We have developed an ultraflexible magnetic sensor matrix consisted of a giant magnetic resistor (GMR) matrix (2 x 4) and organic circuits, which include bias generator, bootstrapping shift register and signal amplifier. The imperceptible sensor matrix is fabricated on a 1.5-µm-thick parylene film and operates within 4 V. The operating voltage has enabled combining the magnetic sensor matrix with a Si-based wireless communication module and detecting magnetic field on a free surface. Utilizing the system on-skin, we have succeeded in wireless finger motion sensing demonstration.
Magnetic sensors integrated with rigid devices have been utilized for many useful applications such as position and current detection. Recently, flexible magnetic sensors have been reported1,2, which approaches for arbitrary surface deformations and will pave the way for next-generation applications. For example, a flexible magnetic sensor matrix can visualize the 3-D distribution of magnetic fields on a free surface, which will benefit soft robotics and medical applications, e.g. a magnetocardiogram detector to diagnose chronic heart failure. Such a flexible sensor matrix requires flexible analog and digital circuits to drive sensors and to process detected signals. However, a flexible magnetic sensor matrix integrated with flexible analog and digital circuits has not been reported so far. Organic transistor circuits have many advantages in terms of lightweight, flexibility, and compatibility with low-cost fabrication processes on flexible substrates, which are suitable for flexible magnetic sensors. In this study, we have demonstrated the flexible magnetic sensor matrix operated by flexible circuits based on organic transistor technology.
In order to fabricate organic circuits, Al was deposited as gate electrodes on a 1.5-µm-thick parylene film. Next, after oxygen plasma treatment of Al gate electrodes, 45-nm-thick parylene-SR was deposited by chemical vapor deposition to fabricate gate insulator. Organic semiconductor (DNTT) and Au source/drain electrodes were deposited on the insulator. After the fabrication of organic circuits, 1.5-µm-thick parylene was deposited as an interlayer dielectric film. Finally, GMR thin film arrays (Py/Cu ; Py = Ni81Fe19) were deposited and connected to organic circuits by laser drilled via holes. The electric properties of organic circuits and GMR thin film elements did not change even after severe bending and demonstrated excellent mechanical flexibility. As for the sensitivity to the magnetic field, the 4-V-operating magnetic sensor generated 250 mV voltage shift under magnetic fields of 10 mT. The voltage signals were amplified up to 2.6 V via the organic voltage amplifier circuits. In the presentation, we will reveal the details of the organic circuits and demonstrate the usability of the system by wireless finger motion sensing.
1. Y. Zang, et al. Adv. Mater. 27, 7979 (2015).
2. C. Barraud, et al. Appl. Phys. Lett 96, 072502 (2010).