Abstract
An inkjet-printed relative humidity sensor based on capacitive changes which responds to different humidity levels in the environment is presented in this work. The inkjet-printed silver interdigitated electrodes configuration on the paper substrate allowed for the fabrication of a functional proof-of-concept of the relative humidity sensor, by using the paper itself as a sensing material. The sensor sensitivity in terms of relative humidity changes was calculated to be around 2 pF/RH %. The response time against different temperature steps from 3 to 85 °C was fairly constant (about 4–5 min), and it was considered fast for the aimed application, a smart label.
Highlights
The use of paper as flexible substrate material for printed electronics has been increasing when compared to polymer-based substrates
This paper introduces the use of paper as flexible substrate material, and as active sensing layer, responsive to relative humidity changes
The conventional fabrication process requires a sensing material, either deposited or Typically, the conventional fabrication process requires a sensing material, either deposited or printed on top of the interdigitated electrodes (IDE). No such layer was introduced, using the paper as substrate printed on top of the IDE
Summary
The use of paper as flexible substrate material for printed electronics has been increasing when compared to polymer-based substrates. This is due to its attractive characteristics, such as being a widely available substrate and a low-cost material. This paper presents challenges that polymer-based substrates do not present; for example, the porosity or surface roughness of the substrate material, which are crucial parameters when printing conductive lines. Inkjet-printing enables cost-efficient mass manufacturing of electrodes and other functional materials on large and flexible substrates, such as plastic [2], paper [3], and fabrics [4], with a broad area of applications and huge business potential. The reliability of the printed structures is a crucial matter, such as the variation between electrodes’ width, gap, and uniform layer thickness, for instance
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