The Sputtering Deposition And Micro And Nano Fabrication Of CoFeB/MgO/CoFeB Magnetic Tunnel Junctions

As we all know,electrons have two indispensable degrees of freedom:charge and spin.In traditional microelectronics,people focus only on the electrical charge characteristics,but ignore the spin property of electrons.The electronic transport process is controlled by the electric field,and it has promoted the development of traditional microelectronics such as electronic technology and information technology.With the improvement of science and technology,the dimensions of the device gradually developed to submicron/nanometer scale,therefore,researchers seek to exploit the spin feature of the electron to extend the new functions of the device,and then,it lead to a new discipline:spintronics.Spintronics uses both the charge and spin properties of electrons to develop new spintronics devices.Compared with traditional microelectronic devices,it has the advantages of high speed,high integration and low power consumption.Today,the technology based on the production,manipulation and detection of spin-current is gradually mature,more and more spintronics devices enter people's vision,such as non-volatile magnetic random access memory,magnetic sensor and ultra-high density storage magnetic head,etc.New type of multi-functional spin logic devices using electronic charge and spin of dual attribute,greatly improving the information processing speed and transmission density,reduce loss,from a revolutionary technology enables people to get huge gains.In 1988,German scientist Peter Gurunberg and Albert Fert,a French scientist,independently discovered the GMR effect in the Fe/Cr metal multilayer film,making the magnetic recording technology leap forward.The discovery of the GMR effect is not only a milestone in the history of spintronics,but also the Nobel Prize for physics in 2007.Since then,research and application based on magneto-resistance have aroused the enthusiasm of people around the world.Among them,the most important application of the GMR effect is in hard disk drive.In 1997 IBM produced the first readout head based on the GMR effect and then in 2001 the HDD based on TMR head was produced by TDK company.In order to meet the requirement of high density information storage,many magnetic materials with large coercivity is applied to the hard disk.While the limited read head magnetic moment cannot smoothly switch the direction of magnetization of storage unit.In the face of this dilemma,many new kinds of magnetic recording technologies are introduced to improve the storage density and microwave assisted magnetic recording is one of them.The principle of this technology is to use the spin transfer torque(STT)effect within magnetic tunnel junctions,under some kind of specific conditions,to realize stable precession of magnetic moment of the free layer and then generate the high-frequency microwave signal.Most importantly,the device to generate high frequency microwave is the spin transfer torque nano-oscillator.The main work of this paper focuses on the deposition and fabrication of the CoFeB/MgO/CoFeB magnetic tunnel junction,which is used in the spin nano-microwave oscillator.The quality of the magnetic tunnel junction is mainly reflected by the measured TMR ratio.We used magnetron sputtering method to sputter the multilayer in the 8-target sputter of 5x10-6 Pa in the background vacuum.We have designed a set of complete micro processing technology,mainly by using the method of ultraviolet photolithography and argon ion milling.48 magnetic tunnel junctions can be made after the entire flow on a 2.5cm*2.5cm silicon substrate.The total 8 targets in the sputtering chamber are two-inch trgets and they are placed in a circular space.Because MgO layer's quality is especially important in the magnetic tunnel junction,we change the new 3-inch MgO target to replace the original 2-inch MgO target in the middle time of this work.After adjusting the whole design and the structure of the sample,as well as the growth conditions and annealing conditions optimization,the TMR ratio increased from 9%to 52%.This is the maximum TMR ratio we've measured so far.