Electronics for space applications
have stringent requirements
on both performance and radiation tolerance. The constant exposure
to cosmic radiation damages and eventually destroys electronics, limiting
the lifespan of all space-bound missions. Thus, as space missions
grow increasingly ambitious in distance away from Earth, and therefore
time in space, the electronics driving them must likewise grow increasingly
radiation-tolerant. In this work, we show how carbon nanotube (CNT)
field-effect transistors (CNFETs), a leading candidate for energy-efficient
electronics, can be strategically engineered to simultaneously realize
a robust radiation-tolerant technology. We demonstrate radiation-tolerant
CNFETs by leveraging both extrinsic CNFET benefits
owing to CNFET device geometries enabled by their low-temperature
fabrication, as well as intrinsic CNFET benefits
owing to CNTs’ inherent material properties. By performing
a comprehensive study and optimization of CNFET device geometries,
we demonstrate record CNFET total ionizing dose (TID) tolerance (above
10 Mrad(Si)) and show transient upset testing on complementary metal-oxide-semiconductor
(CMOS) CNFET-based 6T SRAM memories via X-ray prompt
dose testing (threshold dose rate = 1.3 × 1010 rad(Si)/s).
Taken together, this work demonstrates CNFETs’ potential as
a technology for next-generation space applications.
Non-radiation hardened P-channel and N-channel MOS transistors were irradiated with Co-60 gamma rays, 0.5 to 22 MeV protons, and 1 to 7 MeV electrons to determine the correlation between the gamma rays and the charged particles. Comparison of electrons to Co-60 showed that for equal absorbed doses, the damage produced was equivalent for all bias conditions. Under zero gate bias conditions, 2 to 22 MeV protons also produced damage in the test devices that was equivalent to Co-60. However, under bias conditions for high drain-source currents, the damage for protons below 22 MeV was always less than Co-60 (the lower the proton energy, the less the damage). The 0.5 MeV proton data showed poor correlation with Co-60 results. No dose-rate dependence was observed in the data. We conclude that, for the silicon MOS devices tested, the radiation damage produced by Co-60 provided a worst case simulation of high energy electron or proton damage.
Metal semiconductor field effect transistors (MESFETs) have been fabricated using a silicon-on-insulator (SOI) CMOS process. The MESFETs make use of a TiSi 2 Schottky gate and display good depletion mode characteristics with a threshold voltage of 0 5 V. The drain current can also be controlled by a voltage applied to the substrate, which then behaves as a MOS back gate. The transistors have been irradiated with 50 keV X-rays to a total ionizing dose in excess of 1 Mrad(Si). After irradiation the threshold voltage of both the top Schottky gate and the back MOS gate shift to more negative values. The shift in threshold is attributed to radiation induced fixed oxide charge at the interface between the SOI channel and the buried oxide.Index Terms-MESFETs, silicon-on-insulator technology, X-ray effects.
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