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…..