Toshifumi Kojima

Low-Loss Chip-to-Chip Optical Interconnection Using Multichip Optoelectronic Package With 40-Gb/s Optical I/O for Computer Applications

We have developed novel optoelectronic packages and optical transmission system using an optical connector with an external optical waveguide to achieve low-loss chip-to-chip optical interconnections for computer systems. In order to connect the package and the connector, we have also proposed a socket as a coupling structure to realize an all passive alignment and high coupling efficiency. We have demonstrated high-speed and error-free signal transmission with four channels at 10-Gb/s/ch and up to 12-Gb/s/ch. Optical input and output (I/O) interfaces, including optical devices and controller integrated circuits (ICs), have been constructed onto the package surface by conventional flip-chip mounting. The optoelectronic package has optical waveguide holes (OWGHs) to pass optical signal vertically from a vertical-cavity surface-emitting laser (VCSEL) and to a photodiode (PD). The OWGHs consist of core and cladding material to enhance optical confinement. The optical connector that is just set underneath the package with two guide pins contains the thin-film polymer waveguide with 45°-ended mirrors to bend the optical signal. Therefore, the shorter optical coupling distance has achieved low-loss optical link without microlenses between packages. We have also proposed an alignment structure to easily enable passive alignment, which is based on existing land grid array (LGA) packages and sockets clamping structures to simultaneously improve cost-competitiveness and usability.

Fine-Pitch Copper Wiring Formed with Super-Inkjet and Oxygen Pump

We have successfully printed wires of 5 µm line widths and spaces in copper nanoparticle ink with a super-inkjet printer. The wires show resistivity as low as 8.1 µΩcm after sintering at 250 °C in an extremely low oxygen atmosphere generated by an oxygen pump. To our knowledge, this is the first report of micron-scale copper wiring formed by a direct printing method without any masks or templates.

Optoelectronic Package Having Low-Loss Optical Waveguide Hole With Core–Clad Structure for Chip-to-Chip Interconnection

We have developed optoelectronic packages having optical waveguide holes with core-clad structures for chip-to-chip optical interconnection within computer systems. A rate of 10-Gb/s/ch chip-to-chip optical signal transmission has been demonstrated. The optoelectronic package we have developed consists of two guide pins and four-channel optical waveguide holes. The two guide pins are used to align an optical fiber connector with an optical device. The optical waveguide holes are used to transmit optical signals vertically through the optoelectronic package. Using the optical waveguide holes in the optoelectronic package, and high-quality signal transmission has been achieved.

Optical through-hole with high aspect ratio for on-board optical transmission

We developed optical I/Os in packages for chip-to-chip interconnections. The I/Os of 55-µm-diameter and 1.2-mm-long optical through-holes demonstrate low loss and 10-Gb/s transmission. This package aims at future CPU systems with embedded capacitors.

4-Ch × 10-Gb/s chip-to-chip optical interconnections with optoelectronic packages and optical waveguide separated from PCB

We have developed optoelectronic packages for on-board optical interconnections and demonstrated 10-Gb/s and up to 12-Gb/s optical transmissions. In this paper, we describe the structure of the optoelectronic packages and optical interconnect systems that we propose for low-cost chip-to-chip signal transmissions. The optoelectronic package is intended to be pluggable from an LGA socket and an optical connector in order to ease system maintenance. The optical connectors with a polymer optical waveguide are designed to be assembled between the packages and an LGA socket. The polymer optical waveguide is separated from a printed circuit board (PCB) in order to produce the PCB with a mature and low-cost fabrication process. Optical devices flip-chip-mounted on the packages are encapsulated with transparent resin material to enhance their reliability and bonding strength. Signal transmission characteristics and optical interchannel crosstalk are evaluated from a transmitter package (Tx) to a receiver package (Rx).

Compact and 10-Gb/s

A compact 10-Gb/s times 12-channel optical transmitter was developed for very short-reach optical interconnections. The 10-Gb/s/ch operations were achieved without employing the heat pipes or heat sinks typically required to keep vertical-cavity surface-emitting lasers at a low temperature under 85degC. Alumina ceramic substrates with high heat dissipation capability are incorporated in order to maintain the low temperature operation. The optical transmitter is designed to be as compact as a standard mechanically transferable (MT) optical connector. To enhance usability, the transmitter can be directly connected with the MT-type optical connector with guide pins assembled in the alumina substrate. The compactness and usability of the optical module is effective in intrabox and interbox optical interconnections.