本論文旨在研製具優異電性與感光特性之氧化銦鎵鋅(IGZO)薄膜電晶體(Thin film transistors, TFTs)與場效應二極體(field-effect diodes, FEDs)及其於紫外光感測器(ultraviolet photodetectors, UV-PDs)之應用。透過先後沉積鉑(Pt)與氧化鎳(NiO)於TFT背通道表面作為雙覆蓋層結構(Double capping layer, DCL)，一方面利用Pt之高功函數(5.65 eV)與n型通道形成蕭基接面(Schottky contact)，藉此增強通道層之全空乏(fully depletion)程度，進一步抑制暗電流(I_dark)；另一方面藉由NiO與通道形成之pn異質接面(heterojunction, HJ)，於照光下將其空乏區產生之光生載子注入通道，提升通道載子濃度及降低臨界電壓以增加光電流。另外，本研究透過將TFT使用二極體連接方式製備FED，比較兩者於光響應性能與可靠度之優劣。
於實驗中，所有元件皆使用等效氧化層厚度(equivalent oxide thickness, EOT)為10 nm之(氧化矽鉿) Hf0.82Si0.18O閘極介電層。TFTs (W/L=200 m/50 m)依CL結構分為without CL/NiO CL/Pt CL/DCL四類，採用射頻（RF）濺鍍製備IGZO通道層和NiO CL以及使用電子束蒸鍍製備Pt CL。本研究係使用波長為275-400 nm與功率為1.25 mW/cm2之UV光照射進行元件之光響應特性分析。透過光響應度(R_ph)、光靈敏度(S_ph)與檢測率(D^*)等參數，探討IGZO通道層和CL結構參數與UV光響應特性之折衷關係，製備最適化之TFT UV-PDs元件結構。並透過金屬連接線將元件之汲極與閘極連接，製備為FED UV-PDs元件結構，並與對應TFT之光電特性與元件可靠度進行比較。此外，動態光響應行為上，IGZO通道層中之氧空缺容易造成持續光電導(persistent photoconductivity, PPC)效應，本研究採用一正值之閘極脈衝使元件導通，透過外部電路將殘餘之光生載子清除，從而充分消除PPC現象。
本論文研究內容主要分為「IGZO TFT操作原理及TFT元件光電特性分析」、「DCL結構於IGZO TFT UV-PDs之光電特性改善」與「DCL IGZO TFT與FED UV-PDs之可靠度分析」三大部分，茲依序分述如下：
第一部份於「IGZO TFT操作原理及TFT元件光電特性分析」之研究，旨在分析通道膜厚(T_ch)對於元件光電特性之影響，TFT屬無接面之電晶體，係透過閘極與通道之功函數差將通道(n型)全空乏，以達到關閉元件之效果。一般而言，TFT元件關閉漏電流(I_off)主要來自於閘極漏電流與通道漏電流，於元件處於全空乏狀態時，I_off幾乎由閘極漏電流主導而最小化；若元件處於部分空乏狀態，元件將會操作於次臨界區導致通道漏電流使I_off大幅提升，由於UV-PDs應用TFT的暗電流(I_Dark)由I_off決定，此將導致光暗電流比大幅下降，不利於光靈敏性及待機功耗之表現。於實驗上係分別以Hf0.82Si0.18O及IGZO作為介電層與通道層，並以氧化鋅鋁(AZO)與鈦(Ti)作為緩衝層與閘極電極金屬，製備具25、30、35與40 nm四種T_ch之TFTs進行光電特性分析。採用較薄通道(25 nm)可以獲得全空乏狀態，雖可使TFT具有較低的I_off，然亦將減少產生光生載子的空間，不利光電流之提升；使用較厚的通道(40 nm)雖可有效地提升元件導通與光響應特性，然亦導致臨界電壓(V_th)大幅負偏移，造成暗電流(I_dark)明顯增大，進而大幅降低UV-PDs的光靈敏度(S_ph)與檢測率(D^*)。
第二部分於「DCL結構於IGZO TFT UV-PDs之光電特性改善」旨在利用Pt與p-NiO材料於通道上方沉積區域性堆疊DCL，藉此改善元件之光電特性。其中Pt與n型通道形成蕭基接面，並在背通道表面形成空乏區，可允許元件在相同的有效通道厚度(T_che)下，提升主動層厚度，降低串聯電阻與增加照光下光生載子之實空間；NiO與通道形成之pn HJ於照光下可將電子注入通道提升通道載子濃度以增加光電流，且電子濃度提升亦有助於縮小空乏區範圍，增加通道導電性。結合Pt與NiO CL之優勢，以最大化元件之光響應性能。為發揮DCL最大效益，本研究分別對Pt與NiO CL結構參數進行調變，Pt屬不透明之金屬材料，故採用較短Pt CL長度(L_(CL(Pt))= 5、10與15 μm)進行沉積；NiO目的在於增加光生載子整體數量，故採用較長NiO CL長度(L_(CL(NiO))= 20、30與40 μm)進行沉積。Pt CL厚度沉積約10 nm足夠均勻即可，NiO CL厚度則須大於pn HJ空乏區所占範圍並保有一部分中性區，故採用本研究室所製備為80 nm之最佳厚度。所有CL寬度皆與通道寬度相同。在具有相同T_che之無CL (Type A)、具NiO CL (Type B)、具Pt CL (Type C)與具DCL (Type D) IGZO TFT元件光電特性比較下，實驗結果顯示，使用L_(CL(Pt))= 5 μm與L_(CL(NiO))= 40 μm並搭配T_ch= 40 nm之Type D IGZO TFT可得到最佳光響應性能，其光響應性(Photoresponsivity, R_ph)高達1888.07 A/W、光靈敏度(Photosensitivity, S_ph)高達3.37×108 A/A與檢測率(detectivity, D^*)高達3.99×1016 Jones。
第三部分於「DCL IGZO TFT與FED UV-PDs之可靠度分析」之研究，旨在藉由負偏壓應力(Negative bias stress, NBS)測試上述所製備之IGZO TFTs應用於UV-PDs之穩定度，並加入對應之IGZO FEDs進行比較，並透過一週期性("T"="10 s" ) UV光照射(λ="275 nm" ，功率為"1.25 mW"/〖"cm" 〗^"2" )分析其動態光響應行為下之PPC效應。實驗結果顯示，相較於傳統結構之Type A TFT，通道增厚的Type D TFT臨界電壓偏移量(∆V_th)與汲極電流偏移量(∆I_D)於1000 s的NBS測試後，分別降低約55%與83%。值得注意的是，相較於Type D TFT，其對應之Type D FED的∆I_D於1000 s NBS測試後可進一步下降27%。FED較TFT具高可靠度之原因，主要歸因於閘極介電層所承受之電場強度較對應之TFT小，減少整體電特性受偏壓應力的改變。於動態光響應行為上，Type A與D TFTs皆發生明顯的PPC現象，上升時間(τ_r)/下降時間(τ_f)分別為0.99 s/2.32 s與1.04 s/3.15 s，為減輕PPC的現象，利用一30 ms的閘極脈衝(V_G= 4 V)可充分消除PPC現象，Type A與D TFT之τ_f分別降為0.17 s與0.23 s。
本論文提出以DCL覆蓋於IGZO TFTs背通道表面，有效提升元件於UV-PDs應用上的光感測性能，Type D TFT於275 nm之UV光照射下，展現出優異的光響應特性，R_ph、S_ph與D^*分別達到1888.07 A/W、3.37×108 A/A與3.99×1016 Jones。並藉由將閘極與汲極連接之FED偏壓條件降低介電層所承受之電場強度，相較於TFT有更好的穩定性，並可使用單一電源操作。具有傳統TFT製程簡易、成本低廉及可大面積製備之優勢，僅須透過簡易沉積製程可獲得大量光感測性能提升，以及使用簡單電路連接可增加元件穩定性，預計於未來在光感測器之應用將極具潛力。

SUMMARY
In this study, the thin film transistors (TFTs) and field effect diodes (FEDs) with IGZO channel layer and double capping layer (DCL) for the application of ultraviolet photodetectors (UV-PDs) are proposed. The influence of IGZO channel thickness and capping layer (CL) structure on the photoelectric characteristics of TFT is discussed. Experimental results show that the TFT fabricated with a channel thickness (T_ch) of 40 nm and DCL (Pt/NiO) exhibits superior detection performance with R_ph of 1888.07 A/W, S_ph of 2.97×108 A/A, and D^* of 3.58×1016 Jones, respectively. It is attributed to the NiO/IGZO pn HJ contribute a considerable number of photogenerated electrons during UV light irradiation, and Pt CL to increase the T_ch to increase the space for the photogenerated carriers. In addition, the FEDs demonstrate better stability with a less variation of the drain current (∆I_D) as compared to the corresponding TFTs, which due to the low average dielectric electrical field intensity in the FEDs

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