Atmospheric Scavenging
Reactive metallic layers deposited onto the internal surfaces of a vacuum package chemically bind residual gas molecules to maintain a low pressure environment. Thin-film getters are typically composed of titanium or zirconium alloys that react with oxygen and nitrogen to form stable solid compounds. This process ensures the long term stability of microelectromechanical systems by preventing the damping effects and the chemical degradation caused by gas leakage.
Activation Process
Heating the package to a specific temperature after sealing allows the surface oxides on the metallic layer to diffuse into the bulk material. This activation step exposes a fresh, reactive surface that begins the pumping action within the hermetic cavity. Thin-film getters are particularly effective in wafer-level packaging where the available volume for traditional bulk getters is limited.
Capacity Limit
Absorption stops once the surface of the film is completely saturated or the reactive material is fully consumed by the incoming gas. Because the total mass of the scavenging material is small, the hermeticity of the package must be exceptional to prevent premature failure. The thickness of the deposit and the total surface area are the primary variables that determine the lifetime and the pumping speed of the getter.
Integration Method
Physical vapor deposition or sputtering provides the means to incorporate the material directly into the fabrication flow of the semiconductor wafer. This allows for the simultaneous creation of thousands of vacuum sealed cavities in a single process step.
