Ultra-Low-Energy Straintronics Using Multiferroic Composites
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Ultra-Low-Energy Straintronics Using Multiferroic Composites Kuntal Roy School of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47907, U.S.A.
ABSTRACT The primary impediment to continued improvement of charge-based electronics is the excessive energy dissipation incurred in switching a bit of information. With suitable choice of materials, devices made of multiferroic composites, i.e., strain-coupled piezoelectric-magnetostrictive heterostructures, dissipate miniscule amount of energy of ~1 attojoule at room-temperature, while switching in sub-nanosecond delay. Apart from devising memory bits, such devices can be also utilized for building logic, so that they can be deemed suitable for computing purposes as well. Here, we first review the current state of the art for building nanoelectronics using multiferroic composites. On a recent development, it is shown that these multiferroic straintronic devices can be also utilized for analog signal processing, with suitable choice of materials. By solving stochastic Landau-Lifshitz-Gilbert equation of magnetization dynamics at roomtemperature, it is shown that we can achieve a voltage gain, i.e., these straintronic devices can act as voltage amplifiers. INTRODUCTION Electric-field induced magnetization switching is a promising mechanism that can harness an energy-efficient binary switch replacing the traditional charge-based transistors for our future information processing systems [1,2]. With suitable choice of materials, when a voltage of few millivolts is applied across a multiferroic composite device, i.e., a magnetostrictive nanomagnet strain-coupled to a piezoelectric layer (see Fig. 1a) [3-5], it strains the piezoelectric layer and the generated strain is transferred to the magnetostrictive layer. Subsequently, a stress anisotropy is developed in the nanomagnet. This voltage-controlled magnetic anisotropy can switch the magnetization of the nanomagnet between its two stable states that store a binary information 0 or 1 [6-8]. This study has opened up a new field named straintronics [1,9,10] and experimental efforts to realize such devices are considerably emerging [11-14]. Although the experimental efforts have demonstrated the induced stress anisotropy in the magnetostrictive nanomagnets, the experimental demonstration of switching delay and utilizing low-thickness (< 25 nm) piezoelectric layers are still under investigation. So far binary switching of the magnetization in magnetostrictive nanomagnets is investigated. While computing and signal processing tasks are indeed shifted to digital domain, sometimes analog signal processing is fundamentally necessary, e.g., processing of natural signals. When a transmitted signal is received at the receiver end, the signal is weak in magnitude and also noisy due to attenuation and noise in the environment. Hence, the signal needs to be amplified and filtered. Then the signal has to be converted to digital domain via analog-to-digital converter. Only thereafter, the signal is ready for proc
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