Reducing Drift in CMOS ISFET Arrays with Monolayer Graphene Sheets

Abstract

In this paper, we present the scaling of a post-processing method to reduce drift in CMOS Ion-Sensitive Field-Effect Transistor (ISFET) arrays using monolayer graphene sheets. Graphene sheets were transferred using a Polymer Assisted Graphene Transfer (PAGT) process on a 4mm x 4mm chip with a 78x56 dimensional ISFET sensor array. The resulting performance parameters: drift, capacitive attenuation, pH sensitivity, and trapped charge were found, and averaged across all active pixels in the array for 5 dies. The results show, on average, a 55% reduction in drift and an 8% reduction in pH sensitivity for monolayer graphene ISFET arrays compared to plain ISFET arrays, with no effect on trapped charge and capacitive attenuation. Graphene’s impermeability limits the modification of the sensing layers while providing physisorption sites to maintain pH sensitivity for the ISFETs. Furthermore, there is no effect on the spatial distribution of performance parameters across the ISFET array associated with transferring monolayer graphene.