Low power 3D-IC is well-suited to mobile systems; however, it poses a number of challenges associated with thermal stress, particularly in designs with many stacked layers. The use of a low supply voltage (VDD) and power-down mode help to reduce the power consumption of 3D-ICs, while alleviating aging and thermal effects. These solutions require low-voltage memory and power-down circuitry. Memristor-based logic provides good state retention and restore for power-down operation, and resistive RAM (ReRAM) uses a lower write voltage than conventional Flash memory. This paper reviews design challenges associated with low-voltage SRAM, memristor logic, and ReRAM. We also propose a novel scheme involving homogeneous memory with heterogeneous VDD (HMHV) to further reduce the power consumption of 3D-ICs comprising multiple memory layers.