探討綠色還原劑木質素合成還原氧化石墨烯之熱性質

Abstract

高性能電子產品的追求不可避免地導致晶片的功率密度增加；因此，高效的散熱變得至關重要，晶片高功率運作時產生的局部熱點，能夠透過均熱層(Heat spreader)來將熱量擴散至整個表面，使熱點迅速的降溫，以防止元件過熱而造成性能下降或損壞，再透過散熱片(Heat sink) 有效地將積體電路元件產生的熱量傳遞到外部環境。單層石墨烯薄膜具有極高的熱傳導率約為 5000 W/m-K，十分適合作為均熱層的材料。然而，石墨烯薄膜的熱導率隨著厚度增加而降低，而高度純凈的石墨烯薄膜的生產成本昂貴。相反，還原氧化石墨烯（rGO）薄膜的熱導率與石墨烯相當，可以通過一個成本效益的還原過程從氧化石墨烯（GO）輕鬆製備。用於 rGO 合成的傳統還原劑對環境有害。為了促進綠色循環經濟和可持續發展，在這項研究中，木質素被用作還原劑。木質素具有出色的還原能力。研究結果顯示使用木質素成功合成了還原氧化石墨烯（L-rGO）薄膜。將 L-rGO 薄膜在 1400°C 下熱退火以增強其傳熱性能。其中 L-rGO 薄膜的彈性模數較低，在外部應力下容易斷裂。但經由高溫熱退火處理使薄膜更具柔韌性。研究還測量了L-rGO 薄膜的平面熱導率。L-rGO 薄膜的平面熱導率為 3.32 W/m-K。然而，通過熱退火，其熱導率可增加到 50-60 W/m-K。此外架設一擴散熱阻量測系統，量測功率密度約為 1000 W/cm2 的矽加熱片，透過理論計算圓形矽晶片之擴算熱阻為 9.08 K/W，本實驗量測之矽晶片為方形，因此理論誤差約為-2.1 %~+4.5 %；經由擴散熱阻量測系統量測之結果矽晶片之擴散熱阻為 9.175 ± 0.65 K/W，由此結果驗證了此實驗系統之可信度。再將 rGO 作用於矽晶片上以評估它們在降低矽晶片的擴散熱阻方面的效果。通過經退火的 L-rGO 薄膜，矽晶片的擴散熱阻從約 11 K/W 減少到約 5 K/W。

In the relentless pursuit of optimizing the performance of electronic devices, the quest for heightened power invariably leads to an escalation in chip power density, with current levels surging to a remarkable 300 W/cm2. Consequently, the efficacious dissipation of heat assumes critical significance in ensuring operational stability and longevity. Addressing this imperative, the present study delves into the pivotal role of efficient heat management strategies, particularly focusing on the utilization of advanced materials as heat spreaders. Central to this endeavor is the exploration of single-layer graphene membranes, distinguished by their unparalleled thermal conductivity (k) nearing 5000 W/m-K. This attribute positions them as formidable candidates for facilitating heat transfer within electronic devices. However, the practical implementation of graphene membranes is not devoid of challenges. Notably, the reduction in thermal conductivity with increasing thickness, coupled with the substantial costs associated with the fabrication of pristine graphene membranes, underscores the need for alternative solutions. In this context, reduced graphene oxide (rGO) films emerge as promising alternatives, offering thermal conductivities comparable to graphene while affording ease of synthesis from graphene oxide (GO) through cost-effective reduction processes. Crucially, the adoption of environmentally sustainable practices is paramount in contemporary research endeavors. In alignment with this ethos, the present study explores lignin, a naturally abundant biopolymer, as a viable reducing agent for the synthesis of reduced graphene oxide (L-rGO) films. Leveraging the exceptional reduction capabilities of lignin, the study successfully demonstrates the synthesis of L-rGO films, poised to enhance heat transfer efficiency within electronic devices. Furthermore, thermal annealing at elevated temperatures emerges as a pivotal step in enhancing the thermal properties of L-rGO films. Despite 3inherent fragilities attributable to their low elastic modulus, the annealing process imbues these films with augmented flexibility, thereby fortifying their suitability for practical applications. Experimental investigations encompassing the measurement of in-plane thermal conductivity (kin-plane) reveal promising insights into the thermal performance of L-rGO films. Additionally, the deployment of a sophisticated thermal spreading resistance measurement system enables the assessment of power density in silicon substrates, affirming the efficacy of the proposed heat management strategy. Indeed, the integration of annealed L-rGO films yields tangible improvements in thermal spreading resistance, thereby underscoring the transformative potential of this approach in optimizing heat dissipation within electronic devices. This research not only advances our understanding of heat transfer phenomena but also paves the way for the development of innovative solutions with far-reaching implications for electronic device design and functionality.