PhD Alumni

Assanelli Mattia

Present position:

Thesis title:  P-N Junction Avalanche Modeling for High Performance Single Photon Detector Array
Advisor:  Ivan Rech
Research area:  Sensors and instrumentation
Thesis abstract:  
In recent years a growing number of applications demand better and better timing resolution for arrays of Single Photon Avalanche Diodes.
The challenge is to attain the same performances of the single device in arrays of SPADs. These tasks require not only a clear understanding of the physical mechanisms involved but also the development of suitable modeling tools that can drive the device engineering process.
In order to detect a photon, the SPAD current signal is AC coupled to a fast comparator. When the signal crosses a threshold the comparator switches: the threshold value thus sets the SPAD current level at which the avalanche is sensed. Experiments show that the photon timing jitter gets seriously impaired increasing the comparator threshold
level. Therefore to attain the best photon timing a low threshold level (tens of millivolts) must be chosen. In SPAD arrays, however, the electrical crosstalk between devices forces to employ high threshold levels. To develop SPAD arrays with the same performances as the single device we need to devise a SPAD field profile that allows to achieve the same state of art photon timing jitter in a totally independent way from the comparator threshold. Therefore we need to carefully investigate the statistics of the avalanche current growth in order not only to assess the different physical contributions to the total timing jitter but also to develop and validate a predictive model that can help the device engineering process.