Improved Radiation Hardness Research Articles

Fast neutron damage in silicon detectors

Radiation effects of fast neutrons have been measured in silicon detectors of varying resistivity irradiated to ≈ 10 11 n/cm 2 over periods of weeks. The principal damage effect is increased leakage current due to generation of carriers from defect levels in the depletion region. Damage and leakage current constants have been established for detector resistivities between 10 and 27 000 ω cm and lie in the range of (0.7–2) × 10 7 s/cm 2 ( K) for PuBe neutrons. A slight increase in K was observed for higher resistivities which translates into somewhat improved radiation hardness. A fit of these data was attempted to a two-level recombination formulation of the damage constant.

Improved radiation hardness of MOS devices with ultrathin nitrided oxide gate dielectrics prepared by rapid thermal processing

The radiation hardness of MOS devices with ultrathin nitrided oxides ( approximately 100 AA) prepared by rapid thermal nitridation (RTD) of thin oxides has been studied. The radiation was performed by exposing devices under X-rays of 50 keV to a dose of 0.5 Mrad(Si). Compared with conventional thermal oxides, the RTN oxide devices exhibit a much smaller increase in both the fixed charge N/sub f/ and the interface state D/sub it/ densities. In addition, it is found that higher RTN temperature and/or longer durations produce smaller Delta N/sub f/ and Delta D/sub it/. >

Degradation Analysis of Lateral PNP Transistors Exposed to X-Ray Irradiation

Degraded current gain by X-ray irradiation is analyzed for lateral pnp transistors. The relationship between the total dose of X-ray and the surface recombination velocity is also studied. Surface recombination velocity is evaluated in two regions: the depletion region of the emitter-base junction and the non-depleted charge-neutral region of the base surface. X-ray total dose dependency of surface recombination velocity is experimentally derived as: sdep = 0.33D0.9 for depletion regions, and sSur = 3.8D0.8 for non-depleted surface region in the device structure. A radiation hardened structure with a surface potential barrier for lateral pnp transistors is proposed. The possibility of more than one-order of magnitude improvement in radiation hardness is demonstrated by both simulation and experiments.

Radiation Response of 64k-Bit and 128k-Bit Ultraviolet Erasable Programmable Read Only Memories (UVEPROMs)

The radiation response of 64k-bit and 128k-bit UVEPROMs was tested in a dose-rate and total-dose environment to determine their ability to survive a nuclear event and to be used as a bootstrap-reinitialization firmware following a circumvention cycle. A sample of five 64k-bit UVEPROMs experienced no erasure at dose-rates ranging from 3 × 107 rad(si)/second to 3 × 1010 rad(si)/second. They experienced transient upsets (soft errors) caused by the peripheral address and read circuits in that range of dose-rates. A total of 22 samples of 64k-and 128k-bit UVEPROMs experienced total-dose induced failures at levels ranging from 7 to 14 krad(si). This series of radiation tests confirms the improvement in radiation hardness which has been previously reported for UVEPROM[1]. This improvement is primarily attributable to thinner gate oxides resulting from a finer control of the manufacturing process. Further improvement is expected with the scaled-down geometries of the 256k-bit UVEPROMs not yet available. The relatively widespread distribution of total-dose hardness observed in the UVEPROM testing calls for hardness assurance controls to be exercised by the user in radiation-hard applications.

Effects of Metallic Doping on Ionization Damage in MOS FETS

Detailed studies of radiation damage in metaloxide-semiconductor (MOS) transistors show that the damage due to ionizing radiation is substantially different if chromium is added to the gate oxide. Devices with chromium consistently show smaller gate threshold shifts (due to positive charge storage in the gate oxide) when irradiated with zero or negative gate bias; they also show smaller increases in interface state density. The generation of interface states by radiation is also bias dependent in chromium MOS devices. Another difference between devices with conventional and chromium-doped oxides is the lower rate of thermal annealing when chromium is used. An extended anneal at 350°C is required to remove radiation damage from these devices. A considerable degree of control over ionization damage is thus obtained by chromium doping, and it appears this control can be used to improve radiation hardness of MOS transistors.