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Development of Key Technologies in Fabrication of Flexible Display Devices
|關鍵字:||flexible thin-film transistors|
flexible light plate
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|摘要:||在本論文中我們針對開發軟性顯示技術的瓶頸,提出了三項關鍵製程的開發。第一部分在塑膠基材上沉積單層氮化矽阻障膜(barrier)及聚對二甲苯/氮化矽多層氣體阻障膜，分析其阻障特性並觀察撓曲測試後薄膜受破壞的狀況。實驗中的無機膜的破壞包含了裂痕(cracks channeling)和剝離(debonding)，利用電漿表面處理及聚對二甲苯的沉積來改善並抑制缺陷的產生，4 對聚對二甲苯 (600 nm)/氮化矽(100 nm) 沉積於PC後 經過三千次撓曲測試,其透水透氧特性仍然維持在機台量測的極限。第二部分在軟性薄膜電晶體製程上，以玻璃做為載板，沈積聚對二甲苯薄膜(parylene-C)於玻璃上，並在此基板上以標準的薄膜電晶體製程在250°C 溫度下製作氫化非晶矽薄膜電晶體，在製備聚對二甲苯基板上，發現可以藉由控制沉積速率及熱退火的方式，使得聚對二甲苯基板的透明性及操作溫度可以大幅提高。薄膜電晶體的特性不受聚對二甲苯薄膜基板從玻璃基板上剝離的影響，其在聚對二甲苯薄膜基板上之電晶體特性如下:開關電流比>105、臨限電壓：2.19 V、場效遷移率：0.246 cm2/V⋅s。
我們在第三部分，利用自我對準曝光技術及光阻做為電鍍模仁的方式,成功製備出超薄型光源及具電鍍銅散熱基座(heat spreader)之發光二極體。結合高反射率金屬電極將發光二極體陣列在以玻璃為承載基板的可撓性銦錫氧化物透明導電基板上，開發穩定且高壽命的固態光源。製程建立在薄膜技術以及現今半導體製程。在彎曲實驗中，測試不同彎曲半徑對光板的影響，並在撓曲半徑(1.5 cm)測試條件下，光板特性不變。另外，利用相同的製程我們在氮化鎵二極體背面電鍍出3 mm x 3 mm散熱銅基座，其表面為高反射鏡，此銅基座可以有效將整體發光二極體的熱導出，也因為熱量不在累積於內部於是提升了整體的發光效率及發光強度。量測後發現，藉由高反射鏡的散熱銅基座輔助散熱，其光輸出功率在1A下約為700 mW，與原始二極體提高約2.7倍強度。|
In this dissertation, some key technologies in fabrication of flexible display devices have been investigated. Several novel experiment design, material application and characterization of various flexible display devices have been attempted and developed. The first part of this study focused on the effect of single layer and multi-layer structure on high-performance barrier coating. It was found that the observed fracture of barrier was governed by two distinct crack patterns: cracks channeling in the coating and debonding between the coating and substrate. The plasma pretreatment and one specific polymer layer, i.e. parylene, were chosen to suppress the formation of SiNx cracks. The parylene/SiNx/PC structure is overwhelmingly superior barrier layer than the single thin brittle SiNx/PC film. Consequently, using the optimized SiNx and parylene, a multilayer composed by 4 pairs of parylene (600 nm)/SiNx(100 nm) was deposited on the PC substrate. After 3000-times cyclic bending, the water vapor and oxygen transmission rates the four pairs of parylene/SiNx coatings on PC can be maintained at a level near 0.01 g/m2/day and 0.1cc/m2/day, respectively. In the second part, the parylene-C material was introduced as a flexible substrate for amorphous Si thin-film transistors (TFTs) via a lifoff process, where a rigid glass substrate is provided for the parylene-C coating. The deposition rate of parylene-C can be controlled by the vaporization temperature and monomer partial pressure which can improve the optical performance and crystalline form of as-deposited parylene-C film. After annealed the parylene film, it can be processed at higher process temperature. The direct fabrication of a-Si TFTs on an engineered parylene substrate using a direct separation method without any adhesive was demonstrated. Parylene was used predominantly as the substrate of the TFTs. The engineered parylene can be peeled off from the glass carrier after forming the TFT structure. The transfer characteristics of these a-Si TFTs on a parylene substrate exhibited a field effect mobility of 0.246 cm2/V-s, on/off ratio (Ion/Ioff) >105(VDS=10 V), off current (Ioff) <10-10 A, and threshold voltage of 2.19 V. This method could be applied in the fabrication of the active-matrix backplane for flexible displays using the process temperature below 250C. In the third part, a combination of self-alignment and lift-off techniques was used to design and fabricate an ultrathin flexible light plate and high thermal dissipation blue light-emitting diode (LED) on sapphire. Almost the same process flow, we developed two different LED package forms using commercial LEDs. It was found that both the EL intensity and peak position of the flexible light plate were nearly the same after the cyclic bending test (r=1.5 cm). The blue LED chip array can be sandwiched by the ITO and Al electrodes with all the processing temperatures below 250C. In view of the flexible backlight applications, the ITO-coated transparent parylene template can be peeled off from the glass carrier, after forming the ultrathin LED light plat. Finally, according to the above methods, we have also demonstrated an enhanced performance of GaN/sapphire LED embedded in a reflective copper heat spreader. The cup-shaped LED heat sink with a base dimension of 3 mm x 3 mm is electroformed on sapphire directly using the spin-coated photoresist as a mold and coated with the Au/Cr/Ag mirror, which effectively enhances the heat dissipation down to the metal frame and reaps the light flux generated from the side emission. With the aid of a reflective heat spreader, the encapsulated LED sample driven at 1 A yields the light output power of 700 mW and an around 2.7-times increase in the wall-plug efficiency compared to that of the conventional GaN/sapphire LED. Infrared thermal images confirm the GaN/sapphire LED with more efficient heat extraction and better temperature uniformity. These results exhibit an alternative solution to thermal management of high-power LED-on-sapphire samples besides the laser lift-off technique. This method could be extended to improve the thermal and optical performance of yellow or red LEDs .
|Appears in Collections:||材料科學與工程學系|
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