Interdigitated Research Articles

PVA modified ZnO nanowire based microsensors platform for relative humidity and soil moisture measurement

In the present work, we have investigated Polyvinyl Alcohol (PVA) modified Zinc Oxide nanowires (ZnO NW) heterostructure based microsensors platform to measure the relative humidity and gravimetric soil moisture contents for agriculture applications. For this the hydrothermal growth of ZnO NW is carried out on Inter Digitated Electrodes (IDEs) patterned on Si/SiO2 substrates. Further, ZnO NW surface is functionalized by drop casting PVA solution. The surface characterization of the PVA coated ZnO NWs film is carried out by X-Ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and Current-Voltage (IV) measurements. These measurements revealed the successful formation of PVA-ZnO NW heterostructure. The microsensors are exposed to different levels of relative humidity (% RH) ranging from 40 to 90% and various moisture contents of bentonite and red soils. It is observed that the microsensors resistance decreases with increase in humidity (% RH) and gravimetric soil moisture contents (red and bentonite), respectively. The sensor exhibited a sensitivity of 4.6 KΩ/0.1% change in RH. Further, sensitivities of 7.5 and 12.2 KΩ/0.1% change in gravimetric water content when exposed to bentonite and red soil samples respectively were achieved. The low cost, good reproducibility, repeatability and good stability with time indicated that PVA modified ZnO NW heterostructure microsensors platform is potentially useful for measurement of humidity and soil moisture contents in agriculture applications.

Analysis and optimization of acoustic wave micro-resonators integrating piezoelectric zinc oxide layers

This paper reports on the design, simulation, fabrication, and test results of ZnO-based contour-mode micro-resonators integrating piezoelectric zinc oxide (ZnO) layers. The inter-digitated (IDT) type micro-resonators are fabricated on ZnO films and suspended top of 2 μm thick silicon membranes using silicon-on insulator technology. We analyze several possibilities of increasing the quality factor (Q) and the electromechanical coupling coefficient (kt2) of the devices by varying the numbers and lengths of the IDT electrodes and using different thicknesses of the ZnO layer. We designed and fabricated IDTs of different finger numbers (n = 25, 40, 50, and 80) and lengths (L = 100/130/170/200 μm) for three different thicknesses of ZnO films (200, 600, and 800 nm). The measured Q factor confirms that reducing the length and the number of IDT fingers enables us to reach better electrical performances at resonant frequencies around 700 MHz. The extracted results for an optimized micro-resonator device having an IDT length of 100 μm and 40 finger electrodes show a Q of 1180 and a kt2 of 7.4%. We demonstrate also that the reduction of the ZnO thickness from 800 nm to 200 nm increases the quality factor from 430 to 1600, respectively, around 700 MHz. Experimental data are in very good agreement with theoretical simulations of the fabricated devices

Effect of crystallinity on microwave tunability of pulsed laser deposited Ba0.5Sr0.5TiO3 thin films

Barium Strontium Titanate (Ba0.5Sr0.5TiO3) thin films on (100) oriented MgO substrates were deposited by Pulsed Laser Deposition (PLD) technique. The deposition temperature of 750°C is kept constant and the oxygen working pressure is varied from ~1×10−1mbar to 1×10−4mbar. The X-ray diffraction pattern shows that higher oxygen working pressure deposited films are partially crystalline. The lower oxygen working pressure (1×10−4mbar) deposited films showed improved crystallinity. The crystallinity is further increased with a particular orientation as the laser fluence increased from 1.4J/cm2 to 2J/cm2.The microwave dielectric properties of these films were measured using Inter Digitated Capacitor (IDC) test structure. It is found that the maximum tunability (in IDC configuration) of 16.5% at 1GHz is obtained for oxygen working pressure and high fluence (1×10−4mbar and 2J/cm2) deposited films, whereas the other films tunabilities are in the range of 1–2% only. These studies also help us to explore the correlation between structure and microwave dielectric properties. Hence, in the present study the 1×10−4mbar and 2J/cm2 deposition conditions are found to be more helpful in unleashing conditions that lead to better tunability in Ba0.5Sr0.5TiO3 films.

Fabrication of ZnSnO3 based humidity sensor onto arbitrary substrates by micro-Nano scale transfer printing

A flexible humidity sensor has been fabricated by a transfer printing technique. The device is fabricated by spin coating a composite of an equal (1:1) wt% ink of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) and zinc-stannate (ZnSnO3) on a water soluble substrate (WSS), screen printing silver interdigitated (IDT) electrodes and spin coating low modulus Polydimethylsiloxane (PDMS) on top of the IDTs. The water soluble substrate is then dissolved and removed and the device is laminated onto an arbitrary substrate in an inverted configuration. The device performance has been tested by transferring onto curved plastic substrates with different radii of curvature Rc. The devices show impedance change from ∼18MΩ to ∼1.8MΩ from 0% to 90% relative humidity (RH) with a negligible variation in results, over different bending radii. The transfer printing technique reported here would provide efficient and reliable route for the fabrication of flexible electronics on nonconventional substrates in environmental sensing, soft robotics, and artificial skin etc.

Fast Photoconductive Responses in Organometal Halide Perovskite Photodetectors

Inorganic semiconductor-based photodetectors have been suffering from slow response speeds, which are caused by the persistent photoconductivity of semiconductor materials. For realizing high speed optoelectronic devices, the organometal halide perovskite thin films were applied onto the interdigitated (IDT) patterned Au electrodes, and symmetrical structured photoconductive detectors were achieved. The detectors were sensitive to the incident light signals, and the photocurrents of the devices were 2-3 orders of magnitude higher than dark currents. The responsivities of the devices could reach up to 55 mA W(1-). Most importantly, the detectors have a fast response time of less than 20 μs. The light and bias induced dipole rearrangement in organometal perovskite thin films has resulted in the instability of photocurrents, and Ag nanowires could quicken the process of dipole alignment and stabilize the photocurrents of the devices.

C-line Polymorphism and 4th Inter Digital Pattern in Type 2 Diabetes Mellitus Patients

C-line Polymorphism and 4th Inter Digital Pattern in Type 2 Diabetes Mellitus Patients

VEGF Cancer Biomarker Protein Detection in Real Human Serum Using Capacitive Label‐Free Aptasensor

SummaryVascular Endothelial Growth Factor (VEGF) is a signalling protein known as a serum biomarker for a number of diseases including cancer. Therefore, it is necessary to develop a label‐free, rapid and sensitive method for detecting VEGF in its native forms in human serum. In this work, we have demonstrated the proof‐of‐concept of a sensitive label‐free biosensor based on capacitance changes induced by capturing of VEGF in human serum using anti‐VEGF aptamers functionalized on interdigitated (IDE) capacitor arrays (aptasensors). Limit of detection of VEGF protein using this aptasensor was in the range 0.5–2 ng/mL in dilute human serum. The label‐free capacitive aptasensing strategy provides a simple, reliable and effective means of biosensing serum VEGF levels for early cancer diagnosis.

Improvement of magnetoelectric properties in metglas/Pb(Mg1/3Nb2/3)O3–PbTiO3/metglas laminates with screen-printed ID-electrodes by poling optimization

Poling method is very important for ferroelectric and piezoelectric materials and their applications. We propose an interdigitated (ID) electrodes geometry and screen-print the ID electrodes on <001> cut 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 plates. However, it is very hard to pole the piezoelectric phase without cracks, resulting in high dielectric loss and high dielectric noise in corresponding sensors, which should be avoided in ME magnetic sensor devices. Because there appears a malformed region between longitudinal beams and tips of transverse electrodes. In this paper, we propose and adopt high temperature poling technique to reduce the strain and internal stress to reduce cracks. Strain-temperature curve of PMN-PT has a peak at 100 °C and strain at 140 °C (0.32%) is less than ½ of that at 100 °C (0.66%) under the same tested voltage (1000 V/mm). The noise equivalent magnetic induction (NEB) numerical simulation indicates that ME composite with high temperature poled PMN-PT (140 °C) has the lowest NEB, demonstrating that high temperature poling technique can lower dielectric loss and enhance ME effect by improving piezoelectric effects gently.

Theoretical and Experimental Investigation on the Use of a Surface Acoustic Wave Sensor for SU-8 Thin-Film Adhesion Characterization

This paper investigates the application of a surface acoustic wave (SAW) sensor for characterizing the adhesion of SU-8 thin films. The proposed sensor consists of a thin aluminum nitride (AlN) film deposited on a silicon substrate with two sets of interdigital (IDT) electrodes patterned on the AlN film in a delay line configuration. The SU-8 layer is patterned between the input and output IDT electrodes. A theoretical model for calculating the wave dispersion profile for the SU-8/AlN/Si configuration is developed. The effect of changing the adhesion of the SU-8 film on the wave velocity is implemented by assuming the SU-8/AlN interface consists of a layer of distributed massless springs. Different levels of adhesion are accounted for by changing the stiffness of the interfacial springs and the corresponding changes in the wave dispersion profiles are plotted. Four designs for the SAW sensor are fabricated, for each design two sensor configurations are developed to investigate the change in adhesion of the SU-8 film. In the first configuration, a thin gold film is patterned above the AlN film prior to patterning the SU-8 layer. In the second configuration, an Omnicoat layer is patterned above the gold film prior to SU-8 patterning. Omnicoat is an adhesion promoter commonly used to increase the adhesion of SU-8 to gold. The shift in the center frequency values from both configurations is used to characterize the adhesion of SU-8. The theoretical model is then used to find the equivalent spring stiffness values that fit the theoretical to the measured wave velocities.

Analysis, Simulation and Application of SFIT in Microfluidic Systems

In this paper we analyze a special type of Inter Digital Transducer (IDT), named Slanted Finger Transducer (SFIT) that can be used in microfluidic applications. Using SFIT in microfluidic technology are progressing during recent years. We will analyze the structure of basic SFIT and then a simulation is performed using a finite element software.

Characterization of piezoresistive PEDOT:PSS pressure sensors with inter-digitated and cross-point electrode structures.

The piezoresistive characteristics of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) pressure sensors with inter-digitated (IDE) and cross-point electrode (CPE) structures have been investigated. A small variation of the resistance of the pressure sensors with IDE without bottom indium-tin-oxide (b-ITO) film and with CPE structures was observed owing to the single carrier-conducting pathway. For the IDE pressure sensors with b-ITO, the piezoresistive characteristics at low and high pressure were similar to those of the pressure sensors with IDE without b-ITO and with CPE structures, respectively, leading to increased piezoresistive pressure sensitivity as the PEDOT:PSS film thickness decreased. A maximum sensitivity of more than 42 kΩ/Pa was achieved. When the normal pressure was applied, the increased number of conducting points or the reduced distance between the PEDOT oligomers within the PEDOT:PSS film resulted in a decrease of the resistance. The piezoresistive pressure sensors with a single carrier-conducting pathway, i.e., IDE without b-ITO and CPE structures, exhibited a small relaxation time and a superior reversible operation, which can be advantageous for fast piezoresistive response applications.

Modelling based on Spatial Impulse Response Model for Optimization of Inter Digital Transducers (SAW Sensors) for Non Destructive Testing

This study deals with modelling SAW-IDT transducers for their optimization. These sensors are specifically developed to characterize properties of thin layers, coatings and functional surfaces. Among the methods of characterization, the ultrasonic methods using Rayleigh surface waves are particularly interesting because the propagation of these waves is close to the surface of material and the energy is concentrated within a layer under the surface of about one wavelength thick. In order to characterize these coatings and structures, it is necessary to work in high frequencies, this is why in this study, SAW-IDT sensors are realized for surface acoustic wave generation. For optimization of these SAW-IDT sensors, particularly their band-width, it is necessary to study various IDT configurations by varying the number of electrodes, dimensions of the electrodes, their shapes and spacings. Thus it is necessary to implement effective and rapid technique for modelling. The originality of this study is to develop simulation tools based on Spatial Impulse Response model. Therefore it will be possible to reduce considerably computing time and results are obtained in a few seconds, instead of several hours (or days) by using finite element method. In order to validate this method, theoretical and experimental results are compared with finite element method and Interferometric measurements. The results obtained show a good overall concordance and confirm effectiveness of suggested method.

Optimization of electrical stimulation parameters for electro‐responsive hydrogels for biomedical applications

ABSTRACTElectro‐responsive hydrogels (ERH) are highly researched materials for biomedical applications. However, most of the research is concentrated on the synthesis of novel hydrogels for various applications, and little effort has been made to investigate electrode configuration and optimization of electrical stimulation parameters. This article used a three‐dimensional interdigitated (IDT) electrode configuration device to investigate the optimization of electrical actuation parameters in order to radially deswell an ERH. A Pluronic‐bismethacrylate hydrogel modified with hydrolyzed methacrylic acid was used as the ERH material. This article reports on using novel electro‐actuation parameters and electrode configurations to maximize radial deswelling of an ERH for biomedical applications. The optimal waveform was assessed for, varying electrode spacing's, voltages, duty cycles, and frequencies. The results show that a maximum deswelling occurred with a DC pulsed monophasic waveform, with IDT electrodes spaced close enough to create a relatively uniform electric field, with a peak voltage of 5 V at 1 kHz, and 50% duty cycle. This resulted in a deswelling of 320% in Krebs solution. Electrochemical impedance spectroscopy results show that the impedance is dependent on the ionic concentration of the fluid environment and that the impedance decreases with increasing frequency. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41687.

Effect of methanol on the phase-transition properties of glycerol-monopalmitate lipid bilayers investigated using molecular dynamics simulations: In quest of the biphasic effect

The effect of methanol on the phase and phase-transition properties of a 2×8×8 glycerol-1-monopalmitate bilayer patch is investigated using a series of 239 molecular dynamics simulations on the 180ns timescale, considering methanol concentrations cM and temperatures T in the ranges 0–12.3M and 302–338K, respectively. The results in the form of hysteresis-corrected transition temperatures Tm are compatible with the expected features of the biphasic effect, with a reversal concentration crev of about 5.2M. Below this concentration, the main transition is between the liquid crystal (LC) and gel (GL) phases, and Tm decreases upon increasing cM. Above this concentration, the interdigitated (ID) phase is the stable ordered phase instead, and Tm slightly increases upon increasing T up to about 10M. The analysis of the structural and dynamical properties also reveals very different sensitivities and responses of the three phases to changes in cM. In particular, the properties of the GL phase are insensitive to cM, whereas those of the LC and ID phases are altered via an increase of the area per lipid. For the LC phase, increasing cM promotes disorder and fluidity. For the ID phase, in contrast, increasing cM up to about 10M slightly increases the ordering and rigidity. Two side issues are also addressed, concerning: (i) the occurrence tilt-precession motions in the GL and ID phases; (ii) the influence of the pressure coupling scheme employed in the simulations, semi- or fully-anisotropic, on the simulation results.

Monitoring of Biodiesel Transesterification Process Using Impedance Measurement

Alternative diesel fuels have been the subject of extensive investigation. Fatty acid methyl ester (FAME) based Biodiesel manufactured from vegetable oils or animal fats is an excellent candidate to replace common diesel fuel being renewable, non-toxic and often giving rise to reduced exhaust gas emissions. The transesterification process has been commonly and widely used to produce biodiesel from vegetable oil or animal fat. Vegetable oils or animal fats generally have viscosities higher than standard diesel oil. This means that it is necessary to reduce the viscosity by means of reacting vegetable oil with alcohol in the presence of a suitable catalyst. The target product for this reaction is methyl ester, with glycerol and potentially soap produced as by products with the process of transesterification. Methylester (Biodiesel) is produced by converting triglycerides to alkylesters. A batch transesterification process has two significant mechanisms, and exhibits a mass transfer controlled region that precedes a second order kinetically controlled region. In order to control the conversion process it is useful to employ process monitoring. In particular monitoring of the mass transfer processes that limits the initial reaction rates could prove to be beneficial in allowing for process optimization and control. This thesis proposes the use of a new method of biodiesel process monitoring using low frequency (15kHz) impedance sensing which is able to provide information regarding the progress of mass transfer and chemical reaction during biodiesel production. An interdigitated (ID) sensor has been used to monitoring the biodiesel process The ID sensor is of simple construction and consists of two sets of interleaved electrodes (fingers). The two sets of electrodes are separated by a gap and when an AC excitation voltage is applied across the interleaved electrodes an oscillating electric field is developed. The response of the fluid surrounding the sensor to the applied excitation was then used to determine progress of the chemical reaction by evaluating the real and complex impedance. A significant and unambiguous change in the components of impedance has been shown to occur during mixing (mass transfer) and transesterification. The impedance measurements gained during transesterification were then used for the development of a system model. A systematic approach was used to select mathematical models and system identification techniques were evaluated. The system identification investigation used real process measurement data in conjunction with the Matlab system identification toolbox.

A theoretical and experimental comparison of 3-3 and 3-1 mode piezoelectric microelectromechanical systems (MEMS)

Two piezoelectric transducer modes applied in microelectromechanical systems are (i) the 3-1 mode with parallel electrodes perpendicular to a vertical polarization vector, and (ii) the 3-3 mode which uses interdigitated (IDT) electrodes to realize an in-plane polarization vector. This study compares the two configurations by deriving a Norton equivalent representation of each approach – including expressions for output charge and device capacitance. The model is verified using a microfabricated device comprised of multiple epitaxial silicon beams with sol–gel deposited lead zirconate titanate at the surface. The beams have identical dimensions and are attached to a common moving element at their tips. The only difference between beams is electrode configuration – enabling a direct comparison. Capacitance and charge measurements verify the presented theory with high accuracy. The Norton equivalent representation is general and enables comparison of any figure of merit, including electromechanical coupling coefficient and signal-to-noise ratio. With respect to coupling coefficient, the experimentally validated theory in this work suggests that 3-3 mode IDT-electrode configurations offer the potential for modest improvements compared against 3-1 mode devices (less than 2×), and the only geometrical parameter affecting this ratio is the fill factor of the IDT electrode.

A flexible sensing device based on a PVDF/MWCNT composite nanofiber array with an interdigital electrode

This study reports the electrospinning of polyvinylidene fluoride (PVDF) piezoelectric nanofiber array on an interdigital (IDT) electrode to fabricate a flexible sensing device. This sensing device can convert the mechanical energies of low-frequency ambient vibrations and impacts into electrical signals. A mixed solution of PVDF and multi-wall carbon nanotube (MWCNT) was filled in a metallic needle injector that was connected with a high voltage of 1200V. When the PVDF droplet in the needle tip was subjected to a high electric field, an extremely fine PVDF fiber can be spun out. The electrospun fibers were collected orderly using an X–Y stage. In the electrospinning process, the fiber was polarized and transformed into the piezoelectric β-crystalline phase. PVDF/MWCNT crystallization as spherical composite structures can enhance the piezoelectric properties of PVDF fibers. Photolithography and etching processes were used to fabricate an IDT electrode with a gap of 100μm on a flexible polyimide (PI) substrate. The PVDF fiber array was packaged with epoxy/PI film. The packaged PVDF fiber array was repolarized in a high electric field of approximately 7V/μm to increase d33 mode conversion efficiency. The comparison of the analytical solution of the composite plate equation and the experimental results shows that the device can generate a peak voltage and current of 20.2mV and 39nA under 6Hz vibration. In addition, at an impact testing at 15Hz, the peak voltage of 24.4mV with a current of 130nA can be obtained.

Manipulation of IDT-Actuated Piezoelectric Membrane Actuators by Silicon Clamping

This paper will introduce a piezoelectric micro membrane actuator with interdigitated (IDT) surface electrodes for polarization and actuation. The thus achieved polarization and generated electric field are highly inhomogeneous and cause therefore also inhomogeneous strain and stress distributions within the piezoelectric material itself. To equalize the strain and stress the material will deform. This deformation can be manipulated due to electrodes design and clamping of the membrane. The most outstanding achievement with this manipulation is the deflection of the membrane towards the actuated surface and not as is common in piezoelectric membrane actuators towards the passive surface of the device.

Electrochemical impedance spectroscopy based MEMS sensors for phthalates detection in water and juices

Phthalate esters are ubiquitous environmental and food pollutants well known as endocrine disrupting compounds (EDCs). These developmental and reproductive toxicants pose a grave risk to the human health due to their unlimited use in consumer plastic industry. Detection of phthalates is strictly laboratory based time consuming and expensive process and requires expertise of highly qualified and skilled professionals. We present a real time, non-invasive, label free rapid detection technique to quantify phthalates' presence in deionized water and fruit juices. Electrochemical impedance spectroscopy (EIS) technique applied to a novel planar inter-digital (ID) capacitive sensor plays a vital role to explore the presence of phthalate esters in bulk fluid media. The ID sensor with multiple sensing gold electrodes was fabricated on silicon substrate using micro-electromechanical system (MEMS) device fabrication technology. A thin film of parylene C polymer was coated as a passivation layer to enhance the capacitive sensing capabilities of the sensor and to reduce the magnitude of Faradic current flowing through the sensor. Various concentrations, 0.002ppm through to 2ppm of di (2-ethylhexyl) phthalate (DEHP) in deionized water, were exposed to the sensing system by dip testing method. Impedance spectra obtained was analysed to determine sample conductance which led to consequent evaluation of its dielectric properties. Electro-chemical impedance spectrum analyser algorithm was employed to model the experimentally obtained impedance spectra. Curve fitting technique was applied to deduce constant phase element (CPE) equivalent circuit based on Randle's equivalent circuit model. The sensing system was tested to detect different concentrations of DEHP in orange juice as a real world application. The result analysis indicated that our rapid testing technique is able to detect the presence of DEHP in all test samples distinctively.

Technique for rapid detection of phthalates in water and beverages

The teratogenic and carcinogenic effects of phthalate esters on living beings are proven in toxicology studies. These ubiquitous food and environmental pollutants pose a great danger to the human race due to their extraordinary use as a plasticizer in the consumer product industry. Contemporary detection techniques used for phthalates require a high level of skills, expensive equipment and longer analysis time than the presented technique. Presented research work introduces a real time non-invasive detection technique using a new type of silicon substrate based planar interdigital (ID) sensor fabricated on basis of thin film micro-electromechanical system (MEMS) semiconductor device fabrication technology. Electrochemical impedance spectroscopy (EIS) was used in conjunction with the fabricated sensor to detect phthalates in deionized water. Various concentrations of di(2-ethylhexyl) phthalate (DEHP) as low as 2ppb to a higher level of 2ppm in deionized water were detected distinctively using new planar ID sensor based EIS sensing system. Dip testing method was used to obtain the conductance and dielectric properties of the bulk samples. Parylene C polymer coating was used as a passivation layer on the surface of the fabricated sensor to reduce the influence of Faradaic currents. In addition, inherent dielectric properties of the coating enhanced the sensitivity of the capacitive type sensor. Electrochemical spectrum analysis algorithm was used to model experimentally observed impedance spectrum to deduce constant phase element (CPE) equivalent circuit to analyse the kinetic processes taking place inside the electrochemical cell. Curve fitting technique was used to extract the values of the circuit components and explain experimental results on theoretical grounds. The sensor performance was tested by adding DEHP to an energy drink at concentrations above and below the minimal risk level (MRL) limit set by the ATSDR (Agency for Toxic Substances & Disease Registry), USA. Results showed that the new sensor was able to detect different concentrations of phthalates in energy drinks. The experimental outcomes provided sufficient indication to favour the development of a low cost detection system for rapid quantification of phthalates in beverages for industrial use.