Xinhai Yu

Novel silicon allotropes: Stability, mechanical, and electronic properties

One quasi-direct gap phase (Amm2) and three indirect gap phases (C2/m-16, C2/m-20, and I-4) of silicon allotropes are proposed. The detailed theoretical study on the structure, density of states, elastic properties, sound velocities, and Debye temperature of these four phases is carried out by using first principles calculations. The elastic constants of these four phases are calculated by strain-stress method. The elastic constants and the phonon calculations manifest all novel silicon allotropes in this paper are mechanically and dynamically stable at ambient condition. The B/G values indicate that these four phases of silicon are brittle materials at ambient pressure. The anisotropy properties show that C2/m-20 phase exhibits a larger anisotropy in its elastic modulus, shear elastic anisotropic factors, and several anisotropic indices than others. We have found that the Debye temperature of the four novel silicon allotropes gradually reduces in the order of C2/m-20 > Amm2 > C2/m-16 > I-4 at ambient pressure.

Analysis of high power microwave induced degradation and damage effects in AlGaAs/InGaAs pHEMTs

Abstract The high power microwave (HPM) induced effects in AlGaAs/InGaAs pseudomorphic high electron mobility transistors (pHEMTs) are investigated by simulation and experiments. Simulated results suggest that the HPM damage mechanism is device burnout, which is caused by emerging current path and strong electric field intensity beneath the gate metal. Besides, analysis points out that the gate metal diffusion may be thermally activated, resulting in DC and RF performance degradation. Specifically, a positive shift will occur to the pinch-off voltage while accordingly the small-signal gain will decrease. The HPM injection experiments on the dual-stage pHEMT low noise amplifiers (LNAs) are carried out. Experimental results substantiate that deterioration happens both in the noise figure and in the small-signal gain, which is in agreement with the simulated results. Failure analysis indicates that the HPM induced failure of LNA is attributed to the failure of the first stage pHEMT. Finally, samples dissection analysis using the scanning electron microscopy (SEM) verifies the simulation analysis of the damage mechanism and the location susceptible to burnout. Meanwhile, the assumption of gate metal diffusion is validated by the observation of pits after removing the gate metal. The performance parameters deterioration can be utilized as the degradation (or damage) criteria, and the mechanisms analysis facilitates making reinforcing design.

First-principles Study of Structural, Elastic, Anisotropic, and Thermodynamic Properties of R3-B_2C

The structural, elastic, anisotropy, and thermodynamic properties of R3-B_2C were investigated using first-principles density functional calculations. The calculated equilibrium parameters are in good agreement with the available theoretical results. The elastic constants, elastic modulus, and elastic anisotropies of R3-B_2C were also determined in the pressure range of 0-100 GPa. The calculated elastic modulus indicates that R3-B_2C is a potential superhard material. The calculated elastic anisotropic factors suggest that R3-B2_C is elastically anisotropic. A band structure study shows that R3-B_2C is a direct semiconductor with band gap of 0.170 eV. Moreover, we predict the thermodynamic properties and obtain the relationships among the thermal expansion, temperature, and pressure, as well as the variations of the isothermal bulk modulus, Debye temperature, Gruneisen parameter, and heat capacity.

Modeling and understanding of the frequency dependent HPM upset susceptibility of the CMOS inverter

In this paper, we interpret and, for the first time, model a frequency dependent high-power microwave (HPM) upset susceptibility. We constructed the analytical models of the total amount of injected charges Ninj, the excess carrier density distribution in P-Substrate, and the frequency dependent HPM upset susceptibility level. The models are validated by simulated results and experimental data, respectively. Results reveal that Ninj is proportional to fα while the exponent a should be adjusted to −0.525. The excess carrier density distribution behaves the frequency dependence as well; the dependence is attributable to the fact that the AC field within the CMOS inverter varies too rapidly for the carriers to follow at high frequency. Meanwhile, the HPM upset susceptibility level is a decreasing function of f. The f dependent HPM upset susceptibility model is verified to be reliable and able to quickly estimate the susceptibility level of CMOS inverter considering IC technology, layout parameters, pulse properties, and operating environment simultaneously. Besides, the empirical formula P = A · fα is proposed to provide instant estimation to the HPM upset power threshold. In conclusion, by aid of the analytical model, we acquired the influence of the layout parameter LB on the HPM susceptibility and demonstrated that the CMOS inverter with minor LB is more susceptible to HPM.创新点1.推导证明CMOS反相器的高功率微波干扰过程与过剩载流子效应密切相关;2.得到注入寄生晶体管基区中的总电荷与频率的-0.525次幂成正比、过剩载流子分布表现出频率相关的结论;3.提出用以计算考虑频率影响的CMOS反相器的高功率微波干扰易发性并同时考虑工艺、脉冲参数以及工作环境的解析模型;4.得到可以快速估算不同频率下高功率微波对CMOS反相器的干扰功率阈值的经验公式。

Damage effect and mechanism of the GaAs pseudomorphic high electron mobility transistor induced by the electromagnetic pulse

The damage effect and mechanism of the electromagnetic pulse (EMP) on the GaAs pseudomorphic high electron mobility transistor (PHEMT) are investigated in this paper. By using the device simulation software, the distributions and variations of the electric field, the current density and the temperature are analyzed. The simulation results show that there are three physical effects, i.e., the forward-biased effect of the gate Schottky junction, the avalanche breakdown, and the thermal breakdown of the barrier layer, which influence the device current in the damage process. It is found that the damage position of the device changes with the amplitude of the step voltage pulse. The damage appears under the gate near the drain when the amplitude of the pulse is low, and it also occurs under the gate near the source when the amplitude is sufficiently high, which is consistent with the experimental results.

First-principles theoretical study on band of strained wurtzite Nb-doped ZnO

The strain effects of the Zn1−xMgxO substrate on the bands structure of wurtzite Nb-doped ZnO bulk materials have been investigated using first-principles calculations based on density functional theory. Firstly, the band gap increases gradually with increasing Nb contents in unstrained Nb-doped ZnO, which is consistent with the experimental results. Secondly, the band gap decreases with increasing substrate stress in Nb-doped ZnO/Zn1−xMgxO. Splitting energies between HHB (Heavy Hole Band) and LHB (Light Hole Band), HHB and CSB (Crystal Splitting Band) in Zn0.9167Nb0.0833O/Zn1−xMgxO almost remain unchanged with increasing substrate stress, while decrease slightly in Zn0.875Nb0.125O/Zn1−xMgxO. In addition, detailed analysis of the strain effects on the effective masses of electron and hole in Nb-doped ZnO/Zn1−xMgxO is also given.

Characterization of Electromagnetic Field-Transmission Line Coupling of Radiated Emission and Immunity Using TEM Cell Measurement

An analytic model is proposed to estimate the electromagnetic field transmission line coupling for both radiated emission and immunity using TEM cell measurements. Further, a coupling impedance is introduced to determine the domination between electric and magnetic fields of the fieldline coupling. Comparison of measurement and calculation results confirms the accuracy of the model. The model and coupling impedance can be helpful for the suppression of radiated emission and the enhancement of radiated immunity of transmission lines in electromagnetic compatibility design of electronic systems.

Ku band damage characteristics of GaAs pHEMT induced by a front-door coupling microwave pulse

Abstract A study on the damage effect of a GaAs pseudomorphic high-electron-mobility transistor (pHEMT) low-noise amplifier (LNA) induced by a Ku-band microwave is presented in this paper based on an experiment and simulation study. The experimental results suggest that the burn-out in the first stage is responsible for the LNA damage. Scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS) were used to observe the damage situation and compare the element composition before and after the high power microwave (HPM) injection. It is found that the gate metal is melted as a result of heat generation. The location beneath the gate near the source side is badly burned and splashes out. A detail simulation is performed by establishing a two-dimensional electric-thermal model considering several physical models and thermal parameters using the simulator Sentaurus-TCAD. The results show that the burn-out location is consistent with the experiment findings. Meanwhile, a temperature elevation occurs in both the positive and negative half cycles. Moreover, the damage to pHEMT shows the working voltage dependence, and the burn-out time increases with the increase in drain voltage.

Modeling and analysis of the HPM pulse-width upset effect on CMOS inverter*

We derive analytical models of the excess carrier density distribution and the HPM (high-power microwave) upset susceptibility with dependence of pulse-width, which are validated by the simulated results and experimental data. Mechanism analysis and model derivation verify that the excess carriers dominate the current amplification process of the latch-up. Our results reveal that the excess carrier density distribution in P-substrate behaves as pulse-width dependence. The HPM upset voltage threshold Vp decreases with the incremental pulse-width, while there is an inflection point which is caused because the excess carrier accumulation in the P-substrate will be suppressed over time. For the first time, the physical essence of the HPM pulse-width upset effect is proposed to be the excess carrier accumulation effect. Validation concludes that the Vp model is capable of giving a reliable and accurate prediction to the HPM upset susceptibility of a CMOS inverter, which simultaneously considers technology information, ambient temperature, and layout parameters. From the model, the layout parameter LB has been demonstrated to have a significant impact on the pulse-width upset effect: a CMOS inverter with minor LB is more susceptible to HPM, which enables us to put forward hardening measures for inverters that are immune from the HPM upset.