Wolfspeed: Managing Risks and Alternative Sourcing Strategies

It has been a long time since Wolfspeed's financial deterioration became a topic of industry conversation. However, there remains a significant gap between recognizing "management risk" and making the decision, "how do we address this next?" This article aims to bridge that gap by organizing the structure of the risks and exploring realistic alternative procurement options.

What is Happening at Wolfspeed? — An Outline of its Finances in Numbers

In fiscal year 2024 (ending June 2024), Wolfspeed faces a structural deficit, with net losses exceeding $1 billion despite sales in the approximately $800 million range. The issue is not a single year of poor performance, but rather the direct impact on earnings from a large investment in a 200mm (8-inch) SiC wafer factory in New York's Mohawk Valley, combined with a mismatch between capacity and utilization due to sluggish EV demand. With reports emerging that the company plans to change its name from Wolfspeed to Cree Energy Solutions in 2025, ongoing revisions to its business strategy cast doubt on the effectiveness of its long-term supply agreements.

Wolfspeed's position in the SiC wafer market remains significant. Its share, cultivated during the 6-inch wafer era, and its early investment in the transition to 200mm have earned it a reputation as the "most scalable supplier." However, in a situation where financial strength is being tested, this "early mover" advantage can become a disadvantage. When there is no clear path to recouping investments, the prioritization of long-term supply agreements and production adjustment risks become more tangible.

This graph illustrates an unusual situation where net losses exceed sales. The confluence of a demand plateau during the equipment investment recovery period has rapidly eroded financial leeway. If the design and procurement plans were based on supply stability, a reassessment of those premises becomes a realistic option.

Interpreting It Not as "Supply Disruption" but as "Supply Uncertainty"

This is not to say that Wolfspeed will immediately cease operations. The problem is more nuanced, which is precisely why it tends to be addressed belatedly. What often occurs with financially distressed suppliers is not an abrupt halt in supply, but rather changes affecting quality and reliability, such as "concentration on priority customers," "extended lead times," and "increased inclusion of off-spec lots."

In the selection of SiC MOSFETs, short-circuit withstand time (SCWT) is a critical parameter that determines the design margin for protection circuits. It indicates the time until the device is destroyed during a load short-circuit, acting as a "time limit" for the gate driver's protection function to intervene.

Since this short-circuit withstand time varies under multiple conditions, including drain voltage, gate voltage, and junction temperature, the basis for judgment should not solely rely on the typical values in the datasheet but also on verification under actual operating conditions. For Microchip's 700V/1200V SiC MOSFETs, typical values are stated as 3μs under specific conditions, serving as the starting point for design margins.

When relationships with suppliers who grasp these detailed specifications falter, cases where the "spec-sheet compatibility" and "actual operational compatibility" of alternative parts do not align are likely to occur. When considering alternative procurement, evaluating based on compatibility with protection circuits, rather than a side-by-side comparison of spec sheets, provides a more accurate picture.

The Capabilities of Alternative Suppliers — Where Differences Emerge

Currently, several manufacturers offer products in the 1200V class SiC MOSFET market. From both a technical perspective and a practical procurement standpoint, notable developments are occurring both domestically and internationally.

Mitsubishi Electric has announced that it has significantly improved short-circuit withstand time by introducing a p-type protective layer into its trench-type SiC-MOSFETs. While trench structures tend to reduce on-resistance compared to planar types, they also face challenges with device damage due to electric field concentration during short circuits. The p-type protective layer is a design change that directly addresses this weakness, demonstrating technical integrity.

Rohm's 4th generation SiC MOSFETs are said to achieve both low on-resistance (RonA) and high short-circuit withstand capability through a proprietary device structure. These two parameters are typically in a trade-off relationship, where improving one often compromises the other.

Onsemi offers a full lineup of SiC MOSFETs, SiC diodes, and SiC modules ranging from 650V to 1700V under the "EliteSiC" brand. They are said to possess the production scale to meet large volume demands, particularly for EVs. The wide range of voltage classes can make them a choice when aiming to cover multiple applications with a single supplier.

The fact that each company is addressing the same challenge of short-circuit withstand capability with different approaches provides more than just a simple spec comparison for decision-making. Determining which approach is most compatible with your company's protection circuit design can be a clue in narrowing down alternative candidates.

Compatibility with Protection Circuits — A Hard-to-See but Essential Check

When considering alternatives for SiC MOSFETs, a simple side-by-side comparison of datasheets fails to reveal compatibility with protection circuits. SiC devices have smaller dies and higher current densities compared to silicon (Si). Consequently, they experience faster temperature rises during short circuits, leaving less time for protection mechanisms to act before device destruction occurs, even under the same current and voltage conditions.

DESAT (de-saturation) protection is a mechanism that monitors the drain-source voltage (VDS) in the on-state and turns off the gate when overcurrent is detected. This protection method, which utilizes the increase in VDS as saturation current rises, is widely adopted for SiC MOSFET short-circuit protection circuits.

For this protection to function, three parameters—the DESAT trigger threshold (VDESAT), DESAT current (IDESAT), and short-circuit blanking time—must be set appropriately for the actual operating conditions. If you switch to a device from a different manufacturer while using a protection circuit tuned for Wolfspeed's devices, discrepancies in these parameters may arise.

Furthermore, the short-circuit withstand capability of SiC MOSFETs tends to improve at higher temperatures. At higher temperatures, RDSon increases, limiting the saturation current and thereby reducing the short-circuit energy. This temperature dependency affects the setting of design margins, but since the magnitude of the temperature coefficient varies by device, verifying performance at the actual operating temperature of an alternative product will improve the accuracy of your judgment.

Four Pillars for Evaluating Alternative Procurement — Including Questions Beyond Specifications

Among these four pillars, the "product generation" perspective is often overlooked in practice. Even if an alternative product has equivalent specifications to the current one, if the supplier is moving towards next-generation products, the supply of the current product may be reduced within a few years. It is worthwhile to confirm the continuity of the roadmap to prevent the same problem from recurring after adoption.

With Wolfspeed's management risks now apparent, the core issue has shifted from "whether to continue using Wolfspeed" to "how to evaluate whether your company's SiC procurement is excessively linked to specific financial risks." While diversifying sources is self-evident, executing it while maintaining consistency in both technical and procurement aspects requires confirmation beyond spec comparisons, which lies at the heart of the problem.