Gas permeation in PDMS monitored by on-site pressure sensors

This paper proposes a new methodology to detect the gas-leakage and the corresponding diffusion coefficient of PDMS. The authors use PDMS instead of Pyrex #7740 glass to seal the backside V-grooves of pressure sensor chips. The packaged sensor is put into a pressure testing machine and pressurized with CO₂ at 300 psi. By observing the output voltage, the time history for CO₂ permeating into cavity of the sensor was easily to be found. In this paper, the authors use several PDMS membranes with different thickness, from 45 to 2000 μm, to package the sensors and investigate the gas-leakage of PDMS. The gas leaking through PDMS is shown to be governed by the diffusion mechanism, and the diffusion coefficients derived from CO₂ leaking history of PDMS chip frames is 2.2×10^-9 m /s, matched with the previous work. The thickness effect of PDMS on the diffusion mechanism is also addressed.