Impactionisation wave mode triggering of thyristors based switches

Impact-ionisation wave mode triggering of thyristors based switches Viliam Senaj, ABTEF meeting 12/09/2017

Very high power (>100 MW) switching: Silicon Controlled Rectifiers (thyristors) is the only semiconductor solution • Widely used industrial standard, relatively inexpensive • High voltage and current ratings up to 8. 5 k. V/90 k. A max (package diam. 180 mm) • Standard thyristors have limited d. I/dt < 1 k. A/us due to limited propagation speed of commutation ~ 0. 5 mm/us • Highly interdigitated gate topology allows more homogeneous triggering propagation and allow for higher commutation speed (20 k. A/us) at the expense of reduced conduction area, significantly increased gate current request and higher production cost • GTO like thyristors used in LBDS are 4. 5 k. V/80 k. A rated; housing diam. ~80 mm; costs ~ 1 k. Chf

Properties of switches triggered by impact ionisation mechanism - Dynistors • Closing switch with 4 layers P+NPN+, with two stable states ON and OFF (like thyristors); no control electrode needed • Once turned ON it can stay on indefinitely (regenerative feedback like thyristors) • Triggering achieved by very fast overvoltage pulse (1 – 10 k. V/ns) leading to a junction area electrical field of 30 – 100 MV/m and creation of fast moving ionisation front – 5 – 20 times faster than saturated velocity of the carriers • Commutation speed from ns down to < 100 ps • Current commutation speed above 100 k. A/us (2. 5 MA/us reported already) • Huge current handling capability (800 k. A on 100 mm diameter wafer reported – reverse switching dynistors – RSD) • Several generations exists: FID (fast ionisation dynistor), DLD (deep level dynistor), RSD (reversely switched-on dynistors), TADBD (tunnelling-assisted delayed breakdown device)

Limitations of the impact ionisation triggering •

Conclusion • Interesting solution for thyratron replacement on fixed voltage generators (injection/extraction kickers) • Dump generators would require modification to triggering system (modulated output voltage) to compensate for the required voltage dynamics • Potential advantage of the fast switch commutation (ns) is “wasted” by a long preparation phase of the triggering circuit (~300 ns); optical pumping based HV high d. U/dt generator to be developed? • Ionising radiation effect to the ionisation to be studied (potentially favourable) • SEB effects (HEH) would require the same approach at GTO today (voltage derating)