how does the barometer work?

hi, so i know that all the iphones after 6(?) have barometers in them which are used to calculate altitude changes for things like improved gps or tracking flights of stairs climbed. however i haven't been able to find any answers online about how the barometer actually works?

i read that the space where the audio jack used to be is now a vent which allows air to flow into the phone so air pressure can be measured. i tested this out by gently blowing on the 'vent' and yep, the air pressure increases! hope i'm not damaging my phone by doing that lol.

but what is the actual sensor? how does is measure the air pressure? i only know how those big, old barometers work with mercury. how does a little sensor in a phone measure air pressure?