Chemical Pump
Reactive metal alloys deposited inside hermetic packages absorb active gas molecules through chemical reactions to maintain a stable vacuum. An integrated non evaporable getter binds water vapor and carbon dioxide directly onto its surface through the formation of stable oxides and hydrides. This chemical trapping prevents the accumulation of outgassed molecules that would otherwise degrade the performance of vacuum-packaged sensors.
Activation Process
Activation of the getter requires heating it to a specific temperature to drive the surface oxide layer into the bulk metal. This heating process exposes a fresh, highly reactive metallic surface that is ready to absorb gas molecules from the surrounding cavity. Once activated, the alloy operates passively at room temperature without requiring electrical power or external connections.
The activation temperature must be carefully controlled to prevent damage to neighboring microelectronic components during the wafer bonding process. This thermal treatment is typically completed during the final vacuum bake before hermetic sealing.
Absorption Limit
Capacity of the getter is determined by the volume of active material and the rate of diffusion into the bulk. Noncondensable gases like hydrogen diffuse rapidly into the metal lattice, whereas heavier species like nitrogen remain trapped at the surface. When the surface becomes saturated with heavy compounds, the absorption rate drops and the getter must be reactivated.
Integration Testing
Verification of getter performance is conducted by monitoring the residual pressure or resonance behavior of a vacuum-sealed microstructure over time. Long-term storage tests at elevated temperatures accelerate outgassing to confirm that the getter has sufficient capacity for the intended operating life. These tests help to establish the long-term stability and reliability of the packaged sensors in the field.
