# A Review of Readout Circuit Schemes Using Silicon Nanowire Ion-Sensitive Field-Effect Transistors for pH-Sensing Applications

## TL;DR

This paper reviews design approaches for pH sensors using silicon nanowire transistors, focusing on improving their performance through advanced readout circuits.

## Contribution

A modified N-type readout scheme with an operational amplifier is proposed to enhance sensitivity and stability in SiNW ISFETs.

## Key findings

- SiNW ISFETs offer high surface-to-volume ratio and CMOS compatibility for pH sensing.
- N-type and P-type current-mirror circuits have distinct strengths and limitations in readout performance.
- The proposed N-type readout design improves gain control, linearity, and noise immunity.

## Abstract

This paper reviews various design approaches for sensing schemes that utilize silicon nanowire (SiNW) ion-sensitive field-effect transistors (ISFETs) for pH-sensing applications. SiNW ISFETs offer advantageous characteristics, including a high surface-to-volume ratio, fast response time, and suitability for integration with complementary metal oxide semiconductor (CMOS) technology. This review focuses on SiNW ISFET-based biosensors in three key aspects: (1) major fabrication processes and device structures; (2) theoretical analysis of key performance parameters in readout circuits such as sensitivity, linearity, noise immunity, and output range in different system configurations; and (3) an overview of existing readout circuits with quantitative evaluations of N-type and P-type current-mirror-based circuits, highlighting their strengths and limitations. Finally, this paper proposes a modified N-type readout scheme integrating an operational amplifier with a negative feedback network to overcome the low sensitivity of conventional N-type circuits. This design enhances gain control, linearity, and noise immunity while maintaining stability. These advancements are expected to contribute to the advancement of the current state-of-the-art SiNW ISFET-based readout circuits.