Have GaN Transistors Become as Easy to Use as MOSFETs?


Scott Wolf, Executive Editor at EE Power

Scott Wolf

I began writing this article with the expectation that the answer to whether GaN transistors have become as easy to use as MOSFET would be “yes.” I also assumed I would find an abundance of online resources to help users easily utilize the power of this new transistor technology.

In my opinion, a great deal of improvement has occurred, and there are some very high-quality resources available. However, transistor manufacturers and vendors still have some work to do in propelling GaN transistor design resources to the same level that MOSFETs occupy.

 

Image 1: MOSFET vs. GaN transistor in structure and size. Image courtesy of Mouser Electronics.

 

Enjoying Your Work

In my experience, MOSFETs are a joy to use in the design of electronic circuits that require gain or low-loss switching. But why is this enjoyment so important?

 

For the Designer

The benefits of enjoyable work to the physical and mental well-being of the designer are obvious and well documented. Less obvious is that the designer may find it easier to stay on task and to give their work the time it deserves. We procrastinate far less on tasks we enjoy doing. 

 

For the Designer’s Client

Not only do we procrastinate less on tasks that we enjoy, but we also dig deeper into the technology supporting those tasks. It is far easier to “master” something that we enjoy. This all translates into better designs delivered to the client and often within an earlier timeframe. 

 

For the Part Supplier

In addition to the benefits mentioned above (which trickle down to the part supplier), the part supplier gains successful and loyal customers. Those attributes also bring a high level of loyalty to the parts provided.

 

Image 2: The structure of a MOSFET. Gate = G. Source = S. Drain terminals = D. B = Body. Image courtesy of Brews Ohare (CC BY-SA3.0).

 

Are MOSFETs Enjoyable to Work With?

An exceedingly rich set of engineering resources are available to the designer contemplating using MOSFETs, which is analogous to a shop with every tool you could ever need conveniently at your disposal. 

In precise terms, the resources available are listed below.

 

A Large Selection

As I write, there are over 6,000 unique discrete MOSFET part numbers listed on the website of popular distributor DigiKey. With numbers like these, finding a suitable transistor for your project is virtually guaranteed, regardless of what it may be. There are countless variations in current carrying capacity, gate capacitance, ON-state resistance, gate trigger voltage, and many other ratings. 

 

A Wide Range of Ratings

Designers frequently need to design circuits for products that will be offered in multiple variations using different power sources (battery, 120 VAC, 220 VAC, 240 VAC). For such products to act correctly, the transistors utilized need consistent behavior. The availability of MOSFET transistors with similar behavior, but different drain-to-source voltage ratings, makes it easy to design a range of circuits to work correctly with different product power voltages.     

More and more, designers are now asked to produce one circuit design that can handle several different power voltages. For these, the sheer number of varying transistor ratings and characteristics helps to make it possible to find one transistor that can cover all power voltage options (along with suitable features for automated circuit re-configuration or level-shifting).  

 

Innovations

I remember one of my first designs using a large power MOSFET back when they were still new. The transistors I selected had a very high current capacity (at the time), and the application took full advantage of this, which made them become quite hot and required the use of a fairly large heat sink to keep things cool. 

Eight years later, the vendor discontinued the part that we had been using, prompting a change to a more modern MOSFET. I was awe-struck when, even under full load, the heat sink and transistor rose barely above room temperature due to the incredibly low ON-state resistance of the new MOSFET. Innovations like this offer the designer some of the most powerful ways to impress the bosses or the clients they work for.

 

Support

Great engineering support can make difficult development situations seem like a walk in the park. Several major vendors of MOSFETs offer amazing support resources for design work, analysis work, regulatory agency work, supply-line optimization work, and many others. 

For example, many vendors now offer computer applications that can be used to design common circuits using their flavors of MOSFET. Larger vendor websites also offer Spice simulation models and CAD files. The reduction in design completion time realized by these tools can be huge.  

When support for a part is lacking, a frustratingly limited amount of information is available from the manufacturer's employees. Sometimes they don’t know much more than you do about their employer's new product. Even if they're scheduled to attend training sessions, that is no help when your design deadline is in a matter of days.

 

Education

Educational resources allow the user to gain a more complete knowledge of the part, which can facilitate maximum performance designs. Most every textbook, magazine, website, database, and library covering electronics today contains large amounts of resources on the use of MOSFETs. 

 

GaN Transistor Resources vs. MOSFET Resources

A one-to-one comparison of the characteristics of both types of transistors does show some substantial differences.

 

Table 1:  How MOSFET & GaN Technologies compare (Data from DigiKey)

Blue = Better 

Red = Less Desirable

  MOSFETs GaN Transistors Notes
Bandgap MOSFETs have a lower bandgap GaN junctions have a higher bandgap Thermal noise must be higher to spill over the bandgap, so GaNs can run hotter without losing performance. 
Switching   Junction capacities are much smaller Supports nano-second switching
Conductive Channel The conductive channel must be doped "n" type HEMET = High Electron Mobility Transistor — no doping required in the conductive channel Reduces electron scattering, which reduces on-state resistance and self-heating. Therefore, GaN transistors can be smaller for the same output.
Structure Somewhat complex structure  Simpler semiconductor stack structure Simpler and smaller = cheaper
Selection 6,000 p/n's ON DK 42 p/n's Discrete p/n's
Ratings

6V - 1,700V

.1 - 557A

0 - 20V

15V - 600V

.5A - 90A

5V (only)

Max drain-source voltage range

Max drain current

Gate drive voltage

Innovation MOSFETs have overlapped many GaN advantages GaN built on silicon — best of both worlds  Due to innovation, special MOSFETs have better Rds-ON than GaN.
Support Extensive and very good Limited but strong quality GaN support is rare, but it is of very high quality where it is available.
Education

Venues are saturated

55,600,000 

52,286 

Mentioned in new classes and books

2,330,000 

14,889 

 

Google hits

IEEE-Xplore papers

 

GaN Design Resources: It's Just a Matter of Time

In spite of their impressive properties and rapidly growing use by OEM manufacturers, GaN transistors are still suffering from the vicious cycle that plagues all new things: they are not used commonly because they are not well-known.

 

Image 3: The cross-section of a GaN Transistor. 

 

Manufacturers and vendors must develop more GaN design resources to reach the convenience level of MOSFET design resources. Designers need to discover their wonderful properties and use them in newer, more common designs. It’s just a matter of time.

 

About the Author

Over his successful 35-year-long career in electrical engineering, Scott Wolf received higher praise for his writing abilities than he did for his notable engineering skills. Scott’s superiors, colleagues, and friends regularly asked him to edit or write critically important business reports, documents, and correspondence.

Scott started his own business three years ago providing engineering consultation, freelance editing, persuasive writing, technical writing, online copy-writing, and correspondence writing services for a variety of clients and e-zine sites.

 

For example, if one looks up a fix for a Windows error online, Scott may have ghostwritten the solution. As an example of international writing exposure, Scott has written for an Australian electrical “tradie” e-zine after performing extensive research into Australian cultural, technical, and electrical-code norms.

His baccalaureate degree in electrical engineering from Purdue University equipped him to approach a very wide range of technical and scientific topics. Many years of business writing provided Scott with a deep understanding of goal-oriented writing and methods of persuasion.