PLANAR COMPATIBLE POLYMER TECHNOLOGY FOR PACKAGING OF CHEMICAL MICROSENSORS

By applying special thick film photolithography it is possible to real ize a highly automative ion-sensitive field effect transistor (ISFET) packaging at the wafer level. In this paper two approaches based on ph otolithographic processing of encapsulating layers are presented. A li ft-off method of commercial thermocurable encapsulants has been invest igated, as well as direct photopolymerization of ultraviolet-curable e ncapsulant compositions, containing either epoxy acrylate or polyureth ane acrylate oligomers together with monomers and photoinitiators. Lif t-off has been developed using either thin or thick photoresist sacrif icial layers. The best compatibility implies thick photosensitive poly imide layers as a sacrificial photoresist together with the encapsulan t material based on alumina-filled epoxy. However, better results are obtained by using photopatternable encapsulant polymers that permit ap plication of thin or thick polymer layers on a wafer substrate contain ing ISFET chips. Windows over the gate region and contact pads are ope ned by exposure to ultraviolet light in a standard mask aligner system . Compositions based on epoxy acrylate oligomers are proved to be more reliable in a packaging process. Lifetime of encapsulated microsensor s for pH measurements is presented.