 The paper introduces mem resonators, non-volatile silicon photonic phase shifters with retention times of 12 hours, switching voltages lower than 5V, and an endurance of 1,000 switching cycles, which can be switched using 300 PS long voltage pulses with a record low switching energy of 0.15 pj. These mem resonators are fabricated on a heterogeneous 3V on-site platform capable of integrating a rich family of active and passive optoelectronic devices directly on chip to enable in-memory photonic computing and further advance the scalability of integrated photonic processors. This article was authored by Basin Tosun, Di Liang, Stanley Chung, and others.