US Patent 7324400 Programming and evaluating through PMOS injection

A PMOS transistor includes a gate, drain, and source in a substrate and is isolated from adjacent transistors in the substrate by shallow trench isolation. The transistor is programmed by applying a gate voltage to the gate and generating a drain-to-source voltage across the transistor that is of sufficient magnitude such that electrons are injected into the shallow trench isolation. This degrades the transistor so that it cannot be turned off. In one embodiment, the magnitude of the source-to-drain voltage depends on the gate voltage.