Printing sensors and electronics over flexible substrates are an area of significant interest due to low-cost fabrication and possibility of obtaining multifunctional electronics over large areas. Over the years, a number of printing technologies have been developed to pattern a wide range of electronic materials on diverse substrates. As further expansion of printed technologies is expected in future for sensors and electronics, it is opportune to review the common features, the complementarities, and the challenges associated with various printing technologies. This paper presents a comprehensive review of various printing technologies, commonly used substrates and electronic materials. Various solution/dry printing and contact/noncontact printing technologies have been assessed on the basis of technological, materials, and process-related developments in the field. Critical challenges in various printing techniques and potential research directions have been highlighted. Possibilities of merging various printing methodologies have been explored to extend the lab developed standalone systems to high-speed roll-to-roll production lines for system level integration.

https://cris.fbk.eu/bitstream/11582/300858/1/Technologies%20for%20Printing%20Sensors%20and%20Electronics%20Over%20Large%20Flexible%20Substrates-A%20Review.pdf

Technologies for Printing Sensors and Electronics Over Large Flexible Substrates: A Review

Humidity measurement is one of the most significant issues in various areas of applications such as instrumentation, automated systems, agriculture, climatology and GIS. Numerous sorts of humidity sensors fabricated and developed for industrial and laboratory applications are reviewed and presented in this article. The survey frequently concentrates on the RH sensors based upon their organic and inorganic functional materials, e.g., porous ceramics (semiconductors), polymers, ceramic/polymer and electrolytes, as well as conduction mechanism and fabrication technologies. A significant aim of this review is to provide a distinct categorization pursuant to state of the art humidity sensor types, principles of work, sensing substances, transduction mechanisms, and production technologies. Furthermore, performance characteristics of the different humidity sensors such as electrical and statistical data will be detailed and gives an added value to the report. By comparison of overall prospects of the sensors it was revealed that there are still drawbacks as to efficiency of sensing elements and conduction values. The flexibility offered by thick film and thin film processes either in the preparation of materials or in the choice of shape and size of the sensor structure provides advantages over other technologies. These ceramic sensors show faster response than other types.

/pdf/humidity-sensors-principle-mechanism-and-fabrication-q8mq7scozc.pdf

Humidity Sensors Principle, Mechanism, and Fabrication Technologies: A Comprehensive Review

The possible applications of humidity sensors in automated systems for environmental control encompass many industrial and domestic fields. Very different operating temperatures and a variety of humidity ranges are needed for these purposes. The different humidity-sensing mechanisms and operating principles identified for ceramics are reviewed. Ceramic humidity sensors are divided into ionic, electronic, solid-electrolyte and rectifying-junction types. Examples of the performance of some ceramic sensors are presented. The correlation between the microstructure of ceramic materials and their humidity-sensitive electrical response is discussed. The improvement of the performance of ionic-type humidity sensors by the addition of alkali ions is explained in terms of influence on the microstructure and on the intrinsic impedance. The recent trend towards the miniaturization and integration of sensors on a single chip requires the production of ceramic films. Ceramic thin films prepared by sol-gel or sputtering processes are investigated. The results obtained on the humidity sensitivity of pn semiconducting oxide heterocontacts are also reported.

Ceramic sensors for humidity detection: the state-of-the-art and future developments

A review of miniaturised humidity sensors is presented. Recent achievements in capacitive-, hygrometric-, gravimetric-, optical- and integrated sensors are discussed. Attention is paid to a general perspective of miniaturised humidity sensors, emphasising on integration issues and technological challenges. A table summarising most of the reviewed devices is included.

Recent achievements in miniaturised humidity sensors—a review of transduction techniques

This review paper focuses on interdigital electrodes-a geometric structure encountered in a wide variety of sensor and transducer designs. Physical and chemical principles behind the operation of these devices vary so much across different fields of science and technology that the common features present in all devices are often overlooked. This paper attempts to bring under one umbrella capacitive, inductive, dielectric, piezoacoustic, chemical, biological, and microelectromechanical interdigital sensors and transducers. The paper also provides historical perspective, discusses fabrication techniques, modeling of sensor parameters, application examples, and directions of future research.

/pdf/interdigital-sensors-and-transducers-540fhwik2c.pdf

Interdigital sensors and transducers

Humidity sensor printed on textile with use of ink-jet technology

A thin-film capacitance humidity sensor

This paper presents a humidity sorption sensor made with an ink-jet printing technique. Nafion was applied as a humidity sorption material. After the presentation of sensor construction and sensor fabrication technology, a lot of effort has been made for detailed sensor tests and characterization. The sensor model based on a RC transmission line with distributed parameters (Jachowicz and Senturia 1981/1982 Sensors Actuators 2 171–86) has been carefully described and validated by a comparison with the sensor empirical parameters, measured in a broad range of measurement frequencies. On the basis of achieved results, some general conclusions for humidity sorption sensors on both the sensor fabrication technology and the sensor modelling have been made and presented in this paper.

https://iopscience.iop.org/article/10.1088/0957-0233/23/1/014003/pdf

The ink-jet printing humidity sorption sensor—modelling, design, technology and characterization

The Capacitive Sensor for Liquid Level Measurement Made with Ink-jet Printing Technology

A new type of silicon dew point detector is presented in this paper. The fabricated detector structures contain a thermometer, two heaters, a capacitive interdigitated sensor for the detection of water, sub-cooled water, as well as ice. The test results of sub-cooled water recognition are carefully described. The theoretical model of the capacitive interdigitated sensor describing the principle of detection is also discussed.

Ryszard Jachowicz

Papers

Humidity sensor printed on textile with use of ink-jet technology

A thin-film capacitance humidity sensor

The ink-jet printing humidity sorption sensor—modelling, design, technology and characterization

The Capacitive Sensor for Liquid Level Measurement Made with Ink-jet Printing Technology

Sub-cooled water detection in silicon dew point hygrometer