Vacuum Maintenance
Reactive metal alloys that chemically bind gas molecules on their surfaces are used to maintain ultra-high vacuum conditions in sealed environments. These non evaporable getters are integrated into the cavities of microelectromechanical systems to absorb residual gases such as carbon monoxide, nitrogen or water vapor. This chemical action preserves the low-pressure environment necessary for the reliable operation of resonant sensors.
Activation Process
Heating the material to a specific activation temperature under vacuum conditions drives the surface oxide layer into the bulk of the alloy. Once activated, the non evaporable getters present a clean metallic surface that reacts with any ambient gas molecules that collide with it. The activation is usually performed during the final wafer-bonding or hermetic-sealing step of the manufacturing process.
Gas Absorption
The capacity of the getter depends on the active surface area and the diffusion rate of the absorbed gases into the bulk material. Active gases are permanently bound as stable chemical compounds, while hydrogen is absorbed reversibly and can be released if the temperature rises. Noble gases like helium, neon and argon are not absorbed by the non evaporable getters, which means the initial packaging process must minimize their presence.
To ensure long-term vacuum stability, the getter volume must be sufficient to handle the expected outgassing from the cavity walls over the lifetime of the sensor.
Quality Verification
Testing the pressure within the sealed cavity over time reveals the getter effectiveness. This is often monitored by measuring the quality factor of an enclosed micro-resonator.
