Sensors and Actuators B 47 (1998) 171–180

A low-cost oxygen sensor fabricated as a screen-printedsemiconductor device suitable for unheated operation at ambient

temperatures

John Atkinson *, Andy Cranny, Cinzia Simonis de ClokeThick Film Unit, Department of Mechanical Engineering, Uni6ersity of Southampton, Highfield, Southampton SO17 1BJ, UK

Accepted 9 December 1997

Abstract

A novel sensor for the determination of atmospheric oxygen levels has been fabricated as a low-cost, screen-printed,conductimetric metal oxide film device. The sensor can be operated at ambient temperatures without recourse to heating of thesensing element and can employ simple detection circuits due to the relatively high level of conductance of the metal oxide films.High sensitivities to changes in oxygen concentration with good repeatability are reported. Device cross-sensitivity to theenvironmental parameters of temperature and humidity have also been investigated. © 1998 Elsevier Science S.A. All rightsreserved.

Keywords: Oxygen sensor; Thick film sensors; Tin oxide

1. Introduction

The use of semiconducting metal oxides in the fabri-cation of conductimetric gas sensors has been exten-sively documented [1,2] in the context of the detectionof a wide range of flammable and toxic gases. Despitethis vast amount of literature, however, there have beenrelatively few commercial implementations of this tech-nology. One reason for this is undoubtedly due to thedifficulty encountered with cross-sensitivity of the metaloxides.

Typically, sensors designed for specific analytes in-variably tend to have relatively strong cross-interfer-ences which severely limit their application where thebackground gases are not well defined. This cross-inter-ference stems from the mechanism of gas sensitivity inmetal oxide conductimetric sensors. Typically, thetarget analyte produces a change in the conductivity ofa metal oxide film by adsorption onto the film surfacein competition with previously adsorbed atmosphericgases, and in particular atmospheric oxygen.

In an n-type semiconductor such as tin oxide, theadsorption of atmospheric oxygen produces a depletionof electrons, which are the majority charge carriers, andhence the conductivity of the semiconductor decreases.This mechanism has been variously described [3,4] butis generally held to be due to ionosorption of theoxygen at the surface of the semiconducting film. If acompeting non-oxidising gas is selectively adsorbedonto a surface site such that the oxygen is desorbed,then the previously depleted electrons are returned tothe oxide film and the conductivity increases.

The device described here makes use of the aboveproperties of tin oxide films to determine levels ofatmospheric oxygen depletion. In this sense the devicecould be considered as a classic metal oxide sensorworking in reverse mode. Whereas most metal oxidegas sensors are generally doped with additives to pro-mote the selective adsorption of the target analytes overatmospheric oxygen, the device described here is delib-erately designed to be wide band in its response tocompeting adsorbed gases. For this reason the devicehas been fabricated as a high-purity tin oxide film.

The use of high-purity metal oxide films generallyresults in very low conductivity devices which renderpractical measurement circuits unsuitable for the detec-

* Corresponding author. Tel.: +44 1703 592616; fax: +44 1703594641; e-mail: jka@soton.ac.uk

0925-4005/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved.

PII S0925-4005(98)00020-3

J. Atkinson et al. / Sensors and Actuators B 47 (1998) 171–180J. Atkinson et al. / Sensors and Actuators B 47 (1998) 171–180172

Fig. 1. Schematic showing single electrode pair of sensor array.

Fig. 2. Schematic diagram showing the arrangement of the automated gas ring.

tion of the changes in conductivity typically encoun-tered. Even when doped with conductivity enhancingadditives, it is generally necessary to employ heatingof the metal oxide films to produce measurable valuesof conductivity. The devices described here, however,have been designed and fabricated to produce rela-tively high levels of conductivity without recourse tothe use of heating. Consequently, they require no ad-ditional power input and can utilise simple, low-costmeasurement circuits.

2. Experimental

2.1. Sensor fabrication

To be able to detect and measure any gas responseexhibited by a semiconducting metal oxide requires

that the conductivity of the oxide can somehow bemeasured. This is most easily achieved by electroni-cally measuring the resistance of a film of the oxidedeposited over a set of electrodes that should ideallyform an ohmic contact with the film. A fabricationtechnology capable of producing electrodes that meetsthis requirement and has proved itself in previous gassensor work is that of thick film printing [5,6]. Here,ohmic electrode structures are formed when thick filmpastes comprised of noble metal powders suspendedin a glass matrix are printed on an alumina substrateand subsequently fired at high temperatures, in excessof the glass transition point, thereby fusing theprinted material to the substrate. Gold is the prefer-able metal to use in the production of thick film elec-trode structures, though pastes comprised of othermetals or alloys can be used (e.g., platinum, plat-inum–gold).

J. Atkinson et al. / Sensors and Actuators B 47 (1998) 171–180J. Atkinson et al. / Sensors and Actuators B 47 (1998) 171–180 173

Table 1Dopant composition and processing parameters for several formulated tin oxide pastes

Paste CatalystAdditive Sintering temp. (°C) Sintering time (h) Firing temp. (°C)

— 1000P-1 2— 8501% InP-2 1% Pt 800 5 750

1% Pd 8001% Sb 5P-3 9501% Pd 1200 5P-4 7500.25% In0.25% Pt 1200 0.51% Sb 950P-5

Fig. 3. Response of differently doped tin oxide gas sensors to cycles of 60 min exposure to nitrogen and air at 0% RH. The dopant compositionsare given in Table 1. Gas flow rate: 0.5 l min−1.

A thick film gas sensor array has been designed thatconsists of five separate gold electrode pairs, each form-ing an individual sensor element when coated by agas-responsive film. It was decided to incorporate aplurality of sensors onto a common substrate as thisfacilitates batch testing of prototype sensor devices andimproves the device to device repeatability during theproduction process. Due to the inherent low conductiv-ities associated with semiconducting gas-sensitive mate-rials such as tin oxide, it is more usual to designelectrode structures that provide a large contact area toprovide measurements of sensor resistance over a prac-tical range. There is often a commercial requirement aswell that sensors be of small size. These two factorsmean that electrode structures usually take the form ofinter-digitated patterns where the opposing limbs of asingle electrode pair are interlaced either as simple stripelectrodes or as more complex branching structures.The latter form of inter-digitated electrode structurewas adopted for the sensor array design since thisexhibits the greater surface homogeneity. The sensorstructure is shown schematically in Fig. 1, with a trackwidth and spacing of 300 mm.

The sensor array was fabricated by sequentiallyprinting and firing a number of standard commercialthick film pastes as well as pastes purposefully formu-lated within our laboratories. The pastes were printedthrough patterned stainless steel printing screens usinga DEK 1202 precision screen printer. The pastes wereprinted on laser profiled 96% pure alumina substrates(Coors, ADSR96) and then dried in an infra-red drier(DEK model 1209) before being fired in a high-temper-ature belt furnace (BTU, model VQ41, six-zone) underan air atmosphere with temperature profiles set inaccordance with the paste manufacturers’ specifications.To produce the electrode patterns of the individualsensor elements, a cermet gold paste was used (ESL,8836). These were then terminated at their remote endswith a silver–palladium alloy paste (ESL 9635-C) toprovide an electrically conducting solderable contact.

Tin oxide pastes were produced in a format suitablefor printing and were deposited over the gold electrodestructures, using the same processing techniques previ-ously described, and were fired with a standard thickfilm temperature profile using a range of peak tempera-tures between 500 and 950°C. By suitably masking

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Fig. 4. Response of differently doped tin oxide gas sensors to cycles of 60 min exposure to nitrogen and air at 0% RH. The response for eachdevice is expressed as the percentage change in resistance from the initial value before the first gas exposure, and the dopant compositions aregiven by paste type in Table 1. Gas flow rate: 0.5 l min−1.

areas of the screen that defined the printed areas of tinoxide paste, it was possible to produce sensor arraysthat comprised more than one formulation of tin oxide.Generally, however, sensor arrays were fabricated usingthe same tin oxide paste on the individual elements.Once completed, the sensor arrays were ‘snapped out’from the alumina substrate which had been laserscribed to yield individual pieces of dimensions match-ing the size of a standard 28-pin dual-in-line integratedcircuit. Electrical lead frames of 0.1¦ pitch were thencrimped to the edges of the sensor array substrates andelectrically connected to the printed termination padsby solder reflow. With the lead frame suitably cropped,individual sensor arrays have the appearance and foot-print of a 28-pin DIL package.

2.2. Paste formulation

Various combinations of tin oxide pastes have beenproduced at the University of Southampton, with theirproduction generally following the same procedure.Firstly, 99.9% pure 325 mesh grade tin (IV) oxidepowder (Aldrich) is calcined in a box furnace at a peaktemperature of 1100°C for 8 h, with temperature riseand fall rates of 12.5°C min−1. The resulting material isfinely ground with an agate pestle and mortar and thispowder is then mixed with any dopants that are to beincluded on a percentage by weight basis. The dopantsconsist of high-purity metallic powders which are in-cluded in the tin oxide paste composition to serve eitheras a catalyst for oxygen detection or as additives toenhance the material conductivity. After further mixingand grinding, the composite powder is then sintered in

a box furnace with the same temperature profile asdescribed above, but with a peak sintering temperatureand sintering time dependant on the composition ofany dopants added. The sintered powder is then groundand sieved to produce a fine powder. To produce a highfiring temperature paste, the sintered powder is mixedwith a commercial thick film printing vehicle (ESL400). The vehicle is a proprietary mixture of solventsand organic binders that are completely ‘burnt out’during the paste firing process. The resultant pastes aretriple roll milled to promote even dispersion of thepaste constituents prior to their use and where neces-sary, thinned with terpineol.

2.3. Automated data acquisition system

In order to evaluate the performance of different tinoxide oxygen sensors, some form of gas handling ap-paratus is required that is capable of supplying pre-defined concentrations of oxygen to the sensor.Additionally, it is highly desirable that the experimentalconditions set by the gas handling apparatus are main-tained to a high degree of repeatability between succes-sive evaluations of different sensors, so that directcomparisons can be made between their responses. Forthese reasons, a fully automated gas rig was constructedas shown in Fig. 2, based on the authors’ previousexperiences with gas sensor testing [7]. Using this ap-paratus, specific oxygen concentrations over a range offlow rates can be achieved by diluting a pre-calibratedcylinder of dry laboratory grade air (20% oxygen) witha cylinder of dry nitrogen gas (oxygen-free). The dilu-tion is achieved under computer control by varying the

J. Atkinson et al. / Sensors and Actuators B 47 (1998) 171–180J. Atkinson et al. / Sensors and Actuators B 47 (1998) 171–180 175

Fig. 5. Response of pure tin oxide gas sensors to cycles of 30 min exposure to air and nitrogen at 100% RH, as a function of the tin oxide pastefiring temperature. Gas flow rate: 0.5 l min−1.

ratios of the separate gas flow rates of the individual gaslines. This is done using two mass flow valves (BrooksInstrument, 5850TR) that are controlled by a centralvalve control unit (Brooks Instrument, 5878) which inturn is controlled by a personal computer through adigital to analogue converter board.

Each of the individual gas lines is passed through aseparate gas-tight flask before being combined into asingle gas stream prior to entering the reaction vesselwhere the sensor array is housed. During such sensorevaluations when a humid gas stream is required, theseflasks are partially filled with deionised water. Thebubbling action of the gases passing through this wateris sufficient to raise the relative humidity of the com-bined gas stream to approximately 100%. At other timesthe flasks remain empty and the relative humidity of thegas stream is approximately equal to that of the cylin-dered gases, i.e., 0%.

The sensor array is held in a zero insertion force socket(ZIF) which is mounted on a printed circuit boardalongside the resistance measurement circuits required todetect a sensor element response. The use of a ZIFsocket to hold the sensor array allows for quick and easyinterchange of different sensor arrays. The ZIF socketand sensor array are completely surrounded by amoulded PTFE block which is used to create a gas-tightseal with a glass vessel which is fitted over them. Theglass vessel is fitted with entry and exit ports for the gasstream, and may be opaque or transparent for investiga-tions into photosensitivity. A temperature sensor hasbeen included on the circuit board and is located next tothe ZIF socket so that an accurate record of the gasstream temperature can be recorded.

Gas responses by tin oxide sensors take the form ofchanges in the sensor conductivity and thus changes intheir resistance. These resistance changes can be detectedelectronically by measuring the change in potential of asimple Wheatstone bridge circuit, comprised of thesensor and a load resistance. Since the load resistancehas no gas response, the value of its resistance shouldremain constant (at constant temperature) and thereforethe output voltage of the bridge circuit with a constantexcitation level will be directly proportional to theresistance of the sensor. Five simple resistive bridgecircuits such as this have been included on the circuitboard to measure the responses of the five individualsensor elements on a single array. The values of individ-ual load resistors for each bridge circuit are appropri-ately chosen based on the initial resistance values of thecorresponding sensor elements. The output voltages ofthe bridge circuits are measured by a high-inputimpedance digital multimeter (Keithley, model 2001)which is connected by a serial cable to the personalcomputer. The computer controls the measurementfunctions of the multimeter, including the rate of dataacquisition, and stores all the measured responses ondisk.

The software running on the personal computer thatcontrols the gas rig was written using TestPoint™. Thisis a Windows™-based, icon-controlled instrument pro-gramming environment that allows simple software to beconstructed to control computer peripherals and remoteintelligent instruments using both RS232 and IEEEprotocols without the need to write complex softwareinstrument drivers. This software package can alsohandle data management and storage, as well as offeringreal time graphical representation of acquired data.

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Fig. 6. Response of 0.5 wt.% antimony doped tin oxide gas sensors to cycles of 30 min exposure to air and nitrogen, showing the effect ofhumidity. Gas flow rate: 0.5 l min−1.

3. Results

3.1. Effects of dopants on sensor response

The effect of dopants in the form of catalysts andconductivity promoters on the oxygen response of tinoxide was evaluated by testing a number of differentpaste formulations printed as sensor elements on asingle sensor array. Previous research using Taguchimethods to determine statistically the significance ofvarious dopant materials and their processing require-ments on the response of tin oxide had yielded asuitable range of candidate paste formulations to evalu-ate [6]. These are summarised in Table 1. The sensorarray was exposed to alternating cycles of 60 minexposure to cylindered nitrogen gas (0% oxygen) fol-lowed by 60 min exposure to cylindered laboratorygrade air (20% oxygen) using the gas rig and automateddata acquisition system. The gas line humidifiers wereremoved from the apparatus so that the gas streamapproximated to 0% relative humidity. The evaluationwas performed at room temperature (21°C) and resultsare displayed in Figs. 3 and 4.

Fig. 3 shows the absolute resistance values of theindividual sensor elements of the array as they experi-ence the gas exposure cycles. The scale of the y-axismakes the interpretation of any oxygen responsedifficult, though clearly the act of including dopantmaterials within the tin oxide paste formulation has amarked effect on the conductivity of the films pro-duced, with measured resistances spanning six orders ofmagnitude. The pure tin oxide film shows the highestresistance (lowest conductivity) among the five pastes

evaluated for sensor elements of nominally the samedimensions. Variations in printed film thickness areexpected for different sensor elements on a single array,but these cannot entirely account for the disparaterange in observed resistance values.

In Fig. 4 the same information is presented but in adifferent format to emphasise any oxygen responses.Individual sensor resistances have been normalised andare expressed as a percentage change in value fromtheir initial resistance prior to exposure to any of thegases. The initial resistances are therefore measuredwhen the sensors are located in an environment wherethe relative humidity is at the laboratory ambient level.As soon as the dry cylindered gases are turned on, thisrelative humidity level rapidly drops towards zero andthe majority of the sensors tested respond to thischange with a concomitant decrease in their respectiveresistances. This is why the majority of the data dis-played appears as negative percentile changes in resis-tance, though again it can be clearly seen that thechemical composition of the dopants added has a dra-matic effect on the oxygen response.

The best oxygen response is obtained from the sensordoped with 1% indium as a conductivity promoter and1% platinum as a catalyst material (P-2). This deviceexhibits an appreciable increase in resistance with oxy-gen concentration and shows good repeatability as thebackground gaseous environment is cycled between ni-trogen and air. The pure tin oxide sensor (P-1) alsoshows a good oxygen response with reasonable re-peatability though this is somewhat masked by anoverall downward trend in the measured resistance as aconsequence of the tin oxide film responding to residual

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Fig. 7. Response of PVC membrane covered pure tin oxide gas sensors to cycles of 40 min exposure to nitrogen and air. Gas flow rate: 0.5 l min−1

at 100% RH.

humidity levels as the sensor slowly dries out over thecourse of the experiment. This residual humidity effectis also observed in sensor P-3, where a less sensitiveoxygen response is nearly completely masked. The tworemaining sensors (P-4 and P-5) show the least responseby comparison, but also appear to be the leasthumidity-sensitive.

3.2. Effect of paste firing temperature on sensiti6ity

The effect of the firing temperature on the oxygenresponse of pure tin oxide was investigated by firingsamples of this paste onto sensor arrays at three differ-ent peak temperatures but with otherwise the sametemperature profile and processing conditions. The re-sponses to alternating cycles of 30 min exposure tocylindered air (20% oxygen) followed by 30 min expo-sure to nitrogen gas (0% oxygen) at 100% relativehumidity and ambient temperature (21°C) are shown inFig. 5. Results are presented as percentage changes inresistance from initial sensor values determined duringa 30 min period prior to the start of the experiment,during which time the sensor array housing was flushedwith humid nitrogen gas to establish the background100% relative humidity level. The results show thatpure tin oxide films exhibit a good repeatable responseto variation in the background oxygen level when thehumidity is stabilised. The magnitude of the response,and hence the sensitivity of a device, increases with thefiring temperature of the paste, but at the expense of anincrease in the noise component of the measured signal.The results also show that regardless of the firingtemperature of the pastes, the sensors never reach a

stable resistance value in either their response or recov-ery within the time limits of the gas exposure periods.This implies that the 30 min exposure intervals are oftoo short duration for equilibrium conditions to occurbetween the concentration of surface adsorbed gas spe-cies with those in the surrounding gas phase.

3.3. Effect of humidity on sensor response

The effect of humidity on the oxygen response of tinoxide films doped with antimony to a level of 0.5% byweight, fired on gold electrodes at 550°C was investi-gated and results are shown in Fig. 6. The sensors wereplaced in the gas rig sensor array housing and subjectedto a number of cycles of 30 min exposure to cylinderedair followed by 30 min exposure to nitrogen at a gasflow rate of 0.5 l min−1. Both gas lines were bubbledthrough separate humidifiers to increase the relativehumidity of the gas stream toward 100% over theduration of the experiment. The humidity level withinthe sensor array housing was monitored throughoutusing a relative humidity probe (Measurement Instru-ments 8004). Individual sensor responses are expressedas percentage changes in resistance value from theirrespective initial resistances prior to the start of theexperiment.

Fig. 6 shows that the relative humidity level in thesensor array housing rises at an exponential rate, re-quiring at least 90 min to reach the 95% level from anambient level of 20%. The results also show that thepure tin oxide sensors have a strong dependency onhumidity, with resistances decreasing over the first twogas exposure intervals as the relative humidity ap-

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Fig. 8. Response of silicone membrane covered pure tin oxide gas sensors to cycles of 40 min exposure to nitrogen and air. Gas flow rate: 0.5 lmin−1 at 100% RH.

proaches approximately 90%. As the experiment pro-gresses, the sensors begin to show a response to thepresence of oxygen, albeit irreversible (within the timeframe of this experiment). During periods of exposureto air, the resistances of each device gradually rise asmore free surface adsorption sites are occupied byoxygen, whilst during the periods of nitrogen exposureno significant change in resistance is observed.

3.4. Effect of membranes on sensor response

One method of reducing the effect of uncontrolledhumidity levels on the response of tin oxide oxygensensors is to cover the sensor with an oxygen-permeablehydrophobic membrane. In addition to repelling watervapour from the sensor surface, this also acts as anoxygen diffusion control barrier, effectively buffering(or integrating) any sudden changes in oxygen concen-tration occurring on the atmospheric side of the mem-brane. Samples of the pure tin oxide paste were firedover gold electrodes at 550°C and coated with one ofthree different membrane materials to compare theireffects on the oxygen response as the relative humiditylevel in the gas rig sensor array housing is adjustedfrom ambient to 100%.

Fig. 7 shows typical results obtained from a pure tinoxide sensor covered by a screen-printed PVC mem-brane when exposed to 40 min cycles of nitrogen andair. The PVC membrane was formed by slowly dissolv-ing high molecular weight PVC (Fluka) in a 1:1 solu-tion of cyclohexanone (Fisons, 99.5%) andtetrahydrofuran (Fluka, 99.5%). This produced a gel-

like paste with good printing characteristics, whichcures at room temperature within 30 min. The resultsshow that the sensor demonstrates reasonably goodrepeatability in its response to oxygen and that thepreviously observed downward drift in resistance due tothe humidity rise over the duration of the investigationis no longer evident. However, a gradual upward trendin the resistance is observed, which may possibly arisedue to temperature changes occurring over the courseof the experiment.

The response of another pure tin oxide sensor, in anidentical experiment, that had this time been coatedwith a screen-printed silicone membrane is shown inFig. 8. The silicone material used was not intended foruse as a membrane material but was in fact an ultravi-olet curable one-part silicone potting gel designed forcomponent encapsulation and environmental protection(GE Silicones, EX17-A0884). The results show that thissensor–membrane combination still functions as anoxygen sensor though the response and recovery char-acteristics appear highly variable. This would suggestthat the oxygen transportation mechanism across themembrane is poorly defined in terms of repeatability.

In Fig. 9 the response of a pure tin oxide sensor to anumber of different concentrations of oxygen is shownfor a device spray coated with a PTFE membrane(MolyKote, PTFE-N). The different oxygen concentra-tions were achieved and maintained by the relativeblending of the individual flow rates of the air andnitrogen gas lines, whilst still maintaining a constantoverall gas flow rate of 0.5 l min−1.

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Fig. 9. Response of PTFE membrane covered pure tin oxide gas sensors to various concentrations of oxygen (shown by percentage) set throughblending cylindered air and nitrogen. Each exposure interval lasts 15 min with a combined gas flow rate of 0.5 l min−1 at 100% RH.

4. Discussion

4.1. Effect of dopants

The addition of either antimony or indium to tinoxide has been found to enhance the conductivity asshown in Fig. 4 (P-2–P-5) with antimony perhapsenhancing the conductivity more than indium. If theconductivity is increased too much, however, the gasresponse becomes swamped by the enhancing additive.This is demonstrated by the response P-5 in Fig. 4,which has no discernible gas response.

The addition of palladium as a catalyst seems to havehad little effect on the sensor response as evidenced byplots P-3 and P-4. By contrast, the addition of platinumdid noticeably enhance the oxygen response (P-2).

The best oxygen response overall was obtainedfrom the sensor made from pure tin oxide (P-1); how-ever, the resulting conductivity was the lowest obtainedfrom the sensors evaluated. This can cause problemswith measurement, in particular, giving rather noisysignals.

4.2. Effect of firing temperature

The effect of increasing the firing temperature was togive an increased sensitivity in the devices (as shown inFig. 5) at the expense of a slight increase in sensornoise. This increased response is probably due to con-tinued crystal growth in the tin oxide during firingproducing more surface adsorption sites.

4.3. Effect of humidity

Because tin oxide exhibits a cross-sensitivity to watervapour, it is important to attempt to control the rela-tive humidity levels within the operating atmosphere ofthe sensor. Although these type of semiconducting sen-sors have been demonstrated to respond to oxygen overa range of humidity levels, repeatability in response isonly realistically achievable in environments where therelative humidity level is maintained at a constantvalue. In certain applications this may be inherent as adirect consequence of the operating conditions, thoughin many areas the use of tin oxide as an oxygen sensormay have to be precluded if humidity control cannot beassured.

The results from using membranes with these sensorsshow PTFE to be an encouraging possibility. Clearly ameans for ensuring repeatability in the deposition ofthis material by screen printing or other methods willbe required before a low-cost ambient sensor can berealised as a fully screen-printed device.

References

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Biographies

John Atkinson began his career as a merchant navyradio and electronics officer in 1972. He graduatedfrom the University of Essex with a B.Sc.(Hons) incomputer engineering in 1981 and subsequently workedin industry in the area of computer pattern recognition.He is currently a Senior Lecturer in the Department ofMechanical Engineering at the University ofSouthampton and manager of the University’s Thick

Film Unit. His research interests include thick filmsensors, instrumentation, pattern recognition and sen-sor arrays.

Andy Cranny graduated from Coventry Polytechnicin 1985 with a B.Sc. in physics and received his Ph.D.in 1992 from Southampton University, where he ispresently employed as a Research Fellow. He is cur-rently working on electrochemical thick film sensors forthe determination of microbial contamination in bloodcultures.

Cinzia Simonis de Cloke is a member of the lecturingstaff of the Department of Mechanical Engineering atthe University of Southampton. Her first degree is inmechanical engineering which she obtained from SimonBolıvar University, Caracas, Venezuela in January1990. She obtained her Ph.D. from the University ofSouthampton in 1994 in the field of spine biomechan-ics, developing a kinematic methodology using parallelcomputation and videofluoroscopic X-ray images foranalysing spinal motion for diagnostic purposes.

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