New release technique of a thick sacrificial layer and residue effects on novel half-coaxial transmission line filters

This paper presents a new release technique for efficient and complete removal of the thick sacrificial layer applicable to surface-micromachined devices and compares this with other conventional release methods. A fully surface-micromachined half-coaxial transmission line filter having a large air-filled gap of 100 µm in thickness is successfully demonstrated using the proposed release technique. The effects of the sacrificial layer residue on the RF responses of the filters, completed by a conventional oxygen plasma ashing process, are analyzed with the aid of x-ray photoelectron spectroscopy (XPS). Experiments show that the proposed new release technique makes it possible to completely remove the thick sacrificial layer, shorten the process time, increase the after-fabrication yield and improve the process reproducibility of the large air-filled gap filters compared to the conventional oxygen plasma ashing method.