共平面金屬-絕緣層-金屬架構之表面電漿共振感測晶片之建構與驗證

Construction and Verification of a Co-Planar Metal-Insulator-Metal Surface Plasmon Resonance Sensor

盧紀瑩(Chi-Ying Lu)

指導教授 ： 林啟萬

國立臺灣大學/工學院/醫學工程學研究所/碩士(2015年)

https://doi.org/10.6342/NTU.2015.02696

摘要

本研究以開發共平面金屬-絕緣層-金屬 (Metal-Insulator-Metal, MIM) 架構表面電漿共振感測元件，建立一體化表面電漿共振晶片系統，以擺脫傳統光路系統中的外部光偵測器架構。在MIM結構中，當電子的能量累積到足夠能量時，部份的電子會跨過金屬-絕緣層-金屬的能障並形成電流。而表面電漿現象可以有效的增大電流，產生高濃度的熱電子可更順利通過薄絕緣層的上方或激發注入。
本論文先以MIM結構原理模擬電流-電壓特性曲線，並設計三種不同的製程參數，分別為A sample：Au 48 nm/ TiO2 30 nm，B sample：Au 48 nm/ TiO2 45 nm，C sample：Au 48 nm/ ZnO 20 nm與 D sample：Au 48 nm/ ZnO 30 nm，以探討不同材料與厚度對MIM結構的影響。實驗結果顯示Sample A ,B ,C, D在偏壓範圍±1.4 V間的表現上，因為厚度影響，使Sample A的電流 (0.14 nA) 略大於Sample B (0.1 nA)；Sample C的電流 (0.32 nA) 略大於Sample D (0.22 nA)，表示愈薄的絕緣層膜愈容易讓電子激發跨越能障。而ZnO與TiO2在導電性質的差異，使電子在薄膜上的穿越更順利。在一樣厚度的薄膜中，Sample D的電流 (0.22nA) 大於Sample A (0.14nA)。
本論文的另一主軸，即為測試MIM表面電漿共振晶片的確效性，使用波長658 nm的二極體經由透鏡與線性偏振片聚焦於晶片上，並調整入射光與晶片角度以在金膜上激發表面電漿共振波，透過漸逝波能量所造成金層載子濃度的改變，間接調變其光電流以達到表面電漿共振晶片感測目的。實驗結果顯示在橫向磁場 (Transverse magnetic polarization ,TM) 下，雷射光強度與MIM晶片的電流有正向的線性關係，且在雷射光強度25 mW下，Sample A在TM波對應到電流比橫向電波 (Transverse Electronic polarization ,TE) 大了近6倍；Sample B的TM波對應到的電流比TE波大了近4倍，而Sample C的TM波對應到電流僅比TE波大約1.2倍。由此可以看出因材料選擇關係，TiO2的屏障高度高於ZnO，使電子激發較不易，因此在無雷射光激發下，Sample C 電流大於Sample A與B。然而在雷射光強度的激發下，晶片對應表面電漿共振現象有特定的電流上升變化，TiO2的薄膜愈薄，被激發的電子跨越能障的機率愈高。
根據以上實驗成果，另以光訊號對照電流訊號與介電係數變化的實驗，以驗證表面電漿共振現象的存在。實驗顯示在定偏壓 (1.4 V) ，定光強度 (25 mW) 下，調變雷射光入射角度時，晶片有電流浮動的現象，且在入射角度55度，接近表面電漿共振角處，電流達到最大值。表面電漿共振晶片在定偏壓 (1.4 V) ，定光強度 (25 mW) 下，在感測區滴入耦合油，電流從0.6 nA微降至0.25 nA，可以看出表面電漿共振晶片對耦合油達到感測功能。
本論文已成功驗證表面電漿共振晶片可藉由光電轉換特性，將被激發在金屬與介質界面傳播的橫向表面電漿振動子波動能量轉換成電訊號並加以量測分析，以電訊號的分析計算取代傳統光訊號分析的方式，並感測到介電係數的變化。未來此技術可縮減表面電漿共振系統的體積，實踐微小化的醫學感測晶片應用。

關鍵字

表面電漿共振 ； 共平面金屬-絕緣層-金屬架構 ； 內部電子放射

並列摘要

Surface plasmons are excited electromagnetic wave propagating at the interface between a dielectric and a conductor, which are evanescently confined in the perpendicular direction. In recent years, it have been widely applied in physical, chemical and biological sensing to achieve real-time and label free sensing.
A system of surface plasmon resonance (SPR) are mostly based on prism coupling for surface plasmon excitation. The far-field scattering at the certain angle is measured and analyzed by a photodiode or an optical detector. The size of a typical optical instrument is large, therefore it usually can’t be further miniaturized. This study attempted to use a co-planar Metal-Insulator-Metal (MIM) device, which was integrated to a surface plasmon chip, to miniaturize the surface plasmon resonance device.
In this thesis, a simulation of current- voltage characteristics was based on the principle of MIM device. And the MIM device as SPR sensor was) designed in three parameters of thickness, namely A sample: Au 48 nm / TiO2 30 nm, B sample: Au 48 nm / TiO2 45 nm, C sample: Au 48 nm / ZnO 20 nm and D sample: Au 48 nm / ZnO 30 nm. Experimental results show that Sample A, B, C, D in a bias voltage of ± 1.4 V, the current of Sample A (0.14 nA) is slightly greater than Sample B (0.1 nA) and also Sample C (0.32 nA) is slightly greater than Sample D (0.22 nA) , which represents that the thinner insulating layer film is, electrons can more easier through the insulator layer. And the electrons in ZnO layer can more easier through the insulator layer of TiO2 on account of the difference conductive properties of TiO2 and ZnO.
In the second part of this thesis, it is to confirm the effectiveness of MIM device. 658 nm laser transmits through the metal layer stack and excites surface plasmas on the top surface. Experimental results show that under the excitation of transverse magnetic polarization (TM) wave, the laser intensity and the current of MIM device have a positive linear relationship. In the power intensity of 25 mW in TM wave, Sample A corresponds to a current larger than the Transverse Electronic polarization (TE) wave of nearly six times; Sample B of TM wave corresponds to the current nearly four times larger than the TE wave, and Sample C of TM wave corresponds to only about 1.2 times greater than the current of TE wave. Because of the selection of material, TiO2 barrier height is higher than ZnO, the tunneling of electrons become more difficult. Therefore, the current of Sample C is greater than Sample A and B under no SPR excited. However, corresponding to surface plasmon resonance phenomenon, the specific changes in the current will rise. The thinner TiO2 thin film is, the higher probability of electron tunneling through the film.
In order to verify the existence of surface plasma resonance, the comparison of light signals and current signal and the detection of dielectric constant are examined. We adjust the incident angle of the laser beam, and record the changes of electrical signals. Experiment results show that when under the fixed bias voltage of 1.4 V and constant laser intensity of 25 mW, the current of the device reachs the maximum value at a incident angle of 55 degrees, which is closed to the surface plasma resonance angle. On the other hand, under the same bais voltage and the laser intensity,in a given bias (1.4 V), under a given light intensity (25 mW), current flows decreases from 0.6 nA to 0.25 nA , when coupling oil dropped in the sensing region. It can be seen that the surface plasma resonance senor can successfully detect the change of dielectric constant by measuring the current.
This thesis has been successfully verified that through photoelectric conversion, the device transferred the excited energy of surface plasmon resonance into electrical signals be measured and analyzed. According to our results, the device can significantly minimize the size of detection system of SPRand reduce the cost of SPR instrument.

並列關鍵字

Surface Plasmon Resonance ； Metal-Insulator-Metal ； Internal Electron Emission

參考文獻

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