Thin-film piezo.

Thin-film piezo is a printhead construction in which the PZT actuator is deposited as a film on a silicon wafer, by sputtering or by a sol-gel process, with the fluid channels and nozzles formed around it by MEMS fabrication. Bulk piezo goes the other way: finely milled ceramic powder is compressed into pucks, sintered in a furnace into crystal grains of random orientation, then poled with a strong electric field that drags those grains into rough alignment. Poling is the distinction worth knowing, because forced alignment tends to revert under heat and stress, while sputtered film grows already aligned on its electrode and takes no separate poling step at all. Head construction is not something you change on the floor, so it reaches you as head life and as drift: a head losing drop velocity part-way through a run leaves a fading solid, a scrapped set of pieces and a press standing while it is swapped.