A novel 3D transformer for ultra-compact signal isolation

In this paper, a novel 3D transformer is proposed for simple and ultra-compact signal isolation. The two coils of the 3D transformer are embedded at the backside of the back-to-back stacked and bonded, transmitter and receiver circuit chips individually, and are connected to the front-side circuits of the chips using through-silicon vias (TSV). High isolation capability is provided by the insulation layer between the two stacked chips. The 0.36 mm² 3D transformer designed shows a coil inductance of 110 nH, a voltage gain of larger than -4 dB over a wide bandwidth of 20 MHz to 860 MHz, and an expected isolation capability of over 4kV. Such electrical performance is comparable with prior arts, while the transformer offers a simple and ultra-compact solution for signal isolation.