SEMICONDUCTOR DEVICE PHYSICS AND DESIGN

472 CHAPTER 9. FIELD EFFECT TRANSISTORS: MOSFET

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bias

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Band to Band tunneling exp

Figure 9.25: As gate lengths in MOSFETs are reduced, subthreshold leakage increases due to
drain induced barrier lowering (DIBL) and band-to-band tunneling, as illustrated at the top of
this figure. At the bottom, we show the ITRS roadmap for subthreshold leakage in future devices.
Illustrations from Solomen et. al., IEDM 2003.

9.6.2 Mobility Variation with Gate Bias .....................

In our simple model for carrier transport, we regarded the carrier mobility as having no de-
pendence upon the gate bias. As the gate bias is changed the electron density in the channel
changes. The electron density in turn is related to the surface fieldEsnormal to the channel