Effect of Al2O3 Passive Layer on Stability and Doping of MoS2 Field-Effect Transistor (FET) Biosensors

Molybdenum disulfide (MoS2) features a band gap of 1.3 eV (indirect) to 1.9 eV (direct). This tunable band gap renders MoS2 a suitable conducting channel for field-effect transistors (FETs). In addition, the highly sensitive surface potential in MoS2 layers allows the feasibility of FET applications in biosensors, where direct immobilization and detection of biological molecules are conducted in wet conditions. In this work, we report, for the first time, the degradation of chemical vapor deposition (CVD) grown MoS2 FET-based sensors in the presence of phosphate buffer and water, which caused false positive response in detection. We conclude the degradation was originated by physical delamination of MoS2 thin films from the SiO2 substrate. The problem was alleviated by coating the sensors with a 30 nm thick aluminum oxide (Al2O3) layer using atomic layer deposition technique (ALD). This passive oxide thin film not only acted as a protecting layer against the device degradation but also induced a strong n-doping onto MoS2, which permitted a facile method of detection in MoS2 FET-based sensors using a low-power mode chemiresistive I-V measurement at zero gate voltage (Vgate = 0 V). Additionally, the oxide layer provided available sites for facile functionalization with bioreceptors. As immunoreaction plays a key role in clinical diagnosis and environmental analysis, our work presented a promising application using such enhanced Al2O3-coated MoS2 chemiresistive biosensors for detection of HIgG with high sensitivity and selectivity. The biosensor was successfully applied to detect HIgG in artificial urine, a complex matrix containing organics and salts.

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Advances in the fabrication of graphene transistors on flexible substrates

Beilstein Journal of Nanotechnology ◽

10.3762/bjnano.8.50 ◽

2017 ◽

Vol 8 ◽

pp. 467-474 ◽

Cited By ~ 16

Author(s):

Gabriele Fisichella ◽

Stella Lo Verso ◽

Silvestra Di Marco ◽

Vincenzo Vinciguerra ◽

Emanuela Schilirò ◽

...

Keyword(s):

Field Effect ◽

Field Effect Transistors ◽

High Mobility ◽

High Sensitivity ◽

Atomic Layer ◽

Transparent Electrode ◽

Large Area ◽

Sensing Applications ◽

Dielectric Performance

Graphene is an ideal candidate for next generation applications as a transparent electrode for electronics on plastic due to its flexibility and the conservation of electrical properties upon deformation. More importantly, its field-effect tunable carrier density, high mobility and saturation velocity make it an appealing choice as a channel material for field-effect transistors (FETs) for several potential applications. As an example, properly designed and scaled graphene FETs (Gr-FETs) can be used for flexible high frequency (RF) electronics or for high sensitivity chemical sensors. Miniaturized and flexible Gr-FET sensors would be highly advantageous for current sensors technology for in vivo and in situ applications. In this paper, we report a wafer-scale processing strategy to fabricate arrays of back-gated Gr-FETs on poly(ethylene naphthalate) (PEN) substrates. These devices present a large-area graphene channel fully exposed to the external environment, in order to be suitable for sensing applications, and the channel conductivity is efficiently modulated by a buried gate contact under a thin Al2O3 insulating film. In order to be compatible with the use of the PEN substrate, optimized deposition conditions of the Al2O3 film by plasma-enhanced atomic layer deposition (PE-ALD) at a low temperature (100 °C) have been developed without any relevant degradation of the final dielectric performance.

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Mist chemical vapor deposition of crystalline MoS2 atomic layer films using sequential mist supply mode and its application in field-effect transistors

Nanotechnology ◽

10.1088/1361-6528/ac30f4 ◽

2021 ◽

Author(s):

Abdul Kuddus ◽

Arifuzzaman Rajib ◽

Kojun Yokoyama ◽

Tomohiro Shida ◽

Keiji Ueno ◽

...

Keyword(s):

Chemical Vapor Deposition ◽

Vapor Deposition ◽

Field Effect ◽

Field Effect Transistors ◽

Chemical Vapor ◽

Atomic Layer ◽

Supply Mode

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Two-dimensional BN buffer for plasma enhanced atomic layer deposition of Al2O3 gate dielectrics on graphene field effect transistors

Scientific Reports ◽

10.1038/s41598-020-71108-5 ◽

2020 ◽

Vol 10 (1) ◽

Author(s):

Michael Snure ◽

Shivashankar R. Vangala ◽

Timothy Prusnick ◽

Gordon Grzybowski ◽

Antonio Crespo ◽

...

Keyword(s):

Atomic Layer Deposition ◽

Buffer Layer ◽

Photoelectron Spectroscopy ◽

Field Effect ◽

Field Effect Transistors ◽

Chemical Vapor ◽

Atomic Layer ◽

Organic Chemical ◽

Two Dimensional ◽

Layer Deposition

Abstract Here, we investigate the use of few-layer metal organic chemical vapor deposition (MOCVD) grown BN as a two-dimensional buffer layer for plasma enhanced atomic layer deposition (PE-ALD) of Al2O3 on graphene for top gated field effect transistors (FETs). The reactive nature of PE-ALD enables deposition of thin (2 nm) dielectrics directly on graphene and other two-dimensional materials without the need for a seed or functionalization layer; however, this also leads to significant oxidation of the graphene layer as observed by Raman. In FETs, we find this oxidation destroys conductivity in the graphene channel. By transferring thin (1.6 nm) MOCVD BN layers on top of graphene channels prior to PE-ALD, the graphene is protected from oxidation enabling BN/Al2O3 layers as thin as 4 nm. Raman and X-ray photoelectron spectroscopy on BN films show no significant oxidation caused by PE-ALD of Al2O3. Inserting the BN layer creates an atomically abrupt interface significantly reducing interface charges between the graphene and Al2O3 as compared to use of a 2 nm Al buffer layer. This results in a much smaller Dirac voltage (− 1 V) and hysteresis (0.9 V) when compared to FETs with the Al layer (VDirac = − 6.1 V and hysteresis = 2.9 V).

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All-Organic, Low Voltage, Transparent and Compliant Organic Field-Effect Transistor Fabricated by Means of Large-Area, Cost-Effective Techniques

Applied Sciences ◽

10.3390/app10196656 ◽

2020 ◽

Vol 10 (19) ◽

pp. 6656

Author(s):

Stefano Lai ◽

Giulia Casula ◽

Pier Carlo Ricci ◽

Piero Cosseddu ◽

Annalisa Bonfiglio

Keyword(s):

Field Effect ◽

Low Voltage ◽

Field Effect Transistors ◽

High Mobility ◽

Chemical Vapor ◽

Cost Effective ◽

Large Area ◽

Parylene C ◽

Biomedical Sensing ◽

Novel Applications

The development of electronic devices with enhanced properties of transparency and conformability is of high interest for the development of novel applications in the field of bioelectronics and biomedical sensing. Here, a fabrication process for all organic Organic Field-Effect Transistors (OFETs) by means of large-area, cost-effective techniques such as inkjet printing and chemical vapor deposition is reported. The fabricated device can operate at low voltages (as high as 4 V) with ideal electronic characteristics, including low threshold voltage, relatively high mobility and low subthreshold voltages. The employment of organic materials such as Parylene C, PEDOT:PSS and 6,13-Bis(triisopropylsilylethynyl)pentacene (TIPS pentacene) helps to obtain highly transparent transistors, with a relative transmittance exceeding 80%. Interestingly enough, the proposed process can be reliably employed for OFET fabrication over different kind of substrates, ranging from transparent, flexible but relatively thick polyethylene terephthalate (PET) substrates to transparent, 700-nm-thick, compliant Parylene C films. OFETs fabricated on such sub-micrometrical substrates maintain their functionality after being transferred onto complex surfaces, such as human skin and wearable items. To this aim, the electrical and electromechanical stability of proposed devices will be discussed.

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