Integrated circuits made on thin layers are said to hold promise for improved thermal characteristics, lightweight stackability and a high degree of flexibility. Thinner layers also provide performance advantages for power electronics, since it offers lower electrical resistance and heat is easier to remove.
According to the team, controlled spalling can be used to produce thin layers from thick GaN crystals without causing crystalline damage. The technique is also said to make it possible to measure basic physical properties of the material system, such as strain-induced optical effects and fracture toughness.
"Our approach to thin film removal is intriguing because it's based on fracture," said research staff member Stephen Bedell. "First, we first deposit a nickel layer onto the surface of the material we want to remove. This nickel layer is under tensile strength.
“Then we simply roll a layer of tape onto the nickel, hold the substrate down so it can't move, and then peel the tape off. When we do this, the stressed nickel layer creates a crack in the underlying material that goes down into the substrate and then travels parallel to the surface.
“We can control how much of the surface is removed by adjusting the thickness of the nickel layer. Because the entire process is done at room temperature, we can even do this on finished circuits and devices, rendering them flexible."
The researchers have demonstrated the transfer of silicon, germanium, gallium arsenide, gallium nitride/sapphire, and even glass. They claim the technique can be applied at nearly any time in the fabrication flow, from starting materials to partially or fully finished circuits.
GaN is the underlying material used to fabricate blue and white LEDs as well as for high power, high voltage electronics. It may also enable ultrathin bioelectronics or implantable sensors.
