氧化鎢薄膜基底超材料於太赫茲頻段之應用研究

Abstract

製備精密幾何結構的人工材料，以達到自然界不存在的物理性質，稱為超材料(Metamaterials)，一般超材料皆由週期性排列結構組成，因為週期性結構排列使表面電荷提供額外動能，產生表面電漿共振(Surface Plasma Res-onance ,SPR)，並運用以及探討在太赫茲頻段的光學特性。過渡金屬氧化物由於有著可調節的電子和光學特性，讓太赫茲頻段元件在材料上多了一種選擇。本實驗週期性結構以Lift-off製程製備，基板選用高阻值Si基板(電阻率>104 Ω/cm)，首先在基板表面覆蓋一層光阻，然後進行曝光和顯影，以製作所需微結構圖案，接著將鎢靶均勻濺鍍在整個基板表面，沉積參數分別在氧氣分壓4.2 SCCM和氬氣25 SCCM，目標電流100 mA的狀態下進行沉積，基板溫度保持室溫，靶材與基板固定距離為9 cm，最後通過化學溶液溶解光阻，連同附著的金屬或其他材料一併去除，留下所需的微結構。本實驗研究氧化鎢(WO3)薄膜在未退火及不同退火溫度下200°C、350°C、500°C的可調介電性質，並使用XRD、FTIR、AFM觀察薄膜表面形貌與微結構，基於氧化鎢的可調光電性質，實驗利用CST Studio Suite®模擬氧化鎢C型環週期性結構在太赫茲頻段下的表面電漿共振性質，並透過太赫茲時域光譜(THz-TDS)量測氧化鎢薄膜超材料結構，並與模擬結果互相比對，以掌握其太赫茲光學性質。經由研究結果發現，在C型環線寬逐漸放大時，共振峰有藍移的趨勢，而不同氧化鎢退火之介電常數，在退火後呈現明顯上升，並由模擬結果驗證，當退火溫度越高，共振峰會往高頻移動。 實驗結果顯示，實做樣品的結果與模擬的共振峰雖有差異，但進一步比對量測數據之共振峰最低點，樣品的頻率接近於模擬的頻率。Metamaterials are artificially engineered structures designed to achieve physical properties not found in nature. Typically, metamaterials consist of pe-riodically arranged structures, where the periodic arrangement enables surface charges to provide additional energy, resulting in Surface Plasma Resonance (SPR). These materials are explored for their optical properties in the terahertz frequency range.Transition metal oxides, due to their tunable electronic and optical proper-ties, offer an alternative material choice for terahertz frequency devices. In this experiment, the periodic structures were fabricated using the Lift-off process, with high-resistivity Si substrates (resistivity> 104 Ω/cm) being selected as the base material. First, a layer of photoresist was applied to the substrate surface, followed by exposure and development to create the desired microstructure pat-terns. Next, a tungsten target was uniformly sputtered across the entire substrate surface. The deposition was conducted with an oxygen partial pressure of 4.2 SCCM and an argon flow rate of 25 SCCM, under a target current of 100 mA, while maintaining the substrate temperature at room temperature and a fixed target-to-substrate distance of 9 cm. Finally, the photoresist, along with any at-tached metal or other materials, was removed using a chemical solution, leaving behind the desired microstructures.This experiment investigates the tunable dielectric properties of tungsten oxide (WO₃) thin films under different annealing temperatures (200°C, 350°C, and 500°C) as well as in the unannealed state. Techniques such as XRD, FTIR, and AFM were used to observe the surface morphology and microstructure of the films. Based on the tunable optoelectronic properties of tungsten oxide, CST Studio Suite® was utilized to simulate the surface plasma resonance properties of a WO₃ C-ring periodic structure in the terahertz frequency range. The te-rahertz optical properties of the WO₃ metamaterial structure were also measured using terahertz time-domain spectroscopy (THz-TDS), and the results were compared with the simulations to understand its terahertz optical properties.The research findings indicate that as the linewidth of the C-ring gradually increases, there is a tendency for the resonance peak to blue-shift. Additionally, the dielectric constant of tungsten oxide after annealing shows a significant in-crease, and the simulation results confirm that higher annealing temperatures result in a shift of the resonance peak towards higher frequencies. Although there are discrepancies between the experimental results and the simulated res-onance peaks, a closer comparison of the lowest points of the resonance peak in the measured data shows that the frequency of the samples closely matches the simulated frequency.