VIII.5. Noise in Transistors a) Noise in Field Effect ...

introduction to radiation Detectors and ElectronicsCopyright 1998 by Helmuth Noise in Noise in Transistorsa) Noise in Field Effect TransistorsThe primary Noise sources in Field Effect Transistors area) thermal Noise in the channelb) gate current in JFETsSince the area of the gate is small, this contribution to thenoise is very small and usually can be velocity fluctuations of the charge carriers in the channelsuperimpose a Noise current on the output spectral density of the Noise current at the drain isThe current fluctuations depend on the number of charge carriers inthe channel NC,tot and their thermal velocity, which in turn depends ontheir temperature Te and low Field mobility 0. Finally, the inducedcurrent scales with 1/L because of Ramo s make practical use of the above expression it is necessary toexpress it in terms of directly measureable device the transconductance in the saturation regionone can express the Noise current aswhere T0= 300K and n is a semi-empirical constant that depends onthe carrier concentration in the channel and the device geometry.

Since they are majority carrier devices, MOSFETs are insensitive to displacement damage, but they are affected by ionization damage, which leads to charge buildup in the oxide and the formation of interface states. See H. Spieler, Introduction to Radiation-Resistant Semiconductor Devices

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  Devices, Introduction, Radiation, Semiconductors, Resistant, Introduction to radiation, Resistant semiconductor devices

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