Giorgio Mattana

Large-area compatible fabrication and encapsulation of inkjet-printed humidity sensors on flexible foils with integrated thermal compensation

This work presents the simultaneous fabrication of ambient relative humidity (RH) and temperature sensors arrays, inkjet-printed on flexible substrates and subsequently encapsulated at foil level. These sensors are based on planar interdigitated capacitors with an inkjet-printed sensing layer and meander-shaped resistors. Their combination allows the compensation of the RH signals variations at different temperatures. The whole fabrication of the system is carried out at foil level and involves the utilization of additive methods such as inkjet-printing and electrodeposition. Electrodeposition of the printed lines resulted in an improvement of the thermoresistors. The sensors have been characterized and their performances analyzed. The encapsulation layer does not modify the performances of the sensors in terms of sensitivity or response time. This work demonstrates the potential of inkjet-printing in the large-area fabrication of light-weight and cost-efficient gas sensors on flexible substrates.

Woven Temperature and Humidity Sensors on Flexible Plastic Substrates for E-Textile Applications

In this paper, a woven textile containing temperature and humidity sensors realized on flexible, plastic stripes is presented. The authors introduce two different sensors fabrication techniques: the first one consists of a conventional photolithography patterning technique; the second one, namely inkjet-printing, is here presented as an effective, low-cost alternative. In both cases, we obtain temperature and humidity sensors that can be easily integrated within a fabric by using a conventional weaving machine. All the sensors are fully characterized and the performances obtained with the two different fabrication techniques are compared and discussed, pointing out advantages and drawbacks resulting from each fabrication technique. The bending tests performed on these sensors show that they can be successfully woven without being damaged. A demonstrator, consisting of a mechanical support for the e-textile, a read-out electronic circuit, and a graphical PC interface to monitor the acquisition of humidity and temperature values, is also presented and described. This paper opens an avenue for real integration between printed electronics and traditional textile technology and materials. Printing techniques may be successfully used for the fabrication of e-textile devices, paving the way for the production of large area polymeric stripes and thus enabling new applications that, at the moment, cannot be developed with the standard lithography methods.

Printed sensors on smart RFID labels for logistics

This communication presents an overview on our activities on the development of printed sensors on flexible polymeric foil for RFID. We are envisioning the direct printing of sensors on different types of products such as smart labels and RFID tags. This technology could bring sensors where there is no sensor at the moment by significantly reducing their production cost and by adding new functionalities. The integration of these sensors fabricated on plastic foil with electronics, communication and powering capabilities will be addressed. The realization of cost-effective smart objects can be one of the key enabling technologies for the deployment of the Internet of Things (IoT).

Printing and encapsulation of electrical conductors on polylactic acid (PLA) for sensing applications

This paper presents the printing of resistive and interdigitated (IDE) capacitive devices for temperature and humidity sensing applications, respectively, on biodegradable polylactic acid (PLA) substrates. Inkjet and gravure printing were evaluated to transfer silver-based nanoparticles inks. Flash photonic ink sintering methodologies were employed to maintain the PLA mechanical integrity due to its low glass transition temperature (58 °C). Between the two printing techniques investigated, gravure-printed devices on 200 μm-thick PLA sheets were shown to have better resolution and higher sensitivities to temperature and humidity (1100 ppmK-1 and 5.6 fF/%RH). Additionally, we demonstrated the inkjet printing of IDE onto thin (25 μm) dissolved-PLA spin-coated substrates, to enhance the mechanical flexibility and to reduce the response time to humidity (from 238 s to 70 s). Finally, a low temperature encapsulation is proposed by embedding the printed structures within PLA sheets.

P1.8.6 All-additive Inkjet Printed Humidity and Temperature Sensors Fabricated and Encapsulated at Foil Level

We present the simultaneous fabrication at foil level of ambient relative humidity (R.H.) and temperature sensors printed on flexible substrate. These sensors are based on capacitors and resistors and their combination allows the compensation of the R.H. signals variations at different temperatures. The whole fabrication of the system is carried out at foil level and involves the utilization of additive methods, namely inkjet printing and electrodeposition, as well as the final encapsulation of the sensors for protection. The sensors have been characterized and their performances analyzed. The sensitivity of the humidity sensor ranged from 1 fF / 1% R.H. in differential mode operation to 3.5 fF / 1% R.H. in single mode actuation. The thermal coefficient of temperature (TCR) of the thermoresistor was 4.3 x 10 °C. This work demonstrates the potential of inkjet printing in the fabrication at foil level of flexible, light-weight and cost-efficient large arrays of gas sensors.

Feasibility of Printing Woven Humidity and Temperature Sensors for the Integration into Electronic Textiles

We demonstrate a woven textile with an integrated humidity and temperature sensor on flexible PI substrates. We discuss the fabrication process of the smart textile and compare two methods of sensor fabrication, first conventional photo lithography and second printing using ink jet. The humidity sensor is based on a capacitive interdigitated transducer covered with a sensing layer while the temperature sensor is made of a resistive metallic meander. An encapsulation method protecting the sensors during dicing, weaving and operation has been successfully implemented. The fabricated structures are tested to bending strain, a main source of failure during the fabrication of textiles. We were able to bend bare electrodes and complete sensors down to a minimal bending radius of 100 μm without loss of functionality. The woven temperature sensor has a temperature coefficient of 0.0027 /°C for lithography made and 0.0029 /°C for printed sensors. The humidity sensor shows a repeatable behaviour in the tested humidity range between 20 to 70 %RH. The weaving process does not damage or change the behaviour of the fabricated sensors. This contribution will highlight the challenges and promises of printing and laminating processes for the large scale fabrication of smart polymeric stripes to be woven into textiles.