Using twin well technology, we can optimise NMOS and PMOS transistors separately. This means that transistor parameters such as threshold voltage, body effect and the channel transconductance of both types of transistors can be tuned independenly.

n+ or p+ substrate, with a lightly doped epitaxial layer on top, forms the starting material for this technology. The n-well and p-well are formed on this epitaxial layer which forms the actual substrate. The dopant concentrations can be carefully optimized to produce the desired device characterisitcs because two independent doping steps are performed to create the well regions.

The conventional n-well CMOS process suffers from, among other effects, the problem of unbalanced drain parasitics since the doping density of the well region typically being about one order of magnitude higher than the substrate. This problem is absent in the twin-tub process.