This paper presents an inductive coupling interface using a relay transmission scheme and a low-skew 3D clock distribution network synchronized with an external reference clock source for 3D chip stacking. A relayed transmission scheme using one coil is proposed to reduce the number of coils in a data link. Coupled resonation is utilized for clock and data recovery (CDR) for the first time in the world, resulting in the elimination of a source-synchronous clock link. As a result, the total number of coils required is reduced to one-fifth of the conventional number required, yielding a significant improvement in data rate, layout area, and energy consumption. A low-skew 3D clock distribution network utilizes vertically coupled LC oscillators and horizontally coupled ring oscillators. The proposed frequency-locking and phase-pulling scheme widens the lock range to $pm$ 10%. Two test chips were designed and fabricated in 0.18 $mu$m CMOS. The bandwidth of the proposed interface using relay transmission ThruChip Interface (TCI) is 2.7 Gb/s/mm$^2$; energy consumption per chip is 0.9 pJ/b/chip. Clock skew is less than 18- and 25- ps under a 1.8- and 0.9- V supply. The distributed RMS jitter is smaller than 1.72 ps.