In this measurement, the VDWTF pad is placed
on the left forearm and the gate electrode is
adhered on the symmetrical position (right
forearm) (Fig. 5D), and each VDWTF pad
works with an Ag/AgCl electrode nearby for
comparison. Among the common challenges
in measuring ECG with conventional Ag/AgCl
electrodes are the motion artifacts due to
sliding, inconsistent adhesion, and a mechan-
ical mismatch at the electrode–skin interface
induced by skin deformation, leading to a
greatly reduced signal-to-noise ratio (SNR),
from 44.3 dB before motion (Fig. 5E) down to
28.5 dB during motion (Fig. 5, F and G). With
the conformal skin-gate transistors, motion
artifacts are mitigated, achieving an essen-
tially comparable SNR of 49.8 dB before hu-
man motion (Fig. 5E and fig. S6) and 49.2 dB
during human motion (Fig. 5, F and G). With
reduced motion artifacts, the ECG signals
recorded by the skin-gate transistors (red line)
show clear P, QRS, and T waves, with no ab-
normal deviations and relatively stable base-
line during human motion (Fig. 5, F and G). In
contrast, such fine signals are less resolvable
by the Ag/AgCl electrodes (Fig. 5G).
High-fidelity, real-time electroencephalogram
(EEG) recording is important for monitoring
cerebral activities, studying cognitive behaviors,
and developing insights into various neurolog-
ical disorders. Cerebral activities can be divided
into five frequency bands: delta wave (0 to
4 Hz), theta wave (4 to 8 Hz), alpha wave (8 to
12 Hz), beta wave (12 to 30 Hz), and gamma
wave (>30 Hz), with each frequency band
associated with different mental states. To testthe ability to acquire high-quality neuro-
physiological signals, we placed the VDWTF
transistor over the left side of the forehead
(Fp1) according to the international 10-20
system of EEG electrode placement ( 17 ) and
recorded voltage differences relative to a ref-
erence electrode placed over the left occip-
ital region (O1) (Fig. 5H). When the human
subject is relaxed with eyes closed, the EEG
background is usually characterized by the
posteriorly dominant alpha rhythm (post-
erior dominant rhythm) with a prominent
8- to 12-Hz (alpha) oscillation (Fig. 5, I and
J), corresponding to brain activities such as
meditation and mindfulness that can reduce
stress levels. The alpha rhythm typically at-
tenuates considerably upon eye opening, as
clearly seen in the spectrogram of the EEGSCIENCEscience.org 25 FEBRUARY 2022•VOL 375 ISSUE 6583 857
Fig. 4. Skin-gate VDWTF
transistors.(A) The structure
of human skin. (B) Schematic
of a skin-gate VDWTF transistor
with Au source and drain
electrodes and an iron rod
gate electrode held by a human
subject. (C) Photograph of the
freestanding VDWTF on a
replica of human skin (left)
and the VDWTF supported by a
1.6-mm-thick polyimide substrate
on a replica of human skin
(right). (DtoG) Height profiles
corresponding to the line scan in
different areas of (C). (H) Skin-
gate VDWTF transistor on human
skin under different types of
mechanical deformation.
(I) Remaining area of VDWTFs
and CVDTFs on skin replicas
as a function of stretching
cycles (10% tensile strain).
Scale bars, 2 mm. (J) Output
and (K) transfer curves of
a skin-gate VDWTF transistor.
(L) Transfer curves under
different types of deformation.
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