Findings on silicon behavior could impact electronics design
Professor Taher Saif recently provided fundamental insights into the mechanism of deformation in single crystal silicon, a commonly used material in most electronics.
“Time-dependent plasticity in silicon microbeams mediated by dislocation nucleation” was published earlier this month in PNAS (the Proceedings of the National Academy of Sciences of the United States of America).
Although silicon is the most used material in the electronics industry, its mechanical behavior is still not fully understood. Silicon is a brittle material, but it becomes ductile at about 540 degrees Celsius, a phenomenon referred to as brittle-to-ductile transition (BDT). Silicon also creeps or deforms with time at higher temperatures. Understanding deformation mechanisms in silicon is critical for reliable design of miniaturized devices operating at high temperatures.
Saif and doctoral student Mohamed Elhebeary, the paper’s first author, discovered that at small scale, silicon can creep at temperatures much less than 540 degrees Celsius, and they found that the creep is mediated by the nucleation of dislocation sites on the surface of the specimen, followed by generation of dislocation from these sites with time. Their combined scanning, transmission electron microscopy, and atomic force microscopy analysis revealed that as the threshold stress was approached, multiple dislocation nucleation sites appeared simultaneously from the high-stressed surface of the beam with a uniform spacing of about 200 nm between them. Dislocations then emanated from these sites with time, lowering the stress while bending the beam plastically. This process continued until the effective shear stress dropped and dislocation activities stopped.
Their findings could impact the design and reliability of silicon devices operating under high temperatures and stresses.
The study was conducted in collaboration with Professor Gerhard Dehm of Max-Planck-Institut für Eisenforschung GmbH, Dusseldorf, Germany.
The Saif Lab studies biomechanics/mechanobiology and nanomechanics. Saif is the Edward William and Jane Marr Gutgsell Professor.