顏料分散彩色濾光片造成TFT-LCD對比度下降機制之討論

Abstract

目前要使TFT-LCD能夠生成彩色的主流方法為在LCD面板上建構顏料分散式彩色濾光片。文獻中的實驗結果顯示，將彩色濾光片置於兩穿透軸方向互相垂直的偏振片中時，兩偏振片會出現漏光的現象。我們認為此現象的成因乃是線性偏振光入射顏料分散式彩色濾光片後，被解偏而造成對比度下降所致。

文獻中的數據已證實此現象與顏料顆粒之大小有關。就我們所知，截至目前為止，並無任何文獻解釋造成此現象的物理機制。故我們假設了兩個光學模型，分別為等效波板（光學非等方向性，anisotropic）與米氏散射（光學等方向性，isotropic）模型，以便解釋此現象。

在等效波板模型中，我們利用瓊斯矩陣計算並得出顏料顆粒大小正比於解偏程度的結果，其與文獻上的結果相符。

然而在米氏散射模型中，我們還無法得到適當的數值結果來解釋文獻中的結果。

The most popular color generation of TFT-LCDs has been based on pigment dispersed (PD) color filters (CFs) built in the LCD panel to produce sub-pixel-red (R), -green (G), and –blue (B) colors from a backlight system attached onto the panel. Experimental results showed that, by placing such PDCF plate between cross polarizers, additional light leakage occurred due to the change of the linearly polarized input light into elliptically polarized output light. We call this effect as the depolarization-induced degradation of contrast ratio (DID-CR) due to the PDCF.

The DID-CR depends on the particle size of PDCF. So far, there have been no prior publications to explain the mechanism of DID-CR of the PDCF. In this thesis, we suggest two optical models: birefringent effect (BRE) and Mie scattering effect (MSE) caused by PDCF particles to explain the phenomenon of DID-CR.

In the BRE model, we use Jones matrix method to calculate the DID effect through a PDCF of fixed thickness but composed of multi-layer pigment-particles of different sizes. Using the BRE model, we have confirmed the occurrence of DID-CR that is proportional to the particle sizes within the PDCF plate consistent with published results.

In our MSE model, we have assumed that the PDCF particles are optically isotropic and the effect of DID-CR disappears for forward-scattered lights independent of particles sizes. For fixed particle size, the effect of DID-CR increases with increasing oblique-scattered angles and the scattered intensity within the same solid angle increases as the particle size decreases. The MSE model at this moment of development is unable to produce suitable numerical results to compare with the experimental results that the effect of DID-CR is more severe with larger particles and much reduced with smaller particles within the PDCF layer.