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We have upgraded a 3-MeV linac at J-PARC. The ion source is same as the J-PARC linac’s, and the old 30-mA RFQ is replaced by a spare 50-mA RFQ, therefore, the beam energy is 3 MeV and the nominal beam current is 50 mA. The main purpose of this system is to test the spare RFQ, but also used for testing of various components required in order to keep the stable operation of the J-PARC accelerator. The accelerator has been already commissioned, and measurement programs have been started. In this paper, present status of this 3-MeV linac is presented.

In J-PARC Linac, some beam dumps are used for beam conditioning and study. A beam window is installed in the beam line of the beam dump. In 2018, a beam study using a 0- degree beam dump in the Linac resulted in damage to the beam window when the beam intensity has exceeded the tolerance. So as not to repeat this experience, it was decided to immediately advance the development of a beam window protection system. The present paper describes the protection system built as an emergency measure and the tests of its performance.

A new interposer with an optical interconnection called optical interposer has been proposed for a high-performance parallel processor system. The optical interposer is composed of polynorbornene (PNB) optical waveguides with 45° micromirrors and a Si substrate having chip-sized through-Si holes of 150 µm depth. The polymeric waveguides are formed on the Si substrate before forming the through-Si holes by deep reactive ion etching (DRIE). Vertical-cavity surface-emitting laser diode (VCSEL) and photodiode (PD) chips are placed onto the photolithographically defined hole patterns that are 15 µm larger than the size of the chips. In addition, the chips can be precisely aligned and recessed into the holes by passive alignment of self-assembly driven by the surface tension of a lead-free solder. We can fabricate the low-loss optical interposer with an insertion loss of below 0.2 dB measured at the waveguide length of 5 cm and a coupling loss of 0.5 dB measured with a 45° micromirror.

The effects of Ge fraction and annealing temperature on the metal-induced lateral crystallization (MILC) of amorphous SiGe films on an insulator have been investigated. It was shown that the progress of the MILC of amorphous SiGe was suppressed by spontaneous nucleation, which was accelerated with increases in Ge fraction and annealing temperature. Thus, MILC could not proceed for amorphous SiGe with high Ge fractions (>70%) at high temperatures (>500 °C). Spontaneous nucleation was significantly suppressed by lowering the annealing temperature ( 20 µm) could be realized for even high Ge fractions (>70%). Transmission electron microscopy suggested that the mechanism of MILC of amorphous SiGe (a-SiGe) with medium and high Ge fractions (>40%) is different from that of a-Si.

An optical interconnection with a new optically transparent polymer called polynorbornene (PNB) was investigated for short-distance and high-speed data transmission on printed circuit boards (PCBs). PNB waveguides were formed by simple photoirradiation followed by heating without development and reactive ion etching (RIE) processes. The PNB waveguides exhibit a high-heat resistance of more than 270 °C and an extremely low optical loss of 0.029 dB/cm at 830 nm. We successfully integrated PNB waveguides into a multilayer PCB, which we call a optical/electrical printed circuit board (O/E-PCB), and confirmed a basic data transmission rate of 10 Gbps.

The fabrication of Ge-channel thin-film transistors (TFTs) with Schottky source/drain (S/D) contacts was investigated. First, the annealing characteristics of Ni/c-Ge stacked structures were examined. NiGe/n-Ge Schottky contacts (Bn=0.51 eV, n=1) with a low reverse leakage current [(2–5)×10-2 A/cm2] were obtained at 200–300 °C. Second, the electrical characteristics of Al/SiO2/c-Ge metal–oxide–semiconductor (MOS) structures were investigated, in which SiO2 films were formed by plasma-enhanced chemical vapor deposition at 250 °C. The MOS structures were proven acceptable for device operation. On the basis of the obtained results, TFTs with NiGe Schottky S/D contacts were fabricated using poly-Ge/quartz substrates. The maximum processing temperature was 500 °C in the solid-phase crystallization of a-Ge films. The TFTs showed good p-channel operation characteristics with a mobility of ~100 cm2 V-1 s-1 without showing kink effects. This is a great advantage for the realization of high-performance TFTs for system-in-displays.

The low-temperature ( 2000 V/cm). These new findings will be a powerful tool for achieving new poly-SiGe with highly controlled crystal structures.

Thin-film transistors (TFTs) with Schottky source/drain (S/D) structures were fabricated using NiSi and laser-annealed polycrystalline silicon (poly-Si) as Schottky barrier metals and active layers, respectively. The whole fabrication process was performed at low temperatures (

A novel flash memory which has FePt magnetic floating gate was proposed. An FePt magnetic floating gate with a high coercivity was successfully fabricated by DC magnetron sputtering with rapid thermal annealing. As for magnetic properties, the switching magnetic fields of 21 Oe for the NiFe film and 1600 Oe for the FePt film were employed for the control gate and the floating gate materials, respectively. The fundamental characteristics of the magnetic flash memory were confirmed using magnetic metal oxide semiconductor (MOS) capacitor devices and magnetic tunneling diode (MTD) devices.

The dose-dependent etching characteristics of SiO2 films irradiated with 40 keV Si2+ focused ion beams (FIBs) were comprehensively investigated. The etching rate in a buffered HF increased with increasing dose (8 ×1013–1 ×1015 cm-2), however it decreased for doses exceeding a critical value (1 ×1015 cm-2). The maximum selectivity of the etching rate of the irradiated region to the nonirradiated region was about 14, which was obtained for irradiation with the critical dose. The numerical simulation indicated that all of the Si atoms in SiO2 were displaced by irradiation with this critical dose. A simple model for the etching characteristics was proposed, in which the enhancement of etching by vacancies and the retardation of etching by implanted Si atoms were considered. The etching characteristics obtained by the experiments were quantitatively explained by the model.

The metal-induced low-temperature (≤550°C) crystallization of a-Si1-xGex (0 ≤x ≤1) on SiO2 has been investigated. A Ge-fraction-dependent crystal growth was observed. In the case of a low-Ge fraction, plane growth dominated, the velocity of which was enhanced by 80% with increasing Ge fraction from 0 to 20%. This produced strain-free poly-SiGe with large grains (18 µm). On the other hand, dendrite growth became dominant in the case of intermediate Ge fractions (40–60%). By optimizing the growth conditions (x: 0.4, annealing: 450°C, 20 h), very sharp needlelike crystals (width: 0.05 µm, length: 10 µm) were obtained. These new polycrystalline SiGe films on insulator should be used for system-in-display, three-dimensional ultra large-scall integrated circuits, and novel one-dimensional wires.

Post-annealing characteristics of in situ B-doped poly-SiGe films have been investigated. Thermal stability of substitutional B atoms at a supersaturated concentration was significantly improved by Ge doping, for example, the stability at 800°C for poly-Si0.6Ge0.4 films was nine times as high as that for poly-Si films. Both fast and slow processes exist for the deactivation of B. The fast process was due to movement of B atoms from substitutional to interstitial sites, enhanced by a local strain induced by the difference in atomic radii between Si and B atoms, and the slow process was due to trapping of B at grain boundaries during grain growth. The mechanism of the improved thermal stability of B atoms is discussed on the basis of local strain compensation by Ge atoms.

Recent progress in the crystal growth of group-IV-based semiconductor-on-insulators is reviewed from physical and technological viewpoints. Liquid-phase growth based on SiGe-mixing-triggered rapid-melting growth enables formation of hybrid (100) (110) (111)-orientation Ge-on-insulator (GOI) structures, which show defect-free GOI with very high carrier mobility (~1040 cm2 V−1 s−1). Additionally, SiGe mixed-crystals with laterally uniform composition were obtained by eliminating segregation phenomena during the melt-back process. Low-temperature solid-phase growth has been explored by combining this process with ion-beam irradiation, additional doping of group-IV elements, metal induced lateral crystallization with/without electric field, and metal-induced layer exchange crystallization. These efforts have enabled crystal growth on insulators below 400 °C, achieving high carrier mobility (160–320 cm2 V−1 s−1). Moreover, orientation-controlled SiGe and Ge films on insulators have been obtained below the softening temperatures of conventional plastic films (~300 °C). Detailed characterization provides an understanding of physical phenomena behind these crystal growth techniques. Applying these methods when fabricating next-generation electronics is also discussed.

Self-pumped phase-conjugated (SPPC) images produced by two SPPC beams generated from a single nanosecond-pulsed laser beam are successfully obtained at beam power ratios of up to 4:1. The two SPPC beams are incident on opposite faces [(100) and (100)] of a photorefractive barium titanate (BaTiO3) crystal, and the SPPC images are reproduced on the respective crystal faces with high quality due to the reduced interference between the two SPPC beams owing to the delay between the nanosecond pulses of each beam. The quality of the images and the maximum power ratio at which both images are observable are superior to the continuous-wave configuration.

Epitaxial growth of the ferromagnetic silicide Fe3Si on Si substrates was investigated using molecular beam epitaxy. X-ray diffraction (XRD) measurements revealed that the Fe3Si phase was formed at 60–300 °C, and the FeSi phase was formed at 400 °C. From the results of XRD and transmission electron microscopy measurements, it was found that the Fe3Si(111) layers were epitaxially grown on Si(111) substrates, while random poly-crystal Fe3Si layers were formed on Si(100) substrates. Detailed XRD measurements showed that a small amount of DO3-type Fe3Si was formed together with the B2-type Fe3Si. Vibrating sample magnetometer measurements revealed that Fe3Si(111) layers on Si(111) substrates have in-plane magnetic anisotropy with a period of 180°.

The oxidation-induced Ge condensation of SiGe/Si-on-insulator structures was investigated. The relaxation rate of SiGe on insulator (SGOI) abruptly decreased with SiGe thickness below 50 nm. To enhance the relaxation rate in ultra thin SGOI, a new technique combined with intermediate-dose H+ implantation (5×1015 cm-2) and post annealing (1200 °C) was developed. It was demonstrated that highly relaxed (70%) ultra thin SGOI with a low defect density (

heterostructures with high electron mobility were grown by molecular beam epitaxy (MBE) combined with solid-phase epitaxy (SPE). The SPE growth completely suppressed Ge segregation in the layer on top of the Si channel layer. High-resolution cross-sectional transmission electron microscopy observation revealed that the heterointerfaces formed by the SPE growth technique were very flat compared with those for the MBE-grown samples. The electron mobility for an SPE-grown sample with a graded buffer layer was nearly one order of magnitude higher than without such a layer. A high electron mobility of was obtained at 15 K for the sample with a graded buffer layer ().

We experimentally demonstrated anisotropic damping of the magnetization dynamics in a highly ordered Heusler compound Co3−xFexSi (x = 1.0, 2.0, and 3.0). The field-swept ferromagnetic resonance linewidth as a function of the resonant frequency was measured to exclude extrinsic contributions from two-magnon scattering and inhomogeneous line-broadening. In L21-ordered Co2FeSi film, a wide variation in the intrinsic Gilbert damping constant from 0.0023 to 0.0061 was clearly observed in the (111) plane, where a weak uniaxial magnetic anisotropy was formed via low-temperature epitaxial growth. The large anisotropy of the Gilbert damping constant was suppressed by increasing x, which suppresses the half-metallicity in Co3−xFexSi films.

We show nonlocal spin transport in n-Ge based lateral spin-valve devices with highly ordered Co_2FeSi/n^+-Ge Schottky tunnel contacts. Clear spin-valve signals and Hanle-effect curves are demonstrated at low temperatures, indicating generation, manipulation, and detection of pure spin currents in n-Ge. The obtained spin generation efficiency of ~ 0.12 is about two orders of magnitude larger than that for a device with Fe/MgO tunnel-barrier contacts reported previously. Taking the spin related behavior with temperature evolution into account, we infer that it is necessary to simultaneously demonstrate the high spin generation efficiency and improve the quality of the transport channel for achieving Ge based spintronic devices.

Orientation-controlled large-grain Ge crystals grown on plastic substrates (softening temperature: ∼300 °C) are desired to realize advanced flexible electronics, where various functional devices are integrated on flexible substrates. To achieve this, gold-induced crystallization (annealing temperature: 250 °C) using a-Ge/Au stacked structures is developed on plastic substrates, where thin-Al2O3 layers (thickness: ∼7 nm) are introduced at a-Ge/Au interfaces. Interestingly, (111)-oriented nucleation at the Au/plastic interface dominates over random bulk nucleation in Au layers. As a result, the formation of (111)-oriented large-grain (≥50 µm) Ge crystals directly on flexible plastic substrates is realized. This technique will pave the way for advanced flexible electronics.

We explore epitaxial growth of Co2MnSi films on Si(111) or Ge(111) by means of low-temperature molecular beam epitaxy. We find that as-grown Co2MnSi films consist of mixed phases with L21-ordered structures and microcrystalline ones. As a result, the magnetic moment, which is nearly half of the ideal value, can be obtained even at very low growth temperature. Post-growth annealing was effective to crystallize the microcrystalline phases observed in the as-grown layer, leading to a further enhancement in the magnetic moment. We discuss a difference in growth mechanism between Co2MnSi and other Heusler alloys examined in our previous works.

To inform room-temperature spin functionality of D03-ordered Fe3Si, we explore tunneling magnetoresistance (TMR) effects in magnetic tunnel junctions (MTJs) consisting of Co60Fe40/AlO x /Fe3Si on Si. We clearly observe reproducible TMR ratios of ∼20% at room temperature for all MTJs fabricated. By using Julliere's formula, the room-temperature spin polarization (P) value for D03-ordered Fe3Si can be roughly estimated to be ranging from 0.18 to 0.45 when we assume the P values from 0.5 to 0.2 for Co60Fe40. This study reveals that the room temperature P value for D03-ordered Fe3Si is relatively small compared with that for Co-based Heusler alloys reported previously.