探討以綠色還原劑抗壞血酸合成之還原氧化石墨烯之熱性質

Abstract

隨著近年晶片之快速發展，不斷縮小的晶片導致功率密度的大幅增加，造成電子產品中所面臨到之局部熱點問題日益嚴重，而在熱管理設計中將高熱傳導率之材料整合於晶片，可以有效將熱擴散至更大的表面積，解決熱點問題，並提升晶片壽命，而具備極高平面熱傳導率之石墨烯即為解決熱點問題之絕佳角色，其中，透過氧化還原法所製造出來之石墨烯，能夠在品質及生產效率上取得平衡。 本研究利用天然還原劑抗壞將原本富有含氧基之氧化石墨烯(GO)進行初步之化學還原去氧，並結合1300 °C高溫退火熱處理製備出氧化還原石墨烯(rGO)，達到大幅去氧並修復碳結構之目的，減少薄膜中缺陷之含量，並透過機械壓實使得薄膜結構更微緻密，提升薄膜之熱傳能力。並分別經由能量散射X射線分析(EDS)、X光繞射儀(XRD)以及拉曼光譜儀(Raman)得到樣品之碳氧比(C/O)、層間距、晶格大小以及缺陷程度(ID/IG)，作為材料結構特性之定量方式。薄膜的碳氧比由還原前GO之1.67 ± 0.41提升至還原後A-AAIrGO的38.65 ± 11.8，含氧量大幅降低能夠有效減少薄膜中因含氧基造成的缺陷，層間距由GO之0.875 ± 0.004 nm 降至A-AAIrGO的0.347 ± 0.007 nm，顯示出薄膜結構已經相當趨近於無含氧基的石墨，垂直晶格大小L_c及水平晶格大小L_a皆在化學還原後下降，並於熱還原後上升，說明了薄膜結構於化學還原後受到破壞，並在熱還原後得到修復，與缺陷程度之變化趨勢相符，ID/IG由GO之1.12 ± 0.13提升至AAIrGO的1.40 ± 0.04，再降至A-AAIrGO的0.98 ± 0.18，顯現出熱還原在結構修復上的成效。 接著透過本研究開發之平面及縱向熱傳導率檢測系統，對薄膜之熱傳能力進行量測，薄膜之平面熱傳導率從還原前GO之22.21 ± 3.16 W/m-K提升至還原後A-AAIrGO的75.13 ± 15.91 W/m-K，縱向熱傳導率從0.023 W/m-K大幅提升至0.334 W/m-K，顯示出去氧還原對於薄膜熱傳導率之影響。此外，本研究也透過矽基白金微加熱器模擬晶片之局部熱點，並量測薄膜之擴散熱阻，其值由GO之3.55 ± 0.41 K/W提升至A-AAIrGO之4.40 ± 0.39 K/W，為加熱過後產生之氣穴造成平面與縱向熱阻增加所致。最高熱通量下的熱點溫度從142.68 °C降至137.24 °C，為縱向熱阻提升導致。綜上所述，本研究會聚焦於熱傳量測系統之架設與驗證，並針對自製氧化還原石墨烯薄膜進行材料特性與熱傳研究，展現其於先進電子散熱應用中的潛力。

With the rapid advancement of chip technology in recent years, continuous miniaturization has led to a substantial increase in power density, resulting in increasingly severe local hotspot issues in electronic devices. Integrating high thermal conductivity materials into chip design enables effective heat spreading across larger surface areas, thereby mitigating hotspot effects and extending device lifespan. Graphene, with its exceptionally high in-plane thermal conductivity, has emerged as a promising candidate for addressing these thermal challenges. Among various synthesis routes, the reduction of graphene oxide (GO) offers a practical balance between material quality and production scalability. In this study, GO rich in oxygen-containing functional groups was initially deoxygenated via chemical reduction using the natural reductant L-ascorbic acid. This was followed by thermal annealing at 1300 °C to produce reduced graphene oxide (rGO), with the aim of further removing oxygen functionalities and restoring the carbon lattice structure. Mechanical compression was subsequently applied to densify the film and enhance its thermal transport. The structural characteristics of rGO films were characterized using energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and Raman spectroscopy to quantify key structural parameters, including the carbon-to-oxygen ratio (C/O), interlayer spacing, crystallite size, and defect ratio (ID/IG). The characterization results showed that the C/O ratio increased significantly from 1.67 ± 0.41 for the unreduced GO to 38.65 ± 11.8 for A-AAIrGO, indicating substantial reduction in oxygen concentration and effective mitigation of oxygen-induced defects. The interlayer spacing decreased from 0.875 ± 0.004 nm in GO to 0.347 ± 0.007 nm in A-AAIrGO, suggesting the film structure approached that of nearly oxygen-free graphite. Both vertical (L_c) and lateral (L_a) crystallite sizes decreased after chemical reduction, then increased following thermal reduction, consistent with damage during chemical reduction and subsequent structural restoration through thermal treatment. This trend matched the observed changes in defect levels, with ID/IG increasing from 1.12 ± 0.02 in GO to 1.40 ± 0.01 in AAIrGO, then decreasing to 0.98 ± 0.05 in A-AAIrGO, highlighting the effectiveness of thermal annealing in repairing the carbon structure. Thermal properties are evaluated using self-developed system capable of measuring both in-plane and through-plane thermal conductivity. Results show that the in-plane thermal conductivity increased significantly from 22.21 ± 3.16 W/m-K (GO) to 75.13 ± 15.91 W/m-K (A-AAIrGO), while the through-plane thermal conductivity rose from 0.023 W/m-K to 0.334 W/m-K, highlighting the strong effect of deoxygenation and structural healing. Additionally, we use a silicon-based platinum microheater to simulate localized chip hotspots, the thermal spreading resistance was measured and found to increase from 3.55 ± 0.41 K/W (GO) to 4.40 ± 0.39 K/W (A-AAIrGO), the hotspot temperature with highest heat flux also decreases from 142.68 °C to 137.24 °C, indicating inferior thermal spreading performance after strong reduction, which results from the increased in-plane and through-plane thermal resistance caused by air pockets after film heating. In summary, this study focuses on the setup and validation of thermal measurement systems, as well as the material and thermal characterization of self-fabricated reduced graphene oxide films for potential applications in advanced thermal management.