Langasite ( La3Ga5SiO14 )

Crystal properties    
Density 5.74 g/cm3 Langasite La3Ga5SiO14    
Space Group 32
SAW velocity (Vef) m/s = 2736
Electromechanical coupling coefficient K²s = 0,38
Temperature coefficient
first order:
second order

TCD a1 = 0
TCD a2 = -6,8*10^-8 (1/C°)^2
Working face wafer diameter minus 3 mm  
Orientation Primary flat is perpendicular to X' axis
with accuracy +/-15 min
Yxlt/48.5°/26.6°
 
Edge chipping No chipping inside the working area and on the primary flat. Chipping can be accepted outside the working area if the width is less than 0.5 mm, and the cumulative length is less than 5 mm.  
Polishing No dimples, cracks, unpolished areas, ontaminants in working area under x50 magnification. Scratches visible at x50 magnification are allowed in working area if their quantity is lower than 3 on one wafer and less than 20 in a lot of one hundred wafers.  
Backside face Ra>0.2 microns.  
     
  76,2 mm wafers 100 mm wafers
Diameter 76.2 mm +/- 0.2 mm 100.0 mm +/- 0.15 mm
Thickness 0.50 mm +/- 0.05 mm 0.50 mm +/- 0.05 mm
Primary flat 22 mm +/-2.0 mm 32.5 mm +/-2.5 mm
Flatness (under vacuum) < 10 mm < 10 mm
LTV <2.2 microns
for the base 20 mm x20mm
<2.2 microns
or the base 20 mm x20mm
Bow (free wafer) < 50 mm < 50 mm
Secondary flat 11 mm +/-2.0 mm 11 mm +/-2.0 mm