Ionizing radiation detector for environmental awareness in FPGA-based flight computers

Abstract

Ionizing radiation has a detrimental effect on digital electronics that operate in extraterrestrial environments. When electronics are struck by these high energy particles, the effect on the system can range from temporary faults to permanent damage. Modern reconfigurable digital designs are using new architectures which can utilize environmental awareness to increase the system's tolerance to faults caused by radiation strikes. These digital fabrics are capable of reprogramming circuitry based on information provided to the system by an external source. In this thesis the design, modeling, and characterization of a radiation sensor is presented. This radiation sensor is coupled with an FPGA based reprogrammable computer system to provide spatial information about radiation events to the computer. The radiation sensor uses a PN junction as its fundamental sensing element. As a high energy radiation particle passes through the sensor, the substrate is ionized (electron-hole-pairs are generated). The internal electric field of the PN junction separates these charge carriers which are then collected on the orthogonally placed electrodes on the top and bottom of the sensor. This XY grid of electrodes provides the spatial location of an ionizing radiation strike. These coordinates are then input into the computer system which analyzes the location and reconfigures the system to avoid the potentially damaged circuitry located at the strike coordinates. A high speed event detector is also implemented in the FPGA to aide in the sampling and storing of the incoming radiation strikes. This event detector samples the incoming data at a high rate to ensure that even fast output pulses are detected by the computer system. A model was developed to predict the response of this radiation sensor for a given radiation source. This model was used to predict the signals out of the top and bottom electrodes on the radiation sensor. Extensive testing was then performed using a high energy radiation source. The sensor was able to determine the location of the radiation strike and relay this information to the computer system. The model was also capable of predicting the sensor response with the desired degree of accuracy.