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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

Abstract

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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