Bingxu Ning

Total-Ionizing-Dose Induced Coupling Effect in the 130-nm PDSOI I/O nMOSFETs

The tolerance of partially depleted (PD) silicon-on-insulator nMOSFETs to total-ionizing-dose-induced trapped charge in the buried oxide is investigated. The radiation-induced coupling effect due to the metamorphosis of PD device into a fully depleted one is observed. The coupling effect is responsible for the negative threshold voltage shift, enhanced drain-induced barrier lowering effect, subthreshold slope increase, and transconductance variation in the front channel device. The back channel implantation is introduced as an effective way to suppress the radiation-induced coupling effect.

Comprehensive Study on the Total Dose Effects in a 180-nm CMOS Technology

The effects of total ionizing on a 180-nm CMOS technology are comprehensively studied. Firstly, we show new results on the hump effect which has strong relationship to the STI corner oxide thickness. Secondly, the leakage current degradation in various devices after radiation is investigated. For the intra-device leakage, both body doping concentration and STI corner thickness play very important roles. For the inter-device leakage, due to the low electric field at the STI bottom, it is found to be insensitive to ionizing radiation. Thirdly, a method for extracting the effective threshold voltage of the sidewall parasitic transistor is proposed by studying the leakage output characteristics. Finally, we find that the drain saturation current increases in NMOS transistors after radiation, especially in the narrow-channel ones.

Total Ionizing Dose Enhanced DIBL Effect for Deep Submicron NMOSFET

Radiation enhanced drain induced barrier lowering (DIBL) effect under different bias conditions was experimentally observed and verified by 3D simulation for deep submicron MOSFETs with shallow trench isolation (STI) oxides. The off-state leakage current increased significantly after total ionizing dose (TID) above 200 krad(Si) for PASS ,OFF and ON bias condition. The irradiated devices exhibited enhanced DIBL effect, that is the off-state leakage current increases with drain voltage and DIBL parameter increases with TID. The oxide trapped charge in the STI sidewall enhances the DIBL by decreasing the drain to gate coupling, enhancing the electric field near the STI corner, and increasing the surface potential of lowly doped substrate along STI sidewall. A simple dipole theory describing the enhanced DIBL phenomenon is introduced. The phenomenon is a result of the electrostatic effect, which concentrates drain field on channel into the source along shallow trench isolation oxide. Effective non-uniform charge distribution is applied in the 3D simulation for the radiation enhanced DIBL effect. Good agreement between experiment and simulation results is demonstrated.

Radiation-induced shallow trench isolation leakage in 180-nm flash memory technology

The effects of total ionizing dose (TID) irradiation on the inter-device and intra-device leakage current in a 180-nm flash memory technology are investigated. The positive oxide trapped charge in the shallow trench isolation (STI) oxide is responsible for the punch-through leakage increase and punch-through voltage decrease. Nonuniform radiation-induced oxide trapped charge distribution along the STI sidewall is introduced to analyze the radiation responses of input/output (I/O) device and high voltage (HV) device. At low dose level, the inversion near the STI corner caused by the trapped charge occurs more easily due to the lower doping concentration in this region, which gives rise to the subthreshold hump effect. With total dose level increase, more charge at deep region of the STI oxide is accumulated, predominating the intra-device off-state leakage current. It has been discussed that the STI corner scheme and substrate doping profile play important roles on influencing the device’s performance after radiation.

Simple Method for Extracting Effective Sheet Charge Density Along STI Sidewalls Due to Radiation

A first order model of radiation induced narrow-channel effect (RINCE) is developed by applying charge conservation principle to calculate threshold voltage shift due to total ionizing dose (TID) irradiation. The model provides a way for extracting effective sheet charge density along shallow trench isolation (STI) sidewalls.

A New Method for Extracting the Radiation Induced Trapped Charge Density Along the STI Sidewall in the PDSOI NMOSFETs

The effects of the radiation-induced trapped charge in shallow trench isolation (STI) and buried oxide (BOX) on total ionizing radiation response of 0.13 μm partially-depleted silicon-on-insulator (PDSOI) NMOS technology are analyzed respectively. The positive trapped charge in the STI oxide, but not in the BOX, is responsible for the off-state leakage increase after ON bias radiation. A new method is proposed to calculate the surface charge density along the STI sidewall. This method takes into account the influences of the non-uniform electric field and the variable oxide thickness in the STI region. Moreover, the calculated non-uniform charge density along the STI sidewall is verified by three dimensional simulations. Even though there is charge-accumulation in the BOX, it shows minimal impact on the front-gate characteristics of the PDSOI devices in this 0.13 μm technology, except for the device with low body doping concentration. The positive charge trapped in BOX can induce significant threshold voltage shift in the RVT (regular Vth) I/O NMOSFET through coupling effect.

Comparison of TID response in core, input/output and high voltage transistors for flash memory

Total ionizing dose (TID) response in core, input/output (I/O) and high voltage (HV) transistors for 180 nm flash memory technology is comprehensively investigated. Great influence by irradiation is observed for all these transistors, including threshold voltage shift, appearance of subthreshold hump effect and increase of off-state leakage current. Also, we found that the higher the drain voltage, the larger increase of the off-state leakage, which is well known as radiation enhanced drain induced barrier lowering (DIBL) effect. Radiation enhanced DIBL effect leads to worse characteristic degradation of transistor. The HV transistor is the most sensitive parts in flash memory control circuitry.

The impact of total ionizing radiation on body effect

A new phenomenon, for the first time, shows that radiation-induced body effect factor decrease in NMOS transistors is presented. The results indicate that body effect factor shift decreases as the total ionizing dose (TID) level increases in NMOS transistors, especially in the narrow-channel ones, which can be considered as one of the radiation-induced narrow-channel effect (RINCE). A first-order model is developed by applying charge conservation principle. Good agreement is obtained by comparing the modeling with experimental results. Finally, some implications to mitigate the RINCE effect are discussed.

Radiation Hardening by Applying Substrate Bias

A reverse substrate bias is known to increase the threshold voltage and reduce the off-state leakage current, which is of great interest from a radiation perspective in space applications. In this work, substrate biases during both irradiation and post-irradiation test on the impacts of total ionizing dose effects in a 180 nm CMOS technology are studied. The results indicate that a negative substrate bias during irradiation impairs the radiation hardness while a negative substrate bias during post-irradiation test improves the radiation hardness for nMOS transistors. A simple model is proposed to discuss the net result including the both effects. We find that the substrate bias for radiation hardening does not always work in some special conditions, such as the device with very low body doping and the STI which is very sensitive to the electric field for the buildup of charge.

Influence of the Total Ionizing Dose Irradiation on 130 nm Floating-body PDSOI NMOSFETs

This paper investigates the impact of ionizing radiation on floating body effects for the 130 nm PDSOI NMOSFETs. It is shown that the floating body effects are restrained by the irradiation both for the core device and the input/output (I/O) device. For the core device, the second peak of the front gate transconductance which is known as the gate-induced floating body effect degrades with the incremental total dose. The decline of the second gm peak is ascribed to the impact of the radiation-induced leakage current, but not to the radiation-induced interface traps assisted recombination or the suppression of the electron valence band (EVB) tunneling. For the I/O device, the kink effect and the hysteresis effect in the output characteristic which are observed before irradiation become insignificant after irradiation. These phenomena are due to the fully depleted of the silicon film in the I/O device which is caused by the buried oxide charge trapping. In addition, a radiation-induced latch, which is result from the leakage current-induced impact ionization, is also observed in the I/O device.