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CMOS integration of inkjet-printed graphene for humidity sensing.

Santra S, Hu G, Howe RC, De Luca A, Ali SZ, Udrea F, Gardner JW, Ray SK, Guha PK, Hasan T - Sci Rep (2015)

Bottom Line: The graphene ink is produced via ultrasonic assisted liquid phase exfoliation in isopropyl alcohol (IPA) using polyvinyl pyrrolidone (PVP) polymer as the stabilizer.When the sensors are exposed to relative humidity ranging from 10-80%, we observe significant changes in resistance with increasing sensitivity from the amount of graphene in the inks.Our sensors show excellent repeatability and stability, over a period of several weeks.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, Indian Institute of Technology, Kharagpur, 721302, India.

ABSTRACT
We report on the integration of inkjet-printed graphene with a CMOS micro-electro-mechanical-system (MEMS) microhotplate for humidity sensing. The graphene ink is produced via ultrasonic assisted liquid phase exfoliation in isopropyl alcohol (IPA) using polyvinyl pyrrolidone (PVP) polymer as the stabilizer. We formulate inks with different graphene concentrations, which are then deposited through inkjet printing over predefined interdigitated gold electrodes on a CMOS microhotplate. The graphene flakes form a percolating network to render the resultant graphene-PVP thin film conductive, which varies in presence of humidity due to swelling of the hygroscopic PVP host. When the sensors are exposed to relative humidity ranging from 10-80%, we observe significant changes in resistance with increasing sensitivity from the amount of graphene in the inks. Our sensors show excellent repeatability and stability, over a period of several weeks. The location specific deposition of functional graphene ink onto a low cost CMOS platform has the potential for high volume, economic manufacturing and application as a new generation of miniature, low power humidity sensors for the internet of things.

No MeSH data available.


Related in: MedlinePlus

(a) Stable jetting sequence of graphene ink, the scale bar is 100 μm; (b) Dark field optical microscope image of the IDEs on CMOS μHP (b) without graphene (c) with graphene-PVP deposited on to IDEs, with the targeted printing area marked by dashed lines, the scale bar is 100 μm; (d) SEM image of a small area on the CMOS μHP with graphene-PVP deposited; the IDEs are marked by dashed lines and the scale bar is 3 μm.
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f5: (a) Stable jetting sequence of graphene ink, the scale bar is 100 μm; (b) Dark field optical microscope image of the IDEs on CMOS μHP (b) without graphene (c) with graphene-PVP deposited on to IDEs, with the targeted printing area marked by dashed lines, the scale bar is 100 μm; (d) SEM image of a small area on the CMOS μHP with graphene-PVP deposited; the IDEs are marked by dashed lines and the scale bar is 3 μm.

Mentions: A stable drop generation (single droplet generation for each electrical impulse, without the formation of satellite droplets) and jetting of ink (avoiding deviation of droplet trajectory) is of primary importance for high quality inkjet printing. Otherwise, unstable jetting may lead to uncontrolled amount of ink deposition on to undesired locations. In inkjet printing, a figure of merit, , is commonly used to consider the printability of inks and is defined as: , where is surface tension of the ink (mNm−1), is the density of ink (gcm−3), is the viscosity of the ink (mPa.s) and is the nozzle diameter (μm). As a rule of thumb, it is commonly accepted that value should be <14 for the case of drop-on-demand inkjet printing to avoid secondary or satellite droplets2663. Meanwhile, it should be >1 to optimize droplet formation or ejection to avoid long-lived filament formation, which may result in poor positional accuracy and printing resolution266364. The value of typically falls within 1–10 for commercial inkjet printable inks65. We stress that the acceptable range of values should be established by experiments and numerical simulations and should be considered as a guide only. Indeed, inks with values outside this range may also be printable, in particular, by controlling the shape and intensity of the electrical pulses for droplet generation. To determine the Z value of our graphene ink, we use pendant drop measurement and parallel plate rheometry to measure and , respectively at room temperature. We measure  ~ 28.0 mNm−1 and  ~ 2.34 mPa.s. The density is measured as  ~ 0.8 gcm−3. With a = 22 μm, we calculate Z ~ 9.48, falling into the recommended range for stable jetting. This indicates the formulated ink is suitable for inkjet printing. A stable jetting without the formation of satellite droplet or long filament is thus expected. This is experimentally confirmed by high speed jetting sequence images presented in Fig. 5(a).


CMOS integration of inkjet-printed graphene for humidity sensing.

Santra S, Hu G, Howe RC, De Luca A, Ali SZ, Udrea F, Gardner JW, Ray SK, Guha PK, Hasan T - Sci Rep (2015)

(a) Stable jetting sequence of graphene ink, the scale bar is 100 μm; (b) Dark field optical microscope image of the IDEs on CMOS μHP (b) without graphene (c) with graphene-PVP deposited on to IDEs, with the targeted printing area marked by dashed lines, the scale bar is 100 μm; (d) SEM image of a small area on the CMOS μHP with graphene-PVP deposited; the IDEs are marked by dashed lines and the scale bar is 3 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4663628&req=5

f5: (a) Stable jetting sequence of graphene ink, the scale bar is 100 μm; (b) Dark field optical microscope image of the IDEs on CMOS μHP (b) without graphene (c) with graphene-PVP deposited on to IDEs, with the targeted printing area marked by dashed lines, the scale bar is 100 μm; (d) SEM image of a small area on the CMOS μHP with graphene-PVP deposited; the IDEs are marked by dashed lines and the scale bar is 3 μm.
Mentions: A stable drop generation (single droplet generation for each electrical impulse, without the formation of satellite droplets) and jetting of ink (avoiding deviation of droplet trajectory) is of primary importance for high quality inkjet printing. Otherwise, unstable jetting may lead to uncontrolled amount of ink deposition on to undesired locations. In inkjet printing, a figure of merit, , is commonly used to consider the printability of inks and is defined as: , where is surface tension of the ink (mNm−1), is the density of ink (gcm−3), is the viscosity of the ink (mPa.s) and is the nozzle diameter (μm). As a rule of thumb, it is commonly accepted that value should be <14 for the case of drop-on-demand inkjet printing to avoid secondary or satellite droplets2663. Meanwhile, it should be >1 to optimize droplet formation or ejection to avoid long-lived filament formation, which may result in poor positional accuracy and printing resolution266364. The value of typically falls within 1–10 for commercial inkjet printable inks65. We stress that the acceptable range of values should be established by experiments and numerical simulations and should be considered as a guide only. Indeed, inks with values outside this range may also be printable, in particular, by controlling the shape and intensity of the electrical pulses for droplet generation. To determine the Z value of our graphene ink, we use pendant drop measurement and parallel plate rheometry to measure and , respectively at room temperature. We measure  ~ 28.0 mNm−1 and  ~ 2.34 mPa.s. The density is measured as  ~ 0.8 gcm−3. With a = 22 μm, we calculate Z ~ 9.48, falling into the recommended range for stable jetting. This indicates the formulated ink is suitable for inkjet printing. A stable jetting without the formation of satellite droplet or long filament is thus expected. This is experimentally confirmed by high speed jetting sequence images presented in Fig. 5(a).

Bottom Line: The graphene ink is produced via ultrasonic assisted liquid phase exfoliation in isopropyl alcohol (IPA) using polyvinyl pyrrolidone (PVP) polymer as the stabilizer.When the sensors are exposed to relative humidity ranging from 10-80%, we observe significant changes in resistance with increasing sensitivity from the amount of graphene in the inks.Our sensors show excellent repeatability and stability, over a period of several weeks.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, Indian Institute of Technology, Kharagpur, 721302, India.

ABSTRACT
We report on the integration of inkjet-printed graphene with a CMOS micro-electro-mechanical-system (MEMS) microhotplate for humidity sensing. The graphene ink is produced via ultrasonic assisted liquid phase exfoliation in isopropyl alcohol (IPA) using polyvinyl pyrrolidone (PVP) polymer as the stabilizer. We formulate inks with different graphene concentrations, which are then deposited through inkjet printing over predefined interdigitated gold electrodes on a CMOS microhotplate. The graphene flakes form a percolating network to render the resultant graphene-PVP thin film conductive, which varies in presence of humidity due to swelling of the hygroscopic PVP host. When the sensors are exposed to relative humidity ranging from 10-80%, we observe significant changes in resistance with increasing sensitivity from the amount of graphene in the inks. Our sensors show excellent repeatability and stability, over a period of several weeks. The location specific deposition of functional graphene ink onto a low cost CMOS platform has the potential for high volume, economic manufacturing and application as a new generation of miniature, low power humidity sensors for the internet of things.

No MeSH data available.


Related in: MedlinePlus