequency of 2GHz. The parasitic capacitance is also discussed. One-port lumped parameters equivalent circuit model is then found based on above analysis. According to the optimized structure, we have calculated pull-in voltage and the first-order resonant frequency.The nonlinear analysis is conducted for parallel-plate variable capacitor. The second-order dynamic equation is solved by iterative method, then the dynamic model is built. We have discussed detailedly the effect of air squeeze film damping and direct current (DC) bias on the motion of suspended plate. The bistable state phenomenon which exists in variable capacitor is discovered for the first time, furthermore, the reason for this phenomenon is also explained. At last, the characteristic of bistable state is applied to investigate the tuning range of variable capacitor, and we draw a conclusion that the tuning range may be larger than 50% theoretically.Based on existing process of RF MEMS switch, the surface micromachining process is proposed which is the same with concave shape variable capacitor, and RF MEMS variable capacitor samples are successfully made out. The test results show that quality factor is the更多还原