Super-inkjet printing for three-terminal graphene field effect transistors with 10 μm channel length

Channel length scaling in graphene field effect transistors (GFETs) is key in the pursuit of higher performance in radio frequency electronics for both rigid and flexible substrates. Although two-dimensional (2D) materials provide a superior immunity to short channel effects (SCEs) than bulk materials, they could dominate in scaled GFETs. In this work, we have developed a model that calculates electron and hole transport along the graphene channel in a drift-diffusion basis, while considering the 2D electrostatics. Our model obtains the self-consistent solution of the 2D Poisson’s equation coupled to the current continuity equation, the latter embedding an appropriate model for drift velocity saturation. We have studied the role played by the electrostatics and the velocity saturation in GFETs with short channel lengths Severe scaling results in a high degradation of GFET output conductance. The extrinsic cutoff frequency follows a scaling trend, where the index fulfills The case corresponds to long-channel GFETs with low source/drain series resistance, that is, devices where the channel resistance is controlling the drain current. For high series resistance, decreases down to and it degrades to values of because of the SCEs, especially at high drain bias. The model predicts high maximum oscillation frequencies above 1 THz for channel lengths below 100 nm, but, in order to obtain these frequencies, it is very important to minimize the gate series resistance. The model shows very good agreement with experimental current voltage curves obtained from short channel GFETs and also reproduces negative differential resistance, which is due to a reduction of diffusion current.

Interleukin-6 (IL-6) is an inflammatory cytokine that serves as an important prognostic biomarker for chronic diseases such as cancer and coronavirus disease. Label-free sensors that can conveniently detect IL-6 are essential for health monitoring purposes. Here, we present an aptamer-modified liquid-gated graphene field effect transistor (GFET) biosensor fabricated using inkjet printing techniques that can detect IL-6 levels. In this work, graphene ink suitable for inkjet printing was synthesized and formulated using the ultrasonic liquid exfoliation method. Exfoliated graphene was redispersed into a cyclohexanone/terpineol solvent system and optimized to achieve jettable ink with a Z-number of 13.7. The formulated graphene ink was then used to fabricate the GFET device, which in turn was decorated with IL-6 aptamer using organic linkers. The sensor response of the GFET was measured using the shift in the transistor current-voltage (I-V) transfer curves upon specific binding of the IL-6 with the aptameric GFET. The experimental results showed that the device can sensitively and selectively detect IL-6 in a 1xPBS background with a limit of detection of 372 pM. The fabricated GFET is on a flexible substrate that may be suitably incorporated into a face mask covering that could potentially sample IL-6 from collected saliva.

Graphene field-effect transistors (FETs) provide an efficient platform for enabling the label-free detection of DNA molecules. In this study, we used an interfacial polymer brush layer, which is inserted between graphene and SiO2, to enhance the electrical properties of the DNA sensors based on graphene FETs. When a polymer brush with no net dipole moment was used as a surface modification layer of SiO2, high field-effect mobility and stability were obtained in graphene FETs. In addition, it was confirmed that the graphene FETs exhibited stable operation in aqueous environments. To examine the response of DNA sensors based on graphene FETs, four types of DNA oligomers with homogeneous nucleotides (i.e. 12mer of adenine, thymine, cytosine, and guanine) were consecutively dropped onto the graphene surface and changes of electrical properties in the graphene FETs were monitored after complete drying of DNA solutions. These DNA oligomers n-doped the graphene due to the electron-rich characteristics of the nucleobases. In addition, electron and hole mobilities decreased gradually upon the addition of DNA solution because DNA molecules served as charged impurities. Graphene FETs with polymer brush provide a platform for detecting DNA molecules with low concentration.

The large channel length graphene field-effect transistor (GFET) can outperform its competitors due to its larger active area and lower noise. Such long channel length devices have numerous applications, e.g., in photodetectors, biosensors, etc. However, long channel length graphene devices are not common due to their semi-metallic nature. Here, we fabricate large channel length (up to 5.7 mm) GFETs through a simple, cost-effective method that requires thermally evaporated source-drain electrode deposition, which is less cumbersome than the conventional wet-chemistry based photolithography. The semiconducting nature of graphene has been achieved by utilizing the Li+ ion of the Li5AlO4 gate dielectric, which shows current saturation at a low operating voltage (∼2 V). The length scaling of these GFETs has been studied with respect to channel length variation within a range from 0.2 mm to 5.7 mm. It is observed that a GFET of 1.65 mm channel length shows optimum device performance with good current saturation. This particular GFET shows a “hole” mobility of 312 cm2 V−1 s−1 with an on/off ratio of 3. For comparison, another GFET has been fabricated in the same geometry by using a conventional SiO2 dielectric that does not show any gate-dependent transport property, which indicates the superior effect of Li+ of the ionic gate dielectric on current saturation.

Electronic Circuits made of 2D Materials.

Herein, the effect of metal contact doping on the scaled graphene field effect transistor (GFET) is investigated. Different from the traditional semiconductors device, the drain current of GFET is not inversely proportional to the channel length (LCH). The abnormal scaling behavior for drain current in GFETs can be attributed to the modification of channel resistance induced by the penetration of contact metal doping. In addition, the field‐effect mobility (μEF) of long channel GFET trend to saturate with decreasing LCH, which is consistent with the diffusive transport model. As the channel length is further scaled down, the μEF at first increases drastically and then decreases due to the enhanced effect of electrical property of graphene under the metal electrode as well as the contact resistance on the carrier transport of GFET. This study indicates that there will be a trade‐off between scaled channel length and the best performance of GFET. Further efforts should be made to modulate the properties of graphene both in channel and contact region to improve the scaling behavior of GFET.

This paper studies and investigates various parameters of top-gated graphene field-effect transistors (GFET). In this paper, the study of the relationship of resistance with temperature has led to the fact that we can use GFET as a sensor. Input parameters such as length of the channel, width of the channel, and temperature are taken, and it shows a significant impact on the relationship of various other parameters such as temperature versus position, electron versus density, hole density versus position, electric field versus position, and velocity versus position. It was investigated that the resistance is having a linear relationship with the temperature which shows that the top-gated graphene field-effect transistor (GFET) can be used as a temperature sensor; the value of resistance is insignificantly changing from 2.75 to 2.5 Ω when the length of the channel is 1800 nm; and when the channel length is 1400 nm, the resistance changes from 2.57 to 2.55 Ω for temperature varying from 253 to 313 K. Secondarily, by varying the temperature, the changes in field and velocity were minimal for temperature range from 100 to 300 K, the value of electric field varied from 13 to 14 V/μm, and velocity goes from 180 to 170 km/s. The effect of other input parameters like gate length and temperature on GFET has been observed and represented graphically. The presented graphs were all simulated in the NanoHub’s GFET tool.KeywordsGrapheneGFETElectrical propertiesThermal propertiesDrift–diffusion modelSensor

ABSTRACTIt is essential to control the electronic properties of a graphene field effect transistor (GFET). And the ability to accurately control the intrinsic electrical transport properties and to locally change the carrier density will be significant for graphene devices. We succeeded in achieving and controlling the Dirac point (neutrality point) simply by doping block co-polymer (BCP) covered GFET with CF4 plasma. By exposing polymer covered GFET to CF4 plasma for a short time the electronic transport was altered significantly. The hexagonal structure of BCP produces patterns with nanoscale spacing for heterogeneous patterns which provides a new approach to tune the electron and the hole conductivity simultaneously. Exploitation of fluorine doping provides a general route to control electronic property of any polymer coated GFET. The BCP protected GFET could detect 1mM NaF solution in “dry” condition in 60s. The sensing property demonstrates that BCP protected GFET could be a good candidate for stable and sensitive chemical or biological sensor. Furthermore, the distinct property of two functional groups within BCP facilitates the selective sensing property. These findings pave the way for developing more stable and sensitive sensors under ambient conditions.

The high-frequency performance of top-gated graphene field-effect transistors (GFETs) depends to a large extent on the saturation velocity of the charge carriers, a velocity limited by inelastic scattering by surface optical phonons from the dielectrics surrounding the channel. In this work, we show that, by simply changing the graphene channel surrounding dielectric with a material having higher optical phonon energy, one could improve the transit frequency and maximum frequency of oscillation of GFETs. We fabricated GFETs on conventional SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Si substrates by adding a thin Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> interfacial buffer layer on top of SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Si substrates, a material with about 30% higher optical phonon energy than that of SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , and compared performance with that of GFETs fabricated without adding the interfacial layer. From S-parameter measurements, a transit frequency and a maximum frequency of oscillation of 43 and 46 GHz, respectively, were obtained for GFETs on Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> with 0.5- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> gate length. These values are approximately 30% higher than those for state-of-the-art GFETs of the same gate length on SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . For relating the improvement of GFET high-frequency performance to improvements in the charge carrier saturation velocity, we used standard methods to extract the charge carrier velocity from the channel transit time. A comparison between two sets of GFETs with and without the interfacial Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> layer showed that the charge carrier saturation velocity had increased from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.5\cdot 10^{{7}}$ </tex-math></inline-formula> to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\cdot 10^{{7}}$ </tex-math></inline-formula> cm/s.

Inkjet-printed silver films on textiles for wearable electronics applications

Graphene Field Effect Transistor (GFET) which is scaled down to 15nm is modeled by integrating the effects of contact resistance. The effect of contact resistance cannot be neglected as the device is scaled down. As the contact resistance is directly related to the device drain current, increase in contact resistance results in reduced current flow. In this paper contact resistance formula with respect to sheet resistance, resistivity of the graphene under source-drain contacts and channel length is derived. It is known that Gold (Au) offers lesser contact resistance due to its lower sheet resistivity. Hence the derived formula is validated by proving that the contact resistance of Gold(Au) is lesser than other metals. The derived formula provides easier contact resistance calculation by replacing the sheet resistivity of different materials. A comparative study is made by having different metals as contacts and the total contact resistance offered by each metal is estimated. The model that has been developed to incorporate the contact resistance is used to determine drain current, which is computed by analyzing the channel potential and electric field. A novel method is adopted to analyze the channel potential by segmenting the channel. This method is key feature in modeling a purely ballistic transport at 15nm channel length. The ballistic structure resulted in lower channel potential drop due to the reduced scattering of electrons. Mobility which is considered to be a key factor of Graphene is being analyzed with respect to carrier concentration, conductivity and temperature. The realized mobility is found to be higher of 2497 cm /Vs. Simulation of a digital application-GFET Inverter with lesser fall time is presented in this paper.

We investigated the effect of capacitively coupled Ar plasma treatment on contact resistance (<TEX>$R_c$</TEX>) and channel sheet resistance (<TEX>$R_{sh}$</TEX>) of graphene field effect transistors (FETs), by varying their channel length in the wide range from 200 nm to <TEX>$50{\mu}m$</TEX> which formed the transfer length method (TLM) patterns. When the Ar plasma treatment was performed on the long channel (<TEX>$10{\sim}50{\mu}m$</TEX>) graphene FETs for 20 s, <TEX>$R_c$</TEX> decreased from 2.4 to <TEX>$1.15k{\Omega}{\cdot}{\mu}m$</TEX>. It is understood that this improvement in <TEX>$R_c$</TEX> is attributed to the formation of <TEX>$sp^3$</TEX> bonds and dangling bonds by the plasma. However, when the channel length of the FETs decreased down to 200 nm, the drain current (<TEX>$I_d$</TEX>) decreased upon the plasma treatment because of the significant increase of channel <TEX>$R_{sh}$</TEX> which was attributed to the atomic structural disorder induced by the plasma across the transfer length at the edge of the channel region. This study suggests a practical guideline to reduce <TEX>$R_c$</TEX> using various plasma treatments for the <TEX>$R_c$</TEX> sensitive graphene and other 2D material devices, where <TEX>$R_c$</TEX> is traded off with <TEX>$R_{sh}$</TEX>.

In this research work, the electrical and thermal properties of Graphene field effect transistor (GFET) has been simulated by varying the width of graphene channel. Here, the electrical characteristics, like electron density, hole density, I-V Characteristics and charge carrier velocity profile in the channel region has been studied for three different values of graphene channel width- 1 nm, 2 nm and 3 nm. To analyze the thermal properties of the GFET device, the temperature profile of the graphene channel has been simulated for 1, 2 and 3 nm channel width. After analyzing the simulation of this characteristics, it is concluded that, both electrical and thermal properties of GFET can be improved by fabricating the channel with larger width in the GFET device.

In this paper, the electrical and thermal properties of Graphene field effect transistor (GFET) has been simulated by varying the width of graphene channel. Here, the electrical characteristics, like electron density, hole density, I-V Characteristics and charge carrier velocity profile in the channel region has been studied for three different values of graphene channel width: 1 nm, 2 nm and 5 nm. To analyse the thermal properties of the GFET device, the temperature profile of the graphene channel has been simulated for 100, 300 and 500K. After analysing the simulation of this characteristics, it is concluded that, both electrical and thermal properties of GFET can be improved by fabricating the channel with larger width in the GFET device.

In this paper, the total dose effects of graphene field-effect transistors (GFETs) with different structures and sizes are studied. The irradiation experiments are carried out by using the 10-keV X-ray irradiation platform with a dose rate of 200 rad(Si)/s. Positive gate bias (&lt;i&gt;V&lt;/i&gt;&lt;sub&gt;G&lt;/sub&gt; = +1 V, &lt;i&gt;V&lt;/i&gt;&lt;sub&gt;D&lt;i&gt; &lt;/i&gt;&lt;/sub&gt;= &lt;i&gt;V&lt;/i&gt;&lt;sub&gt;S&lt;i&gt; &lt;/i&gt;&lt;/sub&gt;= 0 V) is used during irradiation. Using a semiconductor parameter analyzer, the transfer characteristic curves of top-gate GFET and back-gate GFET are obtained before and after irradiation. At the same time, the degradation condition of the dirac voltage &lt;i&gt;V&lt;/i&gt;&lt;sub&gt;Dirac&lt;/sub&gt; and the carrier mobility &lt;i&gt;μ&lt;/i&gt; are extracted from the transfer characteristic curve. The experimental results demonstrate that &lt;i&gt;V&lt;/i&gt;&lt;sub&gt;Dirac&lt;/sub&gt; and carrier mobility &lt;i&gt;μ&lt;/i&gt; degrade with dose increasing. The depletion of &lt;i&gt;V&lt;/i&gt;&lt;sub&gt;Dirac&lt;/sub&gt; and carrier mobility &lt;i&gt;μ&lt;/i&gt; are caused by the oxide trap charge generated in the gate oxygen layer during X-ray irradiation. Compared with the back-gate GFETs, the top-gate GFETs show more severely degrade &lt;i&gt;V&lt;/i&gt;&lt;sub&gt;Dirac&lt;/sub&gt; and carrier mobility, therefore top-gate GFET is more sensitive to X-ray radiation at the same cumulative dose than back-gate GFET. The analysis shows that the degradation of top-gate GFET is mainly caused by the oxide trap charge. And in contrast to top-gate GFET, oxygen adsorption contributes to the irradiation process of back-gate GFET, which somewhat mitigates the effect of radiation damage. Furthermore, a comparison of electrical property deterioration of GFETs of varying sizes between the pre-irradiation and the post-irradiation is made. The back-gate GFET, which has a size of 50 μm×50 μm, and the top-gate GFET, which has a size of 200 μm×200 μm, are damaged most seriously. In the case of the top-gate GFET, the larger the radiation area, the more the generated oxide trap charges are and the more serious the damage. In contrast, the back-gate GFET has a larger oxygen adsorption area during irradiation and a more noticeable oxygen adsorption effect, which partially offsets the damage produced by irradiation. Finally, the oxide trap charge mechanism is simulated by using TCAD simulation tool. The TCAD simulation reveals that the trap charge at the interface between Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; and graphene is mainly responsible for the degradation of top-gate GFET property, significantly affecting the investigation of the radiation effect and radiation reinforcement of GFETs.