also increase payload mass, power
consumption, and overall cost.
At the device level, radiation
tolerance of standard device varies
widely. Bipolar devices generally
have higher radiation tolerance than
CMOS devices. Wide-bandgap-
semiconductor devices based on
silicon carbide (SiC) or gallium
nitride (GaN) have improved
resistance to deep-level defects. And
SRAMs are superior to DRAMs
When it comes to designing
integrated circuits for improved
radiation performance, there are
two common approaches: Radiation
Hardening by Process (RHBP) and
Radiation Hardening by Design
(RHBD).
Process-based techniques include
changing to insulating substrates such as
silicon on insulator (SOI) and sapphire
(SOS) are commonly used. Space-grade
SOI and SOS devices can survive doses
many orders of magnitude greater than
commercial devices. Another option is
to replace the normal boron (10B)
used in the semiconductor passivation
layer with radiation-resistant depleted
boron (11B).
RBHD approaches include error-correcting memory with additional
parity bits to check for and possibly
correct corrupted data. Since
radiation effects can damage the
memory content at any time, a
“scrubber” circuit must continuously
sweep the RAM: reading the data,
checking the parity for data errors,
and writing back any corrections.
Three circuits can take the place
of a single bit, and “voting logic”
can determine the final result.
Such redundancy provides a real-time solution to a single-bit failure,
whether radiation-induced or not. It
does increase the area of the device
considerably so it is primarily used in
smaller designs.
Examples of Rad-Hardened Devices
Semiconductor suppliers are
paying attention to this market.
In the digital world, Vorago
Technologies, formerly Silicon Space
Technology (SST), has developed
their HardSIL CMOS technology
for both extreme temperature
(up to 250°C) and high-radiation
(up to 300 KRad) applications.
Their product line includes a rad-hardened microcontroller family
based on ARM’s Cortex M0 core
and manufactured in 130-nm
technology. The company also offers
asynchronous SRAMs up to 16 Mbits.
In the analog domain, Texas
Instruments, Intersil, Linear
Technology, and others produce
rad-hardened components for space
applications. Intersil’s ISL70219,
for example, is a high-precision
operational amplifier that is radiation-hardened and designed to recover
quickly from SETs. Figure 3 shows its
output voltage deviation and duration
in response to a linear energy transfer
(LET) test. The LET test quantifies
how much energy an ionizing particle
transfers to the material: in this case
LET = 60 MeV•cm2/mg.
Figure 3: The response of the ISL70219 op
amp to SET. (Source: Intersil)
The radiation-hardened electronics
market is forecast to grow to
$1.3 billion, driven by a growing
global demand for satellites for
both commercial applications and
government intelligence, surveillance,
and reconnaissance operations.
Hopefully, the increasing market
size will spur the development of
improved rad-hardened designs,
and shielding technology. Otherwise,
future space travelers face a bleak
future. ECN
