Insulated Gate Turn-Off Thyristors: The High-Voltage Silicon Power Switch

The electrification of the global economy is accelerating at a staggering pace. From the proliferation of electric vehicles (EVs) and the massive expansion of renewable energy grids to the insatiable power demands of artificial intelligence data centers, the modern world is fundamentally dependent on power electronics. At the very heart of these systems lies a critical component: the high-voltage power semiconductor switch. For over forty years, the workhorse of this domain has been the Insulated Gate Bipolar Transistor (IGBT). However, as the world pushes the boundaries of efficiency and power density, the traditional silicon IGBT is reaching its theoretical limits. Enter a revolutionary breakthrough that is poised to rewrite the rules of power conversion: the Insulated Gate Turn-Off Thyristor, or IGTO.

Hailed as the first major high-voltage silicon power semiconductor innovation since the introduction of the IGBT in the 1980s, the IGTO represents a generational leap in semiconductor physics. By merging the unparalleled current-carrying capacity of a thyristor with the precise, high-speed switching control of an insulated gate, the IGTO delivers a highly efficient, cost-effective, and scalable solution that keeps silicon at the forefront of the global energy transition.

To truly understand the magnitude of the IGTO breakthrough, it is essential to trace the evolutionary lineage of power semiconductors. Power switches are the "valves" of the electrical world, turning current on and off thousands of times per second to convert and regulate electrical energy.

In the early days of power electronics, the standard Thyristor, or Silicon-Controlled Rectifier (SCR), was the dominant force. Featuring a four-layer NPNP semiconductor structure, the thyristor is renowned for its immense current-carrying capability and extremely low conduction losses. Once turned on, a thyristor "latches" into a conductive state. However, it possesses a fatal flaw for modern high-frequency applications: it cannot be turned off by the control gate. To turn off a standard thyristor, the main circuit current must be externally forced to zero, making it impractical for compact, high-speed power conversion.

Engineers eventually developed the Gate Turn-Off Thyristor (GTO) and later the Integrated Gate-Commutated Thyristor (IGCT). While these devices could be turned off via a gate signal, they required massive, energy-hungry gate drive circuits to extract the necessary current, making them bulky and expensive.

In the 1980s, the IGBT revolutionized the industry. By combining the simple, voltage-controlled insulated gate of a MOSFET with the high-voltage, high-current bipolar nature of a standard transistor, the IGBT became the undisputed king of power electronics. It allowed for relatively fast switching and easy control, cementing its place in everything from household appliances to bullet trains. Yet, the IGBT relies on a three-layer PNP or NPN structure, which fundamentally limits its current density and conduction efficiency compared to the four-layer thyristor.

For decades, engineers chased the "holy grail" of power electronics: a device that possesses the low conduction losses and high power density of a thyristor, but with the simple, low-energy voltage-controlled turn-off of an IGBT. The Insulated Gate Turn-Off Thyristor (IGTO) is the realization of that dream.

At its core, the IGTO features a four-layer NPNP architecture, which inherently forms parasitic NPN and PNP bipolar transistors within the silicon. When the device is turned on, the product of the current gains (betas) of these two transistors exceeds unity. This triggers a "breakover" or latching effect, flooding the drift region with charge carriers and plunging the device's on-state resistance to incredibly low levels. This is why the IGTO can achieve up to 30 percent lower conduction losses than state-of-the-art IGBTs at high currents and high temperatures.

The true magic of the IGTO, however, lies in its turn-off mechanism. Unlike traditional thyristors that require brute-force current extraction, the IGTO utilizes a highly advanced cellular trench gate structure. When a turn-off voltage is applied to the insulated gate, the internal electric fields aggressively modulate the base width of the internal transistors. This action forcefully drops the product of the transistor betas below one, breaking the thyristor latch-up and rapidly sweeping carriers out of the conduction path.

This differentiated operational physics allows the IGTO to be turned off with the exact same low-power voltage signal used by an IGBT, while operating at high switching frequencies. The result is a component that operates with the thermodynamic efficiency of a thyristor but is driven exactly like an IGBT.

The commercialization of this physics breakthrough has been spearheaded by Pakal Technologies, a cutting-edge silicon innovator headquartered in San Francisco. Backed by significant venture capital, including a $25 million Series B funding round in early 2025, Pakal has successfully transitioned the IGTO from theoretical physics to mass-producible reality.

Pakal’s proprietary IGTO(t)™ architecture utilizes a novel trench gate design that actively manages the electric fields and carrier dynamics within the silicon. One of the most critical aspects of Pakal's engineering is that the IGTO(t) was designed from the ground up to be a direct "drop-in" replacement for modern IGBTs.

In the highly risk-averse world of power electronics manufacturing, forcing engineers to redesign circuit boards, gate drivers, and thermal management systems to accommodate a new component is a massive barrier to entry. Because the IGTO(t) mimics the gate-drive requirements of an IGBT and fits into existing power module footprints, manufacturers can upgrade their systems simply by swapping the silicon.

By adopting the IGTO, system designers immediately realize a cascade of system-level benefits. The 30% reduction in conduction losses dramatically lowers the amount of waste heat generated during power conversion. This improved thermal performance means that engineers can either push more power through the same physical space—increasing power density—or they can shrink the size and cost of the liquid or air-cooling systems required to keep the electronics from overheating.

In recent years, the power semiconductor industry has seen a massive influx of capital into Wide Bandgap (WBG) materials like Silicon Carbide (SiC) and Gallium Nitride (GaN). These materials offer incredible switching speeds and efficiency, but they come with a severe drawback: cost. Growing SiC crystals is notoriously slow, energy-intensive, and prone to defects, making SiC chips significantly more expensive than silicon.

While SiC has found a foothold in premium electric vehicles and specific high-frequency applications, the vast majority of the world's power conversion—over 95%—still relies on silicon. Silicon manufacturing is the most mature, heavily optimized, and cost-effective industrial process in human history.

The IGTO bridges the efficiency gap between traditional silicon and expensive SiC. By wringing unprecedented efficiency out of standard silicon wafers, the IGTO provides near-SiC performance at traditional silicon prices. Furthermore, because the IGTO relies on standard silicon fabrication techniques, it can be manufactured in virtually any of the world's existing silicon foundries. This eliminates the supply chain bottlenecks associated with wide bandgap materials and ensures that the technology can scale rapidly to meet the gigawatt-level demands of global electrification.

The introduction of the IGTO is not just a triumph of semiconductor physics; it is a catalyst for major advancements across multiple global industries. Because power conversion is a ubiquitous requirement, the efficiency gains of the IGTO ripple outward to transform a variety of sectors.

The range and performance of an EV are directly tied to the efficiency of its traction inverter—the device that converts the DC power from the battery into the AC power that drives the electric motor. By replacing traditional IGBTs with IGTOs, automakers can significantly reduce inverter losses. This translates directly into more miles of range per charge, or alternatively, allows manufacturers to use smaller, lighter, and cheaper battery packs to achieve the same range. Furthermore, the enhanced thermal performance of the IGTO reduces the strain on the vehicle's cooling system, saving even more energy and weight.

Solar and wind farms rely on massive high-voltage inverters to convert the variable power generated by nature into stable AC power for the electrical grid. In these multi-megawatt systems, even a 1% increase in efficiency can result in gigawatt-hours of additional energy captured over the lifespan of the equipment. The IGTO's lower conduction losses are perfectly suited for the continuous, high-current operation required in renewable energy systems, maximizing energy yield and accelerating the return on investment for green infrastructure.

The explosion of Artificial Intelligence has triggered an unprecedented surge in data center construction. AI training clusters utilize thousands of power-hungry GPUs, requiring massive amounts of electricity. Power distribution and conversion within these data centers generate immense heat, which in turn requires even more electricity to cool. The IGTO is uniquely positioned to optimize data center Uninterruptible Power Supplies (UPS) and power distribution units. By reducing conversion losses, data centers can achieve higher computational density per square foot while simultaneously lowering their exorbitant cooling costs and carbon footprints.

For heavy-duty applications such as rail traction, industrial motor drives, and massive grid-level energy storage, voltages often exceed 3,300 volts (3.3 kV). At these extreme voltages, standard silicon struggles, and SiC becomes prohibitively expensive. The IGTO architecture is highly scalable and maintains its thyristor-like low on-state voltage drop even as the blocking voltage rating increases. This makes it an ideal solution for the heavy industrial sector.

The transformative potential of the IGTO was cemented in February 2026, when Hitachi Energy—a global titan in grid infrastructure and electrification—announced a landmark collaboration with Pakal Technologies. This partnership represents the true commercial validation of the IGTO architecture on the global stage.

Under this agreement, Hitachi Energy is integrating Pakal’s IGTO(t) silicon power switches into its portfolio of market-leading high-voltage power modules. The collaboration specifically targets the highest-performing $\ge$ 3.3 kV power semiconductor modules. By combining Hitachi’s century-long expertise in advanced power module packaging with Pakal’s breakthrough silicon physics, the two companies are poised to deliver unprecedented reliability and efficiency for critical infrastructure.

Hitachi explicitly noted that the IGTO will be deployed in essential applications, including rail systems, energy storage, renewables, and AI infrastructure. For a conservative, reliability-focused sector like high-voltage grid integration to adopt a entirely new semiconductor architecture speaks volumes about the rigorous testing and undeniable performance benefits of the IGTO. As Niklas Persson, Managing Director of Hitachi Energy’s Grid Integration Business Unit, noted, this collaboration presents a critical opportunity to strengthen the global energy ecosystem at its very core.

We are standing at the precipice of the "Electrification of Everything". To successfully navigate this transition without overwhelming global energy resources or breaking the bank, continuous innovation in power electronics is mandatory. While wide bandgap materials like Silicon Carbide and Gallium Nitride will continue to carve out their respective niches, silicon remains the undisputed backbone of the global grid.

The Insulated Gate Turn-Off Thyristor (IGTO) breathes spectacular new life into silicon. By solving the forty-year-old engineering riddle of how to marry the raw current-carrying power of a thyristor with the elegant, high-frequency control of an insulated gate, the IGTO delivers a frictionless upgrade path for global industries. With mass production underway and deep-rooted partnerships with global conglomerates like Hitachi Energy, the IGTO is no longer just a theoretical concept. It is the new beating heart of high-voltage power conversion, ready to power a cleaner, more efficient, and fully electrified future.

Reference: