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.
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