Effects of geometry of thin-film microwaveguides based on yttrium iron garnet and position of microantennas on characteristics of excitation and transmission of magnetostatic waves in them

Abstract

Background and Objectives: Magnetic thin film waveguides of a finite width are considered as the main building blocks for magnonic circuits where the magnetostatic waves are the information carriers. The purpose of this study is to investigate experimentally the effects of the waveguides width, position of microantennas for excitation and detection of the magnetostatic waves, coupling between the waveguides on excitation and transmission characteristics of the magnetostatic waves for the waveguides with the width of ~10 μm based on an yttrium iron garnet film (material that has the lowest magnetostatic wave damping among all known magnetic materials). Materials and Methods: A set of the microwaveguides with the specified width of 15, 10 and 5 μm and with different position of the microantennas integrated with the waveguide as well as systems of two close parallel waveguides with the microantennas was fabricated out of 0.9 μm thick yttrium iron garnet film using photolithography, ion etching and magnetron sputtering. Measurements of the transmission and reflection coefficients as a function of the frequency were performed by a vector network analyzer along with a microwave probe station. The bias field was applied tangentially along or perpendicular to the waveguide. Results and Conclusions: It is found that the used technology provided ~70° tilt of the waveguides sidewalls from the vertical direction. It is also revealed that placing the microantennas near the ends of the waveguides reduces the efficiency of excitation of the long-wavelength part of the magnetostatic waves spectrum. In addition, such an arrangement of antennas was characterized by the absence of the features associated with the excitation of the magnetostatic wave width modes. The latter effect can be used for filtering the width modes if necessary. It is shown that, for ~15 μm wide waveguides based on 0.9 μm thick yttrium iron garnet film, there is a significant (~0.5 GHz) overlap of the spectra of the fundamental modes of magnetostatic surface wave and magnetostatic backward volume wave in transversely and longitudinally magnetized microwaveguides, respectively, at the bias field in the range of 0.5–1.5 kOe. This width can be considered close to optimal for constructing structures from orthogonal waveguides based on such thick yttrium iron garnet films. A further decrease in the width leads to an undesirable decrease in the transmission coefficient. In addition, in this case, the shape anisotropy effect can be excessively strong and move a part of the magnetostatic surface and backward volume waves spectra, narrowing the region of their overlap. It is also shown that for two parallel microwaveguides with a width and distance between them Твердотельная электроника, микро- и наноэлектроника 251 of ~15 μm, the excitation of the magnetostatic wave in one of them leads to energy transfer to the adjacent waveguide with an efficiency of ~ -10–15 dB due to the coupling between the waveguides. This effect must be taken into account when miniaturizing magnonic networks.

Keywords

• magnetostatic waves
• yttrium iron garnet
• microwaveguides of finite width
• microantennas for magnetostatic waves
• transmission and reflection characteristics