- 學位論文
利用化學氣相沉積法製備具高電阻溫度變化係數之V1-xTixO2薄膜
Effect of Titanium Doping on the Characteristics of Temperature Coefficient of Resistance of Multi-phase Vanadium Oxide Thin Films
摘要
半導體感測器(semiconductor sensor)是利用半導體材料易受外界條件影響這一特性製成的感測器，能敏銳地感受某種物理、化學或生物的信息，並將其轉變為電信息，這種元件可由輸入的物理量來命名，如熱敏、光敏、(電)壓敏、(壓)力敏、磁敏、氣敏、濕敏元件。在電子設備中採用敏感元件來感知外界的信息，可以達到或超過人類感覺器官的功能，隨著電子計算機和信息技術的迅速發展，敏感元件的重要性日益增大。 其中，熱敏元件是一種電阻值會隨溫度變化而發生改變的的半導體感測器，它的優點包括有：溫度係數很大，比溫差電偶和線繞電阻測溫元件的靈敏度高幾十倍，適用於測量微小的溫度變化；熱敏電阻體積小、熱容量小、響應速度快，能在空隙和狹縫中測量；它的阻值高、測量結果受引線的影響小，可用於遠距離測量，過載能力強且成本低廉。 熱敏元件按其電阻溫度特性可分為以下三類： (1)負溫度係數熱敏電阻(NTC)：隨溫度的上升，半導體材料中載子濃 度增加、電阻值降低，在工作溫度範圍內，電阻溫度變化係數一般 為-(1∼6)％K-1。 (2)正溫度係數熱敏電阻(PTC)：又分為開關型和緩變型，開關型在居 里點的電阻溫度變化係數約為(10∼60)％K-1°，緩變型則為(0.5∼ 8)％K-1。 (3)臨界負溫度係數熱敏電阻(CTR)：電阻特性會在特定溫度發生急劇變化，適合用於定溫度檢測或限制在較小的溫度範圍內。 而氧化釩正是一種十分優良的熱敏元件材料，此材料在340 K左右會發生金屬—非金屬轉換變化(Metal-insulator transition， MIT)，由於能帶結構之轉換，使得該材料在轉換過渡區域的電阻變化最高可達104倍，電阻溫度變化係數值可達-0.02K-1，為大多數金屬材料的5~10倍，敏感性也頗可取，十分具有應用價值，最宜用來製作熱微感測器。 本實驗的目的即在以有機金屬化學氣相沉積法(Metal-organic chemical vapor deposition，MOCVD)，輔以鈦(Ti)元素的摻雜，藉由摻雜濃度的調變，開發出具有高靈敏度、穩定性和重複性好的氧化釩薄膜。
並列摘要
Vanadium oxides compound (V2O3, V2O5, and VO2, etc.) is a well known thermal-sensitive material, undergoing a phase transition from a low temperature, semiconducting state to a high temperature, metallic state. This change is accompanied by an abrupt resistivity modification near room temperature, made vanadium oxide a candidate material for bolometric sensors application. In this application, the bolometer sensitivity is directly related to the temperature coefficient of resistance (TCR), defined as the slope of log resistivity. To produce a highly sensitive uncooled microbolometer, the development of a thermometric material with a high temperature coefficient of resistance is essential. In this worker, Vanadium oxide thin film was fabricated by metal organic chemical vapor deposition (MOCVD) from pure vanadium tri-isopropoxide oxide precursor. Furthermore, we used Titanium as a dopant during the MOCVD process. Using MOCVD method, offers advantages of both high deposition rate, low fabricated temperature, and particular the ability easily to tailor the chemical composition, The correlations between the crystal structures and the growth recipes were investigated by the x-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and x-ray photoelectron spectroscopy (XPS). Also, the electrical characteristics of vanadium oxide thin films resulted from the crystal structures and phase changes were measured by four-point probe equipment. Compared with pure vanadium oxide thin films, titanium-doped vanadium oxide thin films obviously showed a higher temperature coefficient of resistance, lower resistivty and negligible electrical hysteresis. It can be concluded that the developed vanadium-titanium oxide is an excellent electrochromic material for the fabrication of high performance uncooled mircobolometer.