Diamond wafer, method of estimating a diamond wafer and diamond surface acoustic wave device

A diamond surface acoustic wave device comprising;

• a bulk diamond single crystal or polycrystal substrate being synthesized by an ultrahigh pressure synthesis method or a vapor phase deposition method and having surface defect density of less than 300 particles cm−2 or a diamond substrate consisting of a diamond board or another material board and a single crystal or polycrystal diamond film being synthesized upon the diamond board or another material board and having surface defect density of less than 300 particles cm−2;
• the defect density being defined by d≧W/2 and h≧10 nm, where d is a diameter of a defect, W is the minimum width of electrodes and h is a depth or a height of the defect;
• interdigital transducers produced on the diamond substrate;
• and
• a piezoelectric film deposited on the interdigital transducers and on the diamond substrate;
• wherein the defect density is measured by coating the diamond surface with a thin opaque film, launching laser beams to the coated diamond surface from a laser scanning surface defect detection apparatus for letting the laser beams reflect at a surface of the coating film and an interface between the coating film and the diamond surface, and counting the beams scattered by surface defects or particles on the diamond surface.