GaN Device Development Enters a New Stage

December 2023 - The awards ceremony for the ‘”Ultra’’ Manufacturing Components Award was held in Tokyo.

The award is sponsored by Monozukuri Nippon Kaigi and Nikkan Kogyo Shimbun. 2023 marks the 20th year of the award, targeting components and materials that contribute to enhancing the competitiveness of Japan’s manufacturing industry as well as the development of both industry and society.
ROHM's EcoGaN™, a GaN device that significantly contributes to greater application energy-savings and miniaturization, received the ‘Electrical/Electronic Component Award’, one of six product awards.

From early on, ROHM has been involved in the development of GaN devices, which have been attracting attention worldwide in recent years. This recognition of ROHM’s technological expertise and product development strategy is not only welcome news for members of the Power Stage Product Development Department, which is still in its early stage of business, but was also a signal that the research and development carried out over many years had finally entered the next stage.

Prompted by Customer Feedback

The award was given in recognition of not only the GaN device itself, but also the entire product line, including gate driver ICs that maximize the performance of GaN.
According to Mr. Otake, who has been involved with GaN development for more than 15 years since the era of pioneering research, ‘This speaks to GaN’s position as a next-generation device.’

Surprisingly, when listening to customers who were not ready to adopt GaN, many expressed expectations related to ease of use, involving control-side drivers, package types, and even modularization that incorporates driver ICs.

ROHM’s Unique Approach

You could say that our track record and pride in continuing to produce analog ICs that respond to the needs of the times for more than half a century have inspired and ignited the spirit of our engineers. In the power supply IC field where ROHM excels, we have cultivated wide ranging development knowledge and expertise, along with the personnel and facilities capable of ensuring quality in mass production.

At the same time, we also possess significant advantages regarding GaN devices. Namely production expertise developed early on for mass producing blue GaN LEDs at ROHM Hamamatsu.
In the development process, where achieving high quality stable mass production of GaN crystals is crucial, being able to establish a development base right next to the LED manufacturing line was an invaluable driving force, he says.

A new project was launched to commercialize both power supplies and ICs, bringing together engineers with expertise and knowledge in different technologies. Full-scale development accelerated as we entered the 2020s.

Towards achieving a sustainable society

Here, let’s summarize the expectations for GaN devices along with their characteristics. The figure below is a distribution of applications mapped on the power/frequency axis, showing the dominant area of each power device. Unlike SiC power devices, which have shown increasing promise in recent years for switching in the high-power range, GaN is strong in applications requiring high-frequency operation in the MHz band.

One is improving switching efficiency in the high frequency range above the MHz band. Another important feature is the ability to significantly contribute to set miniaturization.

At this time, the areas where the highest demand is anticipated are the consumer sector, such as fast chargers, and data centers in the telecommunications field. More specifically, power consumption in the telecommunications sector is already estimated to account for 3-5% of the world’s total electricity consumption, and with the increasing number of servers for deep learning utilizing AI-equipped devices together with the advent of the era of Afull-scale autonomous driving, the communication volume is expected to increase by as much as 100- to 1000-fold.

From saving power in social infrastructure to reducing the size and weight of AC adapters, and even extending the flight range of drones, our goal is to provide the value of GaN to customers in a variety of fields not limited to specific applications. To this end, he says that the key phrase is to focus on creating 'GaN products that are easy to use.

At the same time, we asked Mr. Gunji, the engineer in charge, about the ‘difficulty in handling’ GaN from the viewpoint of device development.

Challenging the Gate Breakdown Barrier

As a countermeasure, there have been cases where gate resistors were added to the intermediate circuit to avoid overshoot, but this has a side effect of slowing down the switching speed, leading to repeated trial and error to avoid reducing the advantage over silicon devices.

There is an option of controlling overshoot internally by creating a module that includes a gate driver IC, which ROHM is concurrently developing, but it is also important to meet the demand for discrete components

How strong of a gate can be made... To meet and overcome this challenge head-on, it was necessary to make drastic changes to not only the semiconductor itself, but also to the manufacturing equipment.

The graph below illustrates the performance of <Strong GaN> (achieved after around two years of trial and error) compared to existing products.
Under the 5V drive standard, conventional GaN has a voltage margin of only about 1V, causing damage during overshoot. In contrast, ROHM’s newly developed gate source voltage technology supports voltages up to 8V. High reliability is ensured by providing 3x the voltage margin of previous models.

Dedicated GaN Gate Drivers

While the devices themselves are evolving toward GaN that is easier for customers to use, there have also been technological breakthroughs in the gate driver ICs that drive GaN. One solution that ROHM has come up with in the analog IC field is the development of a GaN-specific gate driver IC.

These insights were shared by Mr. Shinozaki, who joined the Power Stage Product Development Department as an IC design engineer. He remains highly motivated by the opportunity to put his considerable power supply IC development experience to use on this project.

The key phrase in this development is ‘speed in the nanosecond (ns) range.’
Overshoot is suppressed by adopting two special circuits. This enables ultra-fast switching with a minimum gate input pulse width of 1.25ns, maximizing the capabilities of GaN in applications.

Nano Pulse Control™ and System-in-Package

In addition, as the control circuit side also needs to support higher frequencies, ROHM's original power supply technology Nano Pulse Control™ is used as the cornerstone. One of three Nano power supply technologies released in 2017, this was developed by leveraging proprietary analog expertise that allow us to propose power supply solutions for applications requiring higher voltages and frequencies.

Mr. Ando, who like Mr. Shinohara who was recruited to the Power Stage Product Development Dept., mentions that he wants to develop products that further maximize the potential of Nano Pulse Control™ technology by combining with GaN.

Ando states that the controller IC utilizing Nano Pulse Control™ has already reached the level of commercialization. The company is now working at full throttle to develop an all-in-one product for the future.

The GaN device market is expected to become increasingly active as major overseas manufacturers are announcing their entry. However, there remains little doubt that ROHM will demonstrate its considerable expertise as a manufacturer capable of maximizing the performance of GaN from both the device and IC sides.

The evolution of GaN as the third pillar following silicon and SiC has finally entered a new stage.