Internal stress and opto-electronic properties of ZnO thin films deposited by reactive sputtering in various oxygen partial pressures

Abstract

In this article, we propose ZnO thin films as a suitable material for piezoresistors in transparent and flexible electronics. ZnO thin films have been deposited by DC reactive magnetron sputtering at room temperature at various oxygen partial pressures. All the films have a wurtzite structure with a strong (0002) texture measured by XRD and are almost stoichiometric as measured by inductively coupled plasma optical emission spectroscopy. The effect of oxygen concentration on grain growth has been studied by in-situ multi-beam optical stress sensor, showing internal stress going from 350 MPa to −1.1 GPa. The transition between tensile and compressive stress corresponds to the transition between metallic and oxidized mode of reactive sputtering. This transition also induces a large variation in optical properties—from absorbent to transparent, and in the resistivity—from 4×10−2Ω.cm to insulating. Finally, the piezoresistance of the thin film has been studied and showed a gauge factor (ΔR/R)/ε comprised between −5.8 and −8.5.

Evaluation of the Piezoresistivity of a Thin Film of ZnO Doped with Fluorine and Deposited via the Ultrasonic Spray Pyrolysis Technique for Applications in Micro/Nano-Electromechanical Sensors

“…Below, Table 3 summarizes the parameters and results of work reported on ZnO piezoresistive thin films and those of our proposed work. According to the work reported by Cardoso et al [19] and Tuyaerts et al [29], the piezoresistive effect of polycrystalline ZnO thin films is related to the intensity of the preferential orientation (002), where the c-axis of the wurtzite structure is perpendicular to the substrate surface. In addition to this, Cardoso et al [15] observed that increasing the Al doping of ZnO films shifted the (002) preferential orientation to higher 2θ positions, causing a decrease in piezoresistive sensitivity as well as changes in the crystal lattice.…”

“…The piezoresistors obtained a gauge factor of 2.6 [19]. In the study by Tuyaerts et al, a gauge factor value between −5.8 and −8.5 was reported in ZnO films obtained using DC reactive magnetron sputtering [29].…”

Analysis of internal stress build-up during deposition of nanocrystalline Ni thin films using transmission electron microscopy

“…The internal stress was measured in-situ using a high-resolution curvature measurement setup aimed at the substrate in the deposition chamber [17]. Using multiple laser beams directed towards the deposited film, the curvature of the film can be quantified based on the position of the reflected beams [22].…”