Combined x-ray and gamma ray testing to investigate the TID tolerance of flip-chip FPGAs

This paper investigates and proves the use of xray testing as a methodology and/or complement for TID testing of flip-chip FPGAs to identify the most sensitive circuit. This testing methodology can be used to test any flip-chip FPGA, Flash-based and SRAM-based. Microsemi's RTG4 flip-chip FPGA is characterized with gamma ray to prove the concept and in addition do a detailed investigation of RTG4's TID sensitive circuits. The advantage of using x-ray as a proxy for gamma-ray TID testing is that shielding can be used to identify the most sensitive circuits. In this paper both gamma-ray and x-ray results of RTG4 are presented and compared. Furthermore, during this investigation we discovered that the most important mechanism causing the failure of RTG4 re-programming is the degradation of the high voltage devices in the high voltage generation and word line access circuits.