Fabrication and characterization of Al gate n-MOSFET, on-chip fabricated with Si3N4 ISFET

This paper reports the fabrication of n-type MOSFET using Si3N4 as dielectric on the same wafer as ISFET for ISFET characterization. The paper presents the fabrication, simulation and characterization of metal-oxide field-effect transistor (MOSFET). The gate of the ISFET is stacked with Si3N4 sensing membrane layer that has been deposited using LPCVD system to cover the gate area. Output and transfer characteristics of on-chip fabricated MOSFET are obtained and measured in order to study the fabricated ISFET behavior to be used as pH sensor. Silicon nitride is preferred over silicon dioxide sensing film/dielectric (in case of MOSFET) which has better sensitivity and low drift. Process simulations were performed using Silvaco^® TCAD tool.

I. Introduction

The metal-oxide semiconductor field-effect transistor (MOSFET) is a four-terminal device. In addition to the drain, gate and source, there is a substrate, or body contact. Generally, for practical applications, the substrate is connected to the source terminal. The depletion n-MOSFET device is formed from a p-type substrate with physically implanted/thermally diffused n-type source, drain regions. The dielectric material covers the area between the source and drain to provide electrical isolation.