The effects of gamma radiation on digital micromirror devices

Abstract

Digital micromirror devices (DMDs) are well suited for highly multiplexed spectroscopy applications. In astronomy, DMDs can be used as a programmable slit mask in a multi-object spectrometer (MOS). There is strong interest in utilizing DMDs for space-based MOS instruments. Over the past several years, we have carried out a program to evaluate the viability of XGA DMDs for operation in space, including their ability to survive the launch environment. The DMDs we tested did not show any failures or adverse effects after mechanical vibration and shock testing. Using heavy ion irradiation, we found that DMDs are susceptible to single event upsets (SEUs), though all SEUs are non-destructive and can be cleared by loading a new pattern. The estimated SEU rate for ”worst week” conditions in interplanetary space was 5.6 upset micromirrors (out of 786,432) per 24 hours. Using high energy protons, we found that DMDs started to show failures at a total ionizing dose of 30 krad(Si) (which is well above the estimated total-dose for a 4 year mission). In this work, we present the total ionizing dose testing performed using gamma rays from a Co-60 source at NASA GSFC. We tested 14 XGA devices and found that individual micromirrors began failing after the devices accumulated a total dose of 16-19 krad(Si). Devices recovered after annealing at room temperature in as little as 24 hours. Devices subjected to the most severe radiation testing conditions were completely recovered after 18 weeks of annealing at room temperature. We also tested unbiased (powered off) devices, which showed no effects up to a dose of 76 krad(Si) (which is the highest TID we achieved during our testing). This work concludes our efforts to space-qualify XGA DMDs, and shows that these devices are well-suited for deployment in space, except in the harshest radiation environments.