part of the subject in my previous blog. The focus last month was on giving thanks for all our experiences. It was quite a fitting topic considering the holiday at hand this past month. Thinking along the lines of radiation testing and given the fact that we are in the midst of the Christmas season my mind went back to my blog from a few years back, Lit Up Like a Christmas Tree. In several blog posts I have covered various topics surrounding radiation testing from TID testing to SEE testing. In terms of facilities, the focus has been primarily on the cyclotron at Texas A&M University. This is a very popular facility for performing SEE testing with heavy ions. I thought I would expand on this topic a bit more this month and discuss a few more of the available facilities for radiation testing. The focus here will be on a subset of the facilities that are located in the United States. The graphic below gives an illustration of some of these facilities.
Partial List Map of Radiation Test Facilities
TID Test Facilities
Recall that TID (Total Ionizing Dose) testing is performed by exposing a device to a certain dosage of radiation. This device would typically be testing on ATE (Automated Test Equipment) prior to the exposure to radiation and the re-tested after exposure. The idea is to observe any shifts in device performance or any possible damage to the device after the exposure to the radiation. Devices are subject to various levels of TID from 30 kRads up to 100 kRads and above, even up to 200-250 kRads in some cases when performing HDR (High Dose Rate) testing. For HDR testing the device is placed into a chamber like the one in the photo below where the device is subjected to the specified dose of radiation. The dose rate is about 300 Rad/s.
High Dose Rate Test Chamber
For the LDR (Low Dose Rate) testing a radiation source projects radiation onto chambers with devices under test. In this case the radiation dose rate is about 10 mRad/s or less. This means that it takes much longer to reach a 100 kRad total dose; a total time of approximately 18 – 20 weeks!
The radiation test facilities at Cobham-Aeroflex Rad in Colorado Springs, Colorado, as well as VPT Rad in Chelmsford, Massachusetts and the University of Massachusetts at Lowell in Lowell, Massachusetts all support HDR and LDR testing for TID. The Cobham-Aeroflex Rad facility also supports a testing termed flash X-ray which is a type of test that I have not discussed in any of my blogs. Basically, this is a test that would emulate an EMP (Electromagnetic Pulse). The facility at UMass-Lowell offers the ability to perform displacement damage testing in addition to HDR/LDR testing.
In several of my blogs I have discussed SEE (Single Event Effect) testing. In this case, the device is subjected to heavy ions of varying energy levels to observe the response. For this testing there are single event upsets (SEUs) that are observed in the device response. This could be in the form of an output transient event which would be an SET (single event transient), a functional interrupt of the device which would be an SEFI (single event functional interrupt), or a supply domain latchup of the device which would be an SEL (single event latchup). An example of an SEE facility is shown in the image below which shows the ion cannon and the location of the device under test at the cyclotron at Texas A&M University.
Heavy Ion Cannon (SEE Test Facility – Texas A&M Cyclotron)
Three facilities that are used commonly in the United States for SEE testing include the pulsed laser at the Naval Research Lab (NRL) in the Washington, D.C. area, the cyclotron at Texas A&M University, and the Lawrence Berkeley National Lab in Berkeley, CA. The pulsed laser at NRL can be used as an indicator of the heavy ion SEE performance of a device. It also allows for finer resolution of where the radiation energy is applied to be better able to locate specific areas of the die where an SEU may occur. This information could be used to target specific areas of the die that may require modifications to improve the SEE performance of the device. The facilities at Lawrence Berkeley and Texas A&M provide heavy ions to test the SEE performance of a device.
While the facility at Texas A&M is a free air facility as pictured above, the facility at Lawrence Berkeley National Lab utilizes a vacuum chamber. In cases where there is onset of SEUs and/or SETs at low LETs during heavy ion testing there is generally a desire to also subject a device to proton testing. The facilities at both Texas A&M as well as Lawrence Berkeley offer this capability in addition to heavy ions. Unfortunately, a very popular proton test facility at Indiana University closed within the last few years. However, there are other facilities such as the Mayo Clinic in Phoenix, AZ that can be used for proton testing given that the required energy levels are met by the different proton facilities. These different facilities have different energy levels for protons that may or may not be applicable to a given application.
I hope this has provided a bit more insight into the various facilities that are available to do the different types of radiation testing. This list is not exhaustive, but I would like to point out that there is not a long list of places to perform these types of tests. This can make obtaining test time an issue. There are several companies as well as government operations that all request time at this limited number of facilities. Many of these facilities if not all operate 24 hours and 7 days a week (with the exception of the medical proton facilities which generally allow testing only over the weekend). Additionally, test time cost in the thousands of dollars per hour as well. Not a bad place to be if you are a test facility because the demand is high, but it does make radiation testing challenging for the customers of the facilities. It will be interesting to see how things progress in the coming years with the different test facilities since many have been in operation for quite some time. That is a topic for another day however. If you like to learn more about different radiation test facilities, please check out the following presentation from NASA: External Radiation Test Facilities for Testing of Electronics: NASA Overview with Emphasis on Single Event Effects (SEE). Also, I encourage you to take a look at some of the TID and SEE reports available from the ADI Space products page at Analog Devices Space.