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Solution processing is an attractive alternative to standard vacuum fabrication techniques for the large-area manufacturing of metal oxide (MOx)-based electron devices. Here, we report on thin-film...

With the development of our in-situ Laser Processing techniques we provide solutions to both planarize Fused Deposition Modeling (FDM) printed plastics and sintering of inks printed by Direct Ink Writing (DIW). Laser sintering enables fabrication of 3D printed functional and structural layers out of FDM printed thermoplastics and DIW printed conductive inks. As the sintering is in-situ, the sintered conductive layers, produced out of DIW printed silver inks, can be embedded into thermally sensitive FDM printed thermoplastics. In this fashion, vertical stacks out of these materials can be fabricated, in order to achieve capacitive and resistive mechanical transducers.

In this review paper, we summarise the status and trends in the research and development of printed sensors on foil substrates. Our focus includes sensor technologies that have some of their elements printed with a special interest for fully printed structures. The paper reviews the two large physical and chemical sensor families addressing different transduction principles. The paper concludes with a short notice on status and perspectives in the field with some words on the commercial maturity and trends of printed sensors on foil.

We propose an autonomous battery-less wireless sensor node that combines on a single printed circuit board an ultra-wideband (UWB) transmitter and its printed antenna, together with a piezoelectric cantilever and a solar cell array to harvest vibrations and light energy, respectively. The co-design of the solar cell array with the printed UWB antenna allows a prototype size of only 85x35 mm2, i.e., less than 65% of a credit card size. Low-cost is achieved by using inexpensive FR4 dual-layer substrate, standard-ceramic capacitors, and low-cost harvesters. The vibrational energy scavenger is fabricated at the wafer scale based on commercially available bulk polycrystalline Lead Zirconate Titanate (PZT), and the solar cells are fabricated by depositing amorphous-Si on 0.5 mm thick glass substrate. The cold-startup time of the demonstrator is about 42 min under indoor-ambient light conditions, and about 34 min under 700 mg vibrations at a frequency of 100 Hz. Once started, the sensor requires only 12.6 µW to allow a transmission rate of one temperature sensor readout every 34 s, thanks to the UWB transmitter that consumes only 206 pJ per pulse and a custom protocol with a reduced overhead.

Wearable sensors have garnered significant attention in recent years owing to their great promise in personalized health care and fitness monitoring [1]. Among these, recent advancements in wearable technology have enabled the development of sweat analysing sensors for in situ real-time and continuous monitoring of ions, alcohol and metabolites. Comparison and correlation between sweat and blood samples provided a further demonstration of the medical and physiological relevance of sweat [2]. Continuous monitoring of ions present in sweat (such as Na+, K+, Cl- and H+), can provide multiple information on our health status, such as for dehydration. One of the main requirement for facilitating real-time analysis is the development of a soft and flexible platform integrated with microfluidics that can be easily interfaced with the epidermis. This allows direct extraction of sweat and continuous sampling [3]. In this context, printing technologies emerge as a promising method, over the traditional multi-step photolithography process, for rapid, high throughput and cost-effective fabrication of configurable flexible sensing platforms [4]. Here we present a microfluidics-integrated potentiometric-based chemical sensing patch for multiplexed sweat ions analysis. Potentiometric sensor arrays on flexible foil are fabricated by the screen printing process, and assembled into a polymeric microfluidic platform through vertical stacking of thin adhesive layers. The microfluidic structure, which comprises of sweat sampling inlet, guiding channels and collecting reservoirs, are devised and fabricated by a programmed laser-cutter. The developed sweat patch facilitates simultaneous real-time detection of ions present in sweat, such as sodium (Na+), potassium (K+), chloride (Cl-), and pH. Our patches pave the way for simple and low-cost fabrication of wearable sweat sensors for point-of-care medical applications and personalized fitness monitoring. Figure 1(a) shows the optical image of the devised patch for sweat analysis. Flexible and transparent polymeric sheet was used as a substrate for creating microfluidic features and fabricating electrodes array for ion sensing. The microfluidic design, which includes sweat intake inlet, channel, reservoir and outlet, was fashioned by a software-based programmed laser cutter through 2D patterning of the polymeric film. Ion sensing electrodes array was fabricated by screen printing, which included printing of (i) silver layer for current collector, (ii) carbon layer as working electrode for Na+, K+, and pH sensing, and (iii) silver/silver chloride (Ag/AgCl) layer as both reference electrode and Cl- selective electrode. A polyurethane (PU) layer was screen printed as an insulator to encapsulate the electrodes in aqueous environments. Sodium and potassium ion selective electrodes (ISEs) were obtained by drop-casting Na+ and K+ ion-selective membranes (ISMs) onto their respective electrodes. The Ag/AgCl reference electrode was modified with a PVB membrane to get a stable reference. Polyaniline (PANI) was electrodeposited in order to obtain an ISE for pH sensing. The final 3D architecture of the sweat patch was obtained by stacking the sensing electrodes array layer and the microfluidic layer using laser patterned double-sided adhesive layers. A biocompatible medical-grade adhesive was used to mount the patch on the skin for real-time analysis. To evaluate the performance of microfluidic patch for sweat secretion and collection, the patch (without electrodes array) was attached to subjects forearm and used to collect sweat. Figure 1(b) shows the optical image of the real-time, in situ collection of sweat using our patch during indoor activities. This continuous real-time test on human subjects validates the capability of our fabricated patch for sampling and collecting sweat through capillary effect. The sensing characteristics of the fabricated ISEs were tested. Each ion-selective sensor response was characterized individually with their respective analyte solution. Figure 1(c) and (d) show the open circuit potential (OCP) responses of the potassium and sodium ISEs, measured in 2-32 mM potassium chloride solutions and 10-160 mM sodium chloride solutions, respectively. Both ISEs showed a fast response and exhibited a linear relationship between OCP and analyte concentration in sweat range with a Nernstian behaviour. Figure 1(e) and (f) show the representative OCP responses of the pH and chloride ISEs measured in McIlwaine’s buffer (pH 4-8) and 5-160 mM sodium chloride solutions, respectively. The pH sensor showed a stable output voltage with nearly Nernstian behaviour. However, the chloride sensor exhibited low sensitivity, and is being further improved by incorporating Cl- selective membrane to the Ag/AgCl electrode. Interference studies have shown that the fabricated ISEs are selective in physiologically relevant concentrations, as shown for K+ ISE in Figure 1(g). The performance of the fabricated patch demonstrates the capability for real-time multiplexed monitoring of sweat analytes for health care applications with as next text its sensing validation on people. [1] W. Gao, S. Emaminejad, H.Y. Nyein, S. Challa, K. Chen, A. Peck, H.M. Fahad, H. Ota, H. Shiraki, D. Kiriya, D.H. Lien, G.A. Brooks, R.W. Davis, A. Javay, Nature 529, 509- 514(2016); doi:10.1038/nature16521. [2] H.Y. Nyein, M. Bariya, L. Kivimäki, S. Uusitalo, T.S. Liaw, E. Jansson, C.H. Ahn CH, J.A. Hangasky, J. Zhao, Y. Lin, T. Happonen, M. Chao, C. Liedert, Y. Zhao, L. Tai, J. Hiltunen, A. Javay, Science Advance 5(8), 1-12(2019); DOI: 10.1126/sciadv.aaw9906. [3] J.R. Sempionatto, A. Martin, L. García-Carmona, A. Barfidokht, J.F. Kurniawan, J.R. Moreto, G. Tang,Shin, X. Liu, A. Escarpa, J. Wang, Electroanalysis 31(2), 239- 245(2019); DOI: 10.1002/elan.201800414. [4] M.Bariya, Z.Shahpar, H.Park, J.Sun, Y.Jung, W.Gao, H.Y..Nyein, T.S .Liaw, L.C.Tai , Q.P.Ngo, M.Chao,ACS nano12(7):6978-87(2018); DOI: 10.1021/acsnano.8b02505 Figure 1

International audience; We demonstrate the functionality of a new active thermal microchip dedicated to the temperature calibration of scanning thermal microscopy (SThM) probes. The silicon micromachined device consists in a suspended thin dielectric membrane in which a heating resistor with a circular area of 50 lm in diameter was embedded. A circular calibration target of 10 lm in diameter was patterned at the center and on top of the membrane on which the SThM probe can land. This target is a resistive temperature detector (RTD) that measures the surface temperature of the sample at the level of the contact area. This allows evaluating the ability of any SThM probe to measure a surface temperature in ambient air conditions. Furthermore, by looking at the thermal balance of the device, the heat dissipated through the probe and the different thermal resistances involved at the contact can be estimated. A comparison of the results obtained for two different SThM probes, microthermocouples and probes with a fluorescent particle is presented to validate the functionality of the micromachined device. Based on experiments and simulations, an analysis of the behavior of probes allows pointing out their performances and limits depending on the sample characteristics whose role is always preponderant. Finally, we also show that a smaller area of the temperature sensor would be required to assess the local disturbance at the contact point.

This paper presents an analytical and experimental study of a compact configuration to harvest energy from a rotating gear using piezoelectric microelectromechanical system harvesters. The reported configuration realizes a contact-type frequency up-conversion mechanism in order to generate useful electrical energy. The up-conversion mechanism was achieved using an atomic force microscope (AFM)-like piezoelectric cantilever plucked by the teeth of the rotating gear that could be eventually driven by an oscillating mass. This paper describes relevant design guidelines for harvesting energy from the low-frequency mechanical movement of a rotating gear through analytical modeling and finite element method (FEM) simulation followed by experimental validation. Different harvester configurations are investigated to identify the optimal configuration in terms of the output energy and energy conversion efficiency. The latter results are reported for the first time because of the implementation of an original concept based on the coupling of the harvester with a rotational flywheel. The experimental results reveal that free vibrations of the harvester after plucking contribute significantly to the output energy and efficiency. By adding a proof mass, the efficiency of the system can be greatly improved. For plucking speeds between 3 and 19 r/s, average output powers in the order of tens of microwatts were obtained for continuous plucking. By combining interaction energy, friction, and energy absorption, between the harvester and inertial mass, the maximum efficiency of the impact piezoelectric harvesters was found to be 1.4%. The efficiency results obtained were compared with the noncontact magnetic plucking approach further demonstrating the potential of our concept. Finally, different tip-gear materials combinations were evaluated showing the importance of their nature on the reliability of the presented configuration. [2014-0102]

In this work, the fabrication of Rochelle salt based piezoelectric structures is illustrated. Structures composed of paper and Rochelle salt are easily manufactured using simple processes. Both manufacturing and the material itself are environmental friendly. Additionally Rochelle salt is biocompatible. In the paradigm of a cleaner piezoelectric technology, the fabrication of active sensing or actuating devices is developed. Thus processing method, material and piezoelectric properties have been studied: (1) pure crystals are used as acoustic actuator, (2) properties of paper impregnated with Rochelle salt are detailed, (3) charge generation is demonstrated on the impregnated material. Actuating and sensing devices are reported in order to highlight the potential of this green piezoelectric material. © 2015 The Authors. Published by Elsevier Ltd.

We report a simple transducer architecture based on two interdigitated inkjet-printed gold electrodes deposited on polymer substrate. The particularity of this transducer is the double functionality of the heater, since it works as heater and sensor electrode simultaneously. This way, a metal-oxide gas sensor can be realized easily using a two-step fabrication process, the printing of the two electrodes and their coating with the sensing film. The transducer was validated by coating it with tungsten oxide nanoneedles (NNs) functionalized with Pt nanoparticles (NPs) via aerosol assisted CVD method (AACVD) and then tested under different concentrations of H2 gas. The proposed flexible printed transducer allows the simple and cost-effective realization of metal oxide gas sensors. © 2015 Published by Elsevier Ltd.

We describe a scanning thermal microscope that uses a fluorescent nanocrystal as a temperature probe. The nanocrystal is made of an inorganic fluoride material doped with erbium ions. The temperature is determined by measuring the fluorescence intensity ratio between two adjacent fluorescence lines. We first visualized the heating of a Cr stripe, and observed two different heat transfer channels, by direct contact between the tip and the device and by conduction through the air gap. We then measured the temperature map of a Joule heated submicron wide Pt wire and observed that the temperature elevation is uniform all along the wire. The measured images are obtained with a submicron lateral resolution and demonstrate the good reliability of the technique for characterizing the thermal properties of nanoscale devices and structures.

International audience; We report on a micro-hotplate technology platform optimized for the calibration of Scanning Thermal Microscopy probes (SThM) used in surface temperature measurement mode. The three chips designed include the same heating area with a calibration area of 10 × 10 µm2 where the SThM probes can land. The 1st design allows to study the influence of the nature of the material on the SThM probes thermal contact resistance. The 2nd design includes a resistive temperature sensor (RTD) integrated on the contact area, which is dedicated to evaluate the capability of a probe to measure a surface temperature. The 3rd design has a contact area made of a suspended platinum membrane for coupling SThM probes with optical thermal measurements. The thermal response of a thermocouple (TC) SThM probe was extracted demonstrating the relevance of these chips for SThM probes characterization and calibration.

Energy harvesting and sensing triboelectric module based on 3D-printed materials have been developed. Rapid prototyping, 3D-printing method is used to prepare sheets of triboelectric materials and simple film casting technique is employed to deposit electrically conductive carbon based elastomeric composite on these dielectrics. The device exhibits capability to detect and harvest energy from mechanical deformation. The developed 3D printed triboelectric system, under tapping condition, provides the maximum rms power of 41.2 μW for the optimum load resistance of 6.1 MΩ that corresponds to the power density of 10.6 μW/cm2. The processing set the building-block towards fully printed triboelectric devices.

This study reports on the integration of a Silicon MEMS hotplate into a natural gas quality analyzer, i.e., a miniaturized gas viscometer used to measure the Wobbe Index (WI). COMSOL Multiphysics simulation was used for selection of the optimum geometry of the hotplate and gas sensing cell. Experimental characterization of the hotplate confirmed its stability under working condition of the sensor. The sensor has been tested by running various gases such as Nitrogen and Methane. The thermal analysis of the sensor and experimental results show a reduced response time of the sensor at lower power consumption and lower thermal time constant.

We manifest a new method of developing wearable triboelectric band for self-powerd gesture sensing and power generating. Film casting technique, that is easily scalable, was used to patterned soft stretchable elastomers and conductive carbon based composites. The developed triboelectric band showed the capabilities of detecting locomotion of elbow and knee movement and provides electrical signal in response. The rms voltage, current and power of 2.9 V, 0.3 μA and 1.6 μW for elbow stretching, and 1.1 V, 0.11 μA and 0.22 μW for knee stretching was obtained for the optimum load of 10.1 MΩ at operational frequency of 1 ± 0.1 Hz.

We report the modeling, and geometrical and electrical characterization, of inkjet and screen-printed patterns on different polymeric substrates for use as antennas in radio-frequency identification (RFID) applications. We compared the physical and electrical characteristics of two silver nanoparticle-based commercial inkjet-printable inks and one screen-printable silver paste, when deposited on polyimide (PI), polyethylene terephthalate (PET), and polyetherimide (PEI) substrates. First, the thickness of the inkjet-printed patterns was predicted by use of an analytical model based on printing conditions and ink composition. The predicted thickness was confirmed experimentally, and geometrical characterization of the lines was completed by measuring the root-mean-square roughness of the patterns. Second, direct-current electrical characterization was performed to identify the printing conditions yielding the lowest resistivity and sheet resistance. The minimum resistivity for the inkjet-printing method was 8.6 +/- A 0.8 mu I (c) cm, obtained by printing four stacked layers of one of the commercial inks on PEI, whereas minimum resistivity of 44 +/- A 7 mu I (c) cm and 39 +/- A 4 mu I (c) cm were obtained for a single layer of screen-printed ink on polyimide (PI) with 140 threads/cm mesh and 90 threads/cm mesh, respectively. In every case, these minimum values of resistivity were obtained for the largest tested thickness. Coplanar waveguide transmission lines were then designed and characterized to analyze the radio-frequency (RF) performance of the printed patterns; minimum transmission losses of 0.0022 +/- A 0.0012 dB/mm and 0.0016 +/- A 0.0012 dB/mm measured at 13.56 MHz, in the high-frequency (HF) band, were achieved by inkjet printing on PEI and screen printing on PI, respectively. At 868 MHz, in the ultra-high-frequency band, the minimum values of transmission loss were 0.0130 +/- A 0.0014 dB/mm for inkjet printing on PEI and 0.0100 +/- A 0.0014 dB/mm for screen printing on PI. Although the resistivity achieved is lower for inkjet printing than for screen printing, RF losses for inkjetted patterns were larger than for screen-printed patterns, because thicker layers were obtained by screen printing. Finally, several coil inductors for the HF band were also fabricated by use of both printing techniques, and were used as antennas for semi-passive smart RFID tags on plastic foil capable of measuring temperature and humidity.

This paper presents an automated test bench, based on a rigorous measurement procedure, used to fully characterize vibration energy harvesters including determination of the resonance frequency, impedance, optimal load, and output power as a function of both frequency and acceleration. The potential of this method and the performance of the automated test bench allows systematic data acquisition which is essential for a good comparison of all harvesters. A dedicated automation circuit was designed and fabricated. It uses stepper motors to mechanically control trimmers to vary the resistive load and reed relays to switch between the measurement sequences. With this, the setup is able to determine the optimal load of the device-under-test at its resonant frequency for a given acceleration. The test bench was used to fully characterize several types of vibration harvesters fabricated on both silicon and polymeric substrates. A comparison of the characterized devices is discussed using a figure of merit proposed here. A survey and compilation of current practices used to benchmark vibration harvesters is also reported.

In this paper, a woven textile containing temperature and humidity sensors realized on flexible, plastic stripes is presented. The authors introduce two different sensors fabrication techniques: the first one consists of a conventional photolithography patterning technique; the second one, namely inkjet-printing, is here presented as an effective, low-cost alternative. In both cases, we obtain temperature and humidity sensors that can be easily integrated within a fabric by using a conventional weaving machine. All the sensors are fully characterized and the performances obtained with the two different fabrication techniques are compared and discussed, pointing out advantages and drawbacks resulting from each fabrication technique. The bending tests performed on these sensors show that they can be successfully woven without being damaged. A demonstrator, consisting of a mechanical support for the e-textile, a read-out electronic circuit, and a graphical PC interface to monitor the acquisition of humidity and temperature values, is also presented and described. This paper opens an avenue for real integration between printed electronics and traditional textile technology and materials. Printing techniques may be successfully used for the fabrication of e-textile devices, paving the way for the production of large area polymeric stripes and thus enabling new applications that, at the moment, cannot be developed with the standard lithography methods.

Fabrication, textile integration and post-weaving characterization of a robust platform for monolithically integrated, low-power gas and temperature sensing are presented. The platform, consisting of an interdigitated planar capacitor for gas sensing and a resistive temperature sensor, is fabricated on a 50 mu m thick flexible Kapton E (R) film using a simple roll-to-roll compatible process, and particularly targets disposable textile products, such as smart air filters, and medical garments. In order to demonstrate the versatility of the platform, the sensors are functionalized for humidity sensing by spray-coating of a 10 mu m thick Cellulose Acetate Butyrate (CAB) polymer layer. In commercial machine weaving processes, any functional device undergo significant mechanical deformation, mostly due to high bending, and shear forces associated with the process. Bending radii in textiles can be as small as 165 mu m during weaving, corresponding to a strain of about 15%. This imposes stringent mechanical requirements on the textile integrated sensors. Furthermore, the sensors integrated in textiles are exposed to harsh physical and chemical environments during operation. To avoid device failure, the sensor active area is fully encapsulated for protection during singulation, weaving, and operation, and is demonstrated to retain full functionality after weaving and repeated strain and stress tests. Despite the simple sensor structure, rapid and accurate sensor response is demonstrated in differential sensing mode. (c) 2012 Elsevier B.V. All rights reserved.

We report on the properties of ferroelectric Pb(Zr0.2Ti0.8)O3 (PZT) thin films grown epitaxially on (001) silicon and on the performance of such heterostructures for microfabricated piezoelectric energy harvesters. In the first part of the paper, we investigate the epitaxial stacks through transmission electron microscopy and piezoelectric force microscopy studies to characterize in detail their crystalline structure. In the second part of the paper, we present the electrical characteristics of piezoelectric cantilevers based on these epitaxial PZT films. The performance of such cantilevers as vibration energy transducers is compared with other piezoelectric harvesters and indicates the potential of the epitaxial approach in the field of energy harvesting devices.

This paper presents a complete wafer level microfabrication process for the production of unimorph MEMS energy harvesters based on bulk PZT. Recently, piezoelectric harvesters designed to take advantage of the high quality piezoelectric properties of bulk PZT have been fabricated using local placement and bonding of individual PZT pieces and large proof masses at the chip level. With the process presented here, 16 piezoelectric energy harvesters have been fabricated in parallel at the wafer level by bonding a single bulk PZT sheet to a silicon wafer and processing the wafer with standard microfabrication techniques including an electrodeposition step to deposit a thick (> 200 mu m) nickel proof mass. The fabricated harvesters are able to generate an output power of 116 mu W at an acceleration of 1 g and a resonant frequency of 203 Hz. (C) 2012 Elsevier Ltd....Selection and/or peer-review under responsibility of the Symposium Cracoviense Sp. z.o.o.

Low-power humidity and temperature sensors fabricated on Kapton (R) polyimide sheets are successfully woven into textile using a conventional weaving machine. During machine weaving electronic devices undergo mechanical deformation, mostly due to bending, and shear forces. Bending radii in textiles can be as small as 165 mu m during weaving, corresponding to a strain of about 15 %. This imposes stringent mechanical requirements on the textile integrated sensors. In this work, we present gas sensors on plastic foil with encapsulated active area for protection during stripes dicing, weaving, and operation. Basic tests with CAB and PDMS sensing layers on capacitive transducers showed that woven sensors survive the weaving process without loss of functionality. (C) 2011 Published by Elsevier Ltd.

The emergence of the fields of wearable devices, e-textiles and smart packaging brings new requirements on electronics and sensing systems. One or a combination of the following properties can be desired for their proper operation and to meet the functionalities required by the application in order to improve market penetration. Very low-cost, thin, large area, lightweight, flexibility, conformability, transparency, stretchability are some of the characteristics that can be offered by making sensors on polymeric foil. We propose printing processes for the fabrication of these devices to mainly reduce their production cost and to improve the environmental friendliness of their manufacturing. In this communication, we discuss the benefits, drawbacks, potential, and challenges of printing sensors on plastic substrates illustrated with some examples of technical developments performed in our laboratory. We present environmental sensors fabricated on plastic foil and the associated flexible encapsulation method at the foil level. Integration of printed sensing devices on smart RFID tags is also discussed. By using thin polymeric substrates, very small bending radius of curvature can be achieved. Besides the challenges linked to the large area printing of the sensing devices on flexible foil and the reliability of these devices under mechanical cycling, new developments are required on the interconnectivity of these devices with other electronics components to achieve efficient system integration. (C) 2011 Published by Elsevier Ltd.

We report on harsh-environment-compatible Pt-TSVs forming ohmic contacts with a highly doped bulk silicon. They were developed as a part of a Single Wall Carbone NanoTube (SWCNT) resonator device with 3D-packaging. The fundamental properties of the TSVs, experimentally obtained with bulk Si instead of the real working device, are presented. Our concept for the device fabrication is “via first”, followed by the nanodevice fabrication. As such, first ohmic contacts on silicon has been studied to be compatible with several harsh post-processing steps, including high temperature treatments—up to 850°C in air—and concentrated HF-based release steps. Then TSVs withstanding the aforesaid conditions have been developed. These interconnects are also of interest for MEMS devices operating at high temperature.

We demonstrate that doping the semiconductor zinc tin oxide (ZTO) with yttrium leads to a high-voltage thin film transistor (HVTFT) with enhanced switching performance. Adding 5% yttrium leads to an increase in the on-off ratio from 40 to 1000 at an operating voltage of 500 V and to a drop of the subthreshold swing from 65 to 35 V/dec. The performance is improved because of the reduction of the saturation voltage and because of a decrease in the off-current from several μA for undoped ZTO HVTFTs to 100 nA for Y5%ZTO. The decrease in saturation voltage and off-current can be attributed to a lower trap concentration leading to enhanced space-charge limited current and to a decrease in the background charge carrier concentration. At a 500 V bias voltage, an inverter circuit with a yttrium-doped ZTO HVTFT can control the output voltage between 50 V and 500 V, while the undoped ZTO HVTFT can only control the output voltage between 150 V and 450 V. The improvement in high voltage performance of yttrium-doped ZTO HVTFTs is important for future work related to high voltage thin film transistors made of amorphous oxide semiconductors as it demonstrates that this technology enables HVTFTs with simultaneously high operation voltage, high on-current, and high on-off ratio.We demonstrate that doping the semiconductor zinc tin oxide (ZTO) with yttrium leads to a high-voltage thin film transistor (HVTFT) with enhanced switching performance. Adding 5% yttrium leads to an increase in the on-off ratio from 40 to 1000 at an operating voltage of 500 V and to a drop of the subthreshold swing from 65 to 35 V/dec. The performance is improved because of the reduction of the saturation voltage and because of a decrease in the off-current from several μA for undoped ZTO HVTFTs to 100 nA for Y5%ZTO. The decrease in saturation voltage and off-current can be attributed to a lower trap concentration leading to enhanced space-charge limited current and to a decrease in the background charge carrier concentration. At a 500 V bias voltage, an inverter circuit with a yttrium-doped ZTO HVTFT can control the output voltage between 50 V and 500 V, while the undoped ZTO HVTFT can only control the output voltage between 150 V and 450 V. The improvement in high voltage performance of yttrium-doped ZT...

Selective multi-gas detection is often based on spectroscopic methods in the infrared region. The resulting setup consists of a spectrometer and the probing setup where often the spectrometer makes the sensing device large and heavy and does not allow easy on the field integration. We report on the application of a silicon micromachined lamellar grating interferometer in a Fourier transform infrared spectrometer for the detection of gases in the mid infrared region. The spectrometer heart was miniaturized consequently to fit in a box of 30mm×30mm×55mm. The Fourier transform infrared spectrometer was equipped with mid infrared optical fibers for light coupling. Gas measurements in the mid infrared region were focused on specific gases (CO2 andCH4) in order to determine the limit of detection and the selectivity that could be obtained using such a micro-spectrometer. Using two different spectral regions we were able to detect concentrations of carbon dioxide over a span from 100 to 9000ppm with a theoretical detection limit evaluated less than 10 ppm. The performed gas measurements showed the proof of principle of a miniaturized Fourier transform infrared gas analyzer based on a micromachined spectrometer and fiber optics.

Temperature, gas and humidity resistive/capacitive sensors on plastic substrates, suitable for mobile applications, like smart RFID tags, have been produced and investigated. The sensor concept is providing simple, versatile and low power solutions for temperature, humidity and gas detection. The device structure was devised together with the data evaluation strategies based on the latest generation ΣΔ analog (resistance and capacitance) to digital converters. The possibility of developing gas sensors on humidity sensitive substrates, having temperature corrected responses is demonstrated. The proposed sensor is aimed to evolve towards “flexible and full plastic” implementations.

This paper presents the design, fabrication and characterisation of surface micromachined polysilicon microheaters to be used as microigniters for micropropulsion applications. The microigniters are heated up by Joule effect and the thermal losses through the substrate are minimised by suspending the microheaters above the substrate. The developed process was compatible with the integration of the nozzle part of the microthruster. The electrical, thermal and mechanical characteristics of the microheaters were studied with the aim of evaluating their reliability. Temperatures up to 470 °C could be reached with an electrical power of 45 mW/beam. The current–voltage relation followed a linear characteristic at low power; at high bias voltages, a drift of the electrical resistance was measured after a few I–V cycles at power higher than 40 mW/beam. The elastic and plastic deformation threshold of the microheaters in operation and their maximum deflection before rupture were measured. The microheaters could dissipate relatively high constant powers for a few minutes to hours. The fabricated microheaters are promising candidates for the ignition of solid propellant microthrusters.

International audience; In this paper, we present the conception, fabrication and characterization of a thermopile designed to detect terahertz electromagnetic fields at room temperature. The thermopile is made of four doped silicon/titanium thermocouples. The absorber consists of a metallic grid made of titanium, deposited at the same time as the metal part of the thermocouples. The design of the grid is based on a theoretical multilayer model using equivalent resistivity and taking into account small diffraction effects. The grid is deposited on a 2.4 mm × 2.4 mm silicon nitride square membrane. The time constant of the sensor is measured at 0.3 THz to be 10 ms, which is consistent with finite elements simulations. The responsivity is evaluated at 4.8 μV/(W m−2). Due to a large impedance, which leads to a large Johnson noise, the noise equivalent power is 1.5 × 10−6 W Hz−1/2.

International audience; This paper presents the optimization of a micro gas preconcentrator (μ-GP) system applied to atmospheric pollution monitoring, with the help of a complete modeling of the preconcentration cycle. Two different approaches based on kinetic equations are used to illustrate the behavior of the micro gas preconcentrator for given experimental conditions. The need for high adsorption flow and heating rate and for low desorption flow and detection volume is demonstrated in this paper. Preliminary to this optimization, the preconcentration factor is discussed and a definition is proposed.

An EC funded MicroPyros project has permitted to develop the technologies to fabricate, assemble and command solid propellant microthrusters arrays for thrusts of a few of milli Newtons The prototype built for space application has 100 individually addressed ∅ 1.5 mm × 1.5 mm thrusters on 576 mm2. Nozzles’ throats are 250 μm and 500 μm. This paper reviews the prototype structure and details the final processes for the fabrication and assembling. This paper presents also a new addressing technology based on polysilicon threshold elements used for the addressing and heating of each thruster in the array. With polysilicon threshold element, ignition success is of 100% with an input power of 250 mW using a zirconium perchlorate potassium (ZPP) material. Then, the combustion of a glycidyle azide polymer (GAP) is sustained in the chamber and generate thrusts in the range of 0.3–2.3 mN depending of the micronozzle dimension.

A new method for realizing three-dimensional structures based on the standard silicon-on-insulator microelectromechanical systems is developed using vertically buckled bridges as structural elements. The vertical displacement, profile of the bridge, and obtainable accuracy of the displacement are examined. Using the lateral dimension control of the bridge and the supporting beams, the vertical positioning is realized based on the planer photolithography. As a demonstration, a vertical comb drive actuator is prepared and its performance is examined.

This communication presents a modulated mode of operation for MOSFET gas sensors. A low-power micromachined device allows pulsing the temperature of MOSFET gas sensors with a time constant less than 100ms. Modulating the temperature during the gas exposure modifies the kinetics of the gas reactions with the sensing film. The way the sensor response is modified by the temperature modulation depends on the sensor "history", on the nature of the surrounding gaseous atmosphere, and on the type of materials used as catalytic sensing film. Pulsing the temperature up just after the gas exposure can reduce the recovery time for specific applications, such as for hydrogen detection. Cycling the temperature can allow the discrimination between different gas mixtures. Discrimination was shown for gaseous mixtures of hydrogen and ammonia in air. The results obtained indicate that a "smart" combination of sample and temperature profile could be used to expand the information content in the sensor response. © 2003 Elsevier Science B.V. All rights reserved.

We have performed thermal measurements and electrothermal simulations (finite element modelling) with the aim of optimizing the power consumption and the temperature distribution of micro-hotplates for gas-sensing applications. A silicon island was added underneath the membrane of the micro-hotplate to improve the temperature distribution of drop-coated metal-oxide gas sensors and to thermally isolate MOSFET gas sensors. The temperature distribution over the sensing area and the power consumption depend on the silicon island thickness, which was optimized for both applications using the software MEMCAD from Microcosm Technologies. In the optimization process, we considered the thermal conductivity of silicon and dielectric membrane, the operating temperature, the geometry and the area of the heater, and the processing of the silicon island. The thickness of the silicon island was optimized to ensure a good temperature distribution over the gas-sensing area for metal-oxide and MOSFET gas sensors with specific geometry.

Flexible high-voltage thin-film transistors (HVTFTs) operating at more than 1 kV are integrated with compliant dielectric elastomer actuators (DEA) to create a flexible array of 16 independent actuators. To allow for high-voltage operation, the HVTFT implements a zinc-tin oxide channel, a thick dielectric stack, and an offset gate. At a source-drain bias of 1 kV, the HVTFT has a 20 µA on-current at a gate voltage bias of 30 V. Their electrical characteristics enable the switching of DEAs which require drive voltages of over 1 kV, making control of an array simpler in comparison to the use of external high-voltage switching. These HVTFTs are integrated in a flexible haptic display consisting of a 4 × 4 matrix of DEAs and HVTFTs. Using a single 1.4 kV supply, each DEA is independently switched by its associated HVTFT, requiring only a 30 V gate voltage for full DEA deflection. The 4 × 4 display operates well even when bent to a 5 mm radius of curvature. By enabling DEA switching at low voltages, flexible metal-oxide HVTFTs enable complex flexible systems with dozens to hundreds of independent DEAs for applications in haptics, Braille displays, and soft robotics.

In this paper we report the detection of explosive compounds using a miniaturized gas preconcentrator (μGP) made of porous silicon (PS) filled in with Carbopack B as an adsorbent material. The μGP includes also a platinum heater patterned at the backside and fluidic connectors sealed on the glass cover. Our μGP is designed and optimized through fluidic and thermal simulations for meeting the requirements of trace explosives detection. The thermal mass of the device was minimized while the flow rate was maximized for a reduced cycle time. A detection limit below 200ppb of 2, 4-dinitrotoluene (DNT) was demonstrated with our Carbopack-PS μGP. © 2014 The Authors. Published by Elsevier Ltd.

Here we describe a novel ChemFET sensor array that utilises carbon black composite polymers for the detection of organic vapours. Three vapour-sensitive composite polymers have been used as the gate materials of FET devices. A shift in the threshold voltage to toluene is observed with a linear dependence to concentration (Henry’s law) and a voltage sensitivity of up to 2.8 μV/ppm. The effects of humidity and temperature have also been examined and the magnitude of the response shows little dependence to humidity but an exponential fall with increasing temperature. We believe that this reduction in response is primarily due to a modification in the bulk solubility of the polymer. The shift in device threshold voltage may be caused by a change in the work function of the polymer composite, a swelling effect or a charge transfer effect. A generalised linear model is proposed here for the response of a ChemFET to an organic vapour at different humdities.

Reference EPFL-ARTICLE-172617doi:10.1166/sl.2010.1279View record in Web of Science Record created on 2011-12-16, modified on 2016-08-09

This paper reports on the design, fabrication, and characterization of the first low-power consumption MOSFET gas sensor, The novel MOSFET array gas sensor has been fabricated using anisotropic bulk silicon micromachining. A heating resistor, a diode used as temperature sensor, and four MOSFETs are located in a silicon island suspended by a dielectric membrane. The membrane has a low thermal conductivity coefficient and, therefore, thermally isolates the electronic components from the chip frame. This low thermal mass device allows the reduction of the power consumption to a value of 90 mW for an array of four MOSFETs at an operating temperature of 170/spl deg/C. Three of the MOSFETs have their gate covered with thin catalytic metals and are used as gas sensors. The fourth one has a standard gate covered with nitride and could act as a reference. The sensor was tested under different gaseous atmospheres and has shown good gas sensitivities to hydrogen and ammonia. The low-power MOSFET array gas sensor presented is suitable for applications in portable gas sensor instruments, electronic noses, and automobiles.

This works describes the fabrication process of an array of printed MEMS microbridges on polymeric foil, performed in only four easy steps. Each functional material was deposited exclusively by inkjet-printing technique, compatible with large-area fabrication. The array occupies an area of 2 mm x 2 mm and consists of 80 individual microbridges of 120 mu m x 80 mu m size each. When connecting all the bridges in parallel, the array displays a total capacitance value of 1.5 pF. The potential of the fabricated array has been demonstrated by employing it as a swelling-based capacitive humidity sensor where the polymeric substrate acts directly as the sensing layer.

This paper presents the design of a dual-mode (direct/differential) switched-capacitor (SC) interface system for an inkjet-printed capacitive sensor. The proposed system consists of a single-stage SC capacitance-to-voltage (C2V) converter and a 10-bit successive approximation register (SAR) ADC. The specifications of C2V are optimized at system level, emphasizing the C2V operation followed by the data converter. Cascade amplification is avoided to simplify the front-end. Both reference capacitor and feedback capacitor are calibrated to match the required value with 25 fF step. Correlated double sampling (CDS) technique attenuates the DC offset and flicker noise. Gain-boosting amplifier is adopted to improve linearity with low feedback factor. The 10-bit capacitive cascaded-binary-weighted (CBW) digital to analog converter (DAC) makes up the charge redistribution converter and achieves a balance between area, power and accuracy. Self-timing SAR logic uses extra half cycle and relaxes the settling time of pre-amplifiers. The entire interface system operates at 46 kHz sampling rate with 62 uW power consumption. Post layout simulation results show 3.5 mLSB integral non-linearity (INL) at the output of C2V and 9.9 bit ENOB of ADC. The active core area is 0.6mm2.

This paper presents the design of a single stage dual-mode switched-capacitor (SC) capacitance-to-voltage converter (C2V) for the inkjet-printed capacitive humidity sensor. The specifications of C2V are optimized at the system level, emphasizing the C2V operation followed by the data converter. A closed form of the maximum output range of single stage C2V is given to avoid the cascade amplification. A gain-boosting amplifier is adopted to improve the linearity. Correlated double sampling (CDS) technique attenuates the DC offset and low frequency flicker noise. This design is simulated in 0.18 μm CMOS technology with 1.8 V supply. Post layout simulation results show 3.5 mLSB integral non-linearity (INL). Output noise powers are 230 μVrms and 290 μVrms in two modes. The entire C2V operates at 50 kHz sampling rate with 54 μW power consumption.

In this work we report on a self-standing parallel-plate capacitive humidity sensor on a thin dry photoresist film with integrated resistive temperature sensor and heater on each electrode, respectively. The simple concept proposes dry photoresist film as substrate but also as dielectric humidity sensing layer. The characteristics of the temperature sensor (TCR ~900 ppmK-1), resistive heater (0.65 °C/mW) and humidity sensor (response time ~230 seconds, sensitivity ~23 fF / 1%R.H) were measured and are reported. FEM simulations were used to visualize the temperature distribution generated by the integrated heater.

Platinum TSVs compatible with harsh-environment post-processing were fabricated on an SOI wafer. This study was part of a larger project for the development of a SWCNT resonator, 3D-integrated, in a “via-first” approach, with its driving electronics. After their passivation, they are compatible with the harsh-environment post-processes necessary for the fabrication of the SWCNT resonator: the growth of CNT at a high temperature of 850 °C in an oxidizing environment, and their release in concentrated HF solution. The TSV metallization formed a stable ohmic contact with the silicon device layer on which the CNT resonator will be standing. We present RF (radio frequency) simulations correlated with RF measurements of the Pt-TSVs from 0.3 to 5 GHz. A reflection coefficient of -20 dB and transmission coefficient of -4 dB were measured at 5 GHz.

A scanning thermal microscope working in passive mode using a micronic thermocouple probe is presented as a quantitative technique. We show that actual surface temperature distributions of microsystems are measurable under conditions for which most of usual techniques cannot operate. The quantitative aspect relies on the necessity of an appropriate calibration procedure which takes into account of the probe-to-sample thermal interaction prior to any measurement. Besides this consideration that should be treated for any thermal contact probing system, the main advantages of our thermal microscope deal with the temperature available range, the insensitivity to the surface optical parameters, the possibility to image DC, and AC temperature components up to 1 kHz typically and a resolution limit related to near-field behavior. (C) 2013 AIP Publishing LLC.

This chapter reviews micromachined semiconductor gas sensors. First, this chapter briefly discusses the history of this technology. It then addresses the microhotplates' concept that has led to the development of different types of micromachined gas sensor devices. The different realizations of micromachined semiconductor gas sensors are presented: thin- and thick-film metal oxide, field effect, and those using complementary metal oxide semiconductors and silicon on insulator technologies. Recent developments on gas-sensitive nanostructures integrated on micromachined transducers and semiconductor gas sensors on polymeric foil and their printing are highlighted. Finally, the industrialization of micromachined gas sensors is addressed.

Power generating soft triboelectric based shoe insole fully elastomeric and compatible with large-scale fabrication technique has been developed. During the process, film casting and stencil printing techniques were implemented to deposit/pattern elastomeric and soft/flexible materials, such as, polydimethylsiloxane (PDMS) and polyurethane (PU). Carbon- based elastomeric materials were used as electrodes, which were also film casted. The developed triboelectric generator (TENG) was capable of harnessing electrical power effectively from mechanical deformation of the system during walking or running activities. The performance of the device was tested for walking with frequency of 0.9±0.2 Hz. The power (rms value) of 0.25 mW was achieved for load resistance of 100 MΩ,, which corresponded to the power density (rms value) of 1.9 μW/cm2.

This work reports on the design, fabrication and characterization of an inkjet-printed multisensing platform on flexible polymeric substrates integrated into a printed semi-passive high frequency radio frequency identification (HF RFID) smart label. The printed platform was integrated after fabrication to the main RFID carrier, which contained an NFC RFID chip, a microprocessor, a readout frontend and a screen-printed circuitry and antenna. The multisensing platform has channels for capacitive vapor detection (i.e. humidity), two channels for resistive-based vapor detection (i.e. ammonia) with heating capability, and one resistive channel for temperature detection (RTD). A modular approach was employed where the sensing platform was integrated to the base RFID label carrier using foil-to-foil integration techniques compatible with large area fabrication. Besides wireless communication, the semi-passive label possesses data logging and the possibility of measuring all the sensors simultaneously through a direct readout circuitry. In addition to individual sensor characterization, the full functionality of the smart label was successfully demonstrated by measuring different temperature, humidity and ammonia levels.

Piezoelectric harvesters are considered an alternative power source for applications that can support low to medium data rate transmissions in wireless sensor networks where ambient vibrations can provide microwatts to milliwatts of power. In this paper, we report the design and performance of a proof-of-concept (POC) autonomous sensor-node prototype including: an in-house piezoelectric harvester; a power management unit (PMU) made of discrete components; and an in-house ultra-wide band impulse radio (UWB-IR) transmitter. The piezoelectric harvester provides 54µW at 3.3V rms at 450 milli-g and resonant frequency of 160 Hz. In these conditions, it was observed that the sensor node is capable of sending 1 burst of 100 pulses every 110 seconds consuming an average of 8.2µW, which is much less than the generated energy. The POC sensor node using kinetics energy harvester shows energy autonomy, thus opening range of possibilities for sub 100µW energy harvesting wireless sensor nodes.