The fabrication and rapid replication of WR-10 filter with NOA73 materials

Radio frequency filters are important components in wireless communication systems. To realize the economic and rapid mass production of miniature filters, this paper proposed to precisely replicate filters by combining the multi-alignment exposure of photoresist to ultraviolet (UV) light and the UV curing technology for Norland optical adhensive73 (NOA73). Firstly, the master molds of the filter were prepared on the silicon substrate through multi-alignment exposure. Then, the fabricated master molds were replicated using polydimethylsiloxane (PDMS), thus obtaining several identical negative molds. Afterwards, by pouring NOA73 solution in the PDMS negative molds for the second replication, NOA73 filters with millimeter wave cavities were obtained. Finally, the structure size and performance (e.g. center frequency, bandwidth, insertion loss and return loss) of the replicated NOA73 filter were measured and tested. The results obtained using an electron microscope showed that the sidewall steepness of the NOA73 filter produced using this method was almost 90°, and the structure size was basically consistent with that of the master mold. After device packaging, the electromagnetic performance was proven to be favorable and the filter showed a slight frequency shift compared with the original filter. As this method shows good feasibility and can be used to easily and quickly prepare devices with low cost, it is suitable for the rapid preparation and mass production of microstructures.