### For FETs, Size Does Matter

In case you're wondering, the PFET is twice as wide as the NFET, because PFETs are in general twice as weak as NFETs. Therefore, PFET must be twice as wide as an NFET to be of equal strength. In the context of FETs, width is measured in the direction parallel to the poly. In this case, it's the vertical direction. The lengths of the two, however, are equal; both are 2[lambda] long. The smaller the length, the faster the transistor, so why not make it 1[lambda] long? Each fabrication process has a minimum transistor length under which the device isn't guaranteed to operate correctly; conventionally, lambda is defined as half this length.

Copyright © 1994 - 2017 Linux Journal. All rights reserved.