Shoubin Xue

Impact of proton-radiation-induced spacer damage on the dc characteristics degradation in deep-submicron metal-oxide-semiconductor field effect transistors

The dc characteristics degradation of 0.18 μm metal-oxide-semiconductor field effect transistors (MOSFETs) after 10 MeV proton irradiation is comprehensively investigated in this paper. The measured results show that the off-state drain current is increased in N-channel MOSFETs, which is due to the turn on of the parasitic transistors induced by the shallow trench isolation regions. While in P-channel MOSFETs, the threshold voltage increase (absolute value), the transconductance degradation, and the saturation drain current decrease are observed. From the analysis, it is concluded that the basic damage mechanism is not ascribed to the gate oxide and the isolation region. The origin of the observed changes may be mainly due to the damage in the spacer oxides of the transistors. In order to verify the assumption, the leakage current passing through the spacer between the gate and the drain is measured before and after irradiation with floated source/substrate and grounded drain. We find that the leakage current is two to three times larger after irradiation. Finally, in order to confirm the extrapolation, 2-dimension (2D) simulation has been performed with Synopsys TCAD (technical computer-aided design) Sentaurus Device Simulation tools (ISE 10.0). The behavior of the simulated charges trapped in the spacers is qualitatively consistent with the experimental results.The dc characteristics degradation of 0.18 μm metal-oxide-semiconductor field effect transistors (MOSFETs) after 10 MeV proton irradiation is comprehensively investigated in this paper. The measured results show that the off-state drain current is increased in N-channel MOSFETs, which is due to the turn on of the parasitic transistors induced by the shallow trench isolation regions. While in P-channel MOSFETs, the threshold voltage increase (absolute value), the transconductance degradation, and the saturation drain current decrease are observed. From the analysis, it is concluded that the basic damage mechanism is not ascribed to the gate oxide and the isolation region. The origin of the observed changes may be mainly due to the damage in the spacer oxides of the transistors. In order to verify the assumption, the leakage current passing through the spacer between the gate and the drain is measured before and after irradiation with floated source/substrate and grounded drain. We find that the leakage cur...

A model for radiation-induced off-state leakage current in N-channel metal-oxide-semiconductor transistors with shallow trench isolation

A radiation-induced leakage current model in deep submicron bulk silicon N-channel metal-oxide-semiconductor field effect transistor (NMOSFET) is proposed in this paper for circuit simulations. The model takes into account the impact of the substrate doping concentration, the angle of shallow trench isolation (STI) region, and the junction depth of source/drain, which can predict the off-state leakage current of the NMOSFET with STI region irradiated at different radiation doses. The model is verified by comparing with the experimental results. The model can be easily implemented into the circuit simulator to evaluate the impact of total ionizing dose effect on the performance of circuit.

Total ionizing dose and single-event effect in vertical channel double-gate nMOSFETs

In this paper, the total ionizing dose (TID) and single-event effect (SEE) in vertical channel double-gate (DG) nMOSFETs are comprehensively investigated. Due to the vertical channel structure and the excellent gate control capability, the vertical channel DG transistor is relatively resistant to TID and transient ionization effect. However, the dc characteristics of vertical channel DG device are very sensitive to permanent damage induced by a few ions hitting the device. The on-state current and transconductance of the vertical channel DG MOSFETs show significant degradation after exposure to heavy ions, which is attributed to the formation of displacement damage in the channel. As the device feature size scales down to the deca-nanometer regime, the influence of permanent damage induced by a few ions striking the device static performance cannot be ignored and should be seriously considered in radiation-hardened technologies.

Investigation of the off-State Behavior in Deep-Submicrometer NMOSFETs Under Heavy-Ion Irradiation by 3-D Simulation

The behavior of an off-state leakage current induced by heavy-ion irradiation in deep-submicrometer NMOSFETs is comprehensively investigated by 3-D simulation in this paper. The results show that the off-state drain current is increased, which is mainly due to the positively charged damage region generated by the heavy-ion strike in the shallow-trench isolation (STI) region. As the channel length scales down, the off-state leakage collapse becomes more severe. The dependence of the off-state leakage current on the device channel length and width is studied, which gives the location of the most critical physical damage region in the STI trench oxide. Moreover, the impact of the gate bias during exposure to heavy ions on the device off-state behavior is also analyzed, indicating that a low operating voltage is beneficial to the circuit radiation hardening. At last, to suppress the off-state leakage collapse, some possible solutions are proposed.

Deteriorated radiation effects impact on the characteristics of MOS transistors with multi-finger configuration

The deteriorated radiation effects of very deep-sub-micron (VDSM) MOS transistors with multi-finger are experimentally investigated for the first time. The results show that due to the interaction between reverse narrow channel effect and radiation induced edge effect, multi-finger transistors are more sensitive to radiation in comparison with standard MOSFETs. Larger threshold-voltage shift and higher leakage current are observed. The mechanisms responsible for the effects are briefly discussed. The results demonstrate that special radiation hardening technology should be adopted for multi-finger transistors operating in the radiation environment.

Total ionizing dose effects of novel vertical channel double-gate nMOSFETs

The total ionizing dose effects of novel vertical channel double-gate nMOSFETs (DGMOS) are experimentally investigated and compared with conventional planar nMOSFETs firstly in this paper. The radiation-induced off-state leakage current and subthreshold slope are greatly suppressed in vertical DGMOS devices compared with conventional nMOSFETs. The performance of vertical DGMOS devices under irradiation does not change apparently even when the dose is up to 1 Mrad(Si), which is attributed to its unique device structure for separating the channel from the thick oxide isolation region and preventing the formation of a leakage path. The results indicate that the vertical channel device structure is a promising candidate for future space applications.

Investigations on proton-irradiation-induced spacer damage in deep-submicron MOSFETs

In this paper, we have focused our attention on DC characteristics degradation of 0.18 ¿m MOSFETs after 10-MeV proton irradiation. It is shown that the threshold voltage shift, the transconductance degradation and the saturation drain current decrease are lager in PMOSFETs, while small effects are exhibited in NMOSFETs. From the analysis, it is concluded that the basic damage mechanism is not ascribed to the gate oxide and the isolation. The origin of the observed changes is due to the damage in spacer oxides of the MOSFETs. The mechanism involved is that the energetic protons incident on the spacer region lose their energy to displace the atoms, give rise to many defects, and create a disordered region (displacement damage region), where many defects and traps can capture positive charges to make the static characteristics degraded. Therefore, it is pointed out that the sidewalls are one of sensitive regions for irradiation hardness.