Low-power gas sensors based on work-function measurement in low-cost hybrid flip–chip technology

To implement low-power gas sensors with low component costs, the principle of work-function read out via a hybrid suspended gate FET (SGFET) is being pursued, whereby a freely selectable sensor film undergoes a reversible work-function change corresponding to the build-up of a potential difference on the surface in response to gas adsorption/reaction. This is read out via an ISFET structure. An innovative design which allows cheap manufacturing will be described for the principle that has already been successfully demonstrated. The starting point of the design is a ceramic Al₂O₃ substrate coated with conductor patterns and sensitive materials onto which the FET is mounted in flip–chip technology. By means of the freely selectable sensor film and its preparation method, a wide range of applications can be opened up.     

Nanostructured polyaniline thin films as pH sensing membranes in FET-based devices

Polyaniline (PANI) has become an important conducting polymer for sensing due to its morphological and electrical properties. However, the processing of polyaniline in the form of nanostructured thin films is often limited by the low solubility of the polymer in water. We synthesized nanostructured polyaniline (N-PANI) aimed at improving its solubility to form layer-by-layer (LbL) thin films in conjunction with poly(vinyl sulfonic acid) (PVS) as counter ion. N-PANI was characterized via spectroscopic measurements and SEM images. After assembled as LbL thin films onto gold (Au) substrates, the PVS/N-PANI were employed as separative extended gate pH sensing membrane in FET-based devices presenting pH sensitivity around 58 mV/pH with small voltage drift. The results suggest that N-PANI can be easily processed to form suitable thin films for pH sensing and can be combined with biomolecules to be applied in FET-based biosensors.     

Improving particle detection sensitivity of a microfluidic resistive pulse sensor by a novel electrokinetic flow focusing method

A novel and simple method of improving the particle detection sensitivity of a microfluidic resistive pulse sensor was presented in this paper. This novel electrokinetic flow focusing method utilizes a focusing solution (with high resistivity) flowing from the upstream focusing channel to the downstream focusing channel. The focusing solution in the sensing gate works like a virtual insulation wall that greatly narrows the gate and thus improves the detection sensitivity. An equation was derived to relate the magnitude of the output signal to the resistivity and the width of the focusing solution. The width of the focused particle solution under different voltages was numerically predicted. The results show that the magnitude of output signal increases with the decrease in the width of the focused particle stream. More importantly, the detection sensitivity can be improved by decreasing the space occupied by the focusing solution in the upstream and downstream channels as much as possible. Detection of 1 μm particle with a sensing gate of 30 × 40 × 10 μm (width × length × height) was successfully achieved. The proposed method is simple and advantageous in detecting smaller particles without fabricating a small sensing gate.     

Ultrathin GaN/AlN/GaN solution-gate field effect transistor with enhanced resolution at low source-gate voltage

The pH response of a GaN/AlN/GaN solution-gate field effect transistor (SGFET), with a GaN/AlN barrier of 7.5 nm thick, is analyzed and compared with standard GaN/AlGaN/GaN SGFETs with total barrier thicknesses of 19 and 23 nm. While all types of SGFETs show a similar surface sensitivity to H⁺ ions, a significant improvement in the transducive sensitivity of the SGFET source-drain current under pH changes is found when decreasing the barrier thickness, due to the increased transconductance of the FET structure. Resolution better than 0.005 pH can be estimated in the case of the ultrathin SGFET. Moreover, the maximum transconductance value shifts to gate-drain voltage close to 0 V, which eventually involves no need of reference electrode in less demanding applications, simplifying the final design of the device and making AlN barrier-based SGFETs highly recommended in the broad field of chemical sensors.     

Fabrication of CNT field‐emitter array using a polymer insulator

Abstract— The fabrication process of a carbon‐nanotube (CNT) field‐emitter array (FEA) having a polymer insulator is reported. This polymer material is suitable for a large‐sized FEA because of its coating property and thermal stability. These features contribute to the display‐image uniformity, the tolerance to the thermal‐sealing process, etc. A new method of forming via holes on the insulator instead of gate holes has been developed. The method uses a spin‐wet‐etching (SWE) technique instead of the typical reactive‐ion‐etching (RIE) method. The RIE method damages and contaminates the CNT at the end of the etching process. However, the SWE technique ensures fine gate hole configurations with little under‐cut without any damage nor contamination. An FEA panel 1.5 in. on the diagonal was fabricated by using the method. The FEA showed good emission uniformity with proper surface treatment of the CNT.     

Chemically modified copolymer coatings for mass-sensitive toluene vapor sensors

Styrene-co-chloromethyl styrene copolymers chemically modified with various kinds of monoamines or diamines were synthesized. Their sensing properties based on toluene vapor sorption/desorption behaviors were measured using a quartz crystal microbalance (QCM) technique. Introduction of aliphatic diamine compounds having a proper chain length (e.g., N,N-dimethyl-1,3-propanediamine (DMPDA)) into the structure of the copolymer realized improvements to the toluene vapor sorption capacity, the response time, and reversibility compared to the conventional polymer coatings. FTIR analysis suggests the formation of a loosely cross-linked structure, resulting in the promotion of toluene vapor diffusion into the film.     

Integrated gate driver circuit technology with IGZO TFT for sensing operation

In this paper, we propose a new integrated gate driver circuit for random sensing operation of external compensated organic light‐emitting diode (OLED) display using oxide thin‐film transistor (TFT). Using this technology, we successfully launched 55‐inch and 65‐inch ultrahigh definition OLED TVs with gate in panel (GIP) circuit. The structure of the existing OLED TVs implemented gate signals through the gate integrated circuits (ICs) attached to the left and right sides of the panel. The structure using the gate IC was inferior to the panel structure using the GIP in terms of process and product design and cost. Thus, we propose a new oxide GIP circuit for OLED TV. Like the previous gate IC model, the proposed GIP circuit successfully implemented the random sensing function during the display operation. This GIP circuit is also designed to overcome the problems caused by the negative Vth characteristics of the oxide device.     

基于深度神经网络的语种识别*

语音段的有效表示方法存在易混淆语种和短时语音段识别率较低等问题,为满足不同时长和方言的识别要求,提出基于深度神经网络不同层的有效语音段表示方法.采用含有中间瓶颈层的深层神经网络作为前端特征提取,综合利用该网络的输出层和中间瓶颈层输出结果,得到不同形式的语音段表示并用于语种识别.在美国国家标准技术局语种识别评测2009年和2011年阿拉伯方言数据集上验证了方法的有效性.     

Light-addressable suspended-gate gas sensor

A light-addressable potentiometric sensing (LAPS) system has been applied to construct an oxygen sensor using a suspended-gate electrode. The sensor principally consists of an MIS structure, i.e., suspended gate/air gap/LaF₃/SiO₂/Si. The use of the suspended gate makes it possible to realize a contactless sensing system, which provides a flexible structure to integrate multiple sensing elements on a single-chip semiconductor surface. The sensor shows a stable response at room temperature to oxygen partial-pressure changes in the range 0.25-1.0 atm. The fabrication conditions of the LaF₂ film are also discussed.     

Impact of ZnO gate interfacial layer on piezoelectric response of AlGaN/GaN C-HEMT based ring gate capacitor

We report on a piezoelectric response investigation of AlGaN/GaN circular high electron mobility transistor (C-HEMT) based ring gate capacitor as a new stress sensor device to be potentially applied for dynamic high-pressure sensing. A ring gate capacitor of C-HEMT with an additional ZnO gate interfacial layer was used to measure the changes in the piezoelectric charge induced directly by the variation of piezoelectric polarization of both gate piezoelectric layers (AlGaN, ZnO) for harmonic loading at different excitation frequences. Our experimental results show that about 10 nm thick piezoelectric ZnO layer grown on ring gate/AlGaN interface of C-HEMT can yield almost a 60% increase in the piezoelectric detection sensitivity of the device due to its higher piezoelectric coefficient. A three-dimensional CoventorWare simulation is carried out to confirm the increase in the measured piezoelectric response of ZnO based ring gate capacitor of C-HEMT.     

Semantic speech recognition in the Basque context Part II: language identification for under-resourced languages

This paper describes the development of a Language Identification (LID) system oriented to robust Multilingual Speech Recognition in the Basque context where coexist three languages: Basque, Spanish and French. The LID system is integrated in GorUP, a Semantic Speech Recognition system for industrial complex environments described in Part I. The work presents hybrid strategies for LID, based on the selection of system elements by several classifiers (Support Vector Machines and Multilayer Perceptron) and Discriminant Analysis improved with robust regularized covariance matrix estimation methods oriented to under-resourced languages and stochastic methods for speech recognition tasks (Hidden Markov Models and n-grams). The LID tool manages the main elements of the Automatic Speech Recognition system (Acoustic Phonetic Decoder, Language Model and Lexicons).     

A review of models for low impact urban stormwater drainage

Low-impact development urban stormwater drainage systems (LID) are an increasingly popular method to reduce the adverse hydrologic and water quality effects of urbanisation. In this review, ten existing stormwater models are compared in relation to attributes relevant to modelling LID. The models are all based on conventional methods for runoff generation and routing, but half of the models add a groundwater/baseflow component and several include infiltration from LID devices. The models also use conventional methods for contaminant generation and treatment such as buildup-washoff conceptual models and first order decay processes, although some models add treatment mechanisms specific to particular types of LID device. Several models are capable of modelling distributed on-site devices with a fine temporal resolution and continuous simulation, yet the need for such temporal and spatial detail needs to be established. There is a trend towards incorporation of more types of LID into stormwater models, and some recent models incorporate a wide range of LID devices or measures. Despite this progress, there are many areas for further model development, many of which relate to stormwater models in general, including: broadening the range of contaminants; improving the representation of contaminant transport in streams and within treatment devices; treating baseflow components and runoff from pervious surfaces more thoroughly; linkage to habitat and toxicity models; linkage to automated calibration and prediction uncertainty models; investigating up-scaling for representation of on-site devices at a catchment level; and catchment scale testing of model predictions.     

High strain electromechanical actuators based on electrodeposited polypyrrole doped with di-(2-ethylhexyl)sulfosuccinate

The low-voltage electromechanical actuation of polypyrrole (PPy) doped with di-(2-ethylhexyl)sulfosuccinate (DEHS) has been investigated. The PPy-DEHS has been prepared both chemically (cast as films from solution) and by more conventional electrochemical polymerization. Very large strains of ∼30% were obtained during slow-scan redox cycling of the electrochemically prepared PPy-DEHS films. In constrast, PPy-DEHS films cast from solutions of the chemically polymerized polymer gave actuation strains of ∼2.5%. The polymerization method was also found to have a significant effect on the structure, conductivity and mechanical properties of the PPy-DEHS materials. The conductivity of the electrochemically polymerized PPy-DEHS was 75 S cm⁻¹, considerably higher than that found for the chemically derived polymer (7 S cm⁻¹). The structure of the PPy-DEHS was further elucidated from UV-vis, Raman and FT-IR spectral studies which indicated that the conjugation length of the PPy could be increased significantly by varying the polymerization method. Films obtained by casting chemically prepared PPy-DEHS showed higher modulus (2.3 GPa) than electropolymerized PPy-DEHS (0.6 GPa), but were more brittle. Both materials were electroactive in acetonitrile/water electrolyte. The higher actuation strain observed in the electrochemically prepared films was attributed to a more open molecular structure (as indicated by the lower modulus) allowing for easier ion diffusion and a higher conductivity allowing easier charge transfer.     

A new ISFET technology with back contacts using deep diffusions

A new fabrication method for ion-sensitive field-effect transistors (ISFETs) with back contacts has been developed. The connections between the drain and the source diffusions and the back contacts are achieved by diffusing impurities from both sides of the wafer, until a conductive path has been formed through the thickness of the wafer. After these conductive paths are built, an FET structure is constructed on the front face of the chip. The back access allows for a clean face where the chemically active gate is placed. This contrasts with more traditional devices where the gate and the contacts are placed on the same face of the transistor. It is also set apart from devices featuring back contacts with anisotropically etched pits that require a different processing laboratory separated from the main clean-room facilities. The aim of the present work is to produce ISFET-based chemical sensors with back contacts featuring a clean technology using standard silicon foundry facilities. These sensors are more compact, easier to encapsulate and with a longer lifetime when compared to devices produced with more traditional structures.     

Implicit excitation source features for robust language identification

In present work, the robustness of excitation source features has been analyzed for language identification (LID) task. The raw samples of linear prediction (LP) residual signal, its magnitude and phase components are processed at sub-segmental, segmental and supra-segmental levels for capturing the robust language-specific phonotactic information. Present LID study has been carried out on 27 Indian languages from Indian Institute of Technology Kharagpur-Multi Lingual Indian Language Speech Corpus (IITKGP-MLILSC). Gaussian mixture models are used to develop the LID systems using robust language-specific excitation source information. Robustness of excitation source information has been evinced in view of (i) background noise, (ii) varying amount of training data and (iii) varying length of test samples. Finally, the robustness of proposed excitation source features is compared with the well-known spectral features using LID performances obtained from IITKGP-MLILSC database. Segmental level excitation source features obtained from raw samples of LP residual signal and its phase component perform better at low SNR levels, compared with the vocal tract features.     

Analysis of response mechanism of a proton-pumping gate FET hydrogen gas sensor in air

Two different types of hydrogen response signals (DC and AC) of a proton-pumping gate FET with triple layer gate structure (Pd/proton conducting polymer/Pt) were obtained. The proton-pumping gate FET showed good selectivity against other gases (CH₄, C₂H₆, NH₃, and O₂). For practical use, the hydrogen response characteristics of the proton-pumping gate FET were investigated in air (a gaseous mixture of oxygen and nitrogen). The proton-pumping gate FET showed different hydrogen response characteristics in nitrogen as well as in air, despite the lack of oxygen interference independently. To clarify the response mechanism of the proton-pumping gate FET, a hydrogen response measurement was performed, using a gas flow system and electrochemical impedance spectroscopy. Consequently, the difference in response between nitrogen and air was found to be due to the hydrogen dissociation reaction and the interference with the proton transfer caused by the adsorbed oxygen on the upper Pd gate electrode.     

一种新型的Pt􀀁LaF3 混合膜MISFET 结构溶解氧传感器

基于碳糊成模（carbon paste film forming)方法,我们研制了一种MISFET结构的Pt-LaF混合膜全固态溶解氧传感器,对传感器的器件结构以及Pt-LaF3敏感膜的敏感机制和响应特性进行了分析,并实际测试了器件特性。给出了在不同工作点和不同温度条件下器件的输出电压对溶解氧浓度变化的响应曲线。实验结果表明,我们所提出的器件可以用于测量溶解氧含量。     

Modeling stormwater management at the city district level in response to changes in land use and low impact development

Mitigating the impact of increasing impervious surfaces on stormwater runoff by low impact development (LID) is currently being widely promoted at site and local scales. In turn, the series of distributed LID implementations may produce cumulative effects and benefit stormwater management at larger, regional scales. However, the potential of multiple LID implementations to mitigate the broad-scale impacts of urban stormwater is not yet fully understood, particularly among different design strategies to reduce directly connected impervious areas (DCIA). In this study, the hydrological responses of stormwater runoff characteristics to four different land use conversion scenarios at the city scale were explored using GIS-based Stormwater Management Model (SWMM). Model simulation results confirmed the effectiveness of LID controls; however, they also indicated that even with the most beneficial scenarios hydrological performance of developed areas was still not yet up to the pre-development level, especially where there were pronounced changes from pervious to impervious land.     

Integrated biosensor employing a surface photovoltage technique

A monolithically integrated biosensor is constructed using a surface photovoltage (SPV) technique combined with a new patterning method for multiple enzyme integration. The SPV method provides a contactless sensing system leading to patterning flexibility. Photolithographical patterning methods using a water-soluble photocrosslinkable polymer (copolymer of dimethylacrylamide and cinnamoyloxyethylmethacrylate) are applied to immobilize the enzyme on a semiconductor surface. For bonding the enzyme membrane to the semiconductor surface, photoreactive poly-(meta azide styrene) is used, which bonds covalently with both the enzyme membrane and substrate. A pen-printing method has also been proposed for the patterning of enzyme films, which provides a simple method suitable for mass production.     

Top-gate ZnO thin-film transistors with a polymer dielectric designed for ultraviolet optical gating

We report on the fabrication of ultraviolet (UV)-sensing top-gate ZnO thin-film transistors (TFTs) with a poly-4-vinylphenol (PVP) polymer gate dielectric on glass substrate. Our top-gate ZnO-TFT showed a field-effect mobility of 0.05 cm²/V s, maximum saturation current of 0.11 μA at a gate bias of 10 V and an on/off ratio of 10³ in the dark. Under UV illumination with a wavelength of 364 nm the ZnO-TFT exhibited 4.7 μA for a drain current (at the same gate bias of 10 V), which is 50 times higher than without UV. Such photo-transistor action appeared more pronounced under a depletion regime of 0 V gate bias and the photo-to-dark current ratio was more than about 10⁴. By adopting this high UV-sensitivity, our inverter device with the top-gate ZnO-TFT and a load resistance well demonstrated its optical gating behavior.