Due to the ever-increasing for electric vehicles (EVs), manufacturers are comparing two semiconductor technologies for power electronics applications: silicon carbide and silicon.
Image credit: Buffaloboy/Shutterstock.com
Silicon carbide (SiC) offers high temperature resistance, reduced power consumption, stiffness, as well as supporting smaller, thinner designs that EV power electronics require.
Examples of SiC’s current applications include onboard battery chargers, onboard DC/DC converters, off-board DC fast chargers, automotive lighting for LEDs and EV powertrains.
According to Automotive World, future EV innovations could be enhanced by SiC technology as battery and motor manufacturers reach the physical limits of current technologies leading to the necessity to develop more efficient drivetrains.
During an interview with Semiconductor Engineering, Cree CTO John Palmour compared silicon carbide to silicon in a way that the EV industry, specifically engineers, can appreciate.
You can make the device in silicon carbide that you really wanted in silicon, but due to the physics of silicon isn’t practical in that voltage range.
John Palmour, CTO, Semiconductor Engineering, Cree
The Importance of Bandgap
Silicon carbide’s practicality in EV applications and other power electronics is down to the functionality of its wide bandgap, which is measured in electron volts (eV) and details the energy required to excite electrons from a material’s valence band into its conduction band.
Silicon (Si) has been the semiconductor material of choice for some time for the wafers used in integrated circuits (ICs) and photovoltaics, with a bandgap of 1.12 eV. Gallium arsenide (GaAs), a semiconductor typically used in solar cells, has a bandgap of 1.42 eV. In contrast, silicon carbide has a considerably wider bandgap of 3.26 eV.
Due to the wider bandgap, silicon carbide is well-suited for higher-power applications and the greater temperatures associated with them. Bandgap is related to breakdown voltage, the point at which a section of the insulator becomes electrically conductive.
The breakdown voltage of Silicon is around 600 V, but SiC-based devices can tolerate voltages up to ten times higher. As bandgap shrinks as temperature rises, wider bandgap materials can also tolerate much higher temperatures.
The rigidity of Silicon carbide produces a stable structure that will not expand or contract under the duress of heat.
Silicon carbide’s wider bandgap also facilitates faster, more efficient switching and more compact, thinner devices. SiC devices can be less than a tenth of the thickness of Si devices because silicon carbide’s voltage difference, or electric potential difference, does not need to be spread across as much material.
These rapid and compact solutions have less resistance leading to a reduction in energy and heat loss, meaning greater efficiency. Additionally, silicon carbide’s higher thermal conductivity enables the efficient transportation of heat and can reduce or eradicate the necessity for heat sinks.
SiC Devices for EV Power Electronics: Advantages and Challenges
As reported in IEEE Spectrum, Cree estimated that the market for silicon carbide devices exceeded $100 million (USD) for the first time last year, globally. Today, the company’s SiC solutions are promoting various high voltage, high temperature components in the expanding market for electric vehicles.
Because an EV’s various systems are powered by different voltages, some Si devices have to convert and section out the appropriate voltages to window lifts, lighting, propulsion and HVAC. In contrast, SiC technology facilitates these same functions except with better speed, reliability and efficiency.
Silicon carbide’s unparalleled switching speeds are also supporting the advancement of faster chargers. Off-board chargers transform incoming AC into DC for battery storage. Onboard battery chargers transform DC power from the battery into AC for the main drive motor.
Silicon carbide carries out these functions faster than silicon, with a reduction in heat and energy loss. Silicon carbide components can be half the size (or smaller) than silicon devices.
As SiC manufacturers continue to minimize defects in the material, it is anticipated that the prices for SiC devices will decline – beneficial for future EV applications.
The prospects for silicon carbide’s EV applications are bright, but growing demand for electric vehicles could lead to component defects unless manufacturers fit the correct inspection equipment.
This is of significant importance during research and development (R&D), where poor verification of process tools can drastically reduce yield. MTI Instruments’ Proforma 300iSA system conducts wafer inspection at-scale and increases the throughput of SiC materials.
Identifying defects at volume can be complicated, but MTI’s capacitance-based technology offers significant advantages over confocal systems.
Capacitance Based Technology vs. Confocal Systems
High resolution confocal interferometers are considerably more expensive than capacitance gauges. Laser interferometers also offer relative readings that necessitate instrument calibration to a known thickness by an operator before use. Comparatively, capacitance-based technologies offer absolute measurements.
Plus, the resulting measurement is inaccurate if a laser interferometer loses track of the wafer’s surface. With confocal systems, measuring transparent or translucent semiconductor wafers is also a much more demanding task.
Capacitive-based systems offer other advantages as well. Capacitance circuits are typically more stable and combine low drift with high accuracy, whereas, over time, the laser sensors in confocal systems are prone to drift according to temperature, thermal heating and other factors
The applications for quality control across the semiconductor supply chain can be broadened by capacitance-based technologies such as MTI’s Proforma technology. Vendors that sell SiC wafers can conduct high resolution measurements prior to shipping and subsequently measure SiC wafers upon receipt.
MTI Instruments ProForma 300iSA is a cost-effective capacitance-based off-line measurement tool that supports quality checks early in the manufacturing process.
It has the ability to measure wafer thickness, total thickness variation (TTV), bow and warp and center thickness that is accurate within ±0.25 µm and a resolution of 0.05 um.
With the ability to support R&D projects, the ProForma 300iSA can also be used to calibrate in-line equipment. To improve productivity yields for the SiC wafers used in EV power electronics, learn more and ask MTI for a sample report.
This information has been sourced, reviewed and adapted from materials provided by MTI Instruments Inc.
For more information on this source, please visit MTI Instruments Inc.