Correlations of MOSFET transconductance: Its physical origins and relevance to analog MOSFET modeling and operation

The correlations of MOSFET transconductance across the full operating regime were studied on a statistically significant number of devices. This is to our knowledge the first time such a measurement is reported. We present "device operation phase diagrams" summarizing our findings: there are only a few, typically two, highly intracorrelated regions of the transconductances in the V_g - V_d plane. The diagrams aid analog design by clearly depicting the relative process induced variations of the transconductance between any two operating points. Though crucial for analog design, this correlation structure is not typically captured, nor to our knowledge understood, by circuit design and modeling methodologies. The results also suggest that in order to track, at production, the transconductance process induced variations in the full MOSFET operating regime, it is sufficient to select only a few operating points, sampling each intracorrelated region. Finally, a simple, physics based picture is presented, tracing the origin of the correlation patterns back to the variations of a few physical process parameters common to all modern technologies. We can therefore predict our observations are general, and will extend beyond the 0.25-μm technology we examined.