Why is Gallium nitride important?
Gallium nitride can conduct electrons more efficiently and can withstand higher electric fields than silicon. It exceeds the performance capability of silicon in speed, temperature, power handling and is replacing silicon-based devices in a variety of power conversion and RF applications. The ability of GaN-based systems to offer greater efficiency, significantly reduced size and weight, and improved thermal performance is creating a displacement cycle in traditional silicon markets and enabling new applications such as lidar and RF envelope tracking.
Can GaN replace silicon?
In 1978 the silicon power MOSFETs was launched as a faster alternative to the slower and aging bipolar devices. The early adopters of the power MOSFET were applications where the bipolar just was not fast enough. The signature example for its adoption was the switching power supply for the desktop computer and from there the MOSFET went on to become the power conversion device of choice for the semiconductor industry.
The dynamics of this transition taught us that there are four key factors controlling the adoption rate of a new power conversion technology:
- Does it enable significant new applications?
- Is it easy to use?
- Is it VERY cost effective to the user?
- Is it reliable?
Now, GaN has assumed the position as the presumptive replacement for the aging power MOSFET, but in order for it to take the mantle as the semiconductor technology of choice, it must meet four requirements that all new technologies must meet to this leadership position. So, let’s look at the four key attributes and see where GaN stands in addressing them.
Does it enable significant new applications?
The early success of GaN-based power transistors and integrated circuits initially came from the speed advantage of GaN compared with silicon. GaN-on-Si transistors switch about 10 times faster than MOSFETs and 100 times faster than IGBTs. Applications such as RF envelope tracking for 4G/LTE base stations and light detection and ranging (lidar) systems for autonomous cars, robots, drones, and security systems were the first volume applications to take full advantage of GaN’s high-speed switching ability.
Not only were GaN transistors faster than Si MOSFETs and IGBTs, they were much smaller – about 5 to 10 times smaller. This opened many applications in robotics and medical electronics as well as satellites and drones.
Is it easy to use?
GaN transistors (specifically eGaN FETs) are very similar in behavior to the aging power MOSFETs, and therefore power systems engineers can use their design experience with minimal additional training. To assist design engineers up the learning curve, EPC published the industry’s first GaN transistor textbook (in English and Chinese) – GaN Transistors for Efficient Power Conversion. The second edition was published in 2015 and the third edition in 2019 by J. Wiley & Sons. These textbooks are available through Amazon as well as textbook retailers. Two application-focused handbooks to further assist power designers of DC-DC conversion and wireless power transfer systems in the use of GaN are also available. Additionally, more than 100 universities around the world are working with GaN devices to prepare the next generation of highly-skilled power system designers to extract the highest performance from this technology.
GaN transistors and integrated circuits from EPC are produced using processes similar to silicon power MOSFETs, have many fewer processing steps, and more devices are produced per manufacturing run because GaN devices are much smaller than their silicon counterparts. In addition, lower voltage (<500 V) GaN transistors do not require the costly packaging needed to protect their silicon predecessors. This packaging advantage alone can cut the cost of manufacture in half and, combined with high manufacturing yields and small device size, has resulted in the cost of a GaN transistor from EPC to be lower in cost than a comparable (but slower, bigger) silicon power MOSFET.
To date, several manufacturers of GaN transistors have reported excellent results from in-house stress testing. EPC has established a rigorous reliability program which includes testing parts to the point of failure to establish an understanding of the amount of margin between the data sheet limits, and more importantly, an understanding of the intrinsic failure mechanisms. By knowing the intrinsic failure mechanisms, the root cause of failure, and the device’s behavior over time, temperature, electrical or mechanical stress, the safe operating life of a product can be determined over a more general set of operating conditions.
EPC continues to publish results of this testing, and the Phase 12 Reliability report details field reliability data over 123 billion hours of operation that is unmatched by silicon power devices.
The four requisite attributes for GaN to displace the silicon MOSFET have been achieved.
But this is just the beginning for GaN. Even the latest devices on the market are about 300 times larger than they would be if they could be made at the theoretical limits for GaN.
The most significant opportunity for GaN to impact the performance of power conversion systems comes from the intrinsic ability to integrate both power-level and signal-level devices on the same substrate. EPC has been producing GaN ICs since 2014 with the goal to drive toward complete systems on a single GaN-on-Si chip where the user supplies a logic level input and out comes high-performance power conversion.
Smaller, faster, lower cost, and more integrated…this is “Why GaN?”