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Phase-Change Devices and Their Applications
Published in Khurshed Ahmad Shah, Farooq Ahmad Khanday, Nanoscale Electronic Devices and Their Applications, 2020
Khurshed Ahmad Shah, Farooq Ahmad Khanday
The switching of the RRAM cell is based on the growth of CF inside a dielectric. The CF is a channel having a very less diameter of the order of nanometers, which connects the top and the bottom electrodes of the memory cell. A LRS with high conductivity is obtained when the filament is connected and the high resistance state (HRS) results when the filament is disconnected with a gap between the electrodes [68]. Based on the composition of the CF, RRAM can be classified into the following two types: (1) metal ion-based RRAM also referred to as conductive bridge random-access memory (CBRAM) and (2) oxygen vacancies filament-based RRAM referred to as the “OxRRAM.” It must be noted here that CBRAM is also known as the ECM memory, whereas “OxRRAM” is also known as VCM.
Emerging Non-volatile Memories
Published in Shimeng Yu, Semiconductor Memory Devices and Circuits, 2022
RRAM relies on the conductive filamentary formation and rupture mechanism in an insulator thin film between two electrodes and thus is capable of reversible switching between the insulating state and the conducting state. RRAM can be classified into two major classes: (1) oxide RRAM (OxRAM) where the conductive filament consists of oxygen vacancies; (2) conductive bridge RAM (CBRAM) where the conductive filament is made of metallic atoms. Figure 5.25(a) shows the switching mechanism of RRAM. In OxRAM, the oxygen vacancies are created by a soft breakdown under sufficient applied electric field, the oxygen atoms are ionized (i.e., oxygen ions) and migrated toward the top electrode interface (temporarily stored in a reservoir at one metallic capping layer), and thus a conductive filament is formed. Under the reverse electric field, oxygen ions can migrate back to annihilate oxygen vacancies, thus rupturing the filament. In CBRAM, the metallic atoms are ionized from one of the active metal electrodes (e.g., Ag or Cu, or their alloys) by the applied electric field, and migrated into the insulator layer that is typically chalcogenide or oxide, resulting in a metallic filament. Similarly, under the reverse electric field, the ionized metallic atoms could migrate back toward the top interface, thus rupturing the filament. In the following, OxRAM is used as the default type of RRAM for discussions because OxRAM is more popular in industrial demonstrations. Within OxRAM, HfOx, and TaOx have become the dominant oxide materials for prototyping and commercialization.5 ALD is the common fabrication method for oxide thin film deposition.
Nanopore Structures and Their Applications
Published in Klaus D. Sattler, st Century Nanoscience – A Handbook, 2020
There is increasing demand for new nonvolatile forms of memory for use in electronic products and computing technology, as the commonly used flash memory reaches its physical limits.51 One of the strongest candidates to replace flash memory is RRAM, owing to its simplicity, 52 scalability, 53 and fast and low-energy switching3,16, 17. RRAM is usually referred to as a type of memristor that is able to memorize its resistance state based on the history of applied electrical stimulus. 54,55 The structure of RRAM consists of a metal oxide material sandwiched between two conducting electrodes, and it can alternate between a high- and low-resistance state according to the applied voltage and current. Generally, nanoscale conductive filaments (CFs) in oxide-based RRAM are thought to be responsible for this resistance switching; in principle, their formation and dissolution result from the dominance between an electric field and Joule heating.55 Although nanoscale CFs potentially offer a way to overcome the scaling issues that limit the use of flash memory,53,56,57 the randomness of their formation and their tendency to form multiple fragile CFs, instead of a single robust CF, lead to the degradation of device uniformity, switching performance, and device reliability.58–60 Therefore, if they are to be of use in high-performance RRAM, tight control of CFs is required to overcome these problems. In this section, we introduce an example of fast and scalable SiOx memory, based on a conical nanopore structure for control of CFs.
Resistive Random Access Memory: A Review of Device Challenges
Published in IETE Technical Review, 2020
Varshita Gupta, Shagun Kapur, Sneh Saurabh, Anuj Grover
RRAM is based on resistive switching (RS) between two stable states, namely: the high resistance state (HRS) and the low resistance state (LRS). Depending on these states, the device is said to store a bit “1” or a bit “0” [12]. However, multilevel resistive switching for ultra-high-density applications can also be employed in RRAMs. This can be utilized in multibit memories by assigning multiple bits to the different levels of resistance [13–17].
Hafnia-based resistive switching devices for non-volatile memory applications and effects of gamma irradiation on device performance
Published in Radiation Effects and Defects in Solids, 2018
N. Arun, K. Vinod Kumar, A. P. Pathak, D. K. Avasthi, S. V. S. Nageswara Rao
In modern-day memory technology, n-channel metal oxide semiconductor (NMOS) transistor or a floating gate cell is used for storing a single bit. In each of these single transistor fabrication in the industry for many decades, SiO2 has been effectively serving as gate dielectric material (1–2). As the oxide thickness is reducing to its scalable limit, the gate leakage current due to quantum mechanical tunnelling has attained more significance. The required thickness of the gate oxide, SiO2 has reached 1 nm (3), which leads to unacceptable large leakage currents in the different forms of tunnelling from the substrate to the gate electrode (4). Hence, there is a need for an alternative material which can suitably replace and be compatible with the well-established Si technology. In search of material best adoptable to this Si technology, we find high-k dielectrics such Al2O3, HfO2, ZrO2, Y2O3, TiO2, and Ta2O3 are the possible choices (5). Among those, HfO2 has been opted to be Si technology compatible by taking into consideration certain critical material properties. HfO2 has a reasonably high band gap (5.8 eV), high dielectric constant (∼25) and better thermodynamic stability on the surface of silicon (6). In Non-NVM, Resistive Random Access Memory (RRAM) technology has attracted a wide range of potential applications. Hence, it is important to study the new alternate dielectric material, HfO2, as an insulating medium for RRAMs. HfO2 is sandwiched between two metal electrodes to form a simple Metal–Insulator–Metal (MIM) structure. The RRAM has some key notable features such as fast switching (ns), high storage capacity, high retention and endurance, which make it a potential candidate to replace the conventional memory devices (7–9). Radiation damage and reliability studies attain significance as these memory devices will eventually be used in deep space and other radiation environment like nuclear laboratories.
Synthesis and modification of ZnO thin films by energetic ion beams
Published in Radiation Effects and Defects in Solids, 2021
Richa Krishna, Dinesh Chandra Agarwal, Devesh Kumar Avasthi
RRAM has many advantages, such as low-power dissipation, high-speed operation and simple device structure, which make it more suitable for applications in comparison to other non-volatile random access memory. An insulating film or wide ban gap semiconducting layer sandwiched between two metal contacts constitutes a RRAM device.