Optimized technology for freely positionable Josephson junctions inYBa2Cu3O7-x fabricated by local iondamaging

Freely positionable Josephson junctions in high-temperature superconductor thin films are fabricated by a combination of photo- and electron-beam lithography. In selected regions of YBCO thin films point defects are induced by oxygen implantation. These weak links exhibit resistively shunted junction (RSJ)-like voltage-current characteristics close to the junction transition-temperature. Below this temperature, a transition from RSJ to flux-flow behavior is observed. Fraunhofer patterns appear in magnetic modulation measurements at different temperatures. The temperature dependence of the critical current reveals superconductor/normal conductor/superconductor (SNS) features. The dependence of Shapiro steps on microwave power demonstrates Josephson contributions over the entire temperature range     

Voltage tunable capacitors using high temperature superconductorsand ferroelectrics

In this paper we report the construction of both slot capacitors on bulk substrate and thin film interdigital capacitors using YBa₂ Cu₃O_7-δ (YBCO) and Ba_xSr _1-xTiO₃. Slot capacitors made on bulk Ba_x Sr_1-xTiO₃ (BST) yielded variations in capacitance of more than 6 to 1 at 86 K with a peak electric field strength of 25 kV/cm. With a metal organic deposition (MOD) grown Ba_xSr_1-xTiO₃ 300-nm overcoat on a YBCO thin film, an interdigital capacitor on LaAlO₃ substrate yielded an approximate tuning range of 10% for peak field of 66 kV/cm over temperatures ranging from 50 K to 120 K     

Pt-based metallization of PMOS devices for a compatible monolithic integration of semiconducting/Yba2Cu3O7−δ superconducting devices on silicon

Mo, Pt, Pt/Mo and Pt/Ti thin films have been deposited onto Si and SiO₂ substrates by RF sputtering and annealed in the YBa₂Cu₃O_7−δ (YBCO) growth conditions. The effect of annealing on the sheet resistance of unpatterned layers was measured. A Pt-based multilayered metallization for the PMOS devices was proposed and tested for a compatible monolithic integration of semiconducting devices and YBCO sensors on the same silicon substrate. The best results were obtained with a Pt/Ti/Mo-silicide structure showing 0.472 Ω_□ interconnect sheet resistivity and 2×10⁻⁴ Ω cm² specific contact resistivity after annealing for 60 min at 700 °C in 0.5 mbar O₂ pressure.     

Optical detector using granularYBa2Cu3O7-δ weak link-typejunctions

Experimental photoresponse study of granular YBa₂Cu₃O_7-x (YBCO) weak link is reported. The Josephson critical current I_c is suppressed with light illumination of the junction, produced mainly from optical generation of quasiparticles. At lower temperature (T=64.5 K), the hysteresis in I-V characteristic of the weak link appears, which may be found useful for optical detection purpose. This was supported from preliminary experiments     

Thin film Y-Ba-Cu-O/Ag composites for fluxonic devices

We have investigated thin film composites of YBa₂Cu₃O₇ (YBCO) with Ag for fluxonic device applications. YBCO/Ag composite films are produced by first depositing a layer of Ag onto a substrate and then heating the film to the YBCO deposition temperature of 680°C or higher. YBCO is deposited by off-axis sputtering onto the Ag-coated substrate. The resulting YBCO/Ag film is a composite of YBCO with well-defined Ag regions several microns in size. Scanning electron micrograph images of the films' surfaces show a background of smooth YBCO grains dotted with Ag clusters. For a wide range of increasing Ag composition, the transition temperatures of the composite films on SrTiO₃ remain high, while the critical current densities have been reduced as much as 65 times. On MgO substrates, critical current density has been reduced by more than four orders of magnitude. Also on MgO, significant voltage response is seen in external magnetic fields of less than 1 mT. These measurements suggest that the films may be arrays of superconductor-normal-superconductor (SNS) junctions formed by weakly coupled YBCO grains with Ag in the grain boundaries. The field responsivity and low critical current densities of these composites make them potentially useful for fabrication of fluxonic devices     

Low- and high-temperature superconducting microwave filters

Stripline and microstrip filters at X-band were designed and fabricated using low- and high-temperature superconductors in quarter-wave, parallel-coupled section configurations. Low-temperature superconducting niobium thin films, deposited on single-crystal sapphire, were used to build to six-pole stripline filters with adjacent passbands and approximately 3 dB crossovers and 1.2% bandwidth. Four- and six-pole microstrip filters were made with in situ epitaxial YBa₂Cu₃O₇ (YBCO) films on LaAlO₃ substrates. All the YBCO filters showed 77 K passbands with clean skirts and high out-of-band rejection. The six-pole filters had adjacent passbands with -28 dB crossovers and 1.5% bandwidth     

Coaxial line configuration for microwave power transmission studyof YBa2Cu3O7-δ thin films

Microwave transmission measurements through YBa₂Cu₃O_7-δ (YBCO) high-transition-temperature superconducting thin films on lanthanum aluminate (LaAlO₃) have been performed in a coaxial line at 10 GHz. LaAlO₃ substrates were ultrasonically machined into washer-shaped discs, polished, and coated with laser-ablated YBCO. These samples were mounted in a 50-Ω coaxial air line to form a short circuit. The power transmitted through the films as a function of temperature was used to calculate the normal state conductivity and the magnetic penetration depth for the films     

Critical current characteristics of YBa2Cu3O7 thin films on (110) SrTiO3

The material and electrical characteristics of YBa₂Cu ₃O₇ (YBCO) thin films deposited by inverted cylindrical magnetron sputtering on (110) SrTiO₃ (STO) were investigated. X-ray diffractometry shows the grain orientations to be predominantly the YBCO (110) and (103) with no evidence of c-axis grains, Electron micrographs show the film surface to consist of coupled elongated grains parallel to the (110) STO edge. The films were patterned into small 2.5 mm squares parallel to the substrate edges for electrical characterization. Transport currents parallel and perpendicular to the (110) substrate edge showed a 945:1 anisotropy in film resistance and a factor of two in critical current density for temperatures below 60% of the transition temperature (T_c). The temperature dependence of the critical current near T_c was quadratic-like and strongly dependent on the value of T_c used in the analysis. For the two orientations, there was nearly a 6 K difference in T_c as determined by the point at which the critical current became zero. The response of the critical current to small magnetic fields was greater for transport current along the c-axis direction and was observable over a temperature interval nearly four times greater than for current along the basal plain. These YBCO thin films have good response to small magnetic fields and are suitable for vortex flow device development     

The effects of annealing step-edges on SrTiO3 and MgOsingle-crystal substrates on YBa2Cu3O7Josephson junctions

The effect of annealing step-edges on SrTiO₃ and MgO single-crystal substrates on Josephson junctions of YBa₂Cu ₃O₇, has been studied. The step-edge was fabricated by argon-ion milling technique and was annealed at 1050°C in oxygen atmosphere. YBa₂Cu₃O₇ thin film was deposited on the annealed step-edge by a standard pulsed laser deposition. The effect of annealing the step-edge on the junction was characterized by AFM and current-voltage (I-V)characteristic. The annealed step-edge on SrTiO₃ and MgO substrates showed that the surface of the substrates was smoother and I-V characteristic of Josephson junction improved     

High-Tc ramp-type Josephson junctions on MgO substrates forterahertz applications

The authors successfully fabricated high-Tc ramp-type junctions with PrBa₂Cu_3-xGa_xO_7-δ (PBCGO: x=0.1, 0.4) barriers on MgO substrates. The junctions showed resistively shunted Josephson junction (RSJ)-like I-V curves with thermally and voltage activated conductivity. The I_cR_n products for these junctions scaled very well with the Ga-doping. Maximum response of the junctions for 100-GHz millimeter-wave irradiation could be observed up to 12 mV corresponding to 6 THz. Using far infrared laser radiation, we confirmed a terahertz (THz) response of these junctions. These results show promise for THz-wave applications of ramp-type Josephson junctions     

Effect of bottom electrode materials on the electrical andreliability characteristics of (Ba, Sr)TiO3 capacitors

The dielectric constant and the leakage current density of (Ba, Sr)TiO₃ (BST) thin films deposited on various bottom electrode materials (Pt, Ir, IrO₂/Ir, Ru, RuO₂/Ru) before and after annealing in O₂ ambient were investigated. The improvement of crystallinity of BST films deposited on various bottom electrodes was observed after the postannealing process. The dielectric constant and leakage current of the films mere also strongly dependent on the postannealing conditions. BST thin film deposited on Ir bottom electrode at 500°C, after 700°C annealing in O₂ for 20 min, has the dielectric constant of 593, a loss tangent of 0.019 at 100 kHz, a leakage current density of 1.9×10 ^-8 A/cm² at an electric field of 200 kV/cm with a delay time of 30 s, and a charge storage density of 53 fC/μm² at an applied field of 100 kV/cm. The BST films deposited on Ir with post-annealing can obtain better dielectric properties than on other bottom electrodes in our experiments. And Ru electrode is unstable because the interdiffusion of Ru and Ti occurs at the interface between the BST and Ru after postannealing. The ten year lifetime of time-dependent dielectric breakdown (TDDB) studies indicate that BST on Pt, Ir, IrO₂/Ir, Ru, and RuO₂/Ru have long lifetimes over ten gears on operation at the voltage bias of 2 V     

Sensitivity of Rs-measurement of HTS thin films by threeprime resonant techniques: cavity resonator, dielectric resonator, andmicrostrip resonator

The microwave surface resistance, R_s measurement of YBa ₂Cu₃0_{7 -δ} (YBCO) thin film deposited on 10 mm × 10 mm LaAlO₃ substrate using three prime resonating techniques, namely, cavity end plate substitution technique (20 GHz), dielectric resonator technique (18 GHz), and microstrip resonator technique (5 GHz), is reported. In addition, theoretical analysis for each technique has been performed to calculate the relative percentage error in the measured R_s -value of the YBCO thin film as a function of temperature. It has been found that the shielded dielectric resonator provides far better sensitivity for R.-measurement of the YBCO thin film with minimum relative percentage error (<4%) in the temperature range from 20 K to transition temperature of YBCO thin film compared to the other two techniques     

光学表面粒子污染物散射的单层薄膜调控特性

为了降低超精密低损耗光学元件表面粒子污染物的光散射损耗,文中提出通过在光学表面沉积单层薄膜来调控表面场强分布,从而降低散射损耗的方法。理论分析了K9玻璃超光滑光学表面不同厚度单层二氧化硅（SiO₂）和单层二氧化钛（TiO₂）薄膜表面上方半径为100 nm粒子污染物所在处的电场强度,理论分析结果发现,当SiO₂薄膜厚度为137.4 nm,TiO₂薄膜厚度为12.3 nm时,表面粒子污染物所在处的电场强度最小。在此基础上分别计算了光学元件表面沉积厚度为137.4 nm的单层SiO₂薄膜以及厚度为12.3 nm的单层TiO₂薄膜,表面粒子污染物的总散射损耗(S)和双向反射分布函数(BRDF),计算结果表明,在波长为632.8 nm的光垂直入射时,单层SiO₂薄膜和单层TiO₂薄膜可有效降低其表面粒子的BRDF,且可将K9玻璃表面的总散射分别降低12.40%和25.04%。实验验证了单层SiO₂薄膜对于表面粒子污染物散射降低的有效性。     

Future heat transfer concerns in Josephson junction computers

Using the superconducting properties of Josephson junctions enable extremely high switching speeds unmatched in semiconducting electronics. Much research has been conducted in recent decades in order to produce high performance electronics based on Josephson junction logic. In addition to the high speeds attainable by this technology, also of significance is the very low heat dissipated by Josephson circuits. Josephson devices have made great strides in the last ten years with microprocessors reaching levels of integration as high as 10⁵ junctions/cm². Dissipation in these devices is easily managed, but integrations reaching 10⁷ must be considered if Josephson electronics are to compete with the complexity and functionality of semiconducting electronics. Coupling this level of integration with dissipations of 0.34 and 2.98 μW/junction in low and high temperature cases respectively, produces large heat fluxes difficult to remove at cryogenic temperatures. While other technical difficulties currently overshadow heat transfer concerns, the future of Josephson electronics research will likely need to address them     

Preparation and characterization of YBaCuO high Tcsuperconducting thin films

For thin film metalorganic chemical vapor deposition (MOCVD), a stoichiometric gas phase can be obtained from a mixture of the precursors in the desired mole ratios, in spite of differences in the volatilities of the individual compounds. Proper film composition is obtained by controlling the velocity of a carriage containing the precursors through the heating zone of a vaporizer. YBaCuO (YBCO) superconducting films were prepared on yttrium stabilized zirconia (YSZ) (001) crystal substrates by single source MOCVD using a mixture of powders of Y(thd)₃, Ba(thd)₂ and Cu(thd)₂ as sources. Nondestructive measurements of resistivity, critical current, composition, and surface morphology were performed on these films. A single crystal film with T_co=89 K was made under optimum conditions. Its homogeneity was investigated by resistivity and T_co measurements and by atomic force microscopy (AFM) at several points of the surface along a diameter of this film. The roughness of the film is higher at the edge than at the center, and this appears to be correlated with the normal state resistivity. The c-axis and a-axis YBCO phases compete with each other at substrate temperatures ranging from 750 to 820°C. The c-axis YBCO phase shows spiral growth structure and the spiral step height is about 12     

Substrate and Device Pattern Dependence of the Thermal Crosstalk in Y Ba2Cu 3O7−δ Transition Edge Bolometer Arrays

Using YBa₂Cu₃O_7-delta (YBCO) thin films, pulsed laser deposited on 1-mm-thick LaAlO₃ or SrTiO₃ substrates, we made 4times1 pixel arrays of transition edge bolometers with separations between neighboring pixels ranging from 40 mum to 170 mum for testing purposes. We investigated the effects of the YBCO film thickness (200 and 400 nm), substrate material, and back-etching of the substrate, on the crosstalk between the pixels of the arrays. The investigation was based on the analysis of the voltage response of the dc current biased bolometers versus the modulation frequency of a near-infrared laser source. We observed that the bolometer arrays made of 400-nm-thick films had less interpixel thermal crosstalk than the 200-nm-thick films. The effect of substrate thickness on the response of the pixels was investigated by up to 500 mum back-etching of the substrates. The bolometers made on back-etched LaAlO₃ substrates had anomalous crosstalk response behavior, which was effective at higher modulation frequencies. In addition, we present an analytical thermal model for explaining the observed effects of the thermal crosstalk on the response characteristics of the pixels of the arrays. We report the measured response and the anticipated thermal crosstalk of the characterized bolometers'. We describe the responses based on the thermal models and discrepancies from the model's predictions     

Anomalous microwave response ofYBa2Cu3O7-δ granular thin filmsunder magnetic fields

The microwave response of YBa₂Cu₃O_7-δ (YBCO) granular films has been studied at a microwave frequency of 30.5 GHz. In absence of a magnetic field, the dependencies of a normal microwave response on the bias current was observed at a temperature close to T_c. When a magnetic field ranging from 5.0 to 33.0 mT is applied, the responses broaden and shift toward a lower temperature. In the superconducting state, the responses were found to be highly dependent on the magnetic field. For a current of 5.0 mA and a magnetic field above 17.0 mT, the responses increased and did not vanish, even at a very low temperature, which is believed to be correlative with the anisotropic character of the structure     

The coplanar resonator technique for determining the surfaceimpedance of YBa2Cu3O7-δ thinfilms

We describe how coplanar microwave resonators fabricated from patterned thin films of YBa₂Cu₃O₇(-δ) (YBCO) can he used to measure the ab-plane microwave surface impedance Z_s=R_s+jX_s of the films, in particular the absolute value and temperature dependence of the magnetic penetration depth λ. The current distribution of the resonator is calculated by modelling the resonator as a network of coupled transmission lines of rectangular cross-sections; this is then used to estimate the ab-plane λ(T) from the measurements of resonators of different geometries patterned onto the same film. We obtain values of λ(0) in the range 150-220 nm. The unloaded quality factors of the linear resonators at 7.95 GHz are around 45000 at 15 K and around 6500 at 77 K. We estimate the corresponding values of the intrinsic R_s at 7.95 GHz to be 23 μΩ and 110 μΩ at 15 K and 77 K, respectively. These values are comparable with those of other high quality unpatterned YBCO films reported in the literature. Z_s for the best optimised films appears to be insensitive to the effects of patterning     

准分子激光扫描淀积PZT/YBCO结构铁电薄膜

利用脉冲准分子激光（工作气体ＸｅＣｌ，波长３０８ｎｍ，脉宽２８ｎｓ）在外延ＹＢＣＯ／ＬａＡｌＯ３（１００）单晶基片上淀积了Ｐｂ（Ｚｒ０．５５Ｔｉ０．４５）Ｏ３铁电薄膜，ＹＢＣＯ薄膜既为生长高取向ＰＺＴ薄膜提供了晶体匹配条件，同时也为ＰＺＴ铁电薄膜提供了下电极。讨论了工艺参数对晶相结构和表面形貌的影响。用Ｘ射线衍射表征了该多层膜的晶相结构，扫描电镜观察其表面形貌。ＰＺＴ铁电薄膜的剩余极化为２１μＣ／ｃｍ２，矫顽场为６５ｋＶ／ｃｍ。     

Buffer layers for high-quality epitaxial YBCO films on Si

Efforts aimed at producing device-quality YBa₂Cu₃ O_7-δ (YBCO) films on Si, which have resulted in films with properties comparable to what can be achieved with conventional oxide substrates such as SrTiO₃, are described. It is reported how epitaxial YBCO films were grown on Si(100) using an intermediate buffer layer of yttria-stabilized zirconia (YSZ). Both layers are grown with an entirely in situ process by pulsed laser deposition (PLD). Ion channeling revealed a high degree of crystalline perfection with a channeling minimum yield for Ba as low as 12%. The normal state resistivity was 250-300 μΩ-cm at 300 K; the critical temperature, Tc (R=0), was 86-88 K, with a transition width of 1 K. Critical current densities of 2×10⁷ at 4.2 K and 2.2×10⁶ at 77 K have been achieved. Noise measurements indicate that these films are suitable for use in highly sensitive far-infrared bolometers. Applications of this technology to produce in situ reaction patterned microstrip lines are discussed