Pub Date : 2014-06-03DOI: 10.1109/IWCE.2014.6865812
P. Ellinghaus, M. Nedjalkov, S. Selberherr
The solution of the two-dimensional (2D) Wigner equation has become numerically feasible in recent times, using the Monte Carlo method fortified with the notion of signed particles. The calculation of the Wigner potential (WP) in these 2D simulations consumes a considerable part of the computation time. A reduction of the latter is therefore very desirable, in particular, if self-consistent solutions are pursued, where the WP must be recalculated many times. An algorithm is introduced here - named box discrete Fourier transform (BDFT) - that reduces the computational effort roughly by a factor of five.
{"title":"Efficient calculation of the two-dimensional Wigner potential","authors":"P. Ellinghaus, M. Nedjalkov, S. Selberherr","doi":"10.1109/IWCE.2014.6865812","DOIUrl":"https://doi.org/10.1109/IWCE.2014.6865812","url":null,"abstract":"The solution of the two-dimensional (2D) Wigner equation has become numerically feasible in recent times, using the Monte Carlo method fortified with the notion of signed particles. The calculation of the Wigner potential (WP) in these 2D simulations consumes a considerable part of the computation time. A reduction of the latter is therefore very desirable, in particular, if self-consistent solutions are pursued, where the WP must be recalculated many times. An algorithm is introduced here - named box discrete Fourier transform (BDFT) - that reduces the computational effort roughly by a factor of five.","PeriodicalId":168149,"journal":{"name":"2014 International Workshop on Computational Electronics (IWCE)","volume":"21 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-06-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131662131","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2014-06-03DOI: 10.1109/IWCE.2014.6865862
T. Windbacher, D. Osintsev, A. Makarov, H. Mahmoudi, V. Sverdlov, S. Selberherr
Oscillators belong to the group of fundamental building blocks and are ubiquitous in modern electronics. Especially spin torque nano oscillators are very attractive as cost effective on-chip integrated microwave oscillators, due to their nano-scale size, frequency tunability, broad temperature operation range, and CMOS technology compatibility. Recently, we proposed a micromagnetic structure capable of operating as non-volatile flip flop as well as a spin torque nano oscillator. The structure consists of three anti-ferromagnetically coupled stacks (two for excitation A, B and one for readout Q) and a shared free magnetic layer. Micromagnetic simulations show a current regime, where the structure exhibits large, stable, and tunable in-plane oscillations in the GHz range without the need of an external magnetic field or an oscillating current. In this work the dependence of these oscillations on the shared free layer geometry at a fixed input current is studied. It is shown that the precessional frequency can be controlled by the dimensions of the shared free layer. Most efficient is to utilize the layer thickness to control the precessional frequency, but also changing the layer length can be exploited.
{"title":"Frequency dependence study of a bias field-free nano-scale oscillator","authors":"T. Windbacher, D. Osintsev, A. Makarov, H. Mahmoudi, V. Sverdlov, S. Selberherr","doi":"10.1109/IWCE.2014.6865862","DOIUrl":"https://doi.org/10.1109/IWCE.2014.6865862","url":null,"abstract":"Oscillators belong to the group of fundamental building blocks and are ubiquitous in modern electronics. Especially spin torque nano oscillators are very attractive as cost effective on-chip integrated microwave oscillators, due to their nano-scale size, frequency tunability, broad temperature operation range, and CMOS technology compatibility. Recently, we proposed a micromagnetic structure capable of operating as non-volatile flip flop as well as a spin torque nano oscillator. The structure consists of three anti-ferromagnetically coupled stacks (two for excitation A, B and one for readout Q) and a shared free magnetic layer. Micromagnetic simulations show a current regime, where the structure exhibits large, stable, and tunable in-plane oscillations in the GHz range without the need of an external magnetic field or an oscillating current. In this work the dependence of these oscillations on the shared free layer geometry at a fixed input current is studied. It is shown that the precessional frequency can be controlled by the dimensions of the shared free layer. Most efficient is to utilize the layer thickness to control the precessional frequency, but also changing the layer length can be exploited.","PeriodicalId":168149,"journal":{"name":"2014 International Workshop on Computational Electronics (IWCE)","volume":"39 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-06-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128884803","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2014-06-01DOI: 10.1109/IWCE.2014.6865815
A. Vincent, W. Zhao, Jacques-Olivier Klein, S. Galdin-Retailleau, D. Querlioz
Magnetic Tunnel Junctions (MTJs) - the basic structures of the Spin-Transfer Torque Magnetic RAMs (STT-MRAM) currently reaching the market - present a complex and probabilistic switching behavior. Although some analytical models describing this behavior exist, they can not describe all the switching regimes of the MTJs. They can model low (“subcritical”) and high (“supercritical”) currents, but not the intermediate currents, which are essential for applications. In this work, we present Monte-Carlo simulations of MTJs that have been used to build an analytical model linking the two different current regimes. This model allowed us to perform system-level simulations of an original neuro-inspired chip that uses MTJs as binary stochastic “synapses”.
{"title":"Monte-Carlo Simulations of Magnetic Tunnel Junctions: From physics to application","authors":"A. Vincent, W. Zhao, Jacques-Olivier Klein, S. Galdin-Retailleau, D. Querlioz","doi":"10.1109/IWCE.2014.6865815","DOIUrl":"https://doi.org/10.1109/IWCE.2014.6865815","url":null,"abstract":"Magnetic Tunnel Junctions (MTJs) - the basic structures of the Spin-Transfer Torque Magnetic RAMs (STT-MRAM) currently reaching the market - present a complex and probabilistic switching behavior. Although some analytical models describing this behavior exist, they can not describe all the switching regimes of the MTJs. They can model low (“subcritical”) and high (“supercritical”) currents, but not the intermediate currents, which are essential for applications. In this work, we present Monte-Carlo simulations of MTJs that have been used to build an analytical model linking the two different current regimes. This model allowed us to perform system-level simulations of an original neuro-inspired chip that uses MTJs as binary stochastic “synapses”.","PeriodicalId":168149,"journal":{"name":"2014 International Workshop on Computational Electronics (IWCE)","volume":"23 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128229772","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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