High-Voltage Silicon MOSFETs, GaN, and SiC: All have a place
Questions have arisen about how silicon will compete against wide bandgap (WBG) materials such as Silicon Carbide (SiC) and Gallium Nitride (GaN). There are many different technologies used in high voltage silicon devices today and though Si MOSFETs and WBG technologies will be the focus of this article, IGBTs are reviewed as they are a competing technology within the high voltage market. The MOSFET, IGBT, and JFET (WBG) technologies breakdown as follows:
- Conventional planar technology
- Superjunction technology
- Non-punch through (NPT) technology
- Punch through (PT) technology
- Field stop (FS) technology
- Conventional planar structure
- Normally “ON”
- Normally ”OFF”
There is a lot of interest in the WBG technologies such as SiC and GaN and the purpose here is to show that both Si and WBG materials (SiC and GaN) all have their place within the power industry and neither will completely displace each other.
The power MOSFET market in 2010 was $5.85B with an expected growth of 10.3% to $9.56B in 2015. Silicon conventional planar devices range from voltages under 100V to greater than 1000V, with superjunction ranging from 500V thru 900V and IGBTs from 600V and up to and including 1200V (for this discussion).
This paper defines that equal to and greater than 400V are classified as high voltage devices. The 400V and greater voltage MOSFETs are the fastest growing segment out of all MOSFETs. In 2011 this segment represented $2.05B growing at a CAGR of 12.4% over the next five years. Out of this $2.05B, superjunction devices account for around $500M growing close to $1B by 2016.
Today, much of the demand in superjunction devices is in the 500V to 650V range with a smaller portion in 800V and 900V. That being said just over $1.5B is represented by conventional planar devices with the largest market segments being computer, office equipment, and consumer.
Though IGBTs represent just under a billion dollars (less than 600V to greater than 900V) of the high-voltage device market they have been the fastest growing since the beginning of 2010. A couple reasons for this growth were the demand for solar inverters and a redesign in white goods where China has enacted a five year plan to reduce energy consumption.
If one compares the two Si MOSFET technologies (superjunction and conventional planar) and Si IGBTs based on a similar die size this is what you would see:
Superjunction (performance driven)
· Lower conduction losses: ability to reduce on-resistance four times over a similar voltage conventional planar.
· Lower switching losses: based on the same on-resistance, the ability to reduce switching characteristics such as QGD and reverse transfer capacitance (Crss)
Conventional Planar (value driven)
- Based on the same on-resistance of a superjunction device:
o Greater robustness: due to the larger die size, therefore better for unclamped inductive switching (UIS).
o Better thermals: larger die to dissipate the heat across
- Higher value: lower manufacturing costs, one step Epi growth
- Easier to design in with lower switching speeds
IGBTs (value and performance driven)
· Lowest cost – for the same current rating, IGBTs have higher current density than both Si MOSFET technologies
· Superior for low frequency high power applications
These advantages listed above will ultimately allow silicon technologies to continue to compete into the future as SiC and GaN come online.