Optimization of recess-free AlGaN/GaN Schottky barrier diode by TiN anode and current transport mechanism analysis

:In this work,the optimization of reverse leakage current(IR)and turn-on voltage(VT)in recess-free AlGaN/GaN Schottky barrier diodes(SBDs)was achieved by substituting the Ni/Au anode with TiN anode.To explain this phenomenon,the current transport mechanism was investigated by temperature-dependent current–voltage(I–V)characteristics.For forward bias,the current is dominated by the thermionic emission(TE)mechanisms for both devices.Besides,the presence of inhomogeneity of the Schottky barrier height(qφb)is proved by the linear relationship between qφb and ideality factor.For reverse bias,the current is dominated by two different mechanisms at high temperature and low temperature,respectively.At high temperatures,the Poole–Frenkel emission(PFE)induced by nitrogen-vacancy(VN)is responsible for the high IR in Ni/Au anode.For TiN anode,the IR is dominated by the PFE from threading dislocation(TD),which can be attributed to the decrease of VN due to the suppression of N diffusion at the interface of Schottky contact.At low temperatures,the IR of both diodes is dominated by Fowler–Nordheim(FN)tunneling.However,the VN donor enhances the electric field in the barrier layer,thus causing a higher IR in Ni/Au anode than TiN anode,as confirmed by the modified FN model.

BME Frontiers: A Platform for Engineering the Future of Biomedicine

With immense enthusiasm, we introduce Biomedical Engineering (BME) Frontiers, the third addition to the family ofScience Partner Journals. The launch of BME Frontiers follows a year of intense preparation. As an open-access, peerreviewed academic journal, BME Frontiers covers basicresearch in relevant fields, as well as preclinical and clinicalinvestigations. The content will include innovative fundamental and translational concepts, mechanisms, materials,devices, systems, processes, and methods. BME Frontiers willalso serve as a platform for catalyzing forward-looking discussions about the field and will include perspectives ontraining and educating the future BME workforce.

A high aspect ratio surface micromachined accelerometer based on a SiC-CNT composite material

Silicon carbide(SiC)is recognized as an excellent material for microelectromechanical systems(MEMS),especially those operating in challenging environments,such as high temperature,high radiation,and corrosive environments.However,SiC bulk micromachining is still a challenge,which hinders the development of complex SiC MEMS.To address this problem,we present the use of a carbon nanotube(CNT)array coated with amorphous SiC(a-SiC)as an alternative composite material to enable high aspect ratio(HAR)surface micromachining.By using a prepatterned catalyst layer,a HAR CNT array can be grown as a structural template and then densified by uniformly filling the CNT bundle with LPCVD a-SiC.The electrical properties of the resulting SiC-CNT composite were characterized,and the results indicated that the electrical resistivity was dominated by the CNTs.To demonstrate the use of this composite in MEMS applications,a capacitive accelerometer was designed,fabricated,and measured.The fabrication results showed that the composite is fully compatible with the manufacturing of surface micromachining devices.The Young’s modulus of the composite was extracted from the measured spring constant,and the results show a great improvement in the mechanical properties of the CNTs after coating with a-SiC.The accelerometer was electrically characterized,and its functionality was confirmed using a mechanical shaker.

Study on the controllability of the fabrication of single-crystal silicon nanopores/nanoslits with a fast-stop ionic current-monitored TSWE method

The application of single-crystal silicon(SCS)nanopore structures in single-molecule-based analytical devices is an emerging approach for the separation and analysis of nanoparticles.The key challenge is to fabricate individual SCS nanopores with precise sizes in a controllable and reproducible way.This paper introduces a fast-stop ionic current-monitored three-step wet etching(TSWE)method for the controllable fabrication of SCS nanopores.Since the nanopore size has a quantitative relationship with the corresponding ionic current,it can be regulated by controlling the ionic current.Thanks to the precise current-monitored and self-stop system,an array of nanoslits with a feature size of only 3 nm was obtained,which is the smallest size ever reported using the TSWE method.Furthermore,by selecting different current jump ratios,individual nanopores of specific sizes were controllably prepared,and the smallest deviation from the theoretical value was 1.4 nm.DNA translocation measurement results revealed that the prepared SCS nanopores possessed the excellent potential to be applied in biosensing.

High-speed long-distance visible light communication based on multicolor series connection micro-LEDs and wavelength division multiplexing

Multicolor series connection micro-LED arrays with emission wavelengths of violet, blue, green, and yellow were fabricated, and their optoelectronic properties and communication performances were investigated. The designed series connection micro-LED array exhibited the light output power of multiple milliwatts, whereas mostly keeping a slightly reduced modulation bandwidth, thus, enabling a higher signal-to-noise ratio compared to a single pixel and showing superior performance in the field of long-distance visible light communication(VLC). The achievable data rates of 400-, 451-, 509-, and 556-nm micro-LED arrays using bit/power loading orthogonal frequency division multiplexing were 5.71, 4.86, 4.39, and 0.82 Gbps, respectively. The aggregate data rate of 15.78 Gbps was achieved for the proof-of-concept wavelength division multiplexing system under a transmission distance of 13 m, which was the best data rate-distance product performance for the LED-based VLC to the best of our knowledge. In addition, the long-distance VLC based on yellow micro-LED was also demonstrated for the first time in this paper.

Integrated 64 pixel UV image sensor and readout in a silicon carbide CMOS technology

This work demonstrates the first on-chip UV optoelectronic integration in 4H-SiC CMOS,which includes an image sensor with 64 active pixels and a total of 1263 transistors on a 100mm^(2) chip.The reported image sensor offers serial digital,analog,and 2-bit ADC outputs and operates at 0.39 Hz with a maximum power consumption of 60μW,which are significant improvements over previous reports.UV optoelectronics have applications in flame detection,satellites,astronomy,UV photography,and healthcare.The complexity of this optoelectronic system paves the way for new applications such harsh environment microcontrollers.

Shear strength of LED solder joints using SAC-nano Cu solder pastes

The addition of Cu nanoparticles into the solder pastes by mechanical mixing method creates a positive effect on the microstructure refinement of the LED solder joints. The grain size of β-Sn and Cu6Sn5 decrease obviously due to the increasing concentration of the nanoparticles in the solder pastes. However, the addition of nanoparticles facilitates the formation of voids in the solder joints, especially when the concentration of nanopar- ticles is higher than 0.5 wt% in the solder pastes. Both the microstructure refinement and void percentage affect the shear strength of the solder joints. Since the increase of the void percentage is limited when the concentration of nanoparticles increases from 0 to 0.5 wt%, the microstructure refinement shows a dominant effect on the shear performance and thus improves the shear strength of the solder joints from 49.8 to 55 MPa. Further addition of nanoparticles in the solder pastes leads to a sharp increase of the void percentage. Consequently, the shear strength of the solder joints decreases from 55 to 48.8 MPa when the concentration of doped particles increases from 0.5 to 1 wt% in the solder pastes.

Prognostics of radiation power degradation lifetime for ultraviolet light-emitting diodes using stochastic data-driven models

With their advantages of high efficiency,long lifetime,compact size and being free of mercury,ultraviolet light-emitting diodes(UV LEDs)are widely applied in disinfection and purification,photolithography,curing and biomedical devices.However,it is challenging to assess the reliability of UV LEDs based on the traditional life test or even the accelerated life test.In this paper,radiation power degradation modeling is proposed to estimate the lifetime of UV LEDs under both constant stress and step stress degradation tests.Stochastic data-driven predic-tions with both Gamma process and Wiener process methods are implemented,and the degradation mechanisms occurring under different aging conditions are also analyzed.The results show that,compared to least squares regression in the IESNA TM-21 industry standard recommended by the Illuminating Engineering Society of North America(IESNA),the proposed stochastic data-driven methods can predict the lifetime with high accuracy and narrow confidence intervals,which confirms that they provide more reliable information than the IESNA TM-21 standard with greater robustness.