1/f noise in devices 2004-30348 전광선. what is the 1/f noise? a fluctuation in the conductance...
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1/f noise in devices
2004-30348전광선
What is the 1/f noise?
• A fluctuation in the conductance with a power spectral density proportional to f
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.
1g qn
L
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.( )
2
Em Vg S
cIS 2/
BVS r
bIS 1.5 1.4~ , ~
B cI B I cS I S I
2V rS I S
1/f noise in HBT
• Can not observe a change in the current dependence of because of setting
guessed from
CVS
B CR R
2
2 2[ ]C
CV B rb E re
B
RS I S I S
R
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
2 2[1 ( )] ~ ~E b cm V mc b B I Ig S g r R S S
1B mc bR g r
bIS
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.
,b cI IS S
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
cf
1/f noise in BJT
• Common collector configuration.
• At 1Hz• Both noise have a
changeover of the current dependence at ~ 30EI A
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.
EI1
B m bR g r 2 1 2[ ( )] ~
E ebV T m b B IS g r R S
ebIS
EI2
( )r
rS f
fN
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
2GS
G fN
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 Tran
sistors”,IEEE on ED vol. 39 no.6 1992[2] Vandamme, Xiaosong Li,and D. Rigaud, “1/f noise in MOS Devices, Mobility or Nu
mber 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 Bip
olar 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 Subthresh
old 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…..