介质表面形貌对射频微机械开关隔离度的影响

针对粗糙介质表面造成射频微机械(RF M EM S)开关隔离度衰减的问题,设计了一个双桥电容式RF M EM S开关,分别采用金属A u和A l作为开关的下电极,以S iN作为电容介质制备了样品。微波特性测量表明两种材料开关的隔离度有很大区别。利用原子力显微镜对金属A u和A l上制作的S iN介质层表面进行了测试,表面粗糙度R a值分别为13.050 nm和66.680 nm,分析得到相应的关态电容减少因子分别为0.52和0.15。为获得较好的开关隔离度,介质表面粗糙度须控制在5 nm以下。

Effect of dielectric layer surface roughness on the isolation of an RF MEMS switch

The paper presents study on the surface roughness of the dielectric layer on electrodes and its effect on the isolation of the radio-frequency micoelectromechanical(RF MEMS) switches.The study is based on a double-bridge capacitive RF MEMS switch.In this switch,SiN is used as the dielectric layer with the lower electrode fabricated with gold or aluminum.The RF network measurements show that the isolation performance of the two switches is very different.The surface roughness Ra of the SiN dielectric layer on the different metallic electrodes measured with an atomic force microscope was 13.050 nm for SiN/Au and 66.680 nm for SiN/Al.The corresponding degradation factors of the off-state capacitance for the two electrodes were 0.52 and 0.15.A roughness of less than 5 nm is needed to obtain good isolation performance.