Low frequency noise mechanisms in MOS structures

The causes of noise in MOS structures have been the subject of intensive investigation in past years, and the introduction of charge-coupled devices has brought renewed interest to this area. Unfortunately, the exact nature of the mechanisms involved is still not fully understood. However, the recent development of new measurement techniques has given more insight into the physical mechanisms which cause the noise. The work discussed in this paper represents a two-part investigation of the low-frequency noise in IGFET's using these new techniques. Thermally stimulated currents (TSC) have been used to determine the spatial locations, energies and capture cross-sections of interface states and deep-seated traps present in completed devices. Noise spectra have been measured under many bias conditions with temperature varying continuously from 300° K to 30° K, and graphs of the equivalent noise voltage as a function of temperature with frequency as a parameter exhibit some unusual properties. In some cases, distinct peaks are observed in the noise, and the temperatures at which the peaks occur generally increase with increasing frequency. In other devices, these peaks are not observed.