Imperceptible magnetic sensor matrix system integrated with organic driver and amplifier circuits

Abstract

Artificial electronic skins (e-skins) comprise an integrated matrix of flexible devices arranged on a soft, reconfigurable surface. These sensors must perceive physical interaction spaces between external objects and robots or humans. Among various types of sensors, flexible magnetic sensors and the matrix configuration are preferable for such position sensing. However, sensor matrices must efficiently map the magnetic field with real-time encoding of the positions and motions of magnetic objects. This paper reports an ultrathin magnetic sensor matrix system comprising a 2 × 4 array of magnetoresistance sensors, a bootstrap organic shift register driving the sensor matrix, and organic signal amplifiers integrated within a single imperceptible platform. The system demonstrates high magnetic sensitivity owing to the use of organic amplifiers. Moreover, the shift register enabled real-time mapping of 2D magnetic field distribution.

Fig. 1. Imperceptible active-matrix magnetic e-skin.

(A) Active MSM circuit fabricated on a single parylene wafer (50 × 50 mm²) via monolithic microfabrication on a 1.5-μm-thick substrate. (B) Demonstration of autarkic magnetic e-skin attached to human skin, facilitating position detection of fingers equipped with permanent magnets when approaching the palm. The device exhibits soft adhesion with a small amount of moisture in the palm. (C) Demonstration of robustness of OTFTs and giant magnetoresistance (GMR) sensors when bent to a radius of 145 μm and 2 mm, respectively (photo credit: Masaya Kondo, ISIR, Osaka University, PhotoBIO-OIL).

Fig. 2. Construction of the imperceptible magnetosensory system.

(A) Schematic illustration of the five main circuit blocks of the MSM system. (B) Top view of the imperceptible magnetosensory system with an area of 50 × 50 mm² and comprising organic [dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (DNTT)] electronic circuit and GMR sensors. (C) Separate micrographs for five main building blocks designed and implemented in imperceptible form along with corresponding main characteristics. (I) Optical micrograph of two stages of bootstrap shift register and typical output. (II) Optical micrograph of a switching OTFT and typical transfer curve. (III) Micrograph of a GMR sensor and typical transfer curve. (IV) Optical micrograph of a current mirror (top) and typical output current (bottom). The green bar shows the reference current, whereas the red and blue bars show the mirrored current from the reference. (V) Optical micrograph of a common-source amplifier and typical dc output signal from magnetic sensor. The blue curve shows the raw signal, whereas the red curve shows the amplified signal by the amplifier. (D) Cross-sectional schematic illustrating layered structure of imperceptible magnetosensory system (photo credit: Masaya Kondo, ISIR, Osaka University, PhotoBIO-OIL).

Fig. 3. Proposed organic bootstrap shift register and its performance.

(A) Closeup of the eight stages of bootstrap shift register. (B) Circuit diagram representing the first two stages of the shift register. (C) Basic clocking diagram illustrating the correct function of driving signals for the first two stages, including the main clock (F1 and F2) and frame-start (FS) signals. (D) Typical timing diagram demonstrating the correct operation of the proposed eight-stage p-type imperceptible bootstrap shift register. The inputs F1, F2, and FS have two potentials as high level (V_H = 4 V) and low level (V_L = 0 V). In addition to V_H and V_L, the propagated IN signals have a lower potential (V_BST = −2 V) than V_L owing to bootstrap operation. (E) Boost response graph showing operating speed, which depends on the amplitudes of F1 and F2 signals that determine the charge-discharge cycle of boost capacitance. We applied three different V_H levels (V_H = 4, 3, and 2 V) to F1, F2, and FS. The perpendicular axis is the shift register output normalized by the difference between V_H and V_L (0 V) levels of FS. (F) Frequency response of eight boost capacitors revealing approximately a constant value of 1.2 nF at operating clock speed. (G) Distribution of OTFT parameters, such as mobility and threshold voltages, that do not affect shift register operation (photo credit: Masaya Kondo, ISIR, Osaka University, PhotoBIO-OIL).

Fig. 4. Proposed common-source amplifier layout and its performance.

(A) Magnified view of a common-source amplifier. (B) Circuit diagram representing one stage of a common-source amplifier. (C) Response of OTFT common-source amplifier with voltage transfer and gain characteristics. (D) Demonstration of common-source amplifier in operation in which signals from two sensors within the blue and red circles were recorded on row lines R1 and R2 and amplifier outputs AO1 and AO2 when corresponding sensor locations were approached by a strong NdFeB permanent magnet. The maximum magnetic field of the magnet is more than 500 mT (photo credit: Daniil Karnaushenko, IFW Dresden).

Fig. 5. Demonstration of two-dimensional mapping of magnetic field.

(A) Detection of magnetic field using a weak ferrite permanent magnet placed at various positions within the sensor matrix. The maximum magnetic field of the magnet is approximately 40 mT. (B) Signals of sensor matrix scanned using bootstrap organic shift register and variations in row line voltage as sensor matrix is scanned with the respective magnet position, shown in (A). The detected signal lines have an offset voltage of 150 mV. (C) Two-dimensional (2D) map of applied magnetic field (photo credit: Masaya Kondo, ISIR, Osaka University, PhotoBIO-OIL).