Growth of 4-inch diameter Li/sub 2/B/sub 4/O/sub 7/ single crystals for SAW devices

Abstract

We report crystal growth of 4-inch diameter and 8-inch long lithium tetraborate (Li/sub 2/B/sub 4/O/sub 7/) single crystals for SAW device applications. The crystals were grown by modified Bridgman method along <110> direction using platinum inserted carbon crucible under nitrogen atmosphere. The seed crystals were of same diameter (108 mm) to that of the crystals grown and of 25 mm in length. The crystals were grown at a rate of up to 0.5 mm/h. Wafers were cut at different places along the length of the ingot for studying the dislocation density distribution by chemical etching and X-ray topography. The EPD at center of wafer was found to be higher (1000 cm/sup 2/) than at outer area (100 cm/sup 2/). The SAW velocity has been measured across a 3-inch wafer and it was found that the variation of the velocity at different parts of the wafer was within /spl plusmn/0.04%.