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 f
The cause of 1/f noise
1
• The conductance is g  qn 
L
• 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 ptype 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 upconversion of
1/f noise to
carrier
frequency
1/f noise in GaAs HBT
• At low forward current
(<100uA), the 1/f noise
density gm2 SVE is
determined by S Ic , SVB / r 2
by S Ib ( SI ~ I B1.5 , SI ~ Ic1.4 )
B
c
• At high forward current
(>100uA) the steep
increase is due to the
noise in the parasitic
resistance.( SV  I 2 Sr )
1/f noise in HBT
• Can not observe a
change in the current
dependence of SVC
because of setting
RB   RC guessed
from
2
  RC 
2
2
SVC  
 [ I B S rb  I E S re ]
 RB 
1/f noise in GaAs HBT
• From the equation
gm2 SVE  [1 gmc (rb  RB )]2 SIb  ~ SIc  ~
If RB  gmc 1  rb then the
noise contribution from
the base current is zero.
• But there are no minimum
point.→ S Ib 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 (SIb , SIc )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 fc 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
I E ~ 30 A
1/f noise in BJT
• At low current ( I E <30uA) the 1/f noise can
be strongly reduced by adjusting RB  gm1  rb
and from SV  T2[ gm1  (rb  RB )]2 SI  ~
E
eb
S Ieb is dominant.
2
r
• At high current ( I E >30uA) from Sr ( f )  
fN
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
SG

• Satisfying empirical relation G 2  fN
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, pp48114813, 1985
Etc…..