Scholarly article on topic 'Micro-Newton Detection by Using Graphene-paper Force Sensor'

Micro-Newton Detection by Using Graphene-paper Force Sensor Academic research paper on "Materials engineering"

CC BY-NC-ND
0
0
Share paper
Academic journal
Procedia Engineering
OECD Field of science
Keywords
{"forse sensor" / graphene / "piezoresistive devices"}

Abstract of research paper on Materials engineering, author of scientific article — Amir Yadegari, Meisam Omidi, Mohammadmehdi Choolaei, F. Haghiralsadat, F. Yazdian

Abstract The fabrication of a mechanically flexible piezoresistive load sensor is reported. Inkjet printing offers an inexpensive non-contact fabrication method for microelectronics. Herein we report the first direct fabrication of inkjet-printed graphene arrays, and apply them to electromechanical detection of force. The graphene ink was printed on a cantilever shape paper substrate. The results illustrated a linear resistance change with the applied forces. The force range, force resolution, and sensitivity were found to be 25 mN, 10μN, and 1.2mV/mN, respectively. In addition, graphite ink was also used as the sensing component in order to make a comparison between the piezoresistive effect of graphene and graphite ink. The results show that using graphene ink instead of graphite increases the force range and gauge factor of the sensor, which are two important designing factors. This sensor is inexpensive, simple to fabricate, lightweight, and disposable.

Academic research paper on topic "Micro-Newton Detection by Using Graphene-paper Force Sensor"

(I)

CrossMark

Available online at www.sciencedirect.com

ScienceDirect

Procedía Engineering 87 (2014) 967 - 970

Procedía Engineering

www.elsevier.com/locate/procedia

EUROSENSORS 2014, the XXVIII edition of the conference series

Micro-Newton Detection by Using Graphene-Paper Force Sensor

Amir Yadegarib, Meisam Omidia' *, Mohammadmehdi Choolaeic, F. Haghiralsadata, F.

Yazdiana

aFaculty of New Science and Technology University of Tehran, Tehran, Iran bSchool of Chemical Engineering, College of Engineering, University of Tehran, Tehran, Iran cResearch Institute of Petroleum Industry (RIPI), Tehran, Iran

Abstract

The fabrication of a mechanically flexible piezoresistive load sensor is reported. Inkjet printing offers an inexpensive non-contact fabrication method for microelectronics. Herein we report the first direct fabrication of inkjet-printed graphene arrays, and apply them to electromechanical detection of force. The graphene ink was printed on a cantilever shape paper substrate. The results illustrated a linear resistance change with the applied forces. The force range, force resolution, and sensitivity were found to be 25 mN, 10 |N, and 1.2 mV/mN, respectively. In addition, graphite ink was also used as the sensing component in order to make a comparison between the piezoresistive effect of graphene and graphite ink. The results show that using graphene ink instead of graphite increases the force range and gauge factor of the sensor, which are two important designing factors. This sensor is inexpensive, simple to fabricate, lightweight, and disposable.

© 2014TheAuthors.PublishedbyElsevierLtd.This is an open access article under the CC BY-NC-ND license (http://creativecommons.Org/licenses/by-nc-nd/3.0/).

Peer-review under responsibility of the scientific committee of Eurosensors 2014 Keywords: forse sensor; graphene; piezoresistive devices

1. Experimental

Recently, graphene has attracted considerable attention from both scientists and engineers, because of their exceptional physical and mechanical properties. Owing to the monolayer nature and the effective confinement of electrons in two-dimensions, any applied strain in graphene films is likely to create large changes in conductivity as the electrons are forces to traverse larger potential wells along increased bond-lengths [1-2]. Piezoresistivity is a

* Corresponding author. Tel.: +98-918-331-2585. E-mail address: m_omidi@ut.ac.ir

1877-7058 © 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.Org/licenses/by-nc-nd/3.0/).

Peer-review under responsibility of the scientific committee of Eurosensors 2014 doi:10.1016/j.proeng.2014.11.319

common sensing principle for many micromachined sensors. The main principle of sensors like this is using the piezoresistive effect of the sensing components.

1.1. Principle of paper-based load sensor

Piezoresistivity is a common sensing principle for many micromachined sensors. The main principle of sensors like this is using the piezoresistive effect of the sensing components. In this study, graphene and graphite ink were used as sensing components, and the paper-based sensors were formed in the shape of cantilever beams, using a laser cut. Also, the conductive components were printed using a HP Deskjet 1600CN printer. By applying a concentrated force at the free end of the cantilever beam and measuring the change in resistance of the sensing component, as a result of the deflection, it was possible to calculate the quantity of the applied load.

1.2. Ink preparation process

For preparing the graphene ink, we should make a suspension which includes: graphene, distilled water as solvent, IPA and DEG as co-solvents, and CTAB as surfactant. graphene used in this study were produced by Research Institute of Petroleum Industry (RIPI). IPA, DEG, and CTAB were purchased from Merk.

In order to obtain the printable ink, the suspension with the certain weight percents of components was dispersed by the use of probe and pulse-wave sonication for 60 min. After dispersing graphene, by the use of sonication, the suspension was stirred for 12 h and then centrifuged at 4000 rpm for 15 min to sediment large bundles and force them to precipitate to the bottom of the container. Subsequently, the supernatant of the suspension was collected and centrifuged again. This was continued until a stable dispersion was achieved, which was typically repeated 4 times. The fabricated graphene ink has the viscosity and surface tension of 28 mPa s and 50 mN/m at 25 °C, respectively.

In order to prepare the silver ink, Ag powder was purchased from American Elements with the characteristics of powder particle sizes average in the range of 10-50. Because Ag powder was not functionalized, it was crucial to use an appropriate surfactant in order to have a stable ink. As mention in literature, pluronic F127 was used as surfactant in the silver ink. F127 is a triblock co-polymer, which comprises poly ethylene oxide (PEO) and poly propylene oxide (PPO) sections organized in a PEO-PPO-PEO arrangement. One of these sections is hydrophilic (PEO) and the other is hydrophobic (PPO). The hydrophobic Ag particles are encapsulated by the PPO section. These encapsulated particles are covered by a layer of free PEO, which helps the Ag particles to remain stable. Same as graphene ink, distilled water was used as solvent and both IPA and DEG as co-solvents. The printable ink was obtained by the use of probe and pulse-wave sonication for 90 min of the suspension with certain weight percents of its components. After sonication, the suspension was stirred for 12 h and then centrifuged at 4000 rpm for 20 min. Subsequently, the supernatant of the suspension was collected and centrifuged again. This was continued until a stable dispersion was achieved, which was typically repeated 4 times. The Ag ink showed the viscosity and surface tension of 25 mPa s and 35 mN/m at 25° C, respectively.

Fig. 1. (a) Schematic view of a paper-based cantilever beam load sensor using a graphene resistor as the sensing component cantilever beam; (b) TEM images of graphene ink; (c) The surface resistance versus the number of printing for graphene ink .

1.3. Sensor fabrication process

In order to prepare the cantilever beam, an A4 paper with a thickness of 340 ^m was chosen as the substrate, and it was patterned to the required dimensions (44.5 mm x 7.7 mm) using a laser cut with a precision of 0.12 mm. In the next step, graphene ink was printed at the initial section of the cantilever beam using a HP Deskjet 1600CN printer. This step was repeated by graphite instead of graphene ink on another paper beam. The electrical contact pads were printed using the fabricated silver ink. In order to certify the connections between the printed contact pads and sensing components (graphene and graphite ink) a small drop of silver ink was placed on the connections using a painting brush. At the end, by connecting the contact pads to the multimeter (Keithley 2400 source meter), it was possible to read the resistance change of the system. A simple illustration of the cantilever beam sensor and TEM images of graphene ink can be observed in figure la and lb.

Fig. 2. (a) The electrical resistivity variation of printed graphene ink against applied force (Unload condition indicated when F=0); (b) Calibration plot of the output of the sensor (resistance change) as a function of applied force for printed graphene ; (b) Comparison of the gauge factor

between the graphite and graphene ink.

2. Results and discussion

At first we determined the stiffness of the paper beam by applying forces as a function of deflection (Fig. 3) to the free end of the beam. As the calculations demonstrated the stiffness of the paper beam was about 2 GPa. Then the Young's modulus of the beam was calculated by using Eq. 1:

^ 4FL3

E=---(1)

Here the young's modulus is shown by E, the applied force to the end of the beam is presented by F, the deflection by 8, and the length, width, and thickness of the paper beam are shown by L, W, and H, respectively. By illustrating Eq. 1, the young's modulus calculated for the paper beams was about 2 GPa, which is much lower than that of silicon (130-170 GPa).

The surface resistance of the graphene deposit printed on the paper sensor is plotted versus the number of printing in figures 1c. It was found that the electrical resistance drops with increasing the number of prints, as the layer of graphene increases in thickness and achieves the percolation threshold (after printing 12 times). Figures 2a show the resistance of the cantilever beam sensor at each measurement step. When the paper-based sensor is unloaded, graphene' resistance has returned to its initial value. This confirms that the original graphene -silver contact was a firm contact, i.e. slipping between graphene -silver contact did not occur during the experiments. Figure 2b presents the calculated correlation between the experimental outputs as a function of inputs for printed graphene ink. The results have illustrated a linear resistance change with the applied forces. By studying the calibrated results (Figure 2b), the force range measurement and its force resolution were found to be 25 mN and 10 ^N, respectively. In order to compare the results from sensors made of graphene and graphite ink, we have

calculated the gauge factors for the piezoresistive sensors made of commercialized graphite ink, and printed graphene. The gauge factor is defined as the ratio of relative change in resistance of the resistor (AR/R0) to the applied mechanical strain, which the results are shown in Figure 2c. The higher gauge factor of sensors made by graphene ink indicates higher sensitivity of these sensors in comparison with graphite ink. The results showed that the load sensor is inexpensive, simple to fabricate, light-weighted, and disposable. Due to these characteristics, this sensor can be recognized as an appropriate single-use device in analytical applications such as medical diagnostics.

The comparison of specifications of the fabricated sensor using graphene ink with the commercial MEMS silicon force sensor, and the sensor fabricated by Xinyu Liu et al.[3] has been illustrated in Table 1. The paper-based sensor with graphene ink showed a higher force resolution and lower sensitivity than the commercial silicon-based sensor; however, paper-based sensor is cheaper and simpler to fabricate. however, its low cost, and requires only simple fabrication.

3. Conclusions

In this paper, an attempt has been made to use piezoresistive property of graphene ink in the sensing applications. We have developed a paper-based sensor on the basis of piezoresistive property of graphene ink for measuring the magnitude of applied loads. The results showed that using graphene ink instead of graphite improved the force range and gauge factor of the sensor. Our sensor has exhibited these characteristics: natural frequency of 25 Hz, force range of 0-25 mN, force resolution of 10 ^N, and sensitivity of 1.2 mV/mN. Finally, a monolithic integration of a signal-processing circuit was developed in order to decrease the footprints and noise effects. The paper-based sensor presented in this paper is suitable for force sensing applications that require moderate sensing capabilities, operation in a limited range of temperatures, and consideration of device cost.

Table 1. Comparison of specifications of different types of force sensors.

Specifications

Commercial silicon MEMS sensor [3]

Paper Sensor with graphite ink Paper Sensor with printed graphene [3] ink

Sensing principle

Piezoresistive

Piezoresistive

Piezoresistive

Material

Silicon

Paper, graphite/silver inks

Paper, graphene /silver inks

Beam size (L x W x H) Beam stiffness Natural frequency Force range Force resolution Sensitivity

5 mm x 1 mm x 0.75 mm

2000 mN/mm

12 kHz

2.5 mV/mN

44.5 mm x 7.7 mm x 0.34 mm 44.5 mm x 7.7 mm x 0.34 mm

2 mN/mm 2 mN/mm

25 Hz 25 Hz

0 to 10 mN b 0 to 25 mN

120 ^N 10 ^N

0.84 mV/mN 1.2 mV/mN

References

[1] M. Huang, and J. R. Greer, Measuring Graphene Piezoresistance via in-situ Nanoindentation, ECS Transactions, 35 (3) (2011) 211-216.

[2] Y. Kim et al. Preparation of piezoresistive nano smart hybrid material based on graphene, Current Applied Physics, 11 (1) (2010) S350-S352.

[3] X. Liu, M. Mwangi, XJ. Li, M. O'Brien, GM. Whitesides, Paper-based piezoresistive MEMS sensors. Lab Chip, 11(13) (2011) 2189-2196.