Search

Presented are the results of investigations of the effects of organic solvent vapours and excess noise measurements on drop-coated poly(vinyl butyral)\carbon black nanocomposite gas sensitive resistors. The devices were shown to exhibit significant resistance changes upon exposure to methanol, propanol and particularly hexanol vapours in the concentration range 1000 to 5000 ppm. The effects of the organic solvent vapours on the noise power spectra of the PVB\CB sensors were also investigated, but results were found to yield no information surplus to that of the DC sensor signal. The large values of 1/f noise observed were attributed to inhomogeneity and discontinuity of the deposited sensing layer. The discontinuity of the drop-coated layer was subsequently confirmed by SEM micrographs of the samples.

In this work, screen-printing onto glass and polymer substrates was used to form capacitors with an active area of 2 × 3 mm2. The dielectric was formed using a polymer paste with TiO2 as the functional ingredient. Devices prepared on glass substrates were tested as strain gauges. Their GF was measured to be 30. This is higher than the standard values (3–15) recorded for gauges based on oxide materials. It is thought that the higher sensitivity is a result of the preparation method and small crystallite size of the TiO2 powder. After quantifying the materials sensitivity, the sensors on polymer substrates were attached to planar and cylindrical surfaces. They were then incorporated into a wireless pressure measurement system, consisting of a small size interface circuit and a transmitter. The receiver outputs a voltage reading corresponding to the sensor capacitance. Each device was placed in a liquid environment so that it could be exposed to hydrostatic pressure. A high sensitivity to pressure changes with low hysteresis was observed. It is thought that this system could be used to wirelessly monitor pressure changes in a variety of difficult to reach environments.

This work investigates the effects of gamma-rays on the optical properties of pure and mixed-oxide materials, namely MnO and TeO2 for their possible application as thin film optical gamma radiation sensors. The values of the optical band gap Eopt were obtained in view of the Mott and Davis theory. All samples showed a decrease in Eopt with an increase in radiation dose to a certain level, which was found to be composition dependent. Films with 100 wt.% MnO exhibited the highest sensitivity to low doses of radiation, showing a strong decline in the optical band gap value from 0.64 eV before irradiation to 0.54 eV after a dose of 1.14 mGy. It was experimentally confirmed that both the sensitivity and the working dose range of radiation sensors can be controlled by the composition of the materials used

A prototype gamma radiation monitoring system based on In/sub 2/O/sub 3//SiO thick-film sensors array was designed. Four sensors had an identical pn-heterojunction structure with different material compositions. These sensors were subjected to gamma radiation emitted by /sup 137/Cs source with an activity of 370 kBq. Changes in their current-voltage characteristics were recorded and compared. The performance parameters of the devices, such as sensitivity to /spl gamma/ radiation exposure and working dose region, were found to be highly dependent on the composition of the materials used. To cover a wider range of radiation and improve the overall sensitivity, an approach of using sensor arrays was utilized. A dynamic selection of the multiple sensors of various sensitivities and working dose ranges was implemented by applying a pattern recognition analysis.

The 2-step negative resist image by dry etching (2-step NERIME) focused ion beam top surface imaging process is a novel nanolithography technique for creating nanometer scale resist features using conventional DNQ/novolak resists. We present 90nm resist critical dimensions (CDs) over substrate topography using the 2-step NERIME process. We also demonstrate, for the first time, fabrication of 80nm etched features masked using the 2-step NERIME process. The etched nanoscale features exhibit minimal line edge roughness and excellent profile control, and demonstrate the suitability of the 2-step NERIME process as a nanolithography technique for applications requiring nanometer CD and profile control.

This work investigates the use of NiO / Fe2O3 as a room temperature (RT) polymer thick film gas sensor. To find the optimum ratio of NiO to Fe2O3, three compositions were prepared using different molecular percentages (75 / 25, 50 / 50 and 25 / 75 M wt.%) and prepared as a thick film paste. These pastes were then screen-printed onto glass substrates with interdigitated silver (Ag) electrodes. The final composition of each film was determined using XRD analysis. The films were used to detect methanol, ethanol, propanol, toluene, acetone and tetrahydrofuran (THF) at RT. The response of each device was defined using the formula, (Rgas − Rair) / Rair) × 100, where Rair is the resistance of the film in air and Rgas is the resistance of the film after the exposure to gas vapours. For each composition tested, the highest responses where displayed for toluene and propanol. The sensitivity was determined as the first derivative of response. Their sensitivity to 8000 ppm of toluene was calculated to be 0.008%, 0.0058% and 0.0059% per ppm for compositions with 75 / 25, 50 / 50 and 25 / 75 M wt.% of NiO / Fe2O3, respectively. Their sensitivity to propanol was found to be 0.0030%, 0.0029% and 0.0027% per ppm for compositions in the same order as listed previously. The fastest response and recovery times of each device were found after the exposure to 4000 ppm of toluene and propanol at room temperature. Sensor fabricated using composition 75 / 25 M wt.% of NiO to Fe2O3 showed response/recovery times of 30 / 45 s for propanol and 40 / 48 s for toluene.

PurposeCombination of a number of sensors with different response parameters into sensor arrays would enhance the overall performance of the radiation detection system. This paper presents a conceptual approach to the development of sensor arrays system with instantaneous dose and dose rate readout. A dynamic selection of multiple sensors with various sensitivity and accuracy range is implemented by applying pattern recognition (PR) analysis, which maximizes measurement accuracy. A number of relevant PR methods are discussed.Design/methodology/approachThick films based on NiO, ZnO, In2O3, CeO2, TiO2, CuO and CdO are the key sensing elements in the proposed approach. Pure and carbon‐doped metal oxides were screen‐printed on Si wafers to form pn‐heterojunctions. All devices were exposed to a disc‐type 137 Cs source with an activity of 370 kBq. The values of radiation damage of pn‐junctions were estimated from changes in their current‐voltage characteristics.FindingsSensors showed an increase in the values of current with the increase in radiation dose up to certain levels, exceeding these levels results in unstable dosimetric characteristics.Originality/valueThe sensitivity of metal oxide films to γ‐radiation exposure depends on their composition and thickness. Mixing the oxides in different proportions and the addition of conducting particles, such as carbon, alters films susceptibility to radiation. In particular, sensors based on such films have dose response characteristics with certain level of sensitivity and working dose range, conditioned by particular sensing material properties and the device structure.

The aim of this work is to investigate the properties of gas sensors, with active layers that have been prepared by screen-printing. The active layers primarily consist of zinc ferrite (ZnFe 2 O 4 ), which was prepared using iron oxide (Fe 2 O 3 ) and zinc oxide (ZnO) as the raw materials. X-ray diffraction (XRD) was used to confirm the final composition of the powder while SEM was used to examine the grain size. Following this the ZnFe 2 O 4 powder was combined with NiO, TiO 2 , PVB and carbon black to form a thick film paste and deposited on glass substrates with interdigitated electrodes. The sensor was then interfaced with three resistors to form a bridge circuit. The films were used to detect butanol and pentanol in the concentration range 0–1000 ppm and hexanol from 0–250 ppm. The sensitivity of the devices to gas vapours was calculated as Δ V = ( V gas − V o ). The sensitivity increased with increasing gas vapour concentrations. The device showed its highest sensitivity to hexanol followed by pentanol, butanol, propanol, ethanol and finally methanol. The effect of the temperature on the sensitivity of the device to both propanol and toluene has been studied. The effect of adding TiO 2 and NiO to ZnFe 2 O 4 on the response and recovery times was also addressed.

Presented are the results of excess noise measurements on poly(vinyl butyral)\carbon black nanocomposite gas sensitive resistors. The devices were prepared by a drop-coating technique in which a microlitre syringe was used to deposit the materials onto Cu thin-film parallel electrodes. Noise power spectra of the devices under bias currents ranging from 80 to 150 μA were obtained. The detection limits were found to be 6.3 ppm, 5.2 ppm and 68 ppb for methanol, propanol and hexanol vapour, respectively. The noise index was also evaluated for the devices, with a value of approximately 29 dB being measured.

This paper investigates the use of iron and zinc oxide thick film materials, screen-printed onto glass substrates with silver electrodes. The sensor was interfaced with three resistors to form a bridge circuit. This was then used to detect methanol, ethanol and propanol vapours within a concentration range of 0–3000 ppm. The sensitivity of the sensor is defined as the change in bridge output voltage (mV) per change in gas concentration (ppm). The sensitivity of the sensor to 3000 ppm methanol, ethanol and propanol at room temperature was 3.5, 6.6, 22 μV/ppm while the relative resistance change of the sensor was calculated as (Δ R / R ) × 100 and was 0.84, 2.5 and 5.2, respectively. The device exhibited the highest sensitivity to propanol, followed by ethanol and methanol, respectively. The recorded sensitivity decreased when the temperature was increased from room temperature 25 to 65 °C. The response/recovery times of the sensor to 1000 ppm propanol were seen to improve with increased temperature, being 45/90 s at 25 °C and 22.5/45 s at 65 °C.

The aim of this work is to investigate the feasibility of the use of titanium dioxide (TiO2), zinc oxide (ZnO), copper oxide (CuO) and Cadmium oxide (CdO) in the development of thick film gamma radiation sensors with instantaneous dosage readouts. A number of pn-heterojunctions with various compositions of sensitive layers were formed by screen printing the thick film pastes on silicon wafers. All these devices were exposed to a disc-type 137Cs source with an activity of 370 kBq. It was found that for all samples the values of leakage current increased with increasing radiation dose.

The cruel reality of today's world forces mankind to be alert and prepared for all kinds of terrorist threats, including exposure to radiation. There is a need for cost-effective alternatives to existing commercially available real-time gamma radiation dosimeters. In this paper, numerous oxides such as NiO, CeO/sub 2/, TeO/sub 2/, In/sub 2/O/sub 3/, SiO, MnO, etc., and their mixtures in different proportions were used as the basis for such a substitute. Thin- and thick-film devices were made in the form of resistors and capacitors, structures with interdigitated electrodes, and pn-junctions. These, in different mixtures, were found to change their sensitivity when exposed to /spl gamma/-rays. In general, thin-film devices were found to be more sensitive to lower doses of radiation than the counterpart thick films. However, it was experimentally demonstrated that it is possible to fabricate a device that would satisfy the requirement of a particular application, such as the sensitivity to /spl gamma/-radiation exposure and working dose regions. Based on the above data, these structures might be regarded as a cost-effective alternative for room-temperature real-time /spl gamma/-radiation dosimetry.

In this work the strain sensing properties of interdigitated and sandwich thick film capacitors, using titanium dioxide as the dielectric, are investigated. By pre-firing the TiO 2 powder and forming a polymer thick film paste the use of expensive paste ingredients, such as ruthenium or palladium oxide, was avoided. After firing, XRD was used to verify the composition and crystallite size of the TiO 2 powder, while SEM allowed the particle sizes of the powder to be examined. It was found that the powder has a crystallite and particle size, which is less than 1 μm. Following this, the sensors were fabricated by screen-printing onto glass substrates and placed in a cantilever beam arrangement so that the change in their capacitance with strain could be measured. The gauge factor, which demonstrates the devices sensitivity, was found by dividing the fractional change in capacitance by the applied strain. A gauge factor of 5 and 30 was recorded for interdigitated and sandwich capacitors, respectively. In the case of sandwich capacitors, this gauge factor is higher than normally achieved using oxide films (3–15). Furthermore, the sensors showed a high degree of linearity with low hysteresis. The TCC has been measured for temperatures ranging from 25 to 70 °C so that the effect of temperature on the devices is known. Values, typical of thick film capacitors (876–2834 ppm/°C) have been recorded for temperatures up to 60 °C. Finally, ac electrical measurements have been used to shown that tunnelling is the dominant conduction mechanism within the TiO 2 film.

Telemetry capsules have existed since the 1950s and were used to measure temperature, pH or pressure inside the gastrointestinal (GI) tract. It was hoped that these capsules would replace invasive techniques in the diagnosis of function disorders in the GI tract. However, problems such as signal loss and uncertainty of the pills position limited their use in a clinical setting. In this paper, a review of the capabilities of MicroElectroMechanical Systems (MEMS) and thick film technology (TFT) for the fabrication of a wireless pressure sensing microsystem is presented. The circuit requirements and methods of data transfer are examined. The available fabrication methods for MEMS sensors are also discussed and examples of wireless sensors are given. Finally the limitations of each technology are examined.

Throughout this work radiation-induced changes in the optical, electrical and structural properties of mixed and carbon filled metal oxides were studied. Oxides such as NiO, CeO2, TeO2, In2O3, SiO and MnO in the form of thin and thick films were used. The properties of the materials undergo changes by the influence of γ-rays. The degree of these radiation-induced changes serves as a measure of received radiation dose. Deep understanding of physical properties of the materials under the influence of radiation is vital for the effective design of dosimeters. In this work all films were exposed to a disk-type 137Cs source with an activity of 370 kBq. Carbon filling and mixing oxides in various proportions was found to control the properties of semiconductor films in terms of their susceptibility to radiation exposure. For example, planar NiO thick film structures with Ag interdigitated electrodes showed an increase in the values of current with the increase in radiation dose up to 171 μSv. Doping of NiO thick films with 0.1 wt.% of carbon resulted in larger increments in the values of current and the increasing the working range to 2720 μSv. The possibility to fabricate a device that would satisfy the requirement of particular application, in this case the sensitivity to γ-radiation exposure and working dose region, was experimentally demonstrated.

In recent years, number of studies investigating the use of capacitance effects in mechanical transducers has been undertaken. It was found that changing the dimensions of the chemical constitution of the dielectric material could change the nominal value of the parallel plate. This fact has been used to develop sensors that measure quantities such as strain, acceleration, gas concentration, humidity, etc. [1] . This paper is focused on developing a low-cost pressure sensitive device using thick film technology. The paper illustrates the original design specifications and how the sensor and signal conditioning circuitry performed against expectations. One of the design constrains was ensuring the operation of the sensor in a hostile operating conditions. Several device configurations were made based on both commercial Cermet and a PZT pastes. The relative performance of these materials as a dielectric-sensing element is compared in terms of their sensitivity, repeatability, and hysteresis. An efficient signal conditioning circuitry has been developed. The purpose of the circuitry is to allow the interface to make control decisions based on accurate stable pressure readings obtained by at the circuit. In this paper, the full system design of the pressure sensor and compensation circuitry was considered.

The effect of surfactants on the properties of poly(vinyl acetate) (PVAc)/carbon black (CB) composite gas sensors was examined. Percolation curves of the composites with and without surfactant were prepared. The percolation curves of surfactant treated composites showed that the resistivity of the composite was increased due to better dispersion of the CB and also the prevention of the CB from reagglomerating after shear mixing. TEM images were used to investigate the effect of adding surfactant to the composites. These images confirmed that the surfactants significantly improved the level of dispersion of CB in the composites and prevented reagglomeration of the CB. The response (ΔR/R%) was increased by addition of surfactants and implies that increased dispersion increases response to methanol vapour.

Zinc and iron oxide thick film gas sensors were fabricated using screen-printing technology on glass substrates that had silver interdigitated electrodes. The sensor was used to detect methanol, ethanol and propanol with a concentration range of 0–8000 ppm. Using the formula to calculate a change in resistance, ΔR = Rgas − Rair, resistance was seen to increase linearly alongside increasing concentrations of the gas vapours. The sensor showed the highest sensitivity to propanol followed by ethanol and methanol when the operating temperature was 25 °C. The sensitivities (slope of graphs) of methanol, ethanol and propanol changed from 0.07, 0.5, and 3.54 to 0.075, 0.115, and 0.5 Ω/ppm when the operating temperature was increased from 25 to 50 °C. The response/recovery times of the sensor for 4000 ppm at room temperature were, 10/10, 15/20 and 40/70 s for methanol, ethanol and propanol, respectively. X-ray diffraction (XRD) was used to examine the final composition of the film, while scanning electron microscopy (SEM) was used to examine the final composition of grain size. The final composition has two phases: ZnO and ZnFe2O4

Finely-focused ion beams can be applied for advanced lithography, which provides some advantages over the conventional direct-write electron beam technology. In the focused ion beam technology, however, the ion penetration depth is limited, thus requiring the use of extremely thin resist layers or higher ion acceleration energies. These requirements are often undesirable for the current IC manufacturing processes. One solution to this problem is to exploit the top surface imaging (TSI) technique for dry developed FIB lithography schemes. In this paper, we investigated the novel lithography process, which combines focused Ga^+ ion beam (Ga^+ FIB) exposure, silylation and oxygen dry etching. The negative resist image by dry etching (NERIME) is a TSI scheme for DNQ/novolak based resists and can result in either positive or negative resist images depending on the extent of the ion beam exposure dose. The mechanism of the negative image formation in the NERIME was studied by TEM, and found to be mainly due to the creation of a thin gallium oxide layer during the oxygen dry development. The energy dispersive X-ray spectrometry microanalysis has found that gallium was implanted into the SPR660 resist to a depth of 50nm and the oxidised gallium layer has a thickness of approximately 15nm. It is also shown that the NERIME process can resolve nanometer resist patterns down to 65nm and yet maintaining a high aspect ratio. The NERIME process could be a useful nanofabrication method alternative to the current lithography processes.

This paper investigates the use of NiO particles to enhance the vapour sensing properties of polyethylene adipate (PEA)\carbon black (CB) composite materials. Four PEA\CB suspensions were prepared with 0, 10, 20 and 30 w/w% NiO, respectively. Hypermer PS3 surfactant was shear mixed into each of the suspensions for 300 s to achieve a homogenous dispersion and to prevent reagglommeration of both the CB and NiO particles. A 0.1 μl drop of each composite was deposited between Cu electrodes on a printed circuit board (PCB) substrate using a microlitre syringe. The samples were allowed to dry for 24 h in an oven at 333 K to remove any remaining solvent. After preparation, the sensors were exposed to propanol and butanol at concentrations ranging from 0 to 25 000 ppm in steps of 5000 ppm. The response of the PEA\CB sensors improved significantly as the concentration of NiO particles in the material increased and maximum relative differential responses as high as 37% and 92.8% were recorded after exposure to 25 000 ppm propanol and butanol, respectively. This high response can be explained using the Flory–Huggins interaction parameter along with structural changes in the polymer composite caused by the addition of NiO. This paper concludes that NiO particles can be used as a method to increase the sensitivity of existing conducting polymer composite gas sensing materials.

The development of a sensor microsystems containing all the components of data acquisition system, such as sensors, signal‐conditioning circuits, analog‐digital converter, interface circuits and embedded microcontroller (MCU), has become the focus of attention in many biomedical applications. A review of the microsystems technology is presented in this paper, along with a discussion of the recent trends and challenges associated with its developments. A basic description of each sub‐system is also given. This includes the different front end, mixed analog‐digital, power management, and radio transmitter‐receiver circuits. These sub‐system designs are presented and discussed in a comparative study and final remarks are made. The performance of each sub‐system is assessed regarding many aspects related to the overall system performance.

Numerous efforts were devoted to investigating the influence of radiation on metal oxides and polymer materials for dosimetry applications. Metal oxides, such as NiO, LaFeO/sub 3/, CeO/sub 2/, TeO/sub 2/, In/sub 2/O/sub 3/, SiO and MnO, and polymers, such as CuPc, NiPc, MnPc and CoPc, were used as the active constituents in the fabrication of /spl gamma/-radiation sensors. Thin and thick film devices were made in various topologies to form resistors, capacitors, pn-junctions and transistors. It was found that the properties of the active films (and, hence, their sensitivity to radiation) could be controlled by doping their constituent materials with carbon and mixing them in different proportions. The /sup 60/Co and /sup 137/Cs sources were used to expose the samples to /spl gamma/-radiation. Current-voltage characteristics, optical absorption spectra, Raman spectra, SEM and XRD measurements were recorded for the samples after each exposure procedure and values of radiation damage were estimated. Thin film devices were found to be more sensitive to radiation than their thick film counterparts. Annealing was used to restore the properties of thick film devices after they were damaged with radiation. Thick films could be therefore reused on a repeatable basis, but thin film devices could not, as the heat treatments necessary for annealing were found to cause diffusion of the electrode materials. In this work, the possibility of fabricating a device that would satisfy the requirement of a particular application, such as sensitivity to /spl gamma/-radiation and working dose region, was experimentally demonstrated. Based on the findings, these devices were found to provide a cost-effective alternative for room temperature real time /spl gamma/-radiation dosimeter applications.

Investigations into γ-radiation-induced changes in the electrical properties of CeO2 thick films of various structures were carried out for dosimetry purposes. The detection of radiation was based on the fact, that properties of the materials undergo changes upon the influence of γ-radiation. Carbon doping was used to control the resistivity of the CeO2 polymer thick films. Screen-printed capacitors, resistors and pn-junctions were exposed to a disc-type 137 Cs source with an activity of 370 kBq. All devices showed an increase in the values of current with the increase in radiation dose up to a certain level. Capacitors could be recommended for high-dose applications, as they showed consistent changes in conductance and capacitance values with an increase in radiation dose up to 6.12 mSv. Resistors doped with 0.2 wt.% of C showed gradual increase in the values of current with the increase in dose up to 4.42 mSv, whereas resistors with 0.5 wt.% of C sustained a lower dose of 1.7 mSv and were damaged on further exposure. pn-Junctions formed with CeO2 films, printed on single side polished P〈1 0 0〉 silicon wafers, exhibited the most sensitivity to γ-radiation. They showed significant increase in the values of leakage current with the increase in dose up to 0.57 mSv and are therefore suitable for low-dose dosimetry applications.

Throughout this work oxides are considered as appropriate cost-effective materials for radiation sensing. Thin films of TeO2, In2O3 and SiO and their mixtures were used in this study for the fabrication of pn-junctions. The detection of radiation is based on the fact that properties of the materials undergo changes by the influence of γ-rays. A number of various pn-junctions were made that differ in their materials composition. All the devices were exposed to 60 Co or 137 Cs radiation sources and their current–voltage (I–V) characteristics were examined. Samples made with p-type material (TeO2) and n-type oxides mixture (50 wt.% of In2O3 and 50 wt.% of SiO) showed clearly pronounced pn-junction behaviour. However, the response of these devices to radiation was not consistent as samples were too susceptible to environmental conditions. Devices based on TeO2/In2O3 oxide materials mixtures (p-type) and sulphur (n-type) were more stable and exhibited Zener diode behaviour. It was found that devices with a mixture of 90 wt.% of TeO2 and 10 wt.% of In2O3 have sustained a higher breakdown voltage compared to those with pure TeO2. To improve the stability of the devises response, a number of pn-junctions were manufactured on Si wafers. Samples with TeO2/Si and (In2O3+SiO)/Si configurations were tested. An increase in the values of current with the increase in radiation in a certain dose range makes these devices suitable for dosimetry purposes.

A focused-ion-beam (FIB) machine is a versatile tool used extensively in the integrated circuit (IC) industry for conducting failure analysis, prototype fabrication, and device repair. Lithography can also be performed using FIB for direct patterning of photoresists without using a mask. The FIB technique has several advantages over other maskless processes, such as direct-write e-beam lithography; ion-beam patterning of the photoresist offers higher resist sensitivity and lesser backscattering/proximity effects than the e-beam patterning. In this paper, we investigated a new FIB lithography process, called NERIME (negative resist image by dry etching). The NERIME process is a single-layer resist scheme, which implements a Ga+ FIB exposure of DNQ/novolak-based resists, followed by a near-ultraviolet (NUV) flood exposure, silylation, and oxygen dry etching. The NERIME process could not only yield both positive and negative images, but also achieve a nanometer resolution down to 65 nm and a high aspect ratio for the processed patterns. The principle of the negative image formation was also investigated by TEM and found to be due to the creation of a thin gallium oxide mask layer during etching. The NERIME process could be utilized for specific CMOS processing steps for the next generation technology nodes, such as high-resolution lithography over topographical surfaces.

This paper reviews the range of sensors used in electronic nose (e‐nose) systems to date. It outlines the operating principles and fabrication methods of each sensor type as well as the applications in which the different sensors have been utilised. It also outlines the advantages and disadvantages of each sensor for application in a cost‐effective low‐power handheld e‐nose system.

Throughout this work tellurium dioxide (TeO2), indium oxide (In2O3), silicon monoxide (SiO), nickel oxide (NiO) and LaFeO3 perovskite and their mixtures in different proportions in the forms of thin and thick films were used as materials for the radiation sensing layers. Detection of radiation was performed based on the fact that both electrical and optical properties of the materials undergo changes upon the exposure to gamma radiation. It was found that the optical band gap values decreased with the increase in radiation dose. Influence of radiation resulted in significant alterations of current–voltage characteristics in both thin and thick film devices.

This paper discusses the digital hardware and software that is required for data acquisition in a portable electronic nose (e‐nose) system. A review of current e‐nose systems is presented highlighting the methods employed by these systems to acquire the data from the sensor head.

Thin films of tellurium dioxide (TeO/sub 2/) were investigated for /spl gamma/-radiation dosimetry purposes. Samples were fabricated using thermal evaporation technique. Thin films of TeO/sub 2/ were exposed to a /sup 60/Co /spl gamma/-radiation source at a dose rate of 6 Gy/min at room temperature. Absorption spectra for TeO/sub 2/ films were recorded and the values of the optical band gap and energies of the localized states for as-deposited and /spl gamma/-irradiated samples were calculated. It was found that the optical band gap values were decreased as the radiation dose was increased. Samples with electrical contacts having a planar structure showed a monotonic increase in the values of current with the increase in radiation dose up to a certain dose level. The observed changes in both the optical and the electrical properties suggest that TeO/sub 2/ thin film can be considered as an effective material for room temperature real time /spl gamma/-radiation dosimetry.

The overall performance of an electronic nose system will depend on the individual performance of its constituent elements. Although often overlooked, it is clear that careful design/selection of the front‐end signal conditioning circuit is of critical importance if optimal performance of the odour sensing system is to be achieved. In this paper circuits are reviewed, which have been employed as front‐end signal conditioners for resistance‐based sensors in electronic nose systems, with many of the conclusions drawn being equally applicable to other resistor sensors. The relevant equations governing the behaviour of each circuit methodology are derived and advantages and disadvantages are discussed. The performance of the circuit is then quantitatively assessed in a specific test case, in which the maximum sensitivity of the circuit is calculated in relation to the task of interfacing to a theoretical thin‐film conducting‐polymer sensor.

Top surface imaging (TSI) is an established technique that can be used to improve resolution in optical, ultraviolet and electron-beam lithography into the nanometer region. This paper describes a novel top surface imaging process, which incorporates ion-beam exposure, silylation and dry development, and can support nanometer resolution. The negative resist image by dry etching (NERIME) process is a TSI scheme for DNQ/novolak based resists and can result in either negative or positive resist image depending on the processing conditions. Results show that focused Ga+ ion-beam exposure with a dose in the range of 1-50 µC cm-2 at 30 keV can successfully prevent silylation of the resist, thus resulting in the formation of positive image after the dry etching. A negative image can be formed by using a second ion-beam exposure with a dose higher than 900 µC cm-2 at 30 keV to pattern lines into the original exposed resist area. The NERIME processed patterns down to 0.1 µm have been formed in Shipley SPR505A resist, and exhibit highly vertical sidewalls due to the ion-beam exposure and oxygen dry development. Results show that this novel TSI scheme could be successfully applied for fabrication of critical CMOS process steps, such as deep isolation trench formation and lithography over substantial topography.

Thin films of tellurium dioxide (TeO2) and indium oxide (In2O3) mixtures were investigated for γ‐radiation dosimetry purpose. Samples were fabricated using thermal vacuum evaporation technique. The electrical properties of mixed oxides thin films [(TeO2)1−x(In2O3)x, where x=0 and 10 per cent by weight] and their changes under the influence of γ‐radiation were investigated. Samples with contacts having a planar structure showed increase in the values of current with the increase in radiation dose up to a certain dose level. Thin films in the form of pn‐junctions were fabricated with (TeO2)1−x(In2O3)x as p‐type material and sulphur as n‐type material. These pn‐junctions exhibited Zener diode behaviour. The current‐voltage characteristics for as‐deposited and γ‐irradiated samples were recorded. The level of response for all the fabricated devices was found to be highly dependent on the composition of the exposed material.

The effects of γ‐radiation on both the optical and the electrical properties of Tellurium dioxide (TeO2) thin films were investigated. TeO2 thin films were fabricated using thermal vacuum deposition method. Samples were exposed to a 60Co γ‐radiation source with a dose rate of 6 Gy/min. Absorption spectra for TeO2 thin films were recorded and values of the optical band gap for as‐deposited and γ‐irradiated films were calculated. Sets of measurements based on Hall effect were carried out. From the data received the dependences of sheet resistance, density of charge carriers, mobility and Hall coefficient with radiation dose were determined.

PRIME process with I-line Shipley SPR505A resist was investigated using both simulations and experiments. Modelling of the PRIME process steps for 50-nm lines/spaces grating and 30-nm single line is shown. The liquid-phase silylation step in PRIME with SPR505A resist was experimentally characterised using FT-IR spectroscopy, UV spectroscopy and SIM spectrometry. The silylation agent used was hexamethylcyclotrisiloxane. The results show case II diffusion behaviour of the silicon incorporation in the SPR505A resist. The silylation contrast of the process as determined by the ratio of the silicon uptake in the near UV exposed over e-beam crosslinked regions was found to be 5 to 1.

The results of a statistical design of experiment (Taguchi analysis) study to investigate the factors involved in the preparation and firing of Mn–Zn ferrite components are presented. To relieve cracking, a pressing pressure of no more than 150 MPa was beneficial. Addition of a binder was necessary for complete crack free components. Ferrite formation was achieved at high temperature under all conditions or at low temperature in a vacuum. It was found that the components had to be fired at a high temperature to achieve densification. Resistance was very low for samples fired in vacuum, but quite high when fired in air. A permeable material only occurred when the ferrite was fully formed. The isothermal duration is important to the magnetic properties; a longer time reduces permeability dramatically. The use of alumina as substrate and enclosure was shown to lead to zinc loss and should be avoided. Zinc loss caused a reduction in the materials permeability but was shown to have no effect on resistivity. The designing of experiments, using a statistical approach, was shown to be very effective in studying the effects and interactions of the various process factors.

Manganese phthaloyanine polymer thick films were fabricated using screen-printing techniques. The optical parameters were obtained from the analysis of the absorption spectra over a wavelength range of 385-900nm. The d.c. electrical measurements were carried out in a range of 0-30 volts. The effects of γ-radiation on the optical and the electrical properties were investigated for dosimetry applications. The optical energy band gaps of these films showed a decrease in their values with the increase in the radiation dose. The electronic transition has changed from direct allowed for the as-printed films (unexposed to γ-rays) to indirect allowed for the irradiated samples. Both the as-printed and irradiated Ag/MnPc/Ag devices demonstrated a Schottky conduction mechanism. Both the absorbance and the capacitance of the MnPc thick films displayed a highly consistent linear response to γ-ray exposure. Keywords: Optical band gap, γ-rays, Dosimetry, Manganese phthalocyanine, MnPc Introduction

The investigation into a novel thick film material, a combination of MnO, ZnO and Fe 2 O 3 , is documented for humidity sensing applications. To date, no other accounts using this combination for humidity sensing have been reported in the literature. Different paste preparations have been investigated in full, including the effect of increasing polymer content for the polymer samples, and the effect of different firing profiles for the cermet samples. RuO 2 has been considered as a method for improving the conductivity of the samples. DC and AC conduction studies have been carried out on different polymer and cermet pastes. From the AC conduction studies, it is confirmed that electronic tunnelling is the dominant conduction mechanism. From the DC conduction studies, space charge limited conduction has been observed. A large number of sensor samples have been manufactured and tested. The fabrication and characterization of three typical sensor samples is presented and discussed in this paper, sample 1: vacuum-fired cermet sensor, sample 2: air-fired cermet sensor and sample 3: 10:1 polymer sensor. The sensor pattern consists of an interdigitated conductor on top of which a 30 μm thick sensing layer is printed using screen-printing technology. The thermal effect of the sensors is quite low, ranging from a minimum of 0.0037%/°C (sample 1) to a maximum of 0.0085%/°C (sample 3). In comparison, the measured humidity sensitivity values are much higher, ranging from 0.0356%/RH% (sample 1) to 1.697%/RH% (sample 2). All the samples exhibit a low drift over a 1 year span, low hysteresis, high linearity and reasonably fast response times.

In this work, air core and ferrite core polymer transformers were developed using polymer thick film screen-printing technology. These transformers were printed on 5 × 5cm alumina substrate. The magnetic core material was home-made high permeability Mn–Zn ferrite. An efficiency of 93% and a coupling factor of 0.9 at 500kHz were achieved. This transformer design has five primary turns connected in series and one secondary turn consisting of five turns connected in parallel, the primary and the secondary windings being fully interleaved. All the layers, including the magnetic (Mn–Zn), isolative and conductive layers of the transformers, are made from polymer paste materials. Due to their higher heat radiation, higher power density and lower profile over conventional transformers, these transformers can be used in DC–DC converters for switch mode power supply (SMPS) applications.

Miniaturization of high-efficiency switch-mode power supplies (SMPS) is limited by the size of passive transformers and coils that use large ferrite cores with magnet-wire windings. Fortunately, the availability of planar magnetic transformers and coils (thick and thin films) allows SMPS designers to achieve low-profile architectures that can be easily mounted on a printed circuit board (PCB). The transformer is the key to reduce the size and the cost of the SMPS. Reduction in the size and cost of the transformer can be achieved by changes in both the shape and topology. Improvements in manufacturing technology and reduction in material content can be made by increasing the operating frequency. In this work, polymer thick film transformer was fabricated using thick film screen-printing technology. Polymer base paste is used to print, the magnetic, isolation and conductor layers. The Mn–Zn ferrite material is used as a core material for this transformer. The efficiency for this transformer was measured to be 90% at a frequency of 500 KHz.

This paper investigates the effect of various process parameters on the variation in forward current gain lifetime caused by hot carrier generation of BiCMOS bipolar transistors. Statistical process control and statistical designed experiments were used in this evaluation. The device lifetime in reverse bias operation was calculated from the forward current gain. Various process parameters were examined in this work, i.e., the intrinsic base implant dose and energy, selective collector implant dose, collector plug dose, spacer etch ratio, overetch thickness of nitride spacer and emitter poly etch time. It was deduced that high current gain lifetime can be obtained with high base implant doses, high base implant energies, long bulk nitride etch times and short emitter poly etch times.

The necessity for size decrease in power electronics systems has pushed the operating frequency of these systems into the MHz range. The operation of these systems in the MHz range introduces a number of problems such as excessive coreloss, the skin effect and the proximity effect. In this work, a new high efficiency coreless transformer has been developed using polymer thick film technology, to overcome the coreloss at high frequency. The coils of the transformer are arranged coaxially in two configurations, (1) as a one-layer structure and (2) as two series connected layers in a sandwich structure. The operating principle of this transformer is based on the skin and mutual effect between the coils at high frequency. The copper electroplating process was implemented since an upper limit exists on the thickness of the conductor due to the skin effect under high frequency operation. The well-defined geometry of this thick-film planar transformer renders the parasitic interwinding capacitance and the leakage inductance reproducible. The experimental work performed shows that the polymer thick-film transformer exhibits a low interwinding parasitic capacitance, a high coupling factor of 98% at 9 MHz and shows a maximum efficiency of 98.2% at 10 MHz depending on the load condition.

In this paper a novel strain gauge system on stainless steel and 96% alumina substrates is described incorporating a Wheatstone bridge network, thick-film piezoresistive strain gauges, instrumentation, and a novel thermal and resistor mismatch tolerance correction software. The resistors in the Wheatstone bridge are fabricated with a novel mixture of ruthenium, bismuth and indium oxides and three different thick-film layouts are used. Mechanical measurements are performed using the cantilever beam set-up. The linearity, hysteresis, repeatability, reproducibility, creep, stability and temperature effects are measured for the novel thick-film pastes. The linearity and temperature effect on the output of the different bridge layouts are also examined. The printing of resistors using thick-film technology can result in resistor tolerances of %. Also, thick-film piezoresistors are intrinsically cross sensitive to temperature. These two properties cause an offset voltage to appear at the output of the bridge under no-load/load conditions and a subsequent error in the calculated applied strain. In order to compensate for the offset error voltage, novel correction software has been developed and implemented using a microcontroller. The error in the predicted strain was measured before and after application of the correction software under different bridge layouts and temperature conditions. The error was reduced from a maximum of 45% to approximately 1%. The effectiveness of the correction software in reducing the error suggests that this technique can be used without the need for trimming or bridge balancing.

The electrical properties of fired thick film piezoresistive gauges based on composites of bismuth, indium, cerium and ruthenium oxides are presented. Various material characteristics are analysed, including DC and AC characteristics. The conduction mechanism before and after electroforming is also examined. Structural studies of the fired resistor layers, before and after high field application, are carried out, where evidence of filament growth within the thick film cermet materials is observed. The DC biasing of the MRM device into the negative resistance region shows the ability to produce spontaneous damped oscillations at frequencies up to 3 MHz using a suitable RCL network.

The physical and thermal properties of thick film planar piezoresistive gauges based on composites of bismuth, indium and ruthenium oxides are presented. Various strain gauge characteristics are analysed, including linearity, hysteresis, stability and reproducibility. It is shown that the strain sensitivity of the thick film gauges is directly dependent on the molar percentages of the pastes' functional ingredients, where the measured gauge factor increases from 7 to 17 with increasing Bi 2 O 3 content. Tests carried out on the thermal properties of the fired films exhibited negative temperature coefficients of resistance which, combined with other pertinent electrical and optical studies, indicate the dominance of hopping or tunnelling conduction at high fields.

Up to 70,000 known and emerging chemical, biological, and radiological contaminants may be present in various water resources. To assure the safety and quality of water and to guarantee the situational awareness of safe water supplies, efficient real-time measurement methods with superior sensitivity are required. Current measurement methods of pollutants are mostly based on off-line monitoring which implies low frequency data sampling, delays between sampling and results, and additional chemical use. In this study, a novel sensing system where the interaction of the electromagnetic field with the tested fluid reveals its composition is presented. In particular, it is suggested that microwave based sensors are a suitable technology to fulfill the requirement for a real-time water pollution monitoring platform. A prototype microwave sensor in the form of printed Cu pattern on FR4 substrate was designed and tested for its response to air, deionized water, 500 ppm phosphate solution, and cooking oil samples. This sensor operates based upon the interaction of the electromagnetic waves and the material under test, which manifests itself as a unique spectra as measured for each sample due to its specific permittivity. By considering how the reflected microwave signal (in a form of S11 parameter) varies at discrete frequency intervals, the change in the signal can be linked to the composition of the object under test.

The strain-sensing characteristics of thick-film polymer-based resistors printed and cured on 96% alumina are presented. Two layout configurations have been analysed: planar and sandwich. Various strain-gauge characteristics have been studied, including the mechanical and temperature-dependent properties of the polymeric films. It has been shown that the planar polymer resistors exhibit low sensitivity, comparable to that of metal-foil gauges, whereas the MRM (metal-resistor-metal) configurations exhibit similar characteristics to those of cermet thick-film MRM gauges. It has also been observed that the mechanical properties of the polymeric films are significantly poorer than those of cermet-based gauges. This degradation in performance is attributed to the epoxy/pseudo-plastic structure of the polymeric thick-film resistor layer.

The electrical properties of thick-film sandwich devices based on composites of bismuth, ruthenium and indium oxides are presented. The devices are shown to exhibit Poole-Frenkel bulk limited conduction in the temperature range 290 K to 393 K. The activation energies for the compositions were calculated at between 7-5 to 13meV, leading to the conclusion that hopping is the dominant conduction mechanism. After electroforming, the devices exhibited voltage-controlled differential negative resistance and an increase in the conductivity under atmospheric pressure conditions at between 2 to 2-5 orders of magnitude, indicating the possibility of producing memory-switching devices based on the thick-film metal-resistor-metal configuration.

In this paper, Statistical Process Control (SPC) and statistically designed experiments will be used to optimise a recently developed resist schemes i.e., PRIME ( Positive Resist Image by dry Etching ). Orthogonal experiments are designed and conducted in order to produce 0.2 μm lines repeatably in PLASMASK 302U resist. Design rules of 0.1 μm are used due to proximity effects. The data is then explored and analysed using surface plots, boxplots, analysis of variance (ANOVA) and linear regression. It was deduced that e-beam dose and 2nd step etch time were the most significant parameters in the process. Linewidth of 0.2 gm and below were achieved with low values of e-beam dose (250–350μC/cm 2 ) and high values of silylation temperature (205–215°C). The optimum range for NUV flood dose was easily found.

The electrical properties of a thick-film sandwich device based on a metal-resistor-metal (MRM) structure are presented. A ruthenium-based resistor is sandwiched between two silver-palladium (Ag-Pd) electrodes. The conduction mechanism before and after electroforming is examined. The device exhibits Poole-Frenkel bulk limited conduction at high fields in the temperature range 290 to 393 K. The activation energy at high field and high temperature is estimated to be 4 meV, leading to the conclusion that hopping conduction takes place at high applied fields. The formed devices exhibit voltage-controlled differential negative resistance and an increase in the conductivity under atmospheric pressure conditions. The characteristics are similar to those observed in thin-film metal-insulator-metal (MIM) devices. However, the behaviour is not as pronounced, and this may be attributed to the increased resistor layer thickness. Les proprietes electriques des echantiillons couche epaisses en forme metal-resistance-metal (MRM) sont presentees. Un resistor d'un materiel base l'oxyde de ruthenium et avec les electrodes d'un alliage Ag-Pd est etudie. Le mecanisme de conduction avant et pres la formation electrique est examine et montre une conductibilite aux hauts champs qui suit la loi de Poole et Frenkel. Les mesures sont faites entre 290 et 393 K. L'energie d'excitation electronique aux champs eleves et aux hautes temperatures a une valeur 4 meV en accord avec le concept de ‘hopping’ aux ces champs eleves. Apres la formation on observe une resistance negative differentielle et une augmentation de la conductibilite sous pression atmospherique. Les effets sont comme observes avec les structures couches minces des isolateurs (MIM) quand I signifie l'isolateur, mais ne sont pas si grands que l'on observe avec un echantillon MIM.