Comparison of single and stacked sensing membrane for pH-ISFET

Cheng-En Lue 1Dorota G. Pijanowska 2Chao-Sung Lai 1,3Bohdan Jaroszewicz 4Yi-Tin Lin 1Chia-Ming Yang 5

1. Department of Electronic Engineering, Chang Gung University, Taoyuan 00333, Taiwan
2. Institute of Biochemistry and Biophysics (IBB), Pawińskiego 5A, Warsaw 02-106, Poland
3. Biosensor group, Biomedical Engineering Center, Chang Gung University, Taoyuan 00333, Taiwan
4. Institute of Electron Technology, Al. Lotnikow 32/46, Warsaw 02-668, Poland
5. Inotera memories Inc. Device Department, Taoyuan 00333, Taiwan

Abstract

The first ion sensitive field effect transistor (ISFET) was with SiO2 layer as the sensing membrane. Next, to improve sensing performance, Si3N4 on a SiO2 layer was applied. Some stacked metal oxide layers were also investigated. However, for the high-k technology, the intermediate oxide layer is not necessary.

In this study, to compare the sensing properties between single and stacked sensing membranes, Si3N4, Ta2O5, and TaON layers were deposited on silicon substrates with and without an intermediate oxide layer. For the fabrication process, Si3N4 layer was deposited by low pressure chemical vapor deposition (LPCVD); Ta2O5 and TaON layers were fabricated by reactive rf sputtering with Ta-target in different gases ambient. Besides, a post deposition annealing (PDA) was used on Ta2O5 layer. Before testing of the sensing properties of ISFETs, the electrical parameters of metal insulator field effect transistors (MISFETs) were measured. The on/off current ratio for all samples was higher than 106, and all MISFETs with single insulator showed the lower body effect than the stacked one. The sensing properties of single and stacked layer ISFETs were similar. The sensitivity of ISFETs with Ta based gate materials was higher than 50 mV/pH and around 47 mV/pH for Si3N4

ISFETs. The low drift coefficients, around 1 mV/h, were observed for all samples. Base on these results, it can be state that the single layer sensing membrane is suitable for ISFET application. The advantages are the following: a simple fabrication process, low cost, and high compatibility with high-k technology.

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Presentation: Oral at E-MRS Fall Meeting 2009, Symposium F, by Cheng-En Lue
See On-line Journal of E-MRS Fall Meeting 2009

Submitted: 2009-05-25 20:00
Revised:   2009-06-30 21:02
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