Masaru Nagao

SiC—Emerging Power Device Technology for Next-Generation Electrically Powered Environmentally Friendly Vehicles

The automotive industry is developing a range of electrically powered environmentally friendly vehicles such as hybrid vehicles (HVs), plug-in hybrid vehicles, full electric vehicles, and fuel cell vehicles to help reduce tailpipe CO2 emissions and achieve energy diversification. HVs are regarded as one of the most practical types of environmentally friendly vehicle and have already been widely accepted in the market. Toyota Motor Corporation has positioned HV systems as a core technology that can be applied to all next-generation electrically powered environmentally friendly vehicles and is currently working to enhance the performance of HV system components. Because of its low loss and high-temperature operation properties, silicon carbide (SiC) is regarded as a highly promising material for power semiconductor devices to help reduce the size and weight of the power control unit, one of the key components of a HV system. Wide-ranging activities are under way to meet the challenges of adopting SiC in an automotive environment, such as the development of crystal growth technologies, device structures, process technologies, defect analysis, and application to on-board systems. This paper describes the current situation and future prospects for on-board SiC power devices and the development of SiC-based technologies.

A Silicon Micromachined Gyroscope and Accelerometer for Vehicle Stability Control System

A silicon micromachined gyroscope (angular rate sensor, yaw rate sensor) and accelerometer for vehicle stability control system is presented. The 5.1mmX4.7mm sensor chip is fabricated with a silicon micromachining process using a SOI (Silicon on Insulator) silicon wafer and a deep reactive ion etching. The sensor chip has a pair of resonators which are mechanically coupled and function as a tuning fork. The resonators are driven by electrostatic force and their movements are detected by capacitively sensing angstrom displacements. This sensor chip works not only as a gyroscope but also as an accelerometer with a single senior chip. The sensor unit consists of the sensor chip above, a signal processing IC, a microcomputer and an EEPROM. sigma-delta analog-to-digital conversion (sigma-delta ADC) is adopted to realize the digital calibration of sensor properties. Sigma-delta modulators on the signal processing IC convert the analog signals of angular rate, acceleration and temperature into oversampled 1-bit digital data. These data are transmitted to the microcomputer and converted into high-resolution, multi-bit digital data through the process of digital decimation filter. Sensor variation is calibrated by the microcomputer with the calibration data which has been stored in the EEPROM.

Application of Electrical Circuit Simulations in Hybrid Vehicle Development

This paper describes the application of electrical circuit simulations in intelligent power module development for hybrid vehicles, electric vehicles, and fuel cell vehicles. The limitations of the conventional design and simulation systems are discussed, and efforts for overcoming these limitations are described. The introduction of a physics-based insulated-gate-bipolar-transistor model with a surface-potential MOSFET core into the design flow is described. Finally, future expectations for necessary simulation technology development are given.

Impact of Surface Morphology above Threading Dislocations on Leakage Current in 4H-SiC Diodes

The impact of threading dislocation density on the leakage current of reverse IV characteristics in 1.2 kV Schottky barrier diodes (SBDs), junction barrier Schottky diodes (JBSDs), and PN junction diodes (PNDs) was investigated. The leakage current density and threading dislocation density have different positive correlations in each type of diode. For example, the correlation in SBDs is strong, but weak in PNDs. The threading dislocations were found to be in the same location as the current leakage points in the SBDs, but not in the PNDs. Nano-scale inverted cone pits were observed at the Schottky junction interface in SBDs, and it was found that leakage current increases in these diodes due to the concentration of electric fields at the peaks of the pits. These nano-scale pits were also observed directly above threading dislocations. In addition, this study succeeded in reducing the leakage current variation of 200 A-class JBSDs and SBDs by eliminating the nano-scale pits above the threading dislocations. As a result, a theoretical straight-line waveform was achieved.

Bus driver IC for use in vehicle multiplexing communications

A prototype of a bus driver IC for use in communications, and particularly suited in multiplexed bus operation in an automotive vehicle environment, has been developed. The bus driver consists of amplitude and time matched complementary current sources which minimize bus radio frequency radiation. Bus driving system analysis is presented, together with details of the bus driver IC design. The reduction of the level of radiated radio noise was examined from two approaches: from restraining abrupt transitions in the bus voltage and current, and from using amplitude and time matched complementary signals. The current control type driver had better characteristics in restraining the abrupt transition of the bus voltage and current than the voltage control type.<<ETX>>