We demonstrated 3.3 kV silicon carbide (SiC) PiN diodes using a trenched ring-assisted junction termination extension (TRA-JTE) with PN multi-epitaxial layers. Multiple P⁺ rings and width-modulated multiple trenches were utilized to alleviate electric-field crowding at the edges of the junction to quantitively control the effective charge (Q_eff) in the termination structures. The TRA-JTE forms with the identical P-type epitaxial layer, which enables high-efficiency hole injection and conductivity modulation. The effects of major design parameters for the TRA-JTE, such as the number of trenches (N_trench) and depth of trenches (D_trench), were analyzed to obtain reliable blocking capabilities. Furthermore, the single-zone-JTE (SZ-JTE), ring-assisted-JTE (RA-JTE), and trenched-JTE (T-JTE) were also evaluated for comparative analysis. Our results show that the TRA-JTE exhibited the highest breakdown voltage (BV), exceeding 4.2 kV, and the strongest tolerance against variance in doping concentration for the JTE (N_JTE) compared to both the RA-JTE and T-JTE due to the charge-balanced edge termination by multiple P⁺ rings and trench structures.

Au Bonding wire, which has been widely used in the semiconductor PKG market, is being converted into Cu Bonding wire due to a sharp increase in Au price. The price of Cu is cheaper than Au and Pd coated wire products with improved reliability and workability have been introduced, bringing a large portion of Au Bonding wire usage. However, the sensitive structure of the PKG still uses Au Bonding wire, because of the problem of pad cratering due to the high workhardening of Cu, so the Au Bonding wire cannot be converted to a cheap Cu Bonding wire despite the high Au price. Recently, Ag alloy Bonding wire has been widely evaluated as a low cost Bonding wire for PKG with sensitive structure. However, like the Cu Bonding wire, a gas kit and an inert gas are required to prevent oxidation when forming a FAB (Free Air Ball, the following notation is unified FAB) for ball Bonding. In addition, the high-humidity reliability level of silver alloy Bonding wire is lower than that of Au Bonding wire. In this study, we evaluated the metal coated silver bonding wire as a next generation low cost bonding wire product to replace Au Bonding wire. In order to improve the disadvantages of the Ag alloy Bonding wire in which the elliptical FAB is formed when the inert gas is not used in the 1st ball Bonding, the noble metal coating is performed on the high purity Ag alloy Bonding wire. Gas free Bonding characteristics and high humidity reliability performance were evaluated according to the kind and thickness of noble metal. In the evaluation of high humidity reliability, metal coated silver Bonding wire showed a high humidity reliability performance more than 2 times compared to the conventional silver alloy Bonding wire. Metal coated silver Bonding wire is expected to be an alternative to the new low cost Bonding wire in the PKG market due to gas free Bonding and improved high humidity reliability performance.

We investigated the effects of gate bias regarding the degradation of electrical characteristics during gamma irradiation. Moreover, we observed the punch through failure of 1.2 kV rated commercial Silicon Carbide (SiC) Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) due to the influence of gate bias. In addition, the threshold voltage (V_T) and on-resistance (R_on) of the SiC MOSFETs decreased significantly by the influence of gate bias during gamma irradiation. We extracted the concentration of carriers and fixed charge (Q_F) in oxide using N-type SiC MOS capacitors and Transmission Line Measurement (TLM) patterns to analyze the effects of gamma irradiation. The Total Ionizing Dose (TID) effect caused by high-energy gamma-ray irradiation resulted in an increase in the concentration of holes and Q_F in both SiC and oxide. To analyze the phenomenon for increment of hole concentration in the device under gate bias, we extracted the subthreshold swing of SiC MOSFETs and verified the origin of TID effects accelerated by the gate bias. The Q_F and doping concentration of p-well values extracted from the experiments were used in TCAD simulations (version 2022.03) of the planar SiC MOSFET. As a result of analyzing the energy band diagram at the channel region of 1.2 kV SiC MOSFETs, it was verified that punch-through can occur in 1.2 kV SiC MOSFETs when the gate bias is applied, as the TID effect is accelerated by the gate bias.