Effect of Temperature on mobility of electrons

How the change in temperature affects the mobility of electrons in a MOS????
What is a fast transistor and slow transistor????
Can someone explain pls,,,,,

archunan_m said:

How the change in temperature affects the mobility of electrons in a MOS????
What is a fast transistor and slow transistor????
Can someone explain pls,,,,,

Click to expand...

1. Mobility of charge carriers (electrons and holes) is determined by several scattering mechanisms (scattering is a change in a direction and sometimes energy of carriers caused by imperfections): phonon scattering (by optical and acoustical phonons), ionized impurity scattering, surface scattering, remote charge scattering, etc. Phonon scattering is strongly temperature-dependent since the number (density) of phonons increases with temperature (it follows Bose-Einstein distribution). Usually, mobility decreases with temperature increase.

2. Due to inevitable manufacturing variations (change in implant doses and doping profiles, oxide thickness, etc.) device characteristics change - wafer-to-wafer, lot-to-lot, etc. (global variations). Thus, some transistors will have low Vt and high current ("fast" transistors), and some - high Vt and low current ("slow" transistors). These variations are described in terms of "corners" - Fast (F), Slow (S), and Typical (T), both for n-type and p-type devices - thus the transistor "corners" are defined by pairs - FF, SS, FS, TT, ...

Regarding the temperature behavior, keep in mind that the threshold voltage is also a function of temperature. It decreases with temperature.
Therefore, there are effects: (i) The decrease of mobility with Temp, and (ii) decrease of VTH with temperature. Please, note that both effects lead to different situations. In (i), the drain-source current is decreased. In (ii) is increased.
Which effect dominates?! It depends on the bias conditions. For VGS < Vx (a specific value, the effect of (ii) is more relevant.
Regards.
Regarding the temperature behavior, keep in mind that the threshold voltage is also a function of temperature. It decreases with temperature.
Therefore, there are effects: (i) The decrease of mobility with Temp, and (ii) decrease of VTH with temperature. Please, note that both effects lead to different situations. In (i), the drain-source current is decreased. In (ii) is increased.
Which effect dominates?! It depends on the bias conditions. For VGS < Vx (a specific value, the effect of (ii) is more relevant.
Regards.

With temperature rises, MOS resistance will increase usually.