Design, Fabrication, and Comparison of 3D Multimode Optical Interconnects on Silicon Interposer

While conventional silicon photonic (SiP) waveguides achieve high data rates with low loss, they can only be placed on top of the chip surfaces horizontally. In this article, we present a design approach for multimode chip-to-chip interconnects with similar low-loss and high-bandwidth density properties as SiP waveguides. The state-of-the-art fabrication of optical through silicon via (OTSV) requires conventional back end of line (BEOL) processing with an additional step: metal coating lowers the loss of air-filled TSVs. Alternatively, the TSV is converted into a polymer waveguide by filling of low-loss polymer (Ormocore) to achieve <; 0.1 dB optical power loss over 380 μm distance. A 3D multimode optical interconnect is measured at 40 Gbit/s with the bit error rate (BER) <; 10^-12 at 1550 nm wavelength. The proposed solution supplies a new path for 3D integration of optical waveguides capable of delivering high-speed data within 3D stacked chips.

I. Introduction

Optical communication has had a significant impact to overcome the everlasting high-speed data transmission requirements by enabling high bandwidth and therefore high data transfer rates across the world. For long-haul applications, optical solutions have vanquished the cost barrier and are now used around the world, e.g., from transatlantic communications cables to fiber-to-the-home. However, optical communication has a huge potential for microelectronic applications as well, i.e., at inter- and intra-chip level [1]. Conventional methods to increase the performance of semiconductor devices are approaching their physical limits. Hence, the 3D chip integration is rising as an industry accepted alternative to cope with the expected year-on-year performance growth [2]. With increasing transistor count, the BEOL challenges are also increasing (density, performance limitation, thermal budget, bandwidth, etc.) [3], [4]. The global internet data transfer rate is reaching 0.5 Pbit/s [5].