Stretchability and Self-Healing of Wrinkled GMR Multilayers on Elastomeric Membranes

Abstract

Stretchable magneto-resistive sensing elements have been introduced lately as a novel component providing magnetic functionality to stretchable consumer electronics involving smart skin or medical diagnostic applications. While spin valves already revealed high stretchability and reliability, GMR multilayers still lack mechanical compliance and production yield. Here, we report on two crucial improvements in fabrication of GMR multilayers to address these limiting issues. On the one hand, we increase the stretchability of wrinkled magnetic nanomembranes on freestanding elastomer membranes by photolithographically structuring them into a meander pattern. The meander can be regarded as a 2D spring, which can accommodate tensile strains in addition to the apparent wrinkling. On the other hand, we highlight a self-healing e®ect of GMR multilayers, which occurs due to a thermally induced pre-strain in the elastic support. This causes the soft membrane to contract after the GMR elements are prepared on top and closes cracks often induced during fabrication. Relying on this feature we are able to restore the full GMR

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

“…All approaches to stretchable magnetoelectronics 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, is associated with severe process limitations, preventing significant advances in performance and level of complexity and thus, restricting the applicability of the technology.…”

“…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 only can be achieved, unless cracking of the sensing layer is permitted . 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 applications or for the fine mapping of inhomogeneous magnetic fields and textures.…”

“…Additionally, the advanced microfabrication potential allows combination with compliant meander geometries . With this new approach, we achieve an increase in the stretchability of the GMR multilayer sensors from about 4% up to 30% without relying on the formation of cracks. The latter is of great importance as the senor elements introduced here are truly strain invariant since without cracks almost no resistance change is associated with the tensile deformation.…”

Shapeable magnetoelectronics

“…First of all, the photolithographic structuring on the PDMS surface is challenging for feature sizes well below 100 lm (Ref. 179), and multiple patterning steps, which are absolutely necessary for the integration of magnetoelectronic components into multifunctional stretchable electronics platforms, can hardly be realized on PDMS reliably. Another crucial drawback is related to the limited stretchability of the functional elements relying on wrinkling due to a thermally induced pre-strain.…”

“…Another crucial drawback is related to the limited stretchability of the functional elements relying on wrinkling due to a thermally induced pre-strain. In fact, stretchabilities of a few percent only 101,179 can be achieved in this way, unless cracking of the sensing layer is permitted. Controlled cracking can result in higher stretchabilities, which was demonstrated also with magnetoelectronic sensing elements by means of stretchable spin valves.…”