It can mean "single part", "no change in points of contact", "non-moving", "not liquid", "no liquids or gases", "no atomic displacement", "ideally no atomic displacement", and several other things. Worse yet, people often change the meaning between sentences of the same document.
A lot of times it's used to say no parts that move or slide relative to eachother. Things like piezo transducers and DLP mems chips are still considered solid state. Certainly a fuzzy line at best
Solid state originates in solid state physics, as opposed to physics involving liquids or gases. The MEMS on the device are moving due to solid state physics.
But by that argument a traditional spinning fan is solid state, since the fan is solid rather than gaseous/liquid as well. Same for a spinning hard drive.
Common modern usage of "solid state" in electronics seems to be synoymous with "no moving parts", not solid as opposed to liquid/gas.
Vibration is kind of an edge case though, so I'm not really sure. There's an expectation that solid state components don't usually fail mechanically or need maintenance in that department. I wonder what the lifetime is for this type of vibrating component?
Yes, that's true. Electromagnetics are part of solid state physics. I think there is a tradition to it too, as solid state electronics came to be about semiconductors, and I think still to this day, solid state has that connotation. For that reason I see no problem in calling this a solid state device.
