1,721,170 research outputs found
Analysis of self-oscillating switched-mode circuit for low-voltage energy harvesting
No full textThe operation of a self-oscillating switched-mode circuit topology for low-voltage thermal energy harvesting is analysed and experimental efficiency results are presented. Circuit self-start-up function as well as high-efficiency power transfer are obtained by using only one transformer without additional inductors. It is shown that even without using a maximum power point tracking (MPPT) tracking circuit, it is possible to achieve efficiencies up to 65% over a relatively broad input voltage range which can be optimised by properly varying the transformer turns ratio n
Micro-power photovoltaic harvester based on a frequency-to-voltage MPPT tracker
No full textA micro-power circuit for photovoltaic energy harvesting applications is presented. The system can work in different lighting power ranging from a few tens of microwatts to milliwatts maintaining tracking of the maximum output power operational conditions of the photovoltaic cells. The energy harvesting efficiency ranges from 30 to 70%
Field Plate Devices for RF Power Applications
No full textThe aim of this chapter is to provide to the reader insights into field plate operation and itsgeometrical optimization. After giving some basic definitions concerning the operation of anRF-power device, which will be used in order to quantify the performance of the devicesstudied, the optimization of a gate-connected single field-plate GaAs-based pHEMT will bepresented. Field plate geometrical parameters will be varied in order to show how they canaffect device properties such as breakdown voltage, maximum output power and smallsignal performances. It will be thus possible to quantify the maximum improvement thatcan be achieved by using a gate connected single field plate. Finally, some advanced fieldplate structure will be discussed and compared in order to point out their advantages withrespect to the gate connected single field plate structure
Boost-converter-based solar harvester for low power applications
No full textA novel implementation of a solar harvester circuit based on a boost DC/DC converter topology is presented. The proposed circuit is able to harvest solar energy down to a power level of 1.6 mW while maintaining comparable performance with previously presented results at higher power levels
Off-state breakdown optimization in field plated GaAs-pHEMTs by means of two-dimensional numerical simulation
No full textThe optimization of a field plated pHEMT structure has been presented. It has been shown that by optimizing the FP length (LFP) and the SiN layer thickness the off-state breakdown voltage can be improved as much as four times for the selected pHEMT structure. Choosing the right SiN thickness (in this case in the 40-60nm range) and LFP (in this case in the 0.8-1.2um range) is crucial in order to obtain a significant benefit in the device off-state breakdown
A Novel Temperature Estimation Technique Exploiting Carrier Emission from Buffer Traps
No full textWe propose a novel technique for temperature estimation in electron devices based on the mutual correlation between emission time constant from traps ( τ ) and temperature ( T ). Arrhenius equation is employed as the physical model relating τ and T The reference system used to present the technique is AlGaN/GaN high electron mobility transistors (HEMTs) with Fe-doping in the buffer. Drain Current Transients (DCTs) are used for extracting the emission time constant ( τ ) from Fe traps and non-linear regression through Trust Region Reflective (TRR) optimization algorithm is used to learn the model parameters from data and infer device temperature. Electro-thermal device simulations are employed for validating the proposed technique, showing that this method is able to provide an improved accuracy with respect to conventional electrical techniques (e.g., McAlister method) promoting it as a valid alternative to state of-the-art optical techniques in GaN HEMTs
Dependence of Static and Dynamic GaN HEMT Characteristics from Fe-doped GaN Buffer Parameters
No full textThe influence of Fe-doped buffer parameters on the static and dynamic characteristics of GaN HEMTs have been analyzed by means of two-dimensional numerical simulations. Results obtained on the static characteristics of the simulated devices have shown that thick and highly doped buffers yield better performances in terms of device output conductance and subthreshold conduction, while leaving mainly unaffected other DC parameters. On the other hand, when dynamic characteristics are evaluated, a significant current collapse has been observed pointing out the importance of the correct design of Fe-doped buffer parameters in order to obtain state-of-the-art GaN HEMT performances
Evolution of on-resistance (RON) and threshold voltage (VTH) in GaN HEMTs during switch-mode operation
No full textThe evaluation and investigation of electrical parameters drifts during device operation is one of the mandatory task that has to be performed in order to improve GaN-power devices stability. In this work the authors would like to present a novel characterization method that allows the simultaneous monitoring of both RONand VTHduring the switch-mode operation. By applying the proposed measurement method with different operating parameters it has been possible to provide a preliminary interpretation of the physical mechanisms leading to the observed RONincrease and VTHpositive shift. In particular, the observed RONincrease, which is thermally activated with a 0.83eV activation energy, has been ascribed to the presence of Carbon-related traps within the device buffer layer. On the other hand, the positive VTHshift has instead been related to interface defects at the dielectric/III-N interface and/or to bulk traps in the gate dielectric
Experimental and Numerical Evaluation of RON Degradation in GaN HEMTs during Pulse-Mode Operation
Full text linkThe on-resistance (RON) degradation in normally-OFF GaN high electron mobility transistors has been evaluated both experimentally and by means of numerical simulations by analyzing its drift during device pulse-mode operation. Experimental data showed that the device RON measured during the on-time interval of the switching period increased with time resulting in a thermally activated process with an activation energy eV. For the first time, numerical simulations have been carried out in order to evaluate the device RON drift during pulse-mode operation and to understand the physical phenomena involved. A good qualitative agreement between experimental and simulated data has been obtained when considering in the simulated device simply a hole trap located at 0.83 eV from the GaN valence-band, an energy level which has been linked in previous works to carbon-doping within the GaN buffer
Experimental and numerical analysis of VTH and RON drifts in E-mode GaN HEMTs during switch-mode operation
No full textThe evaluation and investigation of electrical parameters drifts during device operation is one of the mandatory task that has to be performed in order to improve GaN-power devices stability. In this work the authors would like to present novel results concerning the analysis of V TH and R ON drifts in E-mode GaN HEMT observed during their switch-mode operation. Two different mechanisms are observed for the induced positive V TH shift. The first one is related to electron injection from the 2DEG into dielectric/semiconductor traps beneath the gate region of the device, while a second one linked to electron injection from the gate terminal induces a V TH shift linked to a localized negative trapping mechanism in the drain-edge of the gate terminal. The observed R ON increase is instead linked to a hole-emission process taking place in the gate-drain access region within the device carbon-doped buffer layers. The negative charge build-up related to the ionized acceptor traps leads to the 2DEG depletion and consequent R ON increase
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