Patent ID: 7587298

Claim:
A method of diagnosing the presence of and determining the root cause of a performance variation of a second field effect transistor from a first field effect transistor, comprising: (a) determining a linear threshold voltage of said first field effect transistor, said linear threshold voltage being a first gate voltage level at which a source current begins to flow; (b) determining a saturated threshold voltage of said first field effect transistor, said saturated threshold voltage being a second gate voltage level marking a boundary between a linear operating region of said first field effect transistor where said source current is substantially proportional to applied drain voltage and a saturated operating region of said first field effect transistor where said source current is substantially constant with respect to applied drain voltage; (c) based on said linear threshold voltage, measuring a first linear source current of said first field effect transistor at a third gate voltage at which drain current is substantially proportional to applied gate voltage; (d) based on said saturated threshold voltage, measuring a first saturated source current of said first field effect transistor at a fourth gate voltage at which source current is substantially constant with respect to applied drain voltage; (e) based on said linear threshold voltage, measuring a second linear source current of said second field effect transistor at said third gate voltage; (f) based on said saturated threshold voltage, measuring a second saturated source current of said second field effect transistor at said fourth gate voltage; (g) comparing a first ratio of said first linear source current to said first saturated source current to a second ratio of said second linear source current to said second saturated source current; and (h) based on relative values of said first and second ratios, selecting a portion of said second field effect transistor to analyze for physical or process variance.