  Flexible electronics is an emerging field in many applications ranging from
in vivo biomedical devices to wearable smart systems. The capability of
conforming to curved surfaces opens the door to add electronic components to
miniaturized instruments, where size and weight are critical parameters. Given
their prevalence on the sensors market, flexible magnetic sensors play a major
role in this progress. For many high-performance applications, magnetic tunnel
junctions (MTJs) have become the first choice, due to their high sensitivity,
low power consumption etc. MTJs are also promising candidates for non-volatile
next-generation data storage media and, hence, could become central components
of wearable electronic devices. In this work, a generic low-cost regenerative
batch fabrication process is utilized to transform rigid MTJs on a 500 {\mu}m
silicon wafer substrate into 5 {\mu}m thin, mechanically flexible silicon
devices, and ensuring optimal utilization of the whole substrate. This method
maintains the outstanding magnetic properties, which are only obtained by
deposition of the MTJ on smooth high-quality silicon wafers. The flexible MTJs
are highly reliable and resistive to mechanical stress. Bending of the MTJ
stacks with a diameter as small as 500 {\mu}m is possible without compromising
their performance and an endurance of over 1000 cycles without fatigue has been
demonstrated. The flexible MTJs were mounted onto the tip of a cardiac catheter
with 2 mm in diameter without compromising their performance. This enables the
detection of magnetic fields and the angle which they are applied at with a
high sensitivity of 4.93 %/Oe and a low power consumption of 0.15 {\mu}W, while
adding only 8 {\mu}g and 15 {\mu}m to the weight and diameter of the catheter,
respectively.
