Flickernoise

Flickernoise, commonly known as 1/f noise, is a type of electronic noise characterized by a power spectral density that decreases roughly inversely with frequency. Unlike white noise, which has a flat spectrum, flickernoise becomes more prominent at low frequencies and is observed in a wide range of electronic devices, materials, and natural systems.

In semiconductor devices such as transistors, flickernoise arises from fluctuations in the number of charge carriers and from mobility variations caused by charge trapping and detrapping at interfaces and defects. The effect is particularly noticeable in metal-oxide-semiconductor (MOS) structures and field-effect transistors at low frequencies. It is considered a fundamental limit in precision electronics and sensor performance.

Mathematically, the power spectral density S(f) is typically proportional to 1/f over a certain frequency range, often described by S(f) = A/f^α with α close to 1. A widely used empirical model in conductors is Hooge's formula: S_I(f)/I^2 = α_H /(N f), where α_H is Hooge's parameter and N is the number of charge carriers; exact expressions vary by device and measurement context. Temperature, current, and device geometry influence flickernoise magnitude and frequency range.

Implications and applications include limiting low-frequency performance in amplifiers, readout systems, and precision sensors. Flickernoise also serves as a diagnostic tool for material quality and trap dynamics, with improvements in fabrication and device design reducing its impact but not eliminating it. Beyond electronics, 1/f noise has been reported in disciplines such as physics, biology, and economics, contributing to ongoing research on its universal origins.