Leonard E. Dolhert

Preparation of orthorhombic YBa2Cu3O7−δ by spray-drying formate solutions

Abstract A simple, low cost process has been developed for the preparation of orthorhombic YBa2Cu3O7−δ superconducting powder by spray-drying formate solutions. Yttrium oxide, cupric oxide and barium carbonate are dissolved in formic acid and spray-dried. The spray-dried powder is “charred” at 95°C prior to calcination to avoid undesirable melting and/or dissolution. The charred powder is calcined to produce phase-pure, superconducting YBa2Cu3O7−δ product. Superconducting powder can also be prepared from acetate solutions.

Low detectability of excess yttrium or barium by X-ray diffraction in YBa2Cu3O7 prepared by coprecipitation

Abstract Excess CuO, BaCuO 2 , and Y 2 BaCuO 5 (2-1-1) were each separately incorporated into YBa 2 Cu 3 O 7 (1-2-3) samples, in order to test the sensitivity of powder X-ray diffraction to these common impurity phases. The additions were made by two methods: 1. (1) physical blending, by mixing a phase-pure impurity with phase-pure 1-2-3, and 2. (2) chemical addition, by adding the impurities as individual metal nitrates to a stoichiometric YBa 2 Cu 3 nitrate solution, followed by precipitation and calcination. While chemically and physically incorporated CuO display similar X-ray detectabilities, low (2 wt.%) concentrations of chemically added BaCuO 2 and 2-1-1 are far harder to detect than their physically blended counterparts. It was also found that nearly 10 at.% of yttrium in excess of stoichiometry (i.e. “1.1-2-3”) can be chemically incorporated before 2-1-1 X-ray peaks are observed.

Design of metallizations and components for aluminum nitride packages for VLSIC

A program to produce large cofired aluminum nitride (AIN) packages for support of silicon-based high-density multichip modules (MCMs) is discussed. Perimeter leaded packages measuring over 4 in in length and having over 600 leads on 0.025-in centers have been developed. The size and fine lead pitch require tight dimensional control, including 0.1% on both the flatness and the placement of cofired lead pads. These dimensional requirements, as well as the hermeticity and thermal-mechanical reliability requirements for military use, have been met through a combination of engineering/design solutions and the implementations of new material systems and processes. >

Spatial variations in a.c. susceptibility and microstructure for the YBa2Cu3O7−x superconductor and their correlation with room-temperature ultrasonic measurements

The spatial (within-sample) uniformity of superconducting behavior and microstructure in YBa2Cu30(7-x) specimens over the pore fraction range of 0.10 to 0.25 was examined. The viability of using a room-temperature, nondestructive characterization method (ultrasonic velocity imaging) to predict spatial variability was determined. Spatial variations in superconductor properties were observed for specimens containing 0.10 pore fraction. An ultrasonic velocity image constructed from measurements at 1 mm increments across one such specimen revealed microstructural variation between edge and center locations that correlated with variations in alternating-current shielding and loss behavior. Optical quantitative image analysis on sample cross-sections revealed pore fraction to be the varying microstructural feature.

Metallization Behavior in Aluminum Nitride Electronic Packages

Characteristics such as CTE close to that of silicon, high thermal conductivity, and good dielectric properties make aluminum nitride (AIN) an excellent dielectric for packaging silicon-based high density multichip interconnects. However, there remains many aspects of its behavior that have not been characterized. One such example is the behavior of the various metallizations used within a package. As with A1 2 O 3 , these metallizations must contribute toward a hermetic seal separating the die from the environment. However, the chemical behavior of the metallization systems used for A1 2 O 3 may not be compatible with non-oxide ceramics such as AIN. Consequently, these chemical interactions are investigated in view of the requirements for each application within electronic packages. Hermeticity testing results are also included in the discussion.