One of the graduate students I worked with studied the TI micro-mirrors used in DLP projectors. They were designed in the first round of micromachined devices so by EEs rather than MEs, and as a result they used aluminim.
So the question to answer is, "how does a multi-million pixel display unit array of doubly supported tortional Al hinges going through >1% strain survive for 1000s of hours (much longer than the bulbs) oscillating at 100s of kHz". That's ~10^12 cycles each with ppm defect rates!
Since you know that this far exceeds any reasonable fatigue strain and the defect density /dislocation propagation should be huge! The key is that the aluminum is <1um thick a few um wide and <100um long. The majority if the strain is concentrated at the supported ends, but it's so thin that the whole high strain region is single crystal!
TI didn't originally know why it worked... just that it did.
I won't say mechanical gates are a great idea... and at 1MHz they might start failing after a few continuous months. The truly unfortunate part is that the manufacturing processes aren't really designed to control for the grain structure... they're designed for etch repeatability and conduction stability so yield could fall apart while tour processes seem nominal.
So the question to answer is, "how does a multi-million pixel display unit array of doubly supported tortional Al hinges going through >1% strain survive for 1000s of hours (much longer than the bulbs) oscillating at 100s of kHz". That's ~10^12 cycles each with ppm defect rates!
Since you know that this far exceeds any reasonable fatigue strain and the defect density /dislocation propagation should be huge! The key is that the aluminum is <1um thick a few um wide and <100um long. The majority if the strain is concentrated at the supported ends, but it's so thin that the whole high strain region is single crystal!
TI didn't originally know why it worked... just that it did.
I won't say mechanical gates are a great idea... and at 1MHz they might start failing after a few continuous months. The truly unfortunate part is that the manufacturing processes aren't really designed to control for the grain structure... they're designed for etch repeatability and conduction stability so yield could fall apart while tour processes seem nominal.