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The integration of quantum dots (QDs) into device arrays for high-resolution display and imaging sensor systems remains a significant challenge in research and industry because of issues associated with the QD patterning process. It is difficult for conventional patterning processes such as stamping, inkjet printing, and photolithography to employ QDs and fabricate high-resolution patterns without degrading the properties of QDs. Here, we introduce a novel strategy for the QD patterning process by treating QDs with a bifunctional ligand for acid-base reaction-assisted photolithography. Bifunctional ligands, such as MPA (mercaptopropionic acid) or TGA (thioglycolic acid), have a carboxyl group on one side that allows the QDs to be etched along with the photoresist (PR) by the base developer, while on the opposite side the ligands have a thiol group that passivates the QD surface. Passivating MPA ligands on QDs facilitates patterning of QD films and makes them compatible with harsh photolithography processes. We successfully achieved the patterning of QDs down to 5 μm. We also fabricated high-resolution patterned QD light-emitting diodes (LEDs) and QD photodetector arrays. Our patterning process provides precise control for the fabrication of highly integrated QD-based optoelectronic devices.

Previous approaches to induce photomultiplication in organic diodes have increased the photosignal but lacked control over reducing background noise. This work presents a new interlayer design based on a heterojunction bilayer that concurrently enables photomultiplication and suppresses the dark current in organic shortwave infrared detectors to improve the overall detectivity. The heterojunction bilayer consists of a hole-transporting material copper thiocyanate and an electron-transporting material tin oxide, and this combination offers the ability to block charge injection in the dark. Under illumination, the bilayer promotes trap-assisted photomultiplication by lowering the tunneling barrier and amplifying the photocurrent through the injection of multiple carriers per absorbed photon. Upon incorporating the heterojunction interlayer in photodiodes and upconversion imagers, the devices achieve an external quantum efficiency up to 560% and a detectivity of 3.5 × 109 Jones. The upconversion efficiency of the imager doubles with a 1.7 fold improvement in contrast compared to the imager without the heterojunction interlayer. The new interlayer design is generalizable to work with different organic semiconductors, making it attractive and easy to integrate with emerging organic infrared systems.

Enhanced direct Cu/Cu joining by applying current was investigated. Joining was conducted at 240–300 °C for 10–50 min under 40 MPa. Current was applied to Cu wire during joining. Contact resistance of joints decreased and the fracture load of joints increased as the current increased. The joined region increased and the interface became less straight as the current increased. These results are ascribed to electromigration and joule heating effects. The enhanced diffusion contributed significantly to the joining of metals.

This paper proposes a controller design of a distributed power source inverter to be useful both under the stand alone mode and the grid-connected mode to compensate the current harmonics from the local nonlinear load. The PR based multi-loop controller is used to improve the system dynamic performance and to compensate the output voltage or grid current harmonics depending on the operation modes, respectively. The multi-loop controller consists of an outer current controller and an inner voltage controller which also has an inner current controller. The stability of each controller is verified by the Root locus and Bode plot of the transfer function. In this paper, in spite of the current harmonics caused by the local nonlinear load, the controller is designed to regulate the inverter output voltage to be sinusoidal with constant voltage and constant frequency in the stand alone mode and to control the grid current to be sinusoidal in the grid-connected mode, respectively. The validity of the proposed control algorithm and the controller design results have been verified through the PSiM simulation and experimental results.

The effect of applied current in enhancing bonding was studied in Cu-to-Cu direct bonding using Cu microbumps. A daisy-chain structure of electroplated Cu microbumps (20 μm × 20 μm) was fabricated on Si wafer. Cu-to-Cu bonding was performed in ambient atmosphere at 200–300 °C for 10 min under 260 MPa, during which direct current of 0–10 A (2.5 × 106 A/cm2) was applied. With increasing applied current, the contact resistance decreased and the shear strength in the Cu-to-Cu joints increased. The enhanced bonding imparted by the application of current was ascribed to Joule heating and electromigration effects. Subsequently, the joint temperature was calibrated to isolate the electromigration effects for study. In Cu-to-Cu joints joined at the same adjusted temperature, increasing the current caused unbonded regions to decrease and regions of cohesive failure to increase. The enhanced diffusion across the Cu/Cu interfaces under the applied current was the main mechanism whereby the quality of the Cu-to-Cu joints was improved.