December 26, 2011 - A group from the U. of Illinois has devised a new chip structure that identifies and patches flaws in semiconductors within seconds, saving much analysis and manual fixing and sparing otherwise functioning chips from the trash heap. The work is detailed in a paper published in the journal Advanced Materials.
Enabling devices with multiple complex functionalities means packing multiple complex chips into more complex packages and assemblies -- making it increasingly difficult to find and fix any problems, e.g. failure attributed to temperature cycles or fatigue. Any failure anywhere in the circuit can shut down an entire device. In a fab, such reliability testing often means dumping chips that might otherwise be salvageable. "In a multilayer integrated circuit, there's no opening it up. Normally you just replace the whole chip," points out materials science and engineering professor Nancy Sottos. Intelligently improving reliability and repairs has been long explored, including chip designs that diagnose component wear and automatically reroute functionality.
But a new approach aims to solve the problem directly without such circumnavigation. Adapting its previous work in self-healing polymer materials to conductive systems, this Illinois group placed tiny microcapsules (~10μm-dia.) filled with liquid metal on top of a gold line which functions as a circuit. When a crack occurs and propagates (thus breaking the circuit), the microcapsules rupture and fill in the crack, restoring the circuit. Thus not only is the flaw structurally fixed, but conductivity also is restored -- and that's a new angle to reliability, they claim. Up to 90% of samples healed to 99% of original conductivity, even with "a small amount" of such microcapsules.
Their approach not only eliminates the need to integrate various circuit redundancies or diagnostics, it also is localized and autonomous -- only the microcapsules intercepted by a crack are opened, so the repair process is restricted to the point of damage, and no human diagnostics or intervention is needed. The latter is particularly useful for applications where access can be a problem, e.g. in battery devices, or in aircrafts (particularly aerospace/defense) where a problem can occur anywhere along miles of conductive wires.
Future work will look at "further refin[ing] the system" and looking at other ways to use these microcapsules to control conductivity -- e.g. extending the system to batteries. "It's true for a battery too; you can't pull a battery apart and try to find the source of the failure," Sottos said. The research is supported by the US DoE.
the microcapsules rupture (center), filling in the crack and restoring the circuit (bottom).
(Source: U. of Illinois at Urbana-Champaign; graphic by Scott White)