Zero positive zero

Zero Positive Zero (ZPZ) refers to a way of designing electrical components using a three layer structure, consisting of two thin metal layers (with essentially zero resistance) separated by a layer of a material with a positive temperature coefficient (PTC). In this geometry each of the metal layers act effectively as electrodes, and current will flow peripendicular through the construction. The rated voltage of a ZPZ component is primarily set by the thickness of the PTC layer, and secondarily by the electrical characteristics of the PTC layer.

When connected to an external voltage, due to Joule heating in the PTC layer, heat is generated and the temperature of the component will increase. The PTC characteristic ensures that the system is self-regulating: it has a built-in thermostat switching off the current when reaching the maximal temperature. By varying the thermal characteristics of the PTC layer, different temperatures can be reached. Additionally, the geometry ensures that the component will respond to local variations in the ambient conditions, such as the temperature and the thermal transport properties. A typical application for a component with a ZPZ design are as an heating element.