InterDigitated Electrodes (IDEs) is a generic platform for a wide range of diverse applications with their implementation in sensing modules being a major one. We propose the use of IDCs with deep sub-micron critical dimension; equally spaced electrodes of 200 nm width for enhanced sensing performance and also the method of fabrication thereof. The transducer configuration was studied theoretically with a finite element method simulation by using COMSOL Multiphysics. The miniaturization of the IDEs up to 200 nm critical dimension with an adequate sensing area for the deposition of the polymeric materials is considered beneficial in terms of sensitivity gain. The IDCs were designed to deliver capacitance values of few pF in order to be compatible with already developed miniaturized low-power readout electronics. The transducers fabrication is performed with conventional microelectronic/micromachining processing and then coated with several semi-selective polymeric films. Besides the fabrication of multiple sensor arrays (chips) on the same silicon wafer, the miniaturization offers the integration with the readout electronics on the same chip. The evaluation of the sensing performance of the semi-selective polymer coated sensors is performed upon exposure to vapours of pure and binary mixtures of VOCs and humidity in various concentrations. The sensors demonstrate high sensitivity to the examined analyzes as a result of the miniaturization, while their semi-selectivity is a key for applications in complex vapour environment discrimination.

The sensing performance of a self-calibrated Wireless Sensing System (WSS) was evaluated under laboratory and real environment conditions. The Wireless Sensing Node consists of a sensor array based on chemocapacitors, which is integrated with appropriate low power consumption read-out electronics and is connected with appropriate wireless module. The sensing system was evaluated and calibrated under laboratory conditions with two different VOCs transfer methods: dynamic and static. The sensing unit calibration deals with changes of VOCs and/or humidity concentration and temperature variations, simulating the real industrial environment. Finally the WSS was placed in the workspace of a printed flexing packaging industrial installation and comparison with the already installed commercial detectors was performed. A very good agreement between the results of the two measurement systems is demonstrated. Additionally these results showed that the WSS is characterized by fast response with high repeatability and long-term stability. Concluding, this system is suitable for the targeted application.

The realization of a wireless sensing system and its sensing performance evaluation, under laboratory conditions, for the monitoring of specific volatile organic compounds (VOCs) present in printed flexing packaging industries is demonstrated. Prior to the utilization of the wireless mote, we present the microfabrication of appropriate sensor array based on chemocapacitors and its integration with appropriate low power consumption read-out electronics meeting the requirements of the application. The sensing unit is an array of interdigitated chemocapacitors (IDCs). The wireless sensing system is tested upon exposure to VOCs, humidity and gaseous mixtures simulating the real industrial environment and the raw data are transmitted via a wireless network and monitored to a front-end software. Results showed that the sensing system is characterized by very good sensing performance with high repeatability and long-term stability. Further data processing with principal component analysis (PCA) highlights the sensing system's ability to discriminate between gaseous environments with different composition/concentration. Thus the particular wireless sensing system is suitable for remote real-time unattended industrial environment monitoring.

A generalized transmission line method (TLM) that provides reflection and transmission calculations for a multilayer dielectric structure with coherent, partial coherent, and incoherent layers is presented. The method is deployed on two different application fields. The first application of the method concerns the thickness measurement of the individual layers of an organic light-emitting diode. By using a fitting approach between experimental spectral reflectance measurements and the corresponding TLM calculations, it is shown that the thickness of the films can be estimated. The second application of the TLM concerns the calculation of the external quantum efficiency of an organic photovoltaic with partially coherent rough interfaces between the layers. Numerical results regarding the short circuit photocurrent for different layer thicknesses and rough interfaces are provided and the performance impact of the rough interface is discussed in detail.

One-dimensional polymeric photonic crystal (PC) arrays with tuned bandgap properties are designed and fabricated on the same substrate by employing mainstream micropatterning technologies and appropriate photopatternable materials. The two photopatternable materials are based on poly (2-hydroxy ethyl methacrylate) and epoxy polymers with the addition of appropriate photoacid generators and are diluted in orthogonal solvents, ethyl lactate and PGMEA respectively. The tuning of the photonic band gap of each photonic crystal is achieved through carefully tuned lithographic processing conditions with emphasis in low-lithographic contrast operation and gray scale lithography. By applying sequential lithographic steps in orthogonal developers one-dimensional photonic crystal arrays with 10 bi-layers are fabricated with very well defined patterns. With this approach, PC arrays with four distinct areas are realized on the same Si substrate with tuned reflectance spectrum covering the whole visible spectral regime.

Protein detection and characterization based on Broad-band Mach-Zehnder Interferometry is analytically outlined and demonstrated through a monolithic silicon microphotonic transducer. Arrays of silicon light emitting diodes and monomodal silicon nitride waveguides forming Mach-Zehnder interferometers were integrated on a silicon chip. Broad-band light enters the interferometers and exits sinusoidally modulated with two distinct spectral frequencies characteristic of the two polarizations. Deconvolution in the Fourier transform domain makes possible the separation of the two polarizations and the simultaneous monitoring of the TE and the TM signals. The dual polarization analysis over a broad spectral band makes possible the refractive index calculation of the binding adlayers as well as the distinction of effective medium changes into cover medium or adlayer ones. At the same time, multi-analyte detection at concentrations in the pM range is demonstrated.

Broad-band Mach-Zehnder interferometry is analytically described and experimentally demonstrated as an analytical tool capable of high accuracy refractive index measurements over a wide spectral range. Suitable photonic engineering of the interferometer sensing and reference waveguides result in sinusoidal TE and TM spectra with substantially different eigen-frequencies. This allows for the instantaneous deconvolution of multiplexed polarizations and enables large spectral shifts and noise reduction through filtering in the Fourier Transform domain. Due to enhanced sensitivity, optical systems can be designed that employ portable spectrum analyzers with nm range resolution without compromising the sensor analytical capability. Practical detection limits in the 10(-6)-10(-7) RIU range are achievable, including temperature effects. Finally, a proof of concept device is realized on a silicon microphotonic chip that monolithically integrates broad-band light sources and single mode silicon nitride waveguides. Refractive index detection limits rivaling that of ring resonators with externally coupled laser sources are demonstrated. Sensitivities of 20 μm/RIU and spectral shifts in the tens of a pm are obtained.

A complete Mach-Zehnder interferometer monolithically integrated on silicon is presented and employed as a refractive index and bio-chemical sensor. The device consists of broad-band light sources optically coupled to photodetectors through monomodal waveguides forming arrays of Mach-Zehnder interferometers, all components being monolithically integrated on silicon through mainstream silicon technology. The interferometer is photonically engineered in a way that the phase difference of light travelling through the sensing and reference arms is approximately wavelength independent. Consequently, upon effective medium changes, it becomes feasible even with a broad-band source to induce sinusoidal-type of detector photocurrents similar to the classical monochromatic counterparts. The device is completed with its fluidic and interconnect components so that on chip interferometric measurements can be performed. Examples of refractive index and protein sensing are presented to establish the potential of the proposed device for real-time in situ monitoring applications. This is the only silicon device that has achieved complete on-chip interferometry.

The realization and characterization under laboratory conditions of a wireless sensor network for the monitoring of specific Volatile Organic Compounds (VOCs) is presented towards its potential application at industrial installations. The sensing unit is an array of InterDigitated Chemocapacitors (IDCs) coated with semi-selective polymers as sensing layers. The capacitance changes are recorded with a miniaturized read-out electronics module and are transmitted via a wireless network. The recorded responses demonstrate that the system can be potentially applied to remote real-time unattended industrial environment monitoring.

Chemocapacitors, i.e. capacitors where the dielectric layer is a polymeric layer with selective sorption of certain analytes, are extensively used in the monitoring of the environmental humidity and of other volatile analytes. The specifics of the detecting mechanism have been found to rely on a combination of interactions arising from vapor sorption, polymer swelling, and morphology changes. The aim of the present work is to develop a fabrication procedure of InterDigitated Electrodes (IDEs) with high sensing performance. The IDEs layout has been optimized in terms of sensing performance and is in accordance with the read-out electronics specifications. The realization and evaluation of chemocapacitor arrays integrated with read-out electronic module in the presence of various analyte vapours is demonstrated in laboratory environment. The analytes employed in the present study are typical for the printing industry of flexible packaging. (C) 2014 Elsevier B.V. All rights reserved.

In the present study, a one dimensional polymeric photonic crystal is designed, fabricated and evaluated as a humidity sensor. The polymeric photonic crystal is consisted of a multilayer stack of sequential hydrophobic and hydrophilic layers applied using conventional photolithographic steps: spin-coating and DUV exposure. During exposure in a humidity environment, the hydrophilic layers of the sensor swell, hence growing its optical path and giving a red-shift of the reflectance peak and consequently a different color of the device. The spectroscopic humidity sensor does not require external power since its sensing ability is based on the reflectance peak shift of the photonic crystal in the visible spectrum (color change of the sensor). The design, fabrication, evaluation and characterization of the device and its evaluation as humidity sensor is presented.

A miniaturized gas sensing system suitable for real life applications, consisting of an array of 8 polymer-coated capacitive sensors and low power read-out electronics is designed and realized. The chemocapacitor array is fabricated with standard microelectronics/micromachining processes allowing for the realization of planar InterDigitated Electrodes (IDEs) with 2μm critical dimension. The read-out electronics sub-module consists of an analog multiplexer for the sequential measurement of the sensor array elements, a capacitance to 24-bit converter and a USB to I2C interface. The electronic sub-module developed, was evaluated against a standard capacitance meter and presents a noise of ∼0.2fF and therefore capacitance signal (ΔC) of 0.6fF (S/N=3) is detectable. The compact module has been successfully applied in the detection of low concentrations of p-xylene and toluene, according to the international health standards, in the presence of humidity.

A methodology for the prediction of chemocapacitor responses due to the sorption of vapor analytes is introduced. The approach developed, is based on experimental evaluation of the swelling ability of polymeric sensing materials due to sorption of analytes, consequent calculation of the dielectric constant of the swollen film on the basis of an appropriate mixing rule, in conjunction with electromagnetic modeling for the InterDigitated Electrode (IDE) capacitors. The polymeric film swelling is measured through optical reflectance measurements while the mixing rule applied is the Clausius–Mossotti that is known to be valid for small volume fractions of sorbed analytes in polymeric films. The methodology was successfully applied in various non-polar polymer–analyte systems at low vapor concentrations.

Inter Digitated Capacitive (IDC) sensor arrays are fabricated with conventional microelectronics-micromachining technologies on quartz substrates. After fabrication, a polymeric well is patterned around each IDC to precisely define the sensing area and thus deposit coatings of various polymers, by drop casting, in a reproducible and controlled manner. The gas sensing performance of the IDC array is presented for humidity and p-xylene.

The fabrication of a power-free, reversible, color-indicator sensor of the relative humidity in the environment has numerous applications and is considered a challenging task. The device to be developed should be able of color changing according to the degree of humidity change and have a number of characteristics, i.e., reversibility, fast response, low cost, and, ideally, should be flexible. The proposed solution, based on a 1-D polymeric Photonic Crystal (PC) configuration on a microscope glass, can successfully fulfill all the above requirements.

One dimensional (1D) Photonic crystals (PC) are the simplest form of PC consisting of alternative layers of materials having different refractive indices. This periodic structure has very interesting optical properties allowing manipulation and control of light reflectance wavelength. Polymers have already been used as optical components in several devices and recently became candidate materials for the fabrication of PC. In the present work, a polymeric multilayer stack consisting of alternating hydrophobic and hydrophilic layers is fabricated and its response in controlled concentrations of humidity is evaluated towards the development of an optical humidity sensor.

A hybrid gas sensing module consisting of an array of 8 polymer coated capacitive sensors and low power read-out electronics is introduced. The chemocapacitor array is fabricated with standard microelectronics/micromachining processes allowing for the realization of planar InterDigitated Electrodes (IDEs). The read-out electronics sub- module consists of an analog multiplexer for the sequential measurement of the sensor array elements, a capacitance to 24-bit converter and a USB to I2C interface. The compact hybrid module has been successfully applied in the detection of sub-100ppm concentrations of p-xylene and toluene. The responses to various humidity levels have been also evaluated.

Capacitive-type gas sensors rely on changes in the dielectric properties of the sensing polymeric layer due to absorption of Volatile Organic Compounds (VOCs) or moisture. They are promising devices in terms of ease and low cost of fabrication, reversibility and the wide range of sensing material choice. In the present work, the aim is to explore the fabrication issues of the InterDigitated Electrodes (IDE) through a generic simulation model for the prediction of the capacitance of various IDE structures. Based on the simulation results, an IDE layout was selected for the realization and evaluation of chemcapacitor arrays in the presence of different humidity levels and low concentrations of VOCs with dielectric constant close to those of polymers. The extracted results will be further exploited for the fabrication optimization of an InterDigitated Capacitor (IDC) layout with increased selectivity and sensitivity in specific applications.

In this work, we demonstrate all organic flexible polymeric optocouplers by utilizing a donor‐acceptor bulk heterojunction polymer photodetector (PD) as the output unit and a polymer light‐emitting diode (PLED) as the input unit. The input unit is a single‐layer PLED on a glass or a plastic (PET) substrate utilizing a green emitting polyfluorene‐benzothiadiazole copolymer in the active layer. The output unit is a single‐layer PD on a glass substrate utilizing a P3HT:PCBM(1:1 by weight) blend, where P3HT is regioregular poly(3‐hexylthiophene) and PCBM is (6,6)‐phenyl‐C61‐butyric acid methyl ester. The electroluminescence spectrum of the PLED peaks at 530 nm and covers a spectral range that coincides quite well with the PD absorption spectrum (between 450 and 650 nm). The current density transfer ratio reaches 0.012% for an optocoupler that operates at 0 V and 15 V for the PD and PLED, respectively. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)