Why does ADI use polyimide an an isolation material rather than SiO2 like others use?
Polyimide has been proven to be an effective isolation material and is rated for 50 years of life time at 400Vac rms working voltage. One big difference between polyimide and SiO2 is that iCouplers with 20um of polyimide can pass the 10kV surge rating required by VDE for a reinfoirced rating. At 10kV SiO2 will crack, destroying the insulation. I've heard people say that glass (SiO2) is a better insulator than plastics (polyimide). That's just not true, the working voltages and 1 minute withstand voltages are comparable, but the surge rating is where they are very different. If you think about it, optocouplers have used used polymer materials for isolation for decades and can meet all the same ratings as the polyimide, but optocouplers don't have the speed and low power consumption as the modern digital isolators, like iCouplers.