Junpei Sakurai

Combinatorial search for low resistivity Pd-Cu-Si thin film metallic glass compositions

A new combinatorial method to deposit thin films using an arc plasma, Combinatorial arc plasma deposition (CAPD), was applied to search for low resistivity compositions of Pd–Cu–Si thin film metallic glasses (TFMGs). The CAPD setup includes three arc plasma guns (APGs), with each gun shooting a pulse-like plasma of Pd, Cu or Si at specific time intervals to deposit a Pd–Cu–Si thin film on an SiO2 substrate. In this study, a Pd-based compositionally-graded thin film was deposited by controlling the number of shots as well as the plasma strength. The deposited thin film was separated into 1,089 samples (thin film library), and the thickness, composition, phase, and relative resistivity of each sample was evaluated without detaching them from the library. From the samples, three amorphous, low relative resistivity CAPD samples were identified. To verify that these samples were metallic glasses, their compositions were reproduced in samples deposited by sputtering, and their Tg (glass transition temperature) and Tx (crystallization temperature) were measured. The absolute resistivities of the three metallic glass samples were also measured. As the result, the Pd81Cu5Si14 at. % sample showed the lowest absolute resistivity of 64 µ Ω cm and a supercooled liquid region temperature range ( ΔTx=Tx-Tg) of 50 K. This resistivity is 17% lower and the supercooled liquid region is almost two times larger than those of the known Pd-based TFMG composition.

Combinatorial Arc Plasma Deposition of Thin Films

In this paper, we introduce a new combinatorial thin film deposition process that uses arc plasma [combinatorial arc plasma deposition (CAPD)]. The major goal of CAPD in this study is to search for new compositions of amorphous thin film alloys. CAPD uses three cathodic arc plasma guns and the guns shoot the pulse like plasma one by one at a specific time interval. The plasma from each gun is guided onto a substrate by a magnetic field at a specific area on the substrate so as to deposit a compositionally-graded thin film. The deposited thin film is separated into 1,089 samples (the size of each is 1 ×1 mm2) by a trench grid on the substrate. The samples together are called the thin film library and all samples are numbered by the 5-bit row and column marks in the grid. To prove CAPD, a thin film library of a Pd–Cu–Si alloy system was deposited. The composition and non crystallinity of 180 samples were evaluated using energy-dispersive X-ray fluorescence spectrometer (EDX) and imaging-plate X-ray diffractometer (IP-XRD), respectively. Both measurements were performed without detaching the samples from the library. Analysis of 180 samples showed a graded composition, and some of the samples were shown to be amorphous.

A piezoelectric linear ultrasonic motor with the structure of a circular cylindrical stator and slider

A piezoelectric linear ultrasonic motor is proposed, with a cylindrical stator and slider structure. The length and diameter of the motor are about 10 and 1.5 mm, respectively. The stator consists of two piezoelectric ceramic (PZT) tubes connected by a thin film metallic glass (TFMG) pipe. The stator is designed based on theoretical analyses and finite element method (FEM) simulation. The traveling wave propagation is obtained in the FEM simulation under the proper geometrical sizes, suitable boundary conditions and driving voltage signals. The trajectories of particles on the TFMG pipe are elliptical motion. In the experiment, a 25 µm thick TFMG pipe is fabricated using the rotating magnetron sputtering technique and the vibration characteristics of the stator are measured by a laser Doppler vibrometer (LDV) system. Bidirectional motion of the slider is observed around 600 kHz, the maximum velocity is near to 40 mm s − 1 at 50 Vp–p for the loose slider and the maximum output force is 6 mN at 70 Vp–p for the tight slider.

Characteristics of Cu–Zr Thin Film Metallic Glasses Fabricated Using a Carousel-Type Sputtering System

We evaluated the characteristics of Cu–Zr thin film metallic glasses (TFMGs) fabricated using a carousel-type sputtering system. In this system, it is easy to synthesize samples and control their alloy composition by controlling the radio-frequency power for each target independently. In the present study, we demonstrated the fabrication of Cu–Zr TFMGs and evaluated their thermal properties. Cu–Zr samples of various compositions showed a glass transition; however, the thermal properties of the Cu–Zr TFMGs depended on the sputter rate of each element. At the least, the sputter rate of each element during a single rotation of the substrate was set to less than the respective atomic diameter in order to obtain Cu–Zr TFMGs with a stable glass transition.

Searching for Novel Ru-Based Thin Film Metallic Glass by Combinatorial Arc Plasma Deposition

We found out a novel Ru–Zr–Al thin film metallic glass by combinatorial arc plasma deposition (CAPD). To search for Ru-based thin film metallic glasses, first, a library of 1,089 CAPD samples was deposited, of which fifteen amorphous samples were selected by X-ray diffractometry. The compositions of these samples were measured by energy dispersive X-ray fluorescence spectrometry. From the fifteen samples, two samples having low Al content (Ru65Zr30Al5 and Ru67Zr25Al8, at. %) were chosen, and their compositions were reproduced in samples deposited by sputtering, because the CAPD samples were too small for evaluating the glass transition temperature Tg and crystallization temperature Tx by differential scanning calorimetry (DSC). DSC revealed that the two sputter-deposited samples Ru65Zr30Al5 and Ru67Zr25Al8 had a supercooled liquid region (SCLR), showing a Tg, Tx, and width of SCLR ΔTx (=Tx-Tg) of 902, 973, and 71 K in the case of Ru65Zr30Al5, and 913, 979, and 66 K in the case of Ru67Zr25Al8, respectively. Moreover, the sputter-deposited samples Ru65Zr30Al5 and Ru67Zr25Al8 exhibited superior mechanical properties. The fracture stress σf, elastic limit el, and Youngs modulus E were 1.9 GPa, 2.0% and 92.7 GPa, respectively, for Ru65Zr30Al5 and 1.9 GPa, 2.0%, and 91.6 GPa, respectively, for Ru67Zr25Al8.

Vibration characteristics of a cylindrical shell with 25 μm thickness fabricated by the rotating sputtering system

A thin film rotating sputtering system is presented for fabrication of a circular cylindrical shell (CCS). The length, diameter, and thickness of the CCS are 5.0 mm, 1.5 mm, and 25 mum, respectively. To investigate the vibration characteristics, the CCS is fabricated on the outer surface of a piezoelectric ceramic tube (PCT). The vibration of PCT excited by driving voltage signals causes the vibration of the CCS, and the vibration characteristics can be measured using a laser Doppler vibrometer system. Furthermore, a finite element method (FEM) simulation and 2 analytical calculation methods are proposed for comparison with the measurement results. The frequency factor, the key factor that dominates the effective ranges of the 2 analytical methods, is determined as a value of 0.92 through a series of discussions. Combining the results of the 2 analytical calculation methods, good agreement of the analytical, FEM, and measurement results is obtained.

Measurement of Crystallization Temperature Using Thermography for Thin Film Amorphous Alloy Samples

This report describes a new non-contact measurement method for the crystallization temperature (Tx) of a thin film amorphous alloy. The thermal emissivity of the amorphous alloy sample is predicted to be modified when it crystallizes. It was attempted to relate this modification to changes in the apparent temperature by thermography. Thin film amorphous alloys of Pt67Si33 and Pt73Si27 were sputtered onto an Al2O3 substrate and then heated at 20 K/min in vacuum, and the film temperature was monitored by thermography. The Tx indicated by the proposed method coincided with the temperature measured by conventional differential scanning calorimeter within 8 K.

Direct writing of Cu-based micro-temperature detectors using femtosecond laser reduction of CuO nanoparticles

Cu-based micro-temperature detectors were fabricated using femtosecond laser reduction of CuO nanoparticles. Cu-based microstructures were directly created by laser scanning on a CuO nanoparticle solution film. Cu-rich and Cu2O-rich microstructures were selectively formed to electrically connect two Cu thin-film electrodes for use in temperature detectors. Cu-rich and Cu2O-rich micro-temperature detectors were fabricated at scanning speeds of 500 and 1000 µm/s, respectively, at a pulse energy of 1.2 nJ. The temperature coefficient of resistance values of the Cu-rich and Cu2O-rich microstructures were positive and negative, respectively; these temperature behaviors are typical of metal and semiconductor materials, respectively.

Direct fabrication of Cu/Cu2O composite micro-temperature sensor using femtosecond laser reduction patterning

Micro-temperature sensors, which composed of a Cu2O-rich sensing part and two Cu-rich electrodes, were directly fabricated by femtosecond laser reduction patterning of CuO nanoparticles. Patterning of the microstructures was performed by laser scanning with pitches of 5, 10, and 15 µm. Cu2O-rich micropatterns were formed at the laser scan speed of 1 mm/s, the pitch of 5 µm, and the pulse energy of 0.54 nJ. Cu-rich micropatterns that had high generation selectivity of Cu against Cu2O were fabricated at the laser scan speed of 15 mm/s, the pitch of 5 µm, and the pulse energy of 0.45 nJ. Electrical resistivities of the Cu2O- and Cu-rich micropatterns were approximately 10 Ω m and 9 µΩ m, respectively. The temperature coefficient of the resistance of the micro-temperature sensor fabricated under these laser irradiation conditions was −5.5 × 10−3/°C. This resistance property with a negative value was consistent with that of semiconductor Cu2O.

Fabrication of thin-film thermoelectric generators with ball lenses for conversion of near-infrared solar light

We designed and fabricated thin-film thermoelectric generators (TEGs) with ball lenses, which separated visible light and near-infrared (NIR) solar light using a chromatic aberration. The transmitted visible light was used as daylight and the NIR light was used for thermoelectric generation. Solar light was estimated to be separated into the visible light and NIR light by a ray tracing method. 92.7% of the visible light was used as daylight and 9.9% of the NIR light was used for thermoelectric generation. Then, the temperature difference of the pn junctions of the TEG surface was 0.71 K, determined by heat conduction analysis using a finite element method. The thin-film TEGs were fabricated using lithography and deposition processes. When the solar light (A.M. 1.5) was irradiated to the TEGs, the open-circuit voltage and maximum power were 4.5 V/m2 and 51 µW/m2, respectively. These TEGs are expected to be used as an energy supply for Internet of Things sensors.