Maxime Berthou

Monolithically Integrated Temperature Sensor in Silicon Carbide Power MOSFETs

This paper presents the first integrated temperature sensor in a SiC power mosfet. An analytical model has been proposed to assess its behavior up to 300°C. We present the tested design and its advantages compared to other solutions. We also propose possible optimizations in order to simplify it and reduce its size. 2.25 mm2 power mosfets have been fabricated with and without temperature sensor. Measurements show that the temperature sensor does not impact the power mosfet characteristics and its integration does not demand supplementary process steps. To demonstrate the functionality of our integrated sensor, we have calibrated the temperature dependence of its resistance to assess the internal temperature of the device at different bias.

Radiation Defects Produced in 4H-SiC Epilayers by Proton and Alpha-Particle Irradiation

Electronic properties of radiation damage produced in 4H-SiC epilayer by proton and alpha particle irradiation were investigated and compared. 4H-SiC epilayers, which formed the low doped n-base of Schottky barrier power diodes, were irradiated to identical depth with 550 keV protons and 1.9 MeV alphas. Radiation defects were then characterized by capacitance deep-level transient spectroscopy and C-V measurements. Results show that both projectiles produce identical, strongly localized damage peaking at ion’s projected range. Radiation defects have a negligible effect on dynamic characteristic of irradiated 4H-SiC Schottky diodes, however acceptor character of introduced deep levels and their high introduction rates deteriorate diode’s ON-state resistance already at very low irradiation fluences.

Study of 4H-SiC Schottky Diode Designs for 3.3kV Applications

The static performance of different active and termination area designs for SiC-based Schottky diodes, suitable for 3.3kV applications, were investigated by means of extensive numerical simulations. We found quantitatively that the high electric field of SiC close to avalanche-breakdown is shielded most effectively from the Schottky interface by a trench-based design. Moreover, we conclude that the edge termination design with junction termination extension and four implanted p+ guard rings is most robust against oxide interfacial charge.

Rapid and Efficient Oxidation Process of SiC by In Situ Multiple RTP Steps

Rapid Thermal Processing (RTP) has been evaluated as an alternative to conventional furnace technique for oxidation of 4H- and 3C-SiC. We show that the growth of the SiO2 films in a RTP chamber is orders of magnitude faster than in a conventional furnace. As well as being fast, this process leads to oxide films with quality comparable or even better than the one grown in classical furnaces. Studying different gas for oxidizing and annealing ambient, we demonstrate that SiO2/SiC interface is significantly improved when using N2O instead of O2 or even N2-O2 dilution.

4.5kV SiC MOSFET with boron doped gate dielectric

A new process based on Boron diffusion step to improve the SiO2/SiC interface quality is presented in this work. Surprisingly, Boron, a p-type dopant and small size atom, generates similar apparent improvements as previous oxide treatments based on large size atoms, n-type or deep levels dopants. This process has been applied to a thermal oxide grown to fabricate large area (up to 25mm2) 4.5kV 4H-SiC VDMOS. Fabricated devices show a significant improvement in terms of channel effective mobility, on-resistance, and 3rd quadrant behavior in comparison with counterparts without Boron oxide treatment.

Short-Circuit Capability Exploration of Silicon Carbide Devices

With the commercial availability of SiC power transistors, this decade will mark an important breakthrough in power transistor technology. However, in power electronic systems, disturbances may place them in short-circuit condition and little knowledge exist about their SC capability. This paper presents our study of SiC MOSFETs, JFETs and BJT under capacitive load short-circuit up to 600V.

Gate Oxide Stability of 4H-SiC MOSFETs under On/Off-State Bias-Temperature Stress

On- and off-state bias-temperature instability (BTI) measurements of 4H-SiC field effect transistors fabricated in a gate-oxide-first process were performed in the 30-450 °C temperature range. Stable operation under off-state stress at 300 °C is reported. On-state bias-instability stress revealed behavior consistent with the presence of hole traps in the SiC channel. The interface state density Dit increased from 2.5 eV-1cm-2 to 6.6 eV-1cm-2 as a function of positive stress duration.

Comparison of 5kV SiC JBS and PiN Diodes

Recent availability of large SiC wafer with reduced density of defects and maturity of our fabrication process permitted to fabricate 15A-5kV W-JBS (25 mm2) and 15A-5kV PiN (10 mm2) diodes on 4 wafers. We will present and compare their static characteristics. Several W-JBS diodes have been packaged and switched at 2.5kV to study their reverse recovery and demonstrate the major advantages of the SIC-JBS devices at high voltage.

Edge Termination Design Improvements for 10 kV 4H-SiC Bipolar Diodes

10 kV class 4H-SiC bipolar diodes have been fabricated. Two different edge terminations (Mesa/JTE or MESA/JTE with JTE rings) with two different junction bend radius have been designed and tested. Measurement results show that the inclusion of JTE rings improve the edge termination efficiency. The measurements indicate also a better reverse performance of diodes with larger bend radius.

Impact of layout on the surge current robustness of 1.2 KV SiC diodes

This work describes experimental surge current evaluation for various layout design of 1.2kV 4H-SiC JBS diodes. The silicon carbide devices working at temperatures significantly beyond to those of silicon power devices need specific reliability tests, adapted to high temperature operation and/or high power density of this new generation of power devices. Actually, it is not possible to predict the surge current capability by computer simulation because of 3-D effects that occur at high current density. Therefore the only available method for surge current characterization is the experiment. The use of 10ms sinusoidal power current pulses is able to evidence by the I-V characteristic, the temperature developed inside the diode during the power pulse, and the bipolar activation characteristic during the applied power.