Ning Tu

Quantum materials’ limited emission spectrum and easily adjustable color through particle size modification make them a viable option for the next generation of displays. The emission spectrum of quantum materials is sharp and pure, which makes quantum materials ideal for display applications. As display technology advanced, self-emitting display technology eventually replaced liquid crystal display (LCD). Researchers design different types of RGB pixels in the self-emitting display area to achieve the best possible visual impact. However, different types of pixels need quantum color conversion films with various patterns. Additive manufacturing offers a novel method for quicker prototyping of red, green, and blue (RGB) pixels with a faster iteration cycle. With the additive manufacturing technique, especially the inkjet printing method, the sample is not in contact with the surfaces; only the essential components are dispensed and deposited there. The additive manufacturing technique generally reduces sample damage or containment and material waste. This chapter introduces inkjet-printing quantum materials for high-resolution display applications.

Quantum dots (QDs) have attracted a lot of attention over the past decades due to their sharp emission spectrum and color, which can be tuned by changing just the particle size and chromophoric stability. All these advantages of QDs make quantum dot light-emitting diodes (QLEDs) promising candidates for display and light-source applications. This paper demonstrates a large-emitting-area QLED fabricated by a full-solution process. This QLED is composed of indium tin oxide (ITO) as the anode, poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT: PSS) as the hole injection layer (HIL), and poly(N,N′-bis-4-butylphenyl-N,N′-bisphenyl)benzidine (poly-TPD) as the hole-transport layer (HTL). The light-emitting layer (EML) is composed of green CdSe/ZnS quantum dots. By applying the ZnO nanoparticles as the electron-injection/transport layer, QLED devices are prepared under a full-solution process. The large-emitting-area QLED exhibits a low turn-on voltage of around 2~3 V, and the International Commission on Illumination (CIE) 1931 coordinate value of the emission spectrum was (0.31, 0.66). The large emitting area and the unique QLED structure of the device make it possible to apply these features to inkjet printing quantum dot light sources and quantum dot display applications.

The inkjet printing method is a promising method to deposit polymer and functional nanoparticles at the microscale. It can be applied in the fabrication of multicolor polymer light emitting diodes (polyLEDs), polymer base electronics, multicolor color conversion layers, and quantum dot light emitting diodes (QLEDs). One of the main challenges is to print high-resolution polymer dots from dilute polymer solution. In addition, the quality of printed multicolor polyLEDs, QLEDs and multicolor color conversion layers is currently limited by non-uniformity of the printed dots. In this paper, polydimethylsiloxane (PDMS) is selected as the functional polymer, due to its high transparency, good reflective index value, inflammable and flexible properties. The optimal ink to form a uniform PDMS dot array is presented in this paper. Both the solvent and PDMS were tuned to form the uniform PDMS dot array. The uniform PDMS dot array was printed with a diameter of around 50 µm, and the array of closely spaced green quantum dots (QDs) mixed with PDMS ink was also printed on the substrate uniformly. While the green QD-PDMS film was printed at a resolution of 1693 dpi, the uniformity was evaluated using the photoluminescence (PL) spectrum and color coordinate value.

Additive manufacturing has been extensively studied as a promising candidate for complete or partial replacement of traditional photolithography methods. The focus of this paper is on redistribution layers (RDLs) fabricated by aerosol jet (AJ) printing. Nanoparticle silver ink was deposited directly on silicon chips to form the conductive layer, while dielectric ink was used for the passivation layer. As a comparison, chips with copper RDLs, which had the same layout, were prepared using conventional photolithography. After assembling this chip-scale package (CSP) onto a PCB through common SMT processes, the reliability of such assembly under thermal cycling and thermal shock loads was tested. The number of cycles to failure of these samples was monitored in real time through a daisy chain structure. Cross-sectional investigations were performed after tests for failure analysis. Testing results revealed that the adhesion between the printed PI layer and the wafer might be the weakest link in the printed structure.