Flexible display integrated pyroelectric self-powered floating touch sensor array

Abstract

<p indent="0mm">With the rapid development of smart electronic devices, the portable terminals are expected to operate under higher convenience and effectiveness of the input and feedback. Thus, human-computer interaction technology, including the directions input by touch control, voice recognition, visual tracking, and floating touch, is proposed to realize contact and non-contact information input. By integrating the human-computer interaction technology with the display devices, the user experience of the portable terminals can be largely improved. However, as a branch of human-computer interaction technology, floating touch suffers from several issues that impede its development in recognition, energy-efficiency, and portability. For example, the camera is susceptible to the surrounding environment of the recognized object, impacting the recognition accuracy of the sensor; the sensing distance of the millimeter wave sensor is limited by the attenuation phenomenon during the transmission of millimeter wave in the air; the transmitting devices and receiving devices of infrared sensor require high power consumptions, leading to increased energy use of the total portable terminals; the components are difficult to integrate with the flexible screen due to the large space they occupied and additional mechanical system, hampering the design of thin structure of the sensor. In this work, a PVDF-TrFE based flexible pyroelectric sensor is proposed to realize floating touch with portable, self-powered, and accurate recognition functions. Large-area pyroelectric PVDF-TrFE thin film with high uniformity is polarized via our self-designed polarization equipment, which significantly improves the polarization efficiency under low voltage conditions. The maximum polarization area can reach <sc>300 mm×330 mm.</sc> In the experiment, we firstly compare the pyroelectric performance and light transmittance of films of different thicknesses. The optimal thickness of the PVDF-TrFE thin film is screened out to be <sc>20 μm</sc> according to various indicators. Then the influence of movement speed and the distance of the heat source on the intensity of the responsive pyroelectric signal are studied. The results show that our sensor can not only recognize different speeds and feedback signals of different intensities, but also recognize different distances of the heat source. The farthest recognition distance is up to <sc>100 mm.</sc> More importantly, our sensor has a small volume and thickness of only tens of micrometers. Such small occupancy leaves more spaces for integrating with display devices. The sensor also can be operated without external power supply, reducing the power consumption of the total mobile terminal. At present, we integrate the pyroelectric sensor under the metal layer of the display device. Across the whole display module, our sensor can still detect the limb movement track above the screen and record it in the form of electrical signal. Due to high transmittance which is up to 90% of the PVDF-TrFE film, our sensor is expected to lift above the light-emitting layer when integrating with a display device. This can further increase the detection distance, the sensitivity, and strength of the feedback signal. The proposed flexible PVDF-TrFE based sensor will have a broader application prospect in the fields of light and thin electronic products and multi-function integration of display screens.