Abstract. The strong spectral dependence of light absorption of brown carbon (BrC) aerosol is regarded to influence aerosol's radiative forcing significantly. The Absorption Angstrom Exponent (AAE) method was widely used in previous studies to attribute light absorption of BrC at shorter wavelengths for ambient aerosol, with a theoretical assumption that the AAE of "pure" black carbon (BC) aerosol equals to 1.0. In this study, the previous AAE method was improved by statistical analysis and applied in both urban and rural environments in the Pearl River Delta (PRD) region of China. A three-wavelength photo-acoustic soot spectrometer (PASS-3) and aerosol mass spectrometers (AMS) were used to explore the relationship between the measured AAE and the relative abundance of organic aerosol to BC. The regression and extrapolation analysis revealed that the more realistic AAE values for "pure" BC aerosol were 0.86, 0.82, and 1.02 at 405 nm, and 0.70, 0.71, and 0.86 at 532 nm, in the campaigns of urban_winter, urban_fall, and rural_fall, respectively. Roadway tunnel experiments were also conducted, and the results further supported the representativeness of the obtained AAE values for "pure" BC aerosol in the urban environments. Finally, the average aerosol light absorption contribution of BrC was quantified to be 11.7, 6.3, and 12.1 % (with relative uncertainties of 4, 4, and 7 %) at 405 nm, and 10.0, 4.1, and 5.5 % (with relative uncertainties of 2, 2, and 5 %) at 532 nm, in the campaigns of urban_winter, urban_fall, and rural_fall, respectively. The relatively higher BrC absorption contribution at 405 nm in the rural_fall campaign was likely a result of the biomass burning events nearby, which was supported by the biomass burning simulation experiments performed in this study. The results of this paper indicate that the brown carbon contribution to aerosol light absorption at shorter wavelengths is not negligible in the highly urbanized and industrialized PRD region.
Developing E-mode p-channel field-effect transistors (p-FETs) on the standard p-GaN gate HEMT epi-wafer is highly motivated to facilitate the realization of gallium nitride (GaN) complementary logic (CL) circuits and power-integrated circuits (PICs). The gate etching process is commonly employed in the fabrication of E-mode GaN p-FETs. However, due to gate etching-induced damage, the performance of E-mode GaN p-FETs often fails to meet expectations. To address the above issue, a post-etch wet treatment technique was developed in this work to enhance the performance of E-mode GaN p-FETs. The fabricated GaN p-FET with ${L}_{\text {G}}$ = 2 $\mu \text{m}$ exhibits an E-mode operation with ${V}_{\text {th}}$ = −2.9 V. The p-FET with post-etch wet treatment exhibits a current density of 5.4 mA/mm. Compared to the p-FET without wet treatment (1.9 mA/mm), the current density has increased by more than double. Atomic force microscopy (AFM) was utilized to characterize the surface morphology and validate the effectiveness of post-etch wet treatment. To suppress the leakage current, multienergy fluorine ion implantation was implemented for planar isolation of GaN p-FETs, high ${I}_{\text {ON}}/{I}_{\text {OFF}}$ with over $6\times 10^{{5}}$ was obtained.
The p-GaN gate active-passivation HEMT (AP-HEMT) suppresses dynamic R ON degradation owing to the screening effect by mobile holes against the surface traps and the hole emission effect that pumps out the buffer traps. Therefore, the function of AP-HEMT heavily relies on the hole injection into the active passivation from the gate terminal, and thus the gate/p-GaN contact needs to be an ohmic junction. Unlike the more popular Schottky-type p-GaN gate HEMT where a larger gate driving margin is possible, the Ohmic-type p-GaN gate HEMT suffers from a tight gate driving margin (~3.5 V) which makes it difficult to use from the circuit designers' perspective. In this work, we develop an E-mode metal/insulator/p-GaN gate active-passivation HEMT (MIP-AP-HEMT) which includes a main transistor and a D-mode HEMT network. The main transistor features an MIP gate structure which enlarges the gate driving margin. The D-mode HEMT network features two integrated small D-mode HEMTs to provide a well-controlled gate current that supplies mobile holes for active passivation, and to provide a low-resistance path between p-GaN and gate metal to maintain a stable threshold voltage. The fabricated MIP-AP-HEMT demonstrates a large gate driving margin of 19.4 V, while maintains a highly stable threshold voltage and an effective suppression of dynamic R ON degradation.
GaN power devices exhibit deteriorated dynamic ${R}_{\text {ON}}$ after hot electron stress (HES) as new defects/traps are generated at surface or in buffer layer. In this work, we propose a virtual-body p-GaN gate HEMT (VB-HEMT) to improve the ruggedness against hot-electron induced degradation. In the ON-state, the holes injected from p-GaN gate reach the interface between the GaN channel layer and the buried AlGaN layer, forming a hole channel that serves as a "virtual body". The virtual body screens the hot-electron induced buffer trapping. Additionally, the surface trapping effect is also alleviated in the VB-HEMT, which is likely caused by the spillover of holes from virtual body to the surface or by the hole/electron recombination that emits photons to accelerate the recovery of surface trapping. The suppression of hot-electron induced dynamic ${R}_{\text {ON}}$ degradation is verified by HES test with various stressing time, stressing voltage, and stressing current.
The hot-electron-related reliability is an important issue for GaN power devices under harsh operation condition or environment. These high-energy electrons can scatter toward the device surface or buffer layer, introducing newly generated traps/defects and resulting in the degradation of dynamic ON-resistance (RON). This work investigates the dynamic characteristics in active-passivation p-GaN gate HEMTs (AP-HEMTs) after hot-electron stress (HES). Unlike the dielectric passivation whose dynamic RON performance is often reported to severely worsen as hot-electron-induced defects/traps accumulate, the active passivation is found to have a superior robustness against hot-electron stress. In this study, after an HES of 30 min with VD = 200 V and IS = 10 mA/mm, the dynamic RON/static RON of a conventional HEMT increases dramatically from 3.63 to 9.35 for VDS-OFF = 650 V, whereas that of AP-HEMT only shows a slight increase from 1.51 to 1.85. Two mechanisms have been experimentally proved for the improved hot-electron robustness in AP-HEMT. (i) The mobile holes in active passivation layer can effectively screen the preexisting and/or newly generated surface defects/traps from affecting the 2DEG channel. (ii) The recovery of buffer trapping is accelerated by hole injection from gate and active passivation.
The method of upper bound triangular velocity field is used to calculate the temperature jump during high-speed wire finish rolling. Fourier's simplified heat conduction law is used to calculate the temperature drop during the wire finish rolling. Due to the high - speed and poor heat dissipation, it is simplified when calculating the temperature change of the finishing mill. The temperature jump and heat transfer between the roll and the rolling wire are calculated during the rolling deformation zone. The temperature drop caused by the heat radiation of the rolling wire is calculated in the non-deformed zone. Compared with the actual temperature change when a high-speed wire rod was rolled 1Cr13 martensitic stainless steel φ5.5mm wire, the results show that the calculated values of temperature change is about 3.64% lower thanmeasured.
A latching acceleration switch with cylindrical contacts is presented in this paper. The cylindrical contacts can make the switch immune to the fabrication imperfection and off sensitive axis shocks, as well as decrease the contact resistance. Moreover, all the contacts and their beams are separated from the proof-mass so as to prevent the contacts from the impact resulting from the rebound or vibration of the proof mass once the switch is latched. The switch was fabricated by low-cost process and tested. The measured latching shock is 4500 G and the response time is less than 0.1 ms. The total on-resistance is less than 3 ohms while the insulation resistance is more than 200 M ohms and the maximum allowable current is up to 130 mA.
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