Chip-on-Flex Packaging of Optoelectronic Devices in Polymer-Based Planar Optical Interconnects

Abstract

A variety of applications in the use of optical and optoelectronic devices as well as their integrated circuits are increasingly penetrating into our daily routine. One of the most demanding fields is the sensing engineering. Meanwhile, the demand for more mechanical flexibility of systems and lower manufacturing budgets is continuously growing. Since the optical transparency is desired for coupling and transmission of optical signals, cost-effective transparent polymeric films are the promising candidates as carrier substrates. In this work, we aim to establish short-distance planar optical interconnects consisting of light sources/detectors and waveguides on the flexible transparent polymeric films for optical sensing functions. To achieve a miniaturized structure and ensure the flexibility of interconnects, bare chips of optoelectronic light sources/detectors are employed. Here, packaging of these chips carries the burden of all responsibilities in terms of ensuring the mechanical strength, electrical connection, thermal stability as well as the optical performance. It leads to the concept of chip-on-flex (CoF) packaging of optoelectronic devices. We present CoF packaging of a bare edge-emitting laser diode using the previously developed novel optodic bonding. While operating CoF packages, the optical performance of an active diode is strongly impaired by inefficient heat dissipation due to the extremely low thermal conductivity of employed polymeric films. Addressing this challenge, different concepts of thermomanagement are implemented. We elaborate the characterization results that evaluate the performance of CoF packages in terms of mechanical, electrical, thermo-optical, and opto-electronic properties. Two prototypes of planar optical interconnects are presented, with multi- and single-mode polymeric waveguide.