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Abstract To improve our understanding of the perception of odors, researchers are often required to undertake experimental procedures with users exposed to multiple odors in a variety of settings, including to diagnose smell loss in clinics and care homes. Existing smell tests are typically administered using multiple sniffing pens, manually presented to patients by a highly specialized nurse using a time-consuming and complex testing paradigm. Automated odor delivery devices, such as olfactometer systems, exist but are expensive, bulky and typically lab based, making them difficult to use for on the ground odor delivery. Here we have developed a portable, affordable, odor delivery device that can deliver 24 odors through individual channels with high temporal precision and without cross-contamination. The device allows for the rapid, flexible sequencing of odors via digital control using a mobile application and has been experimentally validated in the lab, as well as tested on patients. The design provides several advantages for investigating olfactory perception and offers the possibility that users can one day self-administer smell tests in a range of settings, including at home, allowing smell healthcare services to evolve and become part of a routine practice and self-care culture.

In this paper, the origin of the gate oscillations with a stray capacitance in the load inductor is analyzed with a device/circuit mix-mode simulation. It is found that the gate ringing occurs when the superjunction device reaches its pinch-off potential (the n-pillar and the p-pillar are fully depleted by the lateral depletion process). The progress of the depletion profiles of the superjunction leads to a rapid change of the drain-to-source capacitance and the dV/dt. Finally, the dV/dt causes a sudden change of the current flow rate across the stray capacitance of the load inductor and the device while triggering the parasitic inductances. Based on these results, a comparative study was carried out with an ideal inductive load switching and, finally, the dampers for relieving the gate ringing were investigated.

This work provides an overview of the current state of technology in the field of lateral GaN power devices and presents the characteristics of the main commercially available 650 V GaN power devices and ICs. A comparison is given, both in terms of key parameters as well as of the availability of complex functionality through integration of additional smart features. The features of our new technology, termed ICeGaN™, are presented in this context, focusing on the benefits that may be derived when ICeGaN™ devices are used in common applications. ICeGaN™ is a new concept of a smart HEMT which offers ease-of-use, sensing and protection functions without sacrificing performance.

Abstract We present a miniaturised thermal acoustic gas sensor, fabricated using a CMOS microhotplate and MEMS microphone. The sensing mechanism is based on the detection of changes in the thermal acoustic conversion efficiency which is dependent on the physical properties of the gas. An active sensing element, consisting of a MEMS microphone, is used to detect the target gas while a reference element is used for acoustic noise compensation. Compared to current photoacoustic gas sensors, our sensor requires neither the use of gas-encapsulated microphones, nor that of optical filters. In addition, it has all the benefits of CMOS technology, including production scalability, low cost and miniaturization. Here we demonstrate its application for CO $$_2$$ 2 gas detection. The sensor could be used for gas leak detection, for example, in an industrial plant.

Abstract The gas sensor market is growing fast, driven by many socioeconomic and industrial factors. Mid-infrared (MIR) gas sensors offer excellent performance for an increasing number of sensing applications in healthcare, smart homes, and the automotive sector. Having access to low-cost, miniaturized, energy efficient light sources is of critical importance for the monolithic integration of MIR sensors. Here, we present an on-chip broadband thermal MIR source fabricated by combining a complementary metal oxide semiconductor (CMOS) micro-hotplate with a dielectric-encapsulated carbon nanotube (CNT) blackbody layer. The micro-hotplate was used during fabrication as a micro-reactor to facilitate high temperature (>700 $$^{\circ }$$ ∘ C) growth of the CNT layer and also for post-growth thermal annealing. We demonstrate, for the first time, stable extended operation in air of devices with a dielectric-encapsulated CNT layer at heater temperatures above 600 $$^{\circ }$$ ∘ C. The demonstrated devices exhibit almost unitary emissivity across the entire MIR spectrum, offering an ideal solution for low-cost, highly-integrated MIR spectroscopy for the Internet of Things.

For large scale testability of p-GaN HEMTs it is essential to investigate threshold voltage ( $\text{V}_{\mathrm{ th}}$ ) instability from the perspective of the measurement induced instability. In this paper the impact of accumulated gate bias stress during standard transfer characteristic measurements ( $\text{I}_{\mathrm{ D}}$ - $\text{V}_{\mathrm{ G}}$ ) in a p-GaN AlGaN/GaN-on-Si normally off HEMT is quantitatively analysed and modeled. This illustrates the associated threshold voltage ( $\text{V}_{\mathrm{ th}}$ ) instabilities and leads to a better understanding of the $\text{V}_{\mathrm{ th}}$ measurement challenges of a p-GaN HEMT. Upon an application of a constant gate bias close to nominal $\text{V}_{\mathrm{ th}}$ the drain current $\text{I}_{\mathrm{ D}}$ shows an initial marginal rise, followed by a short stable period ( $\text{I}_{\mathrm{ Dstable}}$ - $\text{T}_{\mathrm{ zone}}$ ) and a steep decay period. The effective bias history built on the gate stack varies when pulse on-time (Ton) or step time (Tstep), corresponding to pulsed or DC step $\text{I}_{\mathrm{ D}}$ - $\text{V}_{\mathrm{ G}}$ measurements, are varied. We find that this can lead to a $\text{V}_{\mathrm{ th}}$ variation of up to 20%. It is also observed that the choice of Ton and Tstep determines whether $\text{I}_{\mathrm{ D}}$ is measured in $\text{I}_{\mathrm{ Dstable}}$ - $\text{T}_{\mathrm{ zone}}$ or the rise or decay periods. Measurement induced $\text{V}_{\mathrm{ th}}$ instability is attributed to trapping of 2DEG electrons at the AlGaN barrier and we demonstrate that an ohmic gate contact, in comparison to the Schottky gate contact, may compensate for the trapped 2DEG electrons by hole injection across the AlGaN barrier. Experimental results of $\text{V}_{\mathrm{ th}}$ stability under the same stress conditions for a Schottky and ohmic gate contact are supported by a detailed TCAD analysis.

In recent years, there has been a growing desire to monitor and control harmful substances arising from industrial processes that impact upon our health and quality of life. This has led to a large market demand for gas sensors, which are commonly based on sensors that rely upon a chemical reaction with the target analyte. In contrast, thermal conductivity detectors are physical sensors that detect gases through a change in their thermal conductivity. Thermal conductivity gas sensors offer several advantages over their chemical (reactive) counterparts that include higher reproducibility, better stability, lower cost, lower power consumption, simpler construction, faster response time, longer lifetime, wide dynamic range, and smaller footprint. It is for these reasons, despite a poor selectivity, that they are gaining renewed interest after recent developments in MEMS-based silicon sensors allowing CMOS integration and smart application within the emerging Internet of Things (IoT). This timely review focuses on the state-of-the-art in thermal conductivity sensors; it contains a general introduction, theory of operation, interface electronics, use in commercial applications, and recent research developments. In addition, both steady-state and transient methods of operation are discussed with their relative advantages and disadvantages presented. Finally, some of recent innovations in thermal conductivity gas sensors are explored.

In this work, we present a novel thermal acoustic gas sensor, fabricated using a CMOS microhotplate and MEMS microphone. The sensing mechanism is based on the detection of changes in the thermal acoustic conversion efficiency which is dependent on the physical properties of the gas. The gas sensor has all the benefits of CMOS technology, including low cost and miniaturization. Here, we demonstrate its application for CO2 gas detection.

Low-cost infrared (IR) thermal cameras are powering a rising market of industrial and consumer applications. Complementary metal-oxide-semiconductor (CMOS)-based thermopile arrays are proven thermal imagers that can be monolithically integrated into low-cost and low-power-consumption formats for high-volume manufacturability. Here we present a simple method to evaluate the cross-talk of these arrays and propose a numerical model for device optimization.

We present a new experimental technique to characterise the crosstalk of a thermopile-based thermal imager, based on bi-directional electrical heating of thermopile elements. The new technique provides a significantly simpler and more reliable method to determine the crosstalk, compared to a more complex experimental setup with a laser source. The technique is used to characterise a novel single-chip array, fabricated on a single dielectric membrane. We propose a theoretical model to simulate the crosstalk, which shows good agreement with the experimental results. Our results allow a better understanding of the thermal effects in these devices, which are at the center of a rising market of industrial and consumer applications.

The current paper reports on a sonochemical synthesis method for manufacturing nanostructured (typical grain size of 50 nm) SrTi0.6Fe0.4O2.8 (Sono-STFO40) powder. This powder is characterized using X ray-diffraction (XRD), Mössbauer spectroscopy and Scanning Electron Microscopy (SEM), and results are compared with commercially available SrTi0.4Fe0.6O2.8 (STFO60) powder. In order to manufacture resistive oxygen sensors, both Sono-STFO40 and STFO60 are deposited, by dip-pen nanolithography (DPN) method, on an SOI (Silicon-on-Insulator) micro-hotplate, employing a tungsten heater embedded within a dielectric membrane. Oxygen detection tests are performed in both dry (RH = 0%) and humid (RH = 60%) nitrogen atmosphere, varying oxygen concentrations between 1% and 16% (v/v), at a constant heater temperature of 650 °C. The oxygen sensor, based on the Sono-STFO40 sensing layer, shows good sensitivity, low power consumption (80 mW), and short response time (25 s). These performance are comparable to those exhibited by state-of-the-art O2 sensors based on STFO60, thus proving Sono-STFO40 to be a material suitable for oxygen detection in harsh environments.

Optical gas sensors play an increasingly important role in many applications. Sensing techniques based on mid-infrared absorption spectroscopy offer excellent stability, selectivity and sensitivity, for numerous possibilities expected for sensors integrated into mobile and wearable devices. Here we review recent progress towards the miniaturization and integration of optical gas sensors, with a focus on low-cost and low-power consumption devices.

Minimizing conductive heat losses in Micro-Electro-Mechanical-Systems (MEMS) thermal (hot-film) flow sensors is the key to minimize the sensors’ power consumption and maximize their sensitivity. Through a comprehensive review of literature on MEMS thermal (calorimetric, time of flight, hot-film/hot-film) flow sensors published during the last two decades, we establish that for curtailing conductive heat losses in the sensors, researchers have either used low thermal conductivity substrate materials or, as a more effective solution, created low thermal conductivity membranes under the heaters/hot-films. However, no systematic experimental study exists that investigates the effect of membrane shape, membrane size, heater/hot-film length and M e m b r a n e (size) to H e a t e r (hot-film length) Ratio (MHR) on sensors’ conductive heat losses. Therefore, in this paper we have provided experimental evidence of dependence of conductive heat losses in membrane based MEMS hot-film flow sensors on MHR by using eight MEMS hot-film flow sensors, fabricated in a 1 µm silicon-on-insulator (SOI) CMOS foundry, that are thermally isolated by square and circular membranes. Experimental results demonstrate that: (a) thermal resistance of both square and circular membrane hot-film sensors increases with increasing MHR, and (b) conduction losses in square membrane based hot-film flow sensors are lower than the sensors having circular membrane. The difference (or gain) in thermal resistance of square membrane hot-film flow sensors viz-a-viz the sensors on circular membrane, however, decreases with increasing MHR. At MHR = 2, this difference is 5.2%, which reduces to 3.0% and 2.6% at MHR = 3 and MHR = 4, respectively. The study establishes that for membrane based SOI CMOS MEMS hot-film sensors, the optimum MHR is 3.35 for square membranes and 3.30 for circular membranes, beyond which the gain in sensors’ thermal efficiency (thermal resistance) is not economical due to the associated sharp increase in the sensors’ (membrane) size, which makes sensors more expensive as well as fragile. This paper hence, provides a key guideline to MEMS researchers for designing the square and circular membranes-supported micro-machined thermal (hot-film) flow sensors that are thermally most-efficient, mechanically robust and economically viable.

This paper addresses the practical implementation of a wireless sensors network designed to actualize cyber-physical systems that are dedicated to structural health monitoring applications in the construction domain. This network consists of a mesh grid composed of LoRaWAN battery-free wireless sensing nodes that collect physical data and communicating nodes that interface the sensing nodes with the digital world through the Internet. Two prototypes of sensing nodes were manufactured and are powered wirelessly by using a far-field wireless power transmission technique and only one dedicated RF energy source operating in the ISM 868 MHz frequency band. These sensing nodes can simultaneously perform temperature and relative humidity measurements and can transmit the measured data wirelessly over long-range distances by using the LoRa technology and the LoRaWAN protocol. Experimental results for a simplified network confirm that the periodicity of the measurements and data transmission of the sensing nodes can be controlled by the dedicated RF source (embedded in or just controlled by the associated communicating node), by tuning the radiated power density of the RF waves, and without any modification of the software or the hardware implemented in the sensing nodes.

This study focuses on the thermal characterization of porous gallium nitride (GaN) usingan extended 3ω method. Porous semiconductor materials provide a solution to the need for on-chipthermal insulation, a fundamental requirement for low-power, high-speed and high-accuracythermal sensors. Thermal insulation is especially important in GaN devices, due to the intrinsicallyhigh thermal conductivity of the material. The results show one order of magnitude reduction inthermal conductivity, from 130 W/mK to 10 W/mK, in line with theoretical predictions for porousmaterials. This achievement is encouraging in the quest for integrating sensors with opto-, powerandRF-electronics on a single GaN chip.

The effect of membrane deflection has been investigated for thermal flow sensors. Catastrophic membrane breakage is a common occurrence in membrane based thermal flow sensors due to thermal expansion and internal stresses. This work analyses three sensors comprising a tungsten heater embedded in buried oxide membrane with a silicon nitride passivation layer, the use of back etching creates a cavity underneath to reduce the thermal conduction. The investigation is done using interferometry to measure the membrane shape at room and operating temperature for three membranes of different sizes. As expected, the deflection increases with temperature up to 15 µm at operating temperature and with the reduction of membrane size the deflection is reduced to a minimum of 3 µm for the smallest membrane. The lower deflection measured in devices with a smaller cavity can be related to a reduced internal stress, improving the long term stability.

We present a novel thermopile-based infrared (IR) sensor array fabricated on a single CMOS dielectric membrane, comprising of poly-silicon p+ and n+ elements. Processing of the chip is simplified by fabricating the entire array on a single membrane and by using standard CMOS Al metal layers for thermopile cold junction heatsinking. On a chip area of 1.76 mm × 1.76 mm, with a membrane size of 1.2 mm × 1.2 mm, we fabricated IR sensor arrays with 8 × 8 to 100 × 100 pixels. The 8 × 8 pixel device has

For the first time, 3D multiphysics finite element modelling has been used to optimise the geometry of a calorimetric thermal flow sensor. The model involves and couples three physics domains: electric, thermal and fluid mechanics. The model is validated against experimental data obtained from a thermoelectronic flow sensor comprising of a tungsten heating resistor and temperature sensing diodes. Upstream and downstream diodes measure the temperature change caused by the asymmetric thermal profile when gas flow is introduced. The optimum distance between the diodes and the heater is shown along with the advantages of altering heater and membrane geometries, providing the knowledge for application-driven sensor optimisation.

An SOI CMOS multi-sensor MEMS chip, which can simultaneously measure temperature, pressure and flow rate, has been reported. The multi-sensor chip has been designed keeping in view the requirements of researchers interested in experimental fluid dynamics. The chip contains ten thermodiodes (temperature sensors), a piezoresistive-type pressure sensor and nine hot film-based flow rate sensors fabricated within the oxide layer of the SOI wafers. The silicon dioxide layers with embedded sensors are relieved from the substrate as membranes with the help of a single DRIE step after chip fabrication from a commercial CMOS foundry. Very dense sensor packing per unit area of the chip has been enabled by using technologies/processes like SOI, CMOS and DRIE. Independent apparatuses were used for the characterization of each sensor. With a drive current of 10 µA–0.1 µA, the thermodiodes exhibited sensitivities of 1.41 mV/°C–1.79 mV/°C in the range 20–300 °C. The sensitivity of the pressure sensor was 0.0686 mV/(Vexcit kPa) with a non-linearity of 0.25% between 0 and 69 kPa above ambient pressure. Packaged in a micro-channel, the flow rate sensor has a linearized sensitivity of 17.3 mV/(L/min)−0.1 in the tested range of 0–4.7 L/min. The multi-sensor chip can be used for simultaneous measurement of fluid pressure, temperature and flow rate in fluidic experiments and aerospace/automotive/biomedical/process industries.

Graphene is a highly promising material in the development of new photodetector technologies, in particular due its tunable optoelectronic properties, high mobilities and fast relaxation times coupled to its atomic thinness and other unique electrical, thermal and mechanical properties. Optoelectronic applications and graphene-based photodetector technology are still in their infancy, but with a range of device integration and manufacturing approaches emerging this field is progressing quickly. In this review we explore the potential of graphene in the context of existing single photon counting technologies by comparing their performance to simulations of graphene-based single photon counting and low photon intensity photodetection technologies operating in the visible, terahertz and X-ray energy regimes. We highlight the theoretical predictions and current graphene manufacturing processes for these detectors. We show initial experimental implementations and discuss the key challenges and next steps in the development of these technologies.