Capacitive-Type Relative Humidity Sensor with Hydrophobic Polymer Films

Sadaoka, Yoshihiko

doi:10.1007/978-0-387-09665-0_3

Cited by 3 publications

(4 citation statements)

References 40 publications

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“…Because some models of polymer sorption equilibrium (e.g. FloryHuggins [24]) contain logarithmic dependencies, it could be possible that some interaction processes in water vapour molecules-polymer chains inside polymeric materials could be described by logarithmic relationships which could not be explicitly observed within a range of medium humidity values, but could only be revealed at low humidity (that might be e.g. hydrogen bond interactions of logarithmically distributed strengths.)…”

Section: Discussionmentioning

confidence: 99%

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Low Humidity Characteristics of Polymer-Based Capacitive Humidity Sensors

Majewski

2017

Metrology and Measurement Systems

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Polymer-based capacitive humidity sensors emerged around 40 years ago; nevertheless, they currently constitute large part of sensors' market within a range of medium (climatic and industrial) humidity 20−80%RH due to their linearity, stability and cost-effectiveness. However, for low humidity values (0−20%RH) that type of sensor exhibits increasingly nonlinear characteristics with decreasing of humidity values. This paper presents the results of some experimental trials of CMOS polymer-based capacitive humidity sensors, as well as of modelling the behaviour of that type of sensor. A logarithmic functional relationship between the relative humidity and the change of sensor output value at low humidity is suggested.

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Section: Discussionmentioning

confidence: 99%

“…Even more precise is the modified Kirkwood's equation [24] for a binary system of dielectric materials, when the number density of polymer is practically independent of the humidity: …”

Section: Modelling Of Polymer-based Capacitive Humidity Sensorsmentioning

confidence: 99%

Low Humidity Characteristics of Polymer-Based Capacitive Humidity Sensors

Majewski

2017

Metrology and Measurement Systems

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“…For the conventional humidity sensors with the sandwich structure, good response linearity up to 90% RH could be obtained without much difficulty by using various sensing polymers such as polyimide (PI), cellulose acetate butyrate (CAB), poly(methyl methacrylate) (PMMA), etc. [ 12 , 13 , 14 , 15 ]. Their less hydrophilic nature is considered to be advantageous in obtaining good response linearity by suppressing the formation of water clusters that have a much higher permittivity (e.g., a value close to that of liquid water) than the individual sorbed molecules [ 15 ].…”

Section: Introductionmentioning

confidence: 99%

“…[ 12 , 13 , 14 , 15 ]. Their less hydrophilic nature is considered to be advantageous in obtaining good response linearity by suppressing the formation of water clusters that have a much higher permittivity (e.g., a value close to that of liquid water) than the individual sorbed molecules [ 15 ].…”

Section: Introductionmentioning

confidence: 99%

Effects and Mechanism of Surface Water Wettability and Operating Frequency on Response Linearity of Flexible IDE Capacitive Humidity Sensor

Yang

Han

Lim

et al. 2021

Sensors

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Flexible capacitive humidity sensors are promising for low-cost, wearable, and radio frequency identification sensors, but their nonlinear response is an important issue for practical applications. Herein, the linearity of humidity response was controlled by surface water wettability and operating frequency of sensor, and the mechanism was explained in detail by surface water condensation. For a sensor with a Ag interdigitated electrode (IDE) on a poly(ethylene terephthalate) substrate, the capacitance showed a small linear increase with humidity up to 70% RH but a large nonlinear increase in the higher range. The response linearity was increased by a hydrophobic surface treatment of self-assembled monolayer coating while it was decreased by an ultraviolet/ozone irradiation for hydrophilicity. It was also increased by increasing the frequency in the range of 1–100 kHz, more prominently on a more hydrophilic surface. Based on experiment and simulation, the increase in sensor capacitance was greatly dependent on the geometric pattern (e.g., size, number, and contact angle) and electrical permittivity of surface water droplets. A larger and more nonlinear humidity response resulted from a larger increase in the number of droplets with a smaller contact angle on a sensor surface with higher water wettability and also from a higher permittivity of water at a lower frequency.

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