Shape memory alloy thin film, method of fabrication, and articles of manufacture
A method of forming a single crystal in a thin film by progressively rapidly heating (and cooling) a narrow band of amorphous material. The amorphous thin film may be of shape memory alloy such as TiNi or CuAlNi. Heating may be accomplished by a line-focused laser beam. The thin film may be formed by sputter deposition on a substrate such as silicon. The thin film crystal that is formed has non-isotropic stress/strain characteristics, and very large recoverable strain in a preferred direction. The single crystal SMA exhibits greater strain recovery; Constant force deflection; Wider transition temperature range; Very narrow loading hysteresis; and Recovery that is repeatable & complete. Single Crystal SMA is manufactured by pulling a single crystal from melt, a method similar to that used by the semiconductor industry to fabricate silicon boules. This process enables manufacture of materials that approach theoretical limits.
1. A method for making a single crystal shape memory alloy thin film comprising the steps of:
depositing a thin film layer of amorphous shape memory alloy material on a substrate;
applying a strip of heat to the amorphous shape memory alloy material to form a crystallization front along the strip;
moving the strip of heat across the amorphous shape memory alloy material in a direction to move the crystallization front across the material;
crystallizing the amorphous material into crystallized material having a single crystal crystallographic orientation; and
cooling the crystallized material with a heat sink.
2. The method of claim 1 wherein the crystallization step comprises using a seed crystal to initiate the crystallization process.
3. The method of claim 1 wherein the crystallized material is superelastic at room temperature.
4. The method of claim 1 wherein the shape memory alloy material is initially a polycrystalline shape memory alloy.
5. The method of claim 1 in which the heat is provided by a device selected from the group consisting of: laser, infrared wavelength light source, visible wavelength light source.
6. The method of claim 1 in which the heat is provided by a scanning electron beam.
7. A method for forming a thin film, single crystal shape metal alloy comprising the steps of:
sputter depositing a thin film of amorphous shape memory alloy material onto a substrate;
heating the thin film amorphous shape memory alloy material with a narrow band of heat so that it reaches its crystallization temperature in the narrow band;
moving the narrow band of heat across the thin film to create a moving crystallization front having a single crystal crystallographic orientation; and
cooling behind the crystallization front to stabilize the single crystal crystallographic orientation formed.
8. The method of claim 7 further comprising using a seed crystal as a starting material.
9. The method of claim 7 wherein the crystallized material is superelastic at room temperature.
10. The method of claim 7 wherein the shape memory alloy material is initially a polycrystalline shape memory alloy.
11. A method of manufacturing a device having a thin film of single crystal shape memory alloy comprising the steps of:
depositing a layer of amorphous shape memory alloy material on a substrate;
applying a strip of heat to a portion of the amorphous material to form a crystallization front along the strip;
moving the strip of heat across the amorphous shape memory alloy material to move the crystallization front across the material;
crystallizing the amorphous shape memory alloy material into a single crystal crystallographic orientation;
cooling the material behind the crystallization front with a heat sink; and
manufacturing a device from the crystallized material.
12. The method according to claim 11 wherein the device is selected from the group consisting of: microactuator, valve, electric switch, relay, optical switch, stent, stent covers, and anastomosis devices.
13. The method of claim 12 wherein the shape memory alloy material is initially a polycrystalline shape memory alloy.