edfas.org 23 ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 25 NO. 3 FAILURE ANALYSIS OF PHOTONIC INTEGRATED CIRCUITS Frieder H. Baumann, Brian Popielarski, Ryan Sweeney, Felix Beaudoin, and Ken Giewont GlobalFoundries, Malta, New York frieder.baumann@globalfoundries.com EDFAAO (2023) 3:23-30 1537-0755/$19.00 ©ASM International® INTRODUCTION In photonics, light is guided and manipulated within a solid-state optical medium. In silicon photonics specifically, the waveguides, which connect the optical devices in the circuit, are made of silicon strips. These silicon bands are surrounded by a lower-index material like silicon oxide, which helps to keep the light confined inside the waveguide. The high refractive index of silicon (n = 3.5) waveguides embedded in oxide (n = 1.5) allows for relatively small bending radii of the waveguides (compared to nitride or silica waveguides), which allows for very compact photonic integrated circuits (PICs). However, the high index can result in higher propagation losses in silicon waveguide due to sidewall roughness of the waveguides. Thus, state-of-the-art processing is needed to bring silicon photonics to the marketplace. The photonics application space is diverse and includes data center interconnects, 5G, telecom, high performance computing, automotive Lidar, aeronautics, and more.[1] In most cases, the large bandwidth offered by optical interconnects compared to electrical interconnects is the main driver to introduce silicon photonics in a new product. This article introduces the reader to silicon photonics in a short tutorial, then describes what is needed for photonics FA, and shows examples of FA in modern silicon photonics circuits. SILICON PHOTONICS IN A NUTSHELL Currently, one primary market for silicon photonics is in the area of optical data transfer between servers in a data center. This article will introduce the reader to silicon photonics by describing the functions of a generic optical transmitter and receiver (“transceiver”) as it can be found in a modern server farm. This rather simple photonic system is sketched out in Fig. 1. Two silicon chips located in different servers in a data center need to communicate optically. To accomplish this task the following elements are required: • Optical light source • On-chip light distribution • Electrical to optical conversion • Optical coupling into fiber (optical input /output IO) • Optical to electrical conversion Before briefly discussing the above steps, it is important to mention the platform in which the PIC is fabricated. ELEMENTS OF A MONOLITHIC PIC There are several approaches to realize the fabrication of a silicon photonics chip. Hybrid solutions consist of different chips for light source, silicon optics, and silicon electronics, which are then packaged on a common interposer in a common package. The most elegant and probably highest-performance solution is a fully monolithic approach using Fig. 1 A very simple photonic system: A bit stream is converted to a train of light pulses, fed into an optical fiber, read out at the destination, and converted back to bits.
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