Negative Channel Metal Oxide Semiconductor Research Articles

Proton radiation effects in 4H-SiC diodes and MOS capacitors

Proton irradiation is used to probe the physics of 4H-silicon carbide (SiC) Schottky barrier diodes (SBDs) and negative channel metal oxide semiconductor (nMOS) capacitors for the first time. Both 4H-SiC SBD diodes and SiC MOS structures show excellent radiation tolerance under high-energy, high-dose proton exposure. Unlike for SiC JBS diodes, which show a strong increase in series resistance after proton irradiation, these SiC SBDs show very little forward bias I--V degradation after exposure to 63.3 MeV protons up to a fluence of 5/spl times/10/sup 13/ p/cm/sup 2/. An improvement in reverse leakage current after irradiation is also observed, which could be due to a proton annealing effect. The small but observable increase in blocking voltage for these SiC SBDs is attributed to a negative surface charge increase, consistent with earlier gamma results. The resultant Q/sub eff/ change of 4H-SiC nMOS capacitors under proton irradiation was used to quantify the radiation induced changes to the blocking voltage in the SBD diodes in MEDICI simulations, and showed a good agreement with the experimental data. Characterization of these capacitors also suggests that 4H-SiC MOS structures are radiation hard.

Diagnosis of NMOS DRAM functional performance as affected by a picosecond dye laser

A picosecond pulsed dye laser beam was at selected wavelengths successfully used to simulate heavy-ion single-event effects (SEEs) in negative channel metal-oxide semiconductor dynamic random access memories (NMOS DRAMs). A DRAM was used to develop the test technique because bit-mapping capability and previous heavy-ion upset data were available. Other investigators have used Nd:Yag lasers to correlate laser and heavy-ion data for devices characterized by prompt charge collection, which is controlled by charge carrier density in the immediate vicinity of a depletion region. However, the present analysis is the first to establish such a correlation for devices, such as the NMOS DRAM, where charge collection is dominated by long-range diffusion, which is controlled by carrier density at remote distances from a depletion region. In the latter case, penetration depth is an important parameter and is included in the present analysis. A single-pulse picosecond dye laser beam (1.5 μm dia.) focused onto a single cell component can upset a single memory cell. In addition, clusters of memory cell upsets (multiple errors) were observed when the laser energy was increased above the threshold energy. The multiple errors were analyzed as a function of the bias voltage and total energy of a single pulse. A diffusion model to distinguish the multiple upsets from the laser-induced charge agreed well with previously reported heavy ion data. This correlation is one more step toward the goal of using a picosecond dye laser for SEE investigations.

Modularizing, minimizing, and interpreting the K&H fault-tree : Mitchell O. Locks. IEEE Trans. Reliab.R-30 (5), 411 (1981)

A picosecond pulsed dye laser beam was at selected wavelengths successfully used to simulate heavy-ion single-event effects (SEEs) in negative channel metal-oxide semiconductor dynamic random access memories (NMOS DRAMs). A DRAM was used to develop the test technique because bit-mapping capability and previous heavy-ion upset data were available. Other investigators have used Nd:Yag lasers to correlate laser and heavy-ion data for devices characterized by prompt charge collection, which is controlled by charge carrier density in the immediate vicinity of a depletion region. However, the present analysis is the first to establish such a correlation for devices, such as the NMOS DRAM, where charge collection is dominated by long-range diffusion, which is controlled by carrier density at remote distances from a depletion region. In the latter case, penetration depth is an important parameter and is included in the present analysis. A single-pulse picosecond dye laser beam (1.5 μm dia.) focused onto a single cell component can upset a single memory cell. In addition, clusters of memory cell upsets (multiple errors) were observed when the laser energy was increased above the threshold energy. The multiple errors were analyzed as a function of the bias voltage and total energy of a single pulse. A diffusion model to distinguish the multiple upsets from the laser-induced charge agreed well with previously reported heavy ion data. This correlation is one more step toward the goal of using a picosecond dye laser for SEE investigations.