Really good long-form article from IEEE Spectrum about semiconductors aging and how to improve measurements.
You know when it’s time to get a new car. Your odometer is far into six digits, perhaps the engine is burning lots of oil, or the transmission is growling. Fixing all that might well cost quite a bit more than your ancient vehicle is worth.
But what about your microprocessor? Unlike automobiles, microprocessors don’t have convenient little gauges that reflect how much wear and tear they’ve endured. And wear they do—though you’ll probably never notice it. The degradation of their transistors over time leads slowly but surely to decreased switching speeds, and it can even result in outright circuit failures.
You generally don’t perceive this deterioration because semiconductor companies always play it very safe—they set the clock-speed rating of their microprocessors so conservatively that almost every one of their products will continue to operate flawlessly throughout its intended lifetime. That strategy works. But it’s kind of like never taking your Ferrari out of the slow lane because you’re concerned that its engine might throw a rod 10 years down the road.
We and other researchers are trying to improve that situation. One critical aspect of the work we did at the University of Minnesota was to develop better ways to study the different physical mechanisms of transistor aging. Today semiconductor engineers measure those aging effects primarily by examining transistors one at a time, using microscopic electrodes to probe a silicon wafer. The necessary equipment can cost tens of millions of dollars, and probing transistors individually is arduous when you’re trying to gather many observations. Sometimes you can’t do those measurements well, no matter how much time you spend.
With better ways to measure transistor aging, chipmakers could let their microprocessors run faster—appreciably faster—than they do now. In the future it might even be possible to use these techniques to build circuits into microprocessors that continuously measure the subtle effects of aging and adjust clock frequency or operating voltages so that the transistors, old or new, could always run at peak speeds.