US Patent 7486098 Integrated circuit testing method using well bias modification

A method for testing a semiconductor circuit (10) including testing the circuit and modifying a well bias (14, 18) of the circuit during testing. The method improves the resolution of IDDQ testing and diagnosis by modifying well bias during testing. The method applies to ICs where the semiconductor well (wells and/or substrates) are wired separately from the chip VDD and GND, allowing for external control (40) of the well potentials during test. In general, the method relies on using the well bias to change transistor threshold voltages.