Book Review: Thick-Film Hybrids—manufacture and design:

layers (e.g. ZnO) on the surface of the silicon, thus producing a smart sensor by providing signal conditioning circuits on the silicon. Chapter Four discusses silicon sensors for thermal signals. Today silicon is used in many commercial1y available temperature sensors. These devices utilise the temperature dependence of the base emitter-junction of a bipolar transistor, or the temperature sensitivity of silicon resistors. Chapter Five of the book is concerned with magnetic sensors. These general1y utilise the Hal1effect,which again is orders of magnitude greater in silicon than metals. Today such transducers are used in keyboards, magnetometers, recording heads, displacement sensors, brushless electromotors, etc. Magnetoresistivity, magnetodiodes and magnetotransistors are also discussed. I personal1y found the chapter (Chapter Six)dealing with chemical sensors the most interesting, and it is probably the area attracting the most research interest at the present time. One class of chemical sensor depends on the measurement of the change of the conductivity of a chemcial layer (i.e.not an intrinsic property of silicon) when subjected to a gas. For instance there are metal oxides which are n-type semiconductors and which change their conductivity when heated and exposed to certain gases. There are also organic materials-conducting polymers-which display the same behaviour at room temperature, but in general the resistance changes are more difficult to detect: Also discussed are a wide range of MOSFET based chemical sensors of which the Ion Sensitive Field Effect Transistor (ISFET) is probably the most successful. In its simplest form this is a MOSFET without a gate contact. When the ISFET is immersed in a solution containing ions, the drain current depends on the ion concentration. These devices have enjoyed considerable success in the field of clinical biosensors, which are devices in which an electronic signal is produced that is proportional to the concentration of specific chemicals (e.g, glucose) in the human body. Although the book is dealing with fairly specialised areas, the authors take great care to explain in some detail the physical (and chemical) properties that are being exploited in a particular device. They also discuss, in similar detail, the technologies employed in producing silicon based sensors. These include silicon planar technology, thin and thick film deposition and micromachining. This makes the book highly accessible to both specialists and non-specialists alike. There are, however, parts which I found a little dry and pedantic. In particular, I felt that the introductory chapter was going to put me off delving futher into the book-I'm glad it didn't. By its very nature the broadest appeal of this work will be to researchers in the field and postgraduates on specialised courses. It is encyclopedic in its coverage and there are almost four hundred and fifty references to published works. I thoroughly recommend it as an invaluable reference work. JOHN V. HATFIELD, Department of Electrical Engineering andElectronics, UMIST