We present an ultra-low quiescent current power management integrated circuit (IC) for interfacing with a piezoelectric (PZE) energy harvester in a self-powering wireless sensor node. The PZE harvester first transforms mechanical energy from vibration into electricity. The AC output from the PZE is then converted into DC power using a full bridge rectifier, and charges a small filter capacitor. The energy is further transferred into a supercapacitor by a Buck-Boost converter with high efficiency, using an impedance matching load to achieve maximum power point tracking (MPPT). A low-dropout (LDO) regulator powers the on-chip CMOS sensor and an external RF transmitter with the energy stored in the super capacitor, providing clean power supply, forming a complete wireless temperature sensor node, which can enable Internet-of-Things (IoT) sensor networks. The circuit is taped out using a 0.5 μm standard CMOS process. Measurements confirm all key features of this design: (i) up to 96% voltage converting efficiency of the rectifier; (ii) a minimum of 102 s charging time to charge a 1 mF supercapacitor from 0 V to 3.3 V of the Buck-Boost converter with impedance matching method; (iii) a 0 nA to 100 μA load current range and at least 85° phase margin (PM) LDO regulator with an ultra-low quiescent current as low as 750 pA.