Metal Oxide Semiconductor Research Articles

Experimental Performance Analysis of Fabricated Si/Ge Thin Film Structure

This paper is devoted to the evaluation of a Silicon/Germanium (Si/Ge) thin film structure based on experimental measurements. An electron beam evaporator was used to fabricatethis structure. The sample was prepared under high vacuum conditions (pressure of 10-5 Torr, power of 6 kV and current of 200 mA). At these conditions, it was possible to get films with thickness of approximately 300 Å. The capacitance–voltage (C–V) and current–voltage (I–V) measurements of the sample were performed by a staircase sweep of voltages from 0 to 5 V and back from 5 to 0 V at room temperature. The sample exhibits a low hysteresis in measurements; this hysteresis is gradually removed when the sample is exposed to temperatures until 80 °C using a Carbolite Oven. It is also observed that both C-V and I-V characteristic curves of the sample has been smoothened. This sample exhibits an electroforming behavior as a metal-oxide-semiconductor (MOS) device over a short time duration of the selected staircase double sweep, hence it can be exploited as a fast switching element in digital microelectronic circuits. In addition, the hysteresis changes over the range from room temperature until 80 °C have opened the door to the possibility of exploiting this sample as a proximity temperature sensor within that range of temperature.

Gas-sensitive synergistic effect of Au-decorated ZnO nano-structured materials for rapid ethanol detection based on simulated sunlight activation

Local surface plasmon resonance (LSPR) and noble metal modification/doping are classical methods for improving the performance of metal-oxide-semiconductor (MOS)-based gas sensors. However, relatively less attention is paid to their synergies. In particular, research on synergistic gas-sensing technology that combines sunlight activation with other methods is significant for using friendly energy. In this study, Au-decorated ZnO (Au/ZnO) nano-structured materials (NMs) are successfully synthesised using a cost-effective nano-seed-assisted chemical bath and UV irradiation growth methods. The sensor based on this material exhibits superior performance in ethanol vapour under simulated sunlight, maintaining high sensitivity and repeatability at a low optimal working temperature. In particular, the sensitivity to 100 ppm of ethanol is 7.5 times better and the response time is 20 times shorter (tres < 1 s) in simulated sunlight than in the dark environment. The limit of detection (LOD) of ethanol is as low as 97 ppb, which is much lower than the concentration in exhaled breath of driving under the influence of alcohol according to Chinese law (20–80 ppm). This study provides a reliable and ultra-fast ethanol detection method, with potential applications in environmental monitoring and traffic safety. A possible gas-sensitive mechanism of the Au/ZnO ethanol vapour sensor is proposed based on the synergistic effect between simulated sunlight activation (LSPR, humidity resistance and thermal activation) and noble metal modification (electron sensitisation and chemical sensitisation). It provides a promising method for exploring the utilisation of sunlight for rapid gas detection.

Improving the photoswitching performance of a transistor with amorphous metal oxide semiconductor thin film by a gradient annealing approach

Metal oxides are attracting attention as electronic mate rials in research and industry. Thin films of amorphous indium gallium zinc oxide (a-IGZO) exhibit low absorbance in the visible spectrum, making them ideal components in transparent electronics. To widen the scope of use for thin film transistor (TFT) devices based on a-IGZO in on-chip sensing applications, photoresponsive behavior has been achieved by proper engineering of the active layers by either introducing a photosensitive top layer or using a method to generate localized states inside the band gap. In this paper, we propose a bilayer structured with the use of thermal annealing of a-IGZO film at different temperatures. Thermal annealing has been shown to improve the electrical performance of the TFT devices because of the improved film quality but negatively affects the photoresponsivity by removing tarp sites that play an important role in both charge generation and photomultiplication via the photogating effect. Therefore, here we propose an a-IGZO film with a high temperature-annealed bottom layer and pristine top layer. The bottom layer plays a vital role in the charge transport behavior, resulting in a low threshold voltage and subthreshold swing similar to the device with a fully annealed film, while the photoresponse of the device is driven by the higher density of gap states in the pristine top layer. This proposed method is advantageous to previously published procedures due to the simplicity of using no additional materials and complex steps to introduce trap sites into the photoactive layer, but only differential annealing temperature.

Graphene Phase Modulators Operating in the Transparency Regime.

Next-generation data networks need to support Tb/s rates. In-phase and quadrature (IQ) modulation combine phase and intensity information to increase the density of encoded data, reduce overall power consumption by minimizing the number of channels, and increase noise tolerance. To reduce errors when decoding the received signal, intersymbol interference must be minimized. This is achieved with pure phase modulation, where the phase of the optical signal is controlled without changing its intensity. Phase modulators are characterized by the voltage required to achieve a π phase shift, Vπ, the device length, L, and their product, VπL. To reduce power consumption, IQ modulators are needed with <1 V drive voltages and compact (sub-cm) dimensions, which translate in VπL < 1Vcm. Si and LiNbO3 (LN) IQ modulators do not currently meet these requirements because VπL > 1Vcm. Here, we report a double single-layer graphene (SLG) Mach-Zehnder modulator (MZM) with pure phase modulation in the transparency regime, where optical losses are minimized and remain constant with increasing voltage. Our device has VπL ∼ 0.3Vcm, matching state-of-the-art SLG-based MZMs and plasmonic LN MZMs, but with pure phase modulation and low insertion loss (∼5 dB), essential for IQ modulation. Our VπL is ∼5 times lower than the lowest thin-film LN MZMs and ∼3 times lower than the lowest Si MZMs. This enables devices with complementary metal-oxide semiconductor compatible VπL (<1Vcm) and smaller footprint than LN or Si MZMs, improving circuit density and reducing power consumption by 1 order of magnitude.

A Switchable Linear Regulator Implemented in GaAs pHEMT for WiFi Application

ABSTRACTCompared to silicon‐based complementary metal oxide semiconductor (CMOS), second‐generation semiconductor materials, such as gallium arsenide (GaAs) pseudomorphic high electron mobility transistor (pHEMT), offer significant advantages for radio frequency (RF) applications. As communication systems become more functional, designing highly integrated on‐chip transceiver systems presents a substantial challenge, where the voltage regulator as part of the power management module is indispensable. Due to lattice defects and other issues, achieving P‐channel metal oxide semiconductor (PMOS) in GaAs pHEMT is difficult, necessitating new circuit architectures to fulfill traditional linear regulator functions. To realize wireless fidelity (WiFi) transceiver systems on chip (SoC) using compound semiconductors for superior RF performance, this paper proposes a switchable linear regulator based on a 0.25 μm GaAs pHEMT process. The proposed linear regulator consumes a quiescent current of 440 μA in no‐load conditions and regulates a 5 V supply voltage down to 2.6 V output voltage. Measured results indicate that the designed linear regulator features a current load capacity of 20 mA, a load regulation rate of 5.8 mV/mA, and a line regulation rate of 1.8 mV/V. The proposed linear regulator circuit has been applied to WiFi transceiver systems, occupying a chip area of 0.054 mm2.

Rational design of ZnO-SnO2 Janus nanofibers for highly sensitive triethylamine detection

Herein, ZnO-SnO2 Janus nanofibers (NFs) were synthesized by a parallel electrospinning method and its sensing performances were tested. Considering the compositions of the two metal oxide semiconductors in Janus structure, different ratios of ZnO and SnO2 were designed and controlled. The optimum ratios of ZnO and SnO2 was 1:2 by analyzing their sensing performances to triethylamine (TEA) gas. Gas sensors based on ZS-12 Janus NFs exhibited a high response to TEA (45.2) and an excellent sensing response/recovery reproducibility. In order to investigate the sensing mechanism of Janus structure, ZnO NFs and SnO2 NFs were synthesized and used as controlled experiment. The results indicated that the heterostructures in Janus NFs is the key factor for the enhanced TEA sensing performances. The electrons flowed in the ZnO-SnO2 Janus structure leading to the variation of ionic oxygen species and electron depletion layer. These phenomena improved the reaction of TEA gas molecules with ionic oxygen species so that the TEA sensing performances were enhanced. Based on the Janus structures, a satisfactory gas sensor for detecting TEA gas were developed. Significantly, this work investigated the sensing mechanism of Janus structures and provided an efficient strategy for the gas sensing materials.

Novel oxygen vacancies-rich 3D porous ZnO for highly sensitive 3-hydroxy-2-butanone biomarker gas sensors

Listeriosis can cause human death via infection by Listeria monocytogenes (LMs) with a high fatality rate of 20–30 %. Detection of 3-hydroxy-2-butanone (3H-2B) biomarker of LMs can achieve estimation of LMs content, which is of great significance for human health. Exploring porous metal oxide semiconductors (MOSs) with rich vacancies towards 3H-2B sensing is quite promising for achieving this goal. Herein, we report a highly sensitive 3H-2B sensor based on novel 3D porous ZnO with rich oxygen vacancies which was facilely obtained by sacrificing Zn foam in oxalic acid and subsequent thermal decomposition. The ZnO sensor displays ultrahigh sensor response of Ra/Rg = 328@5 ppm, super-low detection limit of 0.001 ppm, excellent cycling stability and selectivity and good linear response at 120 °C, showing great potential for precise detection of 3H-2B biomarker. The porous structure and increased oxygen vacancies contribute greatly to the adsorption of active oxygen species therefore the sensing reactions on ZnO surface, which accounts for the high sensing performance. Our work provides an ingenious strategy to produce novel 3D ZnO with rich oxygen vacancies as well as new insights for boosting the detection of LMs.

A Novel Mechanism Based on Oxygen Vacancies to Describe Isobutylene and Ammonia Sensing of p-Type Cr2O3 and Ti-Doped Cr2O3 Thin Films

Gas sensors based on metal oxide semiconductors (MOS) have been widely used for the detection and monitoring of flammable and toxic gases. In this paper, p-type Cr2O3 and Ti-doped Cr2O3 (CTO) thin films were synthesized using an aerosol-assisted chemical vapor deposition (AACVD) method. Detailed analysis of the thin films deposited, including structural information, their elemental composition, oxidation state, and morphology, was investigated using XRD, Raman analysis, SEM, and XPS. All the gas sensors based on pristine Cr2O3 and CTO exhibited a reversible response and good sensitivity to isobutylene (C4H8) and ammonia (NH3) gases. Doping Ti into the Cr2O3 lattice improves the response of the CTO-based sensors to C4H8 and NH3. We describe a novel mechanism for the gas sensitivity of p-type metal oxides based on variations in the oxygen vacancy concentration.

Mechanisms and models of interface trap annealing in positively-biased MOS devices

Abstract We propose a hydrogen anion (H$^-$) passivation mechanism of the interface trap annealing (ITA) in positively-biased metal-oxide-semiconductor (MOS) devices. It is demonstrated that, the protons (H$^+$) released in SiO$_2$ due to H$_2$ cracking on oxide traps can migrate into Si at relatively high temperature, therefore passivating the interfacial $P_b$ centers by capturing two electrons provided by the positive bias. This new mechanism explains the elimination temperature of about 100$^\circ$C in experiments, which is much lower than temperature above 220$^\circ$C predicted by the traditional H$_2$ passivation mechanism. We also derive analytic models of the ITA, based on the coupling transformation dynamics of oxide and interface traps, as well as the concept of hierarchically constrained dynamics in glassy materials. These models can universally describe a generation-to-elimination transition of $P_b$, and predict the enhanced elimination of $E'_\gamma$ as the annealing temperature is elevated. Moreover, we demonstrate that, the defect annealing models can be applied to analysis the nonmonotonic temperature dependence of the annealing of threshold voltage shift in nMOS devices. Our findings provide a theoretical basis for achieving the low temperature elimination of interface traps, and for setting the high temperature stages of accelerated aging and damage evaluations of MOS devices.

Optimization of Impact Ionization in Metal–Oxide–Semiconductor Field-Effect Transistors for Improvement of Breakdown Voltage and Specific On-Resistance

For the past few decades, metal–oxide–semiconductor field-effect transistors (MOSFETs) have been the most important application in IC circuits. In certain circuit applications, the breakdown voltage and specific on-resistance serve as key electrical parameters. This article introduces a readily accessible approach to enhance the source–drain breakdown voltage (BVDS) of MOSFETs based on the Bipolar-CMOS-DMOS (BCD) platform without extra costs. By attentively refining the process steps and intricacies of the doping procedures, the breakdown voltages of NMOS and PMOS experienced increments of 3.4 V and 4.6 V, translating to enhancements of 31.5% and 50.3%. Parallel simulations offer insightful mechanistic explanations through simulation tools, facilitating superior outcomes. This initiative lays significant groundwork for the advancement of a comprehensive BCD process development framework.

Demonstration of aluminum nitride metal oxide semiconductor field effect transistor on sapphire substrate

Abstract Aluminum nitride (AlN) is a promising ultrawide bandgap material with significant advantages for power electronics and optoelectronic applications due to its high breakdown voltage, mobility, and thermal conductivity. AlN Schottky barrier diodes (SBDs) and metal semiconductor field effect transistors (MESFETs) have shown potential but are limited by issues such as high off-state leakage current and complex structures to achieve ohmic contacts. To address these challenges, we report on the fabrication and characterization of an AlN metal oxide semiconductor field effect transistor (MOSFET) with a recessed gate structure. The source and drain contacts were fabricated on n-doped AlN epitaxy using Ti-based contacts with a Ti/Al/Ti/Au metal stack. To evaluate the performance of these contacts, a circular transmission line model (CTLM) was employed, and contacts were annealed at various temperatures ranging from 750 to 950 °C in a nitrogen ambient. Our results reveal that unannealed Ti-based contacts on AlN showed no current conduction. However, annealing these contacts at 950 °C for 30 s significantly reduced the specific contact resistance to 0.148 Ω·cm2, achieving an ~80% reduction compared to samples annealed at 750 °C. Utilizing these optimized contact conditions, we fabricated, to the best of our knowledge, the first AlN MOSFET. The fabricated AlN MOSFET exhibits a threshold voltage of −10.91 V, an effective mobility of 2.95 cm2/Vs, an on-off current ratio spanning two orders of magnitude, and a reverse breakdown voltage of approximately ~250 V in air without a field plate. &amp;#xD;

Accumulation and Erase of Radiation-Induced Charge in MOS Structures

It is shown that when a MOS (metal–oxide–semiconductor) structure is simultaneously exposed to radiation and high-field injection of electrons, part of the radiation-induced positive charge can be erased when interacting with injected electrons, and the density of surface states can increase. These phenomena must be taken into account when operating MOS radiation sensors in high-field charge injection modes. High-field injection modes used for post-radiation erase of positive charge in MOS sensors are analyzed. It has been established that to annihilate one hole (radiation-induced positive charge), it is necessary to inject (0.5–2) × 104 electrons into the gate dielectric; the magnitude of the electric field has almost no effect on the process of erasing the radiation-induced charge.

Dosimetric commissioning of a high-resolution CMOS 2D detector array for patient-specific QA of single-isocenter multi-target VMAT stereotactic radiosurgery.

Stereotactic radiosurgery (SRS) using the single-isocenter-multiple-target (SIMT) technique by volumetric modulated arc therapy is increasingly popular for treating multiple brain metastases. However, the complex nature of SIMT SRS necessitates rigorous patient-specific quality assurance (PSQA). This study presents a multi-institutional dosimetric commissioning of a high-resolution complementary metal oxide semiconductor (CMOS) 2D detector array, the myQA SRS device for SIMT SRS PSQA. Basic dosimetric properties such as dose-rate, field-size, energy and angular dependencies were characterized for the CMOS detectors. Additionally, gamma index analyses were performed between the measured dose and the films for nine simulated and clinical plans. The results showed that the CMOS detector was dose-rate, field-size, energy and beam-angle dependent. Specific to SIMT SRS, angular dependence on gantry rotations was invariant to couch rotations but was sensitive to off-isocenter distances. With appropriate dose calibration and angular corrections, myQA SRS showed a high dosimetric correlation with films. The average gamma index pass rates were 99.9 ± 0.03% and 99.2 ± 1.1% at 3%/2mm/10%thr(global) and 1mm/1%/10%thr(local) criteria, respectively. The average dose difference between myQA SRS and films was 0.4 ± 1.3%. In conclusion, the CMOS 2D detector array has demonstrated its potential as a reliable tool for PSQA for SIMT SRS. The excellent dosimetric agreement with the films was consistent in multiple institutions, further validating the dosimetric accuracy and reproducibility. It provides a timely alternative to film dosimetry for commissioning and quality assurance.

Strain‐Induced Effects on Band‐to‐Band Tunneling and Trap‐Assisted Tunneling in Si Examined by Experiment and Theory

Strain is commonly used in metal–oxide–semiconductor technologies to boost on‐state performance. This booster has been in production for at least a decade. Despite this, a systematic study of the impact of strain on off‐state leakage current has been lacking. Herein, experimental data and ab initio calculations are used to refine existing models to account for the impact of strain on band‐to‐band tunneling and trap‐assisted tunneling in silicon. It is observed that the strain may dramatically increase the leakage current, depending on the type of tunneling involved. For band‐to‐band and trap‐assisted tunneling, low uniaxial strains of 0.1% (or 180 MPa) can increase the leakage current by 60% and 10% compared to the unstrained case, respectively. Using models, it is predicted that compressive strain on the order of 1% (or 2 GPa) can increase the leakage current by 150 times. Conversely, tensile strain may diminish or at most double the leakage current in all observed cases. Though detrimental in conventional inversion‐mode metal‐oxide‐semiconductor field‐effect‐transistor, these processes may be used to boost the performance of tunnel field‐effect transistors, where on‐state current is defined by band‐to‐band tunneling.

Efficient quantum-dot adder optimisation and analysis for future circuits

ABSTRACT In recent years, the rapid scaling of transistors has necessitated the exploration of advanced alternatives to Complementary metal oxide semiconductor(CMOS) technology for future progress. Quantum-dot cellular automata(QCA) technology has emerged as a promising solution, offering highly dense, high-speed, and low-power circuits. Among the critical digital building blocks, adder circuits play a crucial role in arithmetic and logic units. Consequently, optimising these circuits in terms of area, delay, and quantum cost is essential for the development of efficient designs. This paper presents effective multi-layer n-bit ripple carry adder(RCA) circuits, utilising full adder(FA) circuit. The outputs are generated in distinct layers and verified using the QCADesigner-Ev2.2 tool with bi-stable and coherence vector energy setups, employing Euler and Runge-Kutta methods.Additionally, the proposed designs are evaluated for various design metrics at three different scale factors(1,0.8889,and 0.7778), corresponding to cell sizes of 18 × 18 nm , 16 × 16 nm , and 14 × 14 nm respectively. The temperature’s impact on the average output polarisation of the FA is explored. The research demonstrates an n-bit-RCA surpassing existing designs with cost optimisations of 89.5%, 86%, and 90.3% for 4-bit,8-bit and 16-bit circuits, respectively. The paper also provides a thorough energy dissipation analysis for the proposed adder design.

Asynchronous interface circuit for nonlinear connectivity in multicore spiking neural networks

AbstractTo expand the scale of spiking neural networks (SNNs), an interface circuit that supports multiple SNN cores is essential. This circuit should be designed using an asynchronous approach to leverage characteristics of SNNs similar to those of the human brain. However, the absence of a global clock presents timing issues during implementation. Hence, we propose an intermediate latching template to establish asynchronous nonlinear connectivity with multipipeline processing between multiple SNN cores. We design arbitration and distribution blocks in the interface circuit based on the proposed template and fabricate an interface circuit that supports four SNN cores using a full‐custom approach in a 28‐nm CMOS (complementary metal–oxide–semiconductor) FDSOI (fully depleted silicon on insulator) process. The proposed template can enhance throughput in the interface circuit by up to 53% compared with the conventional asynchronous template. The interface circuit transmits spikes while consuming 1.7 and 3.7 pJ of power, supporting 606 and 59 Mevent/s in intrachip and interchip communications, respectively.

Nanofibrous metal oxide semiconductor for sensory face masks

Sensory face masks are designed to integrate sensors that monitor health metrics, such as breathing rate and body temperature, thereby providing continuous physiological data. However, current sensing materials are predominantly in film form. In this study, we report on the use of fibrous amorphous indium gallium zinc oxide, which offers an enlarged surface area to facilitate gas diffusion and transport into charge-carrying sites. A detailed morphological analysis and an electrical investigation of this fibrous network were conducted. By integrating this material with a wireless, miniaturised flexible circuit and mounting it on a face mask, we successfully monitored different human respiratory states in real time. This wearable face mask demonstrates the potential for promising applications in health monitoring.

Anchoring Ni atomic clusters on yolk-shell In2O3 microspheres for highly sensitive, ultra-rapid responding/recovering ppb-level NO2 detections

Highly sensitive, sophisticated and rapidly responding/recovering NO2 sensors are of a pressing demand across various modern applications. However, traditional metal oxide semiconductors (MOSs), such as In2O3, often grapple with issues such as diminished sensitivity and tardy responding/recovering. To address these challenges, we present a novel, simultaneous enhancement strategy centered around Ni atomic clusters (NiAC) integrated into In2O3 yolk-shell microspheres. This innovative structural and compositional design not only enhances NO2 adsorption thermodynamics but also improves kinetics reacting rate. The optimized heterostructured NiAC-In2O3 exhibits exceptional NO2 sensing performances with high response (454.62 to 10 ppm NO2), instantaneous responding/recovering dynamics (1/3 s), and an impressively ultra-low detection limit (1 ppb) at 200 ℃. Reaction kinetics calculation, finite element method (FEM) simulations and further validation through In-situ diffuse reflection infrared Fourier transform spectroscopy (In-situ DRIFTS) and temperature-programmed desorption (TPD) analyses confirms the accelerated NO2 adsorption/desorption dynamics, enhanced NO2 dissociation and trace-concentration NO2 molecule capturing capability attributed to NiAC. Considering these merits, The fabricated NiAC-In2O3 ensures high-precise, instantaneous, ppb-level NO2 detections.

Asymmetric trench SiC MOSFET with integrated channel accumulation diode for enhanced reverse conduction and switching characteristics

A novel asymmetric trench Silicon Carbide Metal Oxide Semiconductor Field Effect Transistor (SiC MOSFET), featuring an integrated channel accumulation diode (CAD-MOS), has been proposed and investigated through numerical simulation. This innovative design aims to mitigate switching losses and eliminate the bipolar degradation of the body diode. The current spreading layer (CSL) channel, strategically positioned in the centre of the dummy gate, offers a low-barrier reverse conduction path. This represents a substantial advancement over the traditional PN body diode, significantly reducing the reverse conduction voltage drop from 2.84 V in the PN body diode to a mere 1.39 V in the CAD-MOS. Meanwhile, the reverse recovery charge of the CAD-MOS is reduced to 0.95 μC/cm2, and the peak reverse recovery current stands at 45 A/cm2. Compared to conventional asymmetrical trench SiC MOSFET (CON-MOS), the CAD-MOS exhibits a 68.1 % reduction in reverse recovery charge and a 63.4 % decrease in peak reverse recovery current. The split-gate design also reduces the device gate to source capacitance (CGS), resulting in a 17.4 % reduction in total switching losses to 3.64 mJ/cm2. CAD-MOS also exhibits a reduced gate turn-on charge and demonstrates an enhancement in high-frequency figure of merit (HF-FOM) by 8.1 %.

ZEROES: Robust Derivative-Based Demodulation Method for Optical Camera Communication

Most of Optical Camera Communication (OCC) systems benefit from the rolling shutter mechanism of Complementary Metal-Oxide Semiconductor (CMOS) cameras to record the brightness evolution of the Light-Emitting Diode (LED) through dark and bright strips within images. While this technique enhances the maximum achievable data rate, the main difficulty lies in the demodulation of the signal extracted from images, subject to blooming effect. Thus, two main approaches were proposed to deal with this issue, using adaptive thresholds whose value evolves according to amplitude changes or detecting signal variations with the first-order derivative. As the second method is more robust, a new demodulation method based on the detection of the zeros of the first-order derivative of the extracted signal was proposed in this paper. Obtained results clearly show an improvement in the extracted signal demodulation compared to other methods, achieving a raw Bit Error Rate (BER) of 10−3 around 50 cm in a Line-Of-Sight scenario, and increasing the maximum communication distance by 43.5%, reaching 330 cm in the case of a Non-Line-Of-Sight transmission.