Integrating Ultra-thin SiGe BiCMOS Power Amplifier Chip in Combination with Flexible Antenna in the Polymer Foil

In this work, a mechanically flexible and high-speed transmitter front-end system is presented as a hybrid System-in-Foil (HySiF) by combining Chip-Film Patch (CFP) technology, a bow-tie dipole antenna, and cost-effective 0.25μm SiGe:C BiCMOS class-A mode power amplifier (PA) in a single compelling field. For the matter of a flexible system, the silicon (Si) chip is thinned down to 38 μm to be embedded into the polymer CFP carrier. For the sake of facilitating the thermal management of the die, an AlSiCu heat spreader is added underneath the thin silicon chip, thereby reducing the predicted temperature rise due to the self -heating loop inside the polymer. The measured gain center frequency of the PA with the ultra-thin silicon substrate shifts about 300 MHz towards higher frequencies due to the eddy current within the AlSiCu plate heat spreader at the backside of the chip. For that purpose, thermal behavior and RF performance of the system w.r.t. the different heat spreader structures are investigated. In addition, the pads of the embedded silicon chip are interconnected to the bow-tie dipole antenna by using a metal layer of AlSiCu through via openings on the foil.