Silicon Devices Research Articles

(Invited) Understanding the Electroluminescence Signature of High-Voltage Vertical GaN Pin Diodes with Different Edge Termination Designs

GaN has superior properties, such as a wide band gap and high critical electric field that make it promising material for future power semiconductor devices. Edge termination for GaN power devices remains a subject of significant interest. In this work, different edge termination designs were systematically evaluated and compared by utilizing broadband electroluminescence technique under various reverse bias conditions. Edge termination is a crucial step in power devices fabrication process, using nitrogen implant is a common step in GaN PiN diode. In this work, Nitrogen ion implantation was used to form junction termination extension (JTE) and Guard Rings (GR). A full 2” wafer was fabricated in a foundry process to build a high current 1.2kV class GaN vertical diodes on non-homogenous GaN substrate. In silicon power devices, a smooth tapered implanted doping profiles are often achieved through a controlled diffusion of the implanted dopant island during activation. Activation and diffusion of acceptor dopants via ion implantation is neither well controlled nor understood in GaN. In this work, based JTE terminations, GR termination and a combination of both were compared. We are comparing several devices on the same wafer type and same fabrication process but with different edge termination designs; and spatially resolving their spectrum, by utilizing the electroluminescence mapping technique to acquire a series of broadband images under high voltage reverse bias. There is a clear difference in the electroluminescence signature. This is the first time we show the impact of edge termination on the evolution of these defects and the transport path of the leakage current. The leakage current, and hence the electroluminescence signature is changing as well with the termination design. All the termination and guard ring designs were based on Nitrogen implant. The nitrogen implant doses and energy are chosen to create enough damage in the p-type region. Stress testing is in-progress to evaluate the impact of these defects on failure mechanisms. JTE only design show a leakage current as a bright ring on the outer perimeter of the device active region closer to trench isolation while a GR only design brings the leakage current near the anode. A combination of both termination designs results in scattered leakage points on the outer perimeter of the device. Simulation results of the filed profiles of the different structures and hyperspectral EL and Raman spectroscopy are in progress along with temperature stressing to understand the nitrogen diffusion mechanisms in GaN. This study will have an impact on the future of GaN power devices and mature its process to compete with SiC technology. Figure 1

Modeling and Analysis of a SiC Microstructure-Based Capacitive Micro-Accelerometer.

In this study, a comb-type capacitive accelerometer based on a silicon carbide (SiC) microstructure is presented and investigated by the finite element method (FEM). It has the advantages of low weight, small volume, and low cross-coupling. Compared with silicon(111) accelerometers with the same structure, it has a higher natural frequency. When the accelerometer vibrates, its resistive force consists of two main components: a viscous damping and an elastic damping force. It was found that viscous damping dominates at low frequency, and elastic damping dominates at high frequency. The second-order linear system of the accelerometer was analyzed in the time-frequency domain, and its dynamic characteristics were best when the gap between the capacitive plates was 1.23 μm. The range of this accelerometer was 0–100 g, which is 1.64 times that of a silicon(111) accelerometer with the same structure. In addition, the accelerometer could work normally at temperatures of up to 1200 °C, which is much higher than the working temperatures of silicon devices. Therefore, the proposed accelerometer showed superior performance compared to conventional silicon-based sensors for inertial measurements.

Reductions in the thermal conductivity of irradiated silicon governed by displacement damage

We report on the measured thermal conductivity of silicon irradiated with an array of ions: ${\mathrm{C}}^{2+},$ ${\mathrm{N}}^{2+},$ ${\mathrm{Al}}^{2+},$ ${\mathrm{Si}}^{2+},$ ${\mathrm{P}}^{2+},$ and ${\mathrm{Ge}}^{2+}$. Results are analyzed in consideration of ion mass, radius, and induced displacement damage. Recrystallization of select samples via annealing demonstrates that structural disorder imparted by incident ions, rather than the ions themselves, drive the reduction in thermal conductivity. This, in turn, is dictated by the mass of the ion. A generalized model is provided to relate thermal conductivity to displacement damage. Knowledge of the displacements-per-atom profile can thus be used to predict thermal conductivity reduction for silicon devices in extreme environments.

Study of doping two tin atoms per unit cell of silicene nanoribbons in the presence of an external electric field

Silicene is a low-dimensional material of interest to many scientists because of its structural properties that are compatible with silicon devices and opens up many new applications for technology. Silicene nanoribbons are one-dimensional structures, the silicene nanoribbons studied here have 12 silicon atoms inside, and the edges are edited by 4 hydrogen atoms per unit cell. There are two doped Sn atoms per unit cell of silicene nanoribbons, the three configurations studied here are ortho, meta, and para configurations. The system is placed in an external electric field of 0.4 V/Angstrom. Use density function theory (DFT) to calculate the formation energy, energy band structure, and state density of the system. The doped systems are stable after optimization. The presence of the external electric field and the doping element Sn is responsible for the changes in the structural properties of the system.

Templated dewetting for self-assembled ultra-low-loss chalcogenide integrated photonics

Integrated photonics is of growing interest but relies on complex fabrication methods that have yet to match optical losses of bulkier platforms like optical fibers or whispering gallery mode resonators. Spontaneous matter reorganization phenomenon (e.g. dewetting) in thin-films provides a way for self-assembled structures with atomic scale surface rugosity, potentially alleviating the problems of roughness scattering loss and fabrication complexity. In this article, we study solid-state dewetting in chalcogenide glass thin-films and demonstrate its applicability to the fabrication of high-quality integrated photonics components. Optimal dewetting parameters are derived from a comprehensive experimental study of thin-film properties under high temperature rapid annealing. Atomic scale surface roughness are obtained using dewetting, with RMS values as low as R q = 0.189 nm. Several integrated photonics components are fabricated using the method and characterized. We show that the use of pre-patterned templates leads to organized, reproducible patterns with large-scale uniformity and demonstrate the record high quality-factor of 4.7 × 106 in compact (R = 50 µm) microdisks, corresponding to 0.08 dB⋅cm−1 waveguide propagation loss. The integrated devices are directly fabricated on standard silicon-on-insulator dice using the micro-trench filling technique and coupled to silicon waveguides, making them readily deployable with existing silicon devices and systems.

Low-Voltage GaN FETs in Motor Control Application; Issues and Advantages: A Review

The efficiency and power density improvement of power switching converters play a crucial role in energy conversion. In the field of motor control, this requires an increase in the converter switching frequency together with a reduction in the switching legs’ dead time. This target turns out to be complex when using pure silicon switch technologies. Gallium Nitride (GaN) devices have appeared in the switching device arena in recent years and feature much more favorable static and dynamic characteristics compared to pure silicon devices. In the field of motion control, there is a growing use of GaN devices, especially in low voltage applications. This paper provides guidelines for designers on the optimal use of GaN FETs in motor control applications, identifying the advantages and discussing the main issues. In this work, primarily an experimental evaluation of GaN FETs in a low voltage electrical drive is carried out. The experimental investigation is obtained through two different experimental boards to highlight the switching legs’ behavior in several operative conditions and different implementations. In this evaluative approach, the main GaN FETs’ technological aspects and issues are recalled and consequently linked to motion control requirements. The device’s fast switching transients combined with reduced direct resistance contribute to decreased power losses. Thus, in GaN FETs, a high switching frequency with a strong decrease in dead time is achievable. The reduced dead time impact on power loss management and improvement of output waveforms quality is analyzed and discussed in this paper. Furthermore, input filter capacitor design matters correlated with increasing switching frequency are pointed out. Finally, the voltage transients slope effect (dv/dt) is considered and correlated with low voltage motor drives requirements.

Comparison of selected general-purpose event generators for particle fluence simulation in LHC silicon trackers

At the LHC era, the detector systems are operating at the harsh hadronic environment with the unprecedentedly high particle flux. Position-sensitive silicon devices are usually positioned at the innermost regions of the experimental setups and must cope with highly non-uniform radiation fields. At the end of LHC Run 2, fluence in silicon trackers reached 10^{15} n_{mathrm{eq}}/cm^2. Initial simulation studies predict that the maximal fluence for the HL-LHC may be up to two orders of magnitude higher than the one seen in LHC Run 1 and Run 2. In this paper, two general-purpose physics event generators used for simulation of proton–proton collisions for the radiation damage studies at LHC energies: PYTHIA 8.2 and Dpmjet-III are compared. Fluences obtained using these models, with the latest tuning to the LHC data, in detectors situated close to the proton–proton interaction point are determined as well. We also indicate a potential new method for actual fluence estimation using experiment real-time data monitoring system.

Heavy-Ion Testing Method and Results of Normally OFF GaN-Based High-Electron-Mobility Transistor

Gallium nitride (GaN) power switches are promising devices for power conversion applications because this new technology enables the design of power converters with higher efficiency and reduced size than those achievable with conventional silicon devices. For space applications, normally-OFF devices are mandatory to avoid potential current shoot through during startup or loss of power control. The use of these devices in space environment shall be carefully considered with respect to natural radiation and especially under heavy-ion impact that can induce the burnout of the device known as single-event effect (SEE) failure. Therefore, radiation hardness evaluation of GaN devices is of prime interest. Another important parameter affecting GaN power device reliability is the current collapse or dynamic <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$R_{\mathrm{\scriptscriptstyle ON}}$ </tex-math></inline-formula> since in particular functioning condition, the device can generate extra losses that may lead to failure. Five commercial off-the-shelf (COTS) GaN high-electron-mobility transistor (HEMT) references were selected and tested under heavy ions. This article presents first the testing methodology and device preparation used for heavy-ion test campaign. Then observations from the irradiation run are presented and discussed. At last, a potential dynamic <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$R_{\mathrm{\scriptscriptstyle ON}}$ </tex-math></inline-formula> issue with respect to heavy-ion safe operating area (SOA) of one reference is highlighted.

Graphene-Silicon Device for Visible and Infrared Photodetection.

The fabrication of a graphene–silicon (Gr-Si) junction involves the formation of a parallel metal–insulator–semiconductor (MIS) structure, which is often disregarded but plays an important role in the optoelectronic properties of the device. In this work, the transfer of graphene onto a patterned n-type Si substrate, covered by Si3N4, produces a Gr-Si device, in which the parallel MIS consists of a Gr-Si3N4-Si structure surrounding the Gr-Si junction. The Gr-Si device exhibits rectifying behavior with a rectification ratio up to 104. The investigation of its temperature behavior is necessary to accurately estimate the Schottky barrier height (SBH) at zero bias, φb0 = 0.24 eV, the effective Richardson’s constant, A* = 7 × 10–10 AK–2 cm–2, and the diode ideality factor n = 2.66 of the Gr-Si junction. The device is operated as a photodetector in both photocurrent and photovoltage mode in the visible and infrared (IR) spectral regions. A responsivity of up to 350 mA/W and an external quantum efficiency (EQE) of up to 75% are achieved in the 500–1200 nm wavelength range. Decreases in responsivity to 0.4 mA/W and EQE to 0.03% are observed above 1200 nm, which is in the IR region beyond the silicon optical band gap, in which photoexcitation is driven by graphene. Finally, a model based on two parallel and opposite diodes, one for the Gr-Si junction and the other for the Gr-Si3N4-Si MIS structure, is proposed to explain the electrical behavior of the Gr-Si device.

CO2 laser fabrication of hydrogel-based open-channel microfluidic devices.

This study proposed a rapid and low-cost fabrication method for open-channel hydrogel-based microfluidic devices using CO2 laser ablation. The agarose hydrogel substrate was prepared with agarose gelation in DI water upon microwave heating, then a commercial CO2 laser system was used for the direct laser ablation of microchannels on the surface of agarose hydrogel substrate, the hydrophilic nature of the microchannels fabricated on hydrogel substrate enables the self-driven of the liquid inside the microchannels with capillary force. The profiles of the laser ablated microchannels on agarose hydrogel substrate with various laser power and scan speed were studied in detail. Due to the loss of water when exposed to the atmosphere, significant deformation of the fabricated microchannels was observed, and the profile change was recorded for 48h for comparison. An easy-to-access storage method of hydrogel-based microfluidic device in DI water was also proposed in this study. Unlike compact silicon or polymer-based microfluidic devices, the hydrogel is formed by cross-linked polymer chains filled with water, for a better understanding of the diffusion of small molecules into the bulk hydrogel material during fluid propagation inside the microchannel, the Nile red fluorescent was added into the liquid and the diffusion across the hydrogel-based microchannels with time was measured and discussed in this study. Several open-channel agarose hydrogel-based microfluidic devices were fabricated in this study for the demonstration of the proposed fabrication method. The CO2 laser ablation approach for agarose hydrogel-based microfluidic devices has the advantages of rapid processing time, low-cost, highly biocompatible, and self-driven without pumps and could have wide application potentials in biological and medical fields.

Dispersively Probed Microwave Spectroscopy of a Silicon Hole Double Quantum Dot

Owing to ever increasing gate fidelities and to a potential transferability to industrial CMOS technology, silicon spin qubits have become a compelling option in the strive for quantum computation. In a scalable architecture, each spin qubit will have to be finely tuned and its operating conditions accurately determined. In this prospect, spectroscopic tools compatible with a scalable device layout are of primary importance. Here we report a two-tone spectroscopy technique providing access to the spin-dependent energy-level spectrum of a hole double quantum dot defined in a split-gate silicon device. A first GHz-frequency tone drives electric-dipole spin resonance enabled by the valence-band spin-orbit coupling. A second lower-frequency tone (approximately 500 MHz) allows for dispersive readout via rf-gate reflectometry. We compare the measured dispersive response to the linear response calculated in an extended Jaynes-Cummings model and we obtain characteristic parameters such as g-factors and tunnel/spin-orbit couplings for both even and odd occupation.

Diagnosis of Faults Induced by Radiation and Circuit-Level Design Mitigation Techniques: Experience from VCO and High-Speed Driver CMOS ICs Case Studies

In this paper, we discuss the diagnosis of particle-induced failures in harsh environments such as space and high-energy physics. To address these effects, simulation-before-test and simulation-after-test can be the key points in choosing which radiation hardening by design (RHBD) techniques can be implemented to mitigate or prevent failures. Despite the fact that total ionising dose (TID) has slow but destructive effects overtime on silicon devices, single-event effect (SEE) impulsively disrupts the typical operation of a circuit with temporary or permanent effects. The recently released SpaceFibre protocol drives the current requirements for space applications, and the future upgrade of the LHC experiment scheduled by CERN will require a redesign of the electronic front-end to sustain a radiation level up to the 1 Grad TID level. The effects that these two environments have on two different architectures for high-radiation and high-frequency data transmission are reported, and the efficiency of the mitigation techniques implemented, based on simulations and measurement tests, in the commercial 65 nm technology, are exploited.

Modern Power Electronic Devices: Physics, Applications, and Reliability [Book News

This book discusses silicon and wide bandgap (WBG) semiconductor-based devices. After the preface, it includes 14 carefully selected chapters to cover recent trends in WBG semiconductors, with the following subjects: power electronics challenges, junction diodes, Si MOSFETs, Si IGBTs, SiC MOSFETs, GaN transistors, module design and reliability, switching cell design, and prospects and outlooks for the power electronics technology. This high-quality book is illustrated with hundreds of highly pedagogical color figures, where important features are easily visible. A table of contents, a note about the editor, a preface, and an index are also present.

Estimation of activation energy and reliability figures of space lattice-matched GaInP/Ga(In)As/Ge triple junction solar cells from Temperature Accelerated Life Tests

Qualification standards are on the base of the high endurance and resilience of space solar cells. In these standards, such as the European ECSS-E-ST-20-08C or the American AIAA S-111A counterpart, life tests related with high temperature accelerated tests (among many others) are included. There are several issues that make it difficult to assess the multijunction solar cell life from temperature tests in these standards. For example, in the European standard, an activation energy of 0.7 eV determined many years ago for silicon devices is assumed. On the other hand, the American standard proposes temperature accelerated tests at the temperatures of 50 °C, 80 °C and 110 °C which are clearly low to really accelerate the life tests of solar cells. Accordingly, in this paper we present the resulting reliability figures (reliability function, failure probability and MTTF) derived of an innovative temperature ALT which allows the proper estimation of the activation energy of commercial lattice matched GaInP/Ga(In)As/Ge triple junction solar cells. The main conclusions are: a) an activation energy of 0.97 eV has been estimated. This value results in significantly higher lifetime values for the tested cells. b) the shape parameter obtained from Weibull failure density function, β, is 1.67; c) the tested solar cells perform as robust devices showing high reliability values in the temperature range of 80 °C–130 °C; d) for higher temperatures, especially beyond 150 °C, the reliability decays significantly; f) reliability functions and parameters can be assessed for any operation temperature and failure criterion. • Innovative temperature Accelerated Life Test for reliability of space solar cells. • Activation energy of 0.97 eV for LM GaInP/Ga(In)As/Ge. Current used value 0.7 eV. • Reliability figures estimated for any operation temperature and failure criteria limit. • Tested solar cells are robust devices for temperatures up to 130 °C. • Tested solar cells reliability decrease significantly for temperatures beyond 150 °C.

High precision integrated photonic thermometry enabled by a transfer printed diamond resonator on GaN waveguide chip.

We demonstrate a dual-material integrated photonic thermometer, fabricated by high accuracy micro-transfer printing. A freestanding diamond micro-disk resonator is printed in close proximity to a gallium nitride on a sapphire racetrack resonator, and respective loaded Q factors of 9.1 × 104 and 2.9 × 104 are measured. We show that by using two independent wide-bandgap materials, tracking the thermally induced shifts in multiple resonances, and using optimized curve fitting tools the measurement error can be reduced to 9.2 mK. Finally, for the GaN, in a continuous acquisition measurement we record an improvement in minimum Allan variance, occurring at an averaging time four times greater than a comparative silicon device, indicating better performance over longer time scales.

Optical see-through augmented reality displays with wide field of view and hard-edge occlusion by using paired conical reflectors.

Optical see-through head-mounted displays are actively developed in recent years. An appropriate method for mutual occlusion is essential to provide a decent user experience in many application scenarios of augmented reality. However, existing mutual occlusion methods fail to work well with a large field of view (FOV). In this Letter, we propose a double-parabolic-mirror structure that renders hard-edge occlusion within a wide FOV. The parabolic mirror increases the numerical aperture of the system significantly, and the usage of paired parabolic mirrors eliminates most optical aberrations. A liquid crystal on silicon device is introduced as the spatial light modulator for imaging a bright see-through view and rendering sharp occlusion patterns. A loop structure is built to eliminate vertical parallax. The system is designed to obtain a maximum monocular FOV of H114∘×V95∘ with hard-edge occlusion, and a FOV of H83.5∘×V53.1∘ is demonstrated with our bench-top prototype.

Heterogeneous integration of single-crystalline rutile nanomembranes with steep phase transition on silicon substrates

Unrestricted integration of single-crystal oxide films on arbitrary substrates has been of great interest to exploit emerging phenomena from transition metal oxides for practical applications. Here, we demonstrate the release and transfer of a freestanding single-crystalline rutile oxide nanomembranes to serve as an epitaxial template for heterogeneous integration of correlated oxides on dissimilar substrates. By selective oxidation and dissolution of sacrificial VO2 buffer layers from TiO2/VO2/TiO2 by H2O2, millimeter-size TiO2 single-crystalline layers are integrated on silicon without any deterioration. After subsequent VO2 epitaxial growth on the transferred TiO2 nanomembranes, we create artificial single-crystalline oxide/Si heterostructures with excellent sharpness of metal-insulator transition (triangle rho /rho > 103) even in ultrathin (<10 nm) VO2 films that are not achievable via direct growth on Si. This discovery offers a synthetic strategy to release the new single-crystalline oxide nanomembranes and an integration scheme to exploit emergent functionality from epitaxial oxide heterostructures in mature silicon devices.

Analysis of the thermal rectification in silicon structure with triangular holes

ABSTRACT Silicon semiconductors with excellent thermoelectric characteristics have been widely used in integrated electronic systems. Thermal rectification has important potential applications in semiconductor devices such as thermal management improvement of electronics and energy saving. The thermal conductivities and thermal rectifications of silicon devices with sets of triangular holes are investigated by nonequilibrium molecular dynamic (NEMD) simulations. The influences of the dimension and angle of the distributed triangular-shaped holes are investigated. The results indicate that the phonon scattering on the side and base of the right-angled triangular holes are quite different, which causes the thermal rectification. The thermal rectification effect is strengthened with the increase of the triangle dimension. However, the variations of the triangular angle have little effect on the thermal conductivities of the silicon device. Besides, the phonon spectral energy density along the frequency axis of the silicon system is given to explain the mechanism behind the rectification phenomenon. Based on the present simulation results, a possible design strategy is proposed for developing highly efficient thermoelectric devices.

Influence of the properties of p-a-Si:H layer and the work function of front contact on silicon heterojunction solar cell performance

Heterojunction c-Si and hydrogenated amorphous silicon (a-Si:H) devices with intrinsic a-Si:H thin layer, known as HIT solar cells, are promising alternatives to conventional c-Si solar cells for the possibility of higher open circuit voltage, low temperature processing and lower costs. We have studied the influence of the properties of p-a-Si:H layer and the work function of the front electrode material on the performance parameters of n-c-Si based HIT solar cells using numerical simulation. The findings are further analyzed using energy band diagrams and carrier concentration profiles at the heterointerface of a-Si:H/n-c-Si to reveal the underlying charge transport mechanisms.

Uncertainty in the Phase Flicker Measurement for the Liquid Crystal on Silicon Devices

Phase flicker has become an important performance parameter for the liquid crystal on silicon (LCOS) devices. Since the phase response of the LCOS device cannot be measured directly, it is usually derived from the intensity response of the modulated light beam when the LCOS device was placed between a pair of crossed polarisers. However, the relationship between the intensity of the beam and the phase response of the LCOS device is periodic. This would lead to uncertainty in the phase flicker measurement. This paper analyses this measurement uncertainty through both simulation and experiments. It also proposed a strategy to minimise the uncertainty.