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## 1/f noise in devices

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**1/f noise in devices**2004-30348 전광선**What is the 1/f noise?**• A fluctuation in the conductance with a power spectral density proportional to**The cause of 1/f noise**• The conductance is • If conductance fluctuation is occurred which is fluctuated among the total carrier number or the mobility or both? • The reason is not revealed clearly.**Number Fluctuation**• Fluctuation of carrier number by traps. • In homogeneous bulk devices, Number fluctuation is not observed • In n-type MOST, Number fluctuation is observed because of the interface of bulk and oxide**Mobility Fluctuation**• Caused by scattering in the bulk region. • Depending on the phonon number fluctuation in bulk. • In MOST devices, mobility fluctuation is not fit to explain 1/f noise but p-type MOST devices.**Frequency up-conversion**• Considered in oscillator and mixer. • Generation of phase noise of output signal to mix the current with impulse sensitivity function(ISF). • To consider power spectral density at the carrier frequency, the frequency range of 1/f noise is shifted upwardly.**Frequency up-conversion**Generation of phase noise Frequency up-conversion of 1/f noise to carrier frequency**1/f noise in GaAs HBT**• At low forward current (<100uA), the 1/f noise density is determined by , by ( ) • At high forward current (>100uA) the steep increase is due to the noise in the parasitic resistance.( )**1/f noise in HBT**• Can not observe a change in the current dependence of because of setting guessed from**1/f noise in GaAs HBT**• From the equation If then the noise contribution from the base current is zero. • But there are no minimum point.→ can be neglected**1/f noise in GaAs HBT**• Sometimes a G-R noise contribution (leveling off of the spectral density) was observed at frequencies above 1kHz due to traps with a time constant lower than 0.1ms. • Comparing the 1/f noise of HBT with npn microwave silicon transistor, at the same current the 1/f noise ( )is much higher in HBT.In silicon npn transistor, 1/f base current noise is dominant and 1/f collector current noise is neglected.**1/f noise in BJT**• Mainly discussed in terms of mobility fluctuation(no oxide interface) • In small BJT, the internal base and emitter series resistance became more important than emitter and base current at high current.**1/f noise in BJT**• At low frequencies 1/f component is proportional to inverse frequency. • At high frequencies white component is independent to frequency. • Most of the spectra have corner frequencies in the range of 10Hz – 10kHz**1/f noise in BJT**• Common collector configuration. • At 1Hz • Both noise have a changeover of the current dependence at**1/f noise in BJT**• At low current ( <30uA) the 1/f noise can be strongly reduced by adjusting and from is dominant. • At high current ( >30uA) from the internal resistance is more important than frequency in 1/f noise.**1/f noise in MOSFET(n-type)**• Mainly explained by carrier number fluctuation by tunneling of free charge into oxide trap close to the interface • Proportional to trap density. • Degradation by hot electron and ionizing irradiation as recent origin of number fluctuation**1/f noise in MOSFET(p-type)**• Generally thought by mobility fluctuation. • Because of larger distance from the interface, less noisy and independent to number fluctuation • Satisfying empirical relation where alpha is constant**1/f noise in MOSFET**• Input noise is proportional to interface state density at fermi level and oxide trap density. • It explains that noise occurred by number fluctuation is affected to traps on oxide trap , oxide interface trap.**1/f noise in MOSFET**• 1/f noise in n-type MOS is independent to gate bias. • It means that 1/f noise in n-type is independent to mobility fluctuation and affected by carrier number fluctuation.**1/f noise in MOSFET**• 1/f noise in p-type MOS is dependent on the gate bias. • The gate bias dependence is explained by buried channel conduction. • It says 1/f noise in p-type MOS is explained by mobility fluctuation.**1/f noise in MOSFET**• P-type MOS suffers from mobility fluctuation generally but at high field condition, carrier fluctuation phenomenon is dominant.**Conclusion**• 1/f noise in electronic devices is explained by both number fluctuation and mobility fluctuation. • To reduce 1/f noise by number fluctuation, growing pure oxide(little trap) and new technique of surface etching are needed. • To reduce 1/f noise by mobility fluctuation, pure bulk is needed to make less scattering in bulk devices.**Reference**[1] Kleinpenning, “Location of Low-Frequency Noise Source in Submicron Bipolar Transistors”,IEEE on ED vol. 39 no.6 1992 [2] Vandamme, Xiaosong Li,and D. Rigaud, “1/f noise in MOS Devices, Mobility or Number Fluctuation?”, IEEE on ED vol. 41, no. 11, 1994 [3] Kleinpenning and A.J.Holden, “1/f Noise in n-p-n GaAs/AlGaAs Heterojunction Bipolar Transistor: Impact of Intrinsic Transistor and Parasitic Series Resistances”, IEEE on ED vol. 40, no. 6, 1993 [4] Hooge, “1/f Noise Sources”, IEEE on ED vol. 41, no. 11, 1994 [5] Thomas H. Lee and A.Hajimiri, “Oscillator Phase Noise : A Tutorial”, IEEE on Solid State Circuits, vol. 35, no. 3, 2000 [6] Chang, Abidi and Viswanathan, “Flicker Noise in CMOS Transistor from Subthreshold to Strong Inversion at Various Temperature”, IEEE on ED vol. 41, no. 11, 1994 [7] Herman et al, “Correlation between 1/f noise and interference state density at the Fermi level in field effect transistor”, J. Appl. Phy., vol. 57, pp4811-4813, 1985 Etc…..