Silicon-based Field-effect Transistors Research Articles

Carbon nanotube integrated circuit technology: purification, assembly and integration

Abstract As the manufacturing process of silicon-based integrated circuits (ICs) approaches its physical limit, the quantum effect of silicon-based field-effect transistors (FETs) has become increasingly evident. And the burgeoning carbon-based semiconductor technology has become one of the most disruptive technologies in the post-Moore era. As one-dimensional nanomaterials, carbon nanotubes (CNTs) are far superior to silicon at the same technology nodes of FETs because of their excellent electrical transport and scaling properties, rendering them the most competitive material in the next-generation ICs technology. However, certain challenges impede the industrialization of CNTs, particularly in terms of material preparation, which significantly hinders the development of CNT-based ICs. Focusing on CNT-based ICs technology, this review summarizes its main technical status, development trends, existing challenges, and future development directions.

Mechanically Gated Transistor.

Silicon-based field effect transistors have underpinned the information revolution in the last 60 years, and there is a strong desire for new materials, devices, and architectures that can help sustain the computing power in the age of big data and artificial intelligence. Inspired by the Piezo channels, a mechanically gated transistor abandoning electric gating altogether, achieving an ON/OFF ratio over three orders of magnitude under a mechanical force of hundreds of nN is developed. The two-terminal device utilizes flexoelectric polarization induced by strain gradient, which modulates the carrier concentration in a Van der Waals structure significantly, and it mimics Piezo channels for artificial tactile perception. This simple device concept can be easily adapted to a wide range of semiconducting materials, helping promote the fusion between mechanics and electronics in a similar way as mechanobiology.

Sub-5 nm Gate-Length Monolayer Selenene Transistors.

Two-dimensional (2D) semiconductors are being considered as alternative channel materials as silicon-based field-effect transistors (FETs) have reached their scaling limits. Recently, air-stable 2D selenium nanosheet FETs with a gate length of 5 µm were experimentally produced. In this study, we used an ab initio quantum transport approach to simulate sub-5 nm gate-length double-gate monolayer (ML) selenene FETs. When considering negative-capacitance technology and underlap, we found that 3 nm gate-length p-type ML selenene FETs can meet the 2013 ITRS standards for high-performance applications along the armchair and zigzag directions in the 2028 horizon. Therefore, ML selenene has the potential to be a channel material that can scale Moore's law down to a gate length of 3 nm.

Reconfiguration Using Bio-Inspired Conduction Mode of Field-Effect Transistors toward the Creation of Recyclable Devices

A bio-inspired conduction mode in silicon-based field-effect transistors was studied here using the frequency-dependent reconfiguration principle in a size-reduced circuit architecture. Analog circuits comprising neuromorphic and reconfigurable behavior were analyzed across their physical quantities using a set of equations governing circuit performance. Practical examples were built, analyzed, and discussed from a phenomenological viewpoint. Upon exploiting their reconfiguration properties when semiconductor devices and passive components are interconnected, novel operating principles might inspire optimized signal processing and manufacturing facilities to design circular device-based complex systems.

Theory of the in-plane photoelectric effect in quasi-one-dimensional electron systems

The in-plane photoelectric (IPPE) effect is a recently discovered [Sci. Adv. 8, eabi8398 (2022)] quantum phenomenon, which enables efficient detection of terahertz (THz) radiation in semiconductor structures with a two-dimensional (2D) electron gas. Here, we develop a theory of the IPPE effect in quasi-one-dimensional electron systems in which the width of the 2D conducting channel is so small that the transverse quantization energy is larger than the thermal energy. We calculate the THz photoresponse of such a system as a function of the THz frequency, control gate voltages, and geometrical parameters of the detector. We show that the transverse quantization of the electron motion manifests itself in oscillating gate-voltage dependences of the photocurrent, if the THz photon energy is less than the one-dimensional quantization energy. Results of the theory are applicable to any semiconductor systems with 2D electron gases, including III--V structures, silicon-based field effect transistors, and the novel 2D layered graphene-related materials.

Strain effect on the field-effect sensing property of Si wires.

Silicon-based field effect transistor (FET) sensors with high sensitivity are emerging as powerful sensors for detecting chemical/biological species. Strain engineering has been demonstrated as an effective means to improve the performance of Si-based devices. However, the strain effect on the field-effect sensing property of silicon materials has not been studied yet. Here, we investigate the strain effect on the field-effect sensing property of silicon wires by taking humidity sensing as an example. The humidity sensitivity of FET sensors based on silicon wires increases with increasing tensile strain but decreases with increasing compressive strain. The sensitivity is very responsive to strain with an enhancement factor of 67 for tensile strain. Theoretical analysis shows that the sensitivity variation under different strains is mainly attributed to the change in adsorption energy between silicon wires and water molecules. This work indicates that strain engineering can be an effective route to modulate the field-effect sensing property of Si wires for constructing highly sensitive Si-based FET sensors.

The device performance limit of in-plane monolayer VTe2/WTe2 heterojunction-based field-effect transistors.

To overcome the scaling restriction on silicon-based field-effect transistors (FETs), two-dimensional (2D) transition metal dichalcogenides (TMDs) have been strongly proposed as alternative materials. To explore the device performance limit of TMD-based FETs, in this work, the ab initio quantum transport approach is utilized to study the transport properties of monolayer VTe2/WTe2 heterojunction-based FETs possessing double gates (DGs) with a 5 nm gate length (Lg). Our theoretical simulations demonstrate that the DG-cold-source VTe2/WTe2 FETs with a 5 nm Lg and 2 or 3 nm proper underlap (UL) meet the basic requirements of the on-state current (Ion), power dissipation (PDP), and delay time (τ) for the 2028 needs of the International Technology Roadmap for Semiconductor (ITRS) 2013, which ensures their high-performance and low-power-dissipation device applications. Moreover, the DG-cold-source VTe2/WTe2-based FETs with a 3 nm Lg and 2 or 3 nm UL meet the high-performance requirements of Ion, τ, and PDP for the 2028 needs of ITRS 2013. Additionally, by further considering the negative capacitance technology in devices, the parameters τ, Ion, and PDP of the VTe2/WTe2-based FETs with a 1 nm Lg and 3 nm UL meet well with the 2028 needs for ITRS 2013 towards high-performance device applications. Our theoretical results uncover that the 2D DG-cold-source VTe2/WTe2 FETs can be used as a new kind of promising material candidate to drive the scaling of Moore's law down to 1 nm.

One dimensional MOSFETs for sub-5 nm high-performance applications: a case of Sb2Se3 nanowires.

Low-dimensional materials have been proposed as alternatives to silicon-based field-effect transistor (FET) channel materials in order to overcome the scaling limitation. In the present research, gate-all-around (GAA) Sb2Se3 nanowire FETs were simulated using the ab initio quantum transport method. The gate-length (Lg, Lg = 5 nm) GAA Sb2Se3 FETs with an underlap (UL, UL = 2, 3 nm) could satisfy the on-state current (Ion) and delay time (τ) of the 2028 requirements for high performance (HP) applications of the International Technology Roadmap for Semiconductors (ITRS) 2013. It is interesting that the Lg = 3 nm GAA Sb2Se3 FETs with a UL = 3 nm can meet the Ion, power dissipation (PDP), and τ of the 2028 requirements of ITRS 2013 for HP applications. Therefore, GAA Sb2Se3 FETs can be a potential candidate scaling Moore's law downward to 3 nm.

Enhanced contact properties of MoTe2-FET via laser-induced heavy doping

The doping technique is vital for applying two-dimensional (2D) materials such as transition metal dichalcogenide (TMDC)-based field effect transistors (FETs), which can control the channel polarity and improve the performance. However, as conventional doping techniques for silicon-based FET are not suitable for 2D materials, the realization of heavy doping of TMDC materials is challenging, especially for n-type heavy doping. This study reports a simple, regioselective, controllable, and chemically stable heavy doping method for 2H-MoTe2 crystal via high-density laser irradiation. The polarity of the doping can be controlled by changing the irradiation environment. For the MoTe2-nFET, good performance with enhanced contact properties was obtained using the contact doping method via laser irradiation in a vacuum environment.

Theory of the in-plane photoelectric effect in two-dimensional electron systems

A new photoelectric phenomenon, the in-plane photoelectric (IPPE) effect, has been recently discovered at terahertz (THz) frequencies in a GaAs/Al$_x$Ga$_{1-x}$As heterostructure with a two-dimensional (2D) electron gas (W. Michailow et al., Sci. Adv. \textbf{8}, eabi8398 (2022)). In contrast to the conventional PE phenomena, the IPPE effect is observed at normal incidence of radiation, the height of the in-plane potential step, which electrons overcome after absorption of a THz photon, is electrically tunable by gate voltages, and the effect is maximal at a negative electron ``work function'', when the Fermi energy lies above the potential barrier. Based on the discovered phenomenon, efficient detection of THz radiation has been demonstrated. In this work we present a detailed theory of the IPPE effect providing analytical results for the THz wave generated photocurrent, the quantum efficiency, and the internal responsivity of the detector, in dependence on the frequency, the gate voltages, and the geometrical parameters of the detector. The calculations are performed for macroscopically wide samples at zero temperature. Results of the theory are applicable to any semiconductor systems with 2D electron gases, including III-V structures, silicon-based field effect transistors, and the novel 2D layered, graphene-related materials.

TCAD based study of parameters affecting the electrical performance of organic thin-film transistors

Field effect transistors (FETs) are widely used in integrated circuits of electronic devices. Mostly silicon-based FETs are used for commercial purposes, but with the recent advancement in organic electronics – organic thin-film transistors (OTFTs) have become trending research topics nowadays. Modeling of organic FETs helps in understanding various electrical characteristics of the device such as on current, threshold voltage, off current, on/off ratio, and so on. Optimization of these factors is needed to enhance the working and overall performance of thin-film transistors. In this paper, the comparative study of the device having bottom-gate with electrode contact on top and bottom of organic semiconductor has been done based on the effects of organic semiconductor's thickness variation, dielectric thickness variation, and dielectric material variation on pentacene based organic transistors.

Tribotronic triggers and sequential logic circuits

In this paper, a floating-gate tribotronic transistor (FGTT) based on a mobile triboelectric layer and a traditional silicon-based field-effect transistor (FET) is proposed. In the FGTT, the triboelectric charges in the layer created by contact electrification can be used to modulate charge carrier transport in the transistor. Based on the FGTTs and FETs, a tribotronic negated AND (NAND) gate that achieves mechanical-electrical coupled inputs, logic operations, and electrical level outputs is fabricated. By further integrating tribotronic NAND gates with traditional digital circuits, several basic units such as the tribotronic S-R trigger, D trigger, and T trigger have been demonstrated. Additionally, tribotronic sequential logic circuits such as registers and counters have also been integrated to enable external contact triggered storage and computation. In contrast to the conventional sequential logic units controlled by electrical signals, contact-triggered tribotronic sequential logic circuits are able to realize direct interaction and integration with the external environment. This development can lead to their potential application in micro/nano-sensors, electromechanical storage, interactive control, and intelligent instrumentation.

Theoretical study of electronic transport properties of lead nanowires doped with silicon

The potential application of nanotechnology is based on the integration of microelectronic function with advanced group IV element technology, such as silicon-based field-effect transistors. In this paper we investigate theoretically the electronic transport properties of lead nanowires doped with silicon by employing molecular dynamics simulations and the non-equilibrium green function method with density functional theory frame. We observed the conductance of lead wires with silicon doping shows ballistic feature and high doping concentration wire have more intense oscillation amplitude because of the resonance transmission peak and the transmission channels. Importantly, the initial cause of negative differential resistance (NDR) effect and bonding mechanism in lead-silicon system have also given explanation.

Contrast enhancement for quantitative image analysis of graphene oxide using optical microscopy for Si-based field effect transistors

Experimental considerations have been performed to obtain the high contrast optical microscopic images of graphene oxide sheets which are useful to probe their quality and morphological information such as a shape, a size, and a thickness. When graphene oxide is used as a semiconducting material in a silicon-based field effect transistor, it is necessary to identify the morphology of graphene oxide on the gate substrate. In this study, we investigated the contrast enhancement of optical microscope images of graphene oxide sheets after hydrazine vapor reduction on a silicon substrate coated with a 300nm-thick silicon dioxide dielectric layer, which is a conventional gate material in field effect transistors. Also, a green-filtered light source gave higher contrast images comparing to optical images under standard white light. Furthermore, it was found that an image channel separation technique can be an alternative to simply identify the morphological information of graphene oxide, where red, green, and blue color values are separated at each pixels of the optical image. The approaches developed in this study can be helpful to set up a simple and easy protocol for the morphological identification of graphene oxide using a conventional optical microscope instead of a scanning electron microscopy or an atomic force microscopy, especially for silicon-based field effect transistors.

Silicon Nanomaterials Platform for Bioimaging, Biosensing, and Cancer Therapy

Silicon nanomaterials are an important class of nanomaterials with great potential for technologies including energy, catalysis, and biotechnology, because of their many unique properties, including biocompatibility, abundance, and unique electronic, optical, and mechanical properties, among others. Silicon nanomaterials are known to have little or no toxicity due to favorable biocompatibility of silicon, which is an important precondition for biological and biomedical applications. In addition, huge surface-to-volume ratios of silicon nanomaterials are responsible for their unique optical, mechanical, or electronic properties, which offer exciting opportunities for design of high-performance silicon-based functional nanoprobes, nanosensors, and nanoagents for biological analysis and detection and disease treatment. Moreover, silicon is the second most abundant element (after oxygen) on earth, providing plentiful and inexpensive resources for large-scale and low-cost preparation of silicon nanomaterials for practical applications. Because of these attractive traits, and in parallel with a growing interest in their design and synthesis, silicon nanomaterials are extensively investigated for wide-ranging applications, including energy, catalysis, optoelectronics, and biology. Among them, bioapplications of silicon nanomaterials are of particular interest. In the past decade, scientists have made an extensive effort to construct a silicon nanomaterials platform for various biological and biomedical applications, such as biosensors, bioimaging, and cancer treatment, as new and powerful tools for disease diagnosis and therapy. Nonetheless, there are few review articles covering these important and promising achievements to promote the awareness of development of silicon nanobiotechnology. In this Account, we summarize recent representative works to highlight the recent developments of silicon functional nanomaterials for a new, powerful platform for biological and biomedical applications, including biosensor, bioimaging, and cancer therapy. First, we show that the interesting photoluminescence properties (e.g., strong fluorescence and robust photostability) and excellent biocompatibility of silicon nanoparticles (SiNPs) are superbly suitable for direct and long-term visualization of biological systems. The strongly fluorescent SiNPs are highly effective for bioimaging applications, especially for long-term cellular labeling, cancer cell detection, and tumor imaging in vitro and in vivo with high sensitivity. Next, we discuss the utilization of silicon nanomaterials to construct high-performance biosensors, such as silicon-based field-effect transistors (FET) and surface-enhanced Raman scattering (SERS) sensors, which hold great promise for ultrasensitive and selective detection of biological species (e.g., DNA and protein). Then, we introduce recent exciting research findings on the applications of silicon nanomaterials for cancer therapy with encouraging therapeutic outcomes. Lastly, we highlight the major challenges and promises in this field, and the prospect of a new nanobiotechnology platform based on silicon nanomaterials.

Variability and Reliability of Single-Walled Carbon Nanotube Field Effect Transistors

Excellent electrical performance and extreme sensitivity to chemical species in semiconducting Single-Walled Carbon NanoTubes (s-SWCNTs) motivated the study of using them to replace silicon as a next generation field effect transistor (FET) for electronic, optoelectronic, and biological applications. In addition, use of SWCNTs in the recently studied flexible electronics appears more promising because of SWCNTs’ inherent flexibility and superior electrical performance over silicon-based materials. All these applications require SWCNT-FETs to have a wafer-scale uniform and reliable performance over time to a level that is at least comparable with the currently used silicon-based nanoscale FETs. Due to similarity in device configuration and its operation, SWCNT-FET inherits most of the variability and reliability concerns of silicon-based FETs, namely the ones originating from line edge roughness, metal work-function variation, oxide defects, etc. Additional challenges arise from the lack of chirality control in as-grown and post-processed SWCNTs and also from the presence of unstable hydroxyl (–OH) groups near the interface of SWCNT and dielectric. In this review article, we discuss these variability and reliability origins in SWCNT-FETs. Proposed solutions for mitigating each of these sources are presented and a future perspective is provided in general, which are required for commercial use of SWCNT-FETs in future nanoelectronic applications.

Aligning the Band Gap of Graphene Nanoribbons by Monomer Doping

Silicon-based field-effect transistors (FETs) are the building blocks of modern digital logic circuitry and therefore part of virtually every electronic device available today. Over the past decades, continuous downscaling of existing designs has met the rising performance requirements, but as the size of FETs approaches the regime of atomic structures, new concepts are required to maintain the current pace at which microelectronics is developing. At small gate channel lengths, the applicability of quantum mechanical principles results in several so-called short-channel effects (e.g. reduced carrier mobility). Since its experimental realization in 2004, graphene has been discussed intensively as a substitute for doped silicon in FETs because of its high charge carrier mobility and its unsurpassably low thickness. Graphene transistors have even been realized but cannot be put into the “off” state because of the lack of a band gap. However, there are concepts available for opening a band gap, for example, applying strain along the sheet or biasing bilayers of graphene. Also, lateral confinement in quasione-dimensional graphene nanoribbons (GNRs) leads to a band gap, which furthermore is highly sensitive to the width and edge shape of the GNR, thus opening possibilities to tailor the electronic properties of a device. Indeed, FETs built from nanoribbons show much higher on/off-ratios than graphene transistors, which makes them more suitable for integration into logic devices. However, the ability to control the electronic properties is essential: while the size of the gap can be engineered by varying the nanoribbon widths, the alignment of the GNR band structure with respect to the Fermi level of a metal electrode is equally important. Such a shifting of the entire band structure is observed both in two-dimensional graphene as well as in chemically synthesized or lithographically patterned GNRs upon doping, particularly with nitrogen atoms. Using present doping techniques, the distribution of dopant atoms will not be well-defined on the nanoscale and the band gap shift upon nitrogen doping depends on the site of the N atom, that is, the bonding configuration to neighboring carbon atoms. Generally, for doped and pristine GNRs, fabrication remains a challenge as well-established top-down approaches using lithography or unzipping of carbon nanotubes yield relatively wide ribbons with an undetermined edge structure. Particularly for small widths on the order of a few nanometers (where the band gap reaches a technologically relevant size) atomically precise edges are necessary and can be realized using Br-substituted precursor molecules, which are thermally activated on a surface and—in a bottom-up synthesis— covalently assemble to a specific nanostructure. In this study, we employed the latter approach to prepare GNRs with an atomically precise edge structure and doping pattern through polymerization of specific monomers directly on the Au(111) surface and studied the position and size of the band gap of these GNRs with surface-sensitive electron spectroscopies. Besides straight armchair edge GNRs, another type of chevron-shaped nanoribbons has previously been fabricated using an on-surface reaction. In this process adsorption of several layers of 6,11-dibromo-1,2,3,4-tetraphenyl-triphenylene (monomer 1 in Scheme 1) on Au(111) and heating at 250 8C leads to desorption of the second and higher layers as well as halogen dissociation and coupling of the resulting activated biradical monomers, yielding a sterically crowded and hence twisted polyphenylene. In a second heating step at 440 8C, this polymer undergoes a subsequent cyclodehydrogenation reaction providing access to the desired chevronshaped GNR with armchair edges. Selective substitution of the parent monomer 1 with either one or two N atoms provided monomers 2 and 3, respectively, which were used to generate GNRs with different doping levels (exemplarily shown for the doubly N doped GNR 5 in Scheme 1) and accordingly with potentially different electronic structure properties. Synthesis of the new monomers 2 and 3 was accomplished by Diels–Alder reactions of an appropriate cyclopentadienone with either mixed phenylpyridyl-acetylene or bispyridylacetylene, followed by immediate cheletropic CO extrusion (for details see the Supporting Information). [*] C. Bronner, S. Stremlau, A. Haase, Prof. Dr. P. Tegeder Fachbereich Physik, Freie Universit t Berlin Arnimallee 14, 14195 Berlin (Germany) E-mail: bronner@zedat.fu-berlin.de petra.tegeder@physik.fu-berlin.de

Investigation on Self-Heating Effect in Carbon Nanotube Field-Effect Transistors

Electrothermal modeling of single-walled carbon nanotube (SWCNT) field-effect transistor (FET) is performed in this paper, with special attention focused on its self-heating effect. The method of finite difference is implemented for solving a 1-D heat conduction equation in the semiconducting channel self-consistently, and its nonuniform temperature distribution is evaluated for 20-, 32-, and 45-nm technology nodes, respectively. The numerical results are presented to show the self-heating effect on the I -V characteristics, signal delay, and cutoff frequency of the carbon nanotube FET (CNTFET). It is further demonstrated that the maximum temperature rise, as well as the performance degradation of the CNTFET, is quite lower than that of the silicon-based FET counterpart. All these advantages are contributed by the excellent electrothermal properties of the SWCNTs, and they have great potential for the development of active devices with low power dissipation and good reliability at high-operating temperature.

Surface immobilizable chelator for label-free electrical detection of pyrophosphate.

A new pyrophosphate (PPi) chelator was designed for surface-sensitive electrical detection of biomolecular reactions. This article describes the synthesis of the PPi-selective receptor, its surface immobilization and application to label-free electrical detection on a silicon-based field-effect transistor (FET) sensor.

Gate Oxides Beyond SiO2

AbstractThis year marks a major materials milestone in the makeup of silicon-based field-effect transistors: in the microprocessors produced by leading manufacturers, the SiO2gate dielectric is being replaced by a hafnium-based dielectric. The incredible electronic properties of the SiO2/silicon interface are the reason that silicon has dominated the semiconductor industry and helped it grow to over $250 billion in annual sales, as reported by the Semiconductor Industry Association (SIA), San Jose, CA. The shrinkage of transistor dimensions (Moore's law) has led to tremendous improvements in circuit speed and computer performance. At the same time, however, it has also led to exponential growth in the static power consumption of transistors due to quantum mechanical tunneling through an ever-thinner SiO2gate dielectric. This has spurred an intensive effort to find an alternative to SiO2with a higher dielectric constant (K) to temper this exploding power consumption. This article reviews the high-Kmaterials revolution that is enabling Moore's law to continue beyond SiO2.