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The paper reports the relative humidity (RH) sensing response of a resistive sensor employing oxidized carbon nanohorns - based sensing layer. The sensing layer is deposited on an interdigitated (IDT) structure, comprising a Si substrate, a SiO 2 layer, and IDT electrodes. The structure exhibits good RH sensitivity when varying RH from 0% up to 90%, either in humid nitrogen or in a humid air environment. The conductivity of the sensing layer decreases, while the RH level increases. During the interaction with the water molecules (acting as electron donors), the number of holes will decrease and oxidized single-walled carbon nanohorns (SWCNHs), considered normally p -type semiconductor, will become more resistive. The sensing mechanism is explained in terms of the Hard Soft Acid Base (HSAB) paradigm, building on the fact that water molecules are hard bases, while oxidized carbon nanohorns can be virtually assimilated with hard acids.

The paper demonstrates how the Hard-Soft Acid Base (HSAB) theory can be used as a valuable criterion in the selection process of semiconducting metal oxides (MOX) suitable as sensing layers for ammonia detection. Six different cases of ammonia detection performed by chemiresistive sensors employing MOX and related nanocomposites as sensing layers are identified and discussed. The role of HSAB as an efficient selection tool for appropriate sensing layer (any type of gas), is further reinforced by analyzing and discussing literature results on MOX-based trimethylamine sensing layers. By analyzing the operation of a fiber-optic ammonia sensor, we demonstrate that the HSAB principle can be also successfully applied to the selection of sensing layers for detectors employing other sensing principles, different than the chemiresistive one. Changing the sensing paradigm (i.e., the amino groups-based compounds are part of the sensing layer, rather than part of the analyte), the paper shows that these types of molecules (polymers, carbon nanotubes, ionic liquids) are appropriate constituents of a CO2 sensing layer, in full accordance to the HSAB criteria.

This paper presents the relative humidity (RH) sensing response of a resistive sensor employing sensing layers based on a ternary nanocomposite comprising graphene oxide-oxidized carbon nanohorns-polyvinylpyrrolidone (GO-CNHox–PVP), at 1/1/1, 1/2/1, and 1/3/1 w/w/w mass ratios. The sensing structure is composed of a silicon substrate, a SiO2 layer, and interdigitated transducers (IDT) electrodes, on which the sensing layer is deposited via the drop-casting method. The morphology and the composition of the sensing layers are investigated through scanning electron microscopy (SEM) and RAMAN spectroscopy. The RH sensing capability of each carbonaceous nanocomposite-based thin film was analyzed by applying a current between the two electrodes and by measuring the voltage difference when varying the RH from 0% to 100% in humid nitrogen. The sensors have a room temperature response comparable to that of a commercial humidity sensor and are characterized by a rapid response, excellent linearity, good sensitivity, and recovery time. The manufactured sensing devices’ transfer functions were established, and we extracted the response and recovery times. While the structures with GO/CNHox/PVP at 1/1/1 ratio (w/w/w) had the best performance in terms of relative sensibility, response time, and recovery time, the sensors employing the GO/CNHox/PVP nanocomposite at the 1/2/1 ratio (w/w/w) had the best linearity. Moreover, the ternary mixture proved to have much better sensing properties compared to CNHox and CNHox-PVP-based sensing layers in terms of sensitivity and linearity. Each component of the ternary nanocomposites’ functional role is explained based on their physical and chemical properties. We analyzed the potential mechanism associated with the sensors’ response, among these, the effect of the p-type semiconductor behavior of CNHox and GO, correlated with swelling of the PVP, was dominant and led to increased resistance of the sensing layer.

This paper reports, for the first time, on the electrical percolation threshold in oxidized carbon nanohorns (CNHox)–polyvinylpyrrolidone (PVP) films. We demonstrate—starting from the design and synthesis of the layers—how these films can be used as sensing layers for resistive relative humidity sensors. The morphology and the composition of the sensing layers are investigated through Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), and RAMAN spectroscopy. For establishing the electrical percolation thresholds of CNHox in PVP, these nanocomposite thin films were deposited on interdigitated transducer (IDT) dual-comb structures. The IDTs were processed both on a rigid Si/SiO2 substrate with a spacing of 10 µm between metal digits, and a flexible substrate (polyimide) with a spacing of 100 µm. The percolation thresholds of CNHox in the PVP matrix were equal to (0.05–0.1) wt% and 3.5 wt% when performed on 10 µm-IDT and 100 µm-IDT, respectively. The latter value agreed well with the percolation threshold value of about 4 wt% predicted by the aspect ratio of CNHox. In contrast, the former value was more than an order of magnitude lower than expected. We explained the percolation threshold value of (0.05–0.1) wt% by the increased probability of forming continuous conductive paths at much lower CNHox concentrations when the gap between electrodes is below a specific limit. The change in the nanocomposite’s longitudinal Young modulus, as a function of the concentration of oxidized carbon nanohorns in the polymer matrix, is also evaluated. Based on these results, we identified a new parameter (i.e., the inter-electrode spacing) affecting the electrical percolation threshold in micro-nano electronic devices. The electrical percolation threshold’s critical role in the resistive relative-humidity sensors’ design and functioning is clearly emphasized.

The objective of this study is to design and synthetize an oxidized single wall carbon nanohorns (SWCNHs) - polyvinylpyrrolidone (PVP) composite film as potential sensing material for resistive humidity sensor. Raman spectroscopy is used to investigate the nanohybrid formation and components interaction. Comparative results are presented for the percolation threshold values determined for 2 study-cases: carbon nanohorns in PVP film deposited on either rigid (Si / SiO 2 ) or flexible substrate (polyimide). While in the first case, the percolation threshold occurs at a concentration of oxidized SWCNHs in the nanocomposite matrix in the range (0.05-0.1)% (w/w), in the second instance, the concentration of SWCNHs for the percolation threshold is between (2-3.5)% (w/w). Experimental findings are explained in terms of size effects in the geometry of the studied structures. The key role played by the electrical percolation threshold in the resistive sensing capabilities of the synthesized nanocomposite towards water molecules is described.

In this study, a resistive humidity sensor for moisture detection at room temperature is presented. The thin film proposed as a critical sensing element is based on a quaternary hybrid nanocomposite CNHox//SnO2/ZnO/PVP (oxidated carbon nanohorns–tin oxide–zinc oxide–polyvinylpyrrolidone) at the w/w/w/w ratios of 1.5/1/1/1 and 3/1/1/1. The sensing structure consists of a Si/SiO2 dielectric substrate and interdigitated transducers (IDT) electrodes, while the sensing film layer is deposited through the drop-casting method. Morphology and composition of the sensing layers were investigated through scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX), X-ray diffraction, and Raman spectroscopy. Each quaternary hybrid nanocomposite-based thin film’s relative humidity (RH) sensing capability was analyzed by applying a direct current with known intensity between two electrodes and measuring the voltage difference when varying the RH from 0% to 100% in a humid nitrogen atmosphere. While the sensor with CNHox/SnO2/ZnO/PVP at 1.5/1/1/1 as the sensing layer has the better performance in terms of sensitivity, the structure employing CNHox//SnO2/ ZnO/PVP at 3/1/1/1 (mass ratio) as the sensing layer has a better performance in terms of linearity. The contribution of each component of the quaternary hybrid nanocomposites to the sensing performance is discussed in relation to their physical and chemical properties. Several alternative sensing mechanisms were taken into consideration and discussed. Based on the measured sensing results, we presume that the impact of the p-type semiconductor behavior of CNHox, in conjunction with the swelling of the hydrophilic polymer, is dominant and leads to the overall increasing resistance of the sensing film.

In this paper, we present the relative humidity (RH) sensing response of a chemiresistive sensor, employing sensing layers based on a ternary nanohybrids comprised of holey carbon nanohorns (CNHox), titanium (IV) oxide, and polyvinylpyrrolidone (PVP) at 1/1/1/(T1), 2/1/1/(T2), and with 3/1/1 (T3) mass ratios. The sensing device is comprised of a silicon-based substrate, a SiO2 layer, and interdigitated transducer (IDT) electrodes. The sensitive layer was deposited via the drop-casting method on the sensing structure, followed by a two-step annealing process. The structure and composition of the sensing films were investigated through scanning electron microscopy (SEM), Raman spectroscopy, and X-ray diffraction (XRD). The resistance of the ternary nanohybrid-based sensing layer increases when H increases between 0% and 80%. A different behavior of the sensitive layers is registered when the humidity increases from 80% to 100%. Thus, the resistance of the T1 sensor slightly decreases with increasing humidity, while the resistance of sensors T2 and T3 register an increase in resistance with increasing humidity. The T2 and T3 sensors demonstrate a good linearity for the entire (0–100%) RH range, while for T1, the linear behavior is limited to the 0–80% range. Their overall room temperature response is comparable to a commercial humidity sensor, characterized by a good sensitivity, a rapid response, and fast recovery times. The functional role for each of the components of the ternary CNHox/TiO2/PVP nanohybrid is explained by considering issues such as their electronic properties, affinity for water molecules, and internal pore accessibility. The decreasing number of holes in the carbonaceous component at the interaction with water molecules, with the protonic conduction (Grotthus mechanism), and with swelling were analyzed to evaluate the sensing mechanism. The hard–soft acid-base (HSAB) theory also has proven to be a valuable tool for understanding the complex interaction of the ternary nanohybrid with moisture.

Many principles and methods have been described in literature for measuring relative humidity (RH) and several types of materials have been employed as RH sensing layers [1,2]. [...]

We report the relative humidity (RH) sensing response of a resistive sensor, employing sensing layers, based on a quaternary organic–inorganic hybrid nanocomposite comprising oxidized carbon nanohorns (CNHox), graphene oxide (GO), tin dioxide, and polyvinylpyrrolidone (PVP), at 1/1/1/1 and 0.75/0.75/1/1/1 mass ratios. The sensing structure comprises a silicon substrate, a SiO2 layer, and interdigitated transducer (IDT) electrodes. The sensing film was deposited via the drop-casting method on the sensing structure. The morphology and the composition of the sensing layers were investigated through Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), and RAMAN spectroscopy. The organic–inorganic quaternary hybrid-based thin film’s resistance increased when the sensors were exposed to relative humidity ranging from 0 to 100%. The manufactured devices show a room temperature response comparable to that of a commercial capacitive humidity sensor and characterized by excellent linearity, rapid response and recovery times, and good sensitivity. While the sensor with CNHox/GO/SnO2/PVP at 0.75/0.75/1/1 as the sensing layer has the best performance in terms of linearity and recovery time, the structures employing the CNHox/GO/SnO2/PVP at 1/1/1/1 (mass ratio) have a better performance in terms of relative sensitivity. We explained each constituent of the quaternary hybrid nanocomposites’ sensing role based on their chemical and physical properties, and mutual interactions. Different alternative mechanisms were taken into consideration and discussed. Based on the sensing results, we presume that the effect of the p-type semiconductor behavior of CNHox and GO, correlated with swelling of PVP, dominates and leads to the overall increasing resistance of the sensing layer. The hard–soft acid–base (HSAB) principle also supports this mechanism.

In this paper, we report the realization and characterization of a condensation sensor based on indium nitride (InN) layers deposited by magnetron sputtering on glass and flexible plastic substrates, having fast response and using potentially low cost fabrication technology. The InN devices work as open gate thin film sensitive transistors. Condensed water droplets, formed on the open gate region of the sensors, deplete the electron accumulation layer on the surface of InN film, thus decreasing the current of the sensor. The current increases back to its initial value when water droplets evaporate from the exposed InN film surface. The response time is as low as 2 s.

© 2016 IEEE. The paper reports upon the design and characterization of a resistive O2 sensor, which is fully CMOS-compatible and is based on an ultra-low-power Silicon on Insulator (SOI) micro-hotplate membrane. The microsensor employs SrTi0.4Fe0.6O2.8 (STFO60) as sensing layer. Thermo-Gravimetric Analysis (TGA) Energy-Dispersive X-ray Spectroscopy (EDX), X-ray Diffraction (XRD) and Scanning Electron Microscope (SEM) techniques have been used to assess the quality of both the sensing layer and STFO-SOI interface. At room temperature, the SOI sensor shows good sensitivity and fast response time (≤ 6 seconds) to O2 concentration ranging from 0% to 20% in a nitrogen atmosphere. This is the first experimental result showing the potential of this structure as O2 sensor.

This paper presents a comparison between SiC and diamond Schottky barrier diodes using the oxide ramp termination. The influences of the dielectric thickness and relative permittivity on the diode’s electrical performance are investigated. Typical commercial drift layer parameters are used for this study. The extension of the space charge area throughout the drift region and the current distribution at breakdown are shown. The efficiency of the termination is also evaluated for both SiC and diamond diodes.

Synthetic diamond power Schottky structures have the capability of sustaining significant reverse voltages with rather thin drift layers. Diamond Schottky barrier diodes (SBDs) also exhibit promising on-state behaviour. This paper looks at the influence of temperature and drift doping on the forward characteristics of these devices. Physical explanations for the variation of the forward current with the forward voltage, together with equations which aim to model this dependence, are also presented.

A classical implementation of the field plate technique is the oxide ramp termination. This paper presents for the first time a comparison between SiC and diamond Schottky barrier diodes (SBD) using this termination. The influences of the ramp angle and oxide thickness on the diodes electrical performance are investigated for both punch-through (PT) and non punch-through (nPT) structures. The efficiency of the termination is also evaluated.

The promising theoretical properties of diamond, together with the recent advances in producing high-quality single crystal diamond substrates, have increased the interest in using diamond in power electronic devices. This paper presents numerical and experimental off-state results for a diamond Schottky barrier diode (SBD), one of most studied unipolar devices in diamond. Finding a suitable termination structure is an essential step towards designing a high voltage diamond device. The ramp oxide structure shows very encouraging electronic performance when used to terminate diamond SBDs. High-k dielectrics are also considered in order to further improve the reliability and electrical performance of the structure.

This paper reports on the design and synthesis of a talc-impregnated polyimide film exhibiting reduced relative humidity (RH) hysteresis. The morphology of both simple polyimide and talc-impregnated polyimide RH sensing layers are investigated by means of Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). When deposited on quartz crystal microbalance (QCM) substrates, the talc-impregnated polyimide layer yields a highly linear response and a resonant frequency hysteresis improvement as high as 36% with respect to simple polyimide. These experimental results recommend the proposed layer as suitable for high performance RH capacitive sensors.

A classical implementation of the field plate technique is the oxide ramp termination. This paper presents improvements of the breakdown voltage for both SiC JBDs and SBDs, obtained by using high-k dielectrics. A study regarding the influence of the dielectric permittivity and thickness on the off-state performances of the diodes is included. It is shown that Si3N4 is to be preferred to SiO2 for the dielectric ramp. Termination efficiencies up to 96% are reported.

The behavior of the MOS switch and of two cascode configurations are evaluated, by using OR-CAD simulations, and the resulting data are comparatively presented. By analytical and numerical investigations, the superior performance of the multiple cascode circuit is demonstrated.

This paper introduces a pressure sensing structure configured as a stress sensitive differential amplifier (SSDA), built on a Silicon-on-Insulator (SOI) membrane. Theoretical calculation show the significant increase in sensitivity which is expected from the pressure sensors in SSDA configuration compared to the traditional Wheatstone bridge circuit. Preliminary experimental measurements, performed on individual transistors placed on the membrane, exhibit state-the-art sensitivity values (1.45mV/mbar).

This paper reviews and addresses certain aspects of Silicon-On-Insulator (SOI) technologies for a harsh environment. The paper first describes the need for specialized sensors in applications such as (i) domestic and other small-scale boilers, (ii) CO 2 Capture and Sequestration, (iii) oil & gas storage and transportation, and (iv) automotive. We describe in brief the advantages and special features of SOI technology for sensing applications requiring temperatures in excess of the typical bulk silicon junction temperatures of 150oC. Finally we present the concepts, structures and prototypes of simple and smart micro-hotplate and Infra Red (IR) based emitters for NDIR (Non Dispersive IR) gas sensors in harsh environments.

Two CO 2 sensing mechanisms, based on the Hard Soft Acids Bases (HSAB) and Bronsted-Lowry theories, are discussed and compared. They are evaluated by selecting amino groups-based coating layers, which are deposited on Surface Acoustic Wave (SAW) devices for CO 2 detection. Experimentally measured CO 2 sensitivities of different coating layers, such as polyallylamine (PAA), polyethyleneimine (PEI), nanocomposite matrix based on PAA-aminocarbon nanotubes and PEI-aminocarbon nanotubes, emeraldine, 4-sulfocalix[4]arene-doped polyaniline, matrix based emeraldine and carbonic anhydrase (PACA) are compared and evaluated according to their corresponding sensing mechanism.

Since Element Six reported in 2002 extremely high holes and electrons mobilities in intrinsic single crystal layers, synthetic diamond emerged as a promising semiconductor suitable for active electronic devices. Having the best physical and electrical theoretical properties among wide band gap semiconductors, diamond might become a serious competitor for silicon carbide (SiC) and gallium nitride (GaN) in the field of power electronics and switching devices. This paper presents the most significant properties and applications of diamond, together figures of merit showing its immense potential. Experimental results on several diamond-based device structures confirm its capacity to withstand breakdown voltages in excess of 1kV and to commute with frequencies in excess of 100GHz.

The synthesis of two new types of nanocomposite matrices, the first based on polyallylamine (PAA) and aminocarbon nanotubes, the second on polyethyleneimine (PEI) and aminocarbon nanotubes, are reported. The surface acoustic wave (SAW) sensors, coated with the two selected nanocomposites, showed good sensitivities when varying the CO2 concentrations in the range (500-5000) ppm. The sensor sensitivity is larger when using polyethyleneimine aminocarbon nanotubes than in the case when only a pure polyethyleneimine layer is considered for coating.

High-quality electronic-grade intrinsic chemical-vapor-deposited (CVD) single-crystal diamond layers having exceptionally high carrier mobilities have been reported by Isberg et al. This makes the realization of novel electronic devices in diamond, particularly for high-voltage and high-temperature applications, a viable proposition. As such, material models which can capture the particular features of diamond as a semiconductor are required to analyze, optimize, and quantitatively design new devices. For example, the incomplete ionization of boron in diamond and the transition to metallic conduction in heavily boron-doped layers require accurate carrier freeze-out models to be included in the simulation of diamond devices. Models describing these phenomena are proposed in this paper and include numerical approximation of intrinsic diamond which is necessary to formulate doping- and temperature-dependent mobility models. They enable a concise numerical description of single-crystal diamond which agrees with data obtained from material characterization. The models are verified by application to new Schottky m-i-p(+) diode structures in diamond. Simulated forward characteristics show excellent correlation with experimental measurements. In spite of the lack of impact ionization data for single-crystal diamond, approximation of avalanche coefficient parameters from other wide-bandgap semiconductors has also enabled the reverse blocking characteristics of diamond diodes to be simulated. Acceptable agreement with breakdown voltage from experimental devices made with presently available single-crystal CVD diamond is obtained.

The paper's goal is the first demonstration of the fabrication of high power Schottky diodes on synthetic diamond using oxide ramp termination. In order to allow full activated impurities at room temperature and a high hole mobility a low boron doping of the drift layer is employed. Several aspects of the manufacturing technology are presented. A termination with a small ramp angle can be obtained using only RIE technique due to diamond wafer non- uniformity (roughness). Experimental forward and reverse characteristics measured on diamond diodes are also included.

Extensive numerical simulations have been carried out to compare the electrical performance of ideal Schottky diodes on diamond and silicon carbide. The influences of the drift layer parameters on the off-state behaviour of the diodes are presented for both punch-through (PT) and non punch-through (nPT) structures. In PT case breakdown voltage was shown to be constant with the drift doping at low concentrations. Analytical expressions of the breakdown voltage variation with doping for nPT diodes are also included.

Diamond Schottky power diodes are currently subject to extensive research. In this paper, the on-state capability of this type of structures is assessed. Measured forward characteristics for different temperatures are included and the use of gold, nickel and aluminium as Schottky metal is evaluated. A theoretical study regarding the influence of different doping profiles at the drift-substrate interface on the electrical performance of the device is also inserted.

The IGBT is a device that combines the advantages of simplicity of drive due to the voltage-controlled device with high impedance gate and low power dissipation due to the conductivity modulation effect. For that reason, the SiC-IGBT is used for applications that require a high breakdown voltage of 5 kV and more. The IGBT presented in this paper has one epilayer, a buffer layer between substrate and epilayer to improving the dynamic characteristics and a guard ring/epilayer junction to increase the saturation current. The SiC-IGBT is used in applications that require: higher current conduction capability, power losses efficiently dissipated, operation at higher temperatures, up to 600 degC, and in very harsh environment

Two termination structures suitable for diamond Schottky diodes are presented in this paper. A thorough comparison between the two structures, concerning both electrical and geometrical aspects, is included. The study is based on theoretical models and extensive numerical results. High termination efficiencies, up to 93%, are reported

A classical implementation of the field plate technique is the oxide ramp termination. This paper presents improvements of the efficiency of this termination for SiC Schottky barrier diodes, obtained by using high-k dielectrics. The effect of the relative dielectrics permittivity and ramp parameters are investigated for punch-through and non punch-through devices. Optimal structure termination parameters were identified

This work is concerned with the behaviour of a hybrid Si/SiC high voltage switch in multiple cascode configuration. The influences of the threshold voltage and of /spl beta/ current factor of the SiC medium power J-FET on the performance of the switch are evinced.

The paper addresses the state-of-art-in SiC power diodes. The best performance of Schottky barrier and junction barrier diodes on SiC is reviewed. The fundamental edge terminations used to relieve the crowding of the electric field of these devices are presented. An effective termination, based on the oxide ramp etching is described and the application of this method to SiC devices is discussed, achieving breakdown voltage of up to 95% from the ideally value.

The paper is concerned with the switching behaviour of the two hybrid Si/SiC high voltage cascode configurations, using OR-CAD simulations. The drive pulse parameters effects are extensively investigated. The cascode circuit with two SiC J-FETs features an easy control via the silicon MOS transistor and the ability of fast turn-on and turn off which are essential in high voltage/high speed applications.

The paper is concerned with the investigation of the UV detection performances of 6H-SiC Schottky and junction barrier diodes with oxide ramp termination. The devices exhibit a high responsivity in UV spectral range with excellent visible rejection ratio. An accurate model for the determination of the quantum efficiency is developed. Excellent agreement between model and simulated data is achieved.

Its outstanding electronic properties and the recent advances in growing single-crystal chemically vapour-deposited substrates have made diamond a candidate for high-power applications. Diamond Schottky diodes have the potential of being an alternative to silicon p-i-n and SiC Schottky diodes in power electronic circuits. Extensive experimental and theoretical results, for both on- and off-state behaviour of metal-insulator-p-type diamond Schottky structures, are presented here. The temperature dependence of the forward characteristics and electrical performance of a termination structure suitable for unipolar diamond devices are also presented.

A comprehensive study on the off-state performance of synthetic single crystal (SSC) diamond Schottky barrier diodes (SBDs) is the subject of this paper. Three termination structures suitable for unipolar diamond power devices are numerically investigated. Comparisons between the three terminations, based on blocking performance and area consumption are presented. Optimum design parameters derived from simulations are included for each structure. Experimental results of reverse-biased diamond SBDs for the first time with ramp angle termination are also presented.

We present our findings on the numerical and experimental analysis of diamond Schottky Barrier diodes (SBDs) comprising of intrinsic single crystal (SC) chemical vapour deposited (CVD) diamond layers grown on highly boron doped substrates also grown by CVD. Good correlation with experimental results has been achieved through numerical modelling that has incorporated previously reported data on transport physics and carrier activation. With our numerical model, we are able to match to within 12 to 15% of the measured forward characteristics of fabricated diamond SBDs up to 2 V in excess of the turn on voltage, for two different Schottky metals.

Recent results proved the possibility of obtaining synthetic single crystal diamond with good crystal quality and excellent consistency. High voltage p-type Schottky barrier diodes (SBDs) have been fabricated on diamond, using gold (Au) as the Schottky metal and boron as doping material. In this study, on-state and off-state experimental and simulated data are presented and excellent theory-experiment agreement is revealed. The usage of diamond SBDs as ultra violet (UV) photodetectors is also analysed. On-state and off-state simulations, for different optical beam power densities, have been carried out and the theoretical data are provided.