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This paper reports on the implementation of low-voltage complementary mechanical logic achieved by using body-biased aluminum nitride (AlN) piezoelectric microelectro-mechanical systems (MEMS) switches. By biasing the equivalent body of a four terminal mechanical switch with a fixed voltage, the threshold voltage of the mechanical transistor has been precisely tuned and the voltage swing used for implementing digital functionalities reduced to very low values (≤ ±2 V). Thanks to the use of a mechanical switching mechanism, the AlN MEMS switches have exhibited an extremely low subthreshold slope (0.065 mV/dec), which sets the promise for even further reduction of the voltage swing to less than 100 mV. By using opposite body biases, the same mechanical switch has been made to operate as an equivalent n-like or p-like (complementary) device. Two basic AlN mechanical switch elements have then been used to form a body-biased inverter operating at 100 Hz with a ±1.5-V voltage swing. Furthermore, low voltage and functionally complete logic elements (NAND and NOR) implemented by using body-biased complementary and thin-film (250 nm thick) AlN-based piezoelectric mechanical switches have been synthesized. Finally, scaling rules for these devices are derived, and the key challenges that will need to be addressed to achieve further miniaturization are presented.