Diyuan Ren

Total dose ionizing irradiation effects on a static random access memory field programmable gate array

SRAM-based FPGA devices are irradiated by 60Co γ rays at various dose rates to investigate total dose effects and the evaluation method. The dependences of typical electrical parameters such as static power current, peak—peak value, and delay time on total dose are discussed. The experiment results show that the static power current of the devices reduces rapidly at room temperature (25 °C) and high temperature (80 °C) annealing after irradiation. When the device is irradiated at a low dose rate, the delay time and peak—peak value change unobviously with an increase in the accumulated dose. In contrast, the function parameters completely fail at 2.1 kGy(Si) when the dose rate increases to 0.71 Gy(Si)/s.

Dose Rate Dependence of Electrical Characteristics of Lead Zirconate Titanate Capacitors

The influence of gamma-radiation dose rate on the electrical properties of lead zirconate titanate capacitors was investigated. More severe degradations in dielectric constant, coercive field, remanent polarization and capacitance-voltage (C-V) curves occurred with increasing radiation dose at lower dose rates. The electrical properties exhibited distinct radiation dose rate dependence and the worst-case degradation occurred at the lowest dose rate. The radiation-induced degradation of parameters such as the coercive field drift and distortion of the C-V curve can be recovered partly through post-irradiation annealing.

Total dose irradiation and hot-carrier effects of sub-micro NMOSFETs

Total dose irradiation and the hot-carrier effects of sub-micro NMOSFETs are studied. The results show that the manifestations of damage caused by these two effects are quite different, though the principles of damage formation are somewhat similar. For the total dose irradiation effect, the most notable damage lies in the great increase of the off-state leakage current. As to the hot-carrier effect, most changes come from the decrease of the output characteristics curves as well as the decrease of trans-conductance. It is considered that the oxide-trapped and interface-trapped charges related to STI increase the current during irradiation, while the negative charges generated in the gate oxide, as well as the interface-trapped charges at the gate interface, cause the degradation of the hot-carrier effect. Different aspects should be considered when the device is generally hardened against these two effects.

The enhanced low dose rate sensitivity of a linear voltage regulator with different biases

A linear voltage regulator was irradiated by 60Co γ at high and low dose rates with two bias conditions to investigate the dose rate effect. The devices exhibit enhanced low dose rate sensitivity (ELDRS) under both biases. Comparing the enhancement factors between zero and working biases, it was found that the ELDRS is more severe under zero bias conditions. This confirms that the ELDRS is related to the low electric field in a bipolar structure. The reasons for the change in the line regulation and the maximum drive current were analyzed by combining the principle of linear voltage regulator with irradiation response of the transistors and error amplifier in the regulator. This may be helpful for designing radiation hardened devices.

Ionizing radiation effects of mobility in fluorinated NMOSFETs

Co-60 radiation responses of carrier mobility in fluorinated NMOSFETs have been investigated. The experimental results show that the radiation induced mobility degradation in fluorinated oxides can be restrained in the F dose range of 1/spl times/10/sup 15/-1/spl times/10/sup 16/ F/cm/sup 2/, the better degradation improvement corresponds to higher fluorine implantation dose due to less interface trap buildup. In addition, the mobility degradation is related to the channel width.

The annealing behavior of oxide trapped charges and interface traps in fluorinated NMOSFETS

The gate bias annealing of threshold voltage, oxide trapped charges and interface traps in fluorinated n-channel MOSFETs has been investigated. The annealing rate of oxide trapped charge is correlated with the value of gate bias. The annealing of interface traps has a turnaround effect. Switching gate bias during anneal results in the creation and banishment of oxide trapped charges. The annealing saturation appear after a long term anneal. The radiation damage can be restrained in fluorinated MOS oxides. Gate bias has a more significant influence on the build-up and annealing of oxide trapped charges in fluorinated NMOSFETs.

Read Static Noise Margin Decrease of 65-nm 6-T SRAM Cell Induced by Total Ionizing Dose

Read static noise margin (SNM) decrease of 65-nm 6-T cell induced by total ionizing dose (TID) was observed in this paper. The static random access memory (SRAM) cell test structure allowing precise measurement of read SNM was specifically designed and irradiated by gamma ray. Experimental results show that read SNM of 65-nm 6-T cell is sensitive to TID irradiation. The largest decrease of read SNM is 48 mV after 1000 krad(Si) irradiation, which is 36% of the value before TID irradiation. Being dependent on the measurement of radiation responses of cell transistors and simulation results, we conclude that the read SNM decrease is due to a threshold voltage shift induced by TID. Because narrow width transistors are employed in SRAM cells, threshold voltage of cell transistors will be shifted by charges trapped in shallow trench isolation, known as “Radiation-Induced Narrow Channel Effect.”

Hot-carrier effects on irradiated deep submicron NMOSFET

We investigate how γ exposure impacts the hot-carrier degradation in deep submicron NMOSFET with different technologies and device geometries for the first time. The results show that hot-carrier degradations on irradiated devices are greater than those without irradiation, especially for narrow channel device. The reason is attributed to charge traps in STI, which then induce different electric field and impact ionization rates during hot-carrier stress.

Double humps and radiation effects of SOI NMOSFET

Radiation experiments have been carried out with a SOI NMOSFET. The behavior of double humps was studied under irradiation. The characterization of the hump was demonstrated. The results have shown that the shape of the hump changed along with the total dose and the reason for this was analyzed. In addition, the coupling effect of the back-gate transistor was more important for the main transistor than the parasitic transistor.

A thermal field oxidation process for ionizing radiation hardness

A thermal field oxidation process for ionizing radiation hardness has been described. It is shown that the failure threshold of 54HC04, in which the hardened thermal field process has been applied, is excess to 1/spl times/10/sup 6/rad(Si).