ARTICLE OPEN
Highly compliant planar Hall effect sensor with sub 200 nT
sensitivity
Pablo Nicolás Granell1,2,3, Guoliang Wang1, Gilbert Santiago Cañon Bermudez1, Tobias Kosub1, Federico Golmar3,4, Laura Steren4,5,6,
Jürgen Fassbender1 and Denys Makarov 1
Being a facet of exible electronics, mechanically reshapeable magnetic eld sensorics enable novel device ideas for soft robotics,
interactive devices for virtual- and augmented reality and point of care diagnostics. These applications demand mechanically
compliant yet robust sensor devices revealing high sensitivity to small magnetic elds. To push the detection limit of highly
compliant and linear magnetic eld sensors to be in the sub-µT range, we explore a new fundamental concept for magnetic eld
sensing, namely the planar Hall effect in magnetic thin lms. With their remarkable bendability down to 1 mm, these compliant
planar Hall effect sensors allow for an efcient detection of magnetic elds as small as 200 nT with a limit of detection of 20 nT. We
demonstrate the application potential of these devices as a direction (angle) as well as proximity (distance) sensors of tiny magnetic
elds emanating from magnetically functionalized objects. With their intrinsic linearity and simplicity of fabrication, these compliant
planar Hall effect sensors have the potential to become a standard solution for low eld applications of shapeable
magnetoelectronics in point of care applications and on-skin interactive electronics.
npj Flexible Electronics ??????(2019)3:3? ; https://doi.org/10.1038/s41528-018-0046-9
INTRODUCTION
The eld of exible electronics ourished over recent years with
numerous fundamental discoveries1–4 which enabled exciting
device concepts ranging from exible displays5,6 and batteries7,8
to implantable devices,9–13 just to name a few. Their success relies
on this novel formulation of electronics being compliant,
wearable, and matching the mechanics of biological tissues.14,15
For each of these applications specic actuating16,17 and sensing
elements are required. In the latter case, diverse types of
mechanically reshapeable sensors have been reported, which
can detect mechanical,18,19 optical,20 thermal21,22, and bioelec-
tric23,24 stimuli, among others.
Flexible magnetic eld sensors have been applied for detecting
the presence of magnetic elds of magnetically functionalized
objects,25–27 for proximity detection in novel touchless human-
machine interaction concepts or for augmented and virtual reality
applications28–31 (Supporting Table 1). State of the art exible
magnetoelectronics operate typically with magnetic elds in the
mT range, which are easily realizable using small permanent
magnets.32 Recent works report on exible magnetic eld sensors
sensitive to the geomagnetic eld, which is of 50 µT only.33–36
While exible, the mechanical performance of the reported
devices does not meet the requirements needed for the eld of
wearable or on-skin electronics. Therefore, although highly
demanded for various applications ranging from point of care
diagnostics to biomedical magnetic eld detection,37,38 there are
no highly compliant magnetic eld sensors with sub-µT sensitivity.
To enable such a high sensitivity in a mechanically compliant form
factor, a new fundamental effect towards magnetic eld sensing
should be introduced in the eld of shapeable magnetoelec-
tronics. In this respect, magnetic eld sensors based on the planar
Hall effect (PHE) are particularly interesting for sensing weak
magnetic elds (lower than the geomagnetic eld), because they
are intrinsically linear around zero eld and show great
sensitivity39 (Supporting Table 2). Furthermore, these sensors are
metal-based and can be easily integrated in an imperceptible
electronics platform as needed to assure for superior mechanical
performance.40–42
Here, we report a highly compliant PHE sensor capable of
detecting magnetic elds in the range of sub 200 nT with a limit of
detection of 20 nT. Owing to the fabrication on mechanically
imperceptible polymeric foils with a thickness of 6 µm only, the
sensor is bendable to a radius of 1 mm without any degradation of
its electrical resistance. This newly explored sensing mechanism
based on the planar Hall effect, allows for an extremely simple
sensor design consisting of one magnetic layer (Permalloy) and
one contact layer. The sensor shows excellent bending perfor-
mance with 0.3% resistance variation after more than 150 bending
cycles. We report a maximum sensitivity of 0.86 V/T in the linear
range of ±50 µT, which makes these sensors sensitive to magnetic
elds down to 20 nT. Although prepared on ultrathin polymeric
foils, the sensitivity of these sensors meets the state of the art
values reported for their rigid counterparts.43–45 We showcase the
performance of the sensor for two application examples in angle
and proximity detection.
Received: 13 September 2018 Accepted: 16 December 2018
1Helmholtz-Zentrum Dresden-Rossendorf e.V., Institute of Ion Beam Physics and Materials Research, Bautzner Landstrasse 400, 01328 Dresden, Germany; 2Instituto Nacional de
Tecnología Industrial (INTI), Centro de Micro- y Nanoelectrónica del Bicentenario (CMNB), Av. Gral Paz 5445, B1650KNA San Martín, Buenos Aires, Argentina; 3Escuela de Ciencia y
Tecnología, UNSAM, Campus Miguelete, B1650KNA San Martín, Buenos Aires, Argentina; 4Consejo Nacional de Investigaciones Cientícas y Técnicas, C1425FQB Ciudad
Autónoma de Buenos Aires, Argentina; 5Instituto de Nanociencia y Nanotecnología, B1650KNA San Martín, Buenos Aires, Argentina and 6Dpto. Materia Condensada, Centro
Atómico Constituyentes, B1650 San Martín, Buenos Aires, Argentina
Correspondence: Pablo Nicolás. Granell (pgranell@inti.gob.ar) or Denys Makarov (d.makarov@hzdr.de)
www.nature.com/npjexelectron
Published in partnership with Nanjing Tech University

RESULTS AND DISCUSSION
Fabrication
The sensor is realized by microfabricating Permalloy (Py) Hall
crosses with a thickness of 20 nm on 6-µm-thick PET foils (Fig. 1a).
Optionally, a 2-µm-thick SU-8 layer can be added to reduce the
surface roughness of the PET foil. To improve the sensor
performance, each stripe of the Hall cross is prepared with a high
aspect ratio of 10:1 to induce a preferred magnetization axis of the
Py structure by shape anisotropy. This is further facilitated by
patterning an elliptically-shaped stripe (Fig. 1b) instead of a
rectangular one.46 As the second and nal fabrication step,
electrical contacts are prepared to interface the Hall cross with the
outside electronics. The integrity of the layer stack upon
mechanical deformations is characterized by scanning electron
microscopy (SEM) imaging (Fig. 1c, d). In addition to the top-view
images, the sample cross-section is investigated upon Focused Ion
Beam (FIB) milling (Fig. 1e), revealing a rm adhesion of the
metallic layer to a polymeric foil.
Magnetoelectrical characterization
To dene the favorable magnetic state of the sensor, we applied a
magnetic eld parallel to the elliptical arm of the Hall cross,
performing a magnetic eld sweep between ±3 mT. This eld is
sufcient to saturate the elliptically shaped Py stripe. After this
standard initialization process,43 we determine the sensitivity axis
of the sensors to be for the elds applied parallel to the elliptical
axis. Figure 2 shows the magnetoresistive response of the sensor
in the at state and bent to a radius of 1 mm. In the at state, the
sensor showed a maximum sensitivity of 0.86 V/T when biased
with a 5 mA direct current (DC). The actual measurement of the
magnetic eld strength experimentally detected by the sensor is
<200 nT for the at sensor (error bars shown in Fig. 2a correspond
to the standard deviation of 200 nT). Even when bent to 1 mm, the
sensors still reveal a remarkably high sensitivity of 0.63 V/T. We
relate the observed change in the sensitivity after bending to the
modication of the magnetic domain pattern due to magnetos-
trictive effects. To assure a direct comparison of the measure-
ments of the same sensor between the bent and at states, we did
not reinitialize the magnetic state of the sensor between the
measurements in the at and bent states. The change of the
magnetic domain pattern in a magnetic thin lm upon bending
was investigated elsewhere.47–49
Ultimately, the sensitivity of the sensors, namely its ability to
measure the smallest elds, is determined by its noise. One of the
great advantages of the metal-based PHE sensors is their small
resistance, which allows for a very low intrinsic sensor noise. As
our compliant PHE sensors have typical resistances of about
100 , their intrinsic thermal noise (Johnson noise) is ~1.3 nV/Hz1/2
(equivalent magnetic eld noise of 1.5 nT/Hz1/2). This remarkably
low noise gure is compromised by the noise of the read-out
electronics. In our experiments, we used electronics with a white
noise density of 55 nV/Hz1/2. Considering the maximum integra-
tion time of 10 s for the compliant PHE sensor in a at
arrangement (corner frequency of 0.1 Hz in the power spectral
density plot; Supporting information), the sensor would be able to
discriminate elds down to 20 nT (limit of detection). We note that
Fig. 1 Fabrication of highly compliant PHE sensors. a Schematics on the fabrication process. An ultrathin polymeric foil is attached to a
supporting glass substrate. Optionally, an SU-8 smoothing layer can be added before the rst patterning step. The magnetic sensing layer is
prepared by photolithography and e-beam evaporation. Contact lines are realized in subsequent lithography and evaporation steps. Finally,
the device is detached from the supporting glass slide. SEM imaging of a compliant PHE sensor in a planar b, biaxially bent c, and uniaxially
bent d states. e SEM image showing a cross-section of the sample prepared using FIB milling
Fig. 2 Magnetoelectrical characterization in the linear range.
Transverse voltage (planar Hall voltage) measured for a compliant
PHE sensor a in the at state (average of 5 measurements) and b
bent to a radius of 1 mm (average of 7 measurements). The scale bar
in panel a corresponds to 300 µm. Solid lines are linear ts to the
experimental data points. Error bars calculated from standard
deviation of measurements
P.N. Granell et al.
2
npj Flexible Electronics (2019) ??3? Published in partnership with Nanjing Tech University
123456
7890():,
;

this number is not generic as it is strongly dependent on the read-
out electronics. For instance, the use of a low noise electronics
(typical white noise density of low noise electronics is 15 nV/Hz1/2)
would boost the limit of detection of a compliant PHE sensor to
10 nT.
Mechanical performance
The key requirement for compliant sensors is that their resistance
remains essentially invariant upon mechanical deformations. We
carried out extensive mechanical testing of the compliant PHE
sensors in a cycling bending apparatus (Figure S2). The sensor was
bent for more than 150 times between 4 mm and 2.4 mm bending
radii (Movie S1). The electrical resistance parallel to the bending
direction was recorded at the initial (4 mm) and nal (2.4 mm)
positions. Figure 3a shows the evolution of the sample resistance
at the nal bending position (2.4 mm), showing a variation of 0.3%
only during the entire cycling test. With this, we have realized a
strain invariant yet mechanically compliant magnetic eld sensor
relying on the planar Hall effect.
Furthermore, we recorded the transverse voltage of the sensor
during the cyclic bending experiment. The results are shown in
Fig. 3a for the case when the sensor is bent to a radius of 2.4 mm.
Only a small variation of the transversal voltage upon cycling is
observed. The voltage variation in this dynamic bending test is
attributed to the change of the voltage offset, which is not related
to any magnetic effect but to the sensor contact geometry. Still,
no degradation of the sensor output is found in the data.
The critical bending radius of the functional Py layer was
characterized using SEM. We folded a sensor device to different
bending radii down to about 100 µm (Fig. 3b). The examination of
the morphology of the bent sensor reveals that the surface
remains continuous without evident lm fracturing if the bending
radius exceeds 290 µm (Fig. 3c). For smaller bending radii, cracks
start to evolve as demonstrated for the case when the bending
radius is 110 µm (Fig. 3d). These experimental results are in a good
quantitative agreement with analytical estimations revealing a
critical bending radius of 265 µm. The corresponding strain
experienced by the Permalloy lm is calculated to be 1.7 × 10−1
for a bending radius of 290 µm and 4.5 × 10−1 for a bending radius
of 110 µm. We note that this remarkable mechanical performance
is achieved due to the use of ultrathin polymeric foils. For
comparison, the use of standard 100-µm-thick polymeric sub-
strates would result in a critical bending radius of about 1 order of
magnitude higher (5 mm, as typically observed experimentally34).
Compliant PHE sensors for detecting magnetic stray elds
Due to their excellent mechanical properties, the sensor devices
can be bent around curved objects and provide information of
tiny magnetic elds emanating from them. In this way, the sensor
can be placed in close proximity to a signal source. For example, it
could be implemented to detect magnetic functionalized objects
owing in a uidic channel or the stray magnetic eld generated
by a current-carrying wire. As a proof of principle, the performance
of compliant PHE sensors was evaluated by measuring the
magnetic eld generated by a pulsing DC current in a stranded
copper wire with an outer diameter of 2 mm (nominal thickness of
the insulation is 0.45 mm). For the measurement, the sensor was
wrapped around the wire to be in the closest proximity to the
source of magnetic eld (Fig. 4a). To determine the magnetic eld
around the wire, we carried out nite element simulations (Finite
Element Method Magnetics v4.2) taking into account the stranded
structure of the inner copper threads (Fig. 4b). It was found out
that the eld on the surface of the wire is only about 20 µT when a
DC current of 100 mA is supplied to it. We note that this eld is
similar to the one typically obtained in a magneto-uidic
experiments.25
For the experiment, we recorded the PHE voltage while
manually switching the DC current circulating through the wire
ON and OFF (Movie S2). A clear jump in the readout voltage is
produced when the current is turned on (Fig. 4d). Furthermore,
the linearity of our sensor is preserved, as seen by the magnitude
of the voltage change when the current is reversed. This conrms
that the magnetic eld effects are being measured instead of a
temperature variation upon Joule heating of the wire. We note
that the performance of the compliant PHE sensors is at least 10
times better compared to the conventional bulky and rigid clamp
meters applied for current sensing.50
Fig. 3 Mechanical integrity tests. a Dynamic cycling of a compliant PHE sensor. The top dataset represents the measured longitudinal
resistance along the bending direction. The bottom dataset shows the measured transversal voltage (Hall voltage) perpendicular to the
bending direction. b SEM images of a bent sensor. The radius of curvature is gradually changing from about 100–300 µm. The close-up images
of the regions indicated in panel b are shown for the case of the bending radius of c 290 µm and d 110 µm
P.N. Granell et al.
3
Published in partnership with Nanjing Tech University npj Flexible Electronics (2019) ??3?

Compliant PHE sensors as angular sensors
We demonstrated the performance of the compliant PHE sensor in
the linear regime to detect weak magnetic elds. Still, the PHE
sensors can also be used for the detection of an angle. In this case,
we take advantage of the angular dependence of the PHE sensor
output with the relative orientation of the magnetization with
respect to the biasing current. We evaluated the angular
dependence of the compliant PHE sensors by applying a
saturating eld of 4 mT. A sin(2θ) angular dependence is expected
according to the off-diagonal terms of the resistivity tensor for
anisotropic ferromagnetic materials (detailed calculations in SI). In
this demonstrator, the sample was placed on a rotating stage in
the center of a pair of Helmholtz coils (Figure S4) and the PHE
voltage was measured. Figure 5 shows the measured transverse
voltage as a function of the angle between the sensor axis and the
applied eld (azimuthal angle) for a sample bent to a radius of
1 mm. The detected response veries the sin(2θ) angular
dependence. When used within its linear range, the sensor could
be used as an angular sensor to provide orientation information in
soft robotics applications, beneting from the high conformability
of the ultrathin polymeric substrate.
Here, we applied a new fundamental physical principle of
magnetic eld sensing for shapeable magnetoelectronics. By
doing this, we realized a compliant yet high-performance
magnetic eld sensor relying on the planar Hall effect in magnetic
thin lms. Even when prepared on mechanically imperceptible 6-
µm-thick polymeric foils, the sensor elements revealed a remark-
able sensitivity to magnetic elds of 0.86 V/T, which allows us to
detect magnetic elds as small as 200 nT in the at state. Owing to
the ultra-thin supporting layer, the compliant planar Hall effect
sensors do not reveal any sign of degradation in a cyclic bending
experiment with a tiny resistance variation of <0.3% when
bending the devices down to a radius of 2.4 mm. The application
potential of the device is showcased in two examples of an angle
and proximity sensors. For the latter, we demonstrate that the
compliant PHE sensor is able to detect small magnetic stray elds
of magnetically functionalized objects as needed for conventional
metrology as well as point of care diagnostics. High sensitivity of
the prepared sensing devices at eld ranges lower than the
geomagnetic eld combined with a remarkable simplicity of
fabrication, is a step forward in the realization of cost efcient
exible magnetoelectronic devices, with possible application in
soft robotics, interactive devices for virtual- and augmented reality
and point of care platforms for the detection of magnetic objects.
MATERIALS AND METHODS
Substrate preparation
For preparing the compliant PHE sensors, we used commercial poly-
ethylenterephthalat (PET) foils (Chemplex Inc., USA) with a nominal
thickness of 6 µm. The foils were attached to a rigid support, i.e. glass
slides, to allow for a convenient manipulation upon lithography and metal
evaporation steps. We prepared the samples in two ways: by direct
patterning onto PET foils or by adding an extra smoothing layer to reduce
the surface roughness. For the latter case, we spin coated a layer of epoxy-
based photoresist SU-8 (Microchem Corp., USA) for 30 s at 2000 rpm,
resulting in a nominal thickness of 2 µm. Then, the samples were soft
baked (1 min at 65 °C followed by 3 min at 95 °C) and exposed to a UV light
(365 nm wavelength) for 10 min. Finally, the resist was cured for 10 min at
150 °C. The overall thickness of the exible support was 8 µm including the
SU-8 layer.
Sensor fabrication
Permalloy structures with a Hall cross geometry were patterned in a rst
lithography step. We spin coated a layer of adhesion promoter TI Prime
(Microchemicals GmbH) at 4000 rpm for 30 s, followed by soft bake for
2 min at 120 °C. Then, image reversal photoresist AZ5214E (Microchemicals
GmbH) was spin coated for 30 s at 4000 rpm. The samples were soft baked
for 50 s at 110 °C and then exposed with a UV laser writer machine
(Heidelberg DWL66). After the rst exposure, image reversal bake followed,
heating the samples for 2 min at 120 °C. Once the samples cooled down,
they were exposed for the second time to a UV light (365 nm wavelength)
for 5 min. Finally, the samples were developed in AZ351B (Microchemicals
GmbH) with a dilution of 1:4 in deionized (DI) water. The development
time was 40 s with minimal agitation. After patterning, a 20-nm-thick layer
of Permalloy (Ni80Fe20) was deposited by electron beam evaporation
(pressure: 8 × 10−8 mbar; deposition rate: 0.13 nm/s), followed by the
evaporation of a protecting 3-nm-thick Au capping layer (pressure: 6.2 ×
10−8 mbar; deposition rate: 0.24 nm/s). In the second fabrication step, we
evaporate and pattern electrical contact pads consisting of [Au(100 nm)/Ti
(3 nm)] bilayers (pressure: 2.2 × 10−8 mbar (Ti) and 5.5 × 10−8 mbar (Au);
deposition rate: 0.02 nm/s (Ti) and 0.55 nm/s (Au)).
Fig. 5 Angular sensor application. The angular dependence of the
transverse voltage was measured using a compliant PHE sensor
exposed to a saturating eld of 4 mT. Solid line is a guide to the eye
Fig. 4 Detection of magnetic stray elds. a A compliant PHE sensor is
wrapped around a copper wire with a radius of 1 mm. White arrows
represent schematically DC current pulses in the wire. b Finite element
simulations reveal a density plot of the magnetic ux, generated by the
wire upon applying DC current pulses of 100 mA. c A prole of the
magnetic ux density from the wire surface indicating an intensity of
20.4 µT at the sensor location. d Transverse voltage measured by the
sensor, clearly separating the incoming current pulses of different
polarity
P.N. Granell et al.
4
npj Flexible Electronics (2019) ??3? Published in partnership with Nanjing Tech University

Magnetoelectrical chararacterization
To evaluate the magnetotransport properties of the fabricated sensors, we
placed a sample in the center of a pair of Hemholtz coils, which were
supplied with a DC current using a Keysight B2902A precision sourcemeter.
The magnetic eld produced by the Helmholtz coils was calibrated using a
Gaussmeter (Goudsmith Magnetic Systems, Netherlands). A Keysight
B2902A sourcemeter was used to set a DC current bias of 5 mA to the
sensor for magnetotransport measurements. A Keysight 34461 A multi-
meter was used for DC voltage readout. For angular dependence
measurements, we placed the sample on a rotating stage controlled by
a stepper motor. Full hysteresis loops were also measured for a eld range
of ± 3 mT and different bending radii (Figure S3).
Mechanical performance
A custom-built cyclic bending machine was employed to dynamically bend
the sensor and simultaneously measure its resistance. The compliant PET
foils were adapted to t into a commercial Flexible Printed Circuit (FPC)
socket (Figure S2b) to ensure mechanically robust contacts during cycling.
The socket was soldered to a printed circuit board (PCB), which was
attached to the moving part of the bending apparatus. On the stationary
side, we xed a small plastic press to hold the other side of the sample
(Figure S2a).
Calculations of critical bending radius
The smallest bending radius tolerable by a Permalloy thin lm can be
estimated relying on the formalism developed in:51
εtop ¼
ðdf þ dsÞ
2R
ð1 þ 2η þ χη2Þ
ð1 þ ηÞð1 þ χηÞ (1)
Where η= df /ds, and Χ= Yf/Ys. df is the total thickness of the active
metallic layers (20 nm Py and 3 nm Au) and ds is the substrate thickness (6-
µm-thick PET). Yf and Ys are the Young’s moduli of the metallic lms and
substrate, respectively. εtop is the surface strain when the structure is bent
to a radius R. In ref. 52 it was found that the critical strain before the rst
fractures in 60-nm-thick Py lm are observed, is in the range of 0.85 to 1%.
Using this data with Equation 1, we estimated that the critical radius for
our device is about 265 m.
Electrical output of planar Hall effect sensors
Referring to the geometry in Figure S1, a uniform current Ix circulating
through a bar-shaped ferromagnetic thin lm of thickness t will produce a
transverse voltage Vy given by:53
Vy ¼
Ixρ sinð2θÞ
2t
(2)
With ρ= ρ||−ρ⊥, where ρ|| and ρ⊥ are the resistivities parallel and
perpendicular to the magnetization direction. A magnetic thin lm in a
single domain state is assumed with in-plane magnetization along the unit
vector ^M ¼ ðcos θ; sin θÞ. This expression is strictly valid for a Hall bar with
innitesimal voltage probes, but it reects the expected angular
dependence for our sensors.
ACKNOWLEDGEMENTS
We thank Bernd Scheumann, Rainer Kaltofen, and Dr. Jens Ingolf Mönch (all HZDR)
for the deposition of metal layer stacks. Support by the Structural Characterization
Facilities Rossendorf at the Ion Beam Center (IBC) at the HZDR as well as the SEM/FIB
characterization facility at the INTI is greatly appreciated. The project is funded in part
via the German Academic Exchange Service (DAAD) and the Ministry of Education of
Argentina for scholarship “Country-related cooperation programme with Argentina –
ALEARG short term scholarship, 2017 (57352687)” and German Research Foundation
(DFG) Grant MA 5144/9-1.
AUTHOR CONTRIBUTIONS
P.N.G. and D.M. formulated the task. P.N.G. carried out experimental work with the
contribution from G.W., T.K., and G.S.C.B.; P.N.G. performed electromagnetic
simulations with the contribution from F.G. and L.S.; P.N.G., D.M., T.K., and G.S.C.B.
analyzed the data with contributions from J.F., L.S., and F.G.; The manuscript was
written by D.M., P.N.G., and T.K. with contributions from J.F., G.W., L.S., F.G., and G.S.C.
B. All authors have given approval to the nal version of the manuscript.
ADDITIONAL INFORMATION
Supplementary information accompanies the paper on the npj Flexible Electronics
website (https://doi.org/10.1038/s41528-018-0046-9).
Competing interests: The authors declare no competing interests.
REFERENCES
1. Bauer, S. Sophisticated skin: exible electronics. Nat. Mater. 12, 871–872 (2013).
2. Bauer, S. et al. 25th anniversary article: a soft future: from robots and sensor skin
to energy harvesters. Adv. Mater. 26, 149–162 (2014).
3. Lipomi, D. J. & Bao, Z. Stretchable and ultraexible organic electronics. MRS Bull.
42, 93–97 (2017).
4. Yu, K. J., Yan, Z., Han, M. & Rogers, J. A. Inorganic semiconducting materials for
exible and stretchable electronics. npj Flexible Electronics 1, 4 (2017).
5. White, M. S. et al. Ultrathin, highly exible and stretchable PLEDs. Nat. Photonics
7, 811–816 (2013).
6. Choi, M. K. et al. Extremely vivid, highly transparent, and ultrathin quantum dot
light-emitting diodes. Adv. Mater. 30, 1703279 (2018).
7. Ha, S. H., Shin, K. H., Park, H. W. & Lee, Y. J. Flexible lithium-ion batteries with high
areal capacity enabled by smart conductive textiles. Small. 1703418 (2018).
https://doi.org/10.1002/smll.201703418
8. Liu, Q.-C., Xu, J.-J., Xu, D. & Zhang, X.-B. Flexible lithium–oxygen battery based on
a recoverable cathode. Nat. Commun. 6, 7892 (2015).
9. Fang, H. et al. Ultrathin, transferred layers of thermally grown silicon dioxide as
biouid barriers for biointegrated exible electronic systems. Proc. Natl Acad. Sci.
USA 113, 11682–11687 (2016).
10. Shin, G. et al. Flexible near-eld wireless optoelectronics as subdermal implants
for broad applications in optogenetics. Neuron 93, 509–521.e3 (2017).
11. Yu, K. J. et al. Bioresorbable silicon electronics for transient spatiotemporal
mapping of electrical activity from the cerebral cortex. Nat. Mater. 15, 782–791
(2016).
12. Park, S. I. et al. Soft, stretchable, fully implantable miniaturized optoelectronic
systems for wireless optogenetics. Nat. Biotechnol. 33, 1280–1286 (2015).
13. Uguz, I. et al. A microuidic ion pump for in vivo drug delivery. Adv. Mater. 29,
1701217 (2017).
14. Amjadi, M., Kyung, K.-U., Park, I. & Sitti, M. Stretchable, skin-mountable, and
wearable strain sensors and their potential applications: a review. Adv. Funct.
Mater. 26, 1678–1698 (2016).
15. Miyamoto, A. et al. Inammation-free, gas-permeable, lightweight, stretchable
on-skin electronics with nanomeshes. Nat. Nanotechnol. 12, 907–913 (2017).
16. Gisby, T. A., O’Brien, B. M. & Anderson, I. A. Self sensing feedback for dielectric
elastomer actuators. Appl. Phys. Lett. 102, 193703 (2013).
17. Anderson, I. A., Gisby, T. A., McKay, T. G., O’Brien, B. M. & Calius, E. P. Multi-
functional dielectric elastomer articial muscles for soft and smart machines. J.
Appl. Phys. 112, 041101 (2012).
18. Yamada, T. et al. A stretchable carbon nanotube strain sensor for human-motion
detection. Nat. Nanotechnol. 6, 296–301 (2011).
19. Ramuz, M., Tee, B. C.-K., Tok, J. B.-H. & Bao, Z. Transparent, optical, pressure-
sensitive articial skin for large-area stretchable electronics. Adv. Mater. 24,
3223–3227 (2012).
20. Ko, H. C. et al. A hemispherical electronic eye camera based on compressible
silicon optoelectronics. Nature 454, 748–753 (2008).
21. Webb, R. C. et al. Ultrathin conformal devices for precise and continuous thermal
characterization of human skin. Nat. Mater. 12, 938–944 (2013).
22. Drack, M. et al. An imperceptible plastic electronic wrap. Adv. Mater. 27, 34–40
(2015).
23. Graudejus, O., Yu, Z., Jones, J., Morrison, B. & Wagner, S. Characterization of an
elastically stretchable microelectrode array and its application to neural eld
potential recordings. J. Electrochem. Soc. 156, P85 (2009).
24. Kim, D.-H. et al. Materials for multifunctional balloon catheters with capabilities in
cardiac electrophysiological mapping and ablation therapy. Nat. Mater. 10,
316–323 (2011).
25. Lin, G. et al. A highly exible and compact magnetoresistive analytic device. Lab
Chip 14, 4050–4058 (2014).
26. Melzer, M. et al. Elastic magnetic sensor with isotropic sensitivity for in-ow
detection of magnetic objects. RSC Adv. 2, 2284 (2012).
27. Melzer, M. et al. Stretchable magnetoelectronics. Nano Lett. 11, 2522–2526
(2011).
28. Melzer, M. et al. Imperceptible magnetoelectronics. Nat. Commun. 6, 6080 (2015).
29. Melzer, M. et al. Wearable magnetic eld sensors for exible electronics. Adv.
Mater. 27, 1274–1280 (2015).
30. Cañón Bermúdez, G. S. et al. Magnetosensitive e-skins with directional perception
for augmented reality. Sci. Adv. 4, eaao2623 (2018).
P.N. Granell et al.
5
Published in partnership with Nanjing Tech University npj Flexible Electronics (2019) ??3?

31. Münzenrieder, N. et al. Entirely exible on-site conditioned magnetic sensorics.
Adv. Electron. Mater. 2, 1600188 (2016).
32. Makarov, D., Melzer, M., Karnaushenko, D. & Schmidt, O. G. Shapeable magne-
toelectronics. Appl. Phys. Rev. 3, 011101 (2016).
33. Li, B., Kavaldzhiev, M. N. & Kosel, J. Flexible magnetoimpedance sensor. J. Magn.
Magn. Mater. 378, 499–505 (2015).
34. Wang, Z. et al. Highly sensitive exible magnetic sensor based on anisotropic
magnetoresistance effect. Adv. Mater. 28, 9370–9377 (2016).
35. Wang, Z., Shaygan, M., Otto, M., Schall, D. & Neumaier, D. Flexible Hall sensors
based on graphene. Nanoscale 8, 7683–7687 (2016).
36. Cañón Bermúdez, G. S. et al. Electronic-skin compasses for geomagnetic eld-
driven articial magnetoreception and interactive electronics. Nat. Electron. 1,
589–595 (2018).
37. Freitas, P. P. et al. Spintronic platforms for biomedical applications. Lab Chip 12,
546–557 (2012).
38. Lin, G., Makarov, D. & Schmidt, O. G. Magnetic sensing platform technologies for
biomedical applications. Lab Chip 17, 1884–1912 (2017).
39. Schuhl, A., Van Dau, F. N. & Childress, J. R. Loweld magnetic sensors based on
the planar Hall effect. Appl. Phys. Lett. 66, 2751–2753 (1995).
40. Kaltenbrunner, M. et al. An ultra-lightweight design for imperceptible plastic
electronics. Nature 499, 458–463 (2013).
41. Salvatore, G. A. et al. Wafer-scale design of lightweight and transparent elec-
tronics that wraps around hairs. Nat. Commun. 5, 2982 (2014).
42. Someya, T., Bauer, S. & Kaltenbrunner, M. Imperceptible organic electronics. MRS
Bull. 42, 124–130 (2017).
43. Mor, V. et al. Planar Hall effect sensors with shape-induced effective single
domain behavior. J. Appl. Phys. 111, 07E519 (2012).
44. Hung, T. Q. et al. Optimization of the multilayer structures for a high eld-
sensitivity biochip sensor based on the planar hall effect. IEEE Trans. Magn. 45,
4518–4521 (2009).
45. Ejsing, L. et al. Planar Hall effect sensor for magnetic micro- and nanobead
detection. Appl. Phys. Lett. 84, 4729–4731 (2004).
46. Telepinsky, Y. et al. Towards a six-state magnetic memory element. Appl. Phys.
Lett. 108, 182401 (2016).
47. Karnaushenko, D. et al. Self-assembled on-chip-integrated giant magneto-
impedance sensorics. Adv. Mater. 27, 6582–6589 (2015).
48. Streubel, R. et al. Magnetic microstructure of rolled-up single-layer ferromagnetic
nanomembranes. Adv. Mater. 26, 316–323 (2014).
49. Streubel, R. et al. Magnetically capped rolled-up nanomembranes. Nano Lett. 12,
3961–3966 (2012).
50. Fluke 325 Clamp Meter User’s Manual. Available at: www.uke.com.
51. Suo, Z., Ma, E. Y., Gleskova, H. & Wagner, S. Mechanics of rollable and foldable
lm-on-foil electronics. Appl. Phys. Lett. 74, 1177–1179 (1999).
52. Wojciechowski, P. H. & Mendolia, M. S. On the multiple fracture of low-elongation
thin lms deposited on high-elongation substrates. J. Vac. Sci. Technol. A 7,
1282–1288 (1989).
53. Henriksen, A. D. et al. Planar Hall effect bridge magnetic eld sensors. Appl. Phys.
Lett. 97, 013507 (2010).
Open Access This article is licensed under a Creative Commons
Attribution 4.0 International License, which permits use, sharing,
adaptation, distribution and reproduction in any medium or format, as long as you give
appropriate credit to the original author(s) and the source, provide a link to the Creative
Commons license, and indicate if changes were made. The images or other third party
material in this article are included in the article’s Creative Commons license, unless
indicated otherwise in a credit line to the material. If material is not included in the
article’s Creative Commons license and your intended use is not permitted by statutory
regulation or exceeds the permitted use, you will need to obtain permission directly
from the copyright holder. To view a copy of this license, visit http://creativecommons.
org/licenses/by/4.0/.
? The Author(s) 2019
P.N. Granell et al.
6
npj Flexible Electronics (2019) ??3? Published in partnership with Nanjing Tech University