For example, the topology of the carotid artery area is flat, whereas the finger is curved. The PZT-based tactile sensors fabricated using the novel sol-gel process on a flexible stainless steel substrate can be used as rugged human pulse sensors with high performance. Future work application, the PZT thin film tactile sensor on stainless steel substrate and can be applied the structure health monitoring such as the bridge [31] or engineering structure [32]. In addition, the flexible PZT tactile sensor to apply energy harvesting [33], large area tactile sensors array [34], robot hard [5], touch sensor [35], pressure sensor [36] and fingerprint [37].2.?Experimental Section2.1. Solution Based Process for PZT Thin Film FormationDuring the sol-gel deposition process, the PZT solution was spun on the stainless steel substrate.

Two chemical reactions were performed during the sol-gel process, including hydrolysis and condensation reactions. The chemical reaction equations [38] of the hydrolysis reactions are shown in Equation (1), whereas the chemical reaction equations of the condensation reactions are shown in Equations (2) and (3):M(OR)+H2O��M(OH)+ROH(1)M(OH)+M(OH)��M?O?M+H2O(2)M(OH)+M(OR)��M?O?M+ROH(3)The PZT solution used to prepare the PZT thin-film in the sol-gel process consisted of lead acetate, zirconium n-prop-oxide, and titanium iso-propoxide, and the molar ratio of these compounds was 1.1:0.52:0.48. Organic solvents, such as acetic acid, lactic acid, glycerol, and ethylene glycol can be added to the mixed powders to prepare the PZT mixing solution.

The preparation Entinostat steps of the PZT mixing solution are shown in Figure 1. First, Solution A was prepared by mixing the zirconium n-prop-oxide and titanium iso-propoxideat at room temperature for 30 min. Second, Solution B was prepared by mixing lead acetate and acetic acid at 110 ��C for 5 min. Next, Solution A was mixed with Solution B for 15 min. The mixture of Solutions A and B was subsequently mixed with DI water for 15 min, followed by mixing with lactic acid for 15 min and glycerol/ethylene glycol for 15 min to obtain the final solution with a concentration of 1. 9 M.Figure 1.Preparation process of PZT solution Device.2.2. Device FabricationThe 100 ��m-thick stainless steel substrate for the tactile sensor was cleaned using ultrasound in acetone, isopropyl alcohol, and DI water for 10 min. Next, the PZT sol-gel was spin-coated on the stainless steel substrate followed by the pyrolysis processes at temperatures of 150 ��C and 500 ��C for 10 min and 5 min, respectively. After the pyrolysis process, the thin-film was annealed at 650 ��C for 10 min.