Version 1.0
Kenneth A. LaBel
NASA/GSFC
(301)286-9936
E-mail: Kenneth.A.Label@gsfc.nasa.gov
and
Christina
Seidleck
Hughes/STX
(301)286-1009
October 27, 1995
I. INTRODUCTION
The objective of this study was to determine the threshold linear energy transfers (LETths) and cross-sections for single event upset (SEU) and single event latchup (SEL) due to heavy ions. LETth is defined as the maximum LET at which no errors are seen at a fluence of 1.00E06 particles/cm2. SEU LETthis defined as the minimum LET value to cause an effect at a fluence of 1E6 particles/cm2. SEL LETth is defined as the maximum LET value at which no latchup occurs at a fluence of 1E6 particles/cm2. The saturation cross section of the device is the point at which the cross section curve becomes asymptotic.
II. TEST SAMPLES
Relevant characteristics of the devices are summarized in the following table:
Device Type Mfg. Date Code Ser. # Technology Flash EEPROMs E28F016SB Intel die 1994 NA CMOS
TheE28F016SB is a Space Electronics Inc. (SEI) device with die bought from Intel. Many thanks are due to SEI for their support and device samples.
Sample devices were delidded in order to accommodate beam penetration limits of the test facility.
III. TEST TECHNIQUES AND SETUP
A. Facility Usage
The test facility used was the Brookhaven National Laboratories (BNL) Single Event Upset Test Facility (SEUTF) between August 16-18,1995. This setup utilizes a dual Tandem Van De Graaff accelerator suitable for providing ions and energies for SEU testing. The test devices are mounted on a device-under-test (DUT) board inside a vacuum chamber.
The SEUTF uses a computer-driven monitor and control program to provide a user-friendly interface for running the experiments. Hard copies of the test data and graphs are also made available.
B. Test Hardware, Software and Control
Test hardware, software, etc,... consisted of a DUT board placed in the test chamber, six feet of twisted pair ribbon cable, and two PC-based testers, the Omnilab and VXI systems. Both testers provide test patterns to the test boards and are capable of capturing output when errors occur. The VXI enhances the error capture by using an intrinsic compare and a custom-built FIFO buffer board thereby reducing processing time and eliminating the need for additional hardware on the DUT boards. Both systems are capable of controlling the entire test setup, digital counters, power supplies, waveform generators as well as the BNL computer via an IEEE 488 bus.
C. Device Test Procedure
The test procedure was similar for all devices tested. All tests were either dynamic in nature, (with the exception of strictly latchup testing) meaning that the devices were operating during the test at a nominal rate as they might in a spacecraft application, or in a static mode were the devices were merely biased during irradiation. In dynamic testing, power was first supplied to the device. A stimulus pattern was then loaded and the device began to function normally while exposed to the ion beam. Outputs from the device were constantly monitored by either the Omnilab or VXI and all errors accumulated until either fluence was reached or a latchup condition occurred. In the case of the latter, power and beam to the device were terminated and the test run ended prematurely. Otherwise, error counts were logged to the hard drive. Static mode testing varied by pre-loading the DUT with a known pattern, irradiating the device, then reading back from the device looking for errors. Two to three samples are typically used for testing to gain statistical validity. All DUTs were tested under a (nominal) 25 degrees celsius.
Flash EEPROM Modes tested:
Static or cell storage - device loaded prior to beam, irradiated
to a known fluence, then read back for errors
Read only - device loaded prior to beam, and read continuously
during irradiation.
Write only - device programmed during irradiation, then verified
post-irradiation.
Test pattern used: checkerboard.
Both bits in error and bytes in error were monitored. (If the 2 numbers are the same, all SEUs are single bit data errors. If numbers are not equal, control errors may have occurred as well during write operations.). Unfortunately, the bit counter test hardware failed in the middle of testing. Only byte errors are discussed below.
D. Ion Beam Usage
The following table summarizes the ions used for testing.
ION ATOMIC # ENERGY, MeV LET, MeV*cm2/mg at 0 deg. Si 28 186 7.9 Cl 35 210 11.4 Ni 58 280 26.2 Br 75 285 36.5 I 127 320 59.7
Additional effective LET values were attained by varying the angle of incidence of the ion beam to the device. All LETs discussed are in MeV*cm2/mg. Due to packaging constraints, only shallow angles (30deg or so) were capable of being utilized without shadowing of the test device.
IV. RESULTS AND DISCUSSIONS
E28F016SB
This device, from SEI, is a 16 Mbit (1Mx16) EEPROM, Nominal Vcc/Icc for this device
(standby/operating mode) is 5V/1-5 mA . SEL current was set at 40 mA.
SEL was observed on all test modes starting at LETs of between 26.2 and 29.9 (first observed). SEL was not observed on every test run at LETs =>29.9, hence cross-section at max tested LET (59.9) is < 1E-6cm2 per device. This portends a low predicted SEL rate for most spacecraft.
Control SEUs were observed on write mode tests staring at LETs between 9 and 11.4 (first observed). When this error occured, the device was not completely written to or blocks of errors occur due to an incorrect pointer inside the device. No other data SEUs were observed for write mode.
Sporadic data errors (i.e., bitflips) were seen on only 2 other test runs (1 on read mode, 1 on static mode) out of >20. With such few examples occuring, no statistical data is available. However, data errors may be attributable to test setup noise and may not be directly related to the ion beam. The cell storage mechanism is not expected to upset. No other SEUs were noted on read or static mode.
V. SUMMARY
The findings of these tests are interpreted in the following.
We typically divide SEE test results into the following four categories.
Category 1 - Recommended for usage in all spaceflight applications.
Category 2 - Recommended for usage in spaceflight applications, but may require some SEE
mitigation techniques.
Category 3 - Recommended for usage in some spaceflight applications, but requires
extensive SEE mitigation techniques or SEL recovery mode.
Category 4 - Not recommended for usage in any spaceflight applications.
Category 2 devices for this test trip are:
E28F016SB - if used as a read only device in-flight (reasonably high SEL threshold)
Category 3 devices for this test trip are:
E28F016SB - if used as a read-write device (reasonably high SEL threshold, but potential
for control errors).
VI. ACKNOWLEDGEMENTS
Special thanks to the test team and to Bob Tripp of Odetics and again to SEI.
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