軟性顯示器基板扭轉分析與彎曲之照度探討

Abstract

軟性電子元件為近年來電子科技的發展重心之一，其中最廣泛的應用為下一世代顯示器發展的主力「軟性顯示器」。相較於LCD (液晶顯示器)和LED (發光二極體)，軟性顯示器允許變形。基於可撓曲性是軟性顯示器的最大特徵，因此分析軟性顯示器在受到外加力矩作用時的變形有助於設計軟性顯示器。本研究首先探討軟性顯示器的扭轉行為。分別比較以線性和非線性彈性力學來分析當基板受四個角落作用力和扭矩的撓曲結果。結果顯示當撓曲量變大時，所需單位變形量的力或扭矩也增加。計算結果也顯示當顯示器基板的長宽比增加時，顯示器較容易扭曲。 在實驗上，透過電腦控制電動伺服馬達施與外加扭矩使顯示器產生扭轉，再通過光學編碼器的測量和理論演算求得扭轉角。實驗和理論分別比較各種不同尺寸的PET 和PEN基板，多層PET和多層PET鍍ITO的基板。另外，雷射測距儀和反射式條紋法搭配四步相位移技術分別被運用量測面外的變形與全域式量測去驗證理論模型。 在本文中，也推斷在不同的彎曲角度下針對各種不同尺寸軟性顯示器的照度分析。數值結果顯示最大總光照度取決於顯示器的尺寸大小和接收器位置。當接收器和顯示器之間的距離增加，總光照度在各種的彎曲角度之下的改變較緩慢，並且對於在彎曲下的總光照度分佈方形的顯示器比長方形較均勻。

Flexible electronic devices are under development in modern technology. One of applications is flexible displays, which can serve as next-generation monitors. In contrast to LCD (Liquid Crystal Display) and LED (Light Emitting Diode) displays, the flexible display allows deformation. Flexibility is one of remarkable characteristics of flexible displays. Therefore, the analysis of flexible displays deformation caused by external torques will help its design. This study aims to investigate the torsion behavior of flexible displays. Comparisons are made between deflection results of linear and nonlinear elasticity analyses for substrates subject to four-corner forces and torque, respectively. They show that when deflection becomes large, torques or forces needed for unit deformation also increase. Computational results also show that when the substrate aspect ratio of length/width in display sizes increases, displays are easier to deform under torsion.

In experiments, a servo motor under computer control exerts torque to generate display torsion, whose twist angles are obtained by using both optical encoder measurement and theoretical calculation. Comparisons are made between experimental and theoretical results for bare PEN (polyethylene naphthalate) and PET substrates of different sizes, multilayer PET (polyethylene terephthalate) substrates and ITO (indium tin oxide)-coated PET substrates. In addition, a laser displacement sensor and a fringe reflection method with four-step phase shifting technique are used to measure the out-of-plane deformation and full-field measurement for validating the proposed theoretical model, respectively.

In this work, an analytical derivation is also carried out for illuminance of flexible display of different sizes under various bending angles. Simulation results show that the maximum total illuminance depends on the display size and detector position. As the distance between the detector and display increases, the total illuminance changes slowly under various bending angles and the total illuminance distribution in bending deformation of a square display is more uniform than a rectangular one.