Free-standing parylene C thin films as flexible pH sensing membranes

Parylene C has been extensively used as a biocompatible encapsulation material of implantable microdevices. Towards a new understanding of the material´s potential, we demonstrate a versatile method that enables the deployment of the material both as an encapsulant and as a H^002B; sensing membrane in a single flexible platform using discrete MOSFETs to evaluate its chemical sensing performance. A 40-electrode array was implemented through standard microfabrication techniques on a free-standing 5 μm Parylene film. A thin film (1 μm) of Parylene was finally deposited on top of the array to passivate the electrode tracks. O₂ plasma treatment was employed to selectively functionalize Parylene´s H^002B; sensing capacity. Measured results indicate a chemical sensitivity of 22.8 mV/pH, while the device exhibits relatively low leakage currents (1.2-13.9 nA) and chemical drifts (10-32 mV/h) over a wide pH range (4-10), rendering Parylene a promising material in the field of flexible bio-sensors.