We discuss non-volatile memories (NVM) for space applications. The focus will be both on technologies and devices aimed at the mainstream commercial markets and on rad-hard devices. Commercial NVMs are very attractive for space designers due to their large size (tens of Gbits), even though they have several issues related to ionizing radiation. Rad-hard NVMs offer radiation hardness, but are available only in small size (few Mbits). Most of the emphasis in this review paper will be on the current dominant technology in the mainstream market: floating gate flash memories. A comprehensive discussion of total dose and single event effects results for a wide cross section of NVMs will be presented. Finally, we will conclude with a cursory glance at other emerging non-volatile technologies.Index Terms-Ferroelectric devices, flash memory, magnetoresistive devices, nonvolatile memory, phase change memory, radiation effects.
I. OVERVIEWN ON-VOLATILE memories (NVMs) are used in a variety of space applications, as data or code memories, and are increasingly needed for future missions. This paper will discuss the technologies and devices available for non-volatile storage in the mainstream and in the rad-hard market, with a strong attention to the radiation sensitivity, which is of primary importance for harsh environments such as space.The work is organized as follows: we will first introduce the basic definitions and metrics concerning NVMs, then explore and compare the major storage concepts. In particular, charge-based, phase-change, ferroelectric, and magnetoresistive memories will be presented, with emphasis on density, performance, reliability, and radiation sensitivity. Architectural information concerning the array organization and peripheral circuitry will be given, highlighting known radiation issues and critical building blocks.
A. Key Definitions and MetricsA non-volatile memory is a memory that retains information when powered off. Different terms are used to indicate the act of storing a digital value in a non-volatile memory bit, depending on the memory type and architecture. In charge-based storage, the terms program and erase are used to indicate the injection of Manuscript negative charge into and its removal from (or injection of positive charge into) the charge storage element, respectively. In the context of phase change memories, the terms set and reset are used to indicate the operations leading to the crystallization and amorphization of the phase-change material. For other memories, such as ferroelectric or magnetic, the term write is simply used, as for SRAMs and DRAMs. The association of these operations and terms with the stored digital value ("0" or "1") is arbitrary. In the following we will stick to the conventions most commonly used for each memory type.In addition to familiar parameters such as speed, power consumption, and density, two additional metrics are of main importance for non-volatile memories: retention and endurance. This is because wear-out is usually much stronger in non-volat...
