Pittsburgh-based Coherent Corporation announced on Monday that DENSO and Mitsubishi Electric Corporation each invested $500 million for a 12.5% non-controlling interest in its silicon carbide semiconductor business, operating it as a separate subsidiary and led by executive vice president of wide bandgap electronic technologies Sohail Khan.
This coherent detection approach can significantly cut system costs by forgoing LO and optical frequency-locking loop components, and by employing a simpler state-of-polarization-tracking technique.
Power Electronics
Silicon carbide (SiC) is an attractive choice in power electronics due to its wide band gap, high breakdown field strength, high saturation electron drift velocity and thermal conductivity. SiC’s electric field strength can be up to 10x larger than silicon’s; this allows devices made one tenth thinner while handling higher current densities – leading to less power loss for smaller and more energy-efficient electronics components.
SiC is poised to play an increasingly important role in next-generation energy efficient electric systems due to its remarkable physical properties at higher temperatures, making it an indispensable element. Power electronics that are able to withstand higher operating temperatures while providing greater reliability in smaller form factors will play a crucial role in reducing greenhouse gas emissions, maintaining resilient grid infrastructures, and making electricity affordable for businesses, homes, and vehicles alike.
Automakers and tier suppliers prefer sourcing SiC-based power components from vertically integrated suppliers; that is, companies which develop wafer material from seeding through fabrication of finished devices. This approach ensures quality consistency throughout the supply chain should an issue arise, and prevents finger pointing between vendors should issues arise. Coherent offers large diameter semi-insulating substrates capable of fabricating GaN-on-SiC amplifiers and other RF/microwave devices suitable for high performance electric vehicle applications.
Semi-Insulating Substrates
SiC substrates of superior quality are essential to the creation of cutting-edge power electronics and gallium nitride (GaN) heteroepitaxy microwave RF devices. Their combination of high breakdown voltage, thermal conductivity, and GaN heteroepitaxy performance makes for exceptional RF performance in these devices.
High quality substrates require careful fabrication and inspection to minimize crystalline defects such as carrot defects, polytype inclusions, or scratches on their wafer surfaces that could impede device performance. Common surface inspection methods include scanning electron microscopy, atomic force microscopy and optical microscopy.
Undepleted HPSi (Hexagonal Polytype SiC) substrates produced using physical vapor transport (PVT) or high-temperature chemical vapor deposition (HTCVD) utilize intrinsic defects to introduce deep energy levels within their bandgap and compensate for residual shallow nitrogen and boron donors that linger near its center, forcing the Fermi level closer.
II-VI successfully launched commercial production of 150mm 6H semi-insulating substrates under a 50-50 cost share contract totalling $12M over five years and exceeding $12M of government funding in early 2019. As part of this program, significant efforts were invested into improving manufacturing efficiencies and throughput without impacting quality, including expanding hot zones and installing automated control systems at growing stations – improvements which led to an increase in micropipe density as shown by Figure 2.
RF & Microwave
SiC’s ability to detect coherent spin states meets one of the primary requirements for complex quantum control applications, while also opening doors to optically detected magnetic resonance (ODMR) and photodetection Rabi oscillation applications.
Application-specific radio frequency systems with narrow bandwidths and long-term stability are required for these applications. To accomplish this task, the polarization and spatial distribution of microwave modes must match those of optical WGMs.
Utilizing the directional properties of microwave field can assist with this task, for instance by focusing it on an edge or the equator of the sphere, it is possible to concentrate the microwave mode into regions where optical WGMs reside.
Alternately, an RF signal can be applied by detuning a microwave signal from an on-resonance magnetic field and detuning from its on-resonance position. This allows measurements to be conducted both during on- and off-resonance conditions without waiting for transition between these states to take place.
Coherent (Silicon Carbide Business) manufactures silicon carbide-based semiconductors. The Company provides substrates and epitaxial wafers in silicon carbide to meet customer demand worldwide. Coherent’s Silicon Carbide Businesses have customers all around the globe; for more information about them please view the PitchBook Platform.
Thermal Management
Heat generation, transfer and removal are essential parts of electronic systems. Each device has different temperatures at which it operates optimally; to maximize performance it is vital that they reach optimal performance levels.
One way of managing this issue is using a thermal barrier made of silicon carbide (SiC). SiC has a low coefficient of thermal expansion, meaning its shape doesn’t change drastically during processing or under stress conditions – making thinner wafers possible while maintaining performance while simultaneously decreasing overall device dimensions and costs.
An effective thermal management strategy involves employing solid-state refrigerators such as thermo-electronic coolers (TEC). These passive cooling devices – with no moving parts or controls – provide stable temperatures over long periods and reach operational temperatures well below room temperature.
Power savings for both consumer and industrial applications can be achieved using reaction-bonded Si/SiC (RBSiC) materials TECs; one such TEC uses RBSiC material which reduces baseplate size by 50 percent while providing four times greater thermal capacity than copper TECs. RBSiC’s chromium defect structure yields nondegenerate orbital doublets that offer both short T1 coherence times (Spin T1) and long spin T2 coherence times, thus offering optimal optical and magnetic coherence capabilities.
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