SoM Electron Detector Technology:
Scintillator on (silicon photo-) Multiplier

Silicon Photomultiplier (SiPM): An array of Single Photon Avalanche Photodiodes on a common Silicon substrate.

Important Characteristics of SiPM

  • Small Size
  • High gain (106)
  • High Bandwidth
  • Low Voltage (35-40 volts)
  • Large dynamic range
  • Replaces PMT

4X4 mm2 Silicon Photomultiplier

When a scintillator of appropriate size is coupled to the active face of an SiPM such that the emitted photons are, for the most part, made incident on the SiPM, a SoM device is created. When the incident electron beam scans the sample, electrons are backscattered or emitted which strike the face of the scintillator, creating photons, which in turn enter the SiPM device. The more electrons that hit the scintillator, the larger the number of microcells which fire in response, the higher the signal output from the SiPM, and the brighter the image.

SoMs can be placed in multiple locations in the chamber or column, or within other detectors (as in ON-X: The SDD with Vision).

How SoMs work: Note that the dotted line in output current graph represents normal dark current (noise) that is present in all solid state devices, and is caused by random thermal triggering of an individual microcell. When a real event occurs, such as an electron striking the surface of the scintillator, the result always gives rise to the firing of multiple microcells, and the corresponding output of the SiPM can be readily distinguished from the dark current.

SoMs can be made as small as 1X1X0.5 mm3, or as large as 10X10X1 mm3, and can be arrayed together in standard or custom configurations as a single detector, as in our Segmented Electron Detectors.

Advantages of SoM devices
over generic BSED configurations:

Compared to conventional scintillator detectors:

  • Low Voltage (35-40 volts)
  • Eliminates the PMT and frees up the port that it would occupy
  • Small size
  • High efficiency light coupling between scintillator and SiPM enabled by direct face to face contact
  • Can be segmented
  • Can use multiple scintillation materials

Compared to conventional segmented photodiode design:

  • High gain: 106
  • Adds additional gain of scintillator
  • High bandwidth (able to image at 100nS/pixel)