Detection of sensor passivation failure

A test structure for a sensor, comprising:

• a substrate being part of the sensor, the sensor comprising a resonating structure comprising a piezoelectric layer having an active region, the sensor further comprising a passivation layer overlaying the resonating structure including the active region;
• a moat structure disposed on the substrate and configured to at least partially surround the active region of the resonating structure in plan view;
• an electrode disposed on the substrate and comprising an electrode path configured to cross the moat structure a plurality of times along a majority of the moat structure in plan view, wherein the moat structure at each moat crossing is configured to cause a change in electrical resistance of the electrode if there is passivation failure of the passivation layer at the moat crossing;
• a detector configured to detect the change in electrical resistance of the electrode;
• and
• an analyzer configured to determine passivation failure of the passivation layer based on the detected change in electrical resistance.