Information Functional Devices Based On Magnetoelectric Heterostructures

In recent years,with the rapid development of information technology,it is particularly important to improve the efficiency of information transmission and processing.The new types of information device have gradually become a hot topic of research,such as a universal memory,with characteristics of non-volatility,high read/write speed,high density,huge endurance,low power consumption,inexpensiveness and low voltage.In addition,the human brain has the advantages of ultra-high density,low energy consumption,parallel mode,anti-jamming ability,adaptive learning and high fault tolerance,and it is a new way for improving computing efficiency by developing brain-like synaptic devices.Recently,with the construction of transtor(the fourth fundamental circuit element)based on the magnetoelectric(ME)effects,its corresponding memelement-the memtranstor has attracted increasing interest.Memtranstor can be made by composite or single phase multiferroic materials,and it has the advantages of simple structure,and extensive selection of materials.In this thesis,we have prepared several memtranstors using ME composites,and studied the information devices based on these memtranstors.The main research results are summarized as the following:1. The flexible nonvolatile multilevel memory and the artificial synaptic device based on the Cu/P(VDF-TrFE)/Ni organic memtranstor are studied.The binary information is encoded by the states of the ME voltage coefficient of the memtranstor.Under zero dc bias magnetic field,the states of the ME voltage coefficient can be changed repeatedly among 2~n states by applying suitable electric field pulses,demonstrating the multilevel nonvolatile memory.The synaptic behaviors have been mimicked based on this flexible memtranstor under zero dc bias magnetic field at room temperature.This type of organic memtranstor has the advantages of simple structure,flexibility,energy efficiency of writing operation and nondestructive reading operation.2. The nonvolatile multilevel memory based on the Metglas/PMN-PT/Metglas memtranstor is studied.Under 5 Oe dc bias magnetic field,the electric polarization P of the ferroelectric layer PMN-PT is set to either fully upward or downward by electric pulses,and the ME voltage coefficient are switched between positive and negative two states to encode binary information.The repeatable four and eight stable states of the ME voltage coefficient can be achieved by applying selected electric pulses,demonstrating a nonvolatile multilevel memory.3. The artificial synaptic device based on the Metglas/PMN-PT/Metglas memtranstor is studied.Under 15 Oe dc bias magnetic field,the ME voltage of the memtranstor can be tuned step by step by a series of electric field pulses to mimic the functions of synapse.The ME voltage coefficient is regarded as synaptic weight,the ME voltage is regarded as excitatory or inhibitory postsynaptic potentials,and electric voltage pulses are regarded as action potentials.The long-term potential(depression)and spiking-timing-dependent plasticity behaviors have been emulated based on the Metglas/PMN-PT/Metglas memtranstor.