STMicroelectronics SiC New Fab: Mass Production Progress

STMicroelectronics' New SiC Factory: Is Mass Production "On Schedule"? — What Catania's Expansion Questions

As STMicroelectronics incrementally expands its SiC power semiconductor factory in Catania, Italy, it aims to capture demand from the EV and industrial sectors. Considering the scale and timing of its capital investment, along with the profitability pressures its SiC business faces, it becomes clear that this move is more than just a capacity increase.

Shifting from "Build It and They Will Buy" to "Can We Sell What We've Built?"

From 2024 to 2025, the SiC power semiconductor market has seen a series of downward revisions in demand forecasts. The pace of EV adoption has fallen short of initial optimistic scenarios, leading major manufacturers to re-evaluate their capital investment plans. STMicroelectronics is no exception.

STMicroelectronics experienced a 23% year-on-year decrease in sales for the full fiscal year 2024, a trend that has also impacted its SiC business. The company has centered its strategy on a vertically integrated SiC model—encompassing in-house substrate production, wafer manufacturing, and finished device assembly—primarily at its Catania plant. However, it is now facing scrutiny regarding the prospects for recouping its investments. The crucial question here is not "Is the factory operational?" but rather "At what pace will mass production ramp up, and what are the criteria for making that decision?"

The Structure of the Catania Factory and What Vertical Integration Entails

STMicroelectronics' Catania facility is at the heart of its SiC business. The company is committed to in-house production of SiC ingots and substrates, positioning this upstream integration in the supply chain as a key differentiator in terms of both wafer procurement costs and quality. The transition from 6-inch to 8-inch wafers is also progressing within this vertical integration framework.

The shift to 8-inch (200mm) SiC wafers is a challenge for the entire industry. Major players are already engaged in a race to secure next-generation wafers, as evidenced by Mitsubishi Electric's joint development of 8-inch SiC substrates with Coherent. STMicroelectronics, by seeking to address this challenge through in-house production at its Catania factory, adopts a different approach. The decision to combine external procurement with self-sufficiency directly hinges on whether the priority is supply risk or cost structure.

If successful, the vertical integration model can be a source of cost competitiveness. However, in periods of demand falling short of expectations, high fixed costs can easily strain management. STMicroelectronics is currently positioned within precisely this structural tension.

Short-Circuit Withstand Time: An "Opaque Quality Metric" Revealing the Essence of Mass Production Competition

Focusing solely on a factory's mass production capacity can lead to overlooking another critical issue: device reliability, specifically the short-circuit withstand time (SCWT) of SiC MOSFETs. SCWT is the duration a device can withstand a load short-circuit before failure, serving as an indicator of the margin available for protection circuits to safely shut down.

SiC devices, with their smaller die size and higher current density, experience faster temperature rise compared to Si devices. This necessitates protection circuits to operate in a shorter timeframe, imposing stricter design constraints. Ensuring this characteristic while maintaining uniform quality on the mass production line directly tests the maturity of manufacturing technology.

Microchip's SiC MOSFETs (700V/1200V rated) list a typical short-circuit withstand time of 3μs under specific conditions in their datasheets. More critical than this number itself is how the conditions are defined. Withstand time varies with three parameters: drain voltage, gate voltage, and junction temperature, tending to increase as conditions are relaxed. Consequently, a discrepancy can arise between the "datasheet value" and the "value under actual operating conditions."

This issue tends to become more pronounced as mass production scales up. Variations between manufacturing lots affect short-circuit withstand time, which in turn influences the design margins of protection circuits. This is an inherent challenge faced by all manufacturers accelerating SiC mass production, not just STMicroelectronics.

What Differentiates Competitors — Rohm and Mitsubishi Electric's Direction for "Structural Improvement"

Short-circuit withstand time and on-resistance (Ron) exist in a trade-off relationship. Efforts to enhance a device's robustness against short circuits tend to increase on-resistance and consequently conduction losses. How manufacturers resolve this trade-off reflects differences in their technological prowess.

Mitsubishi Electric is reported to have significantly improved short-circuit withstand time by introducing a p-type protective layer into its trench-type SiC MOSFETs. Rohm's fourth-generation SiC MOSFETs reportedly achieve a balance of low on-resistance (RonA) and high short-circuit withstand time through their proprietary device structure. While detailed structures can be ascertained within the scope of publicly available information, reproducibility in mass production is central to competitiveness.

The specific approach STMicroelectronics is employing at its Catania factory is difficult to ascertain from public information. However, given that it is pursuing in-house process control through vertical integration, the design freedom for device structures may be greater than with external outsourcing. How this translates into performance metrics like short-circuit withstand time and RonA can be understood by examining the datasheets of mass-produced products.

System-Wide Robustness Determined by "Combination" with Protection Circuits

When discussing a device's short-circuit withstand time, the protection functions of the gate driver IC cannot be ignored. The DESAT (desaturation) function, widely used for SiC MOSFET short-circuit protection, monitors the drain-source voltage (VDS) during the on-state and turns off the power transistor upon detecting overcurrent. The timing before protection is activated—the blanking time—becomes a critical issue in alignment with short-circuit withstand time.

In designing DESAT protection, the three main parameters for adjustment are the trigger threshold voltage (VDESAT), DESAT current (IDESAT), and the short-circuit blanking time. If the blanking time is too long, protection may not activate before the device fails. If it is too short, the risk of malfunction due to noise increases. This "appropriate window" varies depending on the absolute value of the short-circuit withstand time of the SiC MOSFET being used and the operating conditions (drain voltage and temperature).

When evaluating STMicroelectronics' SiC products, it is essential to consider not only the device's individual withstand capability but also the system's protection margin when used in combination with gate drivers from the same or affiliated manufacturers. Particularly when applying 1200V rated devices in industrial inverters or automotive powertrains, it is necessary to evaluate them in conjunction with the expected junction temperature range and the temperature dependence of short-circuit withstand time (as junction temperature rises, RDSon increases, leading to a tendency for higher withstand time due to reduced saturation current).

"Where" to Monitor Mass Production Progress — Criteria for Design and Procurement Decisions

There are several points to consider regarding STMicroelectronics' Catania expansion from both design and procurement perspectives.

Firstly, on the technical front, the timing of the transition from 6-inch to 8-inch wafers and the announcement of mass production yields serve as key indicators. As the transition to 8-inch progresses, it is expected that more chips of equivalent performance can be produced from a single wafer, leading to a decrease in unit price. However, quality variations tend to increase during the transition period. Therefore, evaluating the lot-to-lot reproducibility of short-circuit withstand time at an early stage can provide valuable information for shortening subsequent qualification steps.

Secondly, from a supply risk standpoint, the fact that STMicroelectronics is pursuing in-house production through vertical integration needs to be considered in a context separate from supplier concentration risk. While a model independent of external wafer procurement internalizes procurement risk, it also has the aspect of manufacturing-related issues cascading from substrates and wafers to devices. When evaluating SiC products from multiple sources, it is worthwhile to recognize this structural characteristic of STMicroelectronics' supply system.

This graph illustrates the range of voltage ratings. It is publicly announced that onsemi covers from 650V to 1700V in its portfolio, which can be interpreted as a breadth of application coverage spanning industrial, EV, and renewable energy sectors. STMicroelectronics also covers automotive and industrial applications, primarily with its 1200V products, but precise comparisons of voltage rating configurations are best confirmed by consulting each company's latest product listings.

As "visible indicators" of mass production progress, tracking the following three points will provide technical and business insights: ① the conditions and values of short-circuit withstand time listed in datasheets, ② announcements regarding the 8-inch transition and actual mass production start dates, and ③ the status of automotive qualification (AEC-Q101) acquisition. The pace at which STMicroelectronics' Catania expansion builds実績 will partially reveal its answers at the time of the next earnings announcement and the release of evaluation reports for mass-produced products.