Design of a single-chip pH sensor using a conventional 0.6-μm CMOS process

Hammond, P.A., Ali, D. and Cumming, D.R.S. (2004) Design of a single-chip pH sensor using a conventional 0.6-μm CMOS process. IEEE Sensors Journal, 4(6), pp. 706-712. (doi: 10.1109/JSEN.2004.836849)

Abstract

A pH sensor fabricated on a single chip by an unmodified, commercial 0.6-/spl μm CMOS process is presented. The sensor comprises a circuit for making differential measurements between an ion-sensitive field-effect transistor (ISFET) and a reference FET (REFET). The ISFET has a floating-gate structure and uses the silicon nitride passivation layer as a pH-sensitive insulator. As fabricated, it has a large threshold voltage that is postulated to be caused by a trapped charge on the floating gate. Ultraviolet radiation and bulk-substrate biasing is used to permanently modify the threshold voltage so that the ISFET can be used in a battery-operated circuit. A novel post-processing method using a single layer of photoresist is used to define the sensing areas and to provide robust encapsulation for the chip. The complete circuit, operating from a single 3-V supply, provides an output voltage proportional to pH and can be powered down when not required.

• Item Type: Articles
• Keywords: CMOS analogue circuit, ISFET, SoC, encapsulation, ion-sensitive field-effect transistor, pH, system-on-chip.
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Cumming, Professor David
• Authors: Hammond, P.A., Ali, D., and Cumming, D.R.S.
• Subjects: Q Science > QC Physics; T Technology > T Technology (General)
• College/School: College of Science and Engineering > School of Engineering > Electronics and Nanoscale Engineering
• Journal Name: IEEE Sensors Journal
• Publisher: IEEE
• ISSN: 1530-437X
• Copyright Holders: Copyright © 2004 IEEE Computer Society
• First Published: First published in IEEE Sensors Journal 4(6):706-712
• Publisher Policy: Reproduced in accordance with the copyright policy of the publisher.