Research ArticleENGINEERING

Monolithic mtesla-level magnetic induction by self-rolled-up membrane technology

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Science Advances  17 Jan 2020:
Vol. 6, no. 3, eaay4508
DOI: 10.1126/sciadv.aay4508
  • Fig. 1 Fabrication process of S-RuM power inductors.

    Illustration of the fabrication process flow for an air-core S-RuM inductor including the vapor phase releasing and the postfabrication capillary core filling approach for strong magnetic induction.

  • Fig. 2 Multiphysics modeling of an S-RuM architecture for strong magnetic induction.

    (A) FEM quasi-dynamic model for the rolling progress of stacked layer membrane with the thickness of each layer and the inner diameter labeled. (B) SEM image of the fabricated 14-turn S-RuM structure in (A) with the measured inner diameter labeled. (C) FEM electrical-thermal model built in COMSOL for the estimation of the temperature profile of a 12-turn Cu S-RuM structure with input DC current of 175 mA. (D) Comparison between the modeled and the measured data of the maximum temperature and structure resistance rise versus input DC current for the S-RuM structure in (C). (E) FEM electromagnetic model for calculating the S parameters of the S-RuM structure and the intensity of the magnetic induction inside the core before and after the core is filled at 10 MHz. Electrical properties of the structure with 0.813-W input power are measured and then used in the simulation. (F) Comparison between the simulated and the measured S11 of the structure in (E) and the calculated relative permeability and ferromagnetic resonance (FMR) resistance of the ferrofluid material at LF in two different structures.

  • Fig. 3 Representative experimental demonstration of monolithic S-RuM power inductors.

    (A) The planar layout of six batches of successfully fabricated devices with the total rolling length (0.8 to 10 mm) and rolling direction, as well as the number of cells indicated. SEM images show the cross sections of the fully rolled-up devices from batches 1, 4, and 5, with the number of turns indicated. (B to D) Ferromagnetic fluid drawn into a micropipette by capillary action with a droplet hanging at the tip (B); the pipette tip makes contact with the S-RuM air-core inductor tube (B), and capillary action forces the ferrofluid into the core of the inductor tube (C). Then, the pipette was withdrawn and detached from the core-filled S-RuM inductor tube (D). (E) Optical images of a six-cell 21-turn inductor before and after core filling. (F) A single two-cell inductor sitting on a piece of sapphire substrate placed by a U.S. penny for size comparison. (G) Optical image of an array of S-RuM inductor tubes fabricated monolithically.

  • Fig. 4 Measured performance of S-RuM power inductors.

    (A and B) Inductance (solid line) and Q (dashed line) versus frequency of air-core devices from batches as indicated from 10 MHz to 20 GHz (A) and 10 MHz to 3 GHz (B). (C and D) Inductance (C) and Q factor (D) versus frequency of ferrofluid-core devices from batches 4.2, 5.1, and 5.2 at frequency below 10 MHz measured using Keithley Clarius (10 KHz to 4 MHz, solid line) and CMT VNA (2 MHz to 10 MHz, dashed line). (E) Inductance (solid line) and Q factor (dashed line) versus frequency of ferrofluid-core devices from batches 4.2 and 5.2. at frequency above 10 MHz up to resonance frequency. (F) Inductance density versus frequency performance comparison between S-RuM power inductors and other state-of-the-art planar counterparts with/without magnetic core (3640). (G) Left: Measured thermal image of a batch 4 air-core device with an input current of 250 mA. Right: Temperature distribution line scan along the black line drawn across the inductor tube in the image under different input DC current as indicated.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/6/3/eaay4508/DC1

    Section S1. Detailed fabrication flow

    Section S2. The “round corner” design of Cu strip

    Section S3. Detailed core-filling method

    Section S4. Detailed mechanical FEM for inner diameter estimation

    Section S5. Electrothermal modeling of S-RuM architecture

    Section S6. Electromagnetic FEM modeling of S-RuM architecture

    Section S7. IR imaging of S-RuM architecture

    Section S8. Structural dimension of all S-RuM power inductor samples

    Section S9. HF measurement details of S-RuM power inductors

    Fig. S1. Mask-level depiction of the planar inductors.

    Fig. S2. Capillary core-filling material and method for S-RuM architecture.

    Fig. S3. Electrical-thermal modeling of S-RuM architectures.

    Fig. S4. Electromagnetic FEM modeling of S-RuM architecture skin effect.

    Fig. S5. LF (<~100 MHz) equivalent circuit of S-RuM architecture with ferrofluid core with enhanced inductance and introduced additional loss from FMR represented as LFL and RFMR, respectively.

    Fig. S6. The complete FEM model in HFSS to simulate the S parameters and the intensity of magnetic induction in the core of the S-RuM architecture.

    Fig. S7. IR imaging of S-RuM architectures.

    Fig. S8. Temperature profiles measured across the white dotted line of the exemplary structure shown in Fig. 2E (also the batch 2 device) with DC current of 325 mA.

    Fig. S9. Open-through de-embedding patterns and their corresponding lumped equivalent circuits.

    Fig. S10. Mathematical procedure to do the open-through de-embedding.

    Table S1. Material property set in FEM modeling simulation.

    Table S2. Parameters for COMSOL simulations.

    Table S3. Primary dimensional parameters of all batches.

    Movie S1. Ferrofluid filled into a short S-RuM architecture.

    Movie S2. Ferrofluid filled into a long S-RuM architecture.

    Movie S3. The rolling progress of a 1-cm-long S-RuM architecture observed with 10× real speed.

    Movie S4. The rolling progress of 1.6-mm-long S-RuM architecture array observed with 10× real speed.

  • Supplementary Materials

    The PDFset includes:

    • Section S1. Detailed fabrication flow
    • Section S2. The “round corner” design of Cu strip
    • Section S3. Detailed core-filling method
    • Section S4. Detailed mechanical FEM for inner diameter estimation
    • Section S5. Electrothermal modeling of S-RuM architecture
    • Section S6. Electromagnetic FEM modeling of S-RuM architecture
    • Section S7. IR imaging of S-RuM architecture
    • Section S8. Structural dimension of all S-RuM power inductor samples
    • Section S9. HF measurement details of S-RuM power inductors
    • Fig. S1. Mask-level depiction of the planar inductors.
    • Fig. S2. Capillary core-filling material and method for S-RuM architecture.
    • Fig. S3. Electrical-thermal modeling of S-RuM architectures.
    • Fig. S4. Electromagnetic FEM modeling of S-RuM architecture skin effect.
    • Fig. S5. LF (<~100 MHz) equivalent circuit of S-RuM architecture with ferrofluid core with enhanced inductance and introduced additional loss from FMR represented as LFL and RFMR, respectively.
    • Fig. S6. The complete FEM model in HFSS to simulate the S parameters and the intensity of magnetic induction in the core of the S-RuM architecture.
    • Fig. S7. IR imaging of S-RuM architectures.
    • Fig. S8. Temperature profiles measured across the white dotted line of the exemplary structure shown in Fig. 2E (also the batch 2 device) with DC current of 325 mA.
    • Fig. S9. Open-through de-embedding patterns and their corresponding lumped equivalent circuits.
    • Fig. S10. Mathematical procedure to do the open-through de-embedding.
    • Table S1. Material property set in FEM modeling simulation.
    • Table S2. Parameters for COMSOL simulations.
    • Table S3. Primary dimensional parameters of all batches.

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • Movie S1 (.mp4 format). Ferrofluid filled into a short S-RuM architecture.
    • Movie S2 (.mp4 format). Ferrofluid filled into a long S-RuM architecture.
    • Movie S3 (.mp4 format). The rolling progress of a 1-cm-long S-RuM architecture observed with 10× real speed.
    • Movie S4 (.mp4 format). The rolling progress of 1.6-mm-long S-RuM architecture array observed with 10× real speed.

    Files in this Data Supplement:

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