以巴克球作為浮動閘極之有機非揮發性記憶體

Abstract

本論文主要是利用C60來取代傳統多晶矽做為浮動閘極並對此有機非揮發性 記憶體的機制與特性做研究。 在正式製作元件前，首先先利用TEM 驗證薄膜的厚度與晶向結構，並利用 EDS 與ESCA 等方式對沉積薄膜的組成做分析。接著，利用驗證過的薄膜沉積 條件搭配後續低溫氧化層與金屬沉積技術，成功地在矽基板上完成以C60 做為浮 動閘極之電容結構，並得到ΔVFB=4 V 以上的記憶窗大小，且在retention 測試中利用線性外插的方式，亦驗證了其在10 年後其仍可維持ΔVFB=3.038 V 的記憶窗，顯示C60 浮動閘極電容具有作為非揮發性記憶體的潛力。另外，對於實驗中所觀測到的順時針電容遲滯效應，在閘極結構相同的前提下，藉由利用Pt 奈米晶粒記憶體對電荷注入方向做驗證，配合先前所觀測到C60 薄膜的介電常數隨頻率變化之現象，我們提出了氧離子移動模型來做解釋。 在第二部分中，藉由C60 薄膜厚度的微縮，我們成功地觀察到了氧離子移動 與電荷注入等兩種機制並存的現象，且由於C60 薄膜內部承受的跨壓與電場明顯 增加，原先操作速度過慢的問題亦獲得了改善。 在實驗的最後一部分，為了減輕因C60 薄膜厚度縮減所帶來其內部殘存去極 化電場強度過大，而進一步造成元件retention 能力被大幅犧牲的問題，我們藉由共蒸鍍的方式在C60 薄膜中混入有機絕緣材料Poly(N-vinylcarbazole)來減低氧離子在薄膜中的移動能力，並成功地在元件既有特性變化不大的前提下，大幅地改善其retention 特性。

This thesis focuses on using C60 to replace polysilicon as floating gate and explores the properties and operating mechanisms of this organic nonvolatile memory. Before fabricating the devices, we first use TEM to examine the thickness and crystallinity of each film and employ EDS and ESCA to analyze their compositions.Then utilizing the verified deposition conditions followed with low temperature oxide and metal deposition, we successfully fabricate capacitors with C60 as the floating gate on silicon substrate. The device shows a memory window larger than 4 V and during the retention test, it still can retain a memory window as large as ΔVFB=3.038 V even after 10 years, which demonstrates the potential of C60 floating gate capacitor as a promising nonvolatile memory cell. Besides, in order to explain the clockwise C-V hysteresis, we first use Pt nanocrystal memory with same oxide stacking to verify the direction of charge injection. Combining the observed frequency dependent permittivity of C60, the oxygen ion diffusion model is proposed to explain the nonvolatile storage mechanism. In the section two, by scaling down the thickness of C60, we successfully observe the mechanisms of oxygen ion diffusion and charge injection existing simultaneously. Furthermore, owing to the increase of voltage drop and electric field in the C60 thin film, the operation speed is also improved. Finally, to reduce the degradation of retention caused by the enormous depoling filed in the scaled C60 thin film, we co-evaporate C60 with Poly(N-vinylcarbazole) to decrease the mobility of oxygen ions. By this way, we can keep the most memory characteristics nearly unchanged but successfully improve the retention property.