In this paper, we introduce our latest progress in the colloidal quantum dot enhanced color conversion layer for micro LEDs. Different methods of how to deploy colloidal quantum dots can be discussed and reviewed. The necessity of the using color conversion layer can be seen and color conversion efficiency of such layer can be calculated from the measured spectrum. A sub-pixel size of 5 micron of colloidal quantum dot pattern can be demonstrated in array format.

Wafers with smooth Au thin films (rms surface roughness: < 0.5nm, thickness: < 50nm) were successfully bonded in ambient air at room temperature after an Ar radio frequency plasma activation process. The room temperature bonded glass wafers without any heat treatment showed a sufficiently high die-shear strength of 47-70MPa. Transmission electron microscopy observations showed that direct bonding on the atomic scale was achieved. This surface-activated bonding method is expected to be a useful technique for future heterogeneous photonic integration.

Low-temperature bonding methods of optoelectronic chips, such as laser diodes (LD) and photodiode (PD) chips, have been the focus of much interest to develop highly functional and compact optoelectronic devices, such as microsensors and communication modules. In this paper, room-temperature bonding of the optoelectronic chips with Au thin film to coined Au stud bumps with smooth surfaces (Ra: 1.3nm) using argon and hydrogen gas mixture atmospheric-pressure plasma was demonstrated in ambient air. The die-shear strength was high enough to exceed the strength requirement of MIL-STD-883F, method 2019 (×2). The measured results of the light-current-voltage characteristics of the LD chips and the dark current-voltage characteristics of the PD chips indicated no degradation after bonding.

With the aim of achieving heterogeneous integration of compound semiconductors with silicon technology, the fabrication of an InP/InGaAs transferred-substrate HBT (TS-HBT) on a Si substrate is reported. A current gain of 70 and a maximum current density of 12.3 mA/µm2 were confirmed in a TS-HBT with a 340-nm-wide emitter. From microwave characteristics of the TS-HBT obtained after de-embedding, a cutoff frequency (fT) of 510 GHz and a 26% reduction of the base-collector capacitance were estimated. However, the observed fT was too high for an HBT with a 150-nm-thick collector. This discrepancy can be explained by the error in de-embedding, because an open pad is observed to have large capacitance and strong frequency dependence due to the conductivity of the Si substrate.

The heterogeneous integration of GaAs HEMTs on a polyimide-covered AlN ceramic substrate was demonstrated using a fluidic self-assembly (FSA) technique. We used thin device blocks for the FSA, which have various advantages. In particular, they can reduce the drain-source capacitance Cds of the assembled HEMTs if the substrate has a low dielectric constant. This is a novel kind of semiconductor-on-insulator (SOI) technology. The dc and RF properties of the GaAs HEMTs on the polyimide/AlN substrate were studied and the reduction of Cds was confirmed. This technique was successfully applied to the SPDT switch, where a low Cds is essential for good isolation.

Field Configurable Self-assembly is a novel programmable force field based heterogeneous integration technology. Herein, we demonstrate application of the method to rapid, parallel assembly of similar and dissimilar sub-200 µm GaAs-based light emitting diodes at silicon chip substrates. We also show that the method is compatible with post-process collective wiring techniques for fully planar hybrid integration of active devices.