Study On The Fabrication Of ZrB₂ Thin Films And Its Electrical And Optical Properties

In recent years,with the development of the microelectronics field and the expansion of its application scope,there has been increasing attention paid to the development of new high-temperature-resistant and complex-environment microelectronic thin film materials.Zr B₂,as the most important ultra-high temperature ceramic material,is widely used in aerospace and nuclear engineering fields due to its excellent heat resistance,oxidation resistance,high hardness,high conductivity,and outstanding corrosion resistance.Based on Zr B₂ dual properties of ceramics and quasi-metals,the application of its thin film materials in high-temperature-resistant microelectronic components and solar photon energy absorption materials should have significant research significance and broad market prospects.This article used magnetron sputtering technology to systematically investigate the effects of process variations on the microstructure,electrical properties,and optical properties of Zr B₂thin films.Starting from reducing the absolute value of the temperature coefficient of thin film resistivity,the effects of W nanoparticles and Ag nanoparticles doping on the microstructure and electrical properties of Zr B₂-based composite films were studied.The efficacy of using Zr B₂ thin films as the main absorption layer in high-efficiency solar absorber films was also investigated.The main research content and results are as follows:（1）The effects of process conditions such as direct target sputtering,45°oblique target sputtering,and substrate rotation around the central axis during the coating process on the deposition rate,microstructure,phase structure,and electrical properties of Zr B₂ thin films were studied.The research results showed that the deposition rate of 45°oblique target sputtering was approximately 1/3 of that of direct target sputtering under the same process conditions.Rotating the substrate around the central axis during coating caused an intermittent deposition mode in the Zr B₂ thin film,as the target was not aligned with the central axis.This led to a deposition rate 1/6 of that achieved under a fixed substrate.In terms of thin film structure,intermittent coating could provide sufficient time for the adsorbed atoms during the growth process to migrate to lower energy positions,favoring the optimal growth of the thin film,resulting in typical columnar characteristics.On the other hand,in the direct target coating mode,adsorbed atoms were bombarded continuously by sputtered particles,and thus,the Zr B₂ thin film exhibited a dense and structureless microstructure.Regarding the phase structure,no obvious diffraction peaks were observed in the Zr B₂ thin films prepared by direct and oblique target sputtering at low power,such as 100 W.However,in the intermittent coating mode,the XRD spectrum showed significant diffraction peaks,demonstrating that intermittent coating was more favorable for the crystallization of thin films.In terms of electrical properties,the resistivity of amorphous and nanocrystalline Zr B₂ thin films decreased with increasing testing temperature within the range of 77-600 K,exhibiting negative temperature coefficient of resistance（TCR）characteristics.The sudden decrease in the resistivity of the Zr B₂ thin film around 500 K indicated the presence of two thermal activation mechanisms affecting the conductivity properties of the film.（2）To further reduce the absolute value of the temperature coefficient of resistance（TCR）of Zr B₂ films,Zr B₂-W and Zr B₂-Ag composite films were prepared using a multi-target co-sputtering technique based on the compensation principle of positive and negative resistivity temperature coefficients of different materials.The influence of W and Ag nanoparticles doping on the microstructure and electrical properties of Zr B₂-based composite films was studied.The results showed that the resistivity and TCR values of Zr B₂-W composite films could be adjusted by changing the W content in the composite films.As the W content in the Zr B₂-W film increased from 0 to 78.2 vol%,TCR_{300-423 K} decreased from-106.5 to-57 ppm·K^-1,showing reduced temperature sensitivity.In addition,XRD spectra of Zr B₂-W composite films before and after annealing at 700°C for 2 h remained unchanged,suggesting good thermal stability and potential for use as high-temperature precision thin film resistors.Similarly,the resistivity and TCR values of Zr B₂-Ag composite films could be regulated by adjusting the Ag content.The test results showed that when the Ag content in the composite film increased to 33.9 at.%,the TCR_{77-373 K} value was only 3 ppm·K^-1,which could be used to develop low-resistance,near-zero temperature drift composite films to meet the high precision requirements of modern microelectronic devices.（3）Using the finite-difference time-domain（FDTD）method,the effects of the W/Zr B₂/Al₂O₃ solar absorber film structure and the thickness of each layer on the optical properties of the solar absorber film were investigated.FDTD simulations showed that the absorption ratio no longer changes when the thickness of the bottom layer,a W layer for infrared reflection,exceeds 120 nm.The absorption ratio of a composite coating with a 65 nm Zr B₂ solar absorber layer and a 40 nm anti-reflection Al₂O₃ layer was 0.97,but the measured result was 0.86,possibly due to the Zr B₂ film’s reflectivity.To address this,a double absorber layer structure was studied by splitting the Zr B₂ film into two layers using an appropriate thickness of Al₂O₃ film.The simulation results showed that the absorption ratio of the film structure with a W（120 nm）/Zr B₂（65 nm）/Al₂O₃（40 nm）/Zr B₂（20 nm）/Al₂O₃（50 nm）double absorber layer can also reach 0.97.This simulation conclusion was experimentally verified using magnetron sputtering technology,and the actual absorption ratio of the coating in the300-2500 nm wavelength range can reach 0.92,which is close to the simulation results.