Mechanism of improving forward and reverse blocking voltages in AlGaN/GaN HEMTs by using Schottky drain

In this paper, we demonstrate that a Schottky drain can improve the forward and reverse blocking voltages （BVs） simultaneously in A1GaN/GaN high-electron mobility transistors （HEMTs）. The mechanism of improving the two BVs is investigated by analysing the leakage current components and by software simulation. The forward BV increases from 72 V to 149 V due to the good Schottky contact morphology. During the reverse bias, the buffer leakage in the Ohmic- drain HEMT increases significantly with the increase of the negative drain bias. For the Schottky-drain HEMT, the buffer leakage is suppressed effectively by the formation of the depletion region at the drain terminal. As a result, the reverse BV is enhanced from -5 V to -49 V by using a Schottky drain. Experiments and the simulation indicate that a Schottky drain is desirable for power electronic applications.

A review of the etched terminal structure of a 4H-SiC PiN diode

The comparison of domestic and foreign studies has been utilized to extensively employ junction termination extension(JTE)structures for power devices.However,achieving a gradual doping concentration change in the lateral direction is difficult for SiC devices since the diffusion constants of the implanted aluminum ions in SiC are much less than silicon.Many previously reported studies adopted many new structures to solve this problem.Additionally,the JTE structure is strongly sensitive to the ion implantation dose.Thus,GA-JTE,double-zone etched JTE structures,and SM-JTE with modulation spacing were reported to overcome the above shortcomings of the JTE structure and effectively increase the breakdown voltage.They provided a theoretical basis for fabricating terminal structures of 4H-SiC PiN diodes.This paper summarized the effects of different terminal structures on the electrical properties of SiC devices at home and abroad.Presently,the continuous development and breakthrough of terminal technology have significantly improved the breakdown voltage and terminal efficiency of 4H-SiC PiN power diodes.

A Novel Ideal Ohmic Contact SiGeC/Si Power Diode with Graded Doping Concentration

A novel structure of ideal ohmic contact p^＋ （SiGeC）-n^- -n^＋ diodes with three-step graded doping concentration in the base region is presented, and the changing doping concentration gradient is also optimized. Using MEDICI, the physical parameter models applicable for SiGeC/Si heterojunction power diodes are given. The simulation results indicate that the diodes with graded doping concentration in the base region not only have the merit of fast and soft reverse recovery but also double reverse blocking voltage,and their forward conducting voltage has dropped to some extent,compared to the diodes with constant doping concentration in the base region. The new structure achieves a good trade-off in Qs-Vf-Ir ,and its combination of properties is superior to ideal ohmic contact diodes and conventional diodes.

Reverse blocking characteristics and mechanisms in Schottky-drain AlGaN/GaN HEMT with a drain field plate and floating field plates

In this paper, a novel A1GaN/GaN HEMT with a Schottky drain and a compound field plate （SD-CFP HEMT） is presented for the purpose of better reverse blocking capability. The compound field plate （CFP） consists of a drain field plate （DFP） and several floating field plates （FFPs）. The physical mechanisms of the CFP to improve the reverse breakdown voltage and to modulate the distributions of channel electric field and potential are investigated by two-dimensional numer- ical simulations with Silvaco-ATLAS. Compared with the HEMT with a Schottky drain （SD HEMT） and the HEMT with a Schottky drain and a DFP （SD-FP HEMT）, the superiorities of SD-CFP HEMT lie in the continuous improvement of the reverse breakdown voltage by increasing the number of FFPs and in the same fabrication procedure as the SD-FP HEMT. Two useful optimization laws for the SD-CFP HEMTs are found and extracted from simulation results. The relationship between the number of the FFPs and the reverse breakdown voltage as well as the FP efficiency in SD-CFP HEMTs are discussed. The results in this paper demonstrate a great potential of CFP for enhancing the reverse blocking ability in A1GaN/GaN HEMT and may be of great value and significance in the design and actual manufacture of SD-CFP HEMTs.

Technological Analysis on Motor Stall and Its Perspective

The brush lock is due to assembly tightly during assembling three gripper so that it curls after some time in motor and bare motors.The motor happen to have current decreasing and cause rotary too slowly is an important technique problem.At last the motor hasn’t worked due to disconnection.It give company to bring assembly issue for customers.So the motor stall is main issue in motor working.We shall pay more attention to it necessarily and shall be strict quality inspection and we shall monitor the flow line for the sake of decreasing it.We shall solve the problem as soon as possible and communicate with the customer engineers.Unloaded rotation is radical in the base inspection.The engineer need to negotiate with supplying engineers for the qualified material of brush.Increasing inspection into more times is a method to decrease unqualified brushes.Some experiment method is explained to analyze for customer engineers.Two kinds of motors ie.stepping and asynchronous motor and motors used in future in car is explained to further knowledge to motor’s application.Such as the experiment with torque,voice and electric voltage converter.The pseudo soldering results the slow rotary.The reverse voltage is a reason for a motor to slow rotary even stall.

Experimental research on the relationship between bypass diode configuration of photovoltaic module and hot spot generation

A hot spot is a reliability problem in photovoltaic(PV) modules where a mismatched or shaded cell heats up significantly and degrades the PV module output power performance. High PV cell temperature due to a hot spot can damage the cell encapsulate and lead to second breakdown, which both cause permanent damage to the PV module. In present systems, bypass diodes are used to mitigate the hot spot problem. In this work, five commercial polysilicon P V modules configured with different numbers of bypass diodes are used to study the influence of bypass diodes on the reverse bias voltage of a shaded cell and the resulting hot spot phenomenon. The reverse bias voltage of the shaded cell, and the hot spot probability and severity decrease as the number of bypass diodes increases. Negative terminal voltage of a shaded cell accompanied by a switched-off bypass diode are the necessary condition for hot spot generation. In an extreme case where each cell has an individual bypass diode in a P V module, it still cannot avoid the hazards of a hot spot under the shading areas of 5-7 cm2, but the probability of a hot spot is reduced to a minimum of 0.41%.