Proceedings Article | 13 December 2000
KEYWORDS: Microchannel plates, Silicon, Glasses, Sensors, Quantum efficiency, Resistance, Moire patterns, High aspect ratio silicon micromachining, Semiconducting wafers, Photon counting
The emergence of Silicon based microchannel plates (MCP's) has been awaited for a number of years, with many proposed advantages over standard glass MCPs for space-based detectors. Si should have a very low inherent background (< 0.01 events sec-1 cm-2), as well as being a low Z element with low stopping power for x, gamma and cosmic rays. The surface is oxidized and can be baked to very high temperatures (> 800 degrees Celsius), and will not react with photocathodes deposited on the surface. This could potentially allow opaque photocathodes, with their higher resolution and efficiency, to be used in the near UV/optical bands. Since the microchannel positions are determined photolithographically, the pattern will be uniform and coherent, resulting in more uniform flat fields and less differential non-linearity in the spatial response. Microchannel spacing could decrease to the micron regime, while size formats could increase. The potential advantages of Si MCPs encompass increased gain, stability, longevity, event rate, and QE. However, glass MCPs have a strong and successful heritage in space-based detector systems and the advantages of Si MCP's must be demonstrated in the laboratory before being considered for flight applications. We have tested some newly developed silicon (Si) MCP's provided by Nanosciences Corp. Although these are still in the developmental stage we have achieved a number of significant results. The gain, pulse height, response and gain uniformity, and quantum detection efficiency are very similar to glass MCP's. However the Si MCP background is approximately 0.02 events sec-1 cm-2 without shielding, a significant improvement over even low noise MCP's. The small samples we have tested are 25 mm format with 8 micrometer pore spacing, but they are taken from a 75 mm substrate, which offers the possibility of large MCP's in the near future. More testing and process development are underway to probe other operational parameters and optimize the manufacturing process.
