Extracting MOS parameter variations using dual-drain MOSFET offset

We have developed two offset models for dual-drain MOSFETs-one for surface-channel and one for buried-channel MOSFETs. By fitting the models to offsets measured at selected biases, estimates of various MOS parameter variations can be extracted. The models are originally intended to demonstrate that, contrary to current belief, channel implant variations can contribute as much offset to magnetic sensor MOSFETs as mobility variations. The utility of the method, however, extends beyond magnetic sensors. The same approach can be used to extract MOS parameter variations important in circuits such as MOS differential pairs.