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Bill Gates

Résumé

William Henry Gates , dit Bill Gates , né le à Seattle (État de Washington) est un informaticien, entrepreneur et milliardaire américain. Il est connu pour être le cofondateur de Microsoft en 1975 et son principal actionnaire jusqu’en 2014. Grâce au succès commercial de l'empire Microsoft, il est l’un des hommes les plus riches du monde depuis 1992. Le magazine Forbes le consacre 18 fois "homme le plus riche de l'année" entre 1994 et 2017. En 2021, malgré sa mise en retrait de la plupart de ses fonctions, Bill Gates reste la de la planète, avec de dollars. Depuis , Bill Gates se consacre à sa fondation Bill-et-Melinda-Gates, qui a pour mission d’améliorer la santé à l’échelle mondiale, entre-autres avec la planification familiale, le développement de l’agriculture et la vaccination. Biographie Les années de formation : 1955-1975 William Henry III "Bill" Gates naît le à Seattle (État de Washington) aux États-Unis, dans une famille aisée de la bourgeoisie amé

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https://fr.wikipedia.org/wiki/Bill_Gates

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Publications associées (47)

Towards room-temperature deterministic ferroelectric control of ferromagnetic thin films

Zhen Huang

The persisting demand of higher computing power and faster information processing keeps pushing scientists and engineers to explore novel materials and device structures. Within emerging functional materials, there is a focus on multiferroics materials and material-systems possessing both ferroelectric and ferromagnetic orders. Multiferroics with two order parameters coupled through a magnetoelectric interaction are of particular interest for novel information processing technologies. This thesis explores a promising concept of magnetoelectric multiferroic heterostructure incorporating separate ferroelectric and ferromagnetic thin layers with field-effect-mediated coupling through the heterointerface. The major issues related to ferroelectric control of ferromagnetism in multiferroic heterostructures addressed in this thesis include non-volatile magnetoelectric coupling at room temperature, deterministic switching of magnetization via polarization reversal, ferroelectric control of dynamics of magnetic domains and integration of ferroelectric gates on magnetic channels. The major accomplishments of this thesis are the following: Non-volatile ferroelectric control of magnetic properties has been demonstrated in ultra-thin Co layers at room temperature. The ferromagnetic transition Curie temperature, magnetic anisotropy energy and magnetic coercivity are shown to be switchable via the persistent field effect associated with the ferroelectric polarization. The magnitude of the effect is comparable or exceeds the results observed using the conventional (non-ferroelectric) gates. Local control of individual magnetic domain nucleation and propagation in Co channels by creating new ferroelectric domains has been achieved at the ambient conditions. The microscopic ferroelectric domains written on poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] ferroelectric polymer gate projected onto the magnetic channel changing locally the magnetic anisotropy energy, and consequently altering magnetic domain dynamics. Therefore it was possible to promote/impede magnetic domain nucleation and significantly change the domain wall velocity using a non-destructive and reversible procedure of ferroelectric domain writing. Non-volatile control of anisotropic magnetoresistance (AMR) has been demonstrated on diluted magnetic semiconductor (Ga,Mn)(As,P) thin films with integrated P(VDF-TrFE) ferroelectric gate. The field effect induced by the ferroelectric gate has shown the capability to strongly modulate the AMR behavior. Profound qualitative changes of the nature of AMR has been observed, including complete on/off switching of the crystalline component of AMR in (Ga,Mn)(As,P). A workflow for fabrication of integrated FET-type structures comprising a magnetic metal or semiconductor magnetic channel and ferroelectric polymer gate has been successfully developed. Different approaches for enhancement of ferroelectric gate operation were explored including integration of highly resistive hydrophobic interfacial layer and change of polymer composition for lower leakage. A significant increase of the non-volatile gate effect magnitude compared to the state of art was reached via improved quality of the ferroelectric/ferromagnetic interface.

EPFL2015

Chargement

, , , , , ,

Soft-switching power converters based on wide-band-gap (WBG) transistors offer superior efficiency and power density advantages. However, at high frequencies, loss behavior varies significantly between different WBG technologies. This includes losses related to conduction and dynamic ON-resistance (R

_{DS(ON)}

) degradation, also charging/discharging of input capacitance (C

_ISS

) and output capacitance (C

_OSS

). As datasheets lack such important information, we present measurement techniques and evaluation methods for soft-switching losses in WBG transistors which enable a detailed loss-breakdown analysis. We estimate the gate loss under soft-switching conditions using a simple small-signal measurement. Next, we use Sawyer-Tower (ST) and Nonlinear Resonance (NR) methods to measure large-signal C

_OSS

energy losses up to 40 MHz. Finally, we investigate the dependence of dynamic R

_{DS(ON)}

degradation on OFF-state voltage using pulsed-IV measurements. We demonstrate an insightful comparison of soft-switching losses for various normally-OFF Gallium-Nitride (GaN) and Silicon-Carbide (SiC) devices. A p-GaN-gated device exhibits the most severe R

_{DS(ON)}

degradation and the lowest gate loss. Cascode arrangement increases threshold voltage for GaN devices and reduces gate losses in SiC transistors; however, it leads to higher C

_OSS

losses. The study facilitates the evaluation of system losses and selection of efficient WBG devices based on the trade-offs between various sources of losses at high frequencies.

2020

Chargement

Active-Device Losses in Resonant Power Converters: A Case Study with Class-E Inverters

Jessy Anthony Ançay, Armin Jafari, Elison de Nazareth Matioli, Palliyage Srilak Nirmana Perera, Remco Franciscus Peter van Erp

Recent research has reported an undesirable OFF-state loss in high-frequency soft-switching power converters, such as resonant converters. This loss is attributed to a hysteresis loss related to the charging-discharging process of the output capacitance of the power transistor. However, precise estimation of transistor power loss and its breakdown into ON-state and OFF-state losses is challenging in the MHz-range operation due to the small circuit size, parasitic effects, and limited accuracy in existing methods to measure low-loss systems. We present a measurement concept to perform a complete loss breakdown of MHz-range resonant converters, as well, directly determine the OFF-state losses in transistors, which is demonstrated for a GaN-based class-E inverter operating at 10 MHz. A novel and compact calorimeter was designed to measure the converter active-device losses down to 20 mW within a 5% error. This measured loss is then separated into four components using a combination of average and instantaneous electrical measurements: transistor ON-state loss, transistor OFF-state loss, gate-driver internal loss and gate loss. A simple no-load technique was devised to evaluate the gate-driver internal loss. The proposed approach directly determines output-capacitance hysteresis losses during the actual converter operation, which is not possible with existing measurement methods. The presented knowledge of individual loss components permits better optimization of MHz-range power converters.

IEEE2021

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, , , , , ,

_{DS(ON)}

) degradation, also charging/discharging of input capacitance (C

_ISS

) and output capacitance (C

_OSS

_OSS

energy losses up to 40 MHz. Finally, we investigate the dependence of dynamic R

_{DS(ON)}

_{DS(ON)}

degradation and the lowest gate loss. Cascode arrangement increases threshold voltage for GaN devices and reduces gate losses in SiC transistors; however, it leads to higher C

_OSS

losses. The study facilitates the evaluation of system losses and selection of efficient WBG devices based on the trade-offs between various sources of losses at high frequencies.

2020

Towards room-temperature deterministic ferroelectric control of ferromagnetic thin films

Zhen Huang

EPFL2015