2019年JOS入选“中国科技期刊卓越行动计划”
In Press
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• ## Inegration of GaN analog building blocks on p-GaN wafers for GaN ICs

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We demonstrate the key module of comparators in GaN ICs, based on resistor-transistor logic (RTL) on E-mode wafers in this work. The fundamental inverters in the comparator consist of a p-GaN gate HEMT and a 2DEG resistor as the load. The function of the RTL comparators is finally verified by a undervoltage lockout (UVLO) circuit. The compatibility of this circuit with the current p-GaN technology paves the way for integrating logic ICs together with the power devices.

• ## Voltage-dependent plasticity and image Boolean operations realized in a WO x-based memristive synapse

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The development of electronic devices that possess the functionality of biological synapses is a crucial step towards neuromorphic computing. In this work, we present a WOx-based memristive device that can emulate voltage-dependent synaptic plasticity. By adjusting the amplitude of the applied voltage, we were able to reproduce short-term plasticity (STP) and the transition from STP to long-term potentiation. The stimulation with high intensity induced long-term enhancement of conductance without any decay process, thus representing a permanent memory behavior. Moreover, the image Boolean operations (including intersection, subtraction, and union) were also demonstrated in the memristive synapse array based on the above voltage-dependent plasticity. The experimental achievements of this study provide a new insight into the successful mimicry of essential characteristics of synaptic behaviors.

• ## Neuromorphic vision sensors: Principle, progress and perspectives

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Conventional frame-based image sensors suffer greatly from high energy consumption and latency. Mimicking neurobiological structures and functionalities of the retina provides a promising way to build a neuromorphic vision sensor with highly efficient image processing. In this review article, we will start with a brief introduction to explain the working mechanism and the challenges of conventional frame-based image sensors, and introduce the structure and functions of biological retina. In the main section, we will overview recent developments in neuromorphic vision sensors, including the silicon retina based on conventional Si CMOS digital technologies, and the neuromorphic vision sensors with the implementation of emerging devices. Finally, we will provide a brief outline of the prospects and outlook for the development of this field.

• ## The etching process and mechanism analysis of TaSb2Te3 film based on inductively coupled plasma

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Compared to the conventional phase change materials, the new phase change material TaSb2Te3 has the advantages of excellent data retention and good material stability. In this letter, the etching characteristics of TaSb2Te3 were studied by using CF4/Ar. The results showed that when CF4/Ar = 25/25, the etching power was 600 W and the etching pressure was 2.5 Pa, the etching speed was up to 61 nm/min. The etching pattern of TaSb2Te3 film had a smooth side wall and good perpendicularity (close to 90°), smooth surface of the etching (RMS was 0.51nm), and the etching uniformity was fine. Furthermore, the mechanism of this etching process was analyzed by X-ray photoelectron spectroscopy (XPS). The main damage mechanism of ICP etching in CF4/Ar was studied by X-ray diffraction (XRD).

• ## Prediction and observation of defect-induced room-temperature ferromagnetism in halide perovskites

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The possibility to induce a macroscopic magnetic moment in lead halide perovskites (LHPs), combined with their excellent optoelectronic properties, is of fundamental interest and has promising spintronic applications. However, these possibilities remain an open question in both theory and experiment. Here, theoretical and experimental studies are performed to explore ferromagnetic states in LHPs originated from lattice defects. First-principle calculations reveal that shallow-level Br vacancies in defective CsPbBr3 can produce spin-splitting states and the coupling between them leads to a ferromagnetic ground state. Experimentally, ferromagnetism at 300 K is observed in room-temperature synthesized CsPbBr3 nanocrystals, but is not observed in hot-injection prepared CsPbBr3 quantum dots and in CsPbBr3 single crystals, highlighting the significance played by vacancy defects. Furthermore, the ferromagnetism in the CsPbBr3 nanocrystals can be enhanced fourfold with Ni2+ ion dopants, due to enhancement of the exchange coupling between magnetic polarons. Room-temperature ferromagnetism is also observed in other LHPs, which suggests that vacancy-induced ferromagnetism may be a universal feature of solution-processed LHPs, which is useful for future spintronic devices.

• ## Small molecule donors with different conjugated π linking bridges: Synthesis and photovoltaic properties

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Three small molecule (SM) donors, namely B-T-CN, B-TT-CN and B-DTT-CN, with different π conjugated bridges were synthesized in this research. Interestingly, with the conjugated fused rings of the π linking bridge increasing, the SM HOMO levels exhibit a decline tendency with –5.27 eV for B-T-CN, –5.31 eV for B-TT-CN and –5.40 eV for B-DTT-CN. After blending the SM donors with the fullerene acceptor PC71BM, the all SM organic solar cells (OSCs) achieved high Vocs of 0.90 to 0.96 V. However, the phase separation morphology and molecule stacking are also unexpectedly changed together with the enhancement of conjugated degree of π bridges, resulting in a lower power conversion efficiency (PCE) for the B-DTT-CN:PC71BM device. Our results demonstrate and provide a useful way to enhance OSC Voc and the morphology needs to be further optimized.

• ## Research on the photoluminescence of spectral broadening by rapid thermal annealing on InAs/GaAs quantum dots

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A photoluminescence (PL) test was conducted to investigate the effect of rapid thermal annealing (RTA) on the optical performance of self-assembled InAs/GaAs quantum dots (QDs) at the temperatures of 16 and 300 K. It was found that after RTA treatment, the PL spectrum of the QDs sample had a large blue-shift and significantly broadened at 300 K. Compared with the as-grown InAs QDs sample, the PL spectral width has increased by 44.68 meV in the InAs QDs sample RTA-treated at 800 °C. The excitation power-dependent PL measurements showed that the broadening of the PL peaks of the RTA-treated InAs QDs should be related to the emission of the ground state (GS) of different-sized InAs QDs, the InAs wetting layer (WL) and the In0.15Ga0.85As strain reduction layer (SRL) in the epitaxial InAs/GaAs layers.

• ## A review of silicon-based wafer bonding processes, an approach to realize the monolithic integration of Si-CMOS and III–V-on-Si wafers

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The heterogeneous integration of III–V devices with Si-CMOS on a common Si platform has shown great promise in the new generations of electrical and optical systems for novel applications, such as HEMT or LED with integrated control circuitry. For heterogeneous integration, direct wafer bonding (DWB) techniques can overcome the materials and thermal mismatch issues by directly bonding dissimilar materials systems and device structures together. In addition, DWB can perform at wafer-level, which eases the requirements for integration alignment and increases the scalability for volume production. In this paper, a brief review of the different bonding technologies is discussed. After that, three main DWB techniques of single-, double- and multi-bonding are presented with the demonstrations of various heterogeneous integration applications. Meanwhile, the integration challenges, such as micro-defects, surface roughness and bonding yield are discussed in detail.

• ## A 16-bit 1 MSPS SAR ADC with foreground calibration and residual voltage shift strategy

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In this paper, a 16-bit 1MSPS foreground calibration successive approximation register analog-to-digital converter (SAR ADC) is developed by the CMOS 0.25 μm process. An on-chip all-digital foreground weights calibration technique integrating self-calibration weight measurement with PN port auto-balance technique is designed to improve the performance and lower the costs of the developed SAR ADC. The SAR ADC has a chip area of 2.7 × 2.4 mm2, and consumes only 100 μW at the 2.5 V supply voltage with 100 KSPS. The INL and DNL are both less than 0.5 LSB.

• ## The effect of total ionizing dose response on the hot carrier injection of 22 nm bulk nFinFET

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We investigate the hot carrier injection effect (HCI) and how X-ray radiation impacts the HCI of 22-nm nFinFETs as a function of device geometry and irradiation bias conditions in this paper. In the HCI test, the degradation of threshold voltage and saturation current decreases with the increase of fin number, which means that HCI weakens when the fin number increases. The reason is attributed to the coupling effect between fins. Moreover, irradiation is shown to weaken the degradation during the subsequent hot carrier test. The influence of irradiation on HCI is more obvious with ON bias than that of OFF bias and transmission gate bias. It is supposed that the Si–H bonds can be broken by irradiation before the HCI test, which is one reason for the irradiation influence on HCI. Besides, trapped charges are generated in the shallow trench isolation by the radiation, which could reduce the channel electric field, and then weaken the HCI.

• ## An antiferromagnetic two-dimensional material: Chromium diiodides monolayer

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The two-dimensional (2D) ferromagnetic materials and the related van der Waals homostructures have attracted considerable interest, while the 2D antiferromagnetic material has not yet been reported. Based on first-principles calculations, we investigate both electronic structures and magnetic orderings of bulk and monolayer of chromium diiodides (CrI2). We demonstrate a counter-intuitive fact that the ground state of the free-standing monolayer of CrI2 is antiferromagnetic though the bulk possesses macroscopic ferromagnetic ordering. The interlayer interaction remains antiferromagnetic up to few-layer scenarios. The unique feature of CrI2 makes it an ideal workbench to investigate the relation between magnetic couplings and interlayer van der Waals interactions, and may offer an opportunity to 2D antiferromagnetic spintronic devices.

• ## Performance of hydrogenated diamond field-effect transistors on single and polycrystalline diamond

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In this work, we investigate the influence of defects concentration of the diamond substrates on the performance of hydrogen-terminated diamond field-effect transistors by Raman spectra, pulsed IV characteristics analysis, and radio frequency performances measurements. It is found that a sample with higher defect concentration shows larger drain-lag effect and lower large-signal output power density. Defects in the diamond act as traps in the carrier transport and have a considerable influence on the large-signal output power density of diamond field-effect transistors. This work should be helpful for further performance improvement of the microwave power diamond devices.

• ## Energy band adjustment of 808 nm GaAs laser power converters via gradient doping

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The gradient doping regions were employed in the emitter layer and the base layer of GaAs based laser power converters (LPCs). Silvaco TCAD was used to numerically simulate the linear gradient doping and exponential gradient doping structure, and analyze the transport process of photogenerated carriers. Energy band adjustment via gradient doping improved the separation and transport efficiency of photogenerated carriers and reduced the total recombination rate of GaAs LPCs. Compared with traditional structure of LPCs, the photoelectric conversion efficiency of LPCs with linear and exponential gradient doping structure were improved from 52.7% to 57.2% and 57.7%, respectively, under 808nm laser light at the power density of 1 W/cm2.

• ## Comprehensive study of crystalline AlN/sapphire templates after high-temperature annealing with various sputtering conditions

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High-quality AlN/sapphire templates were fabricated by the combination of sputtering and high-temperature (HT) annealing. The influence of sputtering parameters including nitrogen flux, radio frequency power, and substrate temperature on the crystalline quality and surface morphology of annealed AlN films were investigated. With lower substrate temperature, lower power, and lower N2 flux, the full width at half maximum of the X-ray rocking curve for AlN (0002) and (10\begin{document}$\bar {1}$\end{document}2) were improved to 97.2 and 259.2 arcsec after high-temperature annealing. This happens because the increased vacancy concentration of sputtered AlN films can facilitate the annihilation of dislocations by increasing the recovery rate during HT annealing. Step and step-bunching morphologies were clearly observed with optimized sputtering conditions.

• ## RF performance evaluation of p-type NiO-pocket based β-Ga2O3/black phosphorous heterostructure MOSFET

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The radio-frequency (RF) performance of the p-type NiO-pocket based β-Ga2O3/black phosphorous heterostructure MOSFET has been evaluated. The key figure of merits (FOMs) for device performance evaluation include the transconductance (gm) gate dependent intrinsic-capacitances (Cgd and Cgs), cutoff frequency (fT), gain bandwidth (GBW) product and output-conductance (gd). Similarly, power-gain (Gp), power added efficiency (PAE), and output power (POUT) are also investigated for large-signal continuous-wave (CW) RF performance evaluation. The motive behind the study is to improve the β-Ga2O3 MOS device performance along with a reduction in power losses and device associated leakages. To show the applicability of the designed device in RF applications, its RF FOMs are analyzed. With the outline characteristics of the ultrathin black phosphorous layer below the β-Ga2O3 channel region, the proposed device results in 1.09 times improvement in fT, with 0.7 times lower Cgs, and 3.27 dB improved GP in comparison to the NiO-GO MOSFET. The results indicate that the designed NiO-GO/BP MOSFET has better RF performance with improved power gain and low leakages.

• ## Anomalies in Young's modulus behavior after annealing in polycrystalline SmS

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In this paper, the dependencies of Young's modulus and attenuation decrement on samarium sulfide polycrystals (SmS) under various annealing temperatures are studied by the piezoelectric ultrasonic composite oscillator technique at a frequency of 100 kHz in the temperature range of 80–300 K. A decrease in Young's modulus with an increase of the annealing temperature due to the texturing of the material was revealed. At the same time, attenuation peaks were observed at temperatures about 90 and 125 K, presumably due to Niblett-Wilks and Bordoni relaxations.

• ## Self-powered circularly polarized light detector based on asymmetric chiral metamaterials

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Circularly polarized light (CPL) has been given great attention because of its extensive application. While several devices for CPL detection have been studied, their performance is affected by the magnitude of photocurrent. In this paper, a self-powered photodetector based on hot electrons in chiral metamaterials is proposed and optimized. CPL can be distinguished by the direction of photocurrent without external bias owing to the interdigital electrodes with asymmetric chiral metamaterials. Distinguished by the direction of photocurrent, the device can easily detect the rotation direction of the CPL electric field, even if it only has a very weak responsivity. The responsivity of the proposed detector is near 1.9 mA/W at the wavelength of 1322 nm, which is enough to distinguish CPL. The detector we proposed has the potential for application in optical communication.

• ## Theoretical study of a group IV p–i–n photodetector with a flat and broad response for visible and infrared detection

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We report a theoretical study of a broadband Si/graded-SiGe/Ge/Ge0.9Sn0.1 p–i–n photodetector with a flat response based on modulating thickness of the layers in the active region. The responsivity of the photodetector is about 0.57 A/W in the range of 700 to 1800 nm. This structure is suitable for silicon-based epitaxial growth. Annealing is technically applied to form the graded-SiGe. The photodetector reaches a cut-off wavelength at ~2300 nm and a low dark-current density under 3 V reverse bias about 0.17 mA/cm2 is achieved theoretical at room temperature. This work is of great significance for silicon-based detection and communication, from visible to infrared.

• ## Design of GGNMOS ESD protection device for radiation-hardened 0.18 μm CMOS process

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In this paper, the ESD discharge capability of GGNMOS (gate grounded NMOS) device in the radiation-hardened 0.18 μm bulk silicon CMOS process (Rad-Hard by Process: RHBP) is optimized by layout and ion implantation design. The effects of gate length, DCGS and ESD ion implantation of GGNMOS on discharge current density and lattice temperature are studied by TCAD and device simulation. The size of DCGS, multi finger number and single finger width of ESD verification structures are designed, and the discharge capacity and efficiency of GGNMOS devices in ESD are characterized by TLP test technology. Finally, the optimized GGNMOS is verified on the DSP circuit, and its ESD performance is over 3500 V in HBM mode.