It has been found that the analytical extraction methods cannot be applied to the usual test structure of the switch high electron-mobility transistor (HEMT) with a large-value gate grounded resistor. The significant effect of the precise multicapacitive current path on switch model precision has also been found. The multicapacitive current path here is different from the seemingly similar hypothesis proposed for the distributed parasitic effects at high frequencies (eg, D-band). In fact, for switch based HEMT, it is important to distinguish between the capacitive current paths accurately even at relatively low frequencies. Due to the existing of the large gate resistance, the usual capacitance mix decreases the accuracy of the switch model significantly. Thus an analytical method has been developed to calculate parasitic capacitances (the capacitance to ground and the interelectrode capacitance) through full-wave electromagnetic analysis. For practical applications and further verification, the whole HEMT switch small-signal models and the direct extraction methods are presented. The simulated results fit well with the measurements up to 40 GHz. K E Y W O R D S electromagnetic analysis, high electron-mobility transistor, interelectrode parasitic capacitance, microwave switches, small-signal model 1 | INTRODUCTION In 1988, Dambrine et al.proposed an analytical way to extract FET small-signal equivalent circuit parameters. 1 All the parasitic parameters were analytically extracted by using cold-FET method. After de-embedding all the parasitic effects from the whole S parameters, the intrinsic parameters were calculated by analytical equations. 2 De-embedding methods, cold-FET techniques, and analytical equations 3 are used by lots of FET small-signal model extraction methods today. Note that Reference 1 also has some limitations, for example, the pinch-off intrinsic model used to determine the parasitic capacitance parameters tends to overestimate the value of the drain to ground capacitance (C pd ). The high positive gate bias condition used to determine the parasitic inductances and resistances have the potential to destroy the gate Schottky diode. 4 In addition, for high electron-mobility transistors (HEMTs), it is difficult to apply enough high gate bias to ignore the gate capacitance effect. 5,6 Many works are making improvements to meet the needs of new semiconductor technologies and new applications like high frequency applications. 7-11 The small-signal modeling is also the basis of the large-signal and noise modeling. [12][13][14] As stated above, lots of articles and effort has been dedicated to common-source FET small-signal modeling, but high-frequency switch FET small-signal modeling is still difficult. Very few works concern switch FET small-signal modeling. [15][16][17][18][19][20][21] Numerical solutions concern intrinsic effects only and are difficult to meet measured behavior. [15][16][17] The simplified equivalent circuits cannot capture full feature of the switch HEMT at high frequencies. 18,19...

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In recent years, the algae-bacteria symbiotic system has played a significant role in the sustainable development of wastewater treatment. With the continuous expansion of research outputs, publications related to wastewater treatment via algal-bacterial consortia appear to be on the rise. Based on SCI-EXPANDED database, this study investigated the research activities and tendencies of algae-bacteria symbiotic wastewater treatment technology by bibliometric method from 1998 to 2017. The results indicated that environmental sciences and ecology was the most productive subject categories, followed by engineering. Bioresource Technology was the most prominent journal in this field with considerable academic influence. China (146), USA (139) and Spain (76) had the largest amount of publications. Among them, USA was in a leading position in international cooperation, with the highest h-index (67) in 79 countries/territories. The cooperation between China and USA was the closest. The cooperative publishing rate of the Chinese Academy of Sciences was 83.33%, but most of them were in cooperation with domestic institutions, while international cooperation was relatively limited. Methane production, biofuel production, and extracellular polymeric substance were future focal frontiers of research, and this field had gradually become a multi-perspective and inter-disciplinary approach combining biological, environmental and energy technologies.

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An improved HBT small-signal parameter extraction procedure is presented in which all the equivalent circuit elements are extracted analytically without reference to numerical optimization. Approximations required for simplified formulae used in the extraction routine are revised, and it is shown that the present method has a wide range of applicability, which makes it appropriate for GaAs-and InP-based single and double HBT's. Additionally, a new method is developed to extract the total delay time of HBT's at low frequencies, without the need to measure 21 at very high frequencies and/or extrapolate it with 20 dB/dec roll-off. The existing methods of finding the forward transit time are also modified to improve the accuracy of this parameter and its components. The present technique of parameter extraction and delay time analysis is applied to an InGaP/GaAs DHBT and it is shown that: 1) variations of all the extracted parameters are physically justifiable; 2) the agreement between the measured and simulated-and-parameters in the entire range of frequency is excellent; and 3) an optimization step following the analytical extraction procedure is not necessary. Therefore, we believe that the present technique can be used as a standard extraction routine applicable to various types of HBT's.

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This paper presents a new solution to a particular problem of high electron‐mobility transistor (HEMT) equivalent‐circuit modeling, that is, complete parasitic‐capacitance‐shell extraction of high‐frequency single‐gate and dual‐gate switch‐based HEMTs, which is very important to the accuracy of high‐frequency HEMT switch models, but not important in the conventional common‐source HEMT modeling for amplifier‐applications. A full‐wave electromagnetic (EM) analysis based method is proposed to analytically extract the complete parasitic‐capacitance‐shell of single‐gate and dual‐gate switch‐based HEMTs. All the 6 parasitic capacitances of the single‐gate switch‐based HEMT and all the 10 parasitic capacitances of the dual‐gate switch‐based HEMT are extracted by linear equations. No resistance parameter is needed to calculate the capacitance‐to‐ground and the interelectrode‐capacitance, and for the first time, all the 10 parasitic capacitances of the dual‐gate switch‐based HEMT are completely considered and analytically extracted. Then, a consistent and systematic modeling procedure of single‐gate and dual‐gate switch‐based HEMT is verified. With the complete parasitic‐capacitance‐shells extracted, the accurate intrinsic model of the single‐gate HEMT can be directly embedded into the parasitic‐shell of the dual‐gate HEMT. The predicted scattering parameters of the single‐gate and dual‐gate series switches fit well with the measurements up to 40 GHz, and accurate linear scalability are also found.