Hiroji Yamada

DC-SQUID with High-Critical-Temperature Oxide-Superconductor Film

Voltage vs magnetic-flux characteristics of a DC-SQUID using YBa2Cu3O7-δ film have been studied. YBa2Cu3O7-δ film SQUID was fabricated by lithographical patterning. The DC-SQUID operated up to 72 K.

Effects of underlayer roughness on Nb/AlO/sub x//Nb junction characteristics

The effects of underlayer roughness on Nb/AlO/sub x//Nb Josephson junction characteristics are clarified. MoN/sub x/ and SiO films with 0.1-2.7-nm surface roughness are used as underlayers for the junctions. MoN/sub x/ films with varying levels of roughness are prepared by sputter-etching. SiO films retain a smooth surface after sputtering etching. The existence of grain boundaries in the MoN/sub x/ films causes surface roughness. Subgap leakage current of junctions on MoN/sub x/ underlayers is higher than that of junctions on SiO underlayers, and it increases with the roughness of the underlayers. The roughness of the underlayers surface is reflected in the Nb base electrodes surface; however, the roughness of the Nb surface is not directly reflected in the AlO/sub x/ surface. The AlO/sub x/ surface is smoother than the Nb surface. The cause of the leakage increase in the junctions on rough underlayers may be dispersion in the deposited-Al thickness.<<ETX>>

Characterization of a planar spiral inductor on a composite-resin low-impedance substrate and its application to microwave circuits

The Q-factors of planar spiral inductors built on a polyimide-SiO/sub 2/-Si substrate are characterized as a function of the polyimide thickness. We found that inductor quality as high as that on a GaAs-microwave and millimeter-wave integrated circuit (MMIC) requires a polyimide thickness of over 100 /spl mu/m, resulting in a Q-factor of over 17. The applicability of a low-impedance substrate was confirmed through the investigation of a novel RF-MCM in a face-up-type structure for cellular phone systems using a composite epoxy resin-metallic substrate. A fabricated power amplifier module exhibited 28.5-dBm output power and 16% power efficiency at 1.75 GHz.

High-frequency properties of SrTiO3 thin-film capacitors fabricated on polymer-coated alloy substrates

Low-temperature (200 °C) sputter deposition of SrTiO3 (STO) thin films by using ultrahigh-density ceramic target enabled us to fabricate capacitors on polyimide-isoindroquinazoline dione (PIQ)- or benzocyclobutene (BCB)-coated alloy substrates. Complex impedances of the capacitors were analyzed. Capacitances of the 0.01 mm2 area capacitors with 200-nm-thick STO films were around 22 pF and were not dependent on frequency up to 8 GHz. Leakage-current densities of the films were lower than 10−6 A/cm2 at an applied voltage of 10 V and dielectric loss tangents were lower than 10−6.

A DC-powered Josephson logic family that uses hybrid unlatching flip-flop logic elements (Huffles)

This paper describes the development of a dc-powered Josephson logic family that uses hybrid unlatching flip-flop logic elements (Huffles). The Huffle circuit used in this study is modified by adding a parallel resistor to the original Hebard-type Huffle circuit. Analysis of the circuits operation shows that the undesirable hung-up phenomena are prevented by this modification. Based on the result of the analysis, the circuits parameters are derived and a typical operating margin of /spl plusmn/26% is obtained. Besides AND/OR operations using a threshold logic operation, two-input exclusive OR (XOR), two-input multiplexor (MUX), and three-input majority (MAJ) operations are realized using a Huffle gate in which 2-Josephson-interferometers (2JI) in the standard Huffle gate are replaced by stacked-2JIs. Thus, a Huffle logic family, formed from NOT, AND, OR, XOR, MUX, MAJ, and flip-flop (FF), are constructed. By using this Huffle logic family, a 6-b arithmetic logic operating unit (ALU), a 6-b analog-to-digital converter (ADC), and a 6-b gray-to-binary converter (GBC) have been successfully operated. During high-speed testing, a 1-b comparator was operated up to an input bandwidth of 6 GHz.

A 4-bit, 250-MIPS processor using Josephson technology

An experimental 4-bit Josephson processor that demonstrates the possibility of a Josephson computer system with a gigahertz clock is presented. Constructed from 2066 gates on a 5-mm*5-mm die, it implements an eight-instruction set to enable the basic operations of digital signal processing. The basic structure and operating principles of the Josephson device are reviewed, and the design of and operating results for the processor are presented. The focus is mainly on the circuit techniques required to realize a gigahertz clock in a Josephson processor. Circuit techniques to suppress the crosstalk from the AC power to the I/O lines and ways to improve the clock frequency are introduced. The problems remaining in the effort to enhance performance are discussed.<<ETX>>

Optical characteristics of one-dimensional photonic crystals fabricated with high-aspect-ratio Si etching

We demonstrate optical properties of one-dimensional photonic crystals which are fabricated by using high-aspect-ratio Si etching. The measured transmission spectrum shows an obvious band gap and is well reproduced by theoretical calculation.