Table of Contents

Abstract: In this paper, a preprocessing circuit for ISFETs (Ion-sensitive field-effecttransistors) to measure hydrogen-ion concentration in electrolyte is presented. A modifiedflip-flop is the main part of the circuit. The modification consists in replacing the standardtransistors by ISFETs and periodically switching the supply voltage on and off.Concentration of hydrogen ions to be measured discontinues the flip-flop value symmetry,which means that by switching the supply voltage on the flip-flop goes to one of two stablestates, ‘one’ or ‘zero’. The recovery of the value symmetry can be achieved by changing abalanced voltage, which is incorporated to the flip-flop, to bring the flip-flop to a 50%position (probability of ‘one’ equals to probability of ‘zero’). Thus, the balanced voltagereflects the measured concentration of hydrogen ions. Its magnitude is set automatically byusing a feedback circuit whose input is connected to the flip-flop output. The preprocessingcircuit, as the whole, is the well-known δ modulator in which the switched flip-flop servesas a comparator and a sampling circuit. The advantages of this approach in comparison tothose of standard approaches are discussed. Finally, theoretical results are verified bysimulations with TSPICE and a good agreement is reported.

Abstract: Microfabricated semiconductor devices are becoming increasingly relevant, alsofor the detection of biological and chemical quantities. Especially, the “marriage” ofbiomolecules and silicon technology often yields successful new sensor concepts. Thefabrication techniques of such silicon-based chemical sensors and biosensors, respectively,will have a distinct impact in different fields of application such as medicine, foodtechnology, environment, chemistry and biotechnology as well as information processing.Moreover, scientists and engineers are interested in the analytical benefits of miniaturisedand microfabricated sensor devices. This paper gives a survey on different types ofsemiconductor-based field-effect structures that have been recently developed in ourlaboratory.