电容式RF MEMS开关在控制高功率射频信号时会发生自锁失效,由于开关桥膜与介电层之间的粗糙接触,开关的down态电容会发生退化,因此很难建立开关自锁失效阈值功率的高保真预测模型。提出了3D电磁-等效电路仿真对比建模的方法。建立开关的3D电磁仿真模型,仿真得到具有任一表面粗糙度水平的介电层粗糙开关的隔离度(S21)曲线;再建立同一开关的等效电路模型,通过调谐其down态电容值,使得仿真得到的S21曲线与3D电磁模型仿真结果尽可能吻合;此时,可以确定一组根据开关3D电磁仿真模型设定的表面粗糙度水平与等效电路模型调谐好的down态电容值的关系;改变开关介电层的表面粗糙度水平,并重复上述步骤,确定了任一开关的介电层表面粗糙度与开关down态电容退化的关系。采用文献的down态电容实测数据,初步验证了该方法的可行性和合理性。并利用所得的开关down态电容随介电层表面粗糙度退化的特性,对简化的(介电层光滑)开关自锁失效阈值功率解析计算式进行了修订,可扩展用于预测介电层粗糙开关的功率容量。

Capacitive RF MEMS switch will latch at high power RF signal handling situations. Due to the roughly contact between the switch membrane and the dielectric layer, the down-state capacitance of the switch degrades. The high-fidelity analytical computation model of the latching failure threshold power for a capacitive RF MEMS switch is very hard to establish. The comparative modelling method between a 3D electromagnetic simulation and an equivalent circuit simulation is proposed. First of all, the 3D electromagnetic simulation model is established. The simulation curve of the switch isolation(S21)is got at different surface roughness. And then the equivalent circuit model of the same switch is established. The simulation curve of the S21 of the switch equivalent circuit and the simulation result of the 3D electromagnetic are matched by tuning the down-state capacitance in the equivalent circuit. The set of function relationship between the surface roughness of dielectric layer and the down-state capacitance is identified. And the function relationships between the surface roughness of dielectric layer and the degradation of down-state capacitance are identified by changing the surface roughness level of dielectric layer and repeating the above steps. The rationality of the method is verified by comparing the calculated values of the down-state capacitance with the measured values in related literature. The analytical formula of latching failure threshold power of the switch with smooth dielectric layer is revised using the function relationships between the surface roughness of dielectric layer and the degradation of down-state capacitance to predict the power handling capacity of the switch with rough dielectric layer.