Total dose radiation response of modified commercial silicon-on-insulator materials with nitrogen implanted buried oxide

Nitrogen ions of various doses are implanted into the buried oxide （BOX） of commercial silicon-on-insulator （SOI） materials, and subsequent annealings are carried out at various temperatures. The total dose radiation responses of the nitrogen-implanted SOI wafers are characterized by the high frequency capacitance-voltage （C-V） technique after irradi- ation using a Co-60 source. It is found that there exist relatively complex relationships between the radiation hardness of the nitrogen implanted BOX and the nitrogen implantation dose at different irradiation doses. The experimental results also suggest that a lower dose nitrogen implantation and a higher post-implantation annealing temperature are suitable for improving the radiation hardness of SOI wafer. Based on the measured C V data, secondary ion mass spectrometry （SIMS）, and Fourier transform infrared （FTIR） spectroscopy, the total dose responses of the nitrogen-implanted SOI wafers are discussed.

Total Ionizing Dose Radiation Effects in the P-Type Polycrystalline Silicon Thin Film Transistors

The total ionizing dose radiation effects in the polycrystalline silicon thin film transistors are studied. Transfer characteristics, high-frequency capacitance-voltage curves and low-frequency noises (LFN) are measured before and after radiation. The experimental results show that threshold voltage and hole-field-effect mobility decrease, while sub-threshold swing and low-frequency noise increase with the increase of the total dose. The contributions of radiation induced interface states and oxide trapped charges to the shift of threshold voltage are also estimated. Furthermore, spatial distributions of oxide trapped charges before and after radiation are extracted based on the LFN measurements.

Total Ionizing Dose Radiation Effects of RF PDSOI LDMOS Transistors

The effects of total ionizing dose radiation on direct current （DC） and small-signal radio frequency （RF） performance of multi-finger RF partial deplete silicon-on-insulator lateral double diffused MOS （PDSOI LDMOS） transistors are investigated. The radiation response of the LDMOS transistors with different device structures is characterized for an equivalent gamma dose up to 1Mrad（Si） at room temperature. The front and back gate threshold voltages, off-state leak- age, transconductance, and output characteristics are measured before and after radiation, and the results show a significant degradation of DC performance. Moreover, high frequency measurements for the irradiated transistors indicate remarkable declines of S-parameters, cutoff frequency, and maximum oscillation frequency to 1Mrad（Si） exposure levels. Compared to the transistors with the BTS contact structure,the transistors with the LBBC contact do not show its excellent DC radiation hardness when the transistors operate at alternating current （AC） mode.

Total dose radiation effects on SOI NMOS transistors with different layouts

Partially-depleted Silicon-On-Insulator Negative Channel Metal Oxide Semiconductor （SOI NMOS） transistors with different layouts are fabricated on radiation hard Separation by IMplanted OXygen （SIMOX） substrate and tested using 10 keV X-ray radiation sources. The radiation performance is characterized by transistor threshold voltage shift and transistor leakage currents as a function of the total dose up to 2.0×10^6 rad（Si）. The results show that the total dose radiation effects on NMOS devices are very sensitive to their layout structures.

A total dose radiation model for deep submicron PDSOI NMOS

In most of the total dose radiation models, the drift of the threshold voltage and the degradation of the carrier mobility were only studied when the bulk potential is zero. However, the measured data indicate that the total dose effect is closely related to the bulk potential. In order to model the influence of the bulk potential on the total dose effect, we proposed a macro model. The change of the threshold voltage, carrier mobility and leakage current with different bulk potentials were all modeled in this model, and the model is well verified by the measured data based on the 0.35μm PDSOI process developed by the Institute of Microelectronics of the Chinese Academy of Sciences, especially the part of the leakage current.

Total dose radiation and annealing responses of the back transistor of Silicon-On-Insulator pMOSFETs

The total dose radiation and annealing responses of the back transistor of Silicon-On-Insulator （SOI） pMOSFETs have been studied by comparing them with those of the back transistor of SOI nMOSFETs fabricated on the same wafer. The transistors were irradiated by 60Co γ-rays with various doses and the front transistors were biased in a Float-State and Off-State, respectively, during irradiation. The total dose radiation responses of the back transistors were characterized by their threshold voltage shifts. The results show that the total dose radiation response of the back transistor of SOI pMOSFETs, similar to that of SOI nMOSFETs, depends greatly on their bias conditions during irradiation. However, with the Float-State bias rather than the Off-State bias, the back transistors of SOI pMOSFETs reveal a much higher sensitivity to total dose radiation, which is contrary to the behavior of SOI nMOSFETs. In addition, it is also found that the total dose radiation effect of the back transistor of SOI pMOSFETs irradiated with Off-State bias, as well as that of the SOI nMOSFETs, increases as the channel length decreases. The annealing response of the back transistors after irradiation at room temperature without bias, as characterized by their threshold voltage shifts, indicates that there is a relatively complex annealing mechanism associated with channel length, type, and bias condition during irradiation. In particular, for all of the transistors irradiated with Off-State bias, their back transistors show an abnormal annealing effect during early annealing. All of these results have been discussed and analyzed in detail by the aid of simulation.

Effect of total ionizing dose radiation on the 0.25 μm RF PDSOI nMOSFETs with thin gate oxide

Thin gate oxide radio frequency （RF） PDSOI nMOSFETs that are suitable for integration with 0.1μm SO1 CMOS technology are fabricated, and the total ionizing dose radiation responses of the nMOSFETs having four different device structures are characterized and compared for an equivalent gamma dose up to 1 Mrad （Si）, using the front and back gate threshold voltages, off-state leakage, transconductance and output characteristics to assess direct current （DC） performance. Moreover, the frequency response of these devices under total ionizing dose radiation is presented, such as small-signal current gain and maximum available/stable gain. The results indicate that all the RF PDSOI nMOSFETs show significant degradation in both DC and RF characteristics after radiation, in particular to the float body nMOS. By comparison with the gate backside body contact （GBBC） structure and the body tied to source （BTS） contact structure, the low barrier body contact （LBBC） structure is more effective and excellent in the hardness of total ionizing dose radiation although there are some sacrifices in drive current, switching speed and high frequency response.

Stereotactic radiotherapy for the treatment of nasopharyngeal carcinoma: a Meta-analysis of 1371 cases in China

Objective The aim of this study was to clarify the outcomes of stereotactic radiotherapy for the treatment of local residual and(or) local recurrent nasopharyngeal carcinoma and to promote scientific clinical treatment and research on it in China and other countries by creating a large data resource.Methods This Meta-analysis conducted a literature search using the China National Knowledge Infrastructure database for all clinical research articles on stereotactic radiotherapy for the treatment of local residual and(or) local recurrent nasopharyngeal carcinoma in China.Data on patient cohort numbers and other research factors were recorded for every relevant clinical research article.Calculated and analyzed these fact sheets to pave the way for the objective of this project.Results A total of 40 clinical research articles including 1,371 patients in China from 1998 to 2012 were identified.The average cohort size was 34 patients(range 9-98 patients).The average total radiation dose range was 16-33.6 Gy.The average study or treatment duration was 3.51 years.The calculated average follow-up time was 31.59 months.Conclusion The study provided the largest resource for further research and Meta-analyses to determine the clinical pathway of stereotactic radiotherapy for the treatment of local residual and(or) local recurrent nasopharyngeal carcinoma.The results indicated that variability in the total radiation dose,treatment or research time,and follow-up duration may have contributed to the complications and side effects of stereotactic radiotherapy for local residual and(or) local recurrent nasopharyngeal carcinoma in China.The calculated average total radiation dose,follow-up time,and treatment and research durations may be referenced for future treatment and research.This study also proposed worldwide cooperation for the metaanalysis of research articles on stereotactic radiotherapy for treating local residual and(or) local recurrent nasopharyngeal carcinoma.

Effects of Si implantation on the total dose hardness of fully-depleted SIMOX wafers

Total dose hardened fully-depleted SOI materials are fabricated on separation by implanted oxygen （SIMOX） materials by silicon ion implantation and annealing. The ID-VG characteristics of pseudo-MOS transistors pre- and post-irradiation are tested with ^60Co gamma rays. The chemical bonds and the structure of Si in the buried oxide are also studied by X-ray photoelectron spectroscopy and cross-sectional high-resolution transmission electron microscopy, respectively. The results show that Si nanocrystals in the buried oxide produced by ion implantation are efficient deep electron traps, which can significantly compensate positive charge buildup during irradiation. Si implantation can enhance the total-dose radiation tolerance of the fully-depleted SOI materials.

Radiation response of pseudo-MOS transistors fabricated in hardened fully-depleted SIMOX SOI wafers

The total dose radiation response of pseudo-MOS transistors fabricated in hardened and unhardened FD （fully-depleted） SIMOX （Separation by Implanted Oxygen） SOI （Silicon-on-insulator） wafers is presented. At 1 Mrad（Si） radiation dose, the threshold voltage shift of the pseudo-MOS transistor is reduced from -115.5 to -1.9 V by the hardening procedure. The centroid location of the net positive charge trapped in BOX, the hole-trap density and the hole capture fraction of BOX are also shown. The results suggest that hardened FD SIMOX SOI wafers can perform well in a radiation environment.