Application of an alternating phase-shifting mask design method to near-field photolithography for fabricating more than 2 GHz SAW devices

We use an alternating phase-shifting mask design method (APSMDM) to design and fabricate a specially designed surface acoustic wave (SAW) filter mold that has a linewidth pattern of only 5 mum (not small). A basic SAW filter mold [having a general interdigital transducer (IDT) pattern] also is fabricated for comparison. A near-field phase shift lithographic (NFPSL) process is applied in the fabrication of the narrow gap SAW devices, during which process the narrow gaps and short optical distance (SOD) electrodes are derived. We note that, in this way, important features (such as floating electrodes, high-metallization ratio, and a narrow gap structure) for enhancing the performance of high-efficiency SAW devices can be produced simultaneously. In addition, the other half of the special IDT pattern strips can be derived by using this APSMDM. This causes a decrease in the periodicity of the IDT pattern and, therefore, a decrease in the acoustic wavelength, in turn leading to an increase in the Deltaf (Deltaf is the difference in frequency between the harmonic and its adjacent harmonic) and a decrease in the insertion loss. A 2.75 GHz SAW filter is fabricated using the APSMDM with a mold with only 5-mum wide linewidth fingers.