Final Technical Report Page: 4 of 19
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aPeak
4. How to integrate the readout at pixel level?
5. Is there amplification needed at pixel level?
6. How to assess the radiation damage and annealing in APGT test pixels?
7. What is the track resolution if using track centroiding?
B. SUMMARY OF PROJECT ACTIVITIES
B.1 Technical objectives
This Phase I program is based on the technology previously developed at aPeak for thin, backside
illuminated tracking detectors mounted on flexible substrates to yield low radiation length high
assembly. Therefore Phase I technical objectives will be focused on developing the segmented
pixel structure and the readout in calorimetric mode.
In Phase I we will evaluate and demonstrate the main elements of the APGT array technology and
measure its performance, namely sensor structure, readout/ reset cell architecture, as well as
radiation/damage and annealing. The Phase I technical objectives are:
(1) Design pixel layout and readout cells;
(2) Fabricate small APGT arrays (containing a variety of test blocks) to help:
(a) select the readout cell layout;
(b) evaluate and identify methods to decrease the crosstalk;
(d) identify operation conditions to help design sub-pixel resolution enhancement algorithms;
(4) Evaluate the radiation damage and damage annealing.
B.1.1 Program tasks
Phase I program comprised of the following tasks:
Task 1: APGT simulation and design
Task 2: APGT fabrication and performance evaluation; and
Task 3: Evaluation of the radiation damage and annealing.
B.2 Task 1- APGT simulation and design
Technical challenges toward integration of high-resolution APGT pixel arrays are: (1) optical
crosstalk; and (2) the guard ring to protect the pixel against premature breakdown.
B.2.1 APGT SPICE simulation
Single Geiger junctions are single-carrier binary devices. Electrons or holes crossing the Geiger
avalanche junction may trigger a Geiger avalanche pulse at 108-charge gain. As the Geiger
avalanche develops within few nanoseconds, the Geiger current may exceed lmA. (108 e x 1.6e 10
19 /-8 sec). The Geiger detector during avalanche is modeled like a switch in series with a
current path, bypassing the reverse biased junction. In a practical configuration, a resistor in series
with the Geiger junction protects the junction against destructive breakdown. The current flowing
through the series resistor drops the voltage on the Geiger junction below the breakdown voltage
and the Geiger avalanche is quenched (the resistor is known as the passive quenching resistor). As
shown in Figure 1 we model the Geiger detector as a p-n junction reverse biased diode in parallel
with a Geiger current bypass controlled by a parallel resistor in series with a voltage controlled
switch S1. Switch S1 opens when the voltage on the p-n junction drops below the breakdown
voltage thus quenching the Geiger avalanche. Switch X1 is a time controlled switch simulating the
onset of the Geiger avalanche.4/19
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Vasile, Stefan & Li, Zheng. Final Technical Report, report, June 17, 2010; United States. (https://digital.library.unt.edu/ark:/67531/metadc1015252/m1/4/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.