The Influence of Buffer Layer Type on the Electrical Properties of Metallic Layers Deposited on Composite Textile Substrates in the PVD Process

In the era of developing wearable electronics, the miniaturization of electronic systems and their implementation in the textile industry is one of the key issues. For this reason, it is important to select the appropriate textile substrates upon which it is possible to produce electroconductive structures, as well as their selection from the point of view of the electrical parameters' stability. For this purpose, research related to the effect of heating a substrate on the resistance of the structures produced in the process of physical vacuum planting was conducted. Textile composites with a buffer layer made of polyurethane, Teflon, and acrylic were used as substrates in the tests. Such layers are an integral part of textile composites and a necessary element for producing structures with continuous electrical conductivity. The conducted tests showed that a buffer layer made of polyurethane (thermal conductivity, e.g., PERMACOL 5450 resin 0.16 W/mK) heated to 15 °C above room temperature was a layer that introduced changes into the surface resistance of the structures. The resistance values of the samples produced on a substrate containing a buffer layer of polyurethane varied in the range of 9-23%, depending on the manufacturer of the composite in the case of a self-heating mode, and in the case of an external heating mode, these changes were smaller and ranged from 8 to 16%. Such a phenomenon occurred regardless of the type of applied metal, and this was not observed in the case of composites with a Teflon or acrylic sublayer. For this reason, it is necessary to take into account the fact that textronic structures made on substrates containing a polyurethane layer may change the surface resistance depending on the temperature. The electrical parameters of such structures were checked by heating the structure using an external heater and self-heating mechanism. The same phenomenon was observed in both cases.

Laser Patterning a Graphene Layer on a Ceramic Substrate for Sensor Applications

This paper describes a method for patterning the graphene layer and gold electrodes on a ceramic substrate using a Nd:YAG nanosecond fiber laser. The technique enables the processing of both layers and trimming of the sensor parameters. The main aim was to develop a technique for the effective and efficient shaping of both the sensory layer and the metallic electrodes. The laser shaping method is characterized by high speed and very good shape mapping, regardless of the complexity of the processing. Importantly, the technique enables the simultaneous shaping of both the graphene layer and Au electrodes in a direct process that does not require a complex and expensive masking process, and without damaging the ceramic substrate. Our results confirmed the effectiveness of the developed laser technology for shaping a graphene layer and Au electrodes. The ceramic substrate can be used in the construction of various types of sensors operating in a wide temperature range, especially the cryogenic range.

Electrical and Thermal Properties of Heater-Sensor Microsystems Patterned in TCO Films for Wide-Range Temperature Applications from 15 K to 350 K

This paper presents an analysis of the electrical and thermal properties of miniature transparent heaters for use in a wide range of temperature applications, from 15 K to 350 K. The heater structures were produced in transparent conducting oxide (TCO) layers: indium tin oxide (ITO) and ITO/Ag/ITO on polymer substrates-polyethylene naphthalate (PEN) and polyethylene terephthalate (PET), by direct laser patterning. Thermo-resistors for temperature measurement were created in the same process, with geometry corresponding to the shape of the heating path. The thermo-resistors integrated with the heating structure allowed easy control of the thermal state of the heaters. Laser patterning provided high precision and repeatability in terms of the geometry and electrical properties of the heater-sensor structures. Measurements at temperatures from 15 K to above room temperature (350 K) confirmed the excellent dynamics of the heating and cooling processes, due to current flow. The largest value for surface heating power was over 3 W/cm². A heater-sensor structure equipped with a small capacity chamber was successfully applied for controlled heating of small volumes of different liquids. Such structures have potential for use in research and measurements, where for various reasons controlled and accurate heating of small volumes of liquids is required.

A Fully Transparent Flexible Sensor for Cryogenic Temperatures Based on High Strength Metallurgical Graphene

Low-temperature electronics operating in below zero temperatures or even below the lower limit of the common -65 to 125 °C temperature range are essential in medical diagnostics, in space exploration and aviation, in processing and storage of food and mainly in scientific research, like superconducting materials engineering and their applications-superconducting magnets, superconducting energy storage, and magnetic levitation systems. Such electronic devices demand special approach to the materials used in passive elements and sensors. The main goal of this work was the implementation of a fully transparent, flexible cryogenic temperature sensor with graphene structures as sensing element. Electrodes were made of transparent ITO (Indium Tin Oxide) or ITO/Ag/ITO conductive layers by laser ablation and finally encapsulated in a polymer coating. A helium closed-cycle cryostat has been used in measurements of the electrical properties of these graphene-based temperature sensors under cryogenic conditions. The sensors were repeatedly cooled from room temperature to cryogenic temperature. Graphene structures were characterized using Raman spectroscopy. The observation of the resistance changes as a function of temperature indicates the potential use of graphene layers in the construction of temperature sensors. The temperature characteristics of the analyzed graphene sensors exhibit no clear anomalies or strong non-linearity in the entire studied temperature range (as compared to the typical carbon sensor).