The unique conditions of microgravity in low Earth orbit (LEO) offer unparalleled opportunities for innovation and the development of advanced materials and products with characteristics that are difficult, if not impossible, to replicate on Earth. The absence of Earth’s gravity in microgravity environments allows for the production of semiconductors with superior qualities such as increased uniformity, reduced defects, and enhanced electrical and optical properties. These improvements are attributed to the altered behavior of liquids and gases in microgravity, which enables more precise and efficient manufacturing processes.
Microgravity can provide an environment for optimal layering of a thin film via CVD. The lack of sedimentation allows the film to form more evenly when the coating is applied. Due to dominance of surface forces, that helps the film adhere more strongly to the substrate. A weakly or unevenly bonded film is likelier to produce more defects in the material, which can lead to inferior physical properties (mechanical, electrical, thermal, etc.). Number of defects is directly correlated to material performance, and previous investigations have shown that the microgravity environment enables materials to be produced with significantly less defects (up to several orders of magnitude in some cases as estimated by former ISS NL Chief Scientist and Bell Labs Fellow).
Formulation of materials utilizing crystallization in a furnace (using various methods) has been a common technique in microgravity. For various types of materials, it has been shown that crystals with far fewer defects can be produced in microgravity furnaces compared to ground-based counterparts. This leads to the microgravity produced material having far superior physical properties compared to a similar material produced on the ground.
An example of this is GaN (gallium nitride) which is the key component used to make green and blue LEDs and lasers, and are also used in certain radio frequency applications, most notably military radars. GaN is difficult to solidify in large amounts at a time on Earth because its two constituent molecules don’t always bind perfectly, leading to defects. Reducing the movement of the melted fluid as hotter and less-dense fluid rises, which occurs because of gravity, can decrease those defects. ZBLAN optical fibers, which are used in a broad range of industries including medical device data telecommunications, defense, information technology, telecoms and networking and industrial areas are impacted by the gravitational effects of convection and sedimentation, which have a direct impact on the phase diagram of these materials and influence melting properties, crystallization temperatures, and viscosity of the elemental mix during the manufacturing process. Such factors limit yield, transmission quality, and strength and value of these fibers. Specifically, higher performance ZBLAN fibers are enabled when microgravity suppresses convection-driven nucleation and crystallization which directly affect attenuation properties. Benefits for crystallization materials in space/microgravity:
Laser Annealing is effected by microgravity with its diffusion driven environment (since there is minimal convection). Therefore, this driving force can be isolated and controlled without interference to produce a more precise layer or film. Also, the elimination of convection reduces density gradients, thus making it easier for the lighter oxygen to sink into the heavier substrate material, and therefore less power would be needed to achieve the same level of oxidation as compared to on the ground.
