University of Michigan's Space Physics Research Laboratory
The information below is excerpted from a long test report on the reliability of Pico's programmable substrates in a high radiation environment.
"Testing was performed with the Co60 gamma-ray source at the University of Michigan's Phoenix Memorial Laboratory. This report documents the procedures and
the findings of that test."
"...The MCM concept is novel in the fact that it allows a standardized silicon substrate to be fabricated onto which IC dies may by bonded and wired. The circuit
interconnections between the dies are then programmed into the substrates. The silicon substrate is laced with cross hatch wiring where interconnections between
wiring levels may be programmed by means of anti-fuse connections. Anti-fuses are elements between two wiring levels that are normally open circuits. Upon
"blowing" the anti-fuse, a short circuit connection may be established between the two levels."
"SPRL's interest in the MCM concept is in qualifying the technique as a low cost alternative to customized electronic hybrid circuits for satellite instrumentation. If the
NRE cost of the MCM device turns out to be substantially lower than standard hybrid devices then a substantial savings in terms of cost as well as size and weight
may be obtained from SPRL's future instrument designs."
"In order to determine if the MCM concept can be qualified for space flight, some knowledge of the devices tolerance to radiation would be desirable. Once the
devices tolerance to radiation level has been determined then a decision can be made as how to best approach qualification of the device and which program to
initially apply the concept."
"The tests were carried out at the University of Michigan's Phoenix Memorial laboratory. The Phoenix laboratory houses an 18,600 Curie Co60 source in a 20 foot
deep immersion pool within an exposure room. Dosimetry monitors and operator controls to raise and lower the source from the pool are located in an adjoining
room. Phoenix laboratory personnel were responsible for setting up the test samples and dosimetry equipment within the exposure room, and for the raising and
lowering of the Co60 source during the test period."
"Test fixtures were set up outside the exposure room and connected to the test sample through 35 feet of wire harnessing."
"An insitu test was developed .......that would allow remote testing of three MCM devices while the devices were exposed to radiation from the Co60 source. Two
of the samples had the antifuses programmed in the "off" (open circuit) state to measure the change in anti-fuse leakage current as a function of dosage. One "off"
state device had a Plexiglass lid while the other had a gold alloy lid. The remaining device was programmed with seven long strings of connections to measure "on"
state fuse resistance. Insitu testing of the device measured the string resistance, including harnessing and fixtures, noting any change in resistance due to exposure of
Number of "on" state antifuses in sample string
String R9 15
String R10 18
String R11 15
String R12 12
String R13 10
String R14 10
String R15 14
"Power was applied only to the two "off" state devices, plus one of seven anti-fuse strings in the "on" state device during the radiation integration period. Supply
current was constantly monitored to determine if latch-up or catastrophic failure of any of the anti-fuse elements had occurred. Every six minutes parametric
information was measured from the samples, usually requiring less than 2 minutes to complete. Parametric test would record the leakage current measurement of
each "off" state devices using a 10v bias and the resistance of each of the seven anti-fuse strings in the "on" state device by measuring the voltage across a 20mA
constant current source. After the parametric measurements were completed another "on" state string would be selected to be biased during the next integration
"During testing, the "off" state devices would have their leakage currents measured with a constant voltage source of 10.0 volts. The "on" state devices would have
their resistance determined by measuring a voltage across a 20mA constant current source. Every eight test periods the polarity of the sources would be reversed."
"Exposure to the Co60 source occurred in four steps. Starting at an exposure rate of 1 Krad/hr and increasing the dose rate by an approximate factor of 10 at each
step. This procedure for the incremental increase in exposure was chosen because the expected radiation limit of the MCM substrate was not know. The test would
terminate when either a failure had occurred or a total dose of 1 Mrad-Si had been reached. A large aluminum block (15.56 cm depth) is used as both a mounting
fixture and a 10x attenuator for the MCM test samples. The first test was performed with the aluminum block in front of the test samples as an attenuator and the
distance calculated for a ~1 Krad/hr exposure rate. After the first hour had expired the test sample was turned around for an exposure rate of ~10 Krad/hr. The
third hour had the test sample moved closer for a 100 Krad/hr exposure rate. And in the final test sample was moved as close to the source a physically possible for
a 1 Mrad/hr exposure rate."
"A dosimetry probe was used to measure the actual radiance during the first and second test periods. The probe agreed so closely with calculated exposure levels
that it was not used for the third and forth tests."
"...ran a full parametric test on the samples both before and after exposure to the Co60 source. Parametric data from ERIM is included with this report. There was
an approximate 2 day annealing time while the test fixture was broken down and the devices were tested for the post radiation parametric."
Actual test data not attached.
"Total Dose radiation testing of the MCM substrate has provided confidence that the technique will operate and survive in radiation environments typically required
for space flight electronics. There were minimal increases noted in the leakage current of the "off" state devices but it is not believed that these increases would
adversely effect the operation of any circuitry built upon the substrate. At no time were latch-up effects nor inadvertent opening or shorting of anti-fuse connections
"Though this test was not meant to be part of a series of space flight qualification test for the device and did not exactly conform to Mil-std-883D method 1019.4, it
did prove that the MCM substrate would operate normally out to a total accumulate dose of 1 Mrad Si thus giving confidence that the MCM technique may be used
in high radiation environments requiring Rad-Hard qualified parts."
Last Revised: February 03, 2010
Digital Engineering Institute
Web Grunt: Richard Katz