MEMS are also made of silicon. quartz oscillators were basically the first MEMS. (i wrote that but actually its not true lol. something else cool is saw filters which kind of build on the concept of quartz oscillators btw) cool fact: the reason helium kills MEMS is because the atoms are so small that they can diffuse their way through the wall of the device, filling it up with helium and the air resistance then stops it from working!