Embedded TiNxOy thin-film resistors in a build-up CSP for 10 Gbps optical transmitter and receiver modules

Integral passive components provide efficient circuit miniaturization while maintaining high performance and reducing assembly costs. The development of practical integral passive components, however, requires advances in the areas of materials, low-cost processes, and structural design. We have developed new TiNxOy thin-film resistors, as well as a termination resistor-embedded CSP, and a process for fabricating integral passive components. Our TiNxOy films exhibit a sheet resistivity in the range of 30-5k Ω/square. To keep costs low, we have made the fabrication process compatible with that for MCM-D/L. Resistors as small as 25 μm square have been successfully produced with this process. The chip scale package (CSP) with embedded resistors has been designed for 10 Gbps optical transmitter and receiver modules. A fabricated version shows excellent return loss for its termination resistor, less than -20 dB in the frequency range of 50 MHz-14 GHz, and its resistors showed high reliability in constant voltage stress tests, with less than 5% change in resistance at 800 mW/mm² over 1000 hours.