Kinetics of Chemical Ageing at the Electrolyte-insulator Interface

Instability of the dc operating point in electrolyte-insulator-semiconductor (EIS)devices has been ascribed to chemical ageing. Chemical ageing at the electrolyte-insulator interface in EIS systems is believed to involve formation of a modified insulator surface layer as a result of hydration of the insulator material. A kinetic model for hydration of the amorphous insulator material is presented. In particular, the kinetics of hydration is modeled based on a hopping and/or trap-limited transport mechanism known as dispersive transport to derive a closed-form expression for the thickness of the hydration layer. The key characteristics associated with dispersive transport is a power law decay of the diffusion coefficient, [عینا مانند مقاله]of theform [عینا مانند مقاله], where [عینا مانند مقاله] is a temperature-dependent diffusion coefficient which obeys the Arrhenius relationship, [عینا مانند مقاله] is the hopping attempt frequency, and _ is the dispersion parameter satisfying 0< _<1. The power-law time dependence of the diffusion coefficient will be shown to lead to a stretched-exponential decay, exp [عینا مانند مقاله] in the density of sites or traps occupiedby the hydrating chemical species undergoing dispersive transport, where is the time constant associated with structural relaxation. The kinetics associated with the dispersive - diffusionlimited hydration reaction has been shown to lead to a hydration layer thickness exhibiting a time dependence of the form [عینا مانند مقاله]. The instability of the dc operating point in pH-sensitive ISFETs has the same time-dependence as that of the hydration layer thickness. A rate equation has been deduced based on the kinetics of the growth of the hydration layer to account for chemical ageing at the electrolyte-insulator interface.

Keywords:

Dispersive Transport , Eloctrolyte-Insulator-semiconductor (EIS) , Hydration kinetics , Instability , Stretched Exponential Decay