Microfabrication Method for Amorphous Wires GMI Magnetic Sensors

Objective Compared with amorphous ribbons and thin films, amorphous wires exhibit superior Giant MagnetoImpedance (GMI) performance, making them promising materials for GMI magnetic sensors. Their flexible and heterogeneous morphology, however, complicates precise positioning during device fabrication. Additionally, the poor wettability of amorphous wires hinders control of contact resistance during soldering, often resulting in inconsistent device performance. This study proposes a microfabrication method for GMI magnetic sensors based on amorphous wires. Through-glass vias are employed as alignment markers, and auxiliary fixtures are used to accurately position and secure the wires on a glass wafer. Using photolithography and electroplating, bonding pads are fabricated to establish reliable electrical interconnections between the wires and the pads, enabling device-level processing and integration. A winding machine is then applied to wind the signal pickup coil on the device surface, completing fabrication of the GMI magnetic sensor. This approach avoids deformation and stress accumulation caused by direct coil winding on the amorphous wires, thereby improving manufacturability and ensuring stable performance of amorphous wire-based GMI magnetic sensors. Methods A glass wafer is employed as the substrate, owing to its high surface flatness and mechanical rigidity, which provide stable support for the flexible amorphous wire structure. To mitigate deformation caused by wire flexibility during winding, a microelectronics process integration scheme based on the glass wafer is implemented. A metal seed layer is first deposited by magnetron sputtering. Ultraviolet lithography and electroplating are then applied to form a high-precision array of electrical interconnection pads on the wafer surface. The ends of the amorphous wire are threaded through through-glass vias fabricated along the wafer edge by laser ablation and subsequently secured, ensuring accurate positioning over the bonding pad area while maintaining the natural straight form of the wire (Fig. 4). The amorphous wire is interconnected with the pads using electroplating. Standardized devices with an amorphous wire-glass substrate-interconnection structure are obtained by wafer dicing. After the microstructure of the amorphous wire and substrate is established, a winding machine is used to wind enameled wire onto the structure to form the signal pickup coil. The number of turns and spacing are precisely controlled according to the design. The sensor structure with the wound pickup coil is mounted on a Printed Circuit Board (PCB) with bonding pads. Finally, flip-chip bonding is performed to achieve secondary interconnection between the sensor structure and the PCB, completing fabrication of the sensor device. Results and Discussions The fabricated sensor device based on microelectronics processes is shown in Fig. 6(a). A 40 mm diameter enameled wire is uniformly wound on the substrate surface to form the signal pickup coil, with the number of turns and spacing precisely controlled by programmed parameters of the winding machine. As shown in the magnified view in Fig. 6(b), the bonding pad areas at both ends of the amorphous wire are completely covered by a copper layer. The copper plating defines the electrical connection area of the amorphous wire, while polyimide provides reliable fixation and surface protection on the substrate. The performance of five fabricated amorphous wire GMI magnetic sensors is presented in Fig. 13 and Table 1. The standard deviation of sensor output ranges from 0.0272 to 0.0163, and the sensors exhibit similar sensitivity, indicating good consistency. The output characteristic curves are shown in Fig. 14. Fitting analysis shows that both the Pearson correlation coefficient and the coefficient of determination are close to 1, demonstrating excellent linearity. When a 1 MHz excitation signal is applied to the amorphous wire, the output voltage exhibits a linear relationship with the external magnetic field within the range of –1 Oe to +1 Oe, with a sensitivity of 5.7 V/Oe. The magnetic noise spectrum, measured inside a magnetic shielding barrel, is shown in Fig. 15. The results indicate that the magnetic noise level of the sensor is approximately 55 pT/^√Hz. Conclusions A fabrication method for amorphous wire-based GMI magnetic sensors is proposed using a glass substrate integration process. The sensor is constructed through microfabrication of a glass substrate-amorphous wire microstructure. The method is characterized by three features: (1) highly reliable interconnections between the amorphous wire and bonding pads are established by electroplating, yielding a 10 mm × 0.6 mm × 0.5 mm microstructure with fixed amorphous wires; (2) a signal pickup coil is precisely wound on the microstructure surface with a winding machine, ensuring accurate control of coil turns and spacing; and (3) electrical connection and circuit integration with a PCB are completed by flip-chip bonding. Compared with conventional amorphous wire GMI sensors, this approach provides two technical advantages. The microfabrication interconnection process reduces contact resistance fluctuations, addressing sensor performance dispersion. In addition, the combination of conventional winding and microelectronics techniques ensures device consistency while avoiding the high cost of full-process microfabrication. This method improves process compatibility and manufacturing repeatability, offering a practical route for engineering applications of GMI magnetic sensors.