Recent advances in biomaterials, thin film processing, and nanofabrication offer the opportunity to design electronics with novel and unique capabilities, including high mechanical stability and biodegradation, which are relevant in medical implants, environmental sensors, and wearable and disposable devices. Combining reliable electrical performance with high mechanical deformation and chemical degradation remains still challenging. This work reports temperature sensors whose material composition enables full biodegradation while the layout and ultrathin format ensure a response time of 10 ms and stable operation demonstrated by a resistance variation of less than 0.7% when the devices are crumpled, folded, and stretched up to 10%. Magnesium microstructures are encapsulated by a compostable-certified flexible polymer which exhibits small swelling rate and a Young's modulus of about 500 MPa which approximates that of muscles and cartilage. The extension of the design from a single sensor to an array and its integration onto a fluidic device, made of the same polymer, provides routes for a smart biodegradable system for flow mapping. Proper packaging of the sensors tunes the dissolution dynamics to a few days in water while the connection to a Bluetooth module demonstrates wireless operation with 200 mK resolution prospecting application in food tracking and in medical postsurgery monitoring.

Biodegradable and Highly Deformable Temperature Sensors for the Internet of Things

Nonpolar resistive switching (RS), which is the coexistence of unipolar and bipolar RS characteristics, in the Pt/MgO/Pt memory device with the nonforming nature is demonstrated. The nonforming nature is ascribed to the relatively high defect density of the MgO film deposited by using the ion beam sputtering in Ar atmosphere. The results of Auger electron spectroscopy and x-ray photoelectron spectroscopy analyses combing with the temperature dependence of resistance suggest that metallic Mg filaments are formed in the low resistance state. The voltage-polarity-independent RESET process implies that filaments may be ruptured by local Joule heating, leading to nonpolar characteristics.

Nonpolar resistive switching in the Pt/MgO/Pt nonvolatile memory device

Blends of poly (ethylene-co-methacrylic acid) (PEMA) and poly (vinyl alcohol-co-ethylene) (EVOH) were studied for encapsulating Schottky structured organic devices. A calcium degradation test was used to determine water vapor transmission rates and to determine the moisture barrier performance of neat and blend films. Moisture barrier analysis for the neat and blend compositions was discussed concerning the interactions in the blend, diffusivity of water molecules through the unit cell systems, and the occupiable free volumes available in the unit cells using molecular dynamics simulations. The experimental results of water vapor permeation were correlated with diffusion behavior predicted from molecular dynamics simulations results. The effectiveness of the blend as a suitable barrier material in increasing the lifetime of an encapsulated Schottky structured organic device was determined.

Ionomer based blend as water vapor barrier material for organic device encapsulation.

Flexible, nano-composite moisture barrier films of poly(vinyl alcohol-co-ethylene) with surface modified montmorillonite fabricated by solution casting were used to encapsulate organic devices The composite films were characterized by FTIR, UV-visible spectroscopy and SEM imaging Thermal and mechanical properties of the composite films were studied by DSC and UTM Calcium degradation test was used to determine the transmission rate of water vapour through the composite films, which showed a gradual reduction from ∼01 g m−2 day−1 to 00001 g m−2 day−1 with increasing modified montmorillonite loading in the neat copolymer The increase in moisture barrier performance is attributed to the decreased water vapour diffusivity due to matrix–filler interactions in the composite The accelerated aging test was carried out for non-encapsulated and encapsulated devices to evaluate the efficiency of the encapsulants The encapsulated devices exhibited longer lifetimes indicating the efficacy of the encapsulant

Flexible poly(vinyl alcohol-co-ethylene)/modified MMT moisture barrier composite for encapsulating organic devices

A new, flexible, gas barrier material has been synthesized by exfoliating organically modified nano-clays (MMT) in the blends of Surlyn (PEMA) using a copolymer of vinyl alcohol (EVOH) and demonstrated as a gas barrier material. The materials were characterized by Fourier transform infra red (FTIR) and UV-visible spectroscopy, differential scanning calorimetry (DSC), thermo-gravimetric analysis (TGA) and tensile studies. The oxygen and water-vapor permeabilities of the fabricated films were determined by calcium degradation test and a novel permeability setup based on cavity ring down spectroscopy, respectively. Hierarchical simulations of these materials helped us to understand the effect of intermolecular interactions on diffusivities of oxygen and water molecules in these materials. Schottky structured poly(3-hexylthiophene) based organic devices were encapsulated with the fabricated films and aging studies were carried under accelerated conditions. Based on permeability test results and accelerated aging studies, the fabricated PEMA/EVOH/MMT composites were found to be effective in decreasing the permeabilities for gases by about two orders of magnitude and maintaining the lifetime of organic devices.

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Performance of an ionomer blend-nanocomposite as an effective gas barrier material for organic devices

Deposition and study of calcium films were achieved under ultrahigh vacuum. The latter was obtained with the use of an ion pump and a helium cryopump. The temperature of the substrate ranged between 90 and 400 K. The electrical resistance was measured with the use of a four-probe method with a constant current. Film thicknesses were in the range between 20 and 300 nm. To obtain a stable film structure, samples were annealed to a temperature near 400 K. The electrical resistivity of the annealed films exhibited a linear and reversible variation with temperature. It was shown to be thickness dependent. For the thickest deposits, electrical resistivity reached a constant value which no longer depended on the thickness, but was a function of the film-deposition temperature. With the help of electron photomicrographs and with use of the conduction model proposed by Mayadas and Schatzkes, we calculated the fraction $p$ of electrons which are specularly reflected at the surface of the film and the parameter $\ensuremath{\alpha}$ depending on the reflection on grain boundaries. The influence of grain boundaries was calculated and the mean free path was deduced from these results.

J.P. Pétrakian

Papers

Grain-boundary effect in calcium thin films

Electron transport properties of magnesium thin films

Electron transport properties of strontium thin films

Détermination précise de l'angle d'incidence moyen d'un faisceau lumineux à partir de mesures de flux réfléchis

The influence of annealing on the conductivity of magnesium films