Avalanche ISFET: A highly sensitive pH sensor for genome sequencing

In this paper a novel Avalanche Ion Sensitive Field Effect Transistor (A-ISFET) is presented and experimentally demonstrated. It is shown that a similar model for impact ionization in avalanche photodiodes is also applicable for A-ISFETs. To demonstrate the benefit of A-ISFETs, a test chip with ~35,000 arrays of A-ISFETs is designed and fabricated using a standard 0.25μm CMOS process from TSMC. The transconductance of the fabricated A-ISFET is measured for various Vgs and Vds, to optimize the bias point for maximum sensitivity in avalanche mode. A multiplication gain of ~6.0 was experimentally achieved. Using the optimum bias points, the arrays of A-ISFETs are also tested with sample solutions to demonstrate the increase in sensitivity due to multiplication gain.