Kazuyuki Hirose

We investigated proton irradiation effects on Cu(In,Ga)Se-2 (CIGS) solar cells with a structure of ZnO/CdS/CIGS using photoluminescence (PL) spectroscopy. After proton irradiation, near band-edge emission from the CIGS layer was considerably reduced, while deep-level emission emerged at 0.8 eV. Subsequent annealing restored the intensity of the near band-edge emission slightly, and reduced the 0.8 eV band substantially. An anomalous spectral variation caused by the annealing suggests that the 0.8 eV band does not originate from a single irradiation-induced defect. After the irradiation, the 1.35 eV emission from the US layer was moderately reduced, and the band-edge emission from the ZnO layer had disappeared. These bands recovered to the initial state after the annealing. Qualitative correlation was observed between the PL properties and the electrical properties of the cell.

We investigated proton irradiation effects on Cu(In,Ga)Se-2 (CIGS) solar cells with a structure of ZnO/CdS/CIGS using photoluminescence (PL) spectroscopy. After proton irradiation, near band-edge emission from the CIGS layer was considerably reduced, while deep-level emission emerged at 0.8 eV. Subsequent annealing restored the intensity of the near band-edge emission slightly, and reduced the 0.8 eV band substantially. An anomalous spectral variation caused by the annealing suggests that the 0.8 eV band does not originate from a single irradiation-induced defect. After the irradiation, the 1.35 eV emission from the US layer was moderately reduced, and the band-edge emission from the ZnO layer had disappeared. These bands recovered to the initial state after the annealing. Qualitative correlation was observed between the PL properties and the electrical properties of the cell.

We calculate the difference between the valence charges of the ground state and the Slater transition state for several types of Si compounds and Al compounds. We assume the dipole moment induced by core-hole generation at the Slater transition state to be the product of the valence charge difference and the bond length of the compounds. We find that the calculated dipole moment has a strong linear correlation well with (ε-1) / (ε+2), which is deduced from experimental values of the optical dielectric constant ε. © 2008 American Institute of Physics.

We find a new relationship between the optical dielectric constant of Al dielectric films and their chemical shifts measured by X- ray photoelectron spectroscopy (XPS). We measure the difference between core-level binding energy shift for Al 1s and core-level binding energy shift for Al 2p, Delta E-1s - Delta E-2p, for AlN using high- resolution high- energy synchrotron radiation. We find that Delta E-1s - Delta E-2p correlates well with the optical dielectric constants of Al, AlN, and Al2O3. This is consistent with the case of our previously reported Si compounds. First-principles calculations are performed to determine the mechanism behind the observed correlation.

A table-based technique for estimating single-event transient pulses is evaluated in the most crucial case for bulk MOSFET technologies where an ion penetrates the drain region. A device model of a bulk MOSFET is built in a 2-D numerical device simulation framework, and heavy-ion-induced transient currents flowing through its drain terminal are calculated. From the currents, single-event transient voltage pulses in an inverter are estimated with the table-based estimation technique. The results are compared with ones simulated in the mixed mode with the same device model and circuit configuration. The estimated pulses are comparable to the results in the mixed-mode device simulations. Moreover, the estimation accuracy can be improved by using a drain-capacitance compensation technique. An extrapolation technique based on the drain-voltage dependency of heavy-ion-induced transient currents is also presented to reduce the experimental costs for modeling.

The effects of heavy ion energy and nuclear interactions on the single-event upset (SEU) and single-event latchup (SEL) response of commercial and radiation-hardened CMOS ICs are explored. Above the threshold LET for direct ionization-induced upsets, little difference is observed in single-event upset and latchup cross sections measured using low versus high energy heavy ions. However, significant differences between low- and high-energy heavy ion test results are observed below the threshold LET for single-node direct ionization-induced upsets. The data suggest that secondary particles produced by nuclear interactions play a role in determining the SEU and SEL hardness of integrated circuits, especially at low LET. The role of nuclear interactions and implications for radiation hardness assurance and rate prediction are discussed.

The Japanese spacecraft, HAYABUSA, was launched on May 9, 2003 and spent more than 2.5 years approaching the asteroid ITOKAWA. This spacecraft used 13.2 Ah lithium-ion secondary cells. After HAYABUSA touched down on ITOKAWA in December 2005, it could not communicate for seven weeks due to a malfunction of the attitude control. During this period, four of 11 lithium-ion secondary cells were over-discharged, and solar power was unavailable due to the spacecraft's tumbling motion. However, the battery power was still indispensable for sealing the container with the asteroid sample. The seven remaining healthy cells were slowly recharged using minimum current. During this time, ground simulation tests using similarly-built and intentionally short-circuited cells were carried out to evaluate the battery's operational safety. After its safety was confirmed, the lithium-ion secondary battery was used to transfer, latch, and successfully seal the sample container into the reentry capsule. The necessary power for these actions was supplied by the battery.

JAXA is developing a Venus orbiter PLANET-C to be launched in 2010. This paper gives a summary of its power system and results of performance tests of the solar arrays and batteries. The solar arrays were confirmed to endure severe thermal cycles in the range of ?-170〜+170℃. The battery cells are subjected to simulation tests assuming practical operations, focusing on methods to control their deterioration.

In order to confirm benefits of a deep sub-micron FD-SOI and to identify possible issues concerning front-end circuits with the FD-SOI, we have submitted a small design to Oki Electric Industry Co., Ltd. via the multi-chip project service of VDEC, the University of Tokyo. The initial test results and future plans for development are presented. (c) 2007 Elsevier B.V. All rights reserved.

Described is an estimation technique,of single event transient voltage pulses in VLSI circuits from heavy-ion-induced transient currents measured in a single MOSFET. Waveforms of the transient voltage pulses are fully estimated by using transient current data obtained in various drain voltage conditions. Modeling of the irradiated device behavior for use in device/circuit simulations is not required. The concept is validated using a 2-D mixed-mode device simulation.

The impact of heavy ion energy on SEU and SEL in commercial and radiation-hardened CMOS SRAMs is explored. Provided the ion range is large enough for the ions to reach the sensitive device region, standard low-energy heavy ion testing is conservative with respect to high-energy heavy ions, at least for LETs above the threshold for direct ionization-induced upsets. However, below the threshold LET for direct ionization-induced effects we find some differences between low- and high-energy tests. These differences are attributed to the effects of nuclear reaction-induced secondary particles. Implications for hardness assurance testing and error rate calculations are discussed.

'HAYABUSA' is a Japanese interplanetary spacecraft for the exploration of an asteroid named 'ITOKAWA.' The spacecraft is powered by a 13.2 Ah lithium-ion secondary battery. To realize maximum performance of the battery for long flight operation, the state-of-charge (SOC) of the battery was maintained at ca. 65% during storage in case it is required for contingency operations. To maintain this SOC condition, the battery is charged once a week. We further charge the battery up to 4.1 V/cell using bypass circuits to balance the cells every four months. The capacity of the battery was measured during the flight operation, which revealed the appropriate capacity for the expected mission.

We studied HfAlOx(N)/SiO2/Si films which were fabricated by the layer-by-layer deposition and annealing (LL-D&amp A) method with different annealing conditions. In this time, in-situ annealing was performed at various temperatures in an NH3 ambient. In addition, post-deposition annealing (PDA) was performed for some samples. For each sample, the interfacial lattice strain was evaluated using extremely asymmetric X-ray diffraction and the local dielectric constant near the Al atoms was measured by X-ray photoelectron spectroscopy (XPS). Observation of the strain field was done by measuring the X-ray rocking curve of the Si 113 reflection of the Si (001) substrate under grazing incidence conditions. It was found that in the case of the samples without PDA, for higher in-situ annealing temperatures compressive strain is introduced and the local dielectric constant becomes lower. For the samples with PDA, the differences of the lattice strain and the local dielectric constant are small for different in-situ annealing temperatures. © 2007 IOP Publishing Ltd.

We describe state-of-the-art photoelectron spectroscopy studies of SiO(2)/Si interfaces that play fundamental roles in metal-oxide-semiconductor (MOS) field-effect transistors. We show comprehensive photoelectron spectra Of SiO(2)/Si interfaces, which were taken from SiO(2)/Si samples of extremlye high-quality by the high-resolution photoelectron spectroscopy technique with either synchrotron or laboratory X-ray sources. The spectra discussed here include the Si 2p, the Si 1s, the O 2s, and N 1s core-level spectra, and the valence-band spectra. We perform quantitative analysis using selected values of the photoionization cross-section and the electron escape depth, which is governed by both inelastic scattering and elastic scattering in SiO(2). On the other hand, we analyze peak energies by considering peak energy shifts that are due to several factors. Atomic structures are discussed in terms of intermediate oxidation states at SiO(2)/Si(1 0 0) interfaces and strained Si-O-Si bonds near the interfaces, while electronic structures are discussed in terms of valence-band offset at the interfaces and dielectric constants near the interfaces. Applications of photoelectron spectroscopy study to advanced oxide formation are also shown in terms of depth profiling of oxynitride films and interface structures of low-temperature oxide. (C) 2006 Elsevier Ltd. All rights reserved.

We propose a new method to estimate the local dielectric constant of an ultrathin gate insulator film formed on Si substrates by using X-ray photoelectron spectroscopy (XPS). First we measure the difference of core-level binding energy shifts for Si Is and Si 2p, ΔE1s - ΔE 2p, for various Si compounds using high-resolution high-energy synchrotron radiation. We find that the ΔE1s - ΔE 2p values are in very good correlation with the dielectric constant values of the Si compounds. Then, using this relation, we deduce the local dielectric constant for ultrathin SiO2 film formed on Si substrates. The results are in good agreement with values predicted by a first-principles calculation. © 2006 IEEE.

A scan flip-flop (FF) is designed to observe both single event transient (SET) and single event upset (SEU) soft errors in logic VLSI systems. The SET and SEU soft errors mean the upset caused by latching an SET pulse that originates in combinational logic blocks and the upset caused by a direct ion hit to the FF, respectively. An irradiation test method using the scan FF is proposed to obtain SET and SEU soft-error rates at each FF distributed in logic VLSI systems. A test chip is designed using a 0.2-mu m fully-depleted silicon-on-insulator standard cell library. The basic concepts have been validated with Verilog timing simulations. The cell-level implementation costs of the proposed scan FF are estimated to be reasonable.

We describe state-of-the-art photoelectron spectroscopy studies of SiO(2)/Si interfaces that play fundamental roles in metal-oxide-semiconductor (MOS) field-effect transistors. We show comprehensive photoelectron spectra Of SiO(2)/Si interfaces, which were taken from SiO(2)/Si samples of extremlye high-quality by the high-resolution photoelectron spectroscopy technique with either synchrotron or laboratory X-ray sources. The spectra discussed here include the Si 2p, the Si 1s, the O 2s, and N 1s core-level spectra, and the valence-band spectra. We perform quantitative analysis using selected values of the photoionization cross-section and the electron escape depth, which is governed by both inelastic scattering and elastic scattering in SiO(2). On the other hand, we analyze peak energies by considering peak energy shifts that are due to several factors. Atomic structures are discussed in terms of intermediate oxidation states at SiO(2)/Si(1 0 0) interfaces and strained Si-O-Si bonds near the interfaces, while electronic structures are discussed in terms of valence-band offset at the interfaces and dielectric constants near the interfaces. Applications of photoelectron spectroscopy study to advanced oxide formation are also shown in terms of depth profiling of oxynitride films and interface structures of low-temperature oxide. (C) 2006 Elsevier Ltd. All rights reserved.

Heavy-ion-induced SET-pulse widths in NOR-logic cells fabricated by a 0.2-mu M FD-SOI technology are directly measured by using an on-chip self-triggering Flip-Flop circuit. The pulse widths are distributed. from 0.3 to 1.0 ns under a constant LET of 40 MeV center dot cm(2)/mg.

The statistical transient response of floating body SOI and bulk devices is measured under proton and heavy ion irradiation. The influence of the device architecture is analyzed in detail for several generations of technologies, from 0.25 mu m to 70 nm. The effects of the measured transients on SET sensitivity are investigated. The amount of collected charge and the shape of the transient currents are shown to have a significant impact on the temporal width of propagating transients. Finally, based on our measured data, the threshold LET and the critical transient width for unattenuated propagation are calculated for both bulk and floating body SOI as a function of technology scaling. We show that the threshold LETs and the critical transient widths for bulk and floating body SOI devices are similar. Body ties can be used to harden SOI ICs to digital SET. However, the primary advantage of SOI technologies, even with a floating body design, mostly lies in shorter transients, at a given ion LET, for SOI technologies than for bulk technologies.

Heavy-ion-induced SET-pulse widths in NOR-logic cells fabricated by a 0.2-mu M FD-SOI technology are directly measured by using an on-chip self-triggering Flip-Flop circuit. The pulse widths are distributed. from 0.3 to 1.0 ns under a constant LET of 40 MeV center dot cm(2)/mg.

Current components of heavy-ion-induced transient currents in a 0.2-mu m fully-depleted SOI MOSFET are analyzed in the time domain. The analysis demonstrates that the transient currents have another slow-decay current component that is different from the two conventional current components: a prompt discharge current and a slow-decay parasitic bipolar current. The slow-decay component revealed here is a flow of deposited carriers stored in the body region to maintain quasi-neutrality, and it drastically widens the transient pulse.

The authors measure the difference of core-level binding energy shifts for Si 1s and Si 2p, Delta E-1s-Delta E-2p, for various Si compounds using high-resolution high-energy synchrotron radiation. They find that the Delta E-1s-Delta E-2p values are in very good correlation with the dielectric constant values of the Si compounds. Using this relation, they deduce the local dielectric constant for each of the Si intermediate oxidation states formed at the SiO2/Si interface. The results are in good agreement with values predicted by a first-principles calculation. (c) 2006 American Institute of Physics.

As a result of ongoing scale-down of Si-MOS devices, gate SiO_2 films have been thinned down to 0.8nm. In this study, the metal/SiO_2 barrier height for ultrathin SiO_2 films of less than 1-nm thickness has been investigated by X-ray photoelectron spectroscopy (XPS).

We measure the relative chemical shift between Si 1s and Si 2p, Delta E-1s - Delta E-2p, for 0.20-1.96nm-thick SiO2 films formed on Si substrates using high-resolution high-energys x-ray radiation. It is found that Delta E-1s - Delta E-2p is independent of SiO2 film thickness for films thicker than 1.0nm. whereas it is smaller for films thinner than 0.5 nm. The result, in conjunction with first principles molecular orbital calculations, indicates that the valence charge of the Si atom is larger for in ultrathin SiO2 films than in the thicker SiO2 films.

We measure the relative chemical shift between Si 1s and Si 2p, Delta E-1s - Delta E-2p, for 0.20-1.96nm-thick SiO2 films formed on Si substrates using high-resolution high-energys x-ray radiation. It is found that Delta E-1s - Delta E-2p is independent of SiO2 film thickness for films thicker than 1.0nm. whereas it is smaller for films thinner than 0.5 nm. The result, in conjunction with first principles molecular orbital calculations, indicates that the valence charge of the Si atom is larger for in ultrathin SiO2 films than in the thicker SiO2 films.