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Thick‐film technology to implement passive elements, network and hybrid circuits has been widely used for four decades and its importance is still growing. While on one hand the technology has been improved to meet the requirements for more sophisticated circuits, on the other hand a better knowledge of its outstanding properties has promoted its application to a certain number of sometimes exotic devices, many of which are in the sensor and actuator area. This paper presents examples of a variety of applications to illustrate what thick film technology can offer outside the familiar area, and to stimulate the imagination of scientists towards possible new applications.

For the production of sensor elements, thick film technology can be used. Advantages of this technology such as ease of production, low cost, high reliability and the possibility of integration with front‐end electronic circuits, make the thick film sensor an interesting alternative to existing sensor elements. In this paper two examples of thick film thermal sensors are presented.

The University of Southampton has been active in the area of thick‐film sensors since their initial conception through to the present. Recent research at the university has concerned the use of thick‐film sensor arrays for the discrimination of chemical species in both gaseous and dissolved form. In addition, the detection of many physical parameters is now being addressed through the use of arrays of sensing elements with a view to improving on factors such as noise immunity, environmental cross‐sensitivity and long‐term accuracy. In the area of chemical sensing, extensive use has been made of thick‐film technology to allow low‐cost arrays of chemical sensors to be fabricated. The lack of specificity exhibited by the individual sensing elements has been demonstrably overcome through the use of signal processing techniques applied to the outputs of the array of sensors. Thick‐film chemical sensor research currently under way at Southampton includes a UK DTI/SERC funded LINK project concerning dissolved species monitoring for water quality assessment. Additionally, gas sensor arrays for the detection of toxic and flammable gases are being explored as part of a well established ongoing research programme. The use of thick‐film technology for the fabrication of physical sensors has been extensively documented. Current research at the University of Southampton includes an industrially sponsored project involving the use of thick‐film strain sensing resistors in the design of an accelerometer. The use of Z‐axis piezoresistivity and an array approach to solving noise and drift problems is seen as a significant novelty in this work.

The bulk batch fabrication process of thick film technology has been utilised in the design and production of miniature amperometric dissolved oxygen sensors based on potentiostatic and voltammetric operation. Three different polymers have been investigated as membrane materials – cellulose acetate, PTFE and PVC. PTFE has been deposited on the devices by aerosol spray and PVC and cellulose acetate by screen‐printing. These methods have been shown to be effective membrane fabrication techniques, and have significant implications in the field of chemical sensors as a whole. All the membrane covered devices investigated were found to exhibit sensitive and linear responses to dissolved oxygen. The effects of temperature and flow rate on sensor response have been investigated and the use of PVC and PTFE in place of cellulose acetate have been shown to reduce both effects. These membranes have also been shown to reduce the detrimental effects of fouling observed on the surfaces of cellulose acetate covered devices as they are powered in tap water.

The University of Southampton Thick‐Film Unit (TFU) was originally established in the Department of Electronics in 1985 to service the requirements of a transducer research group. This group originally pioneered the concept of the intelligent transducer and the thick‐film unit was initially used to explore the opportunities for fabricating low‐cost miniature and robust electronic interface circuits suitable for incorporation within transducers. The benefits to be derived from these thick‐film fabrication techniques soon become evident and the unit rapidly grew in stature with the commencement of several research programmes in the area of thick‐film sensors. The 1989 review of advanced sensor technologies undertaken by the DTI reported that the Southampton group was emerging as a centre of expertise in a technology offering significant short to medium‐term scope for commercial exploitation. This prediction is rapidly being fulfilled with an ever increasing number of thick‐film sensors being made commercially available.

The purpose of this paper is to report thick film environmental and chemical sensor arrays designed for deployment in both subterranean and submerged aqueous applications.

Various choices of materials for reference electrodes employed in these different applications have been evaluated and the responses of the different sensor types are compared and discussed.

Results indicate that the choice of binder materials is critical to the production of sensors capable of medium term deployment (e.g. several days) as the binders not only affect the tradeoff between hydration time and drift but also have a significant bearing on device sensitivity and stability. Sensor calibration is shown to remain an issue with long‐term deployments (e.g. several weeks) but this can be ameliorated in the medium term with the use of novel device fabrication and packaging techniques.

The reported results indicate that is possible through careful choice of materials and fabrication methods to achieve near stable thick film reference electrodes that are suitable for use in solid state chemical sensors in a variety of different application areas.

The aim of this paper is to investigate the behavior of a new nanometric particle NTC thermistor paste and thick films obtained by screen printing.

Nanometric powder of NTC thermistors based on complex spinel was made by calcination of an oxide mixture and ultra fast ball milling. Characterization of the new powder was done on compacts sintered in different conditions. Segmented thermistors were screen printed on alumina substrata, dried and fired in a conveyor furnace at 850°C/10 min. Segmented thermistors were indirectly heated by a glass sealed heater placed between them in the middle. The system was put in a tube with a regulated air flow to serve as a volume thermistor sensor based on heat loss.

The sintered thick film samples and NTC powder compacts measurements could help in choosing the optimal technology conditions during the production of NTC devices. The NTC segmented thermistors were suitable both for heated sensors and self heated sensors.

Low temperature thick film thermistor pastes based on nanometer powder of complex spinel are of interest due to their importance in sensor applications.

This work predicts that high temperature pastes of the same material can be realized with characteristics superior to those of low temperature paste such as NTC 3K3 or similar.

The development of new, inexpensive, robust and miniaturised sensors is continuously being sought and it is believed that thick‐film technology can help to achieve these goals. A strain sensor utilising the piezoresistive properties of thick‐film resistors is described here. Characterisation of the sensing element has revealed that the gauge factor is significantly higher than that of metal foil strain gauges and the temperature coefficients are generally lower than those found for semiconductor strain gauges. Results show how the gauge factor can be optimised by varying the production parameters.

The purpose of this paper is to show how to obtain better response, selectivity and fast response and recovery from nanocrystalline ZnO‐based gas sensors as compared to conventional materials.

Nanocrystalline ZnO powders were prepared from the ultrasonic spray pyrolysis method. Aqueous solution of zinc acetate was atomized using ultrasonic atomizer. The aerosol generated was fed to the reaction furnace for pyrolysis. Nanocrystalline ZnO crystallites were collected using simple but novel trapping system. Thick film resistors of this powder were fabricated using screen printing technique.

As‐prepared powder was studied using X‐ray diffraction, transmission electron microscopy and scanning electron microscopy to know structure, size of nanocrystallites and microtopography, respectively. Absorption spectroscopy is used to determine the band gap energy. The gas‐sensing performance of this film was tested.

The sensor was found to be the most sensitive to NH₃. It gives better response, selectivity and fast response and recovery as compared to conventional materials‐based thick films.

An intelligent gas sensor has been developed using thick‐film techniques to create a semiconducting oxide surface with carefully varied catalytic properties. An integral heater causes the surface to react with combustible gases and the resulting resistance map of the surface forms a signature that can be related to the functional groups present in the gas. For example, alcohols, ketones and alkanes have distinct, recognisable signatures on one sensor model.