Monolithic Integration of Ring-Resonator Optical Switches using Electro-Optic Material, on Si LSI

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The final target of the research is to realize the on-chip optical interconnection for high-speed LSI. The object of this study is to develop a technology for monolithic integration of compact optical switches on Si LSI at low temperatures below 450℃, at which the devices can be fabricated on top layer of the LSI without degradation of the metal-interconnect reliability.In fiscal year of 2005, Mach-Zhender interferometer (MZI) optical switches were integrated using electro-optical material, (Ba,Sr)TiO_3 (BST), spin-coated and annealed at 550℃. Optical modulation was 2% at 90 V. The results were published in Appl. Phys. Lett. 88, 161107 (2006).In 2006, the performance of the MZI was improved to 10% of modulation at 200 V. We have, for the first time, achieved to decrease the growth temperature of the BST film to 450℃, which is the target value (Jpn. J. Appl. Phys. 46, No. 4B, p. 2462 (2007)).In 2007, we have tried to improve the BST film quality by adjusting composition elements and by employing Pt cap annealing. However, the further improvement of the MZI performance has not been obtained. Instead of the BST film, the strained silicon has been applied to the ring-resonator optical switches, and we have achieved the optical modulation of 33% at 200 V (IEICE Technical Report, OPE2007-143, p. 41 (2007) [in Japanese]). This is the first report on the electric-field drive Si ring-resonator switch, while the previous devices were current injection type with high power consumption. However, it was found that the mechanism of the optical modulation is not by electro-optic effect but by the carrier-concentration modulation at the Si surface induced by the electric-field. The small strain may be the reason for the no observation of the electro-optic effect. The further improvement is now under investigation.