Direct Transfer of Magnetic Sensor Devices to Elastomeric Supports for Stretchable Electronics

摘要

A novel fabrication method for stretchable magnetoresistive sensors is introduced, which allows the transfer of a complex microsensor systems prepared on common rigid donor substrates to prestretched elastomeric membranes in a single step. This direct transfer printing method boosts the fabrication potential of stretchable magnetoelectronics in terms of miniaturization and level of complexity, and provides strain-invariant sensors up to 30% tensile deformation. Stretchable electronics1, 2 is one of the most vital technological research fields of the latest years, aiming to revolutionize custom electronic systems toward being arbitrarily reshapeable on demand after their fabrication. This opens up novel application potentials for multifunctional high-speed electronic systems like smart skins,3, 4 active medical implants,5, 6 soft robotics,7, 8 or stretchable consumer electronics.9, 10 A variety of functional components that can be subjected to high tensile deformations have already been introduced, including light emitting diodes,11 solar cells,10 pressure and temperature sensors,12 integrated circuitry,13 batteries,14, 15 antennas,16 and many more. Introducing stretchable highly sensitive magnetosensorics into the family of stretchable electronics17 was envisioned to equip this novel electronic platform with magnetic functionalities. This can be of particular interest for smart skin and biomedical applications promoted by very recent developments of imperceptible12 and transient6 electronics, as magnetoelectronic components can add a sense of orientation, displacement, and touchless interaction. All approaches to stretchable magnetoelectronics17-20 rely on the direct deposition of magnetic multilayers onto elastomeric poly(dimethylsiloxane) (PDMS) membranes, which are thermally prestrained in order to induce wrinkling. This method, although it allowed the first stretchable magnetic field sensorics to be fabricated,17 is associated with severe process limitations, preventing significant advances in performance and level of complexity and thus, restricting the applicability of the technology. First of all, multiple patterning steps, which are absolutely necessary for the integration of magnetoelectronic components into multifunctional stretchable electronics platforms, can hardly be realized reliably on PDMS. Another crucial aspect is related to the limited stretchability of the functional elements relying on wrinkling due to thermally induced prestrain. Indeed, stretchabilities of a few percent only18, 20 can be achieved, unless cracking of the sensing layer is permitted.19 However, stretching due to crack formation is applicable only for functional elements that are much larger than the cracks and hence, this approach contradicts the device miniaturization, which is highly relevant especially for wearable navigation and orientation systems, some biomedical applications1, 21, 22 or for the fine mapping of inhomogeneous magnetic fields and textures. These severe drawbacks call for a novel fabrication strategy of stretchable magnetoelectronic devices that allows for smaller structures and mechanically induced prestrain. Transfer printing23 has evolved to one of the most promising techniques for stretchable devices.24, 25 This method relies on a micropatterned stamp that picks up structures from a donor substrate and releases them on a receiving surface in a two-step process. Here, we successfully demonstrate a direct single-step transfer printing of highly sensitive and miniaturized magnetic field sensorics relying on the giant magnetoresistive (GMR) effect. The developed strategy allows for a transfer of GMR systems with a size down to 6 μm from standard rigid substrates to an elastomeric membrane in a single step, without requiring micropatterned stamps. With the preparation of entire magnetoelectric sensor systems with electrical contacts on silicon wafers, the full potential of state-of-the-art microfabrication methods and th