Protective Coating
The deposition of inert layers on the surface of a microelectronic device shields the active region from chemical and environmental contamination. This process and its resulting layers are called sensor passivations and are critical for the longevity of microelectromechanical systems. Silicon nitride and silicon dioxide are the primary materials used for this purpose.
They prevent moisture and ionic impurities from reaching the sensitive silicon junctions.
Chemical Barrier
In harsh industrial environments, acidic or alkaline vapors can etch the metal interconnects and degrade sensor performance. Standard sensor passivations act as a barrier against these corrosive substances. The thickness of the deposited layer determines the diffusion time of harmful chemical species.
Electrical Stability
Surface states and dangling bonds are neutralized by the passivation layer, reducing surface recombination velocity and leakage currents. This reduction improves the signal-to-noise ratio of the sensor. Stable passivations minimize drift in the sensor offset and sensitivity over long operational periods.
Metrological Reliability
Defects in the protective layer can lead to localized corrosion and unpredictable sensor failure. Accelerated life testing in temperature-humidity chambers evaluates the durability of the sensor passivations under stress. This qualification ensures that the sensor meets its lifetime specification in the field.
