Thermal-Variation Insensitive Force-Touch Sensing System Using Transparent Piezoelectric Thin-Film

A force-touch (z-axis) sensor for display applications has attracted considerable attention. The z-axis sensing layer can be realized by a transparent piezoelectric thin film due to its superior characteristics, such as thinness, flexibility, and an optical transparency. However, this film responds...

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Bibliographic Details
Published in:IEEE sensors journal 2018-07, Vol.18 (14), p.5863-5875
Main Authors: Min-Woo Kim, Dong-Kyu Kim, Kodani, Tetsuhiro, Kanemura, Takashi, Hui-Dong Gwon, Gyu-Hyeong Cho, Kwan-Young Han, Hyun-Sik Kim
Format: Article
Language:English
Subjects:
3D touch sensors
Analog circuits
Circuit design
Commercialization
Design optimization
Detection
Force
force sensors
High gain
Linearity
Microcontrollers
piezoelectric
Piezoelectricity
Polyvinylidene fluorides
Power consumption
pyroelectric
Radio frequency
Signal processing
Thermal force
Thermal sensors
thermal-variation insensitive readout
Thickness
Thin films
thin-film
Three-dimensional displays
Touch
Two dimensional displays
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Summary:A force-touch (z-axis) sensor for display applications has attracted considerable attention. The z-axis sensing layer can be realized by a transparent piezoelectric thin film due to its superior characteristics, such as thinness, flexibility, and an optical transparency. However, this film responds not only to pressure but also to thermal changes (pyroelectric characteristic), which is a major obstacle to commercialization. This paper presents a thermal-variation insensitive, force-touch sensing system using a transparent piezoelectric thin film. In conjunction with optimizations in analog front-end design for high gain and high speed, the threshold-based digital processing scheme, which effectively rejects pyroelectric signals and noises, is proposed. To validate the proposed design and method, the electronic readout system board composed of analog circuits and an eight-bit microcontroller unit was implemented, and it read out the force-touch signal with a ten-bit resolution in power consumption of 6.5 mW. The implemented readout system was experimentally verified with a 3.9-inch polyvinylidene fluoride-copolymer piezoelectric thin-film sensor, with a thickness of 20 μm. The system achieves a force-to-signal gain of 0.6 V/N in a range of 0.3-2.5 N with high linearity. The capability to reject a pyroelectric signal up to ±Δ10 °C/s was also proved through a thermal-shock experiment.
ISSN:1530-437X
1558-1748
DOI:10.1109/JSEN.2018.2839356