Charge collection in HI2L bipolar transistors

Charge-collection measurements were carried out on HI²L transistors in GaAs in order to determine the thickness of the equivalent sensitive volume to be used in calculating single-event-upset (SEU) rates for this technology and to set a lower limit to the critical charge. The measurements were in the form of pulse-height spectra measured between the base-emitter and collector-emitter contacts upon exposure to energetic protons, alpha particles, and sulfur ions. The sulfur data are consistent with the SEU-sensitive junction being the base-emitter junction with an equivalent sensitive volume of thickness 0.1 μm for high-linear-energy-transfer (LET) particles. This value is a factor of two less than the thickness value previously used to estimate error rates in space and is a factor of three less than estimates based on alpha particles, which have lower LET. Comparison of the proton charge-collection data with earlier SEU measurements results in a revision of the estimate of the lower limit to the critical charge for HI²L gate arrays to a value that is higher than previous estimates by more than a factor of two. The combination of reduced charge collection and higher critical charge implies that this technology will be considerably harder to SEUs than previously believed