A comprehensive study of thermal noise in the MOS transistor

Christian Enz

doi:10.1117/12.547090

25 May 2004 A comprehensive study of thermal noise in the MOS transistor

Christian Enz

Proceedings Volume 5470, Noise in Devices and Circuits II; (2004) https://doi.org/10.1117/12.547090
Event: Second International Symposium on Fluctuations and Noise, 2004, Maspalomas, Gran Canaria Island, Spain

Abstract

This paper revisits the fundamental theory of thermal noise in the MOS transistor. It has been recognized quite early that carrier velocity saturation and eventually also carrier heating degrades the thermal noise performance of short-channel MOS devices. This degradation is evaluated in terms of the delta thermal noise parameter defined initially by van der Ziel as the ratio between the thermal noise conductance at the drain and the channel conductance at V_DS=0. For long-channel devices this factor is equal to 2/3. Today, there is still a controversy about what the value of this factor actually is for short-channel devices. Some authors measured a significant degradation of up to 7, attributing it mainly to carrier heating. Some other measured values that where always smaller than 2 on several devices over several technologies and pretend that there is no need of carrier heating to explain this moderate degradation, assuming that velocity saturation only can explain it. More recently, some other authors attribute this degradation to the effect of channel-length modulation. Based on a truly physical charge-based model, this paper tries to clarify the contribution of these different effects on δ. It also highlights the fact that for circuit designers, the real important parameter is not so much the δ factor but rather the ratio of the thermal noise to the transconductance at the same bias point defined as the γ thermal noise excess factor.

Citation Download Citation

Christian Enz "A comprehensive study of thermal noise in the MOS transistor", Proc. SPIE 5470, Noise in Devices and Circuits II, (25 May 2004); https://doi.org/10.1117/12.547090

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