Investigation of lateral spreading current in the 4H-SiC Schottky barrier diode chip

Lateral current spreading in the 4H-SiC Schottky barrier diode (SBD) chip is investigated. The 4H-SiC SBD chips with the same vertical parameters are simulated and fabricated. The results indicate that there is a fixed spreading resistance at on-state in current spreading region for a specific chip. The linear specific spreading resistance at the on-state is calculated to be 8.6 Ω/cm in the fabricated chips. The proportion of the lateral spreading current in total forward current (P sp) is related to anode voltage and the chip area. P sp is increased with the increase in the anode voltage during initial on-state and then tends to a stable value. The stable values of P sp of the two fabricated chips are 32% and 54%. Combined with theoretical analysis, the proportion of the terminal region and scribing trench in a whole chip (K sp) is also calculated and compared with P sp. The K sp values of the two fabricated chips are calculated to be 31.94% and 57.75%. The values of K sp and P sp are close with each other in a specific chip. The calculated K sp can be used to predict that when the chip area of SiC SBD becomes larger than 0.5 cm2, the value of P sp would be lower than 10%.

INVESTIGATION OF THE EFFECTS OF DIFFERENT RETROGRESSION AND RE-AGING PARAMETERS APPLIED TO THE 7075 ALLOY ON THE MICRO-ARC OXIDATION PROCESS

In this paper, retrogression and re-aging (RRA) heat treatment was applied to 7075 aluminum alloy in T6 condition at different times (30 and 90[Formula: see text]min) and temperatures (180∘C and 240∘C). While RRA heat treatments increase the corrosion resistance of the material, it does not harm its mechanical properties. On the other hand, the surface resistance of aluminum is low. Surface modifications are applied to overcome this deficiency. Among these, the micro-arc oxidation (MAO) method increases the corrosion resistance and attains excellent values in surface hardness. To better understand the RRA/MAO relationship, heat-treated (RRA) samples with four different parameters were coated with the MAO method. In this way, a ceramic oxide coating layer was created on the material surfaces. In order to determine the RRA parameter effect, the MAO process parameters are kept constant (anode voltage ([Formula: see text]): 500[Formula: see text]V, cathode voltage ([Formula: see text]): 300[Formula: see text]V, anode voltage open time ([Formula: see text]: 300[Formula: see text][Formula: see text]s, cathode voltage open time ([Formula: see text]): 200[Formula: see text][Formula: see text]s, frequency: 160 coating with Hz, and process time: 20[Formula: see text]min). Surface properties (coating thickness, surface roughness, surface arc duct’s structure, etc.), phase analysis (X-ray diffraction (XRD)) and microstructures (coating cross-section studies: distance-dependent hardness, coating/backing material interface character, coating porosity ratio) were examined. XRD analysis showed that the main phase of the coatings is [Formula: see text]-Al2O3. A coating layer of around 125[Formula: see text][Formula: see text]m was achieved with the growth rate of 6[Formula: see text][Formula: see text]m/min. Surface roughness was between 5.5[Formula: see text][Formula: see text]m and 8[Formula: see text][Formula: see text]m for different RRA parameters. RRA/MAO relation with the characterization made was detailed, and predictions were made for the surface properties of the material (hardness, corrosion resistance, wear, etc.).