Meaning
Silicon-on-insulator substrates exhibit a localized region of mobile carriers at the interface between the silicon film and the underlying oxide layer. This charge accumulation layer arises under the influence of external electric fields or inherent material defects. The phenomenon is confined to the boundary between different dielectric materials where the electric displacement field experiences a discontinuity.
Carrier Concentration
Free electrons or holes pile up when gate bias voltages exceed the flatband voltage threshold. In a charge accumulation layer, the concentration of these mobile charges determines the local conductivity of the region. High concentration levels reduce the overall resistance of the path.
Channel Conductance
Current flow through the localized path increases linearly with the accumulated charge density. The development of a charge accumulation layer can create an unintended shunt pathway that bypasses the controlled region of the transistor. Engineers minimize this shunt pathway by optimizing the doping profile of the silicon film.
Parasitic Interaction
Unwanted signal coupling occurs when alternating current potentials modulate the localized charge region. This modulation in the charge accumulation layer generates high-frequency harmonics and intermodulation products that degrade the linearity of radio frequency switches. Designing substrates with high resistivity or using trap-rich layers helps suppress these unwanted interactions by neutralizing the mobile carriers before they can accumulate.
Consequently, the signal integrity of the integrated system is maintained during high-power operations.
