High‐Performance Flexible Magnetic Tunnel Junctions for Smart Miniaturized Instruments

Abstract

MANUSCRIPT TEXT IntroductionFlexible electronics has become an established field that has seen tremendous developments over the last years. [1][2][3][4][5][6][7][8][9][10] The unique capability to adjust the geometry of devices to curved surfaces or surfaces of changing shape provides vast advantages over conventional electronics on rigid substrates. Hence, flexible printed circuit boards have already become an industrial standard for medical implants or consumer electronics [11][12][13][14] , where the main requirements are: large area, extreme thinness, and conformity to curved surfaces. The recent progress of organic [6,15,16] as well as inorganic [14,17,18] electronics, which are basically performed using printing or thin film technologies, has been very beneficial for the improvement of flexing electronic devices. In combination with other methods like screen or inkjet printing, novel concepts for flexible electronics have been developed for several applications including displays, [19] organic light-emitting diodes, [20] sensors, [21][22][23][24][25] radio frequency identification tags, [26][27][28] and organic solar cells. [29] Meanwhile, there are increasing activities on flexible magnetic field sensors and magnetoelectronics, [30,31] due to ubiquitous use of such kinds of devices. [18,32] By now, high-performance magnetic sensors based on the giant magnetoresistive (GMR) effect and the tunneling magnetoresistive (TMR) effect are mainly prepared using thin film fabrication technologies. [18,[33][34][35][36][37][38][39] This method allows for fabricating extremely sensitive magnetic sensors, especially on Si substrates, and it would therefore be a desirable solution to flex the silicon substrate, where the magnetic elements are fabricated onto. Magnetic tunnel junctions (MTJs) are of particular interest, because they constitute the main component of diverse spintronic devices such as spin-transfer oscillators, magnetic sensors, hard-disk-drive read-heads or Magnetic Random Access Memories. [40] MTJs are made of a magnetic multilayer thin film material. For sensor applications, the low power consumption [41] , high sensitivity and small size make them an attractive option. MTJs with amorphous Al-oxide barriers exhibit TMR ratios below 100 %. This can be improved by using (001)-oriented MgO barriers, achieving TMR ratios over 150 % at room temperature. [42][43][44] These high values can be exploited to design very sensitive TMR sensors, [45][46][47][48][49][50] such as biomagnetic field sensors [51] . They show an important change in resistance versus the magnetic field than other sensors such as those utilizing the anisotropic magnetoresistance or giant magnetoresistance. [52][53][54] Compared to conventionally used Hall effect and AMR sensors, a TMR sensor can also have higher sensitivity, lower power consumption [41] , better temperature stability and, in particular, compared to an AMR sensor, a wider linear range can be obtained. [54] Flexible MTJ devices have been reported with alumina [37,39] and MgO t...

A Triaxial Flexible Magnetic Tunnel Junction Sensor for Catheter Tracking

“…The MTJ sensor fabrication process is described elsewhere [15]. The tri-axes MTJ sensor exploits the shape of the catheter to create three sensors with perpendicularly aligned sensitive directions.…”

“…In this work, we propose a highly miniaturized tri-axes sensor, based on magnetic tunnel junctions (MTJ). In order to maintain a high performance, the MTJ sensors are first fabricated on a standard Si wafer, which is then thinned down [15,16]. The substrate becomes mechanically flexible and can conform to the curvature of the catheter.…”

Perpendicularly magnetized Co/Pd-based magneto-resistive heterostructures on flexible substrates

“…[3][4][5][6][7][8][9][10][11][12][13] Aiming to widen the domain of exible electronics, a signicant effort has been recently pursued to develop spin-related electronic devices with in-plane magnetic anisotropy on exible substrates. 3,5,[14][15][16][17][18][19][20][21][22][23][24] With respect to conventional electronics, spintronic devices exploit electron spin to achieve additional functionality not provided by charge transport. Giant magneto-resistive spin-valves (GMR-SVs) and magnetic tunneling junctions (MTJs) are well-known examples of spintronic elements, which has been largely investigated for the development of advanced devices, including memories and sensors.…”

Biocompatible 3D Printed Microneedles for Transdermal, Intradermal, and Percutaneous Applications

“…In this regard, recent advancements in microtechnology have helped to make remarkable progress in health‐care monitoring and disease therapy. Examples are miniaturized laboratories (Lab‐on‐Chip, LoC) and microsystems able to sense, diagnose, and deliver a drug to the specific target region . In this context, the implementation of MNs for drug delivery is one of the most prominent developments in the drug administration field, due to their painless and minimally invasive operation.…”

“…Examples are miniaturized laboratories (Lab-on-Chip, LoC) and microsystems able to sense, diagnose, and deliver a drug to the specific target region. [7][8][9] In this context, the implementation of MNs for drug delivery is one of the most prominent developments in the drug administration field, [10][11][12] due to their painless and minimally invasive operation. Consequently, MNs have been investigated extensively, involving different materials, such as silicon, [13][14][15][16] glass, [17] polymer, [18,19] and metals, [11,[20][21][22] different designs (solid, coated, dissolvable, hollow, etc.…”