應用微接觸轉印技術於有機薄膜電晶體製作

Application of micro transfer stamping technique on the fabrication of organic thin-film transistor

何慧文(Huei-Wun He)

指導教授 ： 楊申語

國立臺灣大學/工學院/機械工程學研究所/碩士(2010年)

https://doi.org/10.6342/NTU.2010.00158

摘要

軟性電子元件具有可撓性、輕薄短小且易於攜帶，其製造需以有機薄膜電晶體作為顯示器開關，如何將其製作在塑膠薄膜基材上是一大挑戰。微轉印製程簡單、快速且無須昂貴設備，可直接製作無殘留層之微結構。本論文建立微轉印製程技術應用於有機薄膜電晶體製程，包括：一、轉印模具的製作；二、微轉印製程的開發；三、有機薄膜電晶體的製程。
首先轉印模具製作方面，本研究以乾膜光阻搭配塑膠基材定義圖案來製作梳狀微結構母模，再利用PDMS翻鑄技術製作軟模，可完整複製母模微結構，且軟模頂部平整。
接著微結構轉印製程開發部分，首先探討材料表面能的影響與控制機制，再以光學顯微鏡觀察PDMS軟模實際受力變形的狀態。利用微結構轉印製程轉印導電銀膠，以不同的製程參數如轉印壓力、溫度和時間等來控制轉印結果。實驗結果發現：以低溫轉印時，銀膠未能受到足夠加溫而過濕；若加熱溫度過高時，銀膠溶劑揮發太快，銀膠附著於PDMS 上無法轉印。壓力過低則PDMS 無法均勻接觸於基材，壓力過大則會造成模具變形過大，輪廓破碎。轉印時間過短，則未接觸完全；但若過久，銀膠附著於PDMS上，導致轉印失敗。本研究找出適當的製程組合，將銀膠梳狀電極成功轉印至PMMA基材上，且無殘留層。
最後，關於有機薄膜電晶體製程方面，先以旋塗方式製作PMMA介電層，同時探討在不同製程參數下介電層的電容品質與漏電流等特性，接著在介電層上應用微轉印技術直接轉印銀膠製作源極/汲極，驗證可成功轉印微結構電極；最後以液滴塗佈P3HT半導體材料，完成全套有機薄膜電晶體製程。

關鍵字

微轉印技術 ； 銀膠 ； PMMA ； P3HT ； 有機薄膜電晶體

並列摘要

Soft electronics devices based on organic thin-film transistors (OTFTs) possess a lot of advantages, such as flexibility, light weight and portability. The key to fabricate organic thin-film transistors on plastic substrate is one of the biggest challenges. Micro-transfer stamping technique is a simple and low-cost process to directly fabricate microstructure without residual layer. This study develops the micro-transfer stamping technique for the fabrication of OTFTs, including: 1. Investigation and fabrication of stamping mold; 2. Development of micro-transfer stamping process; 3. Implementation of complete process for fabrication of organic thin-film transistors.
First, in the topic of “Investigation and fabrication of stamp mold”, we used dry-film photoresist to rapidly define the interdigitated micro-patterns on the PET substrates, and after developing, the microstructured dry-film photoresist was used as the master mold for casting PDMS mold. The PDMS mold has faithful duplication of micro-patterns in the master mold with smooth bottom surface.
Second, in the topic of “Development of micro-transfer stamping process”, we investigated the effect of surface energy of materials and developed mechanism for effective stamping. The real deformation of PDMS mold was observed using optical microscopy. We demonstrated the micro-transfer stamping technique can be used to transfer conductive silver paste on PMMA substrate, and with different process conditions (pressure, temperature and transfer time), the stamping results can be obtained. It was found that: Under low temperature, the silver paste cannot be adequately heated and the viscosity is too low; but if the temperature is too high, the solvent will quickly evaporate causing the silver paste adhere to PDMS mold. Too low pressure fails to ensure the PDMS in uniform contact with the substrate, while excessive pressure will lead to severe deformation of PDMS mold, crumbling the contour of silver paste. PDMS will fail to be in complete contact with the substrate if the transfer time is too short; on the other hand, if the duration is too long, the silver paste will attach to PDMS mold causing the transfer failure. Under proper process parameters, we have succeeded in directly patterning the interdigitated electrode of silver paste without residual layer.
In the last topic of “Fabrication of organic thin-film transistors (OTFTs)”, the PMMA was spin coated for the dielectric layer on the ITO/PET flexible film that serve as gate/substrate, and the characteristics of dielectric such as capacitance and leakage under various conditions were discussed. We also proved that the stamping technique can apply to directly transferring source/drain structure of OTFTs. The P3HT semiconductive layer was then coated on source/drain electrode by drop casting to complete the fabrication of OTFTs.

並列關鍵字

soft electronics ； micro-transfer stamping ； silver paste ； PMMA ； P3HT ； OTFTs

參考文獻

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