DIRS Laboratory 76-3215
December 18, 2018 at 10:00am
Kevan Donlon
Ph.D. Thesis Defense
Abstract: 

 

 

Hybridization is a process by which detector arrays and read out circuitry can be independently fabricated and then bonded together, typically using indium bumps. This technique allows for the use of exotic detector materials such as HgCdTe for the desired spectral response while benefiting from established and proven silicon CMOS readout structures. However, the introduction of an intermediate layer composed of conductors (indium) and insulators (epoxy) results in a capacitive link between adjacent pixels.

This interpixel capacitance (IPC) results in charge collected on one pixel, giving rise to a change in voltage on the output node of adjacent pixels. In imaging arrays, this capacitance manifests itself as a blur, attenuating high spatial frequency information and causing single pixel events to be spread over a local neighborhood. Due to the nature of the electric fields in proximity to the depletion region of the diodes in the detector array, the magnitude of this capacitance changes as the diode depletes. This change in capacitance manifests itself as a change in fractional coupling. This results in a blur kernel that is non-homogeneous both spatially across the array and temporally from exposure to exposure, varying as a function of charge collected in each pixel. This signal dependent behavior invalidates underlying assumptions key for conventional deconvolution/deblurring techniques such as Weiner filtering or Lucy-Richardson deconvolution. As such, these techniques cannot be relied upon to restore scientific accuracy and appropriately solve this inverse problem.

This dissertation uses first principle physics simulations to elucidate the mechanisms of IPC, establishes a data processing technique which allows for characterization of IPC, formalizes and implements a nonlinear deconvolution method by which the effects of IPC can be undone, and examines the impact that IPC can have on scientific conclusions if left uncorrected.