A Highly Sensitive FET-Type Humidity Sensor with Inkjet-Printed Pt-In2O3 Nanoparticles at Room Temperature

Meile Wu,Xiaoshi Jin,Jong-Ho Lee,Zhanyu Wu

doi:10.1186/s11671-020-03426-6

Meile Wu, Xiaoshi Jin + Show 2 more

Open Access

https://doi.org/10.1186/s11671-020-03426-6

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Abstract

In this work, Pt-doped In2O3 nanoparticles (Pt-In2O3) were inkjet printed on a FET-type sensor platform that has a floating gate horizontally aligned with a control gate for humidity detection at room temperature. The relative humidity (RH)-sensing behavior of the FET-type sensor was investigated in a range from 3.3 (dry air in the work) to about 18%. A pulsed measurement method was applied to the transient RH-sensing tests of the FET-type sensor to suppress sensor baseline drift. An inkjet-printed Pt-In2O3 resistive-type sensor was also fabricated on the same wafer for comparison, and it showed no response to low RH levels (below 18%). In contrast, the FET-type sensor presented excellent low humidity sensitivity and fast response (32% of response and 58 s of response time for 18% RH) as it is able to detect the work-function changes of the sensing material induced by the physisorption of water molecules. The sensing mechanism of the FET-type sensor and the principle behind the difference in sensing performance between two types of sensors were explained through the analysis on the adsorption processes of water molecules and energy band diagrams. This research is very useful for the in-depth study of the humidity-sensing behaviors of Pt-In2O3, and the proposed FET-type humidity sensor could be a potential candidate in the field of real-time gas detection.

Highlights

Humidity sensors are desired for moisture detection and control in various sectors, such as semiconductor and automotive industries, agriculture, and medical field [1,2,3,4]
In Direct current (DC) I-V results, hysteresis can be observed, which is induced by charge trapping in the sensing material and at the interface between the sensing material and the Oxide-nitrideoxide stack (ONO) passivation stacks
Under the traditional working environment of Field-effect transistor (FET) type sensors, DC biases are typically applied to the electrodes for tracing the current sensing signal

Summary

Introduction

Humidity sensors are desired for moisture detection and control in various sectors, such as semiconductor and automotive industries, agriculture, and medical field [1,2,3,4] They can be classified into capacitive type [5,6,7], resistive type [8,9,10], solid electrolyte type [11], surface acoustic waves (SAW) type [12], quartz crystal microbalance (QCM) [13], etc. It was found that the impedance of In2O3 is sensitive to humidity even at room temperature, especially those doped or decorated with noble metals or other oxides [14, 23,24,25]. Most of them present relatively poor resolution and sensitivity for low humidity level detection (lower than 25%) and need further improvement [23, 27]

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