Publications

Publications

[vc_row][vc_column][vc_tta_accordion style=”flat” c_icon=”” active_section=”1″][vc_tta_section i_icon_fontawesome=”fa fa-bookmark” add_icon=”true” title=”Nonvolatile Memory Based on Nonlinear Magnetoelectric Effects.” tab_id=”1518276211332-38e8cb22-cbed”][vc_column_text]J. Shen, J. Cong, Y. Chai, D. Shang, S. Shen, K. Zhai, Y. Tian, and Y. Sun.

Phys. Rev. Applied 6, 021001 (2016).[/vc_column_text][vc_column_text]The magnetoelectric effects in multiferroics have a great potential in creating next-generation memory devices. We use an alternative concept of nonvolatile memory based, on a type of nonlinear magnetoelectric effects showing a butterfly-shaped hysteresis loop. The principle is to utilize the states of the magnetoelectric coefficient, instead of magnetization, electric polarization, or resistance, to store binary information. Our experiments in a device made of the PMN-PT/Terfenol-D multiferroic heterostructure clearly demonstrate that the sign of the magnetoelectric coefficient can be repeatedly switched between positive and negative by applying electric fields, confirming the feasibility of this principle. This kind of nonvolatile memory has outstanding practical virtues such as simple structure, easy operation in writing and reading, low power, fast speed, and diverse materials available.[/vc_column_text][/vc_tta_section][vc_tta_section i_icon_fontawesome=”fa fa-bookmark” add_icon=”true” title=”A multilevel nonvolatile magnetoelectric memory” tab_id=”1518276909444-4c2f0324-8f64″][vc_column_text]J. Shen, J. Cong, D. Shang, Y. Chai, S. Shen, K. Zhai, and Y. Sun.

Scientific Reports 6, 34473(2016).[/vc_column_text][vc_column_text]The coexistence and coupling between magnetization and electric polarization in multiferroic materials provide extra degrees of freedom for creating next-generation memory devices. A variety of concepts of multiferroic or magnetoelectric memories have been proposed and explored in the past decade. Here we propose a new principle to realize a multilevel nonvolatile memory based on the multiple states of the magnetoelectric coefficient (α) of multiferroics. Because the states of α depends on the relative orientation between magnetization and polarization, one can reach different levels of α by controlling the ratio of up and down ferroelectric domains with external electric fields. Our experiments in a device made of the PMN-PT/Terfenol-D multiferroic heterostructure confirm that the states of α can be well controlled between positive and negative by applying selective electric fields. Consequently, two-level, four-level, and eight-level nonvolatile memory devices are demonstrated at room temperature. This kind of multilevel magnetoelectric memory retains all the advantages of ferroelectric random access memory but overcomes the drawback of destructive reading of polarization. In contrast, the reading of α is nondestructive and highly efficient in a parallel way, with an independent reading coil shared by all the memory cells.[/vc_column_text][/vc_tta_section][vc_tta_section i_icon_fontawesome=”fa fa-bookmark” add_icon=”true” title=”Nonvolatile transtance change random access memory based on magnetoelectric P(VDF-TrFE)/Metglas heterostructures” tab_id=”1518277037031-80df9b74-89ff”][vc_column_text]P. Lu, D. Shang, J. Shen, Y. Chai, C. Yang, K. Zhai, J. Cong, S. Shen and Y. Sun.

Scientific Reports 6, 34473(2016).[/vc_column_text][vc_column_text]Transtance change random access memory (TCRAM) is a type of nonvolatile memory based on the nonlinear magnetoelectric coupling effects of multiferroics. In this work, ferroelectric P(VDF-TrFE) thin films were prepared on Metglas foil substrates by the sol-gel technique to form multiferroicheterostructures. The magnetoelectric voltage coefficient of the heterostructure can be switched reproducibly to different levels between positive and negative values by applying selective electric-field pulses. Compared with bulk multiferroic heterostructures, the polarization switching voltage was reduced to 7 V. Our facile technological approach enables this organic magnetoelectric heterostructure as a promising candidate for the applications in multilevel TCRAM devices.[/vc_column_text][/vc_tta_section][vc_tta_section i_icon_fontawesome=”fa fa-bookmark” add_icon=”true” title=”Nonvolatile Multilevel Memory and Boolean Logic Gates Based on a Single Ni/`{`Pb(Mg1/3Nb2/3)O3`}`0.7`{`PbTiO3`}`0.3/Ni Heterostructure” tab_id=”1518277035809-3ae50b40-20fb”][vc_column_text]J. Shen, D. Shang, Y. Chai, Y. Wang, J. Cong, S. Shen, L. Yan, W. Wang and Y. Sun.

Phys. Rev. Applied 6, 064028 (2016).[/vc_column_text][vc_column_text]Memtranstor that correlates charge and magnetic flux via nonlinear magnetoelectric effects has a great potential in developing next-generation nonvolatile devices. In addition to multilevel nonvolatile memory, we demonstrate here that nonvolatile logic gates such as nor and nand can be implemented in a single memtranstor made of the Ni/PMN−PT/Niheterostructure. After applying two sequent voltage pulses (
X1, X2) as the logic inputs on the memtranstor, the output magnetoelectric voltage can be positive high (logic 1), positive low (logic 0), or negative (logic 0), depending on the levels of X1and X2. The underlying physical mechanism is related to the complete or partial reversal of ferroelectric polarization controlled by inputting selective voltage pulses, which determines the magnitude and sign of the magnetoelectric voltage coefficient. The combined functions of both memory and logic could enable the memtranstor as a promising candidate for future computing systems beyond von Neumann architecture.[/vc_column_text][/vc_tta_section][vc_tta_section i_icon_fontawesome=”fa fa-bookmark” add_icon=”true” title=”Mimicking Synaptic Plasticity and Neural Network Using Memtranstors” tab_id=”1518277031330-f9fc9a13-0594″][vc_column_text]J. Shen, D. Shang, Y. Chai, S. Wang, B. Shen and Y. Sun

Advanced Materials, 2018[/vc_column_text][vc_column_text]Artificial synaptic devices that mimic the functions of biological synapses have drawn enormous interest because of their potential in developing brain-inspired computing. Current studies are focusing on memristive devices in which the change of the conductance state is used to emulate synaptic behaviors. Here, a new type of artificial synaptic devices based on the memtranstor is demonstrated, which is a fundamental circuit memelement in addition to the memristor, memcapacitor, and meminductor. The state of transtance (presented by the magnetoelectric voltage) in memtranstors acting as the synaptic weight can be tuned continuously with a large number of nonvolatile levels by engineering the applied voltage pulses. Synaptic behaviors including the long-term potentiation, long-term depression, and spiking-time-dependent plasticity are implemented in memtranstors made of Ni/0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3/Ni multiferroic heterostructures. Simulations reveal the capability of pattern learning in a memtranstor network. The work elucidates the promise of memtranstors as artificial synaptic devices with low energy consumption.[/vc_column_text][/vc_tta_section][/vc_tta_accordion][/vc_column][/vc_row]