| 摘要: | 現今，積體光路(PICs)已被廣泛應用在不同的科技領域，特別是矽光子技術。由於矽光子技術與互補式金屬氧化物半導體(CMOS)製程技術具有高度兼容性和高集成密度的特點，因此被廣泛視為下一代計算解決方案的基礎。在所有的光學元件中，微環形共振腔在PICs扮演重要的角色，包括濾波、調製和檢測等光學功能。對於微環形共振腔來說，品質因子(Q)是決定性能的關鍵參數。在傳統上，品質因子會受到波導材料的吸收損耗以及製程缺陷引起的散射損耗所限制，例如波導的表面粗糙度和側壁垂直度。由於傳統的高限制波導的波導模態主要在導光層中傳輸，為了追求更高的品質因子，本論文降低了導光層的限制，使波導模態能夠與高品質的披覆層大幅重疊，而讓模態在高品質披覆層的有效面積能遠大於傳統的高限制波導。此外，由於較薄的導光層，蝕刻深度較淺，故能更好地控制蝕刻過程。因此，具有較薄導光層的低限制波導有助於降低波導材料的吸收損耗和側壁粗糙度引起的散射損耗。在本論文中，我們使用導光層厚度為100 nm的低限制氮化矽波導，不僅可以實現小於1 mm的彎曲半徑，還達到比毫米級共振腔更高的集成密度。
為了實現最佳的結構設計以降低傳輸損耗，本論文透過RSoft模擬軟體中的FemSIM來研究在不同披覆層的材料下，低限制波導的光消逝深度，確保絕緣層厚度足以防止能量傳至矽基板，並透過RSoft模擬軟體中的BeamPROP來研究在二氧化矽披覆層下，低限制環形波導的彎曲損耗，以此設計最佳的環形波導半徑。在實驗上，為了找出最佳的製程方法以降低波導的材料吸收損耗和散射損耗，本論文嘗試不同的製程方法，包含氮化矽薄膜的沉積方法、披覆層的沉積參數以及是否進行熱退火。
綜合以上探討並驗證不同參數後，實現高品質因子、低損耗的微環形共振腔，其品質因子高達1.2×10⁶、傳輸損耗降低至0.22 dB/cm，且具有可調製性。
本論文提供一個低限制波導的設計和較佳的製程方法，以實現高品質因子、低損耗的微環形共振腔。;Recently, photonic integrated circuits (PICs), especially silicon photonics, have been applied widely in various technologies. Due to their exceptional compatibility with complementary metal-oxide-semiconductor (CMOS) fabrication processes and remarkable integration density, PICs are generally regarded as the cornerstone of next-generation computing solutions. Among all the photonic devices, micro-ring resonators play an important role in PICs, offering optical functionalities such as filtering, modulation, and detection. For micro-ring resonators, the quality factor(Q) is a critical parameter determining performance. Traditionally, the Q factor is limited by waveguide material absorption and scattering loss from the imperfections of the fabrication processes, such as waveguide roughness and sidewall angles. In pursuit of a high Q factor, lightly confining the waveguide mode in the core layer permits the mode field to propagate with significant overlap with the high-quality cladding layer while the effective area of the mode field is much larger than the conventional tightly confined waveguide, in which the mode field is mostly confined in the core layer. In addition, a thin core layer allows a better etching budget with a shallower etching depth. Therefore, low-confined waveguides with a thin core layer serve to minimize both the material loss from the waveguide core and the scattering loss induced by the sidewall roughness. In this thesis, we realize the low-confined Si₃N₄ waveguide with a core layer of 100 nm thickness, enabling a bending radius of less than 1 mm and providing a higher integration density than the millimeter-sized resonators.
To achieve optimal structural design and reduce transmission losses, this paper utilizes the FEMSIM module in RSoft simulation software to investigate the light extinction depth of low-confinement waveguides under different cladding materials. This ensures that the thickness of the insulating layer is sufficient to prevent energy from reaching the silicon substrate. Additionally, through the BeamPROP module in the RSoft simulation software, this paper studies the bending losses of low-confinement ring waveguides under a silicon dioxide cladding layer, aiming to design the optimal radius for the ring waveguide. In experimental investigations, various processing methods are explored to identify the best practices for reducing material absorption and scattering losses in the waveguide. This includes different deposition techniques for silicon nitride film, deposition parameters for the cladding layer, and the impact of thermal annealing.
By integrating and validating various parameters discussed above, we have achieved a high-quality factor, low-loss micro-ring resonator. The quality factor reaches up to 1.2×10⁶, with a reduced transmission loss of 0.22 dB/cm. Moreover, the micro-ring resonator exhibits tunability.
This paper presents a design of low-confinement waveguide and optimal fabrication methods to achieve a high-quality factor, low-loss micro-ring resonator. |
