高介電係數介電層應用於上閘極結構黑磷薄膜電晶體

Abstract

本論文先對黑磷的基本性質做了材料分析。透過光光學顯微鏡及原子力顯微鏡的搭配可以粗略的判斷黑磷薄片的厚度，拉曼光譜儀則能夠用來辨認黑磷薄片的晶體方向。原子力顯微鏡和X射線光電子能譜儀可用來觀察當黑磷暴露在大氣下時，其表面的變化。 透過製程的改良，成功的製造出擁有良好元件特性的背電極黑磷薄膜電晶體。透過選擇適當的黑磷薄片厚度和使用適當的退火條件，元件可以表現出超過400cm2/V*s的場效電子遷移率和高達3個數量級的電流開關比。然而，傳統上使用300奈米二氧化矽做為介電層的背電極黑磷薄膜電晶體，其過大的次臨界擺服和較差的穩定性大大的限制了元件的應用。本論文使用上電極結構和較高介電系數的氧化鋁做為介電層，不但成功的將電晶體的次臨界擺幅從11V/dec降低至0.86V/dec，並改善了元件的穩定性使得元件在暴露在大氣下七天後仍表現出良好的特性。

In this thesis, material analysis are first investigated to study the fundamental properties of the exfoliated black phosphorus (BP). The thickness of BP flakes can be roughly determined by optical microscopy and atomic force microscopy (AFM). The orientation of BP flakes can be recognized by Raman spectroscopy. AFM and X-ray photoelectron spectroscopy are used to observe the changing process on the BP surface when BP nanosheets are exposed in the air. With the improvement of fabrication processes, the back-gated BP thin film transistors (TFTs) are successfully fabricated and show the good device performance. The high mobility over 400cm2/V*s and the on/off ratio up to 3 order of magnitude can be achieved by choosing the appropriate thickness of flakes and annealing conditions. However, the conventional back-gated BP TFTs with 300nm SiO2 have the higher subthreshold swing (SS) and the poor stability, which seriously limit the device applications. The top-gated structure with high-k dielectric capping not only successfully reduced the SS from 11V/dec to 0.86V/dec, but also improved the stability that the device showed the great device performance even for the 7days exposure.