Parylene-oil-encapsulated low-drift implantable pressure sensors
This paper demonstrates a parylene-oil-encapsulated packaging technology that applies to commercial pressure sensors to enable intraocular pressure sensing with minimal drift. Commercial digital-output barometers are chosen to be packaged first with 100,000 cSt silicone oil and then sub-micron thick parylene within the volume of the original housing. It is newly found that parylene type and oil viscosity can decide the sign and magnitude of the intrinsic stress in parylene. Additionally, the effect of deposited thickness and temperature on film stress is studied through induced pressure offset. When properly designed, parylene-oil-encapsulated pressure sensors maintain <0.3% sensitivity drift and <1 to 2 mmHg offset drift for over 50 to 106+ days in 77 °C saline, equivalent to 25 to 53+ months at 37 °C . This new compact packaging method is promising for converting air-operated commercial sensors to be "implantable" with nearly original sensitivity and minimal offset and drift.