局部焦耳熱進行選擇性沉積氧化鋅奈米結構於矽奈米元件 之氣體感測器研究

Abstract

本研究主要為利用焦耳熱以及電漿輔助原子層沉積技術(Plasma-Enhanced Atomic Layer Deposition, PEALD) 選擇性沉積氧化鋅奈米結構於雙接面(n+/n-/n+)多晶矽奈米帶(Polysilicon Nanobelt, PNB)元件上做為氣體感測器使用。我們成功地利用此技術，在n- 區域上選擇性沉積氧化鋅奈米結構，進而分析氣體感測元件對氧氣、氨氣以及濕度的電流響應變化，並且藉由焦耳熱以及電漿輔助原子層沉積在製程參數上的控制，可以調整感測材料的厚度以及覆蓋區域的大小。我們利用COMSOL Multiphysics 多重物理耦合模擬元件在施加焦耳熱電壓時元件的表面溫度分布以及探討局部加熱對PEALD生長速率的影響。為探討感測機制，將製備好的元件置於腔體中進行氧氣、氨氣以及濕度的感測，利用在不同操作電壓下討論焦耳熱溫度對氣體感測機制的影響，訂出最佳的量測條件以進行低濃度的氨氣量測。我們同時也利用感測器的電流-電壓特性來討論氧化性氣體、還原性氣體以及濕度的表面反應機制。

In this thesis, gas sensing behavior of ZnO-functionalized double-junction (n+/n-/n+) polysilicon nanobelt (PNB) device toward oxygen, ammonia and humidity were investigated. The ZnO nanostructures were selectively deposited at the n- region of PNB via device localized Joule heating and plasma-enhanced atomic layer deposition (PEALD). Not only thermal distribution and maximum dissipated temperature of the PNB devices but the growth rates of ZnO PEALD between the localized device Joule heating device and thermal chunk were simulated using COMSOL Multiphysics Software. Selective PEALD ZnO was characterized by AFM, SEM and TEM. The sensing material, whose thickness and morphology controlled by Joule heating parameters, is significantly modulated the performance of PNB devices. The sensing behaviors with respect to self-heating temperature were analyzed. The sensing response differentiated by the types of gas (oxidizing gas and reducing gas) was analyzed from the current-voltage characteristics of the double-junction device. The ZnO-functionalized PNB device exhibits an opposite sensing response behavior to oxygen and ammonia over the range of studied temperature. The reaction between the water vapor and semiconductor oxide (SMO) surface was also characterized from the current-voltage characteristics of the double-junction PNB device. Results showed that the control of the defect density in ZnO nanostructures could be the main factor for a reliable gas sensing application.