LPE Film Research Articles

Crystallographic Axis Transition of Sm1+xBa2−xCu3O7−δ Film Prepared by Liquid Phase Epitaxy (LPE)

The effect of two significant factors, flux composition and growth atmosphere, on the crystallographic axis orientation of the Sm1+xBa2−xCu3O7−δ “SmBCO” film was studied. We succeeded in achieving a pure a-axis SmBCO LPE film by applying Cu-rich Ba−Cu−O flux (Ba/Cu ratio 3:7) and 1 atm oxygen atmosphere. Compared to YBCO, it is more difficult to grow SmBCO along a-axis. Several possible reasons were considered, especially the mutual substitution of Sm3+ and Ba2+, which may prefer c-axis growth. Significant features of the LPE process, like nucleation, supersaturation, and growth rate, manifest tendency to prevent a-axis growth.

Development of low contact resistivity electrode for HTSC films

The electrodes on LPE films for the case of persistent current switches were developed. The electrode was fabricated by the sputtering method using targets of Ag-based metal alloys. In the targets, the different amounts of Cu were added in order to suppress the reaction between the RE123 and the electrode metal films. Consequently, the suitable composition of the Ag–Cu electrode to obtain a low contact resistance was found. When the copper composition in the Ag electrode was controlled to be 1.09 wt.%, the lowest contact resistance of 1.7 × 10 −12 Ω m 2 was obtained. And all of these results are reasonable values as the requirements for the LPE film. Moreover, we found that a thick film is necessary to fabricate electrodes with low contact resistivity since fine grains in a small bare surface area were expended due to vaporization, etc., by the heat treatment in the case of thin films.

Comparative study of LPE and VPE silicon thin film on porous sacrificial layer

Thin film single crystal silicon on foreign substrate is an attractive way to realize cheap and efficient photovoltaic devices. In this paper we will compare epitaxial growth of silicon thin film on double porous sacrificial layers obtained by liquid or vapor phase epitaxy (LPE or VPE). Porous silicon is formed by electrochemical anodisation of monocrystalline silicon in a HF/ethanol solution. VPE is achieved in an atmospheric pressure chemical vapor deposition (APCVD) reactor under H 2 atmosphere. Growth rate is in between 0.5–3 μm/min. LPE is realised in a graphite sliding boat using indium or tin as solvent. Growth rate is in the range 0.1–1 μm/min depending on the temperature, the cooling rate and the solvent. We discuss the substrate orientation, temperature, growth rate, layer homogeneity and electrical properties of the epilayers for both growing techniques. Diffusion length and mobility are measured respectively with LBIC and Hall effect technique. The values obtained for p-type (μ>100 V/cm 2/s and L n>100 μm) allows the realisation of solar cell using interdigitated technology on the top of this layer, which is detached and transferred onto mullite substrate.

Fabrication of meander shaped RE123 LPE films for PCS materials

We have fabricated a meander shaped LPE film to realize a high electric resistance in the normal state as a persistent current switch material. A seed film on an MgO single crystalline substrate was shaped into a meander by a chemical etching method and dipped into solution for further LPE growth of RE123. The meander shaped RE123 LPE film with a long current path on the 2 inch diameter MgO substrate could be successfully grown. This phenomenon can be explained by the change of the growth mode from step growth to a nucleation limited growth on the a(b)-c plane of the crystal. This is further explained by the small step-advancing rate of the RE123 crystal on the MgO surface and above a partly dissolved MgO substrate. The film revealed a high resistance value of about 1.7 /spl Omega/ at 100 K and a high I/sub c/ value of 50 A at 77 K and 0 T which is estimated to about 175 A at 20 K and 3 T.

LPE法を用いた永久電流スイッチ用RE123/BaZrO<SUB>3</SUB>/MgO膜の形状制御機構

LPE法を用いた永久電流スイッチ用RE123/BaZrO<SUB>3</SUB>/MgO膜の形状制御機構

Magnetic imaging of high- Tc films with grain boundaries by a scanning SQUID microscope

The magnetic flux trapped or generated in high- T c films with [0 0 1]-tilt grain boundaries has been observed directly by using a scanning superconducting quantum interference device microscope in a wide temperature range of 6–90 K. In the measurements for a field-cooled NdBa 2Cu 3O y sputtered thin film with a symmetric 36.8° grain boundary, some of the flux quanta trapped at the grain boundary were found to disappear or change their positions at high temperatures near T c, clearly indicating weaker pinning strength at the boundary. For a YBa 2Cu 3O y LPE film with an asymmetric 45° grain boundary, unquantized disordered flux was observed along the grain boundary, of which magnitude was found much larger than that previously reported for PLD films.

Effect of the Bi2201 coexistence on the Bi2212 solidification in the LPE film

The solidification of the Bi2212 phase has been investigated by using the LPE method. The dependence of the relative content of the Bi2212 phase in the as-grown film on the growth temperature has made it clear that the Bi2212 phase can be obtained only from a temperature near 980°C. It has suggested that the narrow solid phase of the Bi2212 phase adjoins to the liquid phase of the Bi2201 phase.

Structure and Lattice Deformation of Ce-Substituted Yttrium Iron Garnet Film Prepared by RF Sputtering

We investigated the structure and lattice deformation of CeY2Fe5-δO12-Z(Ce1·YIG) film prepared by RF sputtering. We found that the lattice constant parallel to the film plane a// is equal to the lattice constant of the substrate as. This shows that this Ce1·YIG film belongs to Region I in the Besser model. Some Ce1·YIG films become a double-layer structure as the lattice constant mismatch || Δa|| increases. This change in the film structure caused by || Δa|| is very different from that of LPE film. In a Faraday rotation θF spectrum of single-layer films deposited on GCGMZG and GGG substrates, the θF dispersion around 800 nm is shifted to the longer wavelength side. We consider this θF shift around 800 nm to be induced by the difference in the film deformation.

Y doping effect on superconducting properties in Bi2Sr2CaCu2Oyfilms prepared by liquid phase epitaxial method

Abstract The Y doping effect on superconducting properties has been studied in Bi2Sr2CaCu2O y films prepared by the liquid phase epitaxial method. The incorporation ratio of each element in the LPE film to that in the melt was investigated as a function of Y content in the solution. The change of the superconducting properties due to the Y doping was connected with the total amount and the composition ratio of Sr, Ca and Y in the film.

Reduction of Optical Absorption in Bi-Substituted Garnet Film by Annealing

LPE film was grown using Bi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> single flux to realize the high Faraday rotation and low absorption provided by high density Bi-substitution required of material used for 0.8 μm optical isolators. The melt from Bi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> single flux does not contain bivalent ions such as Pb <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> , so Pt <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4+</sup> taken into the film or oxygen vacancies occurring within the film generate Fe <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> , and increase optical absorption at 0.8 μm. Generation of Fe <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> was prevented by adding bivalent ions, like Ca <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> , in the melt, and optical absorption declined. This paper reports the results of investigations in which in addition to adding bivalent ions, annealing was used successfully to reduce Fe <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> and optical absorption. Investigation of the relation between the effect of oxygen partial pressure during annealing and annealing temperature established that the equilibrium oxygen partial pressure and reaction rate differ with the electrical type of the film.

Ｂｉ置換ガーネット膜の熱処理による光吸収の低減

LPE film was grown using Bi 2 O 3 single flux to realize the high Faraday rotation and low absorption provided by high density Bi-substitution required of material used for 0.8 ?m optical isolators. The melt from Bi 2 O 3 single flux does not contain bivalent ions such as Pb2+, so Pt4+ taken into the film or oxygen vacancies occurring within the film generate Fe2+, and increase optical absorption at 0.8 ?m. Generation of Fe2+ was prevented by adding bivalent ions, like Ca2+, in the melt, and optical absorption declined. This paper reports the results of investigations in which in addition to adding bivalent ions, annealing was used successfully to reduce Fe2+ and optical absorption. Investigation of the relation between the effect of oxygen partial pressure during annealing and annealing temperature established that the equilibrium oxygen partial pressure and reaction rate differ with the electrical type of the film.

Ionized cluster beam technique

Ionized cluster beams (ICB) are widely used to deposit metal, semiconductor and insulating films. This paper describes the current state of this technology in both fundamental and applications areas. ICB provides tight control of the kinetic energy and ion content of the beam, which gives the technique a unique advantage compared to MBE, VPE, LPE, MOCVD, sputtering or other thin film deposition methods. The development of this technology should allow the deposition of high quality material at low temperature onto a wide variety of substrate surfaces and even permit the formation of thin film materials not previously possible.

Design consideration for a 2-μm-period ion-implanted propagation track (abstract)

We report on the design of ion-implanted propagation tracks with a 2-μm period. Reducing cell size causes increased drive field and margin degradation due to adjacent loop interaction. We investigated the effect of ion-implanted layer properties on these problems. Using conventional photolithography, we fabricated propagation tracks on YSmLuCaGeFeO films with 0.5–0.7 μm bubble diameters by triple implantation of hydrogen and neon ions. After implantation, we exposed the wafers to argon plasma to increase the implantation-induced anisotropy field change (ΔHk), then coated them with rf-sputtered SiO2 film. We next annealed the coated wafers at temperatures ranging from 350 °C to 450 °C. To investigate the effect of the implanted layer thickness and its ratio to LPE film thickness, we proportionally varied the energies of triple implantation at a constant dose. The interaction between adjacent loops and the minimum drive field decreased as the implanted layer thickness decreased. Furthermore, we found that we could reduce the difference in bias field margin between the ion-implanted track and the Permalloy track by decreasing the implanted layer thickness without margin loss. This makes possible to realize high density hybrid devices. A minimum drive field of 38 Oe and bias margin of 68 Oe at a quasi-static drive field of 50 Oe have been obtained. Although the required drive field was larger than that of 4-μm-period tracks, we believe it can be reduced by optimizing LPE film properties and implantation conditions. Inside and outside turns, necessary in folded minor loops, have been successfully designed. Details of designs, including pattern shapes, will be discussed.

Czochralski crystal growth and aluminum segregation coefficient in yttrium gallium aluminum garnet

The aluminum distribution coefficient and the amount of octahedral yttrium aluminum gallium garnet single crystals obtained by the Czochralski method have been determined from lattice constant variations during crystal growth. The value of the aluminum distribution coefficient was close to 2 for those parts of the crystal with a convex solid-liquid interface and it was close to 1 for those with a flat 〈111〉 solid-liquid interface. The large difference between these values can be explained by chemical stresses in the crystal in the meltback region and small changes of the lattice constant in the part of crystal with a flat 〈111〉 solid-liquid interface. Single crystals of yttrium aluminum gallium garnet with a lattice constant appropriate for LPE film growth of yttrium gallium garnet have been grown.

4Mb on-chip-cache bubble memory chips with 4 µm period ion-implanted propagation patterns

4Mb ion-implanted bubble devices (IIBD) with on-chip-cache organization (OCCO) have been designed for 1μm bubbles, and characterized for all functional elements in the devices. The 4Mb memory chip with 9.5×11.8 mm chip size consists of the same two 2Mb units, each of which is divided into 1Mb even and odd sites with 300 strorage loops (s-loops) and cache loops (c-loops), whose bit lengths are 4160 bits and 130 bits, repectively. Basic bit cell size is 4 × 4 μm. The 4Mb chip has an OCCO structure with the following distinguishing functional elements: (1) Bidirectional N-shape transfer gates. (2) A major line replicator with 2 crossed hairpin conductors. (3) DRO detector with folded thin NiFe elements. (4) A hairpin nucleation generator in a 240° super track. (5) Even bit minor loops. Operating margins for the 4Mb IIBD fabricated on (YSmLuBiCa) 3 (FeGe) 5 O 12 are well balanced in all functional elements, and obtained as 25 Oe, sufficient for practical use. It has been found that in-plane holding field applied to stop/start (s/s) direction is necessary for s/s stabilization, and that anisotropy along pattern edges due to stress relief acts a significant role for bit instability and for c-s gate operation. LPE film thickness has been optimized as 1.1 μm for 100-120 keV He+ implantation.

The preparation of low defect density LPE garnet films for magnetic bubble device fabrication

In order to study the cause and to eliminate magnetic domain pinning defects in (YSmLuCa)3(GeFe)5O12 LPE garnet films for use in magnetic bubble devices, a series of experiments have been conducted whereby Gd3Ga5O12 substrates have been intentionally contaminated with specific contaminants likely to be encountered in the substrate preparation and LPE film growth environments. The defects occuring in the films grown on these contaminated substrates have been examined by scanning electron microscopy at high magnifications. The exercise has enabled the identification of the causes of specific defects which occur during routine LPE growth. Other defects resulting from inadequate substrate preparation are discussed with emphasis on defects arising from garnet fragments associated with poor quality wafer edges. As a consequence of this study, defects densities <0.5 cm-2 have been achieved routinely in pilot production quantities on 2 inch diameter substrates.

Bubble propagation direction effects on high frequency bias margin

The bias margin dependence on propagation direction is observed at drive fields higher than 200 kHz, on YY-overlay propagation of 3 μm bubbles in (YSmLuCa)3 (FeGe)5O12 LPE film. This propagation direction effect of bias margin is found to depend on the bias field direction, drive field, bubble-Permalloy spacing and Permalloy pattern shape. These results are discussed in terms of the correlation between the bubble wall state (S=1) and propagation pattern induced bias field gradient on the bubble.

Regression model for LPE film property control : S. J. Lewis. IBM J. Res. Dev.22, (4) 422 (July 1978)

Regression model for LPE film property control : S. J. Lewis. IBM J. Res. Dev.22, (4) 422 (July 1978)

Multifunction integrated optic device using magnetically alterable phase grating

A magnetically alterable phase grating integrated optic coupler-modulator was formed utilizing the magnetic stripe domains in a LPE film of BixYb3−xFe5O12. Light was coupled to a glass waveguide and 72% intensity modulation was achieved.

New magneto-optic memory concept based on compensation wall domains

A new concept of thermomagnetic localized reversible magneto-optic storage is proposed based on the application of compensation wall domains (CWD). Individual CWD's of 12 × 12-μm dimensions in an LPE film of composition Y2.34Gd0.52Yb0.14Fe3.74Ga1.26 O12 with 3-μm thickness have been switched by laser flashes of 10−2 erg/μm2 energy in 5 μs at 5145-Å wavelength using a stationary field of 41 Oe normal to the film plane.