Future Semiconductor Research Articles

Tuning the electronic properties of armchair boron phosphide nanoribbons via H/O/F passivation and Stone–Wales defect

To explore the possibility of various edge-passivating elements for armchair boron phosphide nanoribbons (ABPNR), we performed first-principles computation under the flagship of density functional theory. The bare and H, O, F-passivated structures were considered for the present calculations. The possibility of probable edge-passivation using these elements was assured by the binding energy analysis. Moreover, O emerges as the most efficient passivating element which is stable by more than 400 meV over F-passivation for nanoribbons of smallest width. It is predicted that considered passivating elements affected structural as well as electronic properties of the ABPNR. It is observed that O-passivation leads to narrow band gap behavior while F-passivations yields a band gap of 1.07 eV to 1.55 eV. The Stone–Wales defects are also discussed, showcasing their potential to tune the electronic properties of ABPNR for future semiconductor devices.

Nonlinear electronic devices on single-layer CVD graphene for thermistors

In this article, we present simple, cost-effective, passive (non-gated) electronic devices based on single-layer (SL) chemical vapor deposited (CVD) graphene that show nonlinear and asymmetric current-voltage characteristics (CVCs) at ambient temperatures. Al2O3-Ti-Au contacts to graphene results in a nonlinear resistance to achieve nonlinearity in the CVC. Upon transfer to polyethylene terephthalate, the CVD-grown SL graphene shows mobility of 6200 cm2V-1S-1. We have observed both thermoelectric effect and thermoresistive sensing in the fabricated devices such as voltage and temperature concerning change in electronic power and resistance through asymmetric and nonlinear CVC. The device is stable both at low and high voltages (±200 mV to ±4 V) and temperatures (4 K - 300 K). Graphene-based thermosensing devices can be ultra-thin, cost-effective, non-toxic/organic, flexible, and high-speed for integration into future complementary metal-oxide semiconductor (CMOS) interface, and wearable self-power electronics. A strong negative temeperature coefficent of resistance is demonstrated in the realized nonlinear graphene-integrated resistors for its application in NTC thermistors.

NSF awards $42.4M to support future semiconductors research

NSF awards $42.4M to support future semiconductors research

Bendable non-silicon RISC-V microprocessor.

Semiconductors have already had a very profound effect on society, accelerating scientific research and driving greater connectivity. Future semiconductor hardware will open up new possibilities in quantum computing, artificial intelligence and edge computing, for applications such as cybersecurity and personalized healthcare. By nature of its ethos, open hardware provides opportunities for even greater collaboration and innovations across education, academic research and industry. Here we present Flex-RV, a 32-bit microprocessor based on an open RISC-V (ref. 1) instruction set fabricated with indium gallium zinc oxide thin-film transistors2 on a flexible polyimide substrate, enabling an ultralow-cost bendable microprocessor. Flex-RV also integrates a programmable machine learning (ML) hardware accelerator inside the microprocessor and demonstrates new instructions to extend the RISC-V instruction set to run ML workloads. It is implemented, fabricated and demonstrated to operate at 60 kHz consuming less than 6 mW power. Its functionality when assembled onto a flexible printed circuit board is validated while executing programs under flat and tight bending conditions, achieving no worse than 4.3% performance variation on average. Flex-RV pioneers an era of sub-dollar open standard non-silicon 32-bit microprocessors and will democratize access to computing and unlock emerging applications in wearables, healthcare devices and smart packaging.

Microscopic characterizations for 2D material-based advanced electronics

Two-dimensional (2D) materials have gained significant attention as potential candidates for next-generation electronics, owing to their unique properties such as ultrathin layer thickness, mechanical flexibility, and tunable bandgaps. The distinctive characteristics of 2D materials necessitate the development of nanoscale advanced characterization methods. In this review, we explore the role of microscopy techniques in developing 2D materials-based electronics, from material synthesis and characterization to device performance and reliability. We address the applications of microscopies by delving into the perspectives of channel materials, metal contacts, dielectric materials, and device architectures. Additionally, we provide an outlook on the future directions and potential utilization of microscopy techniques in future 2D semiconductor industry.

Low Contact Resistance via Quantum Well Structure in Amorphous InMoO Thin Film Transistors

The amorphous oxide semiconductor (AOS) thin film transistor (TFT) shows promise for use in advanced integrated circuits, such as 2T0C dynamic random-access memory, due to its excellent electronic performance and ability to be fabricated at low temperatures. Nevertheless, the high contact resistance between the metal and AOS restricts the applicability of AOS-TFT. This study demonstrates the achievement of a reduced contact resistance in InMoO (IMO) transistors by using a MoOx interlayer during fabrication. Increasing the oxygen concentration alters the band structure of MoOx and creates a graded Mo-MoOx-IMO structure with a pronounced quantum well at the interlayer between the metal and channel. Consequently, the quantum well’s ability to attract electrons and shape the band edge suppresses the Fermi-level pinning effect, ultimately leading to the establishment of an ohmic contact. The optimized MoOx interlayer showed a significant improvement in contact resistance (∼400%) through the adjustment of oxygen content during annealing procedures. This finding suggests that it is an attractive approach to provide excellent source/drain contacts in future ultra-scaled amorphous oxide semiconductor thin-films.

Effect of Thickness and Sidewall Slope of Photoresist Mask on Etch Profile of Copper Interconnect

We performed high density plasma reactive ion etching of copper thin films using organic gas mixture to define fine patterns less than 10 μm for the application of display devices. However, since redeposition in dry etching of copper thin films frequently occurs due to extremely low reactivity, the etch variables which affect the formation of redeposition were investigated. In this study, the photoresist (PR) masks were employed to etch copper thin films. The effects of the thickness of PR and the sidewall slope of PR on etch profile and redeposition were examined.The thickness of PR mask were in the range of 3 μm ~ 1 μm and the sidewall slopes of the PR mask were in the range of 90° ~ 45°. The etch profile and etch mechanism of dry etching using different masks were evaluated using field emission scanning electron microscopy and X-ray photoelectron spectroscopy. Finally, an etching method to reduce and/or avoid the redeposition in dry etching of copper thin films will be proposed.Acknowledgement : This research was supported by the MOTIE(Ministry of Trade, Industry & Energy (20019504) and KSRC(Korea Semiconductor Research Consortium) support program for the development of the future semiconductor device.

In Situ transmission Electron Microscope Observation of Biased-Induced Dynamic Evolution of Two-Dimensional CrS2

Two-Dimensional transition-metal dichalcogenides (2D-TMDs) have attracted great attention recently owing to their potential to become the important material for next generation semiconductor devices. While using the device, it needs to ensure high density current and biased voltage for a long time. However, the study on TMDs in high-energy environment is insufficient. In this work, the phase evolution of CrS2 are revealed via in-situ biasing experiments and recorded by transmission electron microscope (TEM) at atomic scale. The ultra-thin layered (~1.6nm) CrS2 was synthesized through atmospheric pressure chemical vapor deposition (APCVD), followed by transferring the as-grown samples onto specialized TEM electrical chips. The TEM characterization of CrS2 initial sample provided the basic understanding of this Cr-based TMD, identified as pure 1T phase with single crystal structure as shown in Figure 1. The advanced in situ technique was employed to record the structural evolution and was tested the endurance of CrS2 during biasing. Moreover, the results can make significant contributions to future semiconductor device designs and demonstrate CrS2 has great potential as a semiconductor device with its outstanding characteristic of biased-endurance. Figure1. (a) Low-magnification TEM image of 1T-CrS2. (b) High-resolution TEM image of 1T-CrS2, corresponding with FFT along [001] zone axis. (c) AFM image of the as-grown CrS2 sample, blue bar in the image is X axis of (d). (d) AFM height profile of as-grown 1T-CrS2 with average thickness of~1.6nm. (e) STEM image of 1T-CrS2 and shows d-spacing~0.336 nm. (f) Low-magnification TEM image of the device, showing that the transferred CrS2 layer was suspended on the membrane with Au electrodes on both sides. (g,h) In-situ TEM observation of the biasing experiment after 5V biasing for 5 min of 1T-CrS2. Time-sequencing TEM images showing the structural evolution of biasing. The inset shows the corresponding FFT-DP to reveal the variation of crystallinity of the sample. (g) Initial structure of 1T-CrS2. (h) 1T-CrS2 under in-situ biasing experiment after 10 minutes. Figure 1

Electrochemical Weakening Material Strength for Accelerated Thinning of Silicon Carbide Substrates

This paper presents a novel approach to expedite the thinning of silicon carbide (SiC) substrates, a crucial step in enhancing material performance and extending chip longevity by reducing volume resistivity. The traditional methods of SiC substrate thinning, such as diamond wheel grinding and plasma etching, have inherent limitations, including the risk of wafer breakage and high processing costs. In response to these challenges, we propose an innovative technique involving the electrochemical etching attenuation of SiC strength, offering a cost-effective and efficient solution.In this study, we employed an electrochemical method to initially weaken the SiC substrate from the surface to a defined depth, followed by fine-tuning its thickness using a conventional diamond grinding wheel. Remarkably, our results demonstrate that SiC substrates subjected to electrochemical treatment exhibit well-structured lattices free from residual stresses. This novel approach not only reduces the risk of wafer breakage but also enhances the material's integrity (Figure 1).To gain deeper insights into the effects of electrochemistry on SiC material strength, advanced characterization techniques, including scanning electron microscopy, were employed. Our findings reveal that the electrochemically treated SiC surface exhibits a sponge-like morphology, with a cross-sectional profile showcasing prominent columnar structures (Figure 2). This sponge-like structure is attributed to the removal of silicon atoms during anodization, affirming the effectiveness of electrochemical methods in rapidly attenuating the material strength of SiC substrates, thereby facilitating their efficient thinning through grinding without compromising substrate integrity.In summary, this research highlights the potential of electrochemical methodologies for the initial weakening of SiC substrates, leading to accelerated and cost-effective thinning processes. This breakthrough not only expedites SiC substrate thinning but also contributes significantly to the advancement of SiC substrate thinning and grinding techniques, promising substantial benefits for future semiconductor device fabrication. Figure 1

Etch Characteristics of Cobalt Thin Films in High Density Plasma of Cl2/O2/Ar Gas Mixture

Inductively coupled plasma reaction ion etching (ICP-RIE) of cobalt thin films patterned with SiO2 hard masks was performed using Cl2/O2/Ar gas mixture. The etch characteristics of cobalt films in Cl2/Ar gas were examined to determine the roles of Cl2 and O2, respectively. The etch rates and etch profiles of cobalt films were investigated by varying the O2 concentration in Cl2/O2/Ar gas mixture.In the optimized Cl2/Ar gas mixture, systematic etching of cobalt films was performed by changing the etch parameters including ICP RF power, DC-bias voltage, and process pressure. As the DC-bias voltage and process pressure was increased, the etch rate increased and the etch profile improved. Through the etching parameters variation experiment, the etching properties were investigated by adding O2 to Cl2/Ar under optimized conditions. X-ray photoelectron spectroscopy and optical emission spectroscopy were used to investigate the etch mechanism in the Cl2/O2/Ar gas mixture. In addition, scanning probe microscope was used to observe roughness on the etched cobalt surface. Finally, the etching of cobalt films patterned with nanometer-scale in the optimized Cl2/O2/Ar gas mixture was successfully achieved with good etch profile.AcknowledgmentThis research was supported by the Ministry of Trade, Industry & Energy (MOTIE) (20019504) and Korea Semiconductor Research Consortium (KSRC) support program for the development of future semiconductor devices. This work was supported by Korea Institute for Advancement of Technology (KIAT) grant funded by the Korea Government (MOTIE) (P0008458, HRD Program for Industrial Innovation).

Atomic Precision Processing of Two-Dimensional Materials for Next-Generation Microelectronics.

The growth of the information era economy is driving the pursuit of advanced materials for microelectronics, spurred by exploration into "Beyond CMOS" and "More than Moore" paradigms. Atomically thin 2D materials, such as transition metal dichalcogenides (TMDCs), show great potential for next-generation microelectronics due to their properties and defect engineering capabilities. This perspective delves into atomic precision processing (APP) techniques like atomic layer deposition (ALD), epitaxy, atomic layer etching (ALE), and atomic precision advanced manufacturing (APAM) for the fabrication and modification of 2D materials, essential for future semiconductor devices. Additive APP methods like ALD and epitaxy provide precise control over composition, crystallinity, and thickness at the atomic scale, facilitating high-performance device integration. Subtractive APP techniques, such as ALE, focus on atomic-scale etching control for 2D material functionality and manufacturing. In APAM, modification techniques aim at atomic-scale defect control, offering tailored device functions and improved performance. Achieving optimal performance and energy efficiency in 2D material-based microelectronics requires a comprehensive approach encompassing fundamental understanding, process modeling, and high-throughput metrology. The outlook for APP in 2D materials is promising, with ongoing developments poised to impact manufacturing and fundamental materials science. Integration with advanced metrology and codesign frameworks will accelerate the realization of next-generation microelectronics enabled by 2D materials.

Atomristor Mott Theory of Sn Adatom Adlayer on a Si Surface

We use a combination of density functional theory (DFT) and dynamical mean field theory (DMFT) to unveil orbital field-induced electronic structure reconstruction of the atomic Sn layer deposited onto a Si(111) surface (Sn/Si(111)−3×3R30∘), also referred to as α-Sn. Our DFT + DMFT results indicate that α-Sn is an ideal testing ground to explore electric field-driven orbital selectivity and Mott memory behavior, all arising from the close proximity of α-Sn to metal insulator transitions. We discuss the relevance of orbital phase changes for α-Sn in the context of the current–voltage (I−V) characteristic for future silicon-based metal semiconductor atomristors.

Effect of electron mobility variation on short channel effects in nanoscale double gate FinFETs: A comparative study

This work investigates the impact of electron mobility variations on short channel effects (SCEs) in different semiconductor materials using FinFETs. Using PADRE simulator, the work examines Gallium Arsenide (GaAs), Gallium Antimonide (GaSb), Gallium Nitride (GaN), and Silicon (Si) FinFETs, analyzing performance metrics such as Drain Induced Barrier Lowering (DIBL), Subthreshold Swing (SS) and Threshold Voltage roll-off. The result shows that GaN-FinFET exhibits lowest subthreshold swing of 63 mV/dec at electron mobility of 10000 cm2/Vs, and threshold voltage of 0.44V at electron mobility of 10000 cm2/Vs, while Si-FinFET exhibits lowest DIBL of 3 mV/V at (4000-10000) cm2/Vs. This finding contributes to advancing the understanding of short channel effects in nanoscale FinFETs and provides valuable insights for optimizing device performance in future semiconductor technologies.

Benchmarking diamond surface preparation and fluorination via inductively coupled plasma-reactive ion etching

Diamond, renowned for its exceptional semiconducting properties, stands out as a promising material for high-performance power electronics, optics, quantum, and biosensing technologies. This study methodically investigates the optimization of polycrystalline diamond (PCD) substrate surfaces through Inductively Coupled Plasma Reactive Ion Etching (ICP-RIE). Various parameters, including gaseous species, flow rate, coil power, and bias power were tuned to understand their impact on surface morphology and chemistry. A thorough characterization, encompassing chemical, spectroscopic, and microscopic methods, shed light on the effects of different ICP-RIE conditions on surface properties. CF4/O2 plasma emerged as a viable treatment for achieving smooth PCD surfaces with minimal etch pit formation. Most notably, surface fluorination, a critical aspect of increasing chemical and thermal stability, was successfully accomplished using CF4, SF6, and other F-containing plasmas. The fluorine concentration and surface chemistry variations were studied, with high resolution X-ray Photoelectron Spectroscopy unveiling differences amongst the sp2 C phase, sp3 C phase, C–O, CO, and C–F bonds. Time-of-flight secondary Ion Mass Spectrometry (ToF-SIMS) and depth-profile analysis unveiled a consistent surface fluorination pattern with CF4/O2 treatment. Furthermore, contact angle measurements showcased heightened hydrophobicity. This study provides valuable insights into precise diamond surface engineering, important for the development of future diamond-based semiconductor technologies.

Low‐temperature chemical vapor deposition growth of 2D materials

AbstractTwo‐dimensional (2D) materials have atomic thickness, and thickness‐dependent electronic transport, optical and thermal properties, highlighting great promise applications in future semiconductor devices. Chemical vapor deposition (CVD) is considered as an industry‐oriented method for macro‐synthesis of 2D materials. In conventional CVD, high temperatures are required for the synthesis of high‐quality large‐size 2D materials, which is incompatible with of back‐end‐of‐line of the complementary metal oxide semiconductor (CMOS) techniques. Therefore, low‐temperature synthesis of 2D materials is of critical importance for the advancement toward practical applications of 2D materials with the CMOS technologies. In this review, we focus on strategies for the low‐temperature growth of 2D materials, including the use of low‐melting‐point precursors, metal‐organic CVD, plasma‐enhanced CVD, van der Waals‐substrate vapor phase epitaxy, tellurium‐assisted CVD, salt‐assisted CVD, etc., with discussions of their reaction mechanisms, applications, associated advantages, and limitations. We also provide an outlook and perspectives of future low‐temperature chemical vapor deposition growth of 2D materials.

Prediction of the Structural, Mechanical, and Physical Properties of GaC: As a Potential Third-Generation Semiconductor Material.

Similar to GaN and SiC semiconductors, GaC may be a potential semiconductor because of the mixed elemental features of Ga and C. Unfortunately, the phase stability and mechanical and physical properties of GaC are unknown. To search for novel third-generation semiconductors, the present study delves into an in-depth analysis of the structural stability and electronic and optical properties of GaC by DFT calculations. Similar to GaN, three GaC phases are discussed. It is found that three GaC phases (two cubic phases and one hexagonal phase) are first predicted. The band gaps of Fm3̅m, F4̅3m, and hexagonal GaC are 0.449, 2.733, and 3.340 eV, respectively. In particular, the band gap of F4̅3m GaC and hexagonal GaC is bigger than that of GaN. Compared to GaN semiconductors, the C-2p state is in the valence band region across the Fermi level, which is beneficial to electronic mobility and electronic transport capacity near the Fermi level. In addition, three GaC phases exhibit ultraviolet properties. The first peak of three GaC phases produces the right migration compared to the GaN semiconductor. Therefore, the author predicts that GaC is a potential third-generation semiconductor material which is potentially used in future third-generation semiconductor industries.

Clarification of Au dimer adsorption sites on Si (111)-7 × 7 surface by AFM/KPFM

Atomic-scale surface adsorption has been a significant research topic in recent years, with a particular emphasis on the adsorption properties of Au/Si(111)-7 × 7, which are vitally important for pioneering future novel semiconductor devices. Here, we investigated the adsorption of Au dimers on the Si(111)-7 × 7 surface with atomic resolution using non-contact atomic force microscopy and Kelvin probe force microscopy at room temperature. Our results show that the Au dimer adsorbs in the vicinity of the Si rest atoms, exhibiting a distinct localized electron distribution. In density functional theory calculations, three candidate Au dimer adsorption sites have been identified, and the most stable site of Au dimer adsorption aligns with experimental findings. Furthermore, the local electron transfer of Au dimer adsorption has been analyzed, confirming the distribution of electrons around the Au dimer adsorption site. This research reveals that the structure and charge transfer of adsorbed Au dimers on Si(111)-7 × 7 provide insight into the mechanism of the metal-semiconductor system.

Controlled lattice deformation for high-mobility two-dimensional MoTe2 growth

Two-dimensional (2D) MoTe2 shows great potential for future semiconductor devices, but the lab-to-fab transition is still in its preliminary stage due to the constraints in the crystal growth level. Currently, the chemical vapor deposition growth of 2D MoTe2 primarily relies on the tellurization process of Mo-source precursor (MSP). However, the target product 2H-MoTe2 from Mo precursor suffers from long growth time and suboptimal crystal quality, and MoOx precursor confronts the dilemma of unclear growth mechanism and inconsistent growth products. Here, we developed magnetron-sputtered MoO3 film for fast and high-mobility 2H-MoTe2 growth. The solid-to-solid phase transition growth mechanism of 2D MoTe2 from Mo and MoOx precursor was first experimentally unified, and the effect mechanism of MSPs on 2D MoTe2 growth was systematically elucidated. Compared with Mo and MoO2, the MoO3 precursor has the least Mo-unit lattice deformation and exhibits the optimal crystal quality of growth products. Meanwhile, the lowest Gibbs free energy change of the chemical reaction results in an impressive 2H-MoTe2 growth rate of 8.07 μm/min. The constructed 2H-MoTe2 field-effect transistor array from MoO3 precursor showcases record-high hole mobility of 85 cm2·V-1·s-1, competitive on-off ratio of 3×104, and outstanding uniformity. This scalable method not only offers efficiency but also aligns with industry standards, making it a promising guideline for diverse 2D material preparation towards real-world applications.

The Importance of Semiconductor Miscibility for the Formation of Light‐Harvesting Polymer:Fullerene Nanoparticle Dispersions

Light‐harvesting layers in organic bulk‐heterojunction solar cells are commonly fabricated from aromatic solvents which are often toxic or hazardous. To fully omit harmful solvents, (surfactant‐free) nanoparticle dispersions of organic semiconductor blends are investigated, but only a very limited choice of materials form blend nanoparticles. This work is a systematic study of the nanoparticle formation by nanoprecipitation of electrostatically stabilized polymer: fullerene blends. It turns out that miscibility of both components is crucial for the incorporation of the fullerenes into the nanoparticles. This finding demystifies why certain polymer:fullerene combinations seemingly randomly form stable nanoparticle dispersion while others do not. The need of miscibility constitutes an important design criterion for processing future semiconductor blends along the nanoparticle route. Some mitigation to the unwanted release of larger amounts of fullerenes can be achieved by using ternary semiconductor blends.

Terahertz sum-frequency excitation of coherent optical phonons in the two-dimensional semiconductor WSe2

Driving fundamental excitations via strong light fields is one of the most important issues in solid state physics, which opens up new avenues to control material properties. Two-dimensional materials are fruitful platforms for future semiconductor applications, including opto-electronic and phononic devices, yet the phonon dynamics and nonlinear phonon–phonon coupling remain under-explored. Here, we demonstrate coherent phonon excitation in thin films of the layered two-dimensional semiconductor WSe2 induced by intense and broadband ultrafast terahertz (THz) pulses. We performed THz Kerr effect spectroscopy and observed coherent phonon oscillations assigned to the E2g optical phonon mode. The phonon amplitude displays a quadratic THz field strength dependence, indicating a sum-frequency THz excitation process. Furthermore, pump–probe polarization and crystal orientation relationships, supported by symmetry analysis of the nonlinear susceptibility and Raman tensors, provide helpful insight into nonlinear phonon–phonon interactions and potential coherent control schemes for the manipulation of phonon polarization and material properties in WSe2.