LTCC toolbox for photonics integration Pentti Karioja, Kimmo Keränen, Mikko Karppinen, Kari Kautio, Veli Heikkinen, Markku Lahti, Jyrki Ollila, Jukka-Tapani Mäkinen, Kari Kataja, Jarkko Tuominen, Tuomo Jaakola, Sang Hyun Park, Pentti Korhonen, Teemu Alajoki, Antti Tanskanen, Jaakko Lenkkeri, Juhani Heilala VTT Technical Research Centre of Finland PO Box 1100, Kaitoväylä 1 FI-90571 Oulu Finland Abstract In photonic module integration, optoelectronic chips, micro-optical elements and integrated circuits are integrated into functional components, sub-assemblies, modules and systems. The building blocks of the photonic system must be fabricated by the use of cost-efficient, reproducible, well-established, high-volume manufacturing technologies. The reliability of the system as well as the tolerances of device alignment are key issue in the integration. We have developed a Low Temperature Co-fired Ceramics (LTCC) toolbox for photonic integration. The primary aim was to process co-fired 3D structures, such as, grooves, cavities, holes, bumps and alignment fiducials for the passive alignment of photonic devices. LTCC provides means for full 3D integration. The tolerances of the alignment structures are typically ±5µm and in some specific cases ±2µm. LTCC structures provide means for the passive alignment of multimode fiber, for example. With Monte-Carlo tolerancing tools, we can simulate and optimize the performance of the system and estimate manufacturing yield in volume production. Thermal management by the use of thermal vias is a well-established technique; liquid cooling channels in the LTCC substrate provide efficient means for high-power laser cooling. LTCC provides inherently hermetic substrate allowing the possibility for hermetic encapsulation. High-speed ICs as well as millimeter-wave circuits can easily be integrated into the LTCC substrate. Novel materials allow the fabrication of advanced systems, especially, for millimeter-wave operation. Keywords: fiber optic, photonic module, cost-efficient, thermal management, hermetic, power laser, optical interconnects 1.0 Introduction In photonic packaging and integration, the basic building blocks of the system, such as, lasers, photo detectors, micro-optical elements, optical fibers, laser drivers and photo detector amplifiers, are integrated into functional components, modules and sub-systems. Hybrid integration is the way to realize photonic systems in such a way that the basic elements are integrated by the use of a common substrate, a ceramic substrate, for example. The parts of the system must be fabricated by the use of cost-efficient, reproducible, well- established, high-volume manufacturing techniques. In photonic packaging, reliability issues as well as alignment tolerances are key issues. Therefore, system in a package concept (SiP) would be the most favorable approach in order to fulfill the requirements of photonic packaging. For photonic integration the following issues must be considered: - Devices alignment with micron accuracy by the use of 3D passive alignment structures. - Integration of high-speed/low-noise/high- power electronics as close as possible to the critical photonic devices, such as, diode laser, optical modulator, photo detector or MEMS devices. - Matching of the thermal expansion coefficients between the devices and substrate. - Provide required internal and external optical, electrical and mechanical interconnects as efficiently as possible. - Provide required thermal management for critical power devices, such as, high-power lasers, laser drivers and amplifiers. - Protect devices against environmental conditions during the use and storage of the modules. - Provide local hermetic sealing of critical devices, such as, diode lasers. Of course, these requirements must be fulfilled by the most cost-efficient means in high- volume production with good production yield and reliability. Our aim was to develop methods and technologies for photonics packaging and integration based on the use of Low Temperature Co-fired Ceramic (LTCC) technology. This paper describes the capabilities of LTCC technology using several photonic modules as illustrating examples. The demonstrators are a fiber pigtailed