NEC develops LSI optical-interconnect technology

Feb. 14, 2006
February 14, 2005, Tokyo, Japan--NEC Corporation says it has developed fundamental silicon (Si) nanophotonics technology that facilitates optical data transmission in large-scale-integration (LSI) chips by eliminating data-transmission bottlenecks.

February 14, 2005, Tokyo, Japan--NEC Corporation says it has developed fundamental silicon (Si) nanophotonics technology that facilitates optical data transmission in large-scale-integration (LSI) chips by eliminating data-transmission bottlenecks.

The technology reduces the footprint area for the optoelectronic signal-transfer apparatus down to a 10-micron-square area (small enough to set onto an LSI chip) by combining an ultrasmall amplifier with an existing Si nanophotodiode. In an optical wavelength-division-multiplexing system, the technology would enable transmission of much more data through a 1-micron waveguide than by conventional copper circuitry.

In a networked society, devices need to operate at higher speeds to be able to process tremendous volumes of data. Conventionally, the operating speed of an LSI chip has been accelerated by increasing the clock rate through miniaturization of transistors. Recently, however, LSI manufacturers have found it difficult to increase clock speed without simultaneously increasing power consumption due to the growing leakage current of transistors as miniaturization advances. To overcome this problem, NEC developed a multicore technology that enables the suppression of clock speed in an LSI chip through parallel processing. This technology already has been commercialized by NEC as an application processor for mobile handsets. However, by 2015, the data-transfer rate for a microprocessor (MPU) is expected to exceed one terabit per second, ten times higher than current rates, and cause difficulty in conventional electrical wiring in high-performance information and network systems. Thus, there is a great need for novel data-transfer technology that is based on light.

Important factors in developing optical wiring technology include reduction of size, increase in speed and reduction in power of the optoelectronic component, which consists of an optoelectronic device and a high-speed amplifier. NEC's Si nanophotodiode has a high-speed response of greater than 50 GHz with a footprint of less than 10 microns square. However, a structure such as this with a high-speed amplifier is very complicated and thus requires a footprint of several tens of microns square, resulting in an unrealistic layout for placement within an LSI chip with an optoelectronic component using conventional technology.

In response to this, NEC used the small electrical capacitance (junction capacitance of about ten aF) of a nanophotodiode to reduce the footprint of the high-speed amplifier by approximately two orders of magnitude. In addition, a high-speed optical-electrical signal transfer was carried out with little power consumption by combining the circuit and nanophotodiode.

NEC has developed technology for realizing ultrasmall optical multiplexers/demultiplexers with a size of about 100 microns square (about one-hundredth the size of conventional devices) with an ultrafine optical waveguide. It has also developed a form of ceramic electro-optic film fabrication by aerosol-deposition for reducing the size of optical modulators to 100 microns (about one tenth the size of conventional devices).

These developments are aimed at simplification of the LSI structure, which is now becoming progressively more complex. These technologies greatly increase the possibility of incorporating waveguides into LSI chips that can realize data transfers 100 times greater than current copper wires with low power and high speed.

Applications include computers and servers, network devices, and network components that require immunity to electromagnetic noise.

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