Patent ID: 8685161

Claim:
A method of forming a sapphire single crystal comprising: providing a melt fixture comprising: a crucible; a die having a length, wherein the die is open to and extends along a length of the crucible; and a plurality of thermal shields overlying a crucible lid and adjacent to the die, wherein: each of the thermal shields has a length, a width, and a thickness, wherein length>width>thickness; the thermal shields include a lower thermal shield and an upper thermal shield; the lower thermal shield is disposed between the crucible lid and the upper thermal shield; and the upper thermal shield has a length that is shorter and extends along a smaller fraction of the length of the die than a length of the lower thermal shield, such that a combination of the lower and upper thermal shields defines a stepped configuration with respect to the length of the die; forming a melt in the crucible; and drawing an as-formed sapphire single crystal sheet from the die.