Abstract
<p style="text-align:justify; text-indent:24.0pt"><span style="font-size:10pt"><span style="text-justify:inter-ideograph"><span style="line-height:150%"><span style="font-family:Calibri,sans-serif"><span lang="EN-US" style="font-size:12.0pt"><span style="line-height:150%"><span style="font-family:"Times New Roman",serif">Nowadays, sensors act as the five senses of the system, receiving information from the environment for more accurate control and feedback. Therefore, the industry is focusing on developing more cost-effective, functional and smaller sensors, regardless of the type of sensor, and flexible tactile sensors are one such area of interest. Tactile sensors quantify the physical contact force between the component and the object, and with their thinness and flexibility, they are already being used in a wide range of consumer electronics and even in smart system construction. Today's flexible tactile sensors are commonly manufactured using lithography processes [1][2] which require longer process times and costs. Laser Induced Metallization (LIM) developed by Industrial Technology Research Institute (ITRI) breaks through the material limitations of the metal circuit process compared to other processes and is suitable for polymers, ceramics, metals and glass. </span></span></span></span></span></span></span></p><p style="text-align:justify; text-indent:24.0pt"><span style="font-size:10pt"><span style="text-justify:inter-ideograph"><span style="line-height:150%"><span style="font-family:Calibri,sans-serif"><span lang="EN-US" style="font-size:12.0pt"><span style="line-height:150%"><span style="font-family:"Times New Roman",serif">In this study, a double-layer electrode capacitive array structure as shown in Figures 1 and 2 was prepared using laser-induced metallization method to investigate the feasibility of a flexible tactile sensor without a mask process, and with the aim to verify its stability after repeated pressing and bending. In this study, PU and TPU were used as the main components of the LIM layer, and the suitable process parameters</span></span></span> <span lang="EN-US" style="font-size:12.0pt"><span style="line-height:150%"><span style="font-family:"Times New Roman",serif">such as spraying and laser parameters were evaluated to obtain the sensor samples.</span></span></span></span></span></span></span></p><p style="text-align:justify; text-indent:24.0pt"><span style="font-size:10pt"><span style="text-justify:inter-ideograph"><span style="line-height:150%"><span style="font-family:Calibri,sans-serif"><span lang="EN-US" style="font-size:12.0pt"><span style="line-height:150%"><span style="font-family:"Times New Roman",serif">After engraving with optimized laser parameters, the electroless-plated copper with TPU as the main component can achieve a resistance of 2.28*10<sup>-7</sup> Ω/m and will not break when bending at a radius of curvature of 1 mm. After 1000 repetitions of pressing, the capacitance signal was measured, and</span></span></span> <span lang="EN-US" style="font-size:12.0pt"><span style="line-height:150%"><span style="font-family:"Times New Roman",serif">the results are shown in Figure 3. Considering the</span></span></span> <span lang="EN-US" style="font-size:12.0pt"><span style="line-height:150%"><span style="font-family:"Times New Roman",serif">measurement error, it can be considered that there is no change in the sensing ability of</span></span></span> <span lang="EN-US" style="font-size:12.0pt"><span style="line-height:150%"><span style="font-family:"Times New Roman",serif">the electrode after 1000 repetitions of pressing. </span></span></span></span></span></span></span></p><p style="text-align:justify; text-indent:24.0pt"><span style="font-size:10pt"><span style="text-justify:inter-ideograph"><span style="line-height:150%"><span style="font-family:Calibri,sans-serif"><span lang="EN-US" style="font-size:12.0pt"><span style="line-height:150%"><span style="font-family:"Times New Roman",serif">To confirm the functional stability, the capacitance value was measured again after flattening the sensor sample after 1000 bending cycles, and the results are shown in Figure 4. As can be seen from the results, even after repeated bending, the copper of the electrode cracked, causing the sheet resistance rise. However, the copper layer remained in contact after flattening, and the capacitance value still increased under contact, indicating that the sensor sample still maintained its sensing function.</span></span></span></span></span></span></span></p><p style="text-align:justify; text-indent:24.0pt"><span style="font-size:10pt"><span style="text-justify:inter-ideograph"><span style="line-height:150%"><span style="font-family:Calibri,sans-serif"><span lang="EN-US" style="font-size:12.0pt"><span style="line-height:150%"><span style="font-family:"Times New Roman",serif">In summary, the Laser Induced Metallization method shows high potential for flexible tactile sensors and has the potential to expand its applications to motion detection, multi-touch panels, anti-collision systems, etc.</span></span></span></span></span></span></span></p>