Download adem.202100896

See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/354822729
A Printed Wireless Triangle‐Wave Generator via a Smartphone
Article in Advanced Engineering Materials · September 2021
DOI: 10.1002/adem.202100896
CITATIONS
READS
5
268
10 authors, including:
Sagar Shrestha
Junfeng Sun
Sungkyunkwan University
Huzhou University
18 PUBLICATIONS 94 CITATIONS
29 PUBLICATIONS 977 CITATIONS
SEE PROFILE
SEE PROFILE
Sajjan Parajuli
Kiran Shrestha
Sungkyunkwan University
Sungkyunkwan University
21 PUBLICATIONS 94 CITATIONS
18 PUBLICATIONS 104 CITATIONS
SEE PROFILE
SEE PROFILE
Some of the authors of this publication are also working on these related projects:
Nickel ink formulation using PVP ( Polyvinylpyrrolidone ) and Ethyl cellulose polymers as binders for roll to roll printed Diode View project
All content following this page was uploaded by Sagar Shrestha on 21 October 2021.
The user has requested enhancement of the downloaded file.
RESEARCH ARTICLE
www.aem-journal.com
A Printed Wireless Triangle-Wave Generator via a
Smartphone
Younsu Jung, Sagar Shrestha, Namsoo Lim, Hyejin Park, Junfeng Sun, Jinhwa Park,
Sajjan Parajuli, Kiran Shrestha, Seongryeong Kim, and Gyoujin Cho*
(CV)-based electrochemical sensor is very
useful to quantitatively and qualitatively
monitor redox-active analytes,[8] which will
be oxidized and reduced on the electrodes
as the time-dependent positive and negative potentials of a triangle-wave form are
alternatively and periodically scanned in
the CV.[9] Therefore, if the CV is available
as a disposable wireless tag, it would open
the door to produce inexpensive PoCTs. To
develop the disposable wireless CV tag, the
operation power to generate the trianglewave form should be transferred through
wireless power transmission (WPT) without using a battery. In general, the WPT
can be grouped into near-field (nonradiative) or far-field (radiative) transmission.[10]
The near-field WPT utilized the magnetic
coupling of conductive loops or coils in a
short distance such as the NFC
(13.56 MHz) of smartphone, whereas the far-field WPT utilizes
the electromagnetic radiation of microwaves in a long-range distance. The far-field WPT is useful in low-power sensor networks.[11] As the wireless CV tag needs a relatively high power
to scan redox-active analytes on the electrodes with positive
and negative potentials of the triangle-wave form, the far-field
WPT cannot be used. Therefore, the disposable wireless CV
tag needs to attain the polarized () DC power through the
near-field WPT using the NFC carrier of smartphone to generate
the triangle-wave form with positive and negative potentials
(Figure 1a). To generate the DC power from the NFC carrier signal of smartphone, the NFC carrier signal is first coupled by an
antenna and then converted to the DC power through the rectifier (Figure 1a). The rectifier circuit is also known as rectenna,
integrated antenna, Schottky diodes, and capacitors. As the rectified DC power can operate the ring oscillator to generate the
triangle wave with positive and negative potentials (Figure 1a),
the printed rectenna is a key unit for developing the wireless
CV tag.
For the first time, our group reported an all-printed, disposable, and wireless (13.56 MHz) CV tag in 2015 utilizing a printed
rectenna and printed 36 p-type thin-film transistors (TFTs) to
demonstrate a printed wireless CV tag using a custom-made
NFC (13.56 MHz) reader through the roll-to-plate (R2P) gravure
printing method.[12] In the printed CV tag, the rectifier was
printed with ZnOpolyaniline (Pan) composite-based ink to render the Schottky junction generated by an aluminum flake electrode with a low work function. The printed ZnOPan-based
An all-printed wireless triangle-wave generator is needed to produce a printed
wireless and disposable cyclic voltammetry (CV)-based biosensor to detect redoxactive analytes. The generator should produce positive and negative potentials
from the smartphone’s near-field-communication (NFC) (13.56 MHz) carrier
signal. However, the printed triangle-wave generator that contains rectenna and
a ring oscillator fails to wirelessly operate with a smartphone because the
polarized () DC power from the NFC carrier signal of the smartphone could not
be provided through the utilization of a printed Schottky diode. Herein, an n-type
indium gallium zinc oxide (IGZO)-based ink is formulated to print the Schottky
junction with a high work function of the printed electrode provided by in situ
doping of printed poly(3,4-ethylenedioxythiophene) polystyrene sulfonate
(PEDOT:PSS) on Ag electrode. The printed IGZO-based rectenna could wirelessly
harvest polarized () DC 10 V from the smartphone to generate a triangle wave
with positive and negative potentials through the printed ring oscillator.
1. Introduction
Electrochemical biosensors transduce a current or potential
(quantitatively or qualitatively) through a specific biochemical
recognition[1,2] and are usually implemented in a point-of-care
test (PoCT).[3–7] Among the biosensors, a cyclic voltammetry
Y. Jung, S. Shrestha, J. Park, S. Parajuli, K. Shrestha, S. Kim, G. Cho
Department of Biophysics, Institute of Quantum Biophysics, Research
Engineering Center for R2R Printed Flexible Computer and Department of
Intelligent Precision Healthcare Convergence
Sungkyunkwan University
Suwon-si 16419, Republic of Korea
E-mail: [email protected]
N. Lim
Sensor System Research Center
Korea Institute of Science and Technology (KIST)
Seoul 02782, Republic of Korea
H. Park
Next Generation Battery Research Center
Korea Electrotechnology Research Institute (KERI)
Changwon-si 51543, Republic of Korea
J. Sun
School of Engineering
Huzhou University
Xueshi Road, No. 1, Huzhou 313000, P. R. China
The ORCID identification number(s) for the author(s) of this article
can be found under https://doi.org/10.1002/adem.202100896.
DOI: 10.1002/adem.202100896
Adv. Eng. Mater. 2021, 2100896
2100896 (1 of 10)
© 2021 Wiley-VCH GmbH
www.aem-journal.com
www.advancedsciencenews.com
Figure 1. Illustration of the gravure-printed rectenna system for the application in a CV tag. a) Schematic illustration of the disposable CV tag system
operated by the NFC carrier signal of a smartphone. b) Energy-level alignment of Ag electrode with different doping levels of PEDOT:PSS and their leakage
current relationship. c) Schematic flowchart for printing rectenna through combined R2R and R2P processes.
rectifier could wirelessly provide a polarized DC () 10 V from
a custom-made 13.56 MHz reader to run a printed TFT-based
ring oscillator to generate the triangle-wave form with positive
and negative potentials to scan printed electrodes. However,
the polarized DC () 10 V could not be harvested from the
NFC (13.56 MHz carrier) of a smartphone due to a high
turn-on voltage (0.9 V) of the ZnOPanAl flake-based
Schottky diode. The printed semiconductors should have a
lower Schottky barrier height and low reverse leakage current
to increase the rectifier efficiency and reduce the turn-on voltage of the printed diode. However, the lower Schottky barrier
height usually increases reverse leakage currents to be contradictory. Therefore, we developed an indium gallium zinc oxide
(IGZO)-based semiconductor ink with a wide bandgap to print
a metalsemiconductorinsulator-type diode. The printed
Adv. Eng. Mater. 2021, 2100896
diode has a laminating aluminum foil as a top electrode to
achieve a turn-on voltage of 0.6 V, while maintaining low
reverse leakage currents.[13] The printed IGZO diode with a
laminated aluminum foil electrode could wirelessly obtain
DC 10 V from the NFC carrier of the smartphone with 50%
efficiency.[14] However, the laminated aluminum foil-based
electrodes were not suited to print inexpensive and practical
rectenna for the printed wireless CV tag, using a scalable
high-throughput printing method. Based on studies on the
IGZO-based Schottky diodes, the large Schottky barrier height
and stable Schottky junction cannot be easily formed even with
sputtered Pt due to the surface defects (oxygen vacancy and
hydroxyl groups) of IGZO, causing an Ohmic junction via
downward band bending.[15] In order words, the robust and
printable high (>5.0 eV)-work function electrodes should be
2100896 (2 of 10)
© 2021 Wiley-VCH GmbH
www.aem-journal.com
www.advancedsciencenews.com
ready to render the reasonable Schottky barrier height to minimize reverse leakage currents with a printed IGZO layer.
Printed Schottky diodes with silver ink have a more practical
output to develop all-printed wireless CV tags as silver ink is characterized well and proven to be reliable in printed electronics
with an inkjet,[16] a screen printer,[17] an offset,[18] and a gravure.[19] However, roll-to-roll (R2R) gravure-printed silver electrodes with silver ink, formulated based on our previous work,[12]
cannot be directly used to render the Schottky junction with
IGZO due to their low work function (4.4 eV). Of course, formulating the silver ink by adding surfactants or binders is possible to
slightly change the work function of the printed silver layer.
However, the changed work function of the printed silver layer
may not be large enough. As a result, they render Ohmic contact
with the printed IGZO. Furthermore, the work function of silver
electrodes can be decreased to 3.6 eV by adsorption-induced
intermolecular dipoles[20] and molecular reorientation.[21]
Polyethylene imine (PEI)- and polyethyleneimine ethoxylated
(PEIE)[20]-coated silver electrodes can lower the work function
down to 3.7 eV. In addition, inorganic metal oxides (ZnO and
TiOx)[22] and alkali metal salts (LiF, Cs2Co3, and Li2CO3)[23,24]
were also used to reduce the work function of the metal electrode.
However, the increase in the metal electrode work function is yet
to be reported, with the exception of graphene using metal salts
such as AuCl3, IrCl3, MoCl3, PdCl3, and RhCl3 through adsorption-induced chemical doping.[25] Although Au, Cu, Pd, Rh, Ir,
Mo, and Os are often used as high-work function electrodes,
these metals are not practical for using on high-throughput
large-scale manufacturing to produce inexpensive and disposable
wireless CV tags. In addition, the self-assembled monolayer
(SAM) treatment method was reported to increase the work function of printed silver electrodes.[26] However, this method would
be difficult to be implemented in scalable high-throughput printing processes such as R2R or R2P gravure because of requiring
longer time to form SAM layers on the silver electrode.
Therefore, developing a printed high-work function electrode
(>5.0 eV) based on the gravure-printed silver electrode can realize IGZO-based Schottky diodes through a scalable printing
method.
In this study, we developed a simple, scalable printing method
to provide high-work function electrodes (5.4 eV) by printing
poly(3,4-ethylenedioxythiophene)
polystyrene
sulfonate
(PEDOT:PSS) (4.8 eV) ink on the printed silver electrode, so that
the printed silverPEDOT:PSS electrodes can provide a high
Schottky barrier height with the printed IGZO layers, while
maintaining low reverse leakage currents with the printed
IGZO (Figure 1b). We utilized the printed silver electrode
(4.4 eV) due to its stability under ambient conditions. The printed
Schottky diode was characterized and integrated as two voltage
triplers (six diodes and six capacitors) with an R2R gravureprinted antenna with capacitors to function as a rectenna to
wirelessly provide polarized DC () 10 V from the NFC
carrier signal of a smartphone. The polarized DC () 10 V could
operate all R2R-printed ring oscillators to generate triangle waves
of positive and negative potentials with 2 Hz. Furthermore, the
stability of the rectenna was studied at 4 C for potential application in disposable wireless CV tags in the smart package[27] for
cold chain.
Adv. Eng. Mater. 2021, 2100896
2. Results and Discussion
As shown in Figure 1c, the R2R gravure was first used to print
silver electrode and antenna on the polyimide (PI) web at the first
printing unit using silver ink with a viscosity of 800 cP and surface tension of 42 mN m1. Dielectric layers for capacitors were
then continuously printed at the second printing unit with a
BaTiO3-based ink with a viscosity of 50 cP and surface tension
of 32 mN m1. After printing dielectric layers, the PI web was
rewound, and the electrodes of capacitors were printed selectively
on printed dielectric layers using Cu ink with a viscosity of 800 cP
and surface tension of 33 mN m1. We selected Cu ink instead of
Ag ink to print the top electrodes of capacitors to attain low leakage current and high device yield, as shown in Figure 2a.
The R2R printing process was maintained to have an overlay
printing registration accuracy of 25 μm at the printing speed
of 6 m min1. All printed inks were completely dried while passing through a 1.5 m-long drying chamber at 150 C. The printed
electrodes and antenna have an equivalent surface roughness of
23 nm and thickness of 0.6 μm (Figure S1, Supporting
Information). The R2R-printed capacitors have a thickness of
8 μm with 3.8 μm dielectric layer thickness and 3.8 μm thickness
of the top Cu electrode (Figure 2b). The end-to-end resistances of
the randomly selected R2R-printed electrodes and antenna were
0.79 0.12 Ω and 320 50 Ω, respectively, and were measured
every 1 m along the 10 m-length printed layers (Figure 2c,d).
After a sintering process at 250 C for 2 h, the end-to-end resistances of the randomly selected R2R-printed electrodes and
antenna were about 0.25 0.06 Ω and 61 5 Ω, which indirectly
proves the reliability of the R2R printing processes (Figure 2c,d).
A critical point in the designed antenna was matching the high
Q-factor at the resonance frequency of 13.56 MHz as the performance of the printed antenna with seven turns is critical to efficiently couple the NFC carrier signal. Figure 2e,f shows the
return loss (dB) at the resonance frequency for the R2R-printed
antenna on the PI film before and after connecting the diode,
capacitors, and ring oscillator (a triangle-wave generator). The
p
attained Q factor (Q ¼ 1/R(resistance) (L(inductance)/
C(capacitance)) was 4.02, which could couple AC 20 V within
the proximity of the smartphone. The six capacitors were printed
per antenna and measured along 10 m of the web. The measured
capacitances in one antenna per every 1 m of the 10 m web (total
ten samples) were in the range of 0.4 0.03 nF, as shown in
Figure 2g. A printed rectenna consisting of six diodes and capacitors was designed to give 10 V of DC voltage to a disposable
NFC-CV tag.[12] In the metalinsulatormetal structure (Ag/
BaTiO3/Cu), with the given voltage range (from 10 to
þ10 V), a low leakage current (<200 pA) was sufficient enough
to use as a capacitor (Figure S2a, Supporting Information).
Although printed silver top electrodes show a relatively high
capacitance (>0.9 nF), they cannot be used due to short or leakage issues (Figure S2b, Supporting Information).
The R2R gravure-printed silver electrodes were modified by
printing PEDOT:PSS ink onto the surface to acquire a high work
function in printed silver electrodes with a scalable printing
method. The printed PEDOT:PSS work function increased as
the printed PEDOT:PSS was further doped on the printed silver
surface.[28] In addition, the pinhole-free topology is critical in
printing devices with vertical structures, and thus, controlling
2100896 (3 of 10)
© 2021 Wiley-VCH GmbH
www.aem-journal.com
www.advancedsciencenews.com
Figure 2. Electrical properties of printed antenna and capacitors. a) Roll image of R2R-printed antenna and capacitors. b) Cross-sectional SEM image of
printed capacitors. c) End-to-end resistance value of printed electrodes from ten selected samples along the 10 m length of R2R gravure-printed web.
d) End-to-end resistance value of printed antenna from ten selected samples along the 10 m length of R2R gravure-printed web. e) Return loss (dB) with a
function of frequency for printed antenna. f ) Return loss (dB) with the function of frequency for printed antenna by loading diodes, capacitors, and a ring
oscillator. g) Capacitance value from ten selected samples along the 10 m length of R2R gravure-printed web. h) Work function variation for Ag electrode
after printing different doping levels of PEDOT:PSS.
the printability of PEDOT:PSS on printed silver electrodes is critical to maintaining the reliable electrical characteristics of the
printed devices. Therefore, the printability of the formulated
PEDOT:PSS ink needs to be optimized by changing the binder
content because the printability depends on the loading amount
of the binder, poly(vinyl alcohol) (PVA). In a low-PVA content
(1 wt%), the PEDOT:PSS layer was printed with defects and high
roughness (Figure S3a, Supporting Information). In contrast, the
printed PEDOT:PSS layers became homogeneous and defect free
with the PVA loading of 3 wt% (Figure S3b, Supporting
Information). As the IV characteristics of printed diodes with
1 and 3 wt% of PVA loading in PEDOT:PSS ink showed, respectively, a high leakage current (>90 μA at 3 V) and a low leakage
current (<0.2 μA at 3 V) from the IV sweep (Figure S3c,d,
Supporting Information), we can indirectly estimate the quality
of printed PEDOT:PSS layers by measuring the leakage currents. However, over the 3 wt% of PVA loading, we observed
a high resistance (2030 kΩ for end-to-end point of the
printed area) and poor output voltage (1 V for 10 Vpp input)
Adv. Eng. Mater. 2021, 2100896
(Figure S3e, Supporting Information) in the 5 wt% of PVAloaded PEDOT:PSS due to large amount of the binder (acts
as an insulator) content. In contrast, as PEDOT:PSS with
3 wt% of PVA had relatively low resistance (25 kΩ), the high
output voltage (>4 V for 10 Vpp input) (Figure S3f, Supporting
Information) was attained and thus we fixed 3 wt% of PVA content in PEDOT:PSS ink.
Measured by ultraviolet photoelectron spectroscopy (UPS), as
shown in Figure 2h, the work function of printed PEDOT:PSS on
silver electrodes can be engineered from 4.4 to 5.4 eV by printing
PEDOT:PSS with four different doping levels. The doping levels
were controlled by loading different amounts of ethanolamine
during ink formulation in 3 wt% of PVA. The attained highest
work function of the R2P-printed PEDOT:PSS on silver electrodes was 5.4 eV by printing PEDOT:PSS (no ethanolamine) on
R2R-printed silver electrodes, and this work function
(5.4 eV) was matched to provide maximum DC converting efficiency (50%) using the printed IGZO-based Schottky diodes.
Based on the ethanolamine loading method in PEDOT:PSS
2100896 (4 of 10)
© 2021 Wiley-VCH GmbH
www.aem-journal.com
www.advancedsciencenews.com
ink, the work functions of the printed electrodes can be tailored
in the range from 4.4 to 5.4 eV by printing PEDOT:PSS with different loading amounts (00.6 wt%) of ethanolamine on the
printed silver electrodes.
R2P gravure was used to print the IGZO layer on the printed
AgPEDOT:PSS electrode to render the Schottky junction,
whereas carbon paste and Cu ink were printed on the printed
IGZO layer, respectively, to give Ohmic junctions. IGZO powder
was prepared using hydrothermal synthesis and then dried in an
70 C oven to formulate the IGZO ink. Once dried in white color,
the IGZO powder was further sintered at a 700 C oven for 2 h
and showed a pale yellow color (Figure S4a, inset image,
Supporting Information). The sintered IGZO powders were
characterized using a scanning electron microscope (SEM)
and X-ray diffraction (XRD). The characterized sizes of the resulting IGZO nanoparticles are in the range of 40170 nm
(Figure S4b, Supporting Information) taken from the SEM
image (Figure S4a, Supporting Information). This size distribution is appropriate for the gravure printing process after formulating IGZO ink. Crystallographic analysis using XRD was also
conducted to identify the sintered IGZO powders and confirmed
the typical characteristic peaks of IGZO (Figure S5, Supporting
Information).[29,30] An IGZO-based semiconducting ink was formulated with PVA as a binder and was printed on PEDOTsilver
electrodes by R2P gravure (Figure S6a, Supporting Information).
The formulated IGZO ink with PVA was also tested for printability. The R2P printing process was done with a roll speed of
20 mm s1 and a roll pressure of 1.65 MPa. These two
parameters are critical to maintaining the printing quality of
IGZO layers and the top electrode. The pinhole-free surface morphology of the printed IGZO could not be attained under various
printing speeds and pressures in an R2P printer (Figure S6b,
Supporting Information) and resulted in poor performance of
the printed Schottky diodes. The morphology of the printed
IGZO was improved after a nonionic surfactant (Tween-80)
was added (1 wt%) to the formulated IGZO ink to attain
defect-free layers of the printed IGZO (Figure S6c, Supporting
Information). An atomic force microscope (AFM) image
(Figure S7, Supporting Information) shows well-dispersed
IGZO nanoparticles in the binder of the printed IGZO layer
on the AgPEDOT electrode (10 μm 10 μm) at 1 wt% of
Tween-80 loading.
The optical image and cross-sectional SEM image of allprinted rectenna are shown in Figure 3a. From the crosssectional SEM image, the thicknesses of R2R gravure-printed silver electrode, R2P gravure-printed PEDOT:PSS, IGZO, and carbon electrodes were, respectively, 700 nm, 500 nm, 1.33 μm, and
2.61 μm without obvious intermixing between layers. Utilizing
the all-printed rectenna with six Schottky diodes and six capacitors (Figure 3a, inset image), we first characterized the printed
diodes with three different top electrodes consisting of carbon,
copper, and silver. As expected from the work functions of
printed silver, copper, and carbon electrodes, the printed
IGZO layers without PEDOT:PSS layers on the bottom electrodes were all shown as Ohmic junctions (Figure 3b) with no rectification for all cases (Ag/IGZO/carbon, Ag/IGZO/Cu, and Ag/
Figure 3. DC characteristics of IGZO-based Schottky diodes with various top electrodes. a) Optical and cross-sectional SEM images of the printed
Schottky diode. b) Semilog IV plots of IGZO Schottky diode with different top electrodes. c) Semilog IV plots of IGZO with/without PEDOT layer.
d) Rectification ratio of printed diodes depending on top electrodes. e) The experimental dV/dln(I) versus I plot obtained from forward bias current
voltage of the Ag/PEDOT/IGZO/carbon diode. f ) The experimental dV/dln(I) versus I plot obtained from forward bias current voltage of Ag/PEDOT/
IGZO/Cu diode. g) 1/C2 versus voltage characteristics of Ag/PEDOT/IGZO/carbon and Ag/PEDOT/IGZO/Cu diodes.
Adv. Eng. Mater. 2021, 2100896
2100896 (5 of 10)
© 2021 Wiley-VCH GmbH
www.aem-journal.com
www.advancedsciencenews.com
IGZO/Ag). Based on the previous study of IV characteristics
with a logarithm scale, the Ag/IGZO/PEDOT/carbon layer also
exhibited an Ohmic junction due to the inability of PEDOT:PSS
to be doped by the surface of printed carbon black to increase the
work function. In contrast, the Schottky diodes were observed in
the Ag/PEDOT/IGZO/carbon structure. Figure 3c, respectively,
shows the IV characteristics of Ag/PEDOT/IGZO/carbon and
Ag/IGZO/carbon diode structures with carbon as the top electrode. The Schottky diode showed the threshold voltage (Vth)
of 0.6 V and a leakage current (Ioff ) of 0.02 mA at the given
voltage range (from 3 to þ3 V), similar to the characteristics of
the printed Schottky diode.[31,32] To understand the mechanism
of the fully printed Schottky diode, we estimated the highest
occupied molecular orbital (HOMO) and lowest unoccupied
molecular orbital (LUMO) of the printed IGZO layer based on
the cyclic voltammogram of the coated IGZO on the working
electrode (Figure S8a, Supporting Information),[33] and the work
functions of the used electrodes were measured by UPS, respectively (Figure S8b, Supporting Information).[34] The rectification
ratios under the bias voltage range of 0 þ 3 V for four diodes,
Ag/PEDOT/IGZO/carbon, Ag/PEDOT/IGZO/Cu, Ag/PEDOT/
IGZO/Ag, and Ag/IGZO/carbon, are shown in Figure 3d.
Among these diodes, Ag/PEDOT/IGZO/carbon diode had rectification ratios of >101.5, being critical for high-frequency rectification and nonlinearities in the measured voltage range.
Rectifying characteristics are expected by the high Schottky barrier height, and the measured data are matched to the expected
rectifying direction. At the Schottky junction, the charge transfer
mechanism is explained by the thermionic emission theory and
is given by Equation (1).[35]
qΦB
qðV IRS Þ
1
(1)
I ¼ AA T 2 exp
exp
nkT
kT
where k is Boltzmann’s constant, q is the elementary electric
charge, T is temperature, A is the area of the diodes, A* is
the Richardson constant for IGZO, and 41 A cm2 K2 from
the effective mass me* ¼ 0.34 mo. ΦB is the Schottky barrier
height, n is the ideality factor of the diode, and Rs is its series
resistance. We tested diodes with copper and carbon top electrodes and calculated the diode parameters using Richardson’s plot
to explore the charge transfer, as shown in Figure 3e,f. The series
resistance and the ideality factor can be drawn from Richardson’s
plot (dV/dlnI vs I) by extrapolating the linear region, where slope
gives series resistance, and y-axis intercept gives the ideality factor. The calculated ideality factor and series resistance were 4.6
and 9.7 kΩ for the Ag/PEDOT/IGZO/Cu diode (Figure 3e). For
the carbon top electrode case, ideality factor and series resistance
were 3.3 and 65 kΩ (Figure 3f ). As the Schottky diodes are all
printed, the attained ideality factor (3.3–4.6) is higher than the
ideal diode and thus, reveals the presence of interfacial states
in the bandgap.[36] We can conclude that the carbon top electrode-based diode showed a lower ideality factor than the copper
top electrode and higher current level for attaining a higherrectified DC voltage by analyzing calculated values.
Furthermore, the built-in potential and depletion charge density
can be estimated with a 1/C2V characteristics plot. The relationship between capacitance and voltage is given by the
MottSchottky plot using Equation (2).[14]
Adv. Eng. Mater. 2021, 2100896
A2
¼
C2
2
ε0 εS N depl
!
V bi kT
q
V
(2)
Vbi denotes the built-in potential, Ndepl is the depletion region
charge density related to the IGZO doping, and k is Boltzmann’s
constant. Figure 3g shows a 1/C2V curve which is replotted
using the capacitancevoltage (CV ) data—measured by
Keithley 4200 connected to a capacitance measurement system.
There is a flat region up to 0 V in the graph, indicating the presence of an abrupt diode junction (e.g., Schottky junction). By
extrapolating the linear region, the Vbi and barrier height of
the diode junction can be obtained. For our case, Vbi and ΦB were
measured to be, respectively, 0.60 and 0.84 eV on the device with
a carbon top electrode, whereas the copper top electrode-based
diode showed 0.95 and 1.19 eV. The depletion layer charge density Ndepl was found to be 4.8 1018 cm3 and 1.4 1015 cm3
for carbon and copper top electrodes, respectively. If the Vbi value
(0.95 eV) is correct, the Fermi energy of IGZO is estimated to be
4.43 eV, corresponding with our calculated energy HOMO
(5.2 eV)LUMO (4.2 eV) energy levels for IGZO.[31]
The output DC voltage of the printed single diode (Ag/
PEDOT/IGZO/carbon) with 1 MΩ load resistor was only characterized with an oscilloscope with 13.56 MHz AC (8 Vpp(peak to
peak)), as the diode with a carbon top electrode was superior.
Figure 4a shows the rectified DC voltage Vout as a function of
the input frequency with amplitude of 8 Vpp. From the output
voltage characteristics at 13.56 MHz, the rectifying efficiency
of a single rectifier is about 50%, whereas the voltage tripler
was also shown to have 50% efficiency. The harvesting efficiency
of wireless DC power was tested by an input frequency
(1013.56 MHz) from the oscilloscope because the IGZO-based
diode mainly focuses on its application in WPT from a smartphone. A high load resistance was required to generate high
power (high DC voltage from diode) and increase the output
DC voltage (Figure 4b). As the rectified output DC voltage is
dependent on the coupled AC voltage from the NFC signal, using
the optimized antenna structure is always important to test the
efficacy of the rectenna. Examining its close relationship to the
printed antenna (resistance, capacitance, and inductance),[27,36]
we adopted an optimal value to design the printed antenna
and R2R printing conditions from our previous works.[37] As
there is a limit to the output voltage from a single-type diode,
a voltage tripler was integrated into this study to harvest a higher
voltage to operate a printed ring oscillator (a triangle-wave generator). As shown in Figure 4c, the final output voltage of þ10 V
could be attained from the tripler structure, consisting of three
diodes and capacitors (see inset image in Figure 3a). The reverse
circuit was further integrated to provide 10 V of output voltage,
as shown in the circuit layout of the inset image in Figure 4c. In
general, the NFC signal from the smartphone is periodically generated in an 8 ms active and few second pause (Figure 4d). The
rectified DC voltage was measured using an NFC carrier signal
of the smartphone, as shown in Figure 4e.
We tested output DC voltage stability under low temperatures
to apply the technology on a cold chain as a smart sensor in food
packaging. Figure 4f shows the output DC voltage of the printed
single diode and capacitor-based rectenna as a function of time
(2 h) under continuous operation in a cold chain environment
2100896 (6 of 10)
© 2021 Wiley-VCH GmbH
www.aem-journal.com
www.advancedsciencenews.com
Figure 4. Examining the performance of fully printed rectenna. a) Plot for showing the frequency-dependent rectification using the printed single rectifier.
b) Plot for showing the load resistance versus output voltage of the printed rectifier by input 8 V with 13.56 MHz. c) Rectifying DC output signal at
13.56 MHz with an input AC signal of 10 Vpp for tripler-type rectenna. d) NFC carrier signal of a smartphone. e) Rectified signal in printed rectenna from
NFC carrier signal of a smartphone. f ) The stability of printed single diodes in cold chain (4 C).
(humidity: 45% and temperature 4 C). Before testing the
low-temperature environment, we confirmed the stable operation of the printed rectenna under ambient environment (humidity: 35% and temperature: 25 C) for a long time (10 days).
In particular, the printed diode operated for more than 2 h with
an initial 13% of small voltage drop. Furthermore, we could harvest the 10 V output voltage from the NFC carrier (Figure 4e) at
13.56 MHz frequency of the smartphone but face a hurdle to
operate any electronic device due to the pause of output signals
for few seconds. Two commercial multilayer ceramic capacitors
(MLCCs) with a capacity of 10 μF were mounted at the end of the
rectenna to carry DC voltage even during the pause of the NFC
signal (Figure 5a). Finally, we could utilize the WPT to provide
more than polarized DC 10 V (Figure 5b) from a smartphone,
which can be further applied to any printed electrochemical sensor devices or disposable CV tags. A complementary metaloxidesemiconductor (CMOS) ring oscillator was printed
through an R2R gravure printer based on our previous report
to verify the performance of the printed rectenna[38] and connected to our printed rectenna samples. The detailed printing
process and basic performance of the R2R-printed CMOS ring
oscillator were reported in a previous paper.[39] In addition,
the optical image and circuit diagram of the printed CMOS ring
oscillator, which consists of five p-type transistors and five n-type
transistors, are shown in Figure S9, Supporting Information.
With the all-printed AgPEDOT/IGZO/carbon-based rectenna,
Adv. Eng. Mater. 2021, 2100896
we were able to wirelessly operate the R2R-printed CMOS ring
oscillator to generate a triangle wave (4 V) with 2 Hz through a
smartphone’s NFC carrier signal (Figure 5c). Therefore, the findings open a door toward a new market with a basic platform for
developing printed and disposable CV tags in PoCTs.
3. Conclusion
An IGZO-based ink with a HOMO level of 5.5 eV and a LUMO
level of 4.2 eV was developed to print a semiconducting layer
between the AgPEDOT:PSS bottom electrode and carbon
top electrode and render the Schottky junction. By increasing
the work function of the printed PEDOT:PSS on the printed
Ag surface, complete R2R and R2P gravures have been successfully integrated to print an IGZO-based Schottky diode. The
obtained all-printed IGZO-based Schottky diodes showed a
turn-on voltage of 0.6 V and an on-current of 0.8 mA cm2.
The resulting printed Schottky diode used two voltage triplers
on the rectenna to generate a polarized DC 10 V from a smartphone’s NFC carrier. The polarized DC 10 V was further utilized to wirelessly generate positive and negative triangle
potentials via simple integration of a printed CMOS ring oscillator in the printed rectenna. The wirelessly generated positive and
negative triangle potentials become the basal step to develop the
disposable NFC-CV tags for scanning redox-active bioanalytes.
As such, we successfully demonstrated a core concept of printed
2100896 (7 of 10)
© 2021 Wiley-VCH GmbH
www.aem-journal.com
www.advancedsciencenews.com
Figure 5. Demonstration of generating a triangle wave utilizing fully gravure-printed rectenna and a ring oscillator with 10 μF commercial capacitors.
a) Real image of testing the rectifier to generate a triangle wave with a smartphone. b) Final output DC voltage of printed rectenna from the NFC carrier
signal of a smartphone. c) A graph for showing a wirelessly coupled 13.56 MHz AC voltage (black), a rectified DC voltage (red), and a generated triangle
wave (green) from a printed CMOS ring oscillator integrated in a printed rectenna.
wireless triangle-wave generators, which can generate positive
and negative triangle potentials from the NFC mode of a smartphone based on a fully printed wireless power transmitter, the
printed rectenna. This basic sensor platform is effectively developed to realize inexpensive and disposable NFC-CV tags when
combined with a fully printed diode and capacitor.
4. Experimental Section
Material: Indium (III) nitrate hydrate (In(NO3)3·xH2O), gallium (III)
zinc
acetate
dihydrate
nitrate
hydrate
(Ga(NO3)3·xH2O),
(Zn(CH3COO)2·2H2O), nickel (II) chloride hexahydrate (NiCl2·H2O),
hydrazine monohydrate (N2H4·H2O), sodium hydroxide (NaOH), 2methoxy ethanol, acetic acid, dimethyl sulfoxide (DMSO), 1-methyl-2-pyrrolidinone (NMP), triton X-100, Tween-80, and 2-methoxy ethanol were all
purchased from Sigma-Aldrich and used without further purification process. Polyvinyl alcohol ((PVA), Mw 66 000), and isopropyl alcohol (IPA)
were purchased from Daejung chemical company (Korea). Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS (PH 1000)) was
purchased from Heraeus Clevios (Germany). Cu ink (ECOSILCOP102HS, Korea) was purchased from Changsung Nanotech and used
to print the top electrode for diode and capacitor without any other formulation process. Carbon black ink (DC-14, Korea) was purchased from
Dozentech and was used to print the top electrode for the diode. Silver
nanoparticle-based ink for printing antenna and bottom electrodes of
diodes was formulated based on our previously reported method.[40]
For dielectric ink for printing capacitors, BaTiO3 nanoparticle-based dielectric ink was formulated based on the reported method.[40]
1.5 mL of DMSO and 1 mL of IPA were dissolved in 20 mL of PEDOT:
PSS solution to prepare the PEDOT:PSS gravure ink. Afterward, 0.05 mL of
Triton X-100 and 0.675 g of PVA were added into PEDOT:PSS mixture solution after stirring for 4 h in room temperature. Here, Triton X-100 was used
to control the surface tension of PEDOT:PSS ink. In general, 28 mN m1 of
surface tension of PEDOT:PSS ink was appropriate to print on the printed
silver layer by the gravure printing method. For modifying the work function of PEDOT:PSS ink, ethanolamine was added into 5 mL of PEDOT:PSS
ink. By controlling the loading amount of ethanolamine, 5.05 and 4.8 eV
Adv. Eng. Mater. 2021, 2100896
work functions of PEDOT:PSS ink were obtained by, respectively, loading
0.2 and 0.6 wt% of ethanolamine.
The basic synthetic process and ink formulation for preparing IGZO
semiconducting ink are similar to the previously reported procedure.
First, 50 g (0.679 mol%) of indium nitrate hydrate, 6.246 g (0.099 mol
%) of gallium nitrate hydrate, and 11.80 g (0.2199 mol%) of zinc acetate
dehydrate were dissolved in 244 mL of 2-methoxy ethanol for the hydrothermal process under stirring for 2 hrs at 70 C in an oil bath. The sample
solution was evaporated to obtain a gel and then the resulting gel was
dried at 70 C vacuum oven for 12 h. The obtained powders were sintered
at 700 C in the ambient conditions for 2 hrs. The resulting IGZO nanopowders were ball milled in the mixed solution (10 mL of acetic acid and
15 mL of DMSO) for 24 h. Second, the sample solution obtained from the
ball-milling process was centrifuged at 4000 rpm for 10 min. Then, 2.0 g of
precipitated IGZO was formulated into gravure inks by adding the mixture
into the solution with 1 wt% of Tween-80 and 1.2 g of DMSO. After stirring
for 1 h at room temperature, 0.4 g of DMSO solution containing 5 wt% of
PVA was added into IGZO ink and stirred for another 24 h to use as
IGZO ink.
R2R and R2P Printing Process: The Ag layers for the bottom electrodes of
diodes, capacitors, and antenna were printed on a polyimide (PI) web having a width of 250 mm and a thickness of 75 μm (GF300, SKC, Korea) via
the R2R gravure printing system (i-PEN, Korea) using silver nanoparticles
ink. For the R2R printing process, the overall printing method and ink conditions were similar to our published results.[40] PEDOT:PSS, IGZO, Cu,
and carbon top electrodes were printed using a R2P gravure printer (i-PEN,
Korea) on the R2R gravure-printed Ag bottom electrodes. After printing
each step, each layer was dried under 150 C for 5 min.
Characterization of Devices: The surface tensions and viscosities of the
inks were measured using a DCAT21 (Dataphysics Co., Germany) and SV-10
Vicro viscometer (A & D Co., Japan), respectively. An Inductance,
Capactance, Resistance (LCR) meter (E4980A, Agilent, USA) and semiconductor analyzer (Keithley 4200, USA) were used to measure capacitancevoltage (CV ) and current–voltage (IV ) characteristics. The
rectifying property of the rectifier was analyzed using a function generator
(Tektronix AFG 3102, USA) and an oscilloscope (Agilent Technologies DPO
4034, USA). The potentiostat (Biological VSP, France) and UPS (Riken Keiki
instrument, AC-2, Japan) were used to measure the work function of inks.
The reverse leakage currents of the printed diodes with different work functions of electrodes were measured by sweeping IV characteristics with the
2100896 (8 of 10)
© 2021 Wiley-VCH GmbH
www.aem-journal.com
www.advancedsciencenews.com
semiconductor analyzer (Keithley 4200, USA). The reverse currents, shown
in Figure 1b, were attained at 20 V from the attained IV characteristics.
Supporting Information
Supporting Information is available from the Wiley Online Library or from
the author.
Acknowledgements
Y.J. and S.S. contributed equally to this work. This work was supported by
Institute of Information & Communications Technology Planning &
Evaluation (IITP) grant funded by the Korea government (MSIT, no.
2018-0-00389, R2R-printed NFC-active QR code label for checking the history of agrofishery products to prevent forged recode using a smart phone)
and the National Research Foundation of Korea (NRF) grant funded by the
Korea government (MSIT, no. 2020R1A5A1019649).
Conflict of Interest
The authors declare no conflict of interest.
Data Availability Statement
Research data are not shared.
Keywords
cyclic voltammetry, near-field communication, roll-to-roll printing,
Schottky diodes, wireless power transmissions
Received: July 18, 2021
Revised: September 20, 2021
Published online:
[1] E. T. S. G. da Silva, D. E. P. Souto, J. T. C. Barragan, J. de F. Giarola,
A. C. M. de Moraes, L. T. Kubota, ChemElectroChem 2017, 4, 778.
[2] B. B. Kou, L. Zhang, H. Xie, D. Wang, Y. L. Yuan, Y. Q. Chai, R. Yuan,
ACS Appl. Mater. Interfaces. 2016, 8, 22869.
[3] J. Min, M. Nothing, B. Coble, H. Zheng, J. Park, H. Im, G. F. Weber,
C. M. Castro, F. K. Swirski, R. Weissleder, H. Lee, ACS Nano. 2018, 12,
3378.
[4] M. J. Russo, M. Han, P. E. Desroches, C. S. Manasa, J. Dennaoui,
A. F. Quigley, R. M. I. Kapsa, S. E. Moulton, R. M. Guijt,
G. W. Greene, S. M. Silva, ACS Sens. 2021, 6, 1482.
[5] A. K. Kaushik, J. S. Dhau, H. Gohel, Y. K. Mishra, B. Kateb, N. Y. Kim,
D. Y. Goswami, ACS Appl. Bio Mater. 2020, 3, 7306.
[6] C. Loncaric, Y. Tang, C. Ho, M. A. Parameswaran, H. Z. Yu, Sensors
Actuators, B Chem. 2012, 161, 908.
[7] A. Yang, F. Yan, ACS Appl. Electron. Mater. 2021, 3, 53.
[8] A. Shougee, F. Konstantinou, T. Albrecht, K. Fobelets, IEEE Trans.
Nanotechnol. 2018, 17, 154.
[9] S. Sun, B. Zhang, J. Wang, K. Li, Y. Gao, T. Y. Zhang, J. Chemom. 2021,
35, 3314.
[10] J. Garnica, R. A. Chinga, J. Lin, Proc. IEEE 2013, 101, 1321.
[11] M. Xia, S. Aïssa, IEEE Trans. Signal Process. 2015, 63, 2835.
[12] Y. Jung, H. Park, J. A. Park, J. Noh, Y. Choi, M. Jung, K. Jung, M. Pyo,
K. Chen, A. Javey, G. Cho, Sci. Rep. 2015, 5, 8105.
Adv. Eng. Mater. 2021, 2100896
[13] K. Kojima, H. Okumura, Appl. Phys. Lett. 2020, 116, 012103.
[14] G. Rajbhandari, P. W. Vanaraj, B. B. Maskey, H. Park, A. Sapkota,
Y. Jung, Y. Majima, G. Cho, Adv. Electron. Mater. 2018, 4,
1800078.
[15] R. Heinhold, G. T. Williams, S. P. Cooil, D. A. Evans, M. W. Allen,
Phys. Rev. B: Condens. Matter Mater. Phys. 2013, 88, 235315.
[16] O. Sushko, M. Pigeon, R. S. Donnan, T. Kreouzis, C. G. Parini,
R. Dubrovka, IEEE Trans. Terahertz Sci. Technol. 2017, 7, 184.
[17] S. Khan, S. Tinku, L. Lorenzelli, R. S. Dahiya, IEEE Sens. J. 2015, 15,
3146.
[18] I. Kim, S. W. Kwak, K. S. Kim, T. M. Lee, J. Jo, J. H. Kim, H. J. Lee,
Microelectron. Eng. 2012, 98, 587.
[19] J. Noh, D. Yeom, C. Lim, H. Cha, J. Han, J. Kim, Y. Park,
V. Subramanian, G. Cho, IEEE Trans. Electron. Packag. Manuf.
2010, 33, 275.
[20] Y. Zhou, C. Fuentes-hernandez, J. Shim, J. Meyer, A. J. Giordano,
H. Li, P. Winget, T. Papadopoulos, H. Cheun, J. Kim, M. Fenoll,
A. Dindar, W. Haske, E. Najafabadi, T. M. Khan, H. Sojoudi,
S. Barlow, S. Graham, J. Brédas, S. R. Marder, A. Kahn,
B. Kippelen, Science 2012, 336, 327.
[21] O. T. Hofmann, H. Glowatzki, C. Bürker, G. M. Rangger, B. Bröker,
J. Niederhausen, T. Hosokai, I. Salzmann, R. P. Blum, R. Rieger,
A. Vollmer, P. Rajput, A. Gerlach, K. Müllen, F. Schreiber, E. Zojer,
N. Koch, S. Duhm, J. Phys. Chem. C 2017, 121, 24657.
[22] T. Kumagai, S. Liu, A. Shiotari, D. Baugh, S. Shaikhutdinov, M. Wolf,
J. Phys. Condens. Matter. 2016, 28, 494003.
[23] J. Huang, Z. Xu, Y. Yang, Adv. Funct. Mater. 2007, 17, 1966.
[24] X. Cai, J. Yu, J. Zhou, X. Yu, Y. Jiang, Jpn. J. Appl. Phys. 2011, 50,
124203.
[25] D. C. Choi, M. Kim, Y. J. Song, S. Hussain, W. S. Song, K. S. An,
J. Jung, Appl. Surf. Sci. 2018, 427, 48.
[26] C. Y. Lin, C. H. Tsai, H. T. Lin, L. C. Chang, Y. H. Yeh, Z. Pei,
Y. R. Peng, C. C. Wu, Org. Electron. 2011, 12, 1777.
[27] B. B. Maskey, J. Lee, Y. Majima, J. Kim, J. Lee, G. Bahk, G. R. Koirala,
G. Cho, J. Sun, K. Shrestha, S. Kim, M. Park, Y. Kim, H. Park, S. Lee,
Y. Han, IEEE Sens. J. 2020, 20, 2106.
[28] V. Sholin, S. A. Carter, R. A. Street, A. C. Arias, Appl. Phys. Lett. 2008,
92, 063307.
[29] P. K. Nayak, T. Busani, E. Elamurugu, P. Barquinha, R. Martins,
Y. Hong, E. Fortunato, Appl. Phys. Lett. 2010, 97, 183504.
[30] Y. H. Lee, P. T. Tsai, C. J. Chang, H. F. Meng, S. F. Horng,
H. W. Zan, H. C. Lin, H. C. Liu, M. R. Tseng, H. C. Yeh, AIP Adv.
2016, 6, 115006.
[31] J. Zhang, Y. Li, B. Zhang, H. Wang, Q. Xin, A. Song, Nat. Commun.
2015, 6, 7561.
[32] S. Steudel, K. Myny, V. Arkhipov, G. Deibel, S. De Vusser, J. Genoe,
P. Heremans, Nat. Mater. 2005, 4, 597.
[33] J. O. Hwang, D. H. Lee, J. Y. Kim, T. H. Han, B. H. Kim, M. Park,
K. No, S. O. Kim, J. Mater. Chem. 2011, 21, 3432.
[34] S. Cells, P. P. Zamora, F. R. Díaz, M. Angelica, L. Cattin, G. Louarn,
J. C. Bernède, Nat. Resour. 2013, 4, 123.
[35] A. Chasin, M. Nag, A. Bhoolokam, K. Myny, S. Steudel, S. Schols,
J. Genoe, G. Gielen, P. Heremans, IEEE Trans. Electron Devices
2013, 60, 3407.
[36] A. Tataroǧlu, Ş. Altindal, J. Alloys Compd. 2009, 484, 405.
[37] J. Sun, K. Shrestha, H. Park, P. Yadav, S. Parajuli, S. Lee, S. Shrestha,
G. R. Koirala, Y. Kim, K. A. Marotrao, B. B. Maskey, O. C. Olaoluwa,
J. Park, H. Jang, N. Lim, Y. Jung, G. Cho, Adv. Mater. Technol. 2020, 5,
1900935.
[38] A. Kiazadeh, H. L. Gomes, P. Barquinha, J. Martins, A. Rovisco,
J. V. Pinto, R. Martins, E. Fortunato, Appl. Phys. Lett. 2016, 109,
051606.
2100896 (9 of 10)
© 2021 Wiley-VCH GmbH
www.aem-journal.com
www.advancedsciencenews.com
[39] Y. Jung, A. M. Kale, J. Park, H. Park, J. Sun, G. R. Koirala, K. Shrestha,
S. Shrestha, S. Parajuli, B. B. Maskey, G. Cho, Macromol. Mater. Eng.
2020, 305, 1900867.
Adv. Eng. Mater. 2021, 2100896
View publication stats
[40] H. Park, J. Sun, Y. Jung, J. Park, B. B. Maskey, K. Shrestha,
G. R. Koirala, S. Parajuli, S. Shrestha, A. Chung, G. Cho, Adv.
Electron. Mater. 2020, 6, 2000770.
2100896 (10 of 10)
© 2021 Wiley-VCH GmbH