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Investigation of hysteresis dependent sensitivity on n and p type Si3N4-EIS structures

Chao-Sung Lai 1,2,  Cheng-En Lue 1,  Yi-Shun Wang 1,  Huang-Chia Lee 1,  Szu-Chieh Wang 1,  Chia-Ming Yang 3

1. Electronic Engineering, Chang Gung University, Taoyuan, Taiwan, Taoyuan 00333, Taiwan
2. Biosensor group, Biomedical Engineering Center, Chang Gung University, Taoyuan 00333, Taiwan
3. Department of Electronic Engineering, Chang Gung University, Taoyuan 00333, Taiwan

Abstract

A differential system on chemical sensors, such as reference field effect transistor (REFET) was proposed as the solution to replace the conventional reference electrode. However, the drawbacks as the complicated fabrication process and short lifetime of organic REFET are still existed. Therefore, an electrolyte insulator semiconductor (EIS) structure with single Si3N4 sensing membrane and p-type substrate was proposed to be a possibility for inorganic REFET application. In this paper, the electrical and sensing properties of n-type and p-type EIS with single Si3N4 sensing membrane was investigated. The pH sensitivity was measured from accumulation region to inversion region, a low sensitivity as 23.75 mV/pH was shown on p-EIS, but high as 46.37 mV/pH on n-EIS.

However, the sensitivities of both structures were high and similar by measuring from an opposite direction (around 46 mV/pH, from inversion to accumulation). To investigate the different sensitivity between these two structures, hysteresis measurement for typical metal oxide silicon capacitor (MOSCAP) was used. A positive voltage shift was performed on p-EIS, but only a slight negative voltage shift was observed for n-EIS. The voltage shift could be caused by the charging and discharging behavior during bias sweep. For the further study, the hysteresis was measured in different pH buffer solutions. In both type of substrate, the hysteresis was increased with pH value, but the hysteresis is much higher on p-EIS than on n-EIS. Based on the result, the hysteresis of p-EIS could be also the explanation of the large variation of pH sensitivity between different bias sweep directions.

The difference of the hysteresis dependent sensitivity on different substrate will be useful on the application of ISFET/REFET pair. Besides, this mechanism can also be used to explain the sensing properties on other high-k membranes which performed a large hysteresis.

 

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Presentation: Poster at E-MRS Fall Meeting 2009, Symposium F, by Yi-Shun Wang
See On-line Journal of E-MRS Fall Meeting 2009

Submitted: 2009-05-25 22:23
Revised:   2009-06-30 21:04