Patent ID: 7949482

Claim:
A method for measuring time-varying change in threshold voltage in a device under test due to voltage stress-induced bias temperature effect, the method comprising: applying stress to particular devices in a delay line formed with elements having delays substantially sensitive to only a stress-induced bias temperature effect of a single polarity in order to cause change in a delay of the delay line due to the stress-induced bias temperature effect; removing the stress; propagating a pulse through the delay line; detecting the position of an edge of the pulse at one of multiple outputs of the delay line at a predetermined time after commencing the propagating to provide an indication of the delay through the delay line; storing the indication of the delay; repeating the detecting and the storing to collect the indications of the delay from repetitions of the detecting; and computing an effect of the stress on the bias temperature effect on the particular devices in the delay line from the collected indications of the delay.