Flexible Miniaturized Nickel Oxide Thermistor Arrays via Inkjet Printing Technology

Abstract

In this study, an inkjet printing process was developed to produce thermistor arrays for temperature sensing applications. First, a formulation process was carefully performed to generate a stable nanoparticle ink for nickel oxide, a material with a large temperature coefficient of resistance. The thermistor was then fabricated by printing a square NiO thin film in between two parallel silver conductive tracks on either glass plates or polyimide films. The printed thermistor, which has an adjustable dimension with a sub-millimeter scale, can operate over a wide range from room temperature to 200 °C with great sensitivity (B values ~4300 K) without hysteretic effects. When printed on polyimide films, the thermistors can also be bent or attached to curved surfaces to provide accurate and reliable temperature measurements. Moreover, the thermistor responds quickly to small temperature changes and provides an effective tool for transient temperature measurements. Finally, a thermistor array was fabricated to show the flexibility of this inkjet printing process and to demonstrate the applicability of the printed devices for temperature sensing applications.

Monitoring of Vital Signs with Flexible and Wearable Medical Devices

“…Body temperature can be measured using thermistors, [15][16][17][18] thermoelectric effects, [ 19 ] or via optical means. [ 20 ] However, the prominent method used in wearable sensors is the thermistor confi guration.…”

“…These performance parameters are comparable to commercially available thermistors. [ 18 ] Jeon et al used nickel microparticle-fi lled binary polymer composites as the temperature sensor, where the polymers had a melting point in the range of 35 to 40 °C. [ 21 ] When the material temperature reaches the melting point of the polymers, the particleparticle distance of the host nickel microparticles increases due to volume expansion of the polymers, which increases the thermistor resistance.…”

“…While promising advances have been made in wearable temperature sensing, a few impediments still hinder accurate temperature measurements. Most reported thermistors show a strain dependence, [ 17,18 ] which is not ideal for wearable sensing because fl exing or twisting the sensor can alter the resistance of the thermistor. Decoupling strain effects from temperature effects in thermistors still remains challenging.…”

“…Additionally, the need for any transfer processes may be eliminated since the sensor may be printed on a wearable substrate. A vast range of wearable sensors such as temperature sensors, [ 18 ] bioelectronic electrodes, [ 4 ] biosensors, [ 105 ] and electrochemical sensors [ 106,107 ] have been demonstrated by printing solution-processable functional inks. The most common solution processing technique for low-viscosity inks of <100 centipoise (cP) is spin coating.…”

Advanced carbon materials for flexible and wearable sensors

“…These sensors generally have a high resolution of temperature, but the complicated structural design and sophisticated fabrication process may hinder their further applications. Active materials with negative temperature coefficients, such as metal oxides [145,146], CNTs [127,147,148], graphene (including rGO) [81,94,149,150], which show decreased resistance with increased temperature, have also been extensively investigated for the fabrication of flexible temperature sensors. The temperature sensors based on these active materials, especially carbon materials, generally have simple fabrication processes and excellent properties, benefiting their applications as wearable sensors for human health monitoring.…”