CMOS scaling is coming to an end due to limitations such as the increasing leakage current and minimum fabrication sizes achievable. Emerging technologies, that could replace CMOS in next years, are currently under investigation. These technologies will be able to process data at an extremely high operating frequency or with a remarkable reduction of consumed power. The ITRS report summarizes several possible technology solutions, among which carbon nano-tubes and graphene based devices, Quantum-dot Cellular Automata (QCA) and silicon nanowire based nanoarrays. Among these candidates, in this manuscript, the attention is focused on Quantum-dot Cellular Automata, and in particular to the Nano Magnetic Logic(NML) implementation since different studies envisage this technology as a promising alternative to CMOS. The Nano Magnetic Logic working principle is based on the interaction of field-coupled nanomagnets with typical dimension of 60nmx90nm or 50nmx100nm. Information are propagated through chains of these elementary devices according to their ferromagnetic and antiferromagnetic interactions. With this technology, binary information can be encoded in the magnetization verse, indeed, thanks to their very small dimension only two stable states can be recognized: Logic 1 are stored with an up magnetization, while Logic 0 are stored with a down magnetization. The main characteristic of NML are: I) the non-volatility of stored information; II) it is immune to radiation noise and high-energy alpha particles; III) it is an interconnection-free technology; IV) there is the possibility to store logic functions and memory onto the same device and V) it can be easily integrated with CMOS technology. In order to study this technology CAD Tools are needed; this can be useful for architectural explorations and to have terms of comparison with traditional CMOS. The ToPoliNano CAD Tool presented in this manuscript represents the answer to these points, it is able to automatically generate and simulate layouts based on NML starting from and architectural VHDL description. In this scenario, the software implementation of a VHDL parser for the internal representation of circuits represent a key point which makes possible to perform all the operations and the optimizations needed to elaborate the final layout. Another important feature of this instrument is the possibility to verify the correctness of the logical behavior of an NML circuit, for this reason an ad-hoc simulation engine has been developed and validated through a huge number of benchmarks. Thanks to ToPoliNano a thorough study on NML architecture has been made. The main features of ToPoliNano are: I) It is flexible and able to handle different emerging technologies; II) It exploits the same top-down approach of CMOS Tools; III) It is able to generate automatically generate layouts; IV) It allows to verify the correctness of logical NML-based circuits thanks to its specifically tailored simulation engines; V) Since the NML technology is not yet settled we need new techniques to take into account faults derived from the manufacturing process. This thesis focuses therefore on NML logic keeping into account these technology presents also some limitations that can be overcome introducing two other NML implementation: Magneto Tunnel Junctions (MTJ) and perpendicular-NML (pNML) as possible alternative to the traditional in-plane NML (iNML) implementation. Indeed, generally, in iNML circuits, the external fields are made through the use of wires carrying current and placed below the magnetic circuits. This principle has as main drawback, in addition of having high consumption in terms of power, not to allow access to the single cell; in other words, it is not possible to write a particular logical value of a single magnet. This limitation has been overcome by MTJ since cells can be driven through three control signals. In fact, the MJT are often used in combination with the access transistor that allows realizing cycles of read / write of the cells. The third interesting implementation of NML is called perpendicular NML or pNML. The characteristic of this device, with respect to traditional in-plane implementation is the out-of-plane magnetization. In other words, perpendicular NML utilize the perpendicular magnetic anisotropy (PMA); exploiting this principle it is possible to store information depending on the verse of the magnetization. Indeed, exactly like it happened in-plane NML, only two stable states are possible: by convention, the up magnetization is considered as Logic 1 while the down magnetization represents the Logic 0. Here, with respect to the iNML case new features are introduced: I) The switching mechanism is tunable through the manufacturing process; II) The propagation direction of signals is controllable; III) Thanks to its intrinsic prosperities it can be used in 3D structures, exploiting this it is possible to obtain a remarkable area reduction; IV) There is no need of a multiphase clock mechanism to guarantee the information propagation. This unique external magnetic field leads to a remarkable reduction in term of power consumption and a significate simplification in the circuit design process. The methodology followed in this manuscript starts with a technological background of the three NML implementation considered: iNML, pNML and MTJ. Then, for each of them a behavioral model has been developed and then reused to design complex circuits and made architectural explorations. Any limitation identified in the design process has been handled creating specific design rules or trying to overcome them with alternative NML implementations. Moreover, for the iNML technology, a complete design flow has been designed and presented in this manuscript. In particular, the VHDL Parser, the logical (switch level) simulation engine and the LLG-based simulation engine (also with fault analysis tools) will be presented in the following sections.

Nano Magnetic Logic: Modeling, Architectural Explorations and Simulation Tools / Turvani, Giovanna. - (2016). [10.6092/polito/porto/2643157]

Nano Magnetic Logic: Modeling, Architectural Explorations and Simulation Tools

TURVANI, GIOVANNA
2016

Abstract

CMOS scaling is coming to an end due to limitations such as the increasing leakage current and minimum fabrication sizes achievable. Emerging technologies, that could replace CMOS in next years, are currently under investigation. These technologies will be able to process data at an extremely high operating frequency or with a remarkable reduction of consumed power. The ITRS report summarizes several possible technology solutions, among which carbon nano-tubes and graphene based devices, Quantum-dot Cellular Automata (QCA) and silicon nanowire based nanoarrays. Among these candidates, in this manuscript, the attention is focused on Quantum-dot Cellular Automata, and in particular to the Nano Magnetic Logic(NML) implementation since different studies envisage this technology as a promising alternative to CMOS. The Nano Magnetic Logic working principle is based on the interaction of field-coupled nanomagnets with typical dimension of 60nmx90nm or 50nmx100nm. Information are propagated through chains of these elementary devices according to their ferromagnetic and antiferromagnetic interactions. With this technology, binary information can be encoded in the magnetization verse, indeed, thanks to their very small dimension only two stable states can be recognized: Logic 1 are stored with an up magnetization, while Logic 0 are stored with a down magnetization. The main characteristic of NML are: I) the non-volatility of stored information; II) it is immune to radiation noise and high-energy alpha particles; III) it is an interconnection-free technology; IV) there is the possibility to store logic functions and memory onto the same device and V) it can be easily integrated with CMOS technology. In order to study this technology CAD Tools are needed; this can be useful for architectural explorations and to have terms of comparison with traditional CMOS. The ToPoliNano CAD Tool presented in this manuscript represents the answer to these points, it is able to automatically generate and simulate layouts based on NML starting from and architectural VHDL description. In this scenario, the software implementation of a VHDL parser for the internal representation of circuits represent a key point which makes possible to perform all the operations and the optimizations needed to elaborate the final layout. Another important feature of this instrument is the possibility to verify the correctness of the logical behavior of an NML circuit, for this reason an ad-hoc simulation engine has been developed and validated through a huge number of benchmarks. Thanks to ToPoliNano a thorough study on NML architecture has been made. The main features of ToPoliNano are: I) It is flexible and able to handle different emerging technologies; II) It exploits the same top-down approach of CMOS Tools; III) It is able to generate automatically generate layouts; IV) It allows to verify the correctness of logical NML-based circuits thanks to its specifically tailored simulation engines; V) Since the NML technology is not yet settled we need new techniques to take into account faults derived from the manufacturing process. This thesis focuses therefore on NML logic keeping into account these technology presents also some limitations that can be overcome introducing two other NML implementation: Magneto Tunnel Junctions (MTJ) and perpendicular-NML (pNML) as possible alternative to the traditional in-plane NML (iNML) implementation. Indeed, generally, in iNML circuits, the external fields are made through the use of wires carrying current and placed below the magnetic circuits. This principle has as main drawback, in addition of having high consumption in terms of power, not to allow access to the single cell; in other words, it is not possible to write a particular logical value of a single magnet. This limitation has been overcome by MTJ since cells can be driven through three control signals. In fact, the MJT are often used in combination with the access transistor that allows realizing cycles of read / write of the cells. The third interesting implementation of NML is called perpendicular NML or pNML. The characteristic of this device, with respect to traditional in-plane implementation is the out-of-plane magnetization. In other words, perpendicular NML utilize the perpendicular magnetic anisotropy (PMA); exploiting this principle it is possible to store information depending on the verse of the magnetization. Indeed, exactly like it happened in-plane NML, only two stable states are possible: by convention, the up magnetization is considered as Logic 1 while the down magnetization represents the Logic 0. Here, with respect to the iNML case new features are introduced: I) The switching mechanism is tunable through the manufacturing process; II) The propagation direction of signals is controllable; III) Thanks to its intrinsic prosperities it can be used in 3D structures, exploiting this it is possible to obtain a remarkable area reduction; IV) There is no need of a multiphase clock mechanism to guarantee the information propagation. This unique external magnetic field leads to a remarkable reduction in term of power consumption and a significate simplification in the circuit design process. The methodology followed in this manuscript starts with a technological background of the three NML implementation considered: iNML, pNML and MTJ. Then, for each of them a behavioral model has been developed and then reused to design complex circuits and made architectural explorations. Any limitation identified in the design process has been handled creating specific design rules or trying to overcome them with alternative NML implementations. Moreover, for the iNML technology, a complete design flow has been designed and presented in this manuscript. In particular, the VHDL Parser, the logical (switch level) simulation engine and the LLG-based simulation engine (also with fault analysis tools) will be presented in the following sections.
2016
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11583/2643157
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