Although TID is typically the first step in determining the radiation tolerance of a device to be used in the space industry, single event effects, or SEE, rank as the next concern for space system designers. The first “must have” is that the device must be free of single event latch-up (SEL). SEL can lead to severe disruption or even catastrophic device failure in the system. Once a devices latches, it can sometimes be recovered by powering down the system and/or performing a system reset. If left unchecked, the increased supply current demand can lead to device burnout. One approach to making a device SEL free, is to use a semiconductor process that is inherently SEL free. TI’s complementary bipolar (BiCOM) processes are manufactured using “silicon over insulator,” deep-trench isolated wafer construction techniques that result in devices that are inherently immune to latch-up. Once a device has been checked to be SEL free, the device will need to be rated as to it’s single event upset or “SEU” tolerance. As charged particles pass through the silicon, they deposit enough energy to cause logical errors to occur in digital devices. This so called bit flipping, i.e. a “1” to “0” state, or “0” to “1” state, can propagate into multiple bit errors, or “MBU’s” and the logic error propagates through the system. Often a system may hang up from these unexpected logic state changes, and may require a device reset, or restart. Unlike the SEL, SEU’s can often be tolerated to some extent, and are classified as errors in time.
The actual SEU rate, or so called Soft Error Rate (SER) is determined by device exposure to heavy ion’s at various energy levels ( LET ) over time, and determining the number of errors that occur. This data can be used to generate a Weibull distribution of the error rate.
Radiation test services
TI offers additional radiation test characterization services to accommodate specific program requirements.
• ELDRS and SEE testing
• Prompt dose characterization
Enhanced low-dose-rate sensitivity (ELDRS) has become an issue in radiation-tolerant applications. To help mitigate this effect, TI improved the ELDRS radiation performance on several bipolar devices indicated in the tables below. Testing was performed at a dose rate of 10mRad/Sec.
Radiation test method
To assure reliable performance under the aforementioned environmental conditions, the HiRel space product line is thoroughly tested for radiation performance as part of the qualification process. The flow diagram shown here illustrates the HiRel radiation test procedure.
The devices are electrically tested before irradiation, with parametrics recorded and datalogged for later comparison. Devices are electrically biased in specialized fixtures within the radiation chamber and exposed to a predetermined radiation level. They are then electrically tested after irradiation to determine if degradation or device failure has occurred. If no measurable degradation has occurred, the devices are irradiated again at a higher dose level and tested once more. This process repeats until the devices fail or reach the maximum predetermined radiation level.
TI space solutions TI has radiation-tolerant, hermetically packaged devices released for each one of the blocks shown in the block diagram.
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