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The low-power/high-speed performance of current-mode logic (CML) D flip-flops based on negative-differential-resistance (NDR) devices is presented. The device count used in the fabricated circuit has been significantly reduced by using the NDR-based D flip-flop topology, leading to enhanced low-power/high-speed performance. The operation of the fabricated NDR-based CML D flip-flop has been confirmed to 36 Gb/s, which is the highest speed among NDR-based differential-mode D flip-flops reported to date. The power consumption of the D flip-flop core circuit was measured to be as low as 20 mW at a power supply voltage of -3.3 V. In addition, a power-delay product of 0.55 pJ has been obtained from the NDR-based CML D flip- flop, which is the lowest value to the authors' knowledge among the previously reported D flip- flops up to operation speeds in the region of 40 Gb/s.