Mini-LEDs with Diffuse Reflection Cavity Arrays and Quantum Dot Film for Thin, Large-Area, High-Luminance Flat Light Source
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nanomaterials Article Mini-LEDs with Diffuse Reflection Cavity Arrays and Quantum Dot Film for Thin, Large-Area, High-Luminance Flat Light Source Zhi Ting Ye 1, * , Yuan Heng Cheng 1 , Ku Huan Liu 2 and Kai Shiang Yang 2 1 Department of Mechanical Engineering, Advanced Institute of Manufacturing with High-Tech Innovations, National Chung Cheng University, No. 168 University Road, Minxiong Township, Chiayi County 621301, Taiwan; g09421023@ccu.edu.tw 2 EPOCH CHEMTRONICS Corp, Hsinchu County 302006, Taiwan; GuuhuannLiu@epoch-optic.com (K.H.L.); t102568060@ntut.org.tw (K.S.Y.) * Correspondence: imezty@ccu.edu.tw Abstract: Mini-light-emitting diodes (mini-LEDs) were combined with multiple three-dimensional (3D) diffuse reflection cavity arrays (DRCAs) to produce thin, large-area, high-brightness, flat light source modules. The curvature of the 3D free-form DRCA was optimized to control its light path; this increased the distance between light sources and reduced the number of light sources used. Experiments with a 12.3-inch prototype indicated that 216 mini-LEDs were required for a 6 mm optical mixing distance to achieve a thin, large-area surface with high brightness, uniformity, and color saturation of 23,044 cd/m2 , 90.13%, and 119.2, respectively. This module can serve as the local dimming backlight in next generation automotive displays. Citation: Ye, Z.T.; Cheng, Y.H.; Liu, K.H.; Yang, K.S. Mini-LEDs with Keywords: mini-light-emitting diode; uniformity; luminance; diffuse reflection cavity array; quantum Diffuse Reflection Cavity Arrays and dot film Quantum Dot Film for Thin, Large-Area, High-Luminance Flat Light Source. Nanomaterials 2021, 11, 2395. https://doi.org/10.3390/ 1. Introduction nano11092395 Display technology has developed rapidly, starting in the second half of the 20th century, and various types of displays have become ubiquitous in daily life. For exam- Academic Editors: Iván Mora-Seró and Jong-Soo Lee ple, light-emitting diodes (LEDs) have replaced conventional cathode-ray tubes. LEDs afford advantages such as higher color performance, low energy consumption, and eco- Received: 29 July 2021 friendliness, and therefore, they are the principal backlight source of liquid crystal displays Accepted: 13 September 2021 (LCDs) [1–4]. However, because of the demand for high resolution, high color saturation, Published: 14 September 2021 and pixel quality, technologies including organic LEDs (OLEDs), mini-LEDs, micro-LEDs, quantum dot LEDs (QD-LEDs), laser displays, and holographic displays have been de- Publisher’s Note: MDPI stays neutral veloped to replace LCDs. Nevertheless, LCDs remain the standard in the market and are with regard to jurisdictional claims in widely used in smartphones, tablet computers, televisions, and other display devices [5–8]. published maps and institutional affil- As mentioned, LED light sources are used as LCD backlight sources. According to the iations. position of the light source, they are divided into direct-type and side-type backlight mod- ules. Direct-type backlights have lower cost, higher optical efficiency, and straightforward design compared with side-type backlights, and therefore, they have become dominant in the large-sized LCD backlight module market [9–11]. Although LCDs feature advantages Copyright: © 2021 by the authors. such as low power consumption, long service life, and low cost, their slow response time, Licensee MDPI, Basel, Switzerland. low color saturation, and low photoelectric conversion efficiency (typically
Nanomaterials 2021, 11, 2395 2 of 12 phosphor β-SiAlON and red phosphor K2 SiF6 are commonly used as a high color gamut space backlight [16–18]. Quantum dots (QDs) are a new color conversion material that have a narrower full width at half-maximum (FWHM); therefore, they have a wider color gamut and higher quantum efficiency. As a result, novel QD-LEDs are gradually being applied to LCD backlight modules [19–22]. In addition, there are many studies that provide related synthesis protocols of quantum dots [23,24]. The strong demand for high-end displays such as gaming monitors, car monitors, and notebook computers has driven an increased demand for high dynamic area contrast backlights (i.e., high dynamic range [HDR]). Conventional LCD edge-lit backlights are only distributed on the light guide plate. Whether single- or double-sided, this architecture allows limited contrast control. Mini-LEDs, because of their smaller size and high current density injection drive, can achieve high-contrast HDR and high brightness. Mini-LEDs are thus considered a promising backlight source for next-generation high-end LCDs [25–27]. Mini-LEDs have a smaller package size than conventional LEDs. The light-emitting angle is limited to approximately 120◦ ; therefore, more LEDs are required to achieve a uniform surface light source. Furthermore, the light line is not adjusted for HDR backlights, resulting in a halo. This problem causes the contrast to decrease, and the smaller area of the light source body causes the problem of heat source concentration [28–31]. Although the thickness of the backlight module can be reduced and the uniformity can be improved by increasing the number of mini-LEDs, this method is not the preferred design. Researchers have optimized the light output angle to reduce the total number of particles in the light source by adjusting the optical design [32,33]. For example, Ye et al. proposed a hollow tube structure containing mini-LEDs with asymmetrical luminous intensity and designed a beveled reflective surface on the side of the mini-LEDs to achieve high efficiency and high uniformity. Moreover, they proposed a flat light source module without a light guide plate with a dot pattern and a completely printed diffuse reflection light guide plate on the bottom surface of the light source module to achieve high efficiency and high uniformity [34,35]. Ohno proposed an LED lighting module with a coaxial light conductor to achieve high efficiency and high wide-angle performance [36]. Lu et al. proposed a transparent array of mini-LEDs on a polyethylene terephthalate (PET) substrate. They found that, at room temperature, the mini-LEDs exhibited high uniformity and wideness and stable color gamut performance. Lin et al. proposed a direct-illuminated LED free-form lens array with a Cartesian candela distribution. Through the incorporation of free lenses and diffusers, the LED lens array was optimized to improve uniformity. Zhu et al. proposed a free-form surface design method for LEDs to achieve diffusion and transmission. This lighting system affords advantages such as high efficiency and high uniformity [37–39]. Huang et al. proposed a chip-level package with a free-form package design that has ultrahigh light extraction efficiency and a batwing-shaped light field to provide a thin, high- wide-angle and low-profile package for reducing the number of LEDs. Li et al. proposed a two-layer encapsulation structure that combines SiO2 and graphite nanoparticles to improve the uniformity and environmental contrast. Chen et al. proposed a direct lighting mini-chip-level packaged LED that combines a QD film with a diffuser and prism films to improve the brightness and uniformity and to reduce the number of LEDs used [40–42]. Park et al. proposed a flip-chip package and a vertical chip package structure for InGaN/GaN stripe LEDs to achieve higher uniformity and to improve the light extraction efficiency. Tang et al. proposed the use of tetramethylammonium hydroxide to construct a layered structure on the sidewall of mini-LEDs by anisotropic etching to improve the light extraction efficiency of the mini-LEDs [43,44]. Zhu et al. proposed double freeform surface lens with diffuse reflection applied in non-imaging optical systems [45]. Zhu et al. proposed diffuse reflective Off-Axis surface for noncircular LED arrays [46]. Although these two designs can achieve large-area light sources, they cannot achieve a thin, high-luminance, flat light source. Sho et al. proposed a
Zhu et al. proposed double freeform surface lens with diffuse reflection applied in non-imaging optical systems [45]. Zhu et al. proposed diffuse reflective Off-Axis surface Nanomaterials 2021, 11, 2395 for noncircular LED arrays [46]. Although these two designs can achieve large-area 3light of 12 sources, they cannot achieve a thin, high-luminance, flat light source. Sho et al. proposed a thin mini-LEDs backlight using reflective mirror dots to obtain high luminance uni- formity for mobile thin mini-LEDs LCDs [47]. backlight using reflective mirror dots to obtain high luminance uniformity In summary, for mobile LCDs [47]. related studies have attempted to improve the light output efficiency, uniformity, In summary, related studiesof and color saturation planar have light sources. attempted However, to improve the output the light use of large-area efficiency, planar light sources uniformity, and color to saturation reduce the ofnumber planaroflight LEDs used requires sources. However, further study. the use of large-area planarThis study light proposes sources mini-LEDs to reduce combined the number withused of LEDs multiple three-dimensional requires further study. (3D) dif- fuse reflection cavity arrays (DRCAs) to achieve a thin, large-area, This study proposes mini-LEDs combined with multiple three-dimensional and high-luminance (3D) dif- planar light source. fuse reflection cavity arrays (DRCAs) to achieve a thin, large-area, and high-luminance planar light source. 2. Materials and Method 2. Materials 2.1. Simulation and Method of Optical Module and Light Film Material Selection for Mini-LEDs 2.1. Simulation of Optical Module and Light Film Material Selection for Mini-LEDs Soliwork3D drawing software and Light Tools optical simulation software were used Soliwork3D to construct drawing the optical software system and Lightthe and optimize Tools optical diffuse simulation reflection software cavity module.wereTheused op- to construct the optical system and optimize the diffuse reflection cavity tical components include multiple 3D DRCAs, diffusers, QD films, and a brightness en- module. The optical components hancement film (BEF). include multipleof3D The influence DRCAs,and brightness diffusers, QD films, uniformity and a brightness was analyzed. Figure 1 enhancement film (BEF). The influence of brightness and uniformity was presents a schematic of the structure of the mini-LEDs combined with the 3D DRCA. analyzed. Figure 1 presents a schematic of the structure of the mini-LEDs combined with the 3D DRCA. BEF1 BEF2 QD film Diffusion plate DCRA Mini LED MCPCB Figure 1. Figure Schematic of 1. Schematic of the the structure structure of of mini-LEDs mini-LEDs combined with 3D DRCA. The light Nanomaterials 2021, 11, x FOR PEER REVIEWThe light source source uses uses Epistar Epistar YR-CV1010BDAN YR-CV1010BDAN mini-LEDs. mini-LEDs. The The package packagelength length4Lof 13 ,, LPKG PKG package width package width W PKG, ,package WPKG package height height H HPKG, ,chip PKG chipPAD PAD length length L LPAD PAD, ,and andchip chip PAD PAD width width WPAD W are11mm, PADare mm,11mm,mm,0.40.4m, m,0.903 0.903mm, mm,and and0.328 0.328mm, mm,respectively, respectively, and and Figure Figure 22 displays displays the package the package size size of of the the mini-LEDs. mini-LEDs. (a) (b) LPKG LPAD WPKG WPAD (c) HPKG H Figure 2. Structure of mini-LEDs. (a) top view, (b) bottom view, and (c) side view. Figure 2. Structure of mini-LEDs. (a) top view, (b) bottom view, and (c) side view. Figure 3 illustrates the light distribution curve of the mini-LEDs. The half-intensity angle FWHM is 160°, and the 0° angle intensity at the center is approximately 90%.
HPKG H Nanomaterials 2021, 11, 2395 4 of 12 Figure 2. Structure of mini-LEDs. (a) top view, (b) bottom view, and (c) side view. Figure Figure 33 illustrates illustrates the the light light distribution distribution curve curve of of the the mini-LEDs. mini-LEDs. The The half-intensity half-intensity angle angle FWHM is 160 , and the 0 angle intensity at the center is approximately 90%. FWHM is 160°, ◦ and the 0°◦ angle intensity at the center is approximately 90%. Figure3. Figure Mini-LEDchip 3.Mini-LED chiplight lightdistribution distributioncurve. curve. 2.2. Model 2.2. ModelConstruction ConstructionofofDRCA DRCA ABezier A Beziercurve curve (B) (B)was wasused usedto toanalyze analyzethe theoptimal optimal curvature curvature for for the the DRCA, DRCA, as as given given by Equation (1). by Equation (1). B( ( ) (1(1 t) = = −−t)3 ) P3a + +3(3(1 1−− t)2 ) + 3+(13(1 tP2b )t2 ) − t− Pc2+ 3 3 t+P d , t ,∈t ∈[0, [0,11] ] (1) (1) where where the the four four points points P Paa,, PPbb, ,PPc,c ,and andPPd ddefine defineaacubic cubicBezier Beziercurve curveininaaplane plane oror in in aa 3D 3D space. The curve goes from P a to Pb in the direction from Pc to Pd. Generally, it does not space. The curve goes from Pa to Pb in the direction from Pc to Pd . Generally, it does pass not passthrough Pb orPPcor through ; these Pc ; these two two points provide points direction provide information. direction The The information. distance be- distance b tween Pa and Pb determines the length of the curve in the direction of Pb before turning to between Pa and Pb determines the length of the curve in the direction of Pb before turning Ptoc. Pc . The The equation equationof of the the Bezier Bezier curve curve is is aa continuous continuous function; function; therefore, therefore, its its derivative derivative isis obtained as follows: obtained as follows: 0 (t) ==3tC B ′( ) 1 ++2tC 3 2 2 ++C 3 (2) (2) 1 2 3 C , C , and C are coefficients that are given as follows: 1, 2, and 3 are coefficients that are given as follows: 1 Nanomaterials 2021, 11, x FOR PEER REVIEW 2 3 5 of 13 C1 = (− Pa + 3Pb − 3Pc + Pd ), C2 = (3Pa − 6Pb + 3Pc ), and C3 = (−3Pa + 3Pb D ) = Pa (3) 1 = (− + 3 − 3 + ), 2 = (3 − 6 + 3 ), and 3 = (−3 + 3 )= (3) The light field shape of the mini-LEDs was used to simulate the diffuse reflection The light field shape of the mini-LEDs was used to simulate the diffuse reflection cavity, and the light was evenly distributed to the diffuser through an optimized design, thereby cavity, evenly and expanding the light thedistributed was evenly projectiontoarea the of the light diffuser source. through Figure 4 presents an optimized design, a sche- thereby evenly expanding the projection area of the light source. Figure 4 presents a matic of the light trace. schematic of the light trace. 4. Schematic Figure 4. Figure Schematicofof diffuse reflection diffuse cavity reflection lightlight cavity trace.trace. The The parameters parametersofof thethe diffuse reflection diffuse cavity reflection were were cavity set to set the to Lambertian diffuse diffuse the Lambertian surface characteristics: the diffuse reflectance was 94%, QD film was set to the Lambertian surface characteristics: the diffuse reflectance was 94%, QD film was set to the Lambertian diffuse transmittance of 50%, reflectance was 50%, refractive index of the BEF was 1.56, and diffuse transmittance of 50%, reflectance was 50%, refractive index of the BEF was 1.56, and apex angle was 90°. The surface of the metal core printed circuit board (MCPCB) was set to the Lambertian diffuse surface reflectance of 90%, center wavelength of the light source was 450 nm, input power was normalized as 1 W, and number of rays was 50 mil- lion for simulation. Table 1 lists the parameter settings.
Nanomaterials 2021, 11, 2395 5 of 12 apex angle was 90◦ . The surface of the metal core printed circuit board (MCPCB) was set to the Lambertian diffuse surface reflectance of 90%, center wavelength of the light source was 450 nm, input power was normalized as 1 W, and number of rays was 50 million for simulation. Table 1 lists the parameter settings. Table 1. Simulation parameter settings. The refractive index = 1.56, BEF1 the apex angle = 90 degrees The refractive index = 1.56, BEF2 the apex angle = 90 degrees Lambertian diffusion surface characteristics, diffuse reflection cavity array, DRCA Reflectance 94% Lambertian diffusion surface characteristics, QD film 50% transmittance and 50% reflectivity Lambertian diffusion surface characteristics, MCPCB Reflectance 90% Input light 1 W Light source Center wavelength 450 nm 50 million rays LDRCA , WDRCA , and HDRCA of the simulated diffuse reflection cavity matrix module were 48.8, 48.72, and 4.57 mm, respectively. Furthermore, the mini-LED spacing mini- LEDsp was 12 mm, optical mixing distance between the mini-LEDs and the diffuser was Nanomaterials 2021, 11, x FOR PEER REVIEW 6 of 13 6 mm, and the simulation of the design optimization was based on a 4 × 4 diffuse reflection cavity matrix. Figure 5 illustrates the 3D structure of the module. LDRCA Diffusion plate WDRCA Mini LEDsP HDRCA OD (a) (b) Figure Figure 5. Schematic 5. Schematic of the of the 3D3D structure structure ofof the the 4×44 4 diffuse ×diffuse reflectioncavity reflection cavitymatrix matrix modules. modules. (a) (a) top topview viewand and(b) (b)side sideview. view. 2.3. Fabrication of QD Film 2.3. Fabrication of QD Film Common QD film materials, such as green QDs (λg: ~530 nm) and red QDs (λg: ~626 nm) Common QD film materials, such as green QDs (λg: ~530 nm) and red QDs (λg: ~626 (both from Unique Materials Co. Ltd., Taichung city, Taiwan), were used. The quantum nm) (both dots usedfrom Unique in this articleMaterials are red andCo.green Ltd.,CdSe/ZnS. Taichung city, 407001, size The particle Taiwan), rangeswere used. of green The and quantum red quantum dots are 2.5–2.8 nm and 4.4–4.6 nm, respectively. The main reaction materialsof dots used in this article are red and green CdSe/ZnS. The particle size ranges green and red quantum are cadmium dots are oxide (CdO), zinc2.5–2.8 nm andsilicon oxide (ZnO), 4.4–4.6 nm, (Se) respectively. and The main Trioctylphosphine reac- oxide tion materials are cadmium oxide (CdO), zinc oxide (ZnO), silicon (TOPO), lauric acid (C12 H24 O2 ), and n-hexane (C6 H14 ) material match reaction. Hexadecyl (Se) and amine (HDA) was used to prevent the agglomeration reaction of QDs; methanol (CH3 OH) Trioctylphosphine oxide (TOPO), lauric acid (C 12H 24O 2 ), and n-hexane (C 6 H 14) material was used match to avoid reaction. agglomeration Hexadecyl amine reaction, (HDA) was and used argonto(Ar) was used prevent the throughout agglomeration the process reaction of to ensure QDs; inert atmosphere methanol (CH3OH) while growing was used the QDs. to avoid agglomeration reaction, and argon (Ar) was used Thethroughout produced QDs were cured the process in Poly(methyl to ensure methacrylate) inert atmosphere while (PMMA); growing the the QDs. weight ratio of quantum dots and PMMA glue is 20:1, and the weight The produced QDs were cured in Poly(methyl methacrylate) (PMMA); the weight percent concentration is 5 wt.%. The volume ratio of the red quantum-dots (QDs) and green ratio of quantum dots and PMMA glue is 20:1, and the weight percent concentration is 5QDs is 1:50. wt.%. The volume ratio of the red quantum-dots (QDs) and green QDs is 1:50. The QD-PMMA layer was coated between two PETS film layers. Subsequently, the PET/QD-PMMA/PET film was laminated and cured using 365 nm ultraviolet radiation. Finally, a light diffusion layer was coated on the PET/QD-PMMA/PET film with a doctor
of QDs; methanol (CH3OH) was used to avoid agglomeration reaction, and argon (Ar) was used throughout the process to ensure inert atmosphere while growing the QDs. The produced QDs were cured in Poly(methyl methacrylate) (PMMA); the weight ratio 2021, Nanomaterials of quantum 11, 2395 dots and PMMA glue is 20:1, and the weight percent concentration is 5 6 of 12 wt.%. The volume ratio of the red quantum-dots (QDs) and green QDs is 1:50. The QD-PMMA layer was coated between two PETS film layers. Subsequently, the PET/QD-PMMA/PET film ThewasQD-PMMA laminatedlayerand was coated cured between using 365two nm PETSultraviolet film layers. radiation. Subsequently, the PET/QD-PMMA/PET film was laminated and cured using Finally, a light diffusion layer was coated on the PET/QD-PMMA/PET film with a doctor 365 nm ultraviolet radiation. Finally, a light diffusion layer was coated on the PET/QD-PMMA/PET film with a doctor blade coater. Figure blade 6 displays the structure. coater. Figure 6 displays the structure. Optical diffusion layer PET substrate layer QD-PMMA layer PET substrate layer Optical diffusion (a) layer (b) Figure 6.Figure 6. Structure Structure of QD of color QD color conversionfilm. conversion film. (a) (a)Various Variouslayers in structure layers and (b)and in structure actual (b)sample. actual sam- ple. 2.4. Simulation and Optimization of DRCA Structure Figure 7 presents the simulation result. First, a simulation was performed to optimize 2.4. Simulation and Optimization of DRCA the diffuse reflection Structure cavity matrix. Subsequently, the diffuser and BEF were added in 1, x FOR PEER REVIEW 7 of 13 sequence, and their influence Figure 7 presents the simulation result. First, on thea uniformity simulation of was the light was analyzed. performed The uniformity to optimize was calculated as Min-luminance/Max-luminance × 100%. Figure 7a reveals the optimized the diffuse reflectiondiffuse cavity matrix. Subsequently, the diffuser and BEF were added in reflection cavity matrix. The mini-LED point light source was converted into a sequence, and their influence on athe character with uniformity wider light outputofarea theand light was analyzed. uniformity The of 72.5%. As uniformity indicated in Figure 7b, expand the projection area and improve the uniformity the diffuse reflection cavity matrix was was calculated as Min-luminance/Max-luminance to projected × 100%. 85.73%. onto 7a Figure Figure an added reveals 7c diffuser shows the to further expand the optimized addition diffuse of the first reflection piece the cavity of thearea projection matrix. BEF. The andThe mini-LEDsimulation improve the results uniformity point light toindicated 85.73%. source was that Figure 7cadjusting converted the the showsinto addition a angle of light helped of improve the first piece the of the BEF. Thetosimulation uniformity 88.99%. results indicated Finally, Figure that 7d adjusting shows thead- the angle of character with a wider light output area and uniformity of 72.5%. As indicated in Figure dition of the first light helped two pieces improve of BEFtheto uniformity adjust to 88.99%. the Finally, Figure concentrated 7dangle light shows the addition again andof the 7b, the diffuse reflection cavity first two piecesmatrix of BEF towas projected adjust onto an the concentrated added light diffuser angle again to further and achieve uniformity achieve uniformity of 90.16%. of 90.16%. Um: 72.5% Um: 85.73% Um: 88.99% Um: 90.16% (a) (b) (c) (d) Figure Figure 7. Simulation and optimization 7. Simulation results of mini-LEDs and optimization results ofcombined mini-LEDs withcombined the diffuse reflection with thecavity matrix. diffuse (a) Mini- reflection LEDs combined with diffuse reflection cavity matrix, (b) additional diffuser, (c) additional diffuser cavity matrix. (a) Mini-LEDs combined with diffuse reflection cavity matrix, (b) additional diffuser, and first BEF, and (d)(c) additional diffuser and second BEF. additional diffuser and first BEF, and (d) additional diffuser and second BEF. 3. Results and Discussion 3. Results and Discussion Figure 8 presents the front and back of the actual sample of the 9 × 8 DRCA. The square Figure 8 presents thetransparent front and part in theoffigure back the is the diffuse actual reflection sample of thecavity, 9 × and the gray The 8 DRCA. and black points in the center of the square are mini-LEDs. square transparent part in the figure is the diffuse reflection cavity, and the gray and black points in the center of the square are mini-LEDs.
square transparent part in the figure 3. Results is the diffuse reflection cavity, and the gray and black and Discussion points in the center of3.the square areDiscussion Results mini-LEDs. Figure and8 presents the front and back of the actual sample of the 9 × 8 Nanomaterials 2021, 11, 2395 squareFigure 8 presents transparent part the front in the andisback figure of the actual the diffuse sample reflection of the cavity, 7 of912the and × 8 gD Nanomaterials 2021, 11, 2395 square 7 of 12 points intransparent part the center of the insquare the figure areismini-LEDs. the diffuse reflection cavity, and the gray points in the center of the square are mini-LEDs. (a) (b) Figure 8. Actual sample of 9 × 8 DRCA. (a) Front view and (b) back view of the diffuse reflection cavity. (a) (b) (a) (b) Actual Figure 8.8. sample of 9 × 8of DRCA. 99 ×× 88(a) Front view and (b) back view of the diffuse reflection cavity. Figure 9 depictsFigure Actual Actual Figureactual the Figure 8.8. sample sample sample Actual of 9of sample × 8ofDRCA. the DRCA. (a) 12.3-inch DRCA. (a)and Front view Front thin, (a) (b) Front view back view large-area, view and and (b) of the (b) back diffuse back view reflection high-brightness view of the ofcavity. the diffu diffuse cavity. Figure 9 9depicts depictsthe theactual sample of the 12.3-inch thin,The large-area, high-brightness flatflat cavity. flat light source module. ItFigure comprises three groups actual sampleof of 9 ×12.3-inch the 8 DRCAs.thin, length, large-area, width, and high-brightness light source light292.8, module. source121,module. It comprises three groups of 9 × 8 DRCAs. The length, width, and height of the module are andIt 4.57 comprises mm,three groups of 9 ×the respectively; 8 DRCAs. opticalThe length, distance mixing width, and height height ofofthe Figure themodule Figure module are 99depictsare292.8, depicts the121, the 292.8, 121, and and 4.57 actual actual 4.57 mm, respectively; sample mm, sample respectively; of the of theoptical the12.3-inch 12.3-inch the optical mixing thin, distancehigh- large-area, mixing thin, distance large-area, hig is 6 mm, number of mini-LEDs is 6 mm, is 6light mm, number is 216, of and mini-LEDs dynamic is 216, designable and dynamic area comprises designable area 216 comprises zones. 216 zones. flat flat lightnumber source source ofmodule. mini-LEDsIt module. Itiscomprises 216, and dynamic comprises three threedesignable groupsof groups area of99comprises ××88DRCAs. 216 zones. DRCAs. The The lengt length, height heightofofthe themodule moduleare are 292.8, 292.8, 121, and and 4.57 4.57mm,mm,respectively; respectively;the theoptical optical mi mixin isis6 6mm,mm,numbernumberof ofmini-LEDs mini-LEDs is 216, 216, and anddynamic dynamicdesignable designablearea area compris comprises RFOR PEER REVIEW PEER REVIEW 8 of 8 of 1313 (a) (b) Figure Figure Figure Actual 9.9. Figure sample Actual 9.Actual Figure 10 sample 10showsof of sample showsa 12.3-inch athe of thin 12.3-inch thinblue a actual the 12.3-inch actual bluelarge-area large-area sample thin sample high-brightness high-brightness diagram blue large-area diagram of the light flat light sourcemodule. source 12.3-inch high-brightness 12.3-inch module. flat(a)(a) white white mini-LEDs mini-LEDs light light light combined combined thin source thin large- mod- large- with DRCA with andand DRCA (b)(b) mini-LEDs mini-LEDs combined combinedwith withDRCA DRCAandand diffuser. (a)diffuser. (b) ule. area (a) area mini-LEDs high-brightness high-brightness combined flat withsource flatlight light DRCA and sourcemodule. (b) mini-LEDs module. (a) Figure Figure 10a combined 10a showsthe shows with DRCA thelight light and module source source diffuser. module(b) that that comprises comprises 216wide-angle 216 Figure Figure wide-angle Figure 9. 1010 shows shows mini-LEDs mini-LEDs Actual theactual the sample actual sample asample combined combined of diagram diagram 12.3-inchwith of ofthe thin DRCAs with DRCAs blue 12.3-inch andwhite thelarge-area 12.3-inch and white QD QD light lightthin color color high-brightness large-area thin large-area conver- conver-flat light sou Figure 9. Actual high-brightness sample flat light of a 12.3-inch source module. thin blue Figure 10a large-area shows the high-brightness light source module flat light s sion sion film.Figure film. Figure10bhigh-brightness 10bule.shows (a) mini-LEDs shows flat mini-LEDs mini-LEDs light source module. combined combined combined Figure QD color with DRCA and 10a color shows the (b)conversion light source film mini-LEDs combined conversion film withthat module without without that and DRCA ule. (a) mini-LEDs comprises comprises 216 combined 216wide-angle wide-angle with DRCA mini-LEDs mini-LEDs combined combined and with(b)DRCAs with mini-LEDs DRCAs and andQD QDcombined color color with DRCA a conversion conversion DRCAs. DRCAs. The The driving driving conditions conditions film. Figure areshows are 10b aaforward forward mini-LEDs voltage voltage of 12 combined 12 QD VV and and color forward forward conversion current current film ofof without 1.65 1.65 DRCAs. film. Figure 10b shows mini-LEDs combined QD color conversion film without DRCAs. A. A. TheThe drivingconditions driving conditionsare areaaforward forward voltage voltage of of 12 12VVandandforward forwardcurrent currentofof 1.65 A.A. 1.65 (a) (b) (a) (b) 10. Actual Figure 10. Figure Actualsample diagram sample of 12.3-inch diagram white light of 12.3-inch whitethinlight large-area high-brightness thin large-area flat light sourceflat high-brightness module, light Figure Figure (a) 10. 10. Actual Actual mini-LEDs sample combined diagram sample QD color of 12.3-inch diagram of white 12.3-inch conversion film with light white DRCAsthin large-area light and (b)thin high-brightness large-area mini-LEDs flatcolor lightconversion high-brightness combined QD sourceflat module, light film source module, (a) mini-LEDs combined QD color conversion film with DRCAs and (b) mini-LEDs (a) mini-LEDs without source combined QD color conversion film with DRCAs and (b) mini-LEDs combined DRCAs.(a) mini-LEDs combined QD color conversion film with DRCAs and (b) mini-LEDs module, QD color conversion film combined QD color conversion film without DRCAs. without DRCAs. combined QD color conversion film11without Figure DRCAs. presents the normalized light distribution curve obtained through an actual Figure 11 presents Figure 11 presents measurement. The black the normalized the lightnormalized line indicates light the distribution distribution light curve distribution curve obtained curve obtained through of mini-LEDs through an actual combined an actual with a DRCA.The measurement. In this case, black linethe central the indicates intensity light value was 39.34%. distribution curve The of red line indicates mini-LEDs combined Figure 11 presents measurement. The blacktheline normalized indicates light the lightdistribution distribution curve curveobtained through of mini-LEDs an actual combined with a DRCA. In this case, the central intensity value was 39.34%. The red line indicates measurement. with a DRCA. The In black this linedistribution the case, light indicates the the centralcurve light intensity distribution value was of mini-LEDs curve 39.34%. combined ofThe with amini-LEDs red and DRCA combined lineaindicates diffuser. In this with the light distribution curve of mini-LEDs combined with a DRCA and a diffuser.indicates a DRCA. In this case, the central intensity value was 39.34%. The red line In this thecase, lightthe distribution curvevalue central intensity of mini-LEDs increased combined to 52.42%. The withgreen a DRCA and a diffuser. line indicates the lightIndis-this
Figure 11 presents the normalized light distribution curve obtained throug measurement. The black line indicates the light distribution curve of mini-LED with a DRCA. In this case, the central intensity value was 39.34%. The red lin Nanomaterials 2021, 11, 2395 8 of 12 the light distribution curve of mini-LEDs combined with a DRCA and a diffu case, the central intensity value increased to 52.42%. The green line indicates th tribution curve of mini-LEDs combined with a DRCA, a diffuser, and the first the light distribution curve of mini-LEDs combined with a DRCA and a diffuser. In this case,the case, the central central intensity intensity value value increased increased to 52.42%.toThe 66.88%. Theindicates green line blue linethe indicates light th distribution curve ofofmini-LEDs tribution curve combinedcombined the mini-LEDs with a DRCA, with a diffuser, a DRCA, and a the first BEF. and diffuser, In the s this case, the central intensity value increased to 66.88%. The blue line In this case, the central intensity value increased to 100%. These results indicindicates the light distribution curve of the mini-LEDs combined with a DRCA, a diffuser, and the second mini-LEDs BEF. combined In this case, with a DRCA the central intensity as well value increased as theThese to 100%. firstresults and indicate the secondthat BEF, light for intensity mini-LEDs can bewith combined increased a DRCA as bywell 1.7asand 2.54and the first times, respectively. the second The differe BEF, the central light intensity intensity can be increased between the twobycenters 1.7 and 2.54 wastimes, 1.494 respectively. times. The difference in light intensity between the two centers was 1.494 times. Figure Figure Light 11.11. distribution Light curve of curve distribution a 12.3-inch of aplanar light source 12.3-inch module planar with light different source structures. module with diffe Nanomaterials 2021, 11, x FOR PEER REVIEW tures. The uniformity of the 12.3-inch white light thin large-area high-brightness planar light source module was measured using the nine-point measurement method commonly used in the industry. Figure 12 presents The uniformity of the the measurement 12.3-inch point white distribution. light thin large-area high-bright light source module was measured using the nine-point measurement method used in the industry. Figure 12 presents the measurement point distribution. Figure Figure Brightness 12.12. measurement Brightness points for the measurement 12.3-inch points for white light thin large-area the 12.3-inch high-brightness white light thin large-area flat light source module. ness flat light source module. The uniformity was calculated as follows: The uniformity was calculated as follows: minimum luminance (nits) Uniformity (%) = 100% × (4) Uniformity maximum luminance (%) = 100% × (nits) ( ) ( ) Table 2 lists the brightness value measured at nine measuring points and the unifor- Table mity value 2 lists of the the mini-LEDs 12.3-inch brightness value measured combined at ninefilm QD color conversion measuring with DRCAs points a of planar light formity value source of themodule. Themini-LEDs 12.3-inch driving conditions are a forward combined QD colorvoltage of 12 V film w conversion and forward current of 1.65 A. On average, the uniformity of the of planar light source module. The driving conditions are a forward module was 87.58% voltage when one BEF was added, and the brightness was 15,240 cd/m2 . Furthermore, the unifor- forward mity of the current module was of 90.13% 1.65 A. Ontwo when average, theadded, BEFs were uniformity of the brightness and the average module was 87 one BEF was added, and the brightness was 15,240 cd/m2. Furthermore, the un the module was 90.13% when two BEFs were added, and the average brig 23,044 cd/m2. Therefore, the difference in average brightness between the tw
Nanomaterials 2021, 11, 2395 9 of 12 was 23,044 cd/m2 . Therefore, the difference in average brightness between the two was 1.51 times. The average luminance value measured and the uniformity value of general mini-LED backlight that mini-LEDs combined QD color conversion film without DRCAs is 19,370 cd/m2 and 74.89%, respectively. Comparison of mini-LEDs backlight combined with DRCAs and without DRCAs shows that luminance is enhanced 1.18 times, and uniformity increases from 74.89% to 90.13%. Table 2. Brightness and uniformity measured at nine points on the actual sample. 1 BEF Luminance (cd/m2 ) 2 BEF Luminance (cd/m2 ) P1 15,910 23,695 P2 14,220 21,785 P3 15,730 23,758 P4 16,218 24,025 P5 14,335 21,884 P6 15,276 23,255 P7 15,832 23,758 P8 14,205 21,655 P9 15,430 23,585 Average luminance/ 15,240/ 230,44/ CIE (x,y) CIE (x 0.3268,y 0.2845) CIE (x 0.3545,y 0.3059) Uniformity (%) 87.58% 90.13% Figure 13 displays the measured CIE color coordinates(x,y)-voltage of wide-angle mini-LEDs combined with a DRCA and QD film light source module. The forward voltage Nanomaterials 2021, 11, x FOR PEER REVIEW is increased from 11.2 V to 13.2 V, and the maximum variations in CIE x,y are 0.0014 and 0.0018, respectively. Figure 13. The measured CIE color coordinates (x,y)–voltage of wide-angle mini-LEDs combined Figure 13. The measured CIE color coordinates (x,y)–voltage of wide-angle mi with a DRCA and QD film light source module. combined with a DRCA and QD film light source module. Figure 14 displays the measured luminance (cd/m2 )–voltage of wide-angle mini-LEDs combined with a14 Figure DRCA and QD the displays film light source module. measured The forward luminance (cd/mvoltage is increased 2)–voltage wide- of from 11.2 V to 13.2 V, the maximum variation percentage of luminance is 2.6%. LEDs combined with a DRCA and QD film light source module. The forwar increased from 11.2V to 13.2V, the maximum variation percentage of luminan
Figure 13. The measured CIE color coordinates (x,y)–voltage of wide-angle mini-LEDs combined with a DRCA and QD film light source module. Figure 14 displays the measured luminance (cd/m2)–voltage of wide-angle mini Nanomaterials 2021, 11, 2395 10 of 12 LEDs combined with a DRCA and QD film light source module. The forward voltage i increased from 11.2V to 13.2V, the maximum variation percentage of luminance is 2.6%. Figure 14.Displays Figure14. Displaysthethe measured measuredluminance (cd/m2 )–voltage luminance of wide-angle (cd/m2)–voltage ofmini-LEDs combined wide-angle mini-LEDs com with a DRCA and QD film light source module. bined with a DRCA and QD film light source module. Figure 15 displays the electroluminescence (EL) spectrum of wide-angle mini-LEDs Figure 15 displays the electroluminescence (EL) spectrum of wide-angle mini-LED combined with a DRCA and QD film light source module. In Figure 15a, the peak emission wavelengthswith combined a DRCA are 450, and 532, and 626QD nm,film light and the source FWHM module. is 20 In Figure nm. These 15a, thethat results indicate peak emis sion the Nanomaterials 2021, 11, x FOR PEER REVIEW wavelengths mini-LEDs havearethe 450, 532, and advantage 626 nm, of high colorand the FWHM purity. is 20 According nm.EL to the These results spectrum indicat in 11 of 13 that the mini-LEDs have the advantage of high color purity. According to the CIE 1931 color gamut coordinates, the mini-LEDs’ NTSC reached 119.2%, as shown in the EL spectrum Figure in the 15b, CIE indicating 1931 colortheir wide gamut color gamut the coordinates, range. mini-LEDs’ NTSC reached 119.2%, as shown in Figure 15b, indicating their wide color gamut range. 100 Normalize spectral 80 radiance(a.u.) 60 40 20 0 350 400 450 500 550 600 650 700 750 Wavelength(nm) (a) (b) Figure Figure 15. (a) 15. (a) NormalizedEL Normalized EL spectrum spectrum and and(b)(b) color gamut color of mini-LEDs gamut combined of mini-LEDs with a DRCA combined withand QD filmand a DRCA optical QD module. film optical module. 4. Conclusions This study optimized the design of mini-LEDs combined with multiple 3D DRCAs for 4. Conclusions application to thin, large-area, high-brightness, flat light source modules. A 12.3-inch white This study optimized the design of mini-LEDs combined with multiple 3D DRCAs light thin, large-area, high-brightness planar light source module was used as a sample. The fordriving application to thin, large-area, high-brightness, flat light source modules. A 12.3-inch condition is a forward voltage of 12 V and a forward current of 1.65 A. At a mixing white light distance of thin, 6 mm,large-area, the averagehigh-brightness luminance reachedplanar 23,044light cd/m source module 2 , and NTSC waswas used as a 119.2%. sample. Comparison of mini-LEDs backlight combined with DRCAs to that without DRCAs showsof 1.65 The driving condition is a forward voltage of 12 V and a forward current A.that At aluminance is enhanced mixing distance of 6 1.18 mm,times, and uniformity the average increases luminance reached from 74.89% 23,044 to 90.13%. cd/m 2, and NTSC The119.2%. was thin, large-area, high-brightness, Comparison of mini-LEDs high-uniformity, high-color-saturation backlight combined with DRCAs planar to thatlight without source module proposed in this study can be employed as the local DRCAs shows that luminance is enhanced 1.18 times, and uniformity increases fromdimming backlight in next-generation 74.89% to 90.13%.automotive The thin, displays. large-area, high-brightness, high-uniformity, high-color-satu- ration planar light source module proposed in this study can be employed as the local dimming backlight in next-generation automotive displays. Author Contributions: Z.T.Y., Y.H.C. and K.S.Y. designed the experiments. Y.H.C. analyzed the
Nanomaterials 2021, 11, 2395 11 of 12 Author Contributions: Z.T.Y., Y.H.C. and K.S.Y. designed the experiments. Y.H.C. analyzed the data. Z.T.Y. and K.H.L. discussed the results and contributed to the writing of the manuscript. All authors have read and agreed to the published version of the manuscript. Funding: This work was financially/partially supported by the Advanced Institute of Manufacturing with High-Tech Innovations from the Featured Areas Research Center Program within the framework of the Higher Education Sprout Project by the Ministry of Education in Taiwan. This research was also supported by the Ministry of Science and Technology the Republic of China (Grant No. MOST 110-2218-E-002 -032 –MBK and 110-2221-E-194 -036) and EPOCH CHEMTRONICS Corp. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: Data sharing is not available. Conflicts of Interest: The authors declare no conflict of interest. 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