Research ArticleAPPLIED SCIENCES AND ENGINEERING

Self-assembly of highly sensitive 3D magnetic field vector angular encoders

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Science Advances  20 Dec 2019:
Vol. 5, no. 12, eaay7459
DOI: 10.1126/sciadv.aay7459
  • Fig. 1 SV structure and self-assembly concept.

    (A) Schematic that shows a simplified layer stack of an SV magnetic field sensor. (B) A set of six SVs arranged within an orthogonal 3D Cartesian base. Each orthogonal plane contains an orthogonal pair of sensors that should be rearranged from their planar unidirectional state. (C) Subjected to an external rotating magnetic field, this sensor has a sinusoidal response. (D) 3D SV sensors reoriented into the specific 3D configuration by applying self-assembling rolled-up technology, resulting in a sin and cos response of each pair of sensors on each planes. (E) Planar state of the SVs with the pinning direction set 45° to the rolling direction.

  • Fig. 2 Wafer-scale fabrication of 3D vector field encoder manufactured on 50 mm by 50 mm square glass substrates and their magnetoelectrical characteristics in the planar state.

    (A) Initial planar devices. (B) Wafer-scale self-assembled devices. (C) Fabricated planar shapeable polymeric stack. (D) Schematic that shows the exact SV stack. (E) Simplified scheme of the complete layer stack involving shapeable polymer platform, sensor elements, contact metallization, and encapsulation layer. The SV ellipses are patterned and then electrically connected with Cr/Au electrodes and protected by a thin PI layer. (F) Schematic that depicts vacuum oven magnetization setup magnetizing SVs at 300°C for 1 hour with a superimposed magnetic field of ~700 mT produced by an electromagnet. Photo credit: Daniil Karnaushenko, Institute for Integrative Nanosciences, Leibniz IFW Dresden.

  • Fig. 3 Planar device with six SV elements characterized with a swept and rotating magnetic field.

    (A) Swept field MR characteristic of one of the SVs measured along the magnetization direction. (B) Rotating field characteristic of one of the SVs (S4) with respect to the field strength (distance to the magnet). (C) Rotating field characterization of six SVs in their initial planar state directly following magnetization. (D) Rotating field characteristic of six SVs measured in an orthogonal plane with respect to the rotating magnetic field plane revealing equivalent switching characteristic for all the sensors. (E) Configuration that was used to measure the responses of the SV with respect to the rotating field plane revealing sinusoidal shape up to 45° tilt, which is sufficient for 3D operation, as beyond this angle, another set of sensors located in the orthogonal principal plane will take over, thus avoiding any blind sectors.

  • Fig. 4 Diced devices are self-assembled into 3D magnetic sensors and their characteristics.

    (A) Planar device with a set of magnetized and electrically connected SVs before self-assembly. (B) The devices after self-assembly revealing two orthogonal tubes with a diameter of ∅250 μm and length of 2.3 mm. The rolling length is 1.58 mm. (C) Magnification of two tubes showing one of eight SVs. (D) The 3D sensor was characterized by rotating the magnetic field of a permanent, radially magnetized magnet. The position of the magnet can be adjusted by tilting the magnet around the sensor and tuning the distance between the magnet and the sensor. The sensor itself can be rotated in the horizontal plane. This allows setting the rotating magnetic field plane to any arbitrary orientation with respect to the sensor. (E) Schematic depicting the electrical series connection of the sensors, their supply, and signal acquisition. (F) Behavior of the XY pair (S2 and S4) of the orthogonal magnetic sensors formed on the opposite sides of the respective tube and the sketch showing the orientation of the rotating magnet with respect to the sensors. (G) Behavior of the XZ pair (S5 and S6) of the orthogonal magnetic sensors formed on the opposite sides of the respective tube and the sketch showing the orientation of the rotating magnet with respect to the sensors. (H) Behavior of the YZ pair (S1 and S3) of the orthogonal magnetic sensors formed on the opposite sides of the respective tube and the sketch showing the orientation of the rotating magnet with respect to the sensors. Photo credit: Daniil Karnaushenko, Institute for Integrative Nanosciences, Leibniz IFW Dresden.

  • Fig. 5 Structures used during the optimization stage.

    (A) Fabricated on planar glass squares of 100 mm by 100 mm; the devices were diced (removed edges). (B) Self-assembled devices into an array of tubes. From a total 180 structures, 168 were self-assembled to reveal a fabrication yield of more than 93% in a parallel wafer-scale process. (C) Demonstration of the self-assembly quality in the magnified view of the tubular structure carrying magnetic field sensors and electrodes. (D) Statistical diameter distribution of 168 assembled devices on the wafer. (E to G) Single principal plane-13 response of sensors arranged on a tube with a diameter of 230 μm (E), 260 μm (F), and 280 μm (G) after amplitude, offset, and phase compensation. (H) Schematics clarifying misorientation of SVs and principal planes due to tube diameter variations. (I) Calculation of azimuthal and projection misorientation of SVs that belong to a single principal plane. (J) Calculation of misorientation of principal planes. Photo credit: Daniil Karnaushenko, Institute for Integrative Nanosciences, Leibniz IFW Dresden.

  • Fig. 6 Characteristics of high-performance SV (S4) after self-assembly.

    (A) Voltage response of the sensor measured near cos (φ), where φ = 90°, revealing a voltage step in response to the change in the field direction from −4.5° to +4.5° for different values of bias current. (B) Noise level independent of bias current with an RMS (root-mean-square) value of 1.86 μV. (C) The noise has a flat power spectral density with a floor better than −130 dB (V2)/Hz. (D) Standard deviations of measured angles correspond to 0.14°, 0.21°, and 0.43° depending on the bias currents of 1.5, 1.0, and 0.5 mA, respectively. (E) 3D angular accuracy response of the sensors was measured using 45° orientation of the rotating magnet plane to all the principal planes where the 9° step was performed. (F) Response of the sensors with equivalent angular accuracies in all directions for all sensors (time axis for the step response is adjusted for better visual perception).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/12/eaay7459/DC1

    Fig. S1. Characteristic of the ZY and XZ pairs (S1 and S3 and S5 and S6, respectively) of the orthogonal magnetic sensors formed on the opposite sides of the respective tube with the field rotating in the XY plane.

    Fig. S2. Characteristic of the XY and XZ pairs (S2 and S4 and S5 and S6, respectively) of the orthogonal magnetic sensors formed on opposite sides of the respective tube with the field rotating in the ZY plane.

    Fig. S3. Characteristic of the XY and ZY pairs (S2 and S4 and S1 and S3, respectively) of the orthogonal magnetic sensors formed on opposite sides of the respective tube with the field rotating in the XZ plane.

    Fig. S4. Electrical breakdown of the sensors due to overheating under electrical stress.

    Fig. S5. Mechanical reliability testing of encapsulated devices.

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. Characteristic of the ZY and XZ pairs (S1 and S3 and S5 and S6, respectively) of the orthogonal magnetic sensors formed on the opposite sides of the respective tube with the field rotating in the XY plane.
    • Fig. S2. Characteristic of the XY and XZ pairs (S2 and S4 and S5 and S6, respectively) of the orthogonal magnetic sensors formed on opposite sides of the respective tube with the field rotating in the ZY plane.
    • Fig. S3. Characteristic of the XY and ZY pairs (S2 and S4 and S1 and S3, respectively) of the orthogonal magnetic sensors formed on opposite sides of the respective tube with the field rotating in the XZ plane.
    • Fig. S4. Electrical breakdown of the sensors due to overheating under electrical stress.
    • Fig. S5. Mechanical reliability testing of encapsulated devices.

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