Quantum Transport Simulations Of A Proposed Logic In-Memory Device Based On Bipolar Magnetic Semiconductor

In the conventional Von Neumann architecture,the data transmission between memory and processor will lead to large energy dissipation and consumes most of the execution time.In addition,the access speed of memory cannot match the increasing computing speed of processors.These problems caused by the performance mismatch between memory and processor are called von Neumann bottlenecks.To break the von Neumann bottleneck,a new paradigm known as in-memory computing has been proposed This technology integrates the computing and storage functions.By implementing the calculation process in storage,the time and energy consumptions of data movements between storage and processor are effectively decreased.Bipolar magnetic semiconductors(BMS)have attracted much attention as a new type of spintronic materials.The valence band maximum(VBM)and conduction band minimum(CBM)of BMS possess opposite spin polarization when approaching the Fermi level.Such a unique electronic structure of BMS offers a new route to integrate data storage and computing functions.In this paper,a new type of field-effect transistor(FET)based on bipolar magnetic semiconductor is proposed,its transfer characteristics is verified by quantum transport simulation,and the feasibility as a new type of logic-in-memory device is also verified by circuit design.We firstly took 2H-VS2 and semihydrogenated graphene as example,calculated and verified their band structure.Secondly,we studied the transfer characteristics of the FET based on 2H-VS2 and semihydrogenated graphene by ab initio quantum transport simulations,and then designed the logic circuits.The transfer characteristic of the two FETs presents the "lowhigh-low" and "high-low-high" trends,respectively.When the input gate voltage is ±1.5 V,the spin polarization of the output current can reach more than 90%,which indicates that the device can provide ideal spin polarization signal and can provide two logic signals through a single transistor.With the top and bottom gates of the transistor serving as two inputs,NOR and NAND/OR logic gates can be realized in a single device.We took the 2H-VS2 device as an example,studied the effect of doping concentrations.The results show that the doping concentration should be adjusted properly to get the ideal output signal.The increase of doping concentration will lead to a significant difference in the magnitude of the two polar-ization currents.When adopted n-type doping with the density of 1×1013 e/cm2,the FET shows a minimum ratio of the two spin-polarized currents for about 1.2.With p-type doping or-high density of n-type doping,the ratio will increase and as the result,it is hard to observe two different spin-polarized current.Considering the issues such as the coupling between the top and bottom gates,we further calculated the transfer characteristics of FET with a thicker dielectric under a same equivalent oxide thickness(EOT).We also found that by adjusting the magnetic state of the channel material,the signal of output current will not change and the spin polarization state of the current will reverse.We further designed a circuit that combines two transistors and a spin valve for spin detection.The analysis shows that this circuit can realize the logic-in-memory function.