Surface-acoustic wave (SAW) filters operating at frequency in the 1 to 3 GHz-range have been widely used in the applications of mobile, wireless, cable modem, cellular phone and remote control. Current lithography techniques are feasible for SAW device fabrication, such as I-line (365nm) UV photolithography, imprint lithography, conformal contact photolithography and near field phase shift photolithography (NFPSL). In common production, the narrowest line width must be around 0.3 mm with the I-line UV photolithography typically used in the industry; this corresponds to a quarter-wavelength, giving a maximum frequency of typically 3 GHz. Therefore, lithography with the ability of high-volume-production over large area for producing high frequency (i.e. 1~3 GHz), low-cost SAW devices is anticipated. The operating frequency is limited by fabrication techniques. In order to operate at high frequency, SAW filters can be efficiently excited at higher harmonics of their fundamental frequency. And in NFPSL, a transparent mask induces abrupt changes of the phase of the light used for exposure, and causes optical attenuation, which is owing to destructive optical interference at the edges of circuit features, at those locations. NFPSL is a low-cost, high-throughput production over large areas method for nano-structure pattern transfer and can be used to fabricate nano-structure pattern by using a mask with micro line width pattern. To meet the demands have low-cost and high-volume-production over large area, near field phase shift photolithography may be a better solution than other lithography.
In this study, we demonstrate the high frequency (i.e. 1~3 GHz) and low-cost SAW devices that are fabricated by using the near field phase shift photolithography, as the line widths of NFPSL finger pattern are 10 and 5 um. The mask, which is duplicated from the special design mold with 10 and 5 um line width finger patterns, of the near field phase shift optical lithography has a potential use in SAW devices operating over the gigahertz range.