Method of forming a single crystal sheet using a die having a thermal gradient along its length
Various single crystals are disclosed including sapphire. The single crystals have desirable geometric properties, including a width not less than about 15 cm and the thickness is not less than about 0.5 cm. The single crystal may also have other features, such as a maximum thickness variation, and as-formed crystals may have a generally symmetrical neck portion, particularly related to the transition from the neck to the main body of the crystal. Methods and for forming such crystals and an apparatus for carrying out the methods are disclosed as well.
1. A method of forming a sapphire single crystal sheet, the method comprising providing a melt in a crucible having a die; and drawing the sapphire single crystal sheet from the die, wherein the sapphire single crystal sheet has a length, a width, and a thickness, wherein the length>width>thickness, the width is not less than 15 cm, and the thickness is not less than 0.5 cm, and a thermal gradient along a length of the die is not greater than 0.6° C./cm.
2. The method of claim 1 , wherein drawing the sapphire single crystal sheet comprises raising the seed crystal at a rate of 3 cm/hour to 30 cm/hour.
3. The method of claim 1 , wherein the thermal gradient is no greater than 0.4° C./cm.
4. The method of claim 1 , wherein the thermal gradient is no greater than 0.3° C./cm.
5. The method of claim 1 , further comprising machining the sapphire single crystal sheet to form a machined sapphire component.
6. The method of claim 5 , wherein machining comprises grinding, lapping, polishing, or bulk material removal/shaping of the sapphire single crystal.
7. The method of claim 6 , wherein machining the sapphire single crystal sheet comprises machining the sapphire single crystal sheet into an optical window.
8. The method of claim 7 , wherein machining the sapphire single crystal sheet comprises machining the sapphire single crystal sheet into a geometric configuration for an infrared and laser guidance, a military sensing and targeting system or an infrared and visible wavelength vision system.
9. The method of claim 1 , wherein the width of the sapphire single crystal sheet is not less than 22 cm.
10. The method of claim 1 , wherein the width of the sapphire single crystal sheet is not less than 28 cm.
11. The method of claim 1 , wherein the thickness of the sapphire single crystal sheet is not less than 0.6 cm.
12. The method of claim 1 , wherein the sapphire single crystal sheet has a mass greater than 4 kg.