Abstract: The radiation degradation of the npnp thyristor radiation-sensitive characteristic, holding current, Iholding, considered.
As the dose of γ-irradiation (Φγ) increased, the distribution of the Iholding shows pulsating change (quasi-periodicity) in quantity
and amplitude of peaks (extremes) of Iholding in a wide range of Φγ. The investigated thyristors samples show real radiation
hardness only up to 200 mSv. At 200 ≤ Φγ ≤ 1000 mSv Iholding S-shape degradation was observed. From a practical point of
view, using such a low-power discrete planar npnp thyristor in the range of 1000 ≤ Φγ ≤ 7·103 mSv is advisable. For the range
of approximately 6·103 ≤ Φγ ≤ 1·105 mSv it's difficult to forecast the value of the Iholding (heavy risk zone). Φγ ≥ 1·105 mSv may
be considered a failure zone of the devices. The evaluation method was proposed for a realistic assessment of the radiation
resistance of discrete devices. It includes the construction of approximating Iholding dose dependence using results of
experimental measurements and calculations to find laminar (smooth) and chaotic (jagged) phases of degradation. The laminar
phase will show the ranges of real radiation hardness (no changes of the holding current) and predictable changes of device
parameters under irradiation. The beginning of the chaotic phase indicates the end of the reliable npnp structure operation and
the possibility of soon device failure. Obtained experimental results agree with previously received theoretical approaches of
other authors.
Keywords: Low power npnp structure, γ-irradiation, Bimodal distribution, Probability, Radiation hardness, Heavy risk zone,
Failure, Phases of the holding current degradation, Realistic assessment of the radiation resistance of discrete devices.
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