Papers by Keyword: Heavy Ion Irradiation

Abstract: Silicon bipolar junction transistors (BJTs), Silicon-germanium heterojunction bipolar transistors (SiGe HBTs) and metal oxide semiconductor (MOS) devices are the key components of BiCMOS integrated circuits. The semiconductor devices need to withstand very high total doses (100’s of Mrad) for reliable operation of electronic circuits for 8-10 years of LHC operation. The study of radiation tolerance of semiconductor devices up to 100 Mrad of total dose takes longer time with conventional ⁶⁰Co gamma, proton and electron irradiation facilities and the effects due to these radiations are well understood. Hence it is important to study the effects of heavy ion irradiation on various semiconductor devices. The irradiation time decreases with increasing linear energy transfer (LET) of incident radiation and LET increases with atomic number of the impinging ions. But it is essential to understand the mechanism of energy transfer by different heavy ions in semiconductor devices. Therefore, here we give an overview of different heavy ion interactions with Si BJTs, MOSFETs and SiGe HBTs by primarily focusing on the electrical characteristics of these devices before and after ion irradiation. We show that the irradiation time needed to reach very high total dose can be reduced by using Pelletron accelerator facilities instead of conventional irradiation facilities.

Abstract: The critical electric field (E_cr) of the gate oxide in 4H-Silicon Carbide (SiC) MOSFETs was measured under inversion bias conditions with ion irradiation. The Linear Energy Transfer (LET) dependence of the E_cr at which the gate oxide breakdown occurred in these MOSFETs was evaluated. The linear relationship between the E_cr^-1 and LET was observed for SiC MOSFETs. The slope of the LET-1/E_cr for SiC MOSFETs is almost the same that of the LET-1/E_cr lines for SiC MOS capacitors. The V_ds dependence of E_cr was also evaluated. The correlation between the direction of electric field of drain-source region and direction of ion incidence affects to instability of E_cr.

Abstract: In this paper the SEE (single event effects) of different parts of device were explored on a 32-bit microprocessor with a five-stage instruction pipeline by laser test and heavy ion test. The cross section curves for different function units were obtained and the comparison of the dates obtained from laser test and heavy ion tests was made. In addition, laser test under different scanning steps were made which indicate that when the scanning step length is in small steps which is considerably equivalent to the laser spot size, there is little change in the number of single event errors caused by each laser pulse. Wherever with the scanning step increasing, the number of single event errors caused by each laser pulse will be reduced. Experiment results suggest that there are differences between laser test and the heavy ion test but have a similar trend. The pulsed laser is an extremely powerful and low-cost technique for SEE testing and will provide invaluable information in characterizing SEE in integrate circuits.

Abstract: Heavy ion irradiation on phase change memory cell was conducted using Monte Carlo simulations. Absorbed dose in the whole memory cell, as well as in its active layer was assessed. Phase change memory cell was modeled as a sandwiched structure of two TiW electrodes and ZnS-SiO₂ films as insulators surrounding the active region. The most commonly used phase change material, Ge₂Sb₂Te₅, was used as active layer of the cell. Ionization effects of heavy ion irradiation were investigated for various thicknesses of phase change layer and different ion energies.

Abstract: The leakage currents through the gate oxide of MOS capacitors fabricated on n-type 4H-Silicon Carbide (SiC) was measured under accumulation bias conditions with heavy-ion irradiation. The Linear Energy Transfer (LET) dependence of the critical electric field (E_cr) at which dielectric breakdown occurred in these capacitors with two different oxide thicknesses was evaluated. The MOS capacitors with thin gate oxide showed higher E_cr values than those with thick gate oxide. The linear relationship between the reciprocal E_cr and LET was observed for both MOS capacitors. The slope of LET dependence of 1/E_cr for SiC MOS capacitors was smaller than that for Si, suggesting that SiC MOS devices are less susceptible to single-event gate rupture (SEGR) than Si MOS devices.

Abstract: Peak value degradation of heavy-ion induced transient currents in Metal-Oxide-Semiconductor (MOS) capacitors fabricated on n-type and p-type 6H-SiC was observed. The capacitances of MOS capacitors measured during the ion irradiation suggest that the depletion layer width decreased with increasing number of incident ions and was saturated. Since the number of incident ions obtained at the peak current saturation corresponded to that at the saturation of the capacitance, the decrease in peak current can be interpreted in terms of the decrease in the depletion layer width.