Radiation-hardening techniques Radiation hardening

radiation hardened die of 1886ve10 microcontroller prior metalization etching



radiation hardened die of 1886ve10 microcontroller after metalization etching process has been used


physical

hardened chips manufactured on insulating substrates instead of usual semiconductor wafers. silicon on insulator (soi) , sapphire (sos) commonly used. while normal commercial-grade chips can withstand between 50 , 100 gray (5 , 10 krad), space-grade soi , sos chips can survive doses many orders of magnitude greater. @ 1 time many 4000 series chips available in radiation-hardened versions (radhard).
bipolar integrated circuits have higher radiation tolerance cmos circuits. low-power schottky (ls) 5400 series can withstand 1000 krad, , many ecl devices can withstand 10 000 krad.
magnetoresistive ram, or mram, considered candidate provide radiation hardened, rewritable, non-volatile conductor memory. physical principles , tests suggest mram not susceptible ionization-induced data loss.
shielding package against radioactivity, reduce exposure of bare device.
capacitor-based dram replaced more rugged (but larger, , more expensive) sram.
choice of substrate wide band gap, gives higher tolerance deep-level defects; e.g. silicon carbide or gallium nitride.
shielding chips use of depleted boron (consisting of isotope boron-11) in borophosphosilicate glass passivation layer protecting chips, boron-10 readily captures neutrons , undergoes alpha decay (see soft error).

logical

error correcting memory uses additional parity bits check , possibly correct corrupted data. since radiation effects damage memory content when system not accessing ram, scrubber circuit must continuously sweep ram; reading out data, checking parity data errors, writing corrections ram.
redundant elements can used @ system level. 3 separate microprocessor boards may independently compute answer calculation , compare answers. system produces minority result recalculate. logic may added such if repeated errors occur same system, board shut down.
redundant elements may used @ circuit level. single bit may replaced 3 bits , separate voting logic each bit continuously determine result. increases area of chip design factor of 5, must reserved smaller designs. has secondary advantage of being fail-safe in real time. in event of single-bit failure (which may unrelated radiation), voting logic continue produce correct result without resorting watchdog timer. system level voting between 3 separate processor systems need use circuit-level voting logic perform votes between 3 processor systems.
hardened latches may used.
a watchdog timer perform hard reset of system unless sequence performed indicates system alive, such write operation onboard processor. during normal operation, software schedules write watchdog timer @ regular intervals prevent timer running out. if radiation causes processor operate incorrectly, unlikely software work correctly enough clear watchdog timer. watchdog times out , forces hard reset system. considered last resort other methods of radiation hardening.




^ leppälä, kari; verkasalo, raimo (1989). protection of instrument control computers against soft , hard errors , cosmic ray effects . citeseerx 10.1.1.48.1291 . 
^ platteter, d.g. (october 1980). protection of lsi microprocessors using triple modular redundancy. international ieee symposium on fault tolerant computing. 
^ krishnamohan, srivathsan; mahapatra, nihar r. (2005). analysis , design of soft-error hardened latches . proceedings of 15th acm great lakes symposium on vlsi. glsvlsi 05.