High-frequency Characterization And Transmission Simulation Of Spin-wave Waveguide Materials

After decades of explosive growth,the semiconductor industry is now in maturity.It is particularly difficult to further increase the integration of devices while controlling production costs and energy losses.The information processing technology taking spin waves as information carrier has become a highly competitive candidate in the “beyond CMOS” times.The motion of electrons is not involved in spin-wave transmission,so the Joule heat existing in semiconductor devices can be avoided.In addition,high frequency,nanoscale wavelength and large propagation speed of spin waves provide the possibility to produce high speed nanoscale devices.The main work of this thesis includes two parts: First,we built the testing system and carried out the investigation of high-frequency characterization on spin-wave waveguide materials;Second,we proposed a novel spin-wave waveguide based on exchange-spring structure and conducted a systematic study utilizing micromagnetic simulations.The thesis firstly introduces the principle of ferromagnetic resonance(FMR)testing and the building of the test platform.Then two common spin-wave waveguide materials yttrium iron garnet(YIG)and permalloy(Py)were chosen to test FMR.Through the improvement of experimental means and post data processing,we explored a stable,reliable and repeatable process of FMR testing.In the experimental level,protuberance on the resonance spectrum was removed by adjusting the placement of samples.In the data processing level,de-embedding eliminated the test error introduced by fixture;phase rotation solved the problem of phase shift;linear correction removed the drift appearing on the resonance spectrum of Py.These processes improve the accuracy of Lorentz fitting and then the accuracy of the material characterization.Secondly,a self-biased spin-wave waveguide based on the exchange-spring structure is proposed.We systematically studied the propagation characteristics of spin waves in the waveguide by micromagnetic simulations.The results show that a channel similar to Neel wall was induced on the soft layer when the system stabilized.Spin waves with a certain frequency can be bound in the channel while the channeling effect would disappear when the frequency is too high.Beamwidth of the bound mode is independent of frequency and is smaller than 24 nm.Its group speed can exceed 1km/s at 1GHz.Then,the thesis discussed the appearance of two other beams on both sides of the channel at a very low excitation frequency.The simulation results indicated that the two spin beams came from the coupling with the middle mode by the long-range dipole-dipole interactions.Finally,we manipulated the maximum frequency of the bound mode by adjusting the anisotropy constant of the hard layer.Compared to domain wall,the studied structure can be easier to realize in the experiment and has stronger immune to the environment.