Mitsuhiko Ogihara

Preparation of BiSrCaCuO Superconducting Thin Film by Molecular Beam Epitaxy with NO2

A BiSrCaCuO superconducting thin film was prepared in situ by molecular beam epitaxy with nitric dioxide gas (NO2). Metal sources were coevaporated onto the MgO (100) substrate at the substrate temperature of ~700°C under the background pressure of the growth chamber of ~5×10-6 Torr. The deposition speed was ~1.8 A/s and the thickness of the thin film was ~3000 A. The zero resistance was obtained at 65 K without the annealing steps. The quality of the BiSrCaCuO superconducting thin film prepared with NO2 is comparable to that prepared with distilled ozone under identical growth condition except for the distilled ozone flux intensity. Oxidation behaviors of NO2 were studied and are compared with those of distilled ozone.

Open tube zinc diffusion into GaAs0.8P0.2 using AlN and SiNx cap films

The open‐tube diffusion of zinc in GaAs0.8P0.2 from a zinc‐doped silica film was investigated in detail. Aluminum nitride (AlN) and silicon nitride (SiNx) films were used as the anneal caps. The dependence of diffusion depth on the thickness of an AlN‐cap was found to differ from its dependence on SiNx‐cap thickness. The selective masked diffusion of zinc using an AlN diffusion‐mask was also systematically studied. The diffusion depth in selective masked diffusion was found to depend on both AlN‐cap thickness and AlN‐diffusion‐mask thickness. The experimental results suggest that diffusion depth is not necessarily governed by either cap thickness or diffusion‐mask thickness. From this standpoint, the role of film stress on diffusion depth was then quantitatively investigated. It was found that diffusion depth can be scaled well with total film stress in the measured film‐thickness range. In this sense, it can be concluded that total film stress is the primary factor that determines the diffusion depth und...

High-speed chip-matrix 1200-dpi LED printhead

We have developed a novel 1200 dot per inch light emitting diode (LED) printhead for a high quality digital color printer in the next generation. Performance tests showed that the LED printhead was really suitable for a color printer printhead: an excellent light output uniformity within +/- 1 percent, a high contrast light spot of 80 percent, a high accuracy light spot position within +/- 20 micrometers , and a very high light output efficiency to realize a high-speed printing of 45 pages per minute. In order to achieve the high performance of the LED printhead, we have developed an original 1200 dpi LED array chip with 8 by 8 matrix-structured wiring. The chip-matrix LED array chip was fabricated on a double hetero structured AlxGa1-xAs epitaxial wafer using our original fabrication techniques and device designs. This is the key for fabricating a super-high resolution array chip with a super- high light output efficiency. Moreover, the CM LED array chip made it possible to reduce an overall super-high- density printhead cost: the number of bonding wires and driver integrated circuit chips on the LED printhead decreases to one-fourth, and one-half, respectively, compared to the conventional 1200 dpi printhead.

High Density Integration of Single Crystal Thin Film Devices by "Epifilm Bonding" Technology

High density integration of dissimilar material devices is one of the most interesting subjects in electronic and optical device technology. Recent our investigation has achieved successful three-dimensional integration of single crystal thin film light-emitting-diodes (LEDs) and CMOS IC drivers by intermolecular force; we call this technology “epifilm bonding (EFB)” technology [1]. Employment of the EFB technology will allow us to form planar wiring structure to connect integrated devices by semiconductor wafer process; this will enable us to manufacture much more compact and higher density integrated device systems. Increasing density of integrated device systems brings more heat into the integrated device system. Heat arising from the device active region of the single crystal thin film (epifilm) will transfer very rapidly when the bonding substrate has higher thermal conductivity. This paper focuses especially on investigation of epifilm bonding on diamond-like carbon (DLC) thin films that have higher thermal conductivities. No report has been found on the application of the DLC thin film in intermolecular force bonding. The point to apply the DLC film in EFB is modification of the DLC thin film surface to achieve higher bonding strength. Figure 1(a) shows the epifilms that are bonded on the DLC thin film by the EFB technology. The epifilm consists of AlGaAs double hetero structure for fabrication of LEDs. The DLC thin film was formed on the Si substrate. The stripe-shape epifilms were released from the GaAs substrate by chemical etching of a sacrificial layer between the epifilm layer and the GaAs substrate [1]. The released epifilms were pressed to bond on the DLC thin film at room temperature after plasma activation of the bonding surfaces. As shown in Fig. 1(a), the epifilms are well bonded on the DLC thin film. No void and no crack are observed on the bonded epifilms on the DLC thin film. The bonded epifilms on the DLC thin film were processed into small pieces (10 mx10 m) in order to test the EFB on the DLC thin film. Figure 1(b) shows the microscope image of the array of the small epiflms after etching of the bonded epifilms shown in Fig. 1(a). As shown in Fig. 1(b), the bonded epifilms are well processed into the array of the small epifilms of an area of 10 mx10 m. This indicates that the epifilms can be considerably well bonded on the DLC thin film by EFB. Characteristics of the epifilm LED array that was bonded on the DLC thin film by the EFB technology were measured. The current-power (I-P) characteristic of the epifilm LED on the DLC thin film was compared with that on the polyimide (PI) layer. (The PI is an example of lower thermal conductivity material.) The test result showed that the emitted light power of the epifilm LED on the DLC thin film was one order of magnitude higher or more than that on the polyimide layer at a high current density of 12.5 kA/cm. This indicates that the epifilm LED bonded on the DLC thin film having higher thermal conductive structure provides higher characteristics by preventing temperature increase at the active region of the epifilm LED. In summary, this paper proves that the single crystal thin film LEDs can be well bonded on the DLC thin film by the EFB technology. The structure of the epifilm devices bonded on the DLC thin film by EFB will allow us to manufacture much higher density integrated device system providing higher characteristics using single crystal semiconductor thin films of dissimilar materials.

Rubidium beam flux dependence of film properties of Ba1-xRbxBiO3 deposited by molecular-beam epitaxy using distilled ozone

We have focused our attention on the dependence of Ba1−xRbxBiO3 (BRBO) film composition ratio and film properties on rubidium‐beam‐flux intensity. BRBO films were deposited on MgO(100) substrates by molecular‐beam epitaxy (MBE) using distilled ozone. Systematic measurements showed that the rubidium content was nearly independent of rubidium‐beam‐flux intensity in a wide beam‐flux range. Therefore, it can be concluded that some degree of self‐control of rubidium stoichiometry is actually possible in BRBO film growth by MBE. This study also revealed that the BRBO film properties had strong dependences on rubidium‐beam‐flux intensity even in the range for self‐control of rubudium stoichiometry. Our study also clarified that rubidium‐beam flux affects the barium content in the BRBO film.

Electric Characteristics of High Tc Superconductor/Semiconductor Junction

We formed BiSrCaCuO and YBaCuO/Nb doped SrTiO3 (STO(Nb)) junctions. We measured current — voltage (I-V) characteristics and capacitance — voltage (C-V) characteristics of both junctions by varying temperature from 300K to 25K. Both samples clearly show the diode characteristics. Near room temperature the I-V curves of forward bias voltage show exponential dependence and the 1/C2(V) decrease linearly with voltage, thus following the usual Schottky relation. At lower temperature, however, the characteristics of samples differ from the Schottky relation.

Oxidation of Si(100) surfaces with Bi and Ag overlayers in ozone atmosphere

Desorption of Bi and Ag deposited on Si(100) surfaces has been studied by Auger electron spectroscopy for heat treatment in distilled ozone atmospheres. Bi was desorbed from the Si surface at a substrate temperature Ts of 350~450°C and Ag was desorbed at Ts of 500~570°C. The reflection high-energy electron diffraction (RHEED) patterns for Ag overlayers suggested that three-dimensional Ag(100) layers are formed on Si(100).

Double-Function Light-Emitting-Diode Array

The development of a double-funaion light-emitring-diode (DFLED) is repofled for the first time. A DFLED is a pn junction which works as a light-emitting-diode (.ED) and works as a photoseNor 8s well. The DFLED has a shallow junction (0.8pm) region and a deep junction (5pm) region. In this work, it is found out that the use of an aluminun oxide (AIOJ thin film is essefiial to fabricate the shallow junction region. It has been confirmed that the DFLED has the super.ior performances ss both of I photosensor and a LED.

In/BRBO/STO(Nb) Three-Terminal Device Using (Ba,Rb)BiO3 Superconductors

We have studied the electrical properties of a three terminal device using the (Ba,Rb)BiO3 thin film. We have succeeded in fabricating a three terminal device with a large current gain in the device structure like a metal-base transistor. A common base current gain α > 0.8 was obtained.

Initial Crystal Growth Stage of BRBO Thin Film

Thin film growth of BaBiO3 (BBO) on SrTiO3(100) and SrTi03(l10) substrates by molecular beam epitaxy was studied precisely. We prepared the BBO thin film of ~500A with surface roughness of ~30A. Surface roughness of the BBO thin film was systematically measured with the atomic force microscope. The crystal orientation and the surface roughness of the BBO thin films strongly depend on Ba-beam-flux intensity and on the orientation of the substrate.