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Frontiers of Materials Science

ISSN 2095-025X

ISSN 2095-0268(Online)

CN 11-5985/TB

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Front. Mater. Sci.    2020, Vol. 14 Issue (1) : 89-95    https://doi.org/10.1007/s11706-020-0493-9
RSEARCH ARTICLE
Optimized optical design of thin-film transistor arrays for high transmittance and excellent chromaticity
Chengzhi LUO1,2, Shiyu LONG2, Guanghui LIU2, COOPER2, Min ZHANG1(), Fei AI2()
1. School of Electronic and Computer Engineering, Peking University, Shenzhen 518055, China
2. Wuhan China Star Optoelectronics Technology Co. Ltd., Wuhan 430078, China
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Abstract

Transmittance and chromaticity are essential requirements for optical performance of thin-film transistor (TFT) arrays. However, it is still a challenge to get high transmittance and excellent chromaticity at the same time. In this paper, optimized optical design by using antireflection film theory and optical phase modulation is demonstrated in low temperature poly-silicon (LTPS) TFT arrays. To realize high transmittance, the refractive index difference of adjacent films is modified by using silicon oxynitride (SiOxNy) with adjustable refractive index. To realize excellent chromaticity, the thicknesses of multilayer films are precisely regulated for antireflection of certain wavelength light. The results show that the transmittance and chromaticity have been improved by about 6% and 18‰, respectively, at the same time, which is a big step forward for high optical performance of TFT arrays. The device characteristics of the TFT arrays with the optimal design, such as threshold voltage and electron mobility, are comparable to those of conventional TFT arrays. The optimized optical design results in enhanced power-conversion efficiencies and perfects the multilayer film design on the basic theory, which has great practicability to be applied in TFT arrays.
Keywords TFT array      transparent dielectric material      chromaticity      antireflection film      optical phase modulation     
Corresponding Author(s): Min ZHANG,Fei AI   
Online First Date: 07 January 2020    Issue Date: 05 March 2020
 Cite this article:   
Chengzhi LUO,Shiyu LONG,Guanghui LIU, et al. Optimized optical design of thin-film transistor arrays for high transmittance and excellent chromaticity[J]. Front. Mater. Sci., 2020, 14(1): 89-95.
 URL:  
https://academic.hep.com.cn/foms/EN/10.1007/s11706-020-0493-9
https://academic.hep.com.cn/foms/EN/Y2020/V14/I1/89
Fig.1  (a) A schematic of the optical path of light passing through multilayer films. (b) Wavelength ranges of different color lights. Transmittance of the normal TFT array as a function of the thickness of (c) buffer SiNx and (d) buffer SiOx. Curves of different colors represent the transmittance of the corresponding color light.
Fig.2  Schematic of cross-sections of (a) the conventional LTPS-TFT array and (b) the optimized optical design for the LTPS-TFT array. It should be noted that the buffer layer SiNx was replaced by SiOx, and PV SiNx was replaced by SiOxNy.
Layer Film thickness/nm
Normal-TFT THK-TFT SiOxNy-TFT
Buffer layer SiNx 50 0 0
Buffer layer SiOx 250 300 300
Gate insulator SiOx 120 120 120
Dielectric interlayer SiNx 300 240 240
Dielectric interlayer SiOx 300 270 270
Organic layer 2500 1700 1700
ITO_Com 60 50 50
Passivtion layer 100a) 80a) 80b)
ITO_Top 50 50 50
Tab.1  Film thickness values of normal-TFT, THK-TFT and SiOxNy-TFT
Fig.3  Optical performances of normal-TFT, THK-TFT and SiOxNy-TFT: (a) transmittance spectra in the visible range; (b) the summary of average transmittance and chromaticity coordinates. Tr is transmittance; wx and wy are x/y values of whitespot color coordinates, respectively.
Fig.4  (a) Refractive index and extinction coefficient as functions of the gas flow ratio of n(NH3)/[n(N2O)+n(NH3)]for SiOxNy samples. (b) FTIR spectra of SiOxNy as function of refractive index indicated above each spectrum. The dotted lines indicate the position shift of the predominant absorption band from Si−O to Si−N vibration modes.
Fig.5  Average transmittance and chromaticity coordinates of TFT arrays using SiOxNy with different refractive indices as the PV layer.
Fig.6  SEM images of (a) normal-TFT and (b) SiOxNy-TFT.
Fig.7  Transfer characteristics of normal-TFT, THK-TFT and SiOxNy-TFT.
TFT array Vth/V Mobility/(cm2·V−1·s−1) Ion/A Ioff/A S-factor
Ave 3σ Ave 3σ Ave Ave Ave
Normal-TFT 1.05 1.11 119.23 22.56 4.81E−5 3.35E−13 0.22
THK-TFT 1.10 0.42 112.90 13.35 4.41E−5 1.83E−13 0.24
SiOxNy-TFT 1.07 0.45 115.69 12.96 4.52E−5 2.13E−13 0.23
Tab.2  Electrical properties of normal-TFT, THK-TFT and SiOxNy-TFT
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