From conventional membrane electrodes to ion-sensitive field-effect transistors

The theory concerning conventional membrane electrodes is often used as a starting point for the theoretical description of the operation of an ion-sensitive field-effect transistor. Although this results in a useful description of the device, a better view of the principles, and consequently the possibilities, of the new ion-sensitive device may result if the analysis is carried out in more detail, especially with respect to measuring concepts. This is presented in the paper. A careful comparison between the operation of a conventional membrane electrode and the i.s.f.e.t. leads to a definite classification of different types of i.s.f.e.t.s. These types are illustrated with corresponding measurements. In addition, the most appropriate application for each type is mentioned

The influence of the pH on the electrolyte-SiO2-Si system studied by ion-sensitive fet measurements and quasi-static C-V measurements

The responses of ion-sensitive FETs (ISFETs) with thermally grown SiO2 gate regions and of electrolyte-SiO2-Si (EOS) structures to stepwise changes in the pH were studied.\ud \ud In addition to a change in the boundary potential at the electrolyte-SiO2 interface which accounts for the observed initial response of ISFETs, a mechanism is also proposed in which one or other hydrogen-bearing species interacts with the surface states at the SiO2-Si interface.\ud \ud This proposed mechanism is based on the observed time drift in the response of ISFETs and on the changes in the shape of the quasi-static C-V curves of the EOS structures

An investigation of the hydration properties of chemically vapour-deposited silicon dioxide films by means of ellipsometry

Time-dependent ellipsometric measurements were made of the water absoprtion in SiO2 films grown by chemical vapour deposition at low temperatures. These films were exposed to water vapour at different pressurures. We determined in the ellipsometric volume percentage of water in the oxide film from the changes in the ellipsometric parameters due to water absorption. We also obtained a diffusion coefficient of water of the order of 1.3 x 10-13 cm2 s-1. From the reversible changes in the ellipsometric parameters due to dehydration we conclude that the water is physically adsorbed

Zinc Oxide Nanowires Deposited on Polymeric Hotplates for Low-power Gas Sensors

Zinc oxides (ZnO) nanowires were successfully deposited on plastic low-power micro-hotplates using the thermal oxidation technique. Metallic zinc layer was deposited on the sensing transducer by RF magnetron sputtering and then oxidized in a controlled atmosphere in order to obtain ZnO nanostructures. Morphological investigations confirmed the nanometric dimensions of the fabricated nanostructures. The n-type behavior of the nanostructured material was evaluated towards different chemical species to highlight the electrical properties of the materials. Calibration curves for the detection of several chemical species were defined. © 2012 The Authors. Published by Elsevier Ltd

A system to measure 3-directional relative displacements for a biomedical application

A micro system for measuring the relative displacements between a bone and an implant in a prosthetic hip of a human being has been realized. Novel are the small dimensions of the system combined with the possibility to measure relative displacements in three directions. The system consists of a microsensor body, a mechanical transducer element made by precision mechanics, electronics, and the final package. The realization and test results of a prototype system are presented. Typical ranges for these prototypes are ±500 μm for lateral directions and ±50 μm in axial direction

Smart SU-8 Pillars Implemented in a Microfluidic Bioreactor for Continuous Measurement of Glucose

In this contribution we explore a new and simple approach for immobilizing enzymes like glucose oxidase on SU-8 surfaces to develop a smart substrate integrated in microfluidics. SU-8 is a well known photoresist often used in microfluidic prototyping. Immobilization of enzymes on such substance can open new possibilities in the microfabrication of enzyme biosensors and bioreactors. To demonstrate the consistency of this approach, we describe the design, fabrication and the simple functionalization of a microfluidic bioreactor employing smart SU-8 pillars for continuous amperometric measurement of glucose. The results reveal the possibility of simply binding enzymes on SU-8 surface. Moreover, a significant improvement in the linear response range is observed compared to the previous published amperometric microfluidic glucose sensors