A polyimide based resistive humidity sensor

Abstract

PurposeTo establish an accurate and sensitive method to characterize the moisture content of a particular environment.Design/methodology/approachThis paper proposes a relatively simple humidity sensor design consisting of electrodes on a suitable substrate coated with a polyimide material. The changes in relative humidity are denoted by a corresponding change in the polyimide material's electrical resistance profile. The design proposed in this work can be microfabricated and integrated with electronic circuitry. This sensor can be fabricated on alumina or silicon substrates. The electrode material can be made up of nickel, gold or aluminum and the thickness of the electrodes ranges typically between 0.2 and 0.3 μm. The sensor consists of an active sensing layer on top of a set of electrodes. The design of the electrodes can be configured for both resistive and capacitive sensing.FindingsThe polyimide material's ohmic resistance changes significantly with humidity variations. Changes in resistance as large as 4‐6 orders of magnitude are attainable over the entire operational humidity range.Research limitations/implicationsAs the sensitivity varies non‐linearly with the humidity, the measurement has to be carried out over a very wide range in order to calibrate the sensor. The sensitivity and output range of the sensor can be easily controlled by changing the electrode spacing or geometry.Practical implicationsThe control of humidity is important in many applications ranging from bio‐medical to space exploration.Originality/valueA simple, easy to fabricate and measure, and low cost resistive‐type humidity sensor was developed. The realized sensor is suitable for integrating with microfabrication. Hence, multiple sensors of varying sensitivities and output ranges could be integrated on the same chip. Over the last few years, newly emerging micro‐electro‐mechanical‐systems technology and micro‐fabrication techniques have gained popularity and importance in the miniaturization of a variety of sensors and actuators.

A resistive-type sensor based on flexible multi-walled carbon nanotubes and polyacrylic acid composite films

“…Polyimide-based resistive-type sensors are very sensitive to humidity changes and robust enough to withstand environmental conditions. However, polymer-based resistance sensors are limited in their ability to detect low levels of humidity [6,7]. This finding has led to the development of more sensitive CNT-based sensors.…”

“…Resistive humidity sensors measure the impedance change in the resistance of a sensor element according to the ambient humidity. Recently, various resistive-type humidity sensors and gas sensors using polymer-based materials [6][7][8][9][10] and/or carbon nanotubes (CNTs) [11,12] have been studied. It is easier and more straightforward to measure humidity using resistive-type sensors than using capacitive-type sensors.…”

Sensing Performance of Nanocrystalline Graphite-Based Humidity Sensors

“…However, ceramic and metal oxide films require higher operating temperatures, and thus, may not be suitable for some applications. Polymer-based humidity sensors, such as polyimide, pentacene, conductive polymers such as polypyrrole and polyaniline, which have lower operating temperatures have also been proposed [10]- [12]. These sensors work by measuring the mechanical (gravimetric, geometrical) or electrical change (capacitance, resistance) of the polymer film due to moisture absorption.…”

Enhanced Moisture-Reactive Hydrophilic-PTFE-Based Flexible Humidity Sensor for Real-Time Monitoring

“…However, issues of aging and large hysteresis have limited their potential as monitoring sensors that require long-term operation and high accuracy. In order to achieve long-term use and reliability, as well as high sensitivity and stability, various kinds of polymer-based sensing materials have been considered [ 13 , 14 ].…”