Large-Area, UV-Optimized, Back-Illuminated Silicon Photomultiplier Arrays

Existing photocathode-based technologies for visible and UV instruments lack sensitivity, are bulky, and have limited reliability. Solid-state silicon photomultipliers (SiPMs) are efficient, light, and reliable, but the front-illuminated designs demonstrated to date have poor UV response, limited sensitive area, and limited optical fill-factor. In the proposed program, back-illuminated, back-thinned SiPMs optimized for UV response and scalable tiling over very large areas will be developed for observation of air showers from ultra-high energy cosmic rays (JEM-EUSO) as well as for visible-wavelength spectrographic and photometric instruments planned for future telescopes (OWL). Short-wavelength light is absorbed near the surface of a silicon detector, and moving the optical entry surface to the back side of the wafer will enhance UV response by ensuring that all photocarriers from UV photons are generated on the correct side of the junction for efficient avalanche multiplication. Placing the optical entry surface on the back of the wafer will also improve optical fill factor because it will no longer be necessary to shine light through the quench resistor network on the front surface of the detector. Lastly, back-thinning the detector wafer will significantly reduce the mass per unit area of the focal plane array. In Phase I, SiPMs will be back-thinned to demonstrate enhanced UV response, and edge-buttable SiPM arrays that make optimal use of a standard 22-mm CMOS reticle will be designed. In Phase II, large-area back-illuminated SiPMs will be fabricated and demonstrated. Voxtel anticipates that its technology will enter the program at TRL=3, finish Phase I at TRL=5 or 6 (goal), and exit the Phase II program at TRL=7.

In addition to the NASA application, there are a broad range of applications for high sensitivity silicon photomultiplier arrays. Multi-channel photon counting systems based on large-area single photon sensitive detectors are needed in multi-lane, highly sensitive DNA sequencing, but are currently unavailable. Improved single photon counting modules are also required for time-correlated single photon counting (TCSPC), fluorescence and luminescence detection, fluorescence correlation spectroscopy, flow cytometry, and LIDAR applications. Moreover, the SiPM offers excellent opportunities in positron emission tomography (PET) and single photon emission computed tomography (SPECT). Cherenkov detectors are an excellent tool for energetic charged particle identification in high energy and nuclear physics experiments.

The proposed technology is required for a family of UV and visible NASA science missions, with application to observation of atmospheric fluorescence (JEM-EUSO), high-velocity-accuracy visual spectrography (CODEX instrument proposed for OWL), and nanosecond-resolution photometry (QuantEYE instrument proposed for OWL).

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