RESEARCH ARTICLE Copyright © 2009 American Scientific Publishers All rights reserved Printed in the United States of America SENSOR LETTERS Vol. 7, 1–5, 2009 Na + and K + Implanted Membranes for Micro-Sensors Development W. Nouira 1 , R. Haddad 1 , H. Barhoumi 1 ∗ , A. Maaref 1 , J. Bausells 2 , F. Bessueille 3 , D. Léonard 3 , N. Jaffrezic-Renault 3 , and A. Errachid 3 1 Laboratoire de Physique et Chimie des Interface, Faculté des Sciences de Monastir 5000, Tunisia 2 Centro Nacional de Microelectrónica (IMB-CSIC) Campus UAB, 08193 Bellaterra (Barcelona), Spain 3 Laboratoire de Sciences Analytiques, UMR CNRS 5180, Université Claude Bernard-Lyon1, Batiment Raulin, 69622 Villeurbanne Cedex, France (Received: 15 January 2009. Accepted: 1 August 2009) Sodium and potassium ion sensitive membranes produced by ion implantation technique are inves- tigated in order to design a selective sodium and potassium ion micro-sensors. Different membranes were obtained by implanting sodium or potassium ion with different energies and doses through an aluminum buffer layer deposited on the silicon dioxide in order to determine the optimum conditions of implantation. The composition of the silicon layer was analyzed using XPS measurements. The sodium or potassium sensitivity, selectivity, reproducibility and life time are studied. The developed sodium and potassium implanted EIS structures demonstrate a high stability and good sensitivity equal to 52 mV · pNa −1 and 49 mV · pK −1 , respectively. These performances remain stable even after two years’ tests. Keywords: Ionic Implantation, Semiconductor Transducer, Capacitance Measurements, Alkaline Ion Sensors. 1. INTRODUCTION The measurement of Na + and K + concentration is of inter- est to biological fluids. For this purpose, there is a growing need for field effect transistors sensitive to sodium and potassium ions. Polymeric membranes modified electrode are commonly employed to detect sodium or potassium ions but they have a problem of short life time which is due to the solubilization of the ionophore in the solution and to their poor adhesion to the FET device surface. An alternative based on NAS glass (sodium aluminosilicate) formation by using the implantation technique is more promising. This process limits the number of interfaces. In addition, the depth and the composition of the implanted layer can be controlled precisely by adjusting the acceler- ating energy and the ion fluence. This approach of ionic implantation was first explored by Sanada et al. 1 who implanted lithium at 50 keV and alu- minum ions at 60 keV into a plasma SiN layer deposited on the ISFET silica insulator. Later, Ito et al. 2 used a multilayered SiO 2 /Si 3 N 4 /oxidized Si 3 N 4 /Al and implanted ∗ Corresponding author; E-mail: Houcine.Barhoumi@fsm.rnu.tn sodium ions at 100 keV energy through an aluminum buffer layer deposited beforehand. More recently, Pham et al. 3–5 investigated the possibility of modulating the selectivity between sodium and potassium ions by vary- ing the fluence ratio of implanted Na + and Al + ions. They implanted aluminum at 30 keV and sodium at 20 keV. Baccar et al. 6 7 implanted Na + at 7 keV and Al + at 10 keV into EIS structures and ISFET devices. They obtained a sensitivity of 53 mV/pNa for implanted EIS and 60 mV/pNa for implanted ISFET. They also implanted K + ions into ISFET devices and the sensitivity was 41–44 mV · pK −1 . 8 Errachid et al. 9 implanted also potas- sium ions and the obtained sensitivity is linear with a slope of 50 mV/pK. The effect of the composition of the surface before implantation was studied by Shin et al. 10 In this work, we present a new approach to prove the feasibility of Na + and K + microsensors obtained by the ion implantation technique and the NAS sensing layer is formed at the surface of the structure through “knock on effect” of the Al + ions from a deposited aluminum layer. The influence of the ion implantation conditions (ion fluence, ion energy and annealing temperature) on the electrical behavior of the EIS structure is studied. The Sensor Lett. 2009, Vol. 7, No. 5 1546-198X/2009/7/001/005 doi:10.1166/sl.2009.1132 1