Development of RF-MEMS switch on PCB substrates with polyimide planarization

This paper describes an improved manufacturing technology for the fabrication of radio frequency (RF) microelectromechanical systems switches on a laminated printed circuit board (PCB). The process simplifies the fabrication process without sacrificing the RF performance of switches on the PCB. The proposed process patterns a 17.5-μm-thick copper layer on the PCB; as a result, the surface becomes highly nonplanarized. Polyimide is then used to planarize the PCB's patterned copper layer. The use of polyimide for planarization has not only made the fabrication process simpler, but it has also reduced the formation of voids in the photoresist sacrificial layer where metallic membrane is deposited and patterned. The switches fabricated with this technology demonstrate a low insertion loss (less than 0.06 dB at 10 GHz) and good isolation (less than 20 dB at 10 GHz).