Si pillar structured thermal neutron detectors: fabrication challenges and performance expectations

Abstract

Solid-state thermal neutron detectors are desired to replace ³He tube tube-based technology for the detection of special nuclear materials. ³He tubes have some issues with stability, sensitivity to microphonics and very recently, a shortage of ³He. There are numerous solid-state approaches being investigated that utilize various architectures and material combinations. Our approach is based on the combination of high-aspect-ratio silicon PIN pillars, which are 2 μm wide with a 2 μm separation, arranged in a square matrix, and surrounded by ¹⁰B, the neutron converter material. To date, our highest efficiency is ~ 20 % for a pillar height of 26 μm. An efficiency of greater than 50 % is predicted for our device, while maintaining high gamma rejection and low power operation once adequate device scaling is carried out. Estimated required pillar height to meet this goal is ~ 50 μm. The fabrication challenges related to ¹⁰B deposition and etching as well as planarization of the three-dimensional structure is discussed.