Channel Of Field Effect Transistor Research Articles

Reversible Transition of Semiconducting PtSe2 and Metallic PtTe2 for Scalable All-2D Edge-Contacted FETs.

Two-dimensional (2D) transition metal dichalcogenide (TMD) layers are highly promising as field-effect transistor (FET) channels in the atomic-scale limit. However, accomplishing this superiority in scaled-up FETs remains challenging due to their van der Waals (vdW) bonding nature with respect to conventional metal electrodes. Herein, we report a scalable approach to fabricate centimeter-scale all-2D FET arrays of platinum diselenide (PtSe2) with in-plane platinum ditelluride (PtTe2) edge contacts, mitigating the aforementioned challenges. We realized a reversible transition between semiconducting PtSe2 and metallic PtTe2 via a low-temperature anion exchange reaction compatible with the back-end-of-line (BEOL) processes. All-2D PtSe2 FETs seamlessly edge-contacted with transited metallic PtTe2 exhibited significant performance improvements compared to those with surface-contacted gold electrodes, e.g., an increase of carrier mobility and on/off ratio by over an order of magnitude, achieving a maximum hole mobility of ∼50.30 cm2 V-1 s-1 at room temperature. This study opens up new opportunities toward atomically thin 2D-TMD-based circuitries with extraordinary functionalities.

(Invited) Switching Characteristics of GaN Power Transistors

A shorter switching time is one of the key advantages of GaN power devices over Si IGBTs. [1] In this paper, we report on the simulation of GaN power transistor switching and investigate the effect on the switching time novel design approaches ranging from the gate edge engineering (beyond just using field plates [2] for optimizing the voltage distribution in the drain-to-gate spacing to using the quantum well channel designs [3] that lead to the electron wave function penetration into wide band gap cladding layers with the commensurate increase in the breakdown voltage while keeping the advantage of high mobility in the device channel. We also report on the effect of a low conducting passivation for smoothing or even eliminating the sharp maximum of the electric field in the vicinity of the gate and field plate edges on switching time.[4] Additional contacts in the drain-to-gate spacing for the field control and variable doping implants could also decrease the switching time. Further optimization could be achieved with the perforated channel designs [5] decreasing the parasitic series resistance and improving the heat dissipation.[1] A. Tüysüz, R. Bosshard, and J. W. Kolar, erformance Comparison of a GaN GIT and a Si IGBT for High-Speed Drive Applications, Proceedings of the International Power Electronics Conference - ECCE Asia (IPEC 2014), Hiroshima, Japan, May 18-21, 2014[2] S. Karmalkar, M. S. Shur, G. Simin and M. A. Khan, Field-Plate Engineering for Heterostructure Field Effect Transistors, IEEE Trans. ED, 52, 12, pp. 2516- 2532, December (2005)[3] M. Dyakonov and M. S. Shur, Consequences of Space Dependence of Effective Mass in Heterostructures, J. Appl. Phys. Vol. 84, No. 7, pp. 3726-3730, October 1 (1998)[4] G. Simin, M. Shur and R. Gaska, SETI-0070: Semiconductor device with low-conducting field-controlling element App. No 13/396,059, November 19, 2013 as US Patent No. 8,586,997[5] G. Simin, M. Gaevski, M. Shur, R. Gaska, Perforated Channel Field Effect Transistor, US patent 9,467,105, October 11, 2016

Graphene transistor-based biosensors for rapid detection of SARS-CoV-2

Field-effect transistor (FET) biosensors use FETs to detect changes in the amount of electrical charge caused by biomolecules like antigens and antibodies. COVID-19 can be detected by employing these biosensors by immobilising bio-receptor molecules that bind to the SARS-CoV-2 virus on the FET channel surface and subsequent monitoring of the changes in the current triggered by the virus. Graphene Field-effect Transistor (GFET)-based biosensors utilise graphene, a two-dimensional material with high electrical conductivity, as the sensing element. These biosensors can rapidly detect several biomolecules including the SARS-CoV-2 virus, which is responsible for COVID-19. GFETs are ideal for real-time infectious illness diagnosis due to their great sensitivity and specificity. These graphene transistor-based biosensors could revolutionise clinical diagnostics by generating fast, accurate data that could aid pandemic management. GFETs can also be integrated into point-of-care (POC) diagnostic equipment. Recent advances in GFET-type biosensors for SARS-CoV-2 detection are discussed here, along with their associated challenges and future scope.

Asymmetric conducting route and potential redistribution determine the polarization-dependent conductivity in layered ferroelectrics.

Precise control of the conductivity of layered ferroelectric semiconductors is required to make these materials suitable for advanced transistor, memory and logic circuits. Although proof-of-principle devices based on layered ferroelectrics have been demonstrated, it remains unclear how the polarization inversion induces conductivity changes. Therefore, function design and performance optimization remain cumbersome. Here we combine ab initio calculations with transport experiments to unveil the mechanism underlying the polarization-dependent conductivity in ferroelectric channel field-effect transistors. We find that the built-in electric field gives rise to an asymmetric conducting route formed by the hidden Stark effect and competes with the potential redistribution caused by the external field of the gate. Furthermore, leveraging our mechanistic findings, we control the conductivity threshold in α-In2Se3 ferroelectric channel field-effect transistors. We demonstrate logic-in-memory functionality through the implementation of electrically self-switchable primary (AND, OR) and composite (XOR, NOR, NAND) logic gates. Our work provides mechanistic insights into conductivity modulation in a broad class of layered ferroelectrics, providing foundations for their application in logic and memory electronics.

Ultrasensitive Carbon Monoxide Gas Sensor at Room Temperature Using Fluorine-Graphdiyne.

Currently, most carbon monoxide (CO) gas sensors work at high temperatures of over 150 °C. Developing CO gas sensors that operate at room temperature is challenging because of the sensitivity trade-offs. Here, we report an ultrasensitive CO gas sensor at room temperature using fluorine-graphdiyne (F-GDY) in which electrons are increased by light. The GDY films used as channels of field-effect transistors were prepared by using chemical vapor deposition and were characterized by using various spectroscopic techniques. With exposure to UV light, F-GDY showed a more efficient photodoping effect than hydrogen-graphdiyne (H-GDY), resulting in a larger negative shift in the charge neutral point (CNP) to form an n-type semiconductor and an increase in the Fermi level from -5.27 to -5.01 eV. Upon CO exposure, the negatively shifted CNP moved toward a positive shift, and the electrical current decreased, indicating electron transfer from photodoped GDYs to CO. Dynamic sensing experiments demonstrated that negatively charged F-GDY is remarkably sensitive to an electron-deficient CO gas, even with a low concentration of 200 parts per billion. This work provides a promising solution for enhancing the CO sensitivity at room temperature and expanding the application of GDYs in electronic devices.

Gate-Tunable Graphene/ZnO-Based Dual- Channel Field-Effect Transistor Gas Sensor for Simultaneous Detection of CO2 and NO2 Gases

Gate-Tunable Graphene/ZnO-Based Dual- Channel Field-Effect Transistor Gas Sensor for Simultaneous Detection of CO₂ and NO₂ Gases

Simulation on the Effect of Channel Thickness on the Performance of Multi-Bridge Channel Field-Effect Transistor

A Multi-Bridge Channel Field-Effect Transistor (MBCFET) structure has been designed and simulated to characterize its electrical performance. An MBCFET is a device designed to bridge single-channel FETs, allowing more flexibility with signal routing and power management in complex designs. However, MBCFET suffers from Short Channel Effects which degrade its performance. Channel thickness is another important parameter that affect the performance of MBCFETs. Thus, the impact of channel thickness variation on MBCFET performance is investigated in this project. The electrical characteristic of MBCFET such as its threshold voltage (Vth), subthreshold swing (SS), on-state current (Ion), and off-state current (Ioff) were obtained and analyzed by using the TCAD simulation tool. Comparing the simulation results to published results indicated that the difference between the results was less than 5% for various parameters. The second part of the simulation work shows that as the channel thickness of an MBCFET increases, Vth decreases, Ion increases, and SS decreases. However, when the channel thickness is too thin, SS increases significantly, which leads to the device consuming higher power with lower performance.

Building Block-Inspired Hybrid Perovskite Derivatives for Ferroelectric Channel Layers with Gate-Tunable Memory Behavior.

Ferroelectric photovoltaics driven by spontaneous polarization (Ps ) holds a promise for creating the next-generation optoelectronics, spintronics and non-volatile memories. However, photoactive ferroelectrics are quite scarce in single homogeneous phase, owing to the severe Ps fatigue caused by leakage current of photoexcited carriers. Here, through combining inorganic and organic components as building blocks, we constructed a series of ferroelectric semiconductors of 2D hybrid perovskites, (HA)2 (MA)n-1 Pbn Br3n+1 (n=1-5; HA=hexylamine and MA=methylamine). It is intriguing that their Curie temperatures are greatly enhanced by reducing the thickness of inorganic frameworks from MAPbBr3 (n=∞, Tc =239 K) to n=2 (Tc =310 K, ΔT=71 K). Especially, on account of the coupling of room-temperature ferroelectricity (Ps ≈1.5 μC/cm2 ) and photoconductivity, n=3 crystal wafer was integrated as channel field effect transistor that shows excellent a large short-circuit photocurrent ≈19.74 μA/cm2 . Such giant photocurrents can be modulated through manipulating gate voltage in a wide range (±60 V), exhibiting gate-tunable memory behaviors of three current states ("-1/0/1" states). We believe that this work sheds light on further exploration of ferroelectric materials toward new non-volatile memory devices.

Building Block‐Inspired Hybrid Perovskite Derivatives for Ferroelectric Channel Layers with Gate‐Tunable Memory Behavior

AbstractFerroelectric photovoltaics driven by spontaneous polarization (Ps) holds a promise for creating the next‐generation optoelectronics, spintronics and non‐volatile memories. However, photoactive ferroelectrics are quite scarce in single homogeneous phase, owing to the severe Ps fatigue caused by leakage current of photoexcited carriers. Here, through combining inorganic and organic components as building blocks, we constructed a series of ferroelectric semiconductors of 2D hybrid perovskites, (HA)2(MA)n‐1PbnBr3n+1 (n=1–5; HA=hexylamine and MA=methylamine). It is intriguing that their Curie temperatures are greatly enhanced by reducing the thickness of inorganic frameworks from MAPbBr3 (n=∞, Tc=239 K) to n=2 (Tc=310 K, ΔT=71 K). Especially, on account of the coupling of room‐temperature ferroelectricity (Ps≈1.5 μC/cm2) and photoconductivity, n=3 crystal wafer was integrated as channel field effect transistor that shows excellent a large short‐circuit photocurrent ≈19.74 μA/cm2. Such giant photocurrents can be modulated through manipulating gate voltage in a wide range (±60 V), exhibiting gate‐tunable memory behaviors of three current states (“‐1/0/1” states). We believe that this work sheds light on further exploration of ferroelectric materials toward new non‐volatile memory devices.

Effect of spin on the instability of THz plasma waves in field-effect transistors under non-ideal boundary conditions

Terahertz (THz) radiation can be generated due to the instability of THz plasma waves in field-effect transistors (FETs). In this work, we discuss the instability of THz plasma waves in the channel of FETs with spin and quantum effects under non-ideal boundary conditions. We obtain a linear dispersion relation by using the hydrodynamic equation, Maxwell equation and spin equation. The influence of source capacitance, drain capacitance, spin effects, quantum effects and channel width on the instability of THz plasma waves under the non-ideal boundary conditions is investigated in great detail. The results of numerical simulation show that the THz plasma wave is unstable when the drain capacitance is smaller than the source capacitance; the oscillation frequency with asymmetric boundary conditions is smaller than that under non-ideal boundary conditions; the instability gain of THz plasma waves becomes lower under non-ideal boundary conditions. This finding provides a new idea for finding efficient THz radiation sources and opens up a new mechanism for the development of THz technology.

(Invited) BioFETs and Nanopore FETs: Nanoscale Silicon Field-Effect Transistors for Single-Molecule Sensing

High read throughput single-molecule sensing is a cornerstone of established third generation long-read DNA sequencing technologies and is crucial for emerging protein sequencing technologies. These omics technologies are of great interest for essential understanding and applications in the life sciences. Field Effect Transistor (FET)-based single-molecule sensors promise advances in omics, by further enhancing read throughput with massive parallelization.Here an overview is given of our recent progress on nanoscale bioFETs and nanopore FETs (NPFETs).A bioFET is a FET gated by a liquid electrolyte rather than by a solid gate. The FET is turned into a biosensor by attaching probe biomolecules to the gate dielectric. These probes bind specifically to the target biomolecule of interest. The attachment of the targets to the probes on the gate dielectric surface shifts the FET threshold voltage.A nanopore FET is an electrolytically gated FET as well, in which the gate gauges potential changes caused by a molecule moving, or translocating, through a nanopore, a nanoscale opening connecting two reservoirs. Nanopores have been firmly established as single-molecule sensors as the ionic current running through them is modulated by passing single molecules.Nanoscale silicon bioFET sensors have single-molecule capabilities within their reach [1-4]. To realize single-molecule sensing the single-molecule signal-to-noise ratio (SNR) must be sufficiently high. Downscaling the device area is key to increase SNR (∝1/√area) [5]. Although many reported FET sensors have nanoscale cross-sections, their gate lengths are typically micron-scale. Our FET modeling work shows that a sufficiently large single-molecule Signal-to-Noise Ratio (SNR) can be obtained when nano-scaling all FET channel dimensions [6]. We have shown significant progress [1] toward single-molecule detection by fabricating and characterizing finFET sensors with a gate length of 50nm and have shown that Si FETs have the potential to enable single-molecule sensing.Noise plays a central role in single-molecule sensing [7,8] and drift can also be a challenge in FET sensors [9]. Perhaps the greatest challenge for bioFETs is electrolyte screening which reduces the signal by masking the charge of target molecules with counterions. We have experimentally established the importance of non-linear screening, and the pH interference effect which can aggravate screening [10,11] and propose solutions.The nanopore FET, senses single molecules translocating through the pore due to the so-called resistive divider effect [6]. The nanopore FET has been experimentally demonstrated as a single-molecule sensor in 2012 [12]. The nanopore FET’s device-level advantage is its potential high > 100 MHz bandwidth with sufficient signal-to-noise ratio (SNR). This has been studied theoretically [13] but is yet to be proven experimentally. The second, and most important advantage, is the superior integrability of nanopore-FETs into large-scale arrays.In our recent simulation work making use of a dedicated nanofluidic nanodevice simulator we reveal that sensitivity can be boosted exponentially by increasing cis-trans bias [14].We have fabricated and characterized a Nanopore-FET milestone device [15,16], which has a nanopore running through a nanoscale silicon FET channel, but without bottom reservoir (see Fig. 1). On this milestone device we obtain excellent electrolytically gated FET transfer and output characteristics demonstrating a low subthreshold swing of 67mV/decade, indicating excellent device quality.Applications of the nanopore FET for omics and DNA data storage will be discussed.FET-based sensing promises to strongly enhance the read throughput of single-molecule sensing by means of massive parallelization.<ECSTEM.jpg>Fig. 1. TEM cross-section of the NPFET milestone device.[1] Santermans et al. IEEE International Electron Devices Meeting, 2020[2] Li et al. ACS Nano 2017, 11, 12789−12795[3] He et al. Angewandte Chemie, 55, 1, 2016[4] Li et al. Nanoscale, 2016, 8, 16172[5] Männik et al. Nano Letters, 8, 2008[6] Santermans et al., to be published[7] Martens et al. Int. Conf. Noise Fluctuations (ICNF), 2019[8] Bergfeld Mori et al. Solid-State Electronics 194, p. 108358, 2022[9] Wuytens et al. IEEE Int. Reliability Physics Symposium, 2020[10] Gupta, et al. IEEE Sensors Journal, 21, 4, p. 4143, 2020[11] Santermans et al. ACS Sensors 6, 3, p. 1049, 2021[12] Xie et al. Nature Nanotechnology, 7(2), pp.119-125, 2012[13] Parkin and Drndić, ACS sensors, 3, 2, p. 313, 2018[14] Verhulst et al., IEEE Sensors Journal, 22, 6, pp.5732-5742, 2022[15] Liu et al., MNE, Leuven, Sep., 2022[16] Martens et al. IEEE International Electron Devices Meeting, 2022 Figure 1

(Invited) Application of Machine Learning in Carbon Nanotube-Based Biosensors

Among electrochemical sensors, electrolyte-gated field-effect transistor (FET) with semiconducting single-walled carbon nanotubes (SWCNTs) is one of the most promising choices for the ultrasensitive biosensors. The biosensing is typically based on the recognition of analytes with capture probes (antibody, aptamer, receptor, enzyme, etc.) attached to SWCNTs. While the capture probes improve the chemical sensitivity and selectivity, the stability of the nanotube-based biosensors is limited by the activity of the capture probes. Another approach involves sensor arrays with different metal nanoparticles/self-assembled monolayers on the SWCNTs that act as nonspecific receptors. These sensor arrays can be trained with machine learning algorithms to distinguish analytes.When analytes bind to the sensor surface and interact with the semiconducting SWCNTs, they can cause modulations of the number of charge carriers in the FET channel, changing the device conductance, and eventually result in change in the FET characteristics, i.e., measured source-drain current vs. applied gate voltage. Rich information regarding the biorecognition process, sensing mechanism and sensing performances can be extracted from the changes in FET transfer characteristics. We proposed 11 features that can be selected to accurately describe the changes in FET transfer curves, including (1) relative change in transconductance, (2) threshold voltage (Vth) shift, (3, 10) relative change in conductance at ±0.6 Vg, (4-9) change in overall conductance normalized to conductance at Vth, and (11) the relative change in minimum conductance (see figure below). The transfer characteristics were extracted as distinct features for model training using established machine learning algorithms.We fabricated SWCNT-FET array functionalized with gold nanoparticles and different self-assembled monolayers (dodecanethiol and lipoic acid) for the sensing of nonmalignant and malignant cells, which were classified by linear discriminant analysis.[1] We have also demonstrated that the SWCNT-FET sensor array could be used for the screening of cell behaviors, and that live/dead mouse B16 melanoma cells could be successfully classified with machine learning.[2] [1] Silva, G. O.; Michael, Z. P.; Bian, L.; Shurin, G. V.; Mulato, M.; Shurin, M. R.; Star, A., Nanoelectronic Discrimination of Nonmalignant and Malignant Cells Using Nanotube Field-Effect Transistors. ACS Sens. 2017, 2, 1128–1132.[2] Liu, Z. R.; Shurin, G. V.; Bian, L.; White, D. L.; Shurin, M. R.; Star, A., A Carbon Nanotube Sensor Array for the Label-Free Discrimination of Live and Dead Cells with Machine Learning. Anal. Chem. 2022, 94, 3565-3573. Figure 1

Simple Fabrication Method for Solution-gated One-piece Transistors for Biosensing Applications

INTRODUCTIONSolution-gated field-effect transistors (FETs) with silicon or other semiconductive materials as channels can specifically and selectively detect ions and biomolecules related to biological functions by chemically modifying the gate electrode surface, and these are known as biologically coupled FETs (Bio-FETs) [1]. Since Bio-FETs can directly detect the charges of ions and biomolecules, they do not require to label fluorescent dyes and to induce redox reactions based on enzymes. Therefore, Bio-FETs are expected to be used as in vitro diagnostic devices for a label-free monitoring of health conditions in daily life.Recently, indium tin oxide (ITO) has been widely used as an electrode material for flat panel displays owing to its transparency and conductivity. Our laboratory previously reported that solution-gate FETs fabricated by one-step sputtering provided a steep subthreshold slope (SS) owing to the absence of the interfaces among source/channel/drain electrodes and the large electric double-layer capacitance caused by direct contact between electrolyte solutions and the channel surface [2]. While this technique was simple, it utilized the diffusion of atoms during sputtering between a modified mask and substrates and was also dependent on the mask size, which limited the miniaturization of the transistor. On the other hand, the conventional fabrication methods of solution-gated FETs facilitate the miniaturization and the precise control of device structure by use of photolithography, but such methods inevitably produce impurities at the source/channel/drain electrode interfaces and may cause the degradation of device performances.In this study, we propose a new method to fabricate solution-gated ITO thin-film channel FETs without interfaces among the source/channel/drain electrodes, which facilitates to miniaturize and control the device structure. A conductive ITO thin film with a thickness of about 100 nm is deposited on a glass substrate by sputtering. Then, the ITO film is protected by photoresist and then the channel area is exposed by photolithography. The exposed area is etched to 20 nm or less thickness, which induces semiconductive characteristics. This method enables the fabrication of the desired solution-gated ITO thin-film channel FET. Furthermore, we evaluate its electrical characteristics and examines its potential for biosensor applications.EXPERIMENTALFirst, photoresist was patterned on a glass substrate by photolithography. ITO thin film (100 nm thickness) was deposited on the patterned area by sputtering, and the photoresist was removed using a solvent. Next, photolithography was used again to deposit the resist film so that the channel area was exposed. Etching was performed by dropping 0.1 M hydrochloric acid on the exposed channel area (Figure). Etching time was controlled by applying a voltage between the source and drain electrodes and measuring the change in current over time. A semiconductor parameter analyzer was used to measure the current during etching, the gate voltage (VG)-drain current (ID) transfer characteristics, and the pH responsivity of the fabricated devices. The film thickness was measured by a white interferometer-equipped laser microscope (Keyence).RESULTS and DISCUSSIONBy controlling the current during etching, the current value was decreased rapidly at the end of the etching. This may be because the thickness of ITO film was thinner and reached about 20 nm, which resulted in the semiconductive characteristics. Then, the etching was stopped to obtain the solution-gated ITO thin-film channel FET. The fundamental electrical characteristics such as VG-ID transfer curves were investigated, and the fabricated device was found to operate as the solution-gated FET. It was also found that the devices showed the Nernst response for the change in pH and a steep subthreshold slope of approximately 90 mV/decade (pH 7.41). Furthermore, the ITO channel thickness was measured by laser microscopy; as a result, it was about 10–20 nm.CONCLUSIONS In this study, we proposed the new method to fabricate the solution-gated ITO thin-film channel FET. The device actually worked as a transistor, and it showed good sensitivity to potential. This method enabled the solution-gated FETs to be produced by the simple method. Thus, the solution-gated ITO thin-film channel FET is applied to biosensors, which is highly sensitive and affordable to detect biomolecules in the future.REFERENCES[1] Sakata, T. ACS Omega, 4, 11852 (2019).[2] Sakata, T.; Nishitani, S.; Saito, A.; Fukasawa, Y. ACS Appl. Mater. Interfaces, 13, 38569 (2021). Figure 1

Terahertz bolometric detectors based on graphene field-effect transistors with the composite h-BN/black-P/h-BN gate layers using plasmonic resonances

We propose and analyze the performance of terahertz (THz) room-temperature bolometric detectors based on the graphene channel field-effect transistors (GC-FET). These detectors comprise the gate barrier layer (BL) composed of the lateral hexagonal-boron nitride black-phosphorus/hexagonal-boron nitride (h-BN/b-P/h-BN) structure. The main part of the GC is encapsulated in h-BN, whereas a short section of the GC is sandwiched between the b-P gate BL and the h-BN bottom layer. The b-P gate BL serves as the window for the electron thermionic current from the GC. The electron mobility in the GC section encapsulated in h-BN can be fairly large. This might enable a strong resonant plasmonic response of the GC-FET detectors despite relatively lower electron mobility in the GC section covered by the b-P window BL. The narrow b-P window diminishes the Peltier cooling and enhances the detector performance. The proposed device structure and its operation principle promote elevated-temperature GC-FET THz detector responsivity values and other characteristics, especially at the plasmonic resonances.

Sybodies as Novel Bioreceptors toward Field-Effect Transistor-Based Detection of SARS-CoV-2 Antigens.

The SARS-CoV-2 pandemic has increased the demand for low-cost, portable, and rapid biosensors, driving huge research efforts toward new nanomaterial-based approaches with high sensitivity. Many of them employ antibodies as bioreceptors, which have a costly development process that requires animal facilities. Recently, sybodies emerged as a new alternative class of synthetic binders and receptors with high antigen binding efficiency, improved chemical stability, and lower production costs via animal-free methods. Their smaller size is an important asset to consider in combination with ultrasensitive field-effect transistors (FETs) as transducers, which respond more intensely when biorecognition occurs near their surface. This work demonstrates the immobilization of sybodies against the spike protein of the virus on silicon surfaces, which are often integral parts of the semiconducting channel of FETs. Immobilized sybodies maintain the capability to capture antigens, even at low concentrations in the femtomolar range, as observed by fluorescence microscopy. Finally, the first proof of concept of sybody-modified FET sensing is provided using a nanoscopic silicon net as the sensitive area where the sybodies are immobilized. The future development of further sybodies against other biomarkers and their generalization in biosensors could be critical to decrease the cost of biodetection platforms in future pandemics.

Complementary inverter and reward-modulated spike timing dependent plasticity circuit based on organic transistors

Organic materials are the key to the next generation of electric memory elements because of their low cost, high flexibility and high scalability. Solution-processed n-channel and p-channel organic field effect transistors (FETs) by spinning coating technique was demonstrated. We use based-poly (vinylcarbazole) (PVK) p-type transistor and based-6-phenyl-C61 butyric acid methyl ester (PCBM) n-type transistor as the channel of bottom gate structure FET, respectively, to fabricate the complementary inverter. The maximum voltage gain of the electrically isolated FET complementary inverter is up to 22, the power consumption is less than 3 μW, and the transition voltage is −4.2 V. In addition, our devices are able to implement “AND”, “NAND”, “OR”, and “NOT” gate logic well. But more than that, p-type transistor based on PVK and n-type transistor based on PCBM were combined with the memristor, reward-modulated spike timing dependent plasticity was implemented by introduced reward/punishment signals to guide synaptic weight updates. It shows great potential in the electronic application system with low cost and high energy efficiency.

Fully Inkjet‐Printed, 2D Materials‐Based Field‐Effect Transistor for Water Sensing

AbstractDespite significant progress in solution‐processing of 2D materials, it remains challenging to reliably print high‐performance semiconducting channels that can be efficiently modulated in a field‐effect transistor (FET). Herein, electrochemically exfoliated MoS2 nanosheets are inkjet‐printed into ultrathin semiconducting channels, resulting in high on/off current ratios up to 103. The reported printing strategy is reliable and general for thin film channel fabrication even in the presence of the ubiquitous coffee‐ring effect. Statistical modeling analysis on the printed pattern profiles suggests that a spaced parallel printing approach can overcome the coffee‐ring effect during inkjet printing, resulting in uniform 2D flake percolation networks. The uniformity of the printed features allows the MoS2 channel to be hundreds of micrometers long, which easily accommodates the typical inkjet printing resolution of tens of micrometers, thereby enabling fully printed FETs. As a proof of concept, FET water sensors are demonstrated using printed MoS2 as the FET channel, and printed graphene as the electrodes and the sensing area. After functionalization of the sensing area, the printed water sensor shows a selective response to Pb2+ in water down to 2 ppb. This work paves the way for additive nanomanufacturing of FET‐based sensors and related devices using 2D nanomaterials.

Optically excited artificial synapse based on α-In2Se3 FETs on Ta2O5

Materials and devices for artificial synapses are being increasingly investigated owing to their promise for brain-inspired computing. Here, we demonstrate an optoelectronic synapse with a light-modulated memory capability in back-gated ferroelectric channel field-effect transistors made of multi-layered 2D α-In2Se3 on Ta2O5. The optical tunability is achieved by exploiting the frequency of the optical signal in vertically stacked layers of In2Se3, which generates a unique persistent photoresponse due to trapping at the In2Se3/Ta2O5 interface. For the 527 nm source wavelengths at intensities of 15 mW cm−2 the In2Se3-FET exhibits a high photoresponsivity at 850 AW−1. These devices can replicate synaptic functions such as photo-induced short-term memory, long-term memory and paired-pulse facilitation—all via optical modulation. We also demonstrate common memory effects that occur in the brain, such as memory loss and memory transitions that depend upon the stimulation rate (i.e., the interval between stimulation pulses). These demonstrations provide a simple and effective strategy for fabricating light-stimulated synaptic transistors with memory and learning abilities which are attractive for building vision-inspired neuromorphic systems.

An investigation into the reliability of newly proposed MoSi2N4/WSi2N4 field-effect transistors: A Monte Carlo study

Recently, the two dimensional complex MA2Z4 structures have been suggested as suitable replacements for silicon channels in field-effect transistors (FETs). Specifically, two materials of MoSi2N4 and WSi2N4 due to their very desirable electrical and thermal properties are noticed. On the other hand, the reliability of transistors, which is determined by the maximum temperature they obtain during the performance, specifies the usefulness of the newly proposed channels for thermal management solution. In this work, the FETs, including MoSi2N4 and WSi2N4 channels, are investigated using Monte Carlo simulation of the phonon Boltzmann equation. In particular, the phonon analysis has been carried out to investigate the peak temperature rise. Our calculations confirm that MoSi2N4 and WSi2N4 present lower maximum temperature than the previously suggested candidate, the blue phosphorene (BP) which itself reaches a shallow temperature. Concretely, the phonon exploration shows that the competition between the dominant heat carrier velocity, and its related frequency settles the maximum temperature value. The material WSi2N4 with much more phonons in TA mode, with almost high velocity and relatively low-frequency, shows adequate thermal condition, and its peak temperature is very low, say 110 K, less than that of BP. The material MoSi2N4 attains the maximum temperature of only 10 K less than BP peak temperature. This behavior attributes to the dominant LA phonons which are fast but also have high frequency and consequently make the temperature get larger than that of the WSi2N4. In summary, WSi2N4, with very low peak temperature, and in the next step MoSi2N4, both with beneficial electrical/thermal properties, are suggested as very suitable candidates for producing more reliable FETs, fulfilling the thermal management.

Comparing surface modification methods for silicon nanowire field-effect transistor biosensors for diagnosis applications: A case study of cardiac troponin I

This study is a debut of a side-by-side comparison of different methods to modify the surfaces of the silica-based substrates for biosensor fabrication. The fabricated biosensors are assessed for the quantification of cardiac troponin I (cTnI), a biomarker of acute myocardial infarction, at ultralow concentrations and small increment resolution in human serum. To accomplish this, silica samples and silicon nanowire field-effect transistor (SiNWFET) channels were modified with (3-aminopropyl)triethoxysilane, 1-(3-aminopropyl)silatrane, and the mixed self-assembly monolayer of silane-polyethylene glycol (silane-PEG, constituting of silane-PEG-NH2 and silane-PEG-OH at the ratio of NH2:OH = 1:10). Afterwards, they were treated with glutaraldehyde to immobilize aptamer probes for cTnI aptasensor detection. Thereafter, the modified-silica samples were investigated for surface roughness and antifouling capability, whereas the SiNWFET aptasensors were employed to determine cTnI. Empirical data revealed that only the silane-PEG-modified samples provided a superior surface for probe immobilization and high antifouling capability for the PEG-SiNWFET aptasensors to determine cTnI at ultralow levels with high resolution in human serum. Therefore, surface modification with silane-PEG provided an option for the challenge of precise quantification of cTnI, as well as of other protein biomarkers, at ultralow levels in bio-samples using the FET-based biosensors.