What is the subthreshold region ?

cmos subthershold region

sir, NOwa days people are saying that they are working at 90nm process and they say that they are operating at subthershold region.I have studiedabout linear region and also the triode region .I want to knoew what is subthershold region??
In olden days aluminium is used as gate elctrode of MOS but now they are using polysilicon gate ? What are the advantages that can be obtained by this change?

Re: cmos subthershold region

subthreshold region is the region where a MOS is being operated below the threshold voltage.There are three operating region for MOS : subthreshold region, linear region and saturation region.You will find a detail description of the three region in the attached pdf file.

Coming back to polysilicon gate :
Such gate yields a compact self-aligned structure with better performance. The poly-silicon gate is used as a mask during the implantation so that the source and drain regions are self-aligned with respect to the gate. This self-alignment structure reduces the device size. In addition, it eliminates the large overlap capacitance between gate and drain, while maintaining a continuous inversion layer between source and drain.[/b][/quote]