With the rapid adoption of silicon carbide (SiC) power devices in high-power, high-efficiency applications like new energy vehicles, power conversion, and industrial control, their long-term stability and reliability have become a key focus for the industry. Bipolar degradation is a typical degradation mode that directly impacts the performance of both SiC MOSFETs and SiC diodes. Many distributors offer a wide range of electronic components to cater to diverse application needs, like 945-14070-0087-000
Understanding the Mechanism of Bipolar Degradation
Bipolar degradation originates from stacking faults (SFs) within the SiC crystal. When the body diode is in conduction, the forward current causes electron-hole pairs to recombine and release energy, which promotes the expansion of these stacking faults and gradually forms localized high-resistance regions.
copyright-Induced Expansion When a SiC device operates under forward bias, minority carriers are injected into the drift region. These carriers interact with the stacking fault defects, causing the faults to expand.
Shockley Stacking FaultsShockley stacking faults are a specific type of stacking error. In high electric field environments, the energy gained by minority carriers further excites these stacking faults, causing them to grow rapidly. This leads to more electrons or holes being trapped, which significantly increases the local resistance of the drift region.
Defect Expansion and Worsening Degradation As the stacking fault area expands, local stress and defects accumulate in the crystal lattice. This is observed as an increase in on-resistance (Ron), a rise in the diode's forward voltage drop (VFSD), and a decrease in the device's switching speed.
The Impact of Bipolar Degradation on Device Performance
Increased Conduction Losses: The rise in Ron directly increases power loss, which lowers overall energy efficiency.
Reduced Current Capacity: Localized high-resistance regions restrict current flow, which reduces the device's maximum output capability.
Worsened Switching Characteristics: Defects cause local electric field distortions that slow down the switching speed, negatively impacting performance in high-frequency applications.
Reliability Concerns: Over long-term operation, this degradation effect can become a bottleneck for system longevity.
It is worth noting that bipolar degradation primarily manifests as a worsening of Ron and VFSD, and does not affect the device's threshold voltage (Vth) or breakdown voltage (Vth).
Strategies to Mitigate Bipolar Degradation
Material Purity and Defect Control Dislocations and initial defects in SiC crystals are the root cause of bipolar degradation. Improving crystal growth processes and reducing dislocation density can suppress the expansion of Shockley stacking faults from the source.
Process Optimization
Thermal Treatment: Appropriate thermal treatment can partially repair stacking faults and reduce their activity.
Hydrogen Passivation: Hydrogen atoms can bond with defects, reducing their ability to trap carriers and slowing down the degradation process.
Circuit and Device Design Improvements
Reduce minority copyright injection into the body diode, for example, by using an external Schottky diode to shunt current. This lowers the risk of Shockley stacking fault excitation.
Optimize driver and protection designs to prevent the device from operating for long periods under excessively high electric fields or high-temperature conditions.
Summary
Bipolar degradation is a unique challenge for SiC devices. It is essentially the expansion of Shockley stacking faults under high electric fields and minority copyright injection. This phenomenon leads to an increase in on-resistance and forward voltage drop, which affects device efficiency and reliability. By improving material purity, optimizing process flows, and enhancing circuit design, this degradation can be effectively slowed or suppressed. As related technologies mature, SiC devices will be better equipped to meet the stringent demands of new energy, automotive electronics, and industrial applications.