Influence of Titanium Concentration on Piezoresistive Characteristics of DLC:Ti Films

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Abstract
Titanium-doped diamond-like carbon (DLC:Ti) films were deposited by magnetron sputtering. The effects of Ti concentration on the microstructure, phase composition and piezoresistive properties of the films were systematically investigated. The surface morphology, crystal structure and chemical bonding states of the samples were characterized using SEM, XRD and XPS. The piezoresistive properties were then assessed by monitoring the resistance change in the thin films using a precision resistance meter under controlled external stimulation. The results demonstrate that the sp2/sp3 ratio of the DLC:Ti films increases with rising Ti concentration, and both Ti–C and Ti–Ti chemical bonds are formed within the films. An excessive β-Ti phase forms when the Ti concentration exceeds 39.7 at.%. The electrical resistance of DLC:Ti films decreases linearly as the applied normal stress increases from 0 to 35 MPa, with a maximum piezoresistive coefficient of −9.0 × 10−2 GPa−1 achieved for the film with a Ti doping concentration of 12.9 at.%. One hundred cyclic loading–unloading tests induce the structural transition from sp3 to sp2, resulting in the graphitization of DLC:Ti films. In addition, external stress facilitates the fracture of Ti–C bonds and the relaxation of residual stress in the DLC:Ti films; the β- to α-Ti phase transformation induced by external loading is also observed in the films. Cyclic piezoresistive tests reveal that the piezoresistive stability of the DLC:Ti films is enhanced with increasing Ti concentration, which is attributed to the increased formation of Ti–C bonds in the films.
Funding Information
  • Natural Science Foundation of Guangdong Province (2025A1515012980)
  • Natural Science Foundation of Guangdong Province (2023B1515120033)
  • Shi Changxu Innovation Center for Advanced Materials (SCXKFJJ202211)

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