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Paper-based Electronics: Passive Components and Low Pass Filters Using
Solvent-free Eco-friendly Fabrication
Conference Paper · June 2021
DOI: 10.1109/FLEPS51544.2021.9469750
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Paper-based Electronics: Passive Components and
Low Pass Filters Using Solvent-free Eco-friendly
Fabrication
Muhammad Hamza Zulfiqar, Umer Hassan, Aftab Alam, Muhammad Zubair, Muhammad Qasim Mehmood,
Kashif Riaz*
Department of Electrical Engineering, Information Technology University (ITU), Lahore 54600, Pakistan.
*kashif.riaz@itu.edu.pk
Abstract— We report an eco-friendly and easy-going way
of fabricating a vast range of passive electronic components
and low pass filters. This is achieved by directly writing
graphite on paper and cutting and pasting aluminum foil and
copper tape on different substrates. Resistance was achieved
from 4 kΩ to MΩ(s) by penciling several sustainable layers of
different graphite to clay content pencils. Capacitors of
capacitance from 2 pF to 10 μF are fabricated using graphite,
aluminum foil, and copper tape as conductive materials on
printing A4, baking, and butter paper as substrate and
dielectric materials as for parallel plate capacitors. Pencil on
paper-based interdigitated capacitors is reported to achieve
lower capacitance and higher cut-off frequency values of low
pass filters. Resistors and capacitors of different values are
fabricated in a plane to design low pass filters with 100 Hz – 2
MHz cut-off frequency range. All the components and circuits
are fabricated from foldable, eco-friendly, and readily
available paper materials as substrates. These paper-based
components are helpful for foldable electronics, foldable
printed circuit boards, and soft robotics.
Keywords—filter circuits; passive components; eco-friendly;
paper electronics; solvent-free fabrication
I. INTRODUCTION
Electronic systems play a vital role in the daily life of
humans. The researcher community takes a reasonable
interest in developing cheaper, eco-friendly, and
biodegradable electronics in the past few years. In this way,
the base of development and production was set by the
research community, of less-weight, easy design, and
foldable electronics, ease in production and its usage in
complex applications, e.g., flexible filters and passive
components [1], monitoring devices in biomedical
applications [2], flexible sensors [3], wearable electronic
circuitry [4], and flexible storage of energy [5]. Flexible
electronics is a favourable issue for traditional transportation
and conventional large area electronics [6]. Flexible and
foldable electronics based on rollable and bendable
substrates require a stable conductor with a flexible substrate
[7]. Folding makes an edge at the point of the fold, which
develops the wrinkles, deformation and this deformation
remains even after unfolding. Therefore, flexible substrates
and conductors are good options, maintaining contact with
each other, even in folded conditions [8].
Paper-based substrate offers many advantages like
excessive availability, low cost, portability, lightweight,
biodegradability, and eco-friendly [9]. These advantages
make the paper an inevitable substrate for a wide range of
electronic devices, including transistors [10], solar cells [11],
radio frequency identification (RFID) tags [12], microfluidic
glucose sensors [13], flexible displays [14], micro-electromechanical systems (MEMS) [15], touch sensors [16],
foldable passive components and circuits [1] and energy
storage devices [5]. Vast availability and realization of paper
substrate-based electronics can activate electronic
applications to be reached out to the existing electronics.
The fabrication technique is one of the vital factors,
especially for the design of flexible electronics. In fabrication
techniques, economically cheap and high-performance
fabrication techniques are more suitable than costly and
high-performance techniques. Recently, many fabrication
techniques reported in the literature, such as inkjet printing
[17], screen printing [18], bench-top [19], and direct writing
[20], have been developed for flexible electronics. In the
fabrication of flexible electronics, substrate, conductive, and
adhesive (if required) materials are necessary raw
components. The fabricated circuits are required to be
disposed of after their use. Fabricated components and
circuits passed from the recycling stages to recycle the
substrate and conductive materials.
In this work, broad range resistors and capacitors have
been fabricated to obtain the wide cut-off frequency of low
pass filter (LPF) circuits. RC filters from pencil-trace on
paper were reported at RCS PCCP 2013 [21], passive RC
filters on paper were reported at RSC Advances 2016 [22],
and pen/pencil-written circuits were reported at Advanced
Electronic Materials 2018 [23]. Our work differs from all the
above reported in capacitor designs and materials used to
ensure the required capacitance, foldability, and circuits'
flexibility. The range of resistance, capacitance, and filter
circuits is very vast in our work. Different electrode and
substrate materials are used to obtain the required
characteristics of capacitors and RC filters.
II. FABRICATION PROCESS
Passive components as resistor and capacitor and passive
circuits as low pass filter circuits were fabricated using
solvent-free, non-expensive, and non-energy consuming
fabrication process as direct writing of pencil-on-paper.
Standard A4 photocopier paper was used as a substrate for
the resistors, capacitors, filter circuits, and a dielectric
material for parallel plate capacitors. Commercially available
pencils of different graphite to clay contents as HB (68 ±
2%), 2B (74 ± 2%), 4B (79 ± 2 %), and 8B (90 ± 2 %)
purchased from the local bookstore were used to fabricate
pencil-on-paper components and circuits. Fig. 1 (a) shows
the process of pencil on the paper-based fabrication process.
Commercially available Al-foils from a local grocery store
were used to fabricate Al-foil on paper-based parallel plate
capacitors using solvent-free adhesive. The cut and paste
fabrication process for the fabrication of parallel plate
capacitors is shown in Fig. 1 (b).
III. RESULTS AND DISCUSSION
Resistors have been fabricated using four different types
of commercial pencils and Fig. 2 shows the relationship
between the sheet resistances of resistors and the graphite
content used to fabricate the resistors. The evaluation of
sheet resistance of resistors fabricated through direct writing
of pencil-on-paper was done using a set of devices of
different areas for each graphite content. Resistors fabricated
from direct writing of pencils with lower graphite-to-clay
ratio to higher graphite-to-clay ratio exhibits sheet
resistances from higher to lower values, as shown in Fig. 2.
Capacitance having a direct effect on the area of parallel
plates of a capacitor and dielectric constant. We achieved
capacitance according to the requirement by varying the
electrode areas of different materials and dielectric materials
like simple printer paper, baking paper, butter paper, tissue
paper, and Teflon tape. Fig. 3 presents the average
capacitance/cm2 of ten different parallel plate capacitors
having electrodes of graphite, aluminium, and copper with
four different types of papers as printer paper, baking paper,
butter paper, and tissue paper substrate, and dielectric
materials.
Fig. 3. The capacitance of capacitors fabricated from graphite, aluminum,
and copper electrodes on four different substrates as a printer, baking, butter,
and tissue paper.
Fig. 1. Fabrication process. (a) Direct writing of pencil-on-paper-based
fabrication process for resistors, capacitors, and filter circuits. (b) Cut and
paste fabrication process for deposition of al-foil and copper tape on paper.
Capacitance is directly proportionate to the dielectric
constant. We fabricated the capacitor on different substrates
to achieve a vast capacitance range, with different electrode
areas and different electrode materials. In the case of comb
and interdigitated capacitors, the capacitance is as follow for
single fringe [24][25]
C = Ԑ×lo×t / d
Fig. 2. The average sheet resistance of 2cm2 resistor patches in Ω's
fabricated using pencils with different percentages of graphite content.
Capacitors have been fabricated using pencil, aluminum
foil and copper tape as electrodes with different paper-based
substrates. To achieve additional capacitance ranges from μF
to pF, we tested different designs like a comb, sandwich, and
in-plane capacitors. For a parallel plate or sandwiched
capacitors, the capacitance C depends upon the area A of
electrodes, the distance d between the electrodes, and
dielectric constant Ԑ, which is the product of relative
permittivity Ԑr and absolute permittivity Ԑo as given in the
equation (1).
C = ԐA/d
(1)
(2)
where lo is the length of fringe, t is the thickness of fingers, d
is the distance between fingers, ɛ is the dielectric constant
between the fingers of the comb. The capacitance of comb
capacitance has been varied by thickness of fingers, the
distance between fingers, and length of fingers of the comb
capacitor. Resistors have been fabricated by direct writing of
pencil on paper. The required resistance of resistors is
achieved by fabricating different graphite to clay content
pencils for different patch areas. These components are
useful for the development of the diversity of circuits.
Resistors and capacitors have been fabricated in a plane in
series to fabricate the filter circuits as a low pass filter circuit.
Fig. 4 shows the fabricated circuit and the circuit diagram of
the RC low pass filter circuit.
Fig. 4. Foldable resistor-capacitor (RC) circuit. (a) Paper-based RC low pass
filter circuit. (b) Circuit diagram of low pass filter.
The paper-based low pass filters have been fabricated by
pencilling a capacitor and resistor in series as shown in Fig.
4 (a). Fig. 4 (b) shows the circuit diagram of the RC low pass
filter circuit. The cut-off frequency Fc of low pass filters
depends upon the capacitance C and resistance R, as
described in equation 3.
Fc = 1 / 2 𝝅 R C
from the 600 kHz low pass foldable resistance capacitor
circuit.
(3)
Resistors and capacitors have been designed to achieve a
cut-off frequency range from 160 Hz to 2 MHz. For this, we
tested capacitors in the range from 5 pF to 10 μF along with
resistors in series from 4 kΩ to 1 MΩ. Here we presented a 6
kHz low pass filter. Fig. 4 (a). shows the low pass fabricated
circuit. The circuit comprises five pairs of fringes, and a
resistor is designed by using 8B pencil on paper.
Fig. 6. The measured and calculated output response of a 600 kHz low pass
filter circuit.
The cross-section lines denote the points of the cut-off at
-3dB gain. At these points, the output is 70.7 % of the input.
It shows the cut-off frequency as 150 Hz and 600 kHz,
respectively. Table I includes the comparison table of RC
low pass filter circuits.
Fig. 7. Output responses of paper-based RC low pass filter circuits for 150
Hz and 600 kHz cut-off frequency.
TABLE I. COMPARISON OF RC FILTER CIRCUITS.
Materials
Fig. 5. Input and output waveforms of low pass filter circuit at different
frequencies. (a) 100 Hz (b) 100 kHz (c) 600 kHz and (d) 1 MHz.
The RC filter circuit consists of a comb capacitor and
resistor. Fig. 4 (b) shows the circuit diagram of the RC low
pass filter. The 2 Vp-p is applied as an input to the RC
circuit. Fig. 5 (a, b, c, d) shows the output waveform of
fabricated low pass filter at 100 Hz, 100 kHz, 600 kHz, and 1
MHz frequency, respectively. The applied input is shown as
a red waveform and output as a yellow waveform. Fig. 6
shows the graph comprised of the output response of the low
pass filter for 0 Hz - 10 MHz frequency. The blue line
represents the out gain obtained from the foldable resistance
capacitor circuit, and the orange line represents the
calculated values. The cross-section lines represent the cutoff point at -3dB gain, where the output is 70.7% of the
input. It shows the cut-off frequency as 600 kHz.
Fig. 7. shows the graph comprised of the output response
of 150 Hz and 600 kHz low pass filter for 0 Hz – 10 MHz
frequency. Blueline represents the output gain obtained from
the 150 Hz, and the orange line represents the gain obtained
Cut-off
Frequency
(fc)
Graphite and Ion
9 kHz
Gel [1]
Graphite [22]
6 kHz
Silver, Nickel,
3 kHz & 60
and Graphite Ink
kHz
[23]
Graphite and
9 kHz
NaCl Salt [26]
Graphite
150 Hz &
[This Work]
600 kHz
SolventFree
Process
Cost
Biodegradable
No
Low
Partially
Yes
Very Low
Yes
Yes
Moderate
Yes
No
Low
Yes
Yes
Very Low
Yes
IV. CONCLUSION
In this work, we proposed low-cost, foldable, and ecofriendly passive components and filter circuits. All the
fabricated components and filter circuits are paper-based and
are foldable. The proposed passive components are used to
design a wide range of low pass filter circuits, with a wide
range (100 Hz to 2 MHZ) cut-off frequency. The results of
passive components and filter circuits remain the same with a
maximum of ± 5% change of values with folding and
bending at different angles. Biodegradable components and
filter circuits fabricated using fabrication lab-free, solventfree, and low-cost fabrication processes are presented here.
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