Single Event Catastrophic Failure of Power Devices

Physical Simulation

When a power device working under high voltage, since there is high electric field, a penetrating energetic particle may cause positive feedback and thus avalanche in ultra-high current, which may consequently burn the device.

Due to their relatively large sizes, 2D TCAD simulation is commonly employed in power devices. But for single event effects, 2D simulation isn't enough. To perform a 2D simulation on (x,z) plane, the particle trajectory on y direction is enlarged infinitely, which gives inaccurate results.

Thanks to modern mesh technique and parallel technology, and also thanks to modern high-performances hardware, 3D simulation on power devices can be practically implemented.

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In TCAD device simulation, the charge carriers generated by the energetic particle are undergoing drift-diffusion in high electric filed, causing possible positive feedback between intrinsic transistor and parasitic transistors. Consequently the local current might be increased to an unusual level, thus the local temperature would be unreasonably high. When this happens, we can decide that SEB is happened.

Pros

  • To have clear understandings of the burnout mechanisms
  • Help to spot the sensitive part in the device
  • Help to find the conditions that triggers SEB
  • Verify any hardening designs

Cons

  • High performance computing server required
  • Experienced TCAD specialist required

Example

Figure below gives cut-plane of 3D simulation. Pseudo colors in figure shows the electron concentration in VDMOS cell array at 10ps, 55ps, 500ps and 1.35ns after the energetic particle strike. The affected area extend from the original central line and spread to neighboring cell, which causes large current in these cells, consequently burnout happened.

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Hardening

Based on our sophisticated simulation and thus the understandings about the mechanism of SEB, some SEB hardened VD-MOS transistors were designed and validated by ground heavy ion tests.

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On-Orbit Reliability Prediction

When working on a certain space orbit, the flux-LET curve can be obtained by tools like CRad. With the knowledge of your power devices, simulated or tested, a reasonable prediction of lifetime of power devices can be obtained.

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