探討在自組層幫助下對五環素有機場效電晶體特性的改善

STUDIES ON THE IMPROVEMENT OF PENTACENE ORGANIC FIELD EFFECT TRANSISTOR WITH SELF-ASSEMBLED MONOLAYER

蔡宗翰(Tsung-Han Tsai)

指導教授 ： 郭欽湊

大同大學/工程學院/化學工程學系所/碩士(2005年)

摘要

本次研究是利用微影技術來製作場效電晶體 ( Field Effect Transistor, FET )，並將導電性寡聚分子五環素利用真空蒸鍍法沈積在SiO2絕緣層上，形成bottom-type FET來測定其電晶體特性，探討蒸鍍條件及絕緣層SiO2之表面處理等對電晶體特性的影響。
結果中發現以真空蒸鍍法沈積五環素薄膜時，場效位移率及開關電流比皆會受到基板溫度的影響，當基版溫度控制在70 ℃時，最佳場效位移率可達 5.33 × 10 - 3 cm 2/Vs (VDS = - 50 V)，而開關電流比為 6.73 × 10 1 (VDS = - 50 V)。
由於絕緣層SiO2之表面具有較大的表面極性且親水性（含－Si－OH），使得有機分子無法在SiO2表面上規則排列而影響元件特性，因此針對SiO2表面利用氧氣電漿處理及自組層表面處理劑處理進行對元件特性影響之探討。
適當的增加氧氣電漿處理時間（10 min）可提高場效位移率為原本的1.5倍可達8.37 × 10 - 3 cm 2/Vs (VDS = - 50 V)，而開關電流比提升1次方為2.89 × 10 2 (VDS = - 50 V)。而以自組層之表面處理劑以旋轉塗佈法處理過後，十八烷基三氯矽烷之最佳場效位移率可提高1次方達6.6 × 10 - 2 cm 2/Vs (VDS = - 50 V)，而開關電流比提高4次方為1.85 × 10 5 (VDS = - 50 V)、十六硫醇之最佳場效位移率可提高1次方達 2.25 × 10 - 2 cm 2/Vs (VDS = - 50 V)，而開關電流比提高3次方為6.63 × 10 4 (VDS = - 50 V)，而且次臨界斜率下降至2 ~ 3 V/decade；而以HMDS加熱蒸發處理有最佳場效位移率1.25 × 10 - 2 cm 2/Vs (VDS = - 50 V)，而開關電流比為4.58 × 10 4 (VDS = - 50 V)。經由處理劑對於SiO2絕緣層之表面處理成自組層幫助下場效位移率可提升1次方（6.6 × 10 - 2 cm 2/Vs at VDS = - 50 V），而開關電流比更可提升4次方（1.85 × 10 5 at VDS = - 50 V），足見經由自組層（SAM）幫助下，元件的功能可大幅改進。

關鍵字

場效電晶體 ； 五環素 ； 自組層

並列摘要

In this study, the field effect transistor (FET) is fabricated by photolithographic technique, and the material of conductive oligomer pentacene is deposited on dielectric layer of SiO2 by vacuum evaporation technique to form a bottom-type FET. The effects of the deposition condition and the surface treatment of SiO2 on the electric characteristics of FET have been investigated.
It is found that the field effect mobility and on-off current ratio of pentacene OFET depends on significantly the temperature of substrate. The optimal mobility and on-off current ratio are 5.33 × 10 - 3 cm 2/Vs and 6.73 × 10 1 at VDS = - 50 V, respectively, which pentacene thin-film deposited at substrate temperature of 70 ℃.
Because of the SiO2 surface exhibits polar and hydrophilic state (－Si－OH), the adhesion of organic materials deposited on SiO2 surface is bad. Hence, the thesis is focused on the influences of modified the surface of SiO2 with oxygen plasma and self-assembled monolayer (SAM) on electrical characteristics of pentacene FET.
The field effect mobility and on-off current are improved with oxygen plasma at 50 mTorr for 10 min. The mobility is increased by almost a factor of 1.5, from 5.33 × 10 - 3 to 8.37 × 10 - 3 cm 2/Vs and on-off current ratio raises one order of magnitude, from 6.73 × 10 1 to 2.89 × 10 2.
Similarly, the field effect mobility of pentacene FET increases one order of magnitude to reach 6.6 × 10 - 2 cm 2/Vs and 2.25 × 10 - 2 cm 2/Vs (VDS = - 50 V), and on-off current ratio increases three to four orders of magnitude to approach 1.85 × 10 5 and 6.63 × 10 4 (VDS = - 50 V) for modification the SiO2 surface with self-assembled monolayer－octadecyltrichlorosilane (OTS) and hexadecaenthiol in toluene, respectively. Furthermore, the subthreshold slope decreases dramatically to about 2 ~ 3 V/decade. On the other hand, the mobility and on-off current ratio (VDS = - 50 V) of pentacene OFET for modification SiO2 surface with HMDS SAM are 1.25 × 10 - 2 cm 2/Vs and 4.58 × 10 4, respectively. With SAM treatment on SiO2 surface, the performances of device are improved dramatically. The mobility and on-off current ratio are increased by one and four orders of magnitude, respectively.

並列關鍵字

field-effect transistor ； pentacene ； self-assembled monolayer

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