Novel concept for flow-rate and flow-direction determination by means of pH-sensitive ISFETs Arshak Poghossian* a , Lars Berndsen* a,b , Hans Lüth* a , Michael J. Schöning** a,b a Institute of Thin Films and Interfaces, Research Centre Jülich b University of Applied Sciences Aachen ABSTRACT Sensor systems for multi-parameter detection in fluidics usually combine different sensors, which are designed to detect only one physical or (bio-)chemical parameter. In the present work, an ISFET (ion-sensitive field-effect transistor), which is well known as a (bio-)chemical sensor, is utilised for the flow velocity and flow direction measurement for the first time. The proposed flow sensor presents a chemical sensor-actuator system and consists of a H + -ion generator and a pH ISFET that detects the in-situ electrochemically generated H + ions. By measuring the time of flight, the flow velocity can be determined. Since this measuring method represents a dynamic method, a calibration of the sensor usually is not required, because only relative changes in the sensor output signal are of interest. Moreover, sensor´s drift, temperature instability and sensitivity discrepancy between the various ISFETs are not relevant. The experimental results show good linearity between the measured flow velocity with the ISFET and the delivered flow rate of the pump. Due to the fast response of the ISFET (usually in the millisecond range), an ISFET-based flow sensor is suitable for the measurement of the flow velocity in a wide range. The results of the flow direction measurement with two ISFETs are presented, too. Keywords: Flow rate sensor, flow direction sensor, ISFET, pH, ion generation, time of flight 1. INTRODUCTION Multi-parameter detection in fluidics is mostly carried out by different sensors, which are usually designed to detect only one physical or (bio-)chemical parameter. Because the structures, sensitive materials and functional principles of physical sensors usually differ from that of (bio-)chemical sensors, there is no single and low-cost technology that allows the fabrication of a wide variety of sensors into the same monolithic chip. In this context, hybrid-assembled systems are more suitable to make a small series production of flexible multi-sensor systems. Therefore, we suggest a novel approach for a multifunctional hybrid sensor module using the same transducer principle and structure for both physical and (bio-)chemical sensors, where the same chemical sensor can also serve as a physical sensor and thus, the number of obtained physical and (bio-)chemical information is higher than the number of the sensors needed. Here, the multifunctionality is achieved by means of different sensor arrangements and/or different operation modes. The possibility of utilising of the same chemical sensor as a physical sensor was demonstrated in [1]. Here, a temperature sensor was developed that is based on a differential set-up of two ISFETs (ion-sensitive field-effect transistor, which is well known as a (bio-)chemical sensor) operating in different working points. In the present work we extend this concept for flow sensors. Miniature liquid flow sensors have become increasing importance in many fields, including industrial process control, biomedical instrumentation, drug delivery systems, flow injection analysis, integrated fluid analysis systems such as μ- TAS (micro total analysis system) and so on. The micro flow sensors should be simple, reliable, small in dimensions, high in accuracy, fast in their dynamic response and consume little energy. Therefore, silicon-based flow sensors using microelectronic fabrication methods are very attractive. A review of recent advances in micro liquid flow sensors can be _________________________________ * a.poghossian@fz-juelich.de; phone 49-2461-612605; fax 49-2461-612940; http://www.fz-juelich.de/isg/sensorik; Institute of Thin Films and Interfaces, Research Centre Jülich GmbH, D-52425 Jülich, Germany; ** m.j.schoening@fz-juelich.de; phone 49-2461- 612973; fax 49-2461-612940; http://www.fz-juelich.de/isg/sensorik; University of Applied Sciences Aachen, Ginsterweg 1, D-52428 Jülich, Germany Microfluidics and BioMEMS, Carlos H. Mastrangelo, Holger Becker, Editors, Proceedings of SPIE Vol. 4560 (2001) © 2001 SPIE · 0277-786X/01/$15.00 19 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 10/09/2015 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx