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This book introduces readers to the latest advances in sensing technology for a broad range of non-volatile memories (NVMs). Challenges across the memory technologies are highlighted and their solutions in mature technology are discussed, enabling innovation of sensing technologies for future NVMs. Coverage includes sensing techniques ranging from well-established NVMs such as hard disk, flash, Magnetic RAM (MRAM) to emerging NVMs such as ReRAM, STTRAM, FeRAM and Domain Wall Memory will be covered.



Chapter 1. Sensing of Spintronic Memories

Leakage power increase due to technology scaling has attracted a lot of attention to developing nonvolatile memory (NVM) technologies. Among the explored NVM candidates by the community, spintronic-based technologies such as magnetic RAM and spin-transfer torque RAM seem to be very promising. Conventionally, the main challenge of employing MRAMs as a possible candidate in universal memories is high power dissipation and long delay during write operation. However, in recent cutting-edge semiconductor technologies, the issue moves from write to read operation mainly due to significant suppression in read margin. Degradation in the read yield emerges from the increase in process variation and lowering of the supply voltage. Therefore, numerous research activities have been recently conducted to improve the read margin. This chapter reviews the sensing techniques, which have been developed to deal with the read margin degradation of MRAMs in scaled technology nodes. In addition, the chapter provides a background on different writing methods of MRAMs and possible solutions to improve the density of bit-cells.
Behzad Zeinali, Farshad Moradi

Chapter 2. Sensing of Resistive RAM

Resistive random-access memory (ReRAM) is a promising non-volatile memory with the configurability of resistance programmed by pulse voltage or current. ReRAM can be used for memory and computation. In this chapter, we will start with these applications and design components for ReRAM. As the sensing schemes dominate the performance, the ReRAM sensing designs in storage and processing-in-memory (PIM) applications will be explained in detail.
Qing Yang, Bonan Yan, Hai Li

Chapter 3. Sensing in Ferroelectric Memories and Flip-Flops

Ferroelectric (FE) materials, by virtue of their polarization retention in the absence of the electric field, offer a unique method to introduce non-volatility in memories and logic. The exploration of FE materials in context of their application in compute and storage has been carried out in two forms: (1) as capacitors, in which the FE material is sandwiched between two metal layers and (2) in ferroelectric transistors (FEFETs), in which, FE is integrated into the gate stack of FETs. Both the devices have been explored to design non-volatile memories and flip-flops. The commonality between the two technologies is that they use remnant polarization in the FE to define the binary logic states. However, the sensing as well as the switching of the polarization requires considerably different techniques for FE capacitors and transistors. Moreover, the requirements of the application (memory, flip-flop, etc.) also dictate the methodology for reading or writing the logic state. This chapter discusses the device–circuit aspects of FE capacitors and FEFETs in the context of non-volatile memory and logic design, with a focus on the sensing techniques. We present a comparative description of the two technologies, highlighting the pros and cons of each and how different device structures yield significantly different sensing strategy.
Ahmedullah Aziz, Sandeep Krishna Thirumala, Danni Wang, Sumitha George, Xueqing Li, Suman Datta, Vijaykrishnan Narayanan, Sumeet Kumar Gupta

Chapter 4. Sensing of Phase-Change Memory

PCM is an emerging non-volatile memory that offers high integration density and high endurance. The speed of PCM is comparable to DRAM. However, PCM sense operation incurs issues due to the resistance drifting phenomenon, high sensing time, sense time variation from cell to cell, etc. Therefore, conventional sensing techniques need to be modified. In this chapter, we describe these issues along with the basics of PCM cell design and PCM read/write operation. We also summarized state-of-the-art PCM-specific sensing schemes proposed to address different PCM-sensing issues.
Mohammad Nasim Imtiaz Khan, Alexander Jones, Rashmi Jha, Swaroop Ghosh


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