  Solid-state memory is an essential component of the digital age. With
advancements in healthcare technology and the Internet of Things (IoT), the
demand for ultra-dense, ultra-low-power memory is increasing. In this review,
we present a comprehensive perspective on the most notable approaches to the
fabrication of physically flexible memory devices. With the future goal of
replacing traditional mechanical hard disks with solid-state storage devices, a
fully flexible electronic system will need two basic devices: transistors and
nonvolatile memory. Transistors are used for logic operations and gating memory
arrays, while nonvolatile memory (NVM) devices are required for storing
information in the main memory and cache storage. Since the highest density of
transistors and storage structures is manifested in memories, the focus of this
review is flexible NVM. Flexible NVM components are discussed in terms of their
functionality, performance metrics, and reliability aspects, all of which are
critical components for NVM technology to be part of mainstream consumer
electronics, IoT, and advanced healthcare devices. Finally, flexible NVMs are
benchmarked and future prospects are provided.
