The paper gives a review of the present knowledge of the piezoresistive properties of thick‐film resistors (TFRs) and shows how they have been exploited for the implementation of…
Abstract
The paper gives a review of the present knowledge of the piezoresistive properties of thick‐film resistors (TFRs) and shows how they have been exploited for the implementation of strain‐related physical‐quantities transducers. Two types of device are described in some detail. These achievements were made possible by a proper choice of resistive and conductive pastes and their firing conditions, since only in this case useful piezoresistive properties can be achieved that make TFR strain gauges competitive with metal and semiconductive materials. After examining some correlations between gauge factors, composition and structure of TFRs, new data are presented showing how the strain sensitivities may be changed by varying the peak firing temperature, dwell time and the nature of the chemical elements which diffuse from terminations in the films.
G.B. Parravicini, G. Samoggia, B. Morten and M. Prudenziati
A weak change of resistivity caused by visible radiation both for commercial and for model thick‐film (cermet) resistors (TFRs) has been observed and studied in the temperature…
Abstract
A weak change of resistivity caused by visible radiation both for commercial and for model thick‐film (cermet) resistors (TFRs) has been observed and studied in the temperature range 10–380 K. A possible origin of this photoelectric effect in terms of photoexcited electrons emitted from the metallic grain surface into the glassy region is discussed.
A. Bellardo and G. Lovati
The results of a characterisation carried out on thick film resistors (TFRs) with dimensions reduced below the usual limits are reported in this paper. The test vehicle was a…
Abstract
The results of a characterisation carried out on thick film resistors (TFRs) with dimensions reduced below the usual limits are reported in this paper. The test vehicle was a purpose‐designed test pattern with resistors whose dimensions reached a limit of 0·3 mm in length and 0·4 mm in width. The proposed aim of the work was to look for dimensional limits where TFRs could still give acceptable performances, though, if possible, keeping unchanged the materials system and the process conditions which are used in the authors' thick film hybrids facility.
B. Morten, G. De Cicco, A. Gandolfi and C. Tonelli
A study has been carried out on the relationship between the composition, poling condition and piezoelectric properties of thick film layers. Pastes based on…
Abstract
A study has been carried out on the relationship between the composition, poling condition and piezoelectric properties of thick film layers. Pastes based on lead‐titanate‐zirconate (PZT) powders, with either PbO or a lead‐alumina‐silicate glass frit as binder, were prepared. Microstructure, electrical and mechanical properties were analysed. Processing and poling conditions modify these properties; then a wide latitude of opportunities is offered in the choice of ferroelectric/piezoelectric characteristics of the layers used as sensing elements for sensors. A pressure sensor was realised where a circular diaphragm of alumina supports two piezoelectric layers obtained by screen printing and firing a PZT/PbO‐based ferroelectric paste. The design and the performance characteristics are described.
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…
Abstract
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.
Marko Hrovat, Darko Belavič, Jaroslaw Kita, Janez Holc, Silvo Drnovšek, Jena Cilenšek, Leszek Golonka and Andrzej Dziedzic
Aims to evaluate different thick‐film materials for use in strain sensors and temperature sensors on low‐temperature co‐fired ceramic (LTCC) substrates.
Abstract
Purpose
Aims to evaluate different thick‐film materials for use in strain sensors and temperature sensors on low‐temperature co‐fired ceramic (LTCC) substrates.
Design/methodology/approach
LTCC materials are sintered at the low temperatures typically used for thick‐film processing, i.e. around 850°C, The thick‐film resistor materials for use as strain and temperature sensors on LTCC tapes are studied. Thick‐film piezo‐resistors in the form of strain‐gauges are realised with 10 kΩ/sq. 2041 (Du Pont)and 3414‐B (ESL), resistor materials; thick‐film temperature‐dependent resistors were made from PTC 5093 (Du Pont), and NTC‐4993 (EMCA Remex) resistor materials.
Findings
The X‐ray spectra of the 2041 and 3414‐Bb low TCR resistors after drying at 150°C and after firing display more or less the same peaks. The electrical characteristics of 2041 resistors fired on alumina and LTCC substrates are similar indicating that the resistors are compatible with the LTCC material. After firing on LTCC substrates the sheet resistivities and TCRs of the 3414‐B resistors increased. Also, there is a significant increase in the GFs from 13 to over 25.
Originality/value
Investigates the compatibility of thick‐film materials and the characteristics of the force and temperature sensors.
Details
Keywords
R. Kužel, J. Broukal, V. Bouše and Z. Votruba
Copper substrates covered with ceramic insulating coating were tested for their ability to be used in thick film technology. The ceramic coating was prepared by screen printing…
Abstract
Copper substrates covered with ceramic insulating coating were tested for their ability to be used in thick film technology. The ceramic coating was prepared by screen printing from a dielectric composition containing special glass and aluminium oxide and was fired at 820°C–1,000°C. The electrical properties of the coatings studied included voltage breakdown, surface and bulk insulation resistance and dielectric constant. Resistor compositions designed for use on ceramic substrates were screen printed, as on the substrates mentioned, on alumina or ceramic‐coated steel substrates and fired up to the required temperatures (820–875°C). The resistivity and TCR of the prepared resistors were measured in relation to firing temperature. The distribution of lead, bismuth, ruthenium, barium, palladium, silver and copper in the system resistor (or conductor) ceramic coating/copper substrate was investigated. Reference was made to the application of ceramic coatings on copper in other fields, e.g., in heavy‐current electronics.
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…
Abstract
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.