In astronomy, multi-object spectrometers (MOS) provide an efficient means to gather large samples of spectral data. Digital Micromirror Devices (DMDs) can be used as programmable slit masks in a MOS. There is strong interest in using DMDs in space-based MOS instruments. Our team has been carrying out an environmental test campaign to qualify eXtended Graphic Array (XGA) DMDs for space deployment. The environmental tests have included mechanical shock and vibration, low temperature, heavy ion radiation, proton radiation, and gamma radiation testing. In each of the tests, the devices were able to withstand the expected conditions of a space mission without adverse effects. Initial gamma radiation testing was performed on fourteen XGA DMDs during June of 2018. Ten of the devices were active and four passive (unbiased) during gamma irradiation. Passive devices accumulated a total ionizing dose (TID) of up to 76 krad(Si) without showing adverse effects. The active devices began to exhibit the appearance of non-latching micromirrors at a TID of 16-19 krad(Si). Non-latching mirrors recovered after annealing at room temperature for as little as 24 hours. The DMDs subjected to the harshest testing conditions were completely recovered after six months. A distinct difference in the pattern of non-latching mirrors was observed between commercial-off-the-shelf (COTS) DMDs with their original windows and re-windowed DMDs. In this work, we present a second round of gamma radiation testing performed on XGA DMDs at the NASA Goddard Space Flight Center in June 2019. One of the main purposes of this testing was to further investigate the differences in TID effects observed between the COTS and re-windowed DMDs. This testing also investigated the use of high temperature annealing to accelerate the recovery of non-latching mirrors. Additionally, DMDs which had previously been irradiated in an unbiased state were tested again while active during gamma irradiation. This work finalizes our efforts to qualify XGA DMDs for use in space and provides a better understanding of the effects of TID on the devices.
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.