An example fluid ejection module typically has a line or an array of nozzles with a corresponding array of flow paths. Each flow path includes a pumping chamber controllable by an associated actuator, such as a piezoelectric actuator. The piezoelectric actuator includes a layer of piezoelectric material that changes geometry (or actuates) in response to a voltage applied across the piezoelectric layer by a pair of opposing electrodes. The pair of opposing electrodes includes a drive electrode and a reference electrode, and the voltage applied across the piezoelectric layer can be controlled by maintaining the reference electrode at a fixed reference voltage or potential while varying a driving voltage or potential on the driving electrode. The piezoelectric actuator is attached to a membrane over the pumping chamber. The actuation of the piezoelectric layer in response to the voltages applied across the piezoelectric layer causes the membrane to flex. The flexing of the membrane pressurizes fluid in the pumping chamber along the flow path and eventually ejects a fluid droplet out of the nozzle.