Thermal Transport
Mass transport within a solid lattice accelerates exponentially with temperature according to an energy barrier relationship. This thermal behavior, described by arrhenius diffusion kinetics, governs the movement of gas atoms through sensor packaging materials. The rate of atomic migration determines how quickly atmospheric helium or moisture can penetrate a hermetically sealed sensor.
Activation Energy
Diffusion coefficients depend on a pre-exponential factor and an activation energy specific to the material pair. Silicon dioxide barriers exhibit higher activation energy than polymer sealants, which limits the passage of contaminant molecules at operational temperatures. This distinction ensures that glass or metal interfaces maintain a stable interior pressure over decades of field operation, which is critical for devices that must function without maintenance in remote locations.
Low-density materials allow faster gas penetration because their molecular structures contain larger interstitial pathways.
Degradation Path
Gas permeation through sealing materials alters the reference atmosphere inside microelectronic sensor packages. When external gases slowly diffuse into a vacuum cavity, the changes in gas density affect the sensor calibration. This mechanism of long-term drift requires designers to select materials with high activation energy barriers.
Verification Test
Measurement of diffusion rates across a range of elevated temperatures determines the parameters of the thermal model. High temperature baking of sample barriers allows the extraction of activation energy values by monitoring the rate of pressure change. These experiments are carried out in specialized vacuum chambers equipped with mass spectrometers.
