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Characterization of the Effects of N+ Doping Concentration and Dielectric Thickness on the Spatial and Temporal Resolutions of AC-Coupled LGAD Sensors

  • Author(s): Hyslop, Sean
  • Advisor(s): Schumm, Bruce A
  • et al.

The next generation of particle detector systems will require sensors that can simultaneously record position and time to great precision. The low gain avalanche detector (LGAD) is a thin n-on-p silicon sensor implementing internal gain which results in a temporal resolution on the order of 10s of picoseconds. However, due to gain layer segmentation, position resolution in LGADs is limited to the millimeter scale. AC-coupled LGADs (AC-LGAD) improve on the position resolution of traditional LGADs through the implementation of a thin dielectric AC-coupling layer between the ?$ implant and readout electrodes, allowing for the use of continuous, planar, ?$ and gain layers. This leads to intrinsic charge sharing between readout electrodes, resulting in a spatial resolution on the order of 10μm. In this thesis, the spatial and temporal resolutions of several AC-LGAD wafers, differing in either ?$ concentration or dielectric thickness, were characterized using the Transient Current Technique with an IR laser set to replicate a MIP. Position resolutions were found to range from 6.9-8.6μm depending on the wafer studied and the position between pads. A straightforward trend relating the wafer fabrication parameters to position resolution was not possible. Timing jitters were found to range from 8.5-13.9ps depending on wafer and position. Overall, it was shown that increasing ?$ concentration (decreasing sheet resistance) and increasing dielectric thickness (decreasing capacitance) both lead to lower timing jitter.

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