“5723745d3f14" target="_blank">SiC Thorough Technology Development and Product Verification Required”
Gate oxide reliability, short circuit robustness, etc. must be considered.
Use of proven products ensures application lifespan
[Editor's Note] According to the data,
SiC power semiconductors are expected to grow at an average annual rate of 72% until 2025. This is because SiC is rapidly emerging as a core component of automobiles to improve the efficiency of automobile batteries and minimize power consumption as the importance of electrification of automobiles, autonomous driving, and in-vehicle computing increases. As the importance and demand for
SiC power semiconductors increase, the issue of selecting reliable SiC semiconductors has also become important. This is because it is necessary to carefully consider how the necessary development or reliability verification process should be conducted differently depending on the product selection. Accordingly, this magazine has prepared an opportunity to point out important points in selecting SiC power semiconductors through
Infineon 's '
CoolSiC™ White Paper - How does Infineon achieve and verify the reliability of SiC power semiconductors? '
■ It is essential to recognize the significant differences in SiC material properties and operation modes.epaper#!?fileId=5546d46272e49d2a01735723745d3f14" target="_blank">SiC power semiconductors significantly improve the figure of merit of power conversion switching devices, enabling superior system performance, increasing efficiency and power density in many applications, reducing system costs, and enabling new applications and topologies.
On the other hand, to fully utilize the benefits of SiC, thorough technology development and product verification procedures must be followed to achieve the life and quality required in power conversion systems.
In particular, although similar to silicon semiconductors, there are significant differences in material properties and operation modes, so careful consideration must be given to how these differences will affect the final application operation and how the required development or reliability verification processes should be different.
.jpg)
▲This figure shows the defects generated during a marathon test on three groups of SiC trench MOSFET samples with different extrinsic defect densities. It shows the Weibull distribution. The test results obtained at VGS=30V were converted to the gate operating voltage of VGS=18V using the linear E-model. F and t are as described in Figure 1. (Source:
Infineon )
■ SiC-based devices require additional reliability testing than Si devices SiC power devices fundamentally use the same device design as silicon devices, but a deeper analysis reveals that SiC-based devices require additional reliability testing that is different from Si-based devices.
This is because the specific structural defects of the material itself, different anisotropic mechanical properties, and wider band gap affect the interface trap density and dynamics in MOS-based devices.
This is because the electric field between the material itself and external boundaries such as the device edge is up to 10 times higher during operation, and it operates in a new operating mode involving high-voltage operation and fast switching.
This requires verification for application and accuracy of SiC-based power devices.
■ Gate oxide reliability for improved FIT rate and lifespanm=referral&utm_campaign=202202_ap_ko_ipc_ipc.p.sic&utm_content=article&utm_term=korea.sicwhitepaper#!?fileId=5546d46272e49d2a01735723745d3f14" target="_blank">To make SiC MOSFETs as reliable as silicon devices, the gate oxide defect density must be minimized during the manufacturing process.
In addition, innovative testing techniques must be developed to filter out vulnerable devices, including through final electrical testing.
By filtering out devices that cause major defects while keeping those that do not or only cause minor defects alive, we can achieve significantly improved gate oxide reliability.
Additionally, DC BTI can be a major reliability issue in SiC devices. This drift must be minimized through device process optimization and thorough testing using appropriate measurement techniques.
▲NBTI time course when using -25 V stress bias at 200℃. Through process improvements,
Infineon 's
SiC MOSFETs have been able to reduce the total drift to almost the same level as Si (silicon) power MOSFETs. (Source:
Infineon )
7197" id="hwpEditorBoardContent">
■ Short circuit robustness Typical industrial IGBTs are designed to withstand a short-circuit time of about 10 μs, while
SiC MOSFETs have no short-circuit withstand capability or only a few μs.
On the other hand, looking a little deeper, it is clear that there are types of IGBTs that cannot handle short circuits, and that by using a specific cell design with SiC MOSFETs, the short circuit capability can be raised to the same level as an IGBT.
Additionally, the decision to enhance short-circuit robustness in the form of guaranteed short-circuit withstand time must be made carefully, and if it is decided to state this in the data sheet, steps must be taken to verify the performance of production devices.
723745d3f14" target="_blank">Infineon's
CoolSiC™ MOSFET products are known to have a short-circuit withstand time specification of up to 3 μs, and they are known to conduct 100% testing at the package level prior to shipment with this specification.
■ Preventing bipolar degradation and suppressing stacking defects by optimizing chip production process Any type of SiC device can experience bipolar degradation during bipolar operation. In this case, the current is very low due to the stacking fault, generating almost no heat, and reducing the active area of the SIC device.
To prevent bipolar degradation from reducing the active area of SiC devices and causing data sheet deviations, optimization of chip production processes to suppress sheeting defects and effective verification are required.
.png)
▲Thermal image (EMMI) images of the device in conduction mode, with a SiC MOSFET having several defects (small black arrow-shaped triangles) and a SiC MOSFET without defects. The colors represent current density (blue is low, red is high), and the dark black lines are inactive areas of the device. (Source:
Infineon )
■ Product-level verification In order to launch a product, tests such as HTRB, H3TRB, and HTGS must be conducted mandatorily, and the results must be documented and provided in a Product Qualification Report (PQR) for each product.
In the case of
Infineonsource=e4ds&utm_medium=referral&utm_campaign=202202_ap_ko_ipc_ipc.p.sic&utm_content=article&utm_term=korea.sicwhitepaper#!?fileId=5546d46272e49d2a01735723745d3f14" target="_blank">It is known that these tests are conducted for at least 3,000 hours to confirm that CoolSiC™ MOSFETs operate reliably, and it appears that high reliability can be confirmed through these tests.
In particular, it is critical that SiC devices use special passivation schemes that are robust enough to operate reliably in real-world applications.
■ For automobiles, verification requirements are more stringent The validation requirements for automotive are more stringent than those for commercial use.
To meet the quality standards for automotive applications, △highly variable usage conditions and loads △15+ year lifespan △ppb level quality target/OEM wants no failures △high reliability according to AEC Q-100/101 is required.
Especially with the growth of electric vehicles in the automotive market, longer stress times are required and new stress conditions must be applied to understand the behavior of new technologies under real-world application conditions.
Additionally, robustness testing must be conducted at a level much higher than standard testing.
In addition, the same high-voltage product for electric vehicles must be able to operate reliably in various operating modes. In charging mode, it must reach an operating time of more than 30,000 hours with a consistently high DC link voltage, and in driving mode, it must reach 8,000 hours with a wide voltage range depending on the high junction temperature and battery performance.It also has the latest features, such as pre-heating the driver's seat before using the car by time reservation or remote control, and the operating time can reach up to 3,000 hours.
Here, humidity resistance is required for automotive components. This is because SiC devices are particularly sensitive to humidity-related failure mechanisms than silicon-based devices.
Regarding this, the white paper stated that Infineon has passed tests under high humidity conditions by using materials with high humidity resistance for edge passivation.
▲Quality coverage can be increased starting from AEC-Q101, the automotive standard for discrete devices. (Source:
Infineon )
sonlen="5582" id="hwpEditorBoardContent">
As discussed above, various comprehensive verification approaches have been proposed to ensure the reliability of
.
On the other hand, this is something that Infineon is implementing, and it is necessary to develop industry standards for device verification at the industry level.
and resolve quality-related issues more easily and quickly.
.png)
