選擇性沉積鈀奈米結構於極薄矽奈米帶元件之氫氣感測器研究

Abstract

本研究不僅運用焦耳熱效應選擇性沉積鈀金屬 (Palladium) 於極薄矽奈米帶元件上做為氫氣感測器使用；也成功地利用焦耳熱效應進行極薄矽奈米帶自我加熱 (self-heating)，並同時在此狀況下即時地測量不同濃度的氫氣。透過厚度為10 nm的極薄矽奈米帶元件設計以及高低濃度摻雜 (n+/n-/n+)的設計，可以精準的控制焦耳熱放熱區域 (低摻雜區)，也可以使對閘極電位變化靈敏的低濃度摻雜區域對感測氣體的能力得到更進一步提升。接著應用 COMSOL多重物理偶合模擬 self-heating時極薄矽奈米帶的表面溫度分布，與供給不同電壓下，聚甲基丙烯酸甲酯 (Polymethylmethacrylate，簡稱PMMA)光阻燒除的情形相互驗證。將製備好的元件置於利用聚二甲基矽氧烷 (Polydimethylsiloxane，簡稱PDMS)製作的小腔體中進行氫氣感測，比較不同厚度的氮化矽水氣阻擋層對氫氣的感測影響，比較不同厚度的鈀金屬偵測氫氣的效率，也比較不同操作電壓下所產生的self-heating效應對氫氣感測的影響，篩選出最佳的氫氣感測器製備條件以及操作條件，使其在大氣中可以靈敏地偵測到濃度為1 ppm的氫氣。我們相信結合極薄矽奈米帶元件以及高低濃度摻雜的這兩項設計，可大幅提升元件對氣體的感測能力，而利用焦耳熱效應技術製備的氫氣感測器可以提升元件在室溫下的應用以及氣體偵測的準確性，並預期此技術對臨床即時人體呼吸氫氣測試以及工業危險氣體洩漏安全檢測有重大的幫助。

In this study, we report the experimental results of selective deposition of Palladium (Pd) via localized Joule heating (JH) on C-Si ultra-thin nanobelt devices as real-time hydrogen sensors. The thickness of ultra-thin nanobelt devices were scaled down to 10 nm, which makes device very sensitive to the surface potential change. The active channels of ultra-thin nanobelt devices were consisted of n+/n-/n+ structure, and localized joule heating is occurred mainly at local high resistance n- region such that a PMMA (Polymethylmethacrylate) nanotemplate can be formed via JH. The surface temperature was estimated by COMSOL simulations at various biases. AFM was used to investigate the morphology of n- region where the PMMA is ablated at various conditions. Devices with selective deposition of Pd at the n- region were then placed in a small PDMS (Polydimethylsiloxane)chamber for hydrogen detection. The impact of different thicknesses of Si3N4 atop device channel was compared on hydrogen sensing so that a optimized thickness was adopted to prevent attack from humidity. The thickness of Pd was also investigated via hydrogen sensing. Furthermore, several self-heating voltages were compared for the best response in hydrogen sensing. The detection limit under atmosphere is about 1 ppm.