Photonic crystal resonator using CMOS process

Attempts are underway to reduce power consumption by processing information that is conventionally processed electrically in the form of light. In particular, research on silicon photonics, which aims to realize low-energy systems by replacing the wiring in chips with light, has been active. Current silicon photonics research focuses on the development of technologies related to the transmission of light within a chip, but in the future, signal processing may also be handled by light to achieve ultimate energy savings. For this purpose, elements called photonic crystal resonators, which can strongly confine light, are considered essential.

Based on this, the goal of this research was to incorporate photonic crystals as a new element in silicon photonics. The first is the difference in fabrication methods. Silicon photonics devices are now mostly fabricated by photolithography in the CMOS process, aiming at future integration with CMOS devices. The second difference is the structure. Silicon photonic devices are composed of SiO₂(silicon dioxide), but conventional photonic crystals require a cross-linked structure. Therefore, it has been difficult to incorporate conventional devices on the same silicon chip.

It was thought that photonic crystals could not be fabricated with the precision of photolithography, the mainstream CMOS process, but this problem was overcome by adopting a design called the width variation type shown in Figure 1(a). In fact, in a resonator called L3, adjacent holes stick to each other, making it impossible to fabricate the device accurately.