Results obtained in 2023

In this stage, is evidenced the interaction between the magnetic field and surface acoustic waves through a ferromagnetic material, in the SAW type device.
Following objectives were achieved:
- Simulation of the magnetic behavior of SAW devices on ScAlN/Si;
- Fabrication of SAW structures on ScAlN/Si for the SAW/SW coupling and for the magnetic sensor;
- Characterization of SAW structures on ScAlN/Si (Rayleigh and Sezawa modes) in magnetic field at room temperature and at cryogenic temperatures;
- Magnetic field characterization of sensor structures manufactured on ScAlN/Si.

1. Magnetostrictive simulation of SAW device on ScAlN/Si at room temperature

The strain and stress values ​​that appear in the Ni layer when the magnetic field is applied were determined. The average stress on each face of the nickel metallization (ferromagnetic domain) was calculated for each element. Figure 1 shows the magnetic field distributions (a), the displacement distributions (b) and the von Mises stress distributions (c), at the value of 7 mT and the displacement distribution for B = 294 mT (d).

On each side of the ferromagnetic field, the average value of the stress tensor was calculated for each direction.

2. Fabrication of SAW structures for magnetic sensor

Single-port SAW structures have been designed and fabricated, as a magnetic sensor. For the SAW structures, have been defined ferromagnetic layers with different geometries, placed near the IDT. The width of the digits for the designed SAW structures is 170 nm, and 100 nm, respectively. The manufacturing process of the structures consisted of the following steps: fabrication of CPW lines from Ti/Au, with a thickness of 100 nm (Ti/10nm, Au/90nm); IDT fabrication using EBL, deposition of the Ti/Au metallization, with a thickness of 50 nm (Ti/5nm, Au/45nm) and configuration of IDT by lift-off process; deposition of an overlayer for the CPW line by a Ti/Au layer with a thickness of 250 nm (Ti/20nm, Au/230nm) achieved also through the lift-off  process; deposition and configuration of the Ni ferromagnetic layer, with a thickness of 12 nm.

3.  Characterization of SAW structures on ScAlN/Si in magnetic field (Rayleigh and Sezawa propagation modes)

The S parameters were measured and were observed two propagation modes: the Rayleigh propagation mode, at the resonance frequency of 4.67 GHz and the Sezawa propagation mode, at the frequency of 8.04 GHz.
The coupling of the spin waves with the SAW acoustic wave is evidenced by the decrease in the amplitude of the transmission parameters (S21, S12) (dB), called absorption, due to the transfer of energy from the SAW wave to the spin waves. This coupling is maximum when the angle between the applied magnetic field and the propagation direction of the SAW wave is 45°. Figure 3 shows that the maximum absorption in the magnetic field occurs at -90mT for Rayleigh mode and has a value of 2.54dB. For the Sezawa mode, the maximum absorption occurs at a magnetic field of -203mT and has a value of 7.24dB.

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Estimated results

- Manufacturing and characterization of SAW structures on ScAlN/Si with finger and finger/interdigit spacing width between 80-170 nm and magnetostrictive material, Ni and/or CoFeB of different thicknesses (in the range 10-45 nm) between the IDTs with resonance frequencies above 4 GHz;
- Analysis of SAW/SW coupling at different angles between magnetic field strength and the SAW propagation direction, performed at room and cryogenic temperatures, for Rayleigh and Sezawa propagation mode. A higher coupling than that reported for other types of materials is expected.
- Nonreciprocal behavior analysis at room and cryogenic temperatures, for SAW structures manufactured on ScAlN/Si, for Rayleigh and Sezawa propagation mode
- Simulation of ScAlN SAW based structures for magnetic sensing at room temperatures and cryogenic temperatures
- Characterization as magnetic sensor at room temperature and also at cryogenic temperatures of single port SAW structures with Ni deposited in the IDTs composition as well as magnetic layers (Ni si/sau CoFeB) in the vicinity of the active IDTs area
- Submission minimum 3 papers in high ranked journals (Q1 or Q2); Minimum 5 participations at conferences two of them where the acceptance rate is <50%; 1 patent.