Siyang Liu

Bio: Siyang Liu is an academic researcher from Southeast University. The author has contributed to research in topics: Gate oxide & LDMOS. The author has an hindex of 14, co-authored 136 publications receiving 759 citations. Previous affiliations of Siyang Liu include North Carolina State University.

Transverse ultra-thin insulated gate bipolar transistor having high current density

Abstract: A transverse ultra-thin insulated gate bipolar transistor having current density includes: a P substrate, where the P substrate is provided with a buried oxide layer thereon, the buried oxide layer is provided with an N epitaxial layer thereon, the N epitaxial layer is provided with an N well region and P base region therein, the P base region is provided with a first P contact region and an N source region therein, the N well region is provided with an N buffer region therein, the N well region is provided with a field oxide layer thereon, the N buffer region is provided with a P drain region therein, the N epitaxial layer is provided therein with a P base region array including a P annular base region, the P base region array is located between the N well region and the P base region, the P annular base region is provided with a second P contact region and an N annular source region therein, and the second P contact region is located in the N annular source region. The present invention greatly increases current density of a transverse ultra-thin insulated gate bipolar transistor, thus significantly improving the performance of an intelligent power module.

Repetitive Unclamped-Inductive-Switching-Induced Electrical Parameters Degradations and Simulation Optimizations for 4H-SiC MOSFETs

Abstract: In this paper, the electrical parameter degradations of high-voltage 4H-SiC MOSFETs under repetitive unclamped-inductive-switching (UIS) stresses were investigated experimentally. The holes injection and trapping into the gate oxide above the JFET region is identified to be the main degradation mechanism, resulting in the increase of OFF-state drain–source leakage current ( $I_{\mathrm {DSS}})$ and the decrease of ON-state resistance ( $R_{\mathrm {dson}})$ . However, during the repetitive UIS stresses, there is not obvious degradation observed for the threshold voltage ( $V_{\mathrm {th}})$ of the device. Moreover, three improved SiC MOSFETs structures, one with step gate oxide above the JFET region, one with step p-body region, and another one with floated shallow p-well in the middle of JFET region, were proposed to reduce the degradations under the repetitive UIS stresses.

Comprehensive Investigations on Degradations of Dynamic Characteristics for SiC Power MOSFET s Under Repetitive Avalanche Shocks

Abstract: In this work, degradations of dynamic characteristics for silicon carbide (SiC) power metal-oxide-semiconductor field-effect transistors under repetitive avalanche shocks are investigated in details. With the help of Silvaco TCAD simulations, gate capacitance versus gate voltage ( Cg – Vg ) measurement, and three-terminal charge pumping test, the main damaged position is demonstrated to be the SiC/SiO2 interface along junction FET (JFET) region instead of the body diode where most of the avalanche current passes through. Dominant avalanche degradation mechanism is then confirmed to be the injection of holes into the gate oxide above the JFET region. Since the channel region and the main junction of body diode are not seriously damaged by the avalanche stress, static parameters all remain stable. Meanwhile, due to the injection of holes, the depletion layer beneath the JFET region gets thinner, resulting in the increase of gate-drain capacitance ( C gd) under low drain-source voltage ( V ds) bias condition. It further takes responsibilities for the increments in input capacitance ( Ciss ), output capacitance ( Coss ), and reverse transfer capacitance ( Crss ). Moreover, it results in the extension of Miller plateau. Therefore, the increase of gate charge and delay of turn- off time after being stressed by repetitive avalanche shocks are monitored. Moreover, turn- on and turn- off dissipated energies after different unclamped-inductive-switching stress cycles are extracted. They are rarely influenced by the stress for the overlapping areas of voltage and current during switching procedures are relatively stable.

Comprehensive Analysis of Electrical Parameters Degradations for SiC Power MOSFETs Under Repetitive Short-Circuit Stress

Abstract: The degradations of electrical parameters for silicon carbide power MOSFETs under repetitive short-circuit (SC) stress are investigated in detail in this paper. It demonstrates that the generation of negative charges along the gate–oxide interface of the channel region is the dominant degradation mechanism, which results in the increase in the threshold voltage ( ${V}_{\text {th}}$ ) and the rise of ON-state resistance ( ${R}_{\text {dson}}$ ) under low gate voltage bias condition. Furthermore, degradations of dynamic characteristics including gate charge ( ${Q}_{\text {g}}$ ) and switching behaviors of the device after the repetitive SC stress are extracted and analyzed for the first time. It illustrates that the increased ${V}_{\text {th}}$ contributes to the rise of the Miller plateau voltage ( ${V}_{\text {gp}}$ ), which further leads to the increase in gate–source charge ( ${Q}_{\text {gs}}$ ). Meanwhile, the increase in the turn-ON time and the reduction of turn-OFF time are observed, which are also resulted from the positive shifts of ${V}_{\text {th}}$ and ${V}_{\text {gp}}$ , leading to the rise of turn-ON switching energy ( ${E}_{{ \text {on}}}$ ) and the decline of turn-OFF switching energy ( ${E}_{\text {off}}$ ), respectively.

Investigations on the Degradations of Double-Trench SiC Power MOSFETs Under Repetitive Avalanche Stress

Abstract: The degradations of electrical parameters for double-trench silicon carbide (SiC) power metal-oxide-semiconductor field-effect transistors (MOSFETs) under repetitive avalanche stress are investigated in this paper. The injection of hot holes into the bottom oxide of the gate trench during avalanche process is demonstrated to be the dominant degradation mechanism, while the channel is rarely influenced by the stress. The injected holes attract extra electrons in the SiC layer along the SiC/SiO2 interface, decreasing the ON-state drain–source resistance ( ${R}_{{dson}}$ ). Due to this reason, the threshold voltage ( ${V}_{{th}}$ ) of the device also reduces slightly. Moreover, other than static electrical parameters, dynamic characteristics including the gate–drain capacitance ( ${C}_{{gd}}$ ) and the switching characteristics of the device also degrade. After being stressed by repetitive avalanche stress, the depletion region beneath the bottom of the gate trench gets thinner, leading to the increase in ${C}_{{gd}}$ , which further influences the switching behaviors. The turn- ON and turn- OFF switching times of the device are calculated. It illustrates that the repetitive avalanche stress results in an obvious delay in the turn- OFF procedure, but hardly influences the turn- ON behaviors of the double-trench SiC MOSFET.

Silicon electro-optic micro-modulator fabricated in standard CMOS technology as components for all silicon monolithic integrated optoelectronic systems *

Abstract: In this paper, optoelectronic characteristics and related switching behavior of one monolithically integrated silicon light-emitting device (LED) with an interesting wavelength range of 400–900 nm are studied. Through the comparison of two types of geometry, Si avalanche-based LED and Si field-effect LED (Si FE LED), in the same device, we establish the dimensional dependence of the switching speed of the LED. Almost-linear modulation curve implies lower distortion is shown for the Si FE LED with light emission enhancement, and technology computer aided design (TCAD) simulations are in line with the experimental results. Our findings indicate that ON–OFF keying up to GHz frequencies should be feasible with such diodes. Potential applications should include Si FE LED integrated into the micro-photonic systems.

Superjunction Power Devices, History, Development, and Future Prospects

Abstract: Superjunction has arguably been the most creative and important concept in the power device field since the introduction of the insulated gate bipolar transistor (IGBT) in the 1980s. It is the only concept known today that has challenged and ultimately proved wrong the well-known theoretical study on the limit of silicon in high-voltage devices. This paper deals with the history, device and process development, and the future prospects of Superjunction technologies. It covers fundamental physics, technological challenges as well as aspects of design and modeling of unipolar devices, such as CoolMOS. The superjunction concept is compared to other methods of enhancing the conductivity of power devices (from bipolar to employment of wide-bandgap materials) to derive its set of benefits and limitations. This paper closes with the application of the superjunction concept to other structures or materials, such as terminations, superjunction IGBTs, or silicon carbide Field Effect Transistors (FETs).

Wireless power transmission with selective range

Abstract: The present disclosure describes a methodology for wireless power transmission based on pocket-forming. This methodology may include one transmitter and at least one or more receivers, being the transmitter the source of energy and the receiver the device that is desired to charge or power. The transmitter may identify and locate the device to which the receiver is connected and thereafter aim pockets of energy to the device in order to power it. Pockets of energy may be generated through constructive and destructive interferences, which may create null-spaces and spots of pockets of energy ranged into one or more radii from transmitter. Such feature may enable wireless power transmission through a selective range, which may limit operation area of electronic devices and/or may avoid formation of pockets of energy near and/or over certain areas, objects and people.

Wireless charging and powering of electronic devices in a vehicle

Abstract: Configurations and methods of wireless power transmission for charging or powering one or more electronic devices inside a vehicle are disclosed. A transmitter capable of single or multiple pocket-forming may be connected to a car lighter, where this transmitter may include a circuitry module and an antenna array integrated within the transmitter, or operatively connected through a cable. This cable may allow the positioning of the antenna array in different locations inside the vehicle suitable for directing RF waves or pockets of energy towards one or more electronic devices. Transmitter's configuration can be accessed by one or more electronic devices through Bluetooth communication in order to set up charging or powering priorities.

Wireless powered house

Abstract: The present disclosure may provide a wireless power system which may be used to provide wireless power transmission (WPT) while using suitable WPT techniques such as pocket-forming. Wireless power system may be used in a wireless powered house for providing power and charge to a plurality of mobile and non-mobile devices. Wireless powered house may include a single base station which may be connected to several transmitters. Base station may manage operation of every transmitter in an independently manner or may operate them as a single transmitter. Connection between base station and transmitters may be achieved through a plurality of techniques including wired connections and wireless connections.