Research On Spin-Orbit Torque Based Logic Operations And Physically Unclonable Function Devices In IrMn/Co/Ru/CoPt Heterojunctions

With the fast development of new applications such as the Internet of Things and cloud computing,data is exploding in information age.The information age not only brings convenience to our life,but also has a more urgent demand for the ability to process massive amounts of information.With the discovery and research of electron spin in recent decades,making full use of the endogenous property of electron spin,the combination of both spintronics with low power consumption and non-volatile properties and traditional integrated circuits is expected to solve the current von Neumann bottleneck,and further improve the information storage density and information processing speed.In recent years,the researchers have made many efforts in Spin-Orbit Torque(SOT)-based Magnetic Random Access Memory(MRAM).SOT-MRAM has the potential to become the next generation of MRAM,especially because of its ultrafast response speed,low power consumption,and non-volatility.Compared to SpinTransfer Torque(STT)MRAM,SOT-MRAM has much better endurance and reliability due to the separation of read and write channels.In addition,SOT-based devices have good antiradiation properties and can be compatible with Complementary Metal Oxide Semiconductor(CMOS),hence,they have prosming applications in areas such as in-memory computing,Neuromorphic Computing devices,microwave detection,and sensors.The studies of SOT switching and its applications in multifunctional devices not only contribute to our understanding of the rich physical mechanisms,but also provide an excellent way to manipulate magnetic moments for the development of novel multifunctional spintronics devices,which are of great practical importance for future magnetic information storage and processing technologies.To achieve deterministic SOT-driven perpendicular magnetization switching,an exteranl magnetic field needs to be applied along the current direction to break the symmetry of the system.However,the presence of an external magnetic field may complicate the design of the device,which needs to be overcomed.In order to achieve magnetic field-free deterministic perpendicular magnetization switching,researchers have explored various methods,including the utilization of in-plane exchange bias field,interlayer exchange coupling,wedged structure,titled anisotropy,spin current manipulation,multiple symmetry broken,and Neel chiral symmetry breaking.Meanwhile,spin logics based on SOT-driven switching have shown their potential to build logic-in-memory architectures with low power consumption,high programmability and fast computational speed.However,the switching polarity(clockwise or counterclockwise)of the SOT induced magnetization switching is usually difficult to be reversibly controlled by external manners.Though remarkable progress has been made in the SOT switching and SOT-based spin logic,including magnetic-field-free magnetization switching,and reconfigurable spin logic under the application of magnetic field and electrical field,complete spin logic within a single nonvolatile memory device by the purely electrical controllable SOT switching has not been realized yet.And it remains a great challenge to achieve flexible manipulation of the multifunctional spintronic devices.In this thesis,we mainly focus on the SOT-driven perpendicular magnetization switching and its logic operations and hardware encryption applications.We have performed researches in the following three areas.1.Controllable spin-orbit torque induced perpendicular magnetization switching in Co/Ru/CoPt heterojunctionsBased on a perpendicularly magnetized CoPt alloy with a composition gradient in the thickness direction,we have prepared Co/Ru/CoPt and IrMn/Co/Ru/CoPt heterostructures,and realized controllable perpendicular magnetization switching based on spin-orbit torque.In two types of magnetic heterostructures,the lower Co layer has in-plane magnetic anisotropy,which provides an in-plane auxiliary magnetic field to the CoPt layer through the Ruderman-KittelKasuya-Yosida(RKKY)interlayer exchange coupling of the Ru layer,enabling field-free spinorbit torque induced perpendicular magnetization switching of CoPt sublayer.It is observed that the direction of the effective field acting on the CoPt layer can be changed by changing the direction of the magnetic moment of the Co layer,thus realizing the control of the CoPt layer reversal polarity(clockwise or counterclockwise).In Co/Ru/CoPt heterojunction,the Co layer magnetic moment can be regulated by the applied magnetic field.And in IrMn/Co/Ru/CoPt heterojunction,the direction of the Co layer magnetic moment can be reversed by the joint effect of the current and the applied magnetic field.The magneto-optical Kerr microscopy measurements in IrMn/Co/Ru/CoPt heterojunction indicate that under the joint effect of magnetic field and current,the positive and negative currents play an almost identical role to the shift of the hysteresis loops,which can exclude the effect of current-generated SOT on the influence of domain wall motion.Meanwhile,we used Superconducting Quantumn Interference Device to measure the hysteresis loops at different temperatures,and investigated the effect of Joule heating on the magnetic moment.It has been demonstrated that the uncompensated magnetic moment at the IrMn/Co interface is disturbed or even reversed under the combined effect of current-generated Joule heating and the applied magnetic field,thereby regulating the exchange bias field and the direction of the Co magnetization.The IrMn/Co/Ru/CoPt heterostructure can be directly used as a basic unit in traditional magnetic tunnel junctions and magnetic spin valves,and the field-free switching and controllable switching polarity provide more freedom for the flexible design of functional memory and logic devices.2.Purely electrical controllable complete spin logic in a single Pt/IrMn/Co/Ru/CoPt magnetic heterojunctionWe prepared Pt/IrMn/Co/Ru/CoPt magnetic heterojunction by using magnetron sputtering,and realized all 16 Boolean logic functions in a single heterojunction.The CoPt alloy has perpendicular magnetic anisotropy,and the Co layer has in-plane magnetic anisotropy.The two magnetic layers are antiferromagnetically coupled to each other through the RKKY effect of a 0.8 nm Ru layer,with a coupling field of 400 Oe.The underlying 5 nm Pt layer can provide additional current paths.We realized all 16 Boolean logic functions in a single Pt/IrMn/Co/Ru/CoPt heterojunction by using four input currents as logic inputs and anomalous Hall voltages as logic outputs.The detailed experimental process is given in the following.First,the CoPt layer switching polarity is regulated by controlling the applied initial current IA along the y-direction.And then,the initial current IB is applied along the x-direction to regulate the initial state of the CoPt magnetization.Finally,two input currents(IC+ID)are simulatneoulsy applied along the x-direction to selectively switch the CoPt magnetization.By controlling the above four input currents(IA,IB,IC,and ID),the magnetization direction of both Co and CoPt sublayers can be manipulated.The realization of fully electrical controllable complete spin logic in a single nonvolatile memory opens a gateway toward practical programmable spinlogic devices.3.Purely electrical controllable spin-orbit torque-based reconfigurable physically unclonable functions in Pt/IrMn/Co/Ru/CoPt heterojunctionsWe have prepared 60 Pt/IrMn/Co/Ru/CoPt magnetic heterojunctions,the reconfigurable physically unclonable function(rPUF)device with relatively good uniqueness and low bit error rate is achieved by taking advantages of the sample growth and micronanofabrication induced variations in coercive fields.By applying orthogonal current pulses along x-and y-axes,the magnetic moment orientations of both in-plane Co layer and the perpendicular CoPt layer in Pt/IrMn/Co/Ru/CoPt magnetic heterojunctions can be controlled.Each heterojunction can be manipulated into four different magnetic configurations.Meanwhile,by using different critical switching current of SOT-driven magnetization switching,we realize random arrangement of the magnetic moment orientation in the the device(60 Hall bars=6 heterojunctions × 10 units)under a setting current of ±15 mA.As a result,four types of PUF device are obtained by comparison method.Moreover,these four types rPUF devices can be transformed into each other by purely electrically controllable way based on spin-orbit torque.Considering the fast development of information security area,the realization of fully electrical controllable rPUF with good stability and reconfigurability provides a promising approach to hardware information security and broadens the potential applications aspects of spintronics.