Gabriela Leal

Evaluation of piezoresistivity properties of sputtered ZnO thin films

Zinc oxide (ZnO) thin films were deposited by RF reactive magnetron sputtering on silicon (100) substrates under different experimental conditions. ZnO films were studied before and after annealing treatment at 600 °C. The crystallinity, electrical resistivity, stoichiometry, thickness, and elastic modulus of the films were investigated. ZnO piezoresistors were produced using microelectronics processes, such as photolithography, lift-off, and reactive ion etching (RIE). Cantilever method was used to determine the gauge factor, and measurements of Temperature Coefficient of Resistance (TCR) were performed on a hotplate. The optimization of the deposition conditions produced ZnO thin films with controlled stoichiometry (ZnO), crystalline microstructure (phase wurzite, 002), high elastic modulus (156 GPa), and low electrical resistivity (0.072 ohm.cm), which are good properties for application as piezoresistive pressure microsensor. In addition, the ZnO piezoresistors had a GF of 2.6 on the deformation in the plane (100) and TCR of –1610 ppm/K up to 250 °C.

Characterization of SiC thin films deposited by HiPIMS

In this work thin films of silicon carbide (SiC) were deposited on silicon wafers by High Power Impulse Magnetron Sputtering (HiPIMS) technique varying the average power of the discharge on a stoichiometric SiC target. X-ray diffraction, Raman spectroscopy, scanning electron microscopy and profilometry were used to analyze the films. It was observed that high values of the average electric power favors the formation of C-C bonds, while low values of the power promote the formation of Si-C bonds. At high power, we have also observed higher deposition rates, but the samples present surface imperfections, causing increase in the roughness and decrease in the film uniformity.

Design and Analytical Studies of a DLC Thin-Film Piezoresistive Pressure Microsensor

Diamond-like carbon (DLC) thin films have been investigated for a wide range of applications due to their excellent electrical and mechanical properties. In the last decade, several researches and development activities have been conducted on the use of these thin films as piezoresistors in MEMS pressure sensors. This paper provides an overview on the design of a piezoresistive pressure sensor constituted of a silicon circular diaphragm with four DLC thin-film piezoresistors arranged in the Wheatstone bridge configuration. The sensor was designed from analytical formulas found in the literature.