In the world of printed electronics, it is all too often presumed that silicon chips are the ideal, a form of perfection that other technologies cannot match, let alone overtake. The opportunity for printed transistors sometimes seems to be limited to wide areas, as with backplane drivers of flexible displays, and maybe low cost simple circuits where the cheapest silicon chips have stuck at a few cents for decades. Certainly the rocketing price of silicon factories and the R&D to support them does not help in applications where ever greater complexity of circuits is not a market need. However, it has recently become clear that silicon is encountering very serious problems that are additional to these.
Transistors on the latest chips are so small that some of their parts are just a few atoms across. At these dimensions things that are meant to be stable turn out to be fluid and fragile. Chip makers are having to come to terms with the idea that the products they make are wearing out and are doing so more quickly than ever.
From the moment the new ultra complex chip with the finer features starts operating, stresses build up within it and atoms begin to move around. IET Magazine investigated. Mike Muller, chief technology officer of microprocessor designer ARM explained to the magazine that:
"Eighteen months after a chip is made it is probably not the same piece of silicon. Five years later it is certainly not the same. It means the longevity of products is going to become an issue."
IMEC predicts that on 45 nm processes, the average time to failure is less than a year. Ian Phillips, principal staff engineer at ARM says engineers will have to live with the fact that the industry will be unable to make chips that work perfectly throughout their expected lifetime. "We will have to take steps to ensure that the system will work even though the software or hardware aren't perfect, and we know that the latter will gradually die," he said.
Printed transistors are possibly going to exceed some silicon in reliability and, in some cases, even frequency performance. Consider, for example, the terahertz printed transistors of Plastic E Print. The silicon chip reliability time-bomb has yet to detonate. No one has made a commercial chip that uses the 45nm process and we will not see many such chips come to market before the end of 2007. It may take until the 32nm generation before big changes are needed to chip designs to ensure they work for more than a few months. But there will be an easy way to tell when reliability issues begin to bite - electronics stores will stop offering extended warranties.