Liquid Crystal Displays. Ernst Lueder

23.40 The mobilities μ_o before and μ_R after bending test of an OTFT with radius R < 10 mm. This figure was reproduced from Katsuhara, M. et al. (2014), Symp. Digest Tech. Papers, 45, pp. 716–719 with permission by The Society for Information DisplayFigure 23.41 The conventional five photolithographic steps for one pattern. This figure was reproduced from Kaelblein, D. et al. (2016), SID 47, p. 869 with permission by The Society for Information DisplayFigure 23.42 Photolithography with direct patterning of an organic semiconductor in two steps. This figure was reproduced from Kaelblein, D. et al. (2016), SID 47, p. 869 with permission by The Society for Information DisplayFigure 23.43 Transfer characteristics of 10 photopatterned organic transistors. This figure was reproduced from Kaelblein, D. et al. (2016), SID 47, p. 869 with permission by The Society for Information DisplayFigure 23.44 I_D = f(V_G) of an organic TFT with a mobility of 4 cm²/Vs. This figure was reproduced from Kaelblein, D. et al. (2016), SID 47, p. 869 with permission by The Society for Information DisplayFigure 23.45 The upper half of a liquid crystal cell with rotated molecules and vertical alignment.

      23 Chapter 24Figure 24.1 Comparison of schematic electrode structure and on-state molecular orientation showing differences between IPS and FFS devices. LC orientations at electrode positions a, b, c are quite different each other such that it has an optic axis at a but no optic axis at cFigure 24.2 Time-dependent transmittance curves in the FFS device when an operating voltage is applied for a LC with positive dielectric anisotropy. The LC switches at first at electrode position c by dielectric torque, giving rise to transmittance around region c only after relaxation of 5 ms and then switches at a (a′) by elastic torque sequentially, giving rise to transmittance even above region a after relaxation of 35 msFigure 24.3 Comparisons of calculated voltage-dependent transmittance curves (a) and electrodeposition dependent transmittance (b) between +LC and –LC in the FFS devices. Here the following cell and LC parameters are used for calculation: w = 3 μm, l = 4.5 μm, d = 3.5 μm, K_{11 =} 9.6 pN, K_{22 =} 5.3 pN, K_{33 =} 11.6 pN, = 84 m Pa s, Δε = 4 (–4) for +LC (–LC), Δn = 0.1028 at 550 nm, angle of initial LC director with respect to Ey ₌ 80° _{(10°) for +LC (–LC). The transmittance of two parallel polarizers is 36.5 percentFigure 24.4 Structure of 5CB (4-cyano-40-pentylbiphenyl), which shows typical nematic phase at room temperature. With random orientation of head to tail of LCs, there is no induced polarity in the liquid crystal director field. In a splay orientation with collective arrangement of head to tail of LCs, the polarization P is induced, which can couple with an applied electric fieldFigure 24.5 LC molecular orientation in a white state and its corresponding transmittance without (normal mode) and with (flexoelectric mode) Pf in IPS cell. In the normal mode, the transmittance does not occur above the centre of the electrodes. In the flexoelectric mode, Pf1 and Pf2 with mirror symmetry are formed along the field direction near the edges of electrodes. During the +frame, the coupling between E and Pf1 occurs in a constructive way while the coupling between E and Pf2 occurs in a destructive way so that transmittance above the signal electrode remains low but that above the common electrode becomes very high. During the –frame, the coupling is reversed and so is the transmittance behaviour. Here w = 5 μm, l = 5 μm, d = 4 μm, Δε = 6, an initial angle between LC director and Ey = 80°Figure 24.6 Experimental observation of flexoelectric effect in the IPS cell. (a) Schematics of the cell geometry (blue and red arrows represent the electric field vector). (b) Voltage-dependent transmittance curves as a function of driving frequencies with a square wave. (c) Local time-dependent transmittance on the indicated location by black arrows under the application of ~3.7 V (50 percent of the maximum transmittance). Insets: POM images with scale bar (10 μm) for positive (top) and negative (bottom) frames. (d) Local time-averaged transmittance after the curves saturated and its standard deviation with respect to the driving frequency f. Here, w = 5 μm, l = 5 μm, d = 5 μm, Δε = 4, an initial angle between LC director and Ey = 80°. This figure was reproduced from Kim et al. (2016), Sci. Rep., 6, pp. 35254, fig. 1 with permission by Springer NatureFigure 24.7 Simulation and experimental results showing typical spatial brightness appearance in the FFS mode without and with flexoelectric coefficients. Along fringe electric field lines, a splay deformation occurs, generating Pf1 and Pf2 each at both regions of pixel electrode edge (b and b′ in Figure 24.2). The simulation without eb and es (normal mode) shows relatively low transmittance above the centre of electrodes (a and a′) compared with that at the edge of the electrode (c), which exactly matches transmittance oscillation in experiments along the y-direction. The simulation with eb and es (flexoelectric mode) shows large transmittance change above the centre of the electrodes (A and B) such that during +frame, the transmittance at A (B) decreases (increases) compared with in the normal mode. During the –frame, the transmittance change is reversed, resulting in increased (decreased) transmittance at A (B). Experimental results of 1 Hz driving exhibit exactly the same behaviour with the simulation results. Here wp = 3 μm, l′ = 5 μm, d = 4 μm, thickness of insulator (h) = 0.4 μm, Δε = 3.8, an initial angle between LC director and Ey = 80°Figure 24.8 Microphotographs of pixels showing large flexoelectric effect with +LC (a, b) and minimized flexoelectric effect with –LC (c, d) in FFS TFT-LCDs with IGZO TFTs and (e) time-dependent luminance during frame change, showing larger fluctuation in +LC than in –LC. This figure was reproduced from Miyake et al. (2016), SID 47, pp. 592–595, fig. 3–5 with permission by The Society for Information DisplayFigure 24.9 Development history of IPS mode and IPS TFT-LCDs. The hatched arrows indicate mass production. This figure was reproduced from Kondo et al. (2005), SID 36, pp. 978–981, fig. 2 with permission by The Society for Information DisplayFigure 24.10 (a) Schematic pixel structure of U-FFS TFT-LCD. Microphotographs of pixel in TFTLCDs: (b, c) IPS (b) and IPS-Pro (FFS) (c) in a white state. This figure was reproduced from Lee et al. (2001), SID 32, pp. 484–487, fig. 6 and Ono et al. (2005), SID 36, pp. 1848–1851, fig. 1 with permission by The Society for Information DisplayFigure 24.11 Schematic comparison of cross-sectional pixel structures near data line and simulated transmittance between advanced FFS (AFFS) (a) and high-aperture-ratio FFS (HFFS) (b) modes. The insulating layers between pixel and common electrodes are inorganicFigure 24.12 Comparison of voltage-dependent transmittance curves in high-resolution mobile TFTLCDs. The high-aperture-ratio FFS (HFFS) mode shows the highest transmittance among all LC modes, and even much better than the advanced FFS (AFFS) mode, as also shown in the microscopic images of pixels. This figure was reproduced from Lim et al. (2006), IDW’06, pp. 807–808, fig. 2 and table 1 with permission by The Society for Information Display and website of HYDIS Co.Figure 24.13 Zigzag pixel TFT arrangement in IPS-Pro II. This figure was reproduced from Ono et al. (2007), IDW’07, pp. 67–70, fig. 1 with permission by The Society for Information DisplayFigure 24.14 History of IPS technology and comparison of cross-sectional pixel structures between IPS-Pro (a) and IPS-Pro Next (b). This figure was reproduced from Ono et al. (2012), IDW’12 in conjunction with Asia Display, pp. 933–936, table 1 and fig. 1 with permission by The Society for Information DisplayFigure 24.15 Front-view photographs of pixels in 47-inch LCDs in IPS-Pro and IPS-Pro-Next. This figure was reproduced from Ono et al. (2012), IDW’12 in conjunction with Asia Display, pp. 933–936, table 3 with permission by The Society for Information DisplayFigure 24.16 Microphotographs of pixels in iPad and mobile phones utilizing the FFS modeFigure 24.17 Timing chart for a refresh rate of 90 Hz LCD with 1700 scan lines (a) and 120 Hz LCD with 2432 scan lines (b). Here, the horizontal axis shows time, the vertical axis shows the panel position. This figure was reproduced from T. Matsushima et al. (2018), SID 49, pp. 667–670, fig. 6 with permission by The Society for Information DisplayFigure 24.18 Comparison}