Enhanced Sensitivity of FeGa Thin-Film Coated SAW Current Sensor

Abstract

A surface acoustic wave (SAW) device is proposed for sensing current by employing the patterned FeGa thin film as the sensitive interface. The layered media structure of FeGa/SiO2/LiNbO3 was established to reveal the working principle of the sensors, and an SAW chip patterned by delay-line and operating at 150 MHz was fabricated photolithographically on 128° YX LiNbO3 substrate. The FeGa thin film with a larger magnetostrictive coefficient was sputtered onto the acoustic propagation path of the SAW chip to build the sensing device. The prepared device was connected into the differential oscillation loop to construct the current sensor. The FeGa thin film produces magnetostrictive strain and so-called ΔE effect at the magnetic field generated by the applied current, which modulates the SAW propagation velocity accordingly. The differential frequency signal was collected to characterize the measurand. Larger sensitivity of 37.9 kHz/A, low hysteresis error of 0.81%, excellent repeatability and stability were achieved in the experiments from the developed sensing device.

The effect of FeNi-AlN layer thickness on the response of magnetic SAW sensor by FEM simulation

“…Combining (3) to ( 6) with (1), (2) and the condition 𝛻 • 𝐷 = 0, we can express the constitutive (7) in index form for the AlN piezoelectric material [4].…”

“…Common constructions for magnetic SAW sensors usually have a magnetic sensitive materials, an intermediate layers, an electrodes and a piezoelectric substrates (magnetic sensitive materials/intermediate layers/electrodes/piezoelectric substrates). Several recent studies indicate that common magnetostrictive sensitive materials, including Ni, FeGa, FeCo, and FeNi, have been combined with quartz and LiNbO3 piezoelectric substrates to measure magnetic field intensity and current with high sensitivity [4]- [6], [10]- [17]. The results show that the thickness of the magnetic materials significantly [4], [11], [15].…”

“…Several recent studies indicate that common magnetostrictive sensitive materials, including Ni, FeGa, FeCo, and FeNi, have been combined with quartz and LiNbO3 piezoelectric substrates to measure magnetic field intensity and current with high sensitivity [4]- [6], [10]- [17]. The results show that the thickness of the magnetic materials significantly [4], [11], [15]. Notely that the simulation approach was used to optimize the design parameters of sensors, in which the electromechanical equations set are solved numerically through finding boundary conditions to satisfy the CHRISTOFFEL equation and using perturbation theory [11].…”

Highly sensitive surface acoustic wave magnetic field sensor based on the loss mechanism

“…The magnetosensitive film is the key influencing factor of the performance of the SAW magnetic field sensor. Typical magnetosensitive materials mostly constitute magnetostrictive materials such as FeCo [7,8], FeNi [9], FeGa [10], FeGaB [11], and AlScN [12]. The combination of FeCoSiB films with SAW technology has in recent years been found to have the potential to achieve increased magnetic field detection sensitivity and ultra-fast response speed owing to its excellent magnetic and mechanical properties [12][13][14].…”

“…The shear modulus increased from 45 GPa to 57 GPa at magnetic field saturation [18]. To improve the detection sensitivity and reduce the hysteresis error, Wang et al designed and fabricated SAW devices with different thin-film patterns (dot, grating, and membrane), and found that the dot-like thin film structure can increase the magnetostrictive effect by fully releasing the internal coericivity of the magnetistrictive [10], and a large current sensitivity (37.9 k A −1 ) can be achieved [19]; as an available way allowing enhancement of adhesion, a Cr thin film was employed as the transition-layer to weaken the mechanical fatigue [20]. Kittmann et al tested SAW magnetic field sensors with different magnetostrictive layer thicknesses and found that the device insertion loss increased from 17 dB to 21 dB with increasing thickness [16].…”