An original DoE-based tool for silicon photodetectors EoL estimation in space environments

Abstract

In our previous works we have demonstrated that Design of Experiments (DoE) is an innovative methodology defining optimized irradiation test plan and particularly valuable for the space qualification of silicon photodetectors. In particular, it provided us with the degradation model of photocurrent, darkness current, and spectral responsivity of silicon based phototransistors arrays with respect to the Total Ionizing Dose (TID) and to the Displacement Damage Dose (DDD), over a wide range of space-mission profiles. In this paper, we will summarize at first main results obtained thanks to the DoE methodology. Then we present how we can easily obtain, by exploiting DoE collected data, End-of-Life predictions of such devices with a reduced number of experiments, with a small batch of devices, and in relatively short time.

Introduction

Design of Experiments is a structured, organized method for determining the relationship between factors affecting a process and the output of this process [1], [2], [3], [4], [5], [6], [7]. This approach is widely deployed in many contexts and for different applications: for example in industrial settings. The primary goal is usually to extract the maximum amount of unbiased information regarding the factors affecting a production process from as few costly observations as possible.

One of the most critical issues in the domain of the reliability of optoelectronic and electronic devices for space applications is to correctly evaluate their degradation with respect to the mission profiles constraints. These include huge vacuum conditions, temperature cycles, and different types of space radiations. Indeed, the devices qualification regarding the radiation aspects in the wide range of satellite missions in Low, Medium, and Geostationary Earth orbits (LEO, MEO, and GEO) environments are very challenging activities. In particular, the correct estimation of the main performances degradation as a function of the Total Ionizing Dose (TID) and the Displacement Damage Dose (DDD) received by the devices in the framework of a specific mission profile remains a problem to overcome. In this context, DoE can represent a helpful and powerful tool to solve this issue. Moreover, the radiation hardness assessment is time-consuming, costly in terms of test facilities and devices, and is mission profile dependent. In this paper, we put forward a new qualification approach based on the DoE methodology that combines protons and gamma rays irradiations realized according to an optimized test plan and provides the radiation engineer with analytical degradation models of the device performances. These models are valid for a wide range of mission profiles included in large study domain, as described further. This approach does not need any physical model of the device degradation, which would be very complex to obtain anyway. In addition it does not require any specific knowledge regarding the devices technology which makes it very useful for qualification purposes. The DoE approach has been used in various contexts, but this is, to our knowledge, the first time that this methodology is applied for the prediction of device degradation with respect to the radiation constraints of a potential space mission profile.

DoE methodology, as described in our previous published works [8], [9], [10], needs to define a study domain as a function of the chosen experimental factors. TID and DDD are the chosen factors for this study. The goal of the suggested methodology is to determine an empirical relationship that relates a device performance to these two factors. This relationship will only be valid within a dose domain called study domain that is defined mainly by the test facilities capability and possibly by constraints among the factors. We applied the methodology on a batch of silicon phototransistor arrays which are currently used as receivers in angular optical encoders. These components are used in Control Moment Gyroscopes in order to control the orientation of a spacecraft.