Study On Laser Direct Writing Technique Based On Preparation Of Surface Acousticwave Device

Surface acoustic wave(SAW) is a kind of elastic wave which is generated on the surface of piezoelectric materials along which it spreads. SAW is used on a large scale in the areas of electronic information transmission, surface-testing, Chemistry and Biology. So far SAW research about use of the SAW in lab-on-a-chip has been focused during recent years. LiNb O3(LN) is one of the most useful piezoelectric materials for its great electromechanical coupling coefficient and temperature coefficient both of which are key factors in the generation of SAW. SAW is generated by an array of interdigital transducers(IDTs) which are made on the surface of the piezoelectric materials. When encountering solid, some SAW was leaked in the solid with energy left behind, so IDT is a core component of SAW Driver.In this paper, fabrication processes for SAW Driver using laser direct writing technique are researched in details. We study some important factors including piezoelectric wafer, photoresist parameters, light intensity, 405 laser photolithography speed and electrode fabrication technique, and finally get optimum parameters to realize fabrication of IDT on the surface of the YZ-LN which can excite SAW. The frequency range is from 10 MHz to 50 MHz.At first, an automatic Laser Direct Writing lithography platform set-up is designed and developed. Visual program of the device is designed and written using Visual Basic which controls lithography speed and lithography motion paths to realize automatic laser direct photolithographic writing technique. Then we study several series of parameters during fabrication processes and get optimum ones. The spinning speed of the positive photoresist is from 1500 r/min to 3000 r/min; the drying temperature is 75 ℃; drying time is 25min; the speed of photolithography is from 400 to 800p/s;the light intensity is from 5 to 40 μm; defocused angle is from 15° to 120°;the developing time is from 15 s to 120 s and so on. At last we achieve a series of parameters to fabricate photolithography line from 5 μm to 70 μm of IDT array.In this paper, a novel method to get ladder groove is studied by photolithographing inverted photoresist-LN. An array of IDT-shaped grooves are etched on positive photoresist using laser direct writing photolithographic technique. Then metal film is deposited in grooves using vacuum evaporation technique, vacuum magnetron sputtering technique and vacuum ion sputtering technique, and the methods are compared. And we get IDT on the surface of the YZ-LN by lifting-off the positive photoresist. Finally the IDT impedance matching is realized in our circuits.