Optical micrograph (cross section), laser-micromachined hole array in InP (hole diameter ~20 mm).
Optical micrograph (cross section), laser-micromachined hole array in InP (hole diameter ~20 mm).

Objective
Improve gamma-ray imaging for astrophysics research and ground based applications (shielded special nuclear material detection) by utilizing modern nano- and micro-fabrication techniques.
Modern radiation detectors are based on high-voltage semiconductor detectors. NRL is increasing their performance by increasing the detector size and thickness, developing novel detector designs, utilizing high atomic number semiconductors, and reducing "inactive" detector area.

Approach

  • Full development cycle in-house: performance simulation → mask design → nano-/microfabrication → testing
  • Finite element simulations (FEM) of the fabrication and electrical performance of semiconductor radiation detectors
  • Use of "state-of-the-art" nano-fabrication methods, e.g. atomic layer deposition (ALD), laser micro-machining (see micrograph), and deep reactive ion etching (DRIE). The nano- and micro-fabrication is done at NRL’s Institute for Nanoscience (NSI), the lab’s centralized nano- and micro-fabrication facility
  • Novel detector designs, e.g. lateral depletion from hole or trench array (see micrograph)
  • Collaborating with top research institutes around the world, including RD50 at CERN and UCSC (University of California Santa Cruz) on "slim edge" designs

Deliverable/Value/Accomplishment

  • NRL showed, for the first time, a silicon strip detector on a full 200 mm silicon wafer
  • Trenched gamma-ray detector in silicon, 2 mm thick substrate with full depletion at 50 V
  • NRL in collaboration with UCSC reduced the inactive area of a detector to
  • In-house fabrication of silicon drift detector (SDD).
  • First use of alumina, Al2O3, as sidewall passivation and “p-stop” material for radiation detectors → regarded worldwide as "breakthrough" technology
  • NRL was awarded 1 US patent and has 6 US patents pending on novel radiation detector designs