Mechanisms for enhancement of sensing performance in CMOS ISFET arrays using reactive ion etching
File(s)
Accepted version
Author(s)
Moser, Nicolas
Panteli, chistoforos
Fobelets, Kristel
Georgiou, Pantelis
Type
Journal Article
Abstract
In this work, we investigate the impact of successively removing the passivation layers of ISFET sensors implemented in a standard CMOS process to improve sensing performance. Reactive ion etching is used as a post-processing technique of the CMOS chips for uniform and accurate etching. The removal of the passivation layers addresses common issues with commercial implementation of ISFET sensors, including pH sensitivity, capacitive attenuation, trapped charge, drift and noise. The process for removing the three standard layers (polyimide, Si3N4 and SiO2) is tailored to minimise the surface roughness of the sensing layer throughout an array of more than 4000 ISFET sensors. By careful calibration of the plasma recipe we perform material-wise etch steps at the top and middle of the nitride layer and top of the oxide layer. The characterisation of the ISFET array proves that the location of the trapped charge in the passivation layers is mainly at the interface of the layers. Etching to the top of the oxide layer is shown to induce an improvement of 80% in the offset range throughout the array and an increase in SNR of almost 40 dB compared to the non-processed configuration. The performance enhancement demonstrates the benefit of a controlled industry-standard etch process on CMOS ISFET array system-on-chips.
Date Issued
2019-08-01
Date Acceptance
2019-04-07
Citation
Sensors and Actuators B: Chemical, 2019, 292, pp.297-307
ISSN
0925-4005
Publisher
Elsevier
Start Page
297
End Page
307
Journal / Book Title
Sensors and Actuators B: Chemical
Volume
292
Copyright Statement
© 2019 Elsevier B.V. All rights reserved. This manuscript is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International Licence http://creativecommons.org/licenses/by-nc-nd/4.0/
Sponsor
Engineering & Physical Science Research Council (EPSRC)
Grant Number
EESA_P76481
Subjects
Analytical Chemistry
0301 Analytical Chemistry
0912 Materials Engineering
Publication Status
Published
Date Publish Online
2019-04-28