Silicon-based Spin Injection Devices And Their Interface Characteristics

The development of silicon-based spintronic devices is one of the hot topics in the semiconductor spintronics application field today. This paper was mainly about developing three-terminal devices for silicon spin injections, and was focused on the preparation of the magnetic tunnel junction of NiFe/HfO₂/Si as well as its interface characteristics. In addition, to gain experience for the development of spin transistor, the research on preparation and electrical characteristics of Ge pMOSFET devices were also carried.（I） The research on the preparation and characteristics of Ni Fe films as magnetic electrodes for silicon spin injection apllications:1. The n-type Si（100） wafers with a doping concentration of 1019 cm-3 were used for the substrates, and NiFe films with different thickness were prepared by using magnetron sputtering deposition, and then some samples were treatment by annealing processes. Systematic studied on the in-plane and out-plane of magnetic anisotropy for the NiFe films with different film thicknesses, as well as the influences of different annealing conditions on their magnetic properties. The results showed that the thickness of NiFe films shall be controlled within 30 nm to meat the requirement of silicon-based spin injections, and the annealing temperature was suggestted to be better at 250 ℃.2. In order to prevent the Ni, Fe of NiFe films spreading into the Si substrate, as well as to form a tunnel junction, the HfO₂ film with thickness of 2 nm was inserted between the NiFe and Si to form NiFe/HfO₂/Si tunnel junction, and then it was annealed. The magnetic properties of the samples were studied, and the analysis of components, chemical bonding and diffusion of the NiFe were also carried by using the XPS measurement, and the results showed that the introduction of the HfO₂ thin layer can restrain the Ni, Fe spread into Si, making the saturation magnetization of Al（22 nm）/NiFe（28 nm）/HfO₂（2 nm）/Si samples increased by about 80% after annealing at 250 ℃, which was advantageous to the silicon-based spin injections.3. Some exploration were taken on the preparation of CoFe films.（II） Preparation, interface and electrical characteristics of about HfO₂ ultrathin films for dielectric layers grown on silicon:1. The HfO₂ ultrathin films with thicknesses range from 0 to 5 nm deposited on high concentration doped n-type Si substrate were prepared both by using atomic layer deposition（ALD） and electron beam evaporation（E-beam） processes, the XPS analysis of depth profile were taken for the analysis of the components, chemical bonding and diffusion of HfO₂ deposited directly on the Silicon substrates, and the results show that the ALD growth of HfO₂ film showed smaller roughness, of about 0.10 nm, and the surface layer was in line with the chemical formula, which was probably suit for the silicon spin injection;2. The I-V characteristics of Metal/HfO₂/n+-Si contacts to the different preparation methods of HfO₂ thickness（E-beam 0-5 nm, ALD 0-2.5 nm） were studied, and the preparation methods of the HfO₂ thin film as tunneling layer for silicon-based spin injections were optimized.3. Studied the I-V characteristics for the NiFe/HfO₂（0-2 nm）/p-Si contacts, and discussed the mechanism about the modulation of the effective schottky barrier height of NiFe/Si by the inserted HfO₂ layer, preparing for the future to spin injection into Si with lower doping concentrations.（III） The development of silicon-based three-terminal devices for spin injections and their performance measurement and analysis:1. According to the technological process based on the results of the two chapters above, the NiFe/HfO₂/Si three-terminal devices for spin injections were prepared, and the NiFe/Al₂O₃/Si devices were also prepared for comparison, and both of the two kinds of samples were treatment by annealing processes, and then the I-V characteristics and Hanle curve mesurements were carried. Results showed that the resistance of the NiFe/HfO₂/Si device was very large to over 2 MW under temperature of 10 K, which was much bigger than NiFe/Al₂O₃/Si device for 2 3 orders of magnitude. After annealing, the resistance of the NiFe/HfO₂/Si device dropped to 0.2 MW under temperature of 10 K, and it is conducive to Hanle curve measurement. The signal feature of Hanle curve measurement for the NiFe/HfO₂/Si device wasn’t deteced until it was annealled under 250℃ for 30 min, and from which we extracted the average life of spin polarization to about 256 ps, and spin diffusion length to about 264 nm, as well as the calculation of spin polarization that injected into Si, which was about 0.85%.2. It was more easier to get the signal feature of Hanle curve measurement for NiFe/Al₂O₃/Si devices, and both of theirs average life of spin polarization and spin diffusion length were slightly larger than the NiFe/HfO₂/Si device’s, except for the spin polarization, which was relatively lower before annealing of only about 0.11%, and it was improved after annealing to about 0.48%.（IV） Study on Ge pMOSFET with schottky source and leakage1. Using an n-type Ge with lower doping concentration of about 1016 cm-3 as a substrate, HfO₂ as a gate dielectric layer, and the NiGe alloy as source and leakage, the schottky source, leakage Ge pMOSFET were prepared;2. In order to get better performance of Ge pMOSFET, Si passivation treatment was taken on the channel Ge, and the devices w/o Si passivations were tested focuses on the transfer as well as output characteristics, the causes for the bipolar of Switch features of Ge pMOSFET devices were also discussed.