Compatibility of ISFET and CMOS technologies for smart sensors

Abstract

Problems concerning the compatibility of ISFET (ion-sensitive field effect transistor) and MOS technologies for manufacturing chemical sensors and intelligent circuitry on the same substrate were studied. For this purpose a batch of polysilicon MOS capacitors which permits the determination of the best procedure for obtaining silicon nitride/oxide and polysilicon/oxide gates together has been processed. From the results the best option was selected and a first batch of ISFETs has been fabricated. The technology is compatible with a 5-micron CMOS process and the masks include MOS transistors and other test structures that make it possible to qualify the process as a good starting point for fabricating smart chemical sensors based on ISFET-REFET (reference FET) combinations.