Yoshiharu Koizumi

Displacement damage degradation of ion-induced charge in Si pin photodiode

Abstract Photonic devices operating in space must exhibit high-radiation hardness due to prolonged exposure to high-energy radiation fields. The device performance can be influenced by both the transient effect of electron–hole plasma generation due to stopping of high-energy particles, and the accumulated effect of damage introduced by a flux of particles. The complex relationship between the two is an increasingly important area of research. Here we investigate charge collection characteristics of in situ ion beam induced damaged samples by measuring single event transient currents induced by heavy ions. Results from this study suggest that the ion-induced charge degradation can be predicted for any ion species and energy using the concept of non-ionizing energy loss and displacement damage dose.

Microstructure and magnetic properties of iron oxide thin films by solid reaction

The ferrite (FeO-Fe 2 O 3 ) thin films have been prepared by solid reaction at low temperature including an oxidation process based on Fe-layer/α-Fe 2 O 3 films. The formation of the iron oxide Fe 3 O 4 requires the choice of a suitable heating rate, when the metallic iron is led to oxidize and produce a change in the magnetite. The optimum heating condition for the reaction of ferrite formation is around 30 C/min from 10 C/min.

Electrical properties of p-type InSb thin films prepared by coevaporation with excess antimony

Abstract InSb thin films with excess antimony were prepared on mica substrates by vacuum evaporation, and their morphology and electrical properties were investigated. Thin films which were coevaporated with more than 4% antimony showed p-type conduction. The electrical properties of p-type films were investigated in relation to the amount of excess antimony. As the amount of excess antimony was increased, the impurity concentrations increased and the electron and hole mobilities decreased. From the X-ray diffraction patterns, the films were found to have the InSb-In crystalline structure owing to the segregated indium. A decrease in indium inclusions was observed as the amount of excess antimony was increased.

Electrical and Magnetic Properties and Colossal Magnetoresistance Effect of La1-xBixMnO3

Perovskite-type La1-xBixMnO3 (LBMO) crystals, which were prepared by doping a Bi atom for a La atom in LaMnO3, were shown to exhibit the colossal magnetoresistance (CMR) effect. Samples were produced by sintering in an air atmosphere that depended on the Bi composition ratio x. X-ray diffraction measurements showed that the LBMO crystal structure can be orthorhombic (or rhombohedral) with γ (=c/a)=1.02 for 0.0<x<0.3, cubic with γ=1.005 for 0.3<x<0.5 or monoclinic with γ=1.014 for 0.5<x. The CMR effect of LBMO for x=0.2 was approximately 400% at 88 K. In addition, the magnetoresistance of LBMO was found to be proportional to the square of magnetization. On the basis of these results, the CMR occurrence mechanics of LBMO were shown to significantly contribute to a Mn3+–Mn4+ double exchange interaction, which is closely associated with the cooperative phenomenon in the Jahn–Teller effect.

Magnetic properties and microstructure of Ni–Fe nitride films by reactive sputtering

Abstract The nickel iron nitride Ni3Fe-N seems to have the face-centered cubic structure of A4B type. It can be considered that the magnetic structure is decided by the relationship of the electronic orbits N-2p and Ni-3d. The thin films of Ni3Fe-N were prepared by a reactive RF-sputtering method. It was found that the amount of the N2 flow rate greatly affects the crystal growth.

Investigation of single-event charge collection from angled ion strikes

Abstract Single-event upsets (SEUs) are a major concern for dynamic random access memory (DRAM) and static random access memory (SRAM) installed in space-based satellites. Recently, large-scale integration of memory devices has made them even more susceptible to multiple-bit upsets (MBUs). MBU generally results when an ion strike passes through, or interferes with, multiple memory cells at the same time. However, the fundamental processes behind MBU have not yet been fully clarified. In order to investigate the mechanism of MBU, we examined the relationship between the amount of the collected charge and the angle of the incident ion to the test device.

Estimation of fast transient current degradation analyzed by non-ionizing energy loss

Abstract In recent years, special interests have been paid to the advantage of using III–V compound semiconductors for the microelectronic and optoelectronic industries because of its high-speed response. Ion beam induced charge (IBIC) and transient-IBIC techniques are useful in order to investigate the single event effects, which is one of the most serious problems to use semiconductor devices in space. During image collection, the ion-induced damage is introduced. Therefore the degradation behavior of collected charge and transient current are important issue to use these techniques most effectively. To estimate degradation behavior, the damage factors of InGaAs devices are compared with that of Si devices by using the concept of non-ionizing energy loss.

Magnetoresistance Effect in a La0.8Bi0.2MnO3/MgO/Co Trilayer Device

The device composed of La_0.8Bi_0.2MnO₃/MgO/Co trilayer (with a tunnnel barrier made of MgO film) as an L_1-xBi_xMnO₃ substrate are prepared, and the magnetoresistance effect of the device is examined. Fundamental temperature properties of electrical conduction of the La_0.8Bi_0.2MnO₃/MgO/Co trilayer device as a function of MgO thickness is determined. It was found that the magnetoresistance was about 33% of the maximum value when the MgO film thickness was 2.0 nm and the device shows damped oscillation with increasing MgO film thickness.

Magnetoresistance Effect of La0.8Bi0.2MnO3/MgO/Co Heterojunction Device

The La0.8Bi0.2MnO3/MgO/Co heterojunction device was fabricated by vacuum evaporation with an electron gun on a well-polished perovskite-type oxide La0.8Bi0.2MnO3 substrate. The magnetoresistance through MgO (thickness: 2.0nm) tunnel junction of these devices was 33% of the maximum value. At this point, a spin polarization value of LBMO was about 0.42. The experiments showed that the devices have a transition temperature at around 240K, namely, between that of the ferromagnetic phase (for low temperature) and that of a semiconductor-like phase (for high temperature).

Modeling of transient charge collection induced by an angled single ion strike

Single-event phenomena (SEP) are common occurrences in electronic devices used in high-radiation fields such as space environments. SEP are primarily caused by the interaction between ionization tracks generated by a high-energy heavy ion and sensitive regions of a semiconductor device. In order to develop SEP tolerance devices, it is necessary to predict the amount of the collected charge at sensitive regions. In this paper, comparing the experimental results obtained from the waveform of the transient current induced by a heavy ion and from a geometrical model, we have studied the ion-induced transient charge as a function of an angle and the linear energy transfer (LET) of the incident ions.