It is shown in this paper that by an appropriate cleaning and forming procedure titanium metal can be anodically oxidized to a low leakage current, which makes it possible to use this material for capacitor fabrication. Experimental data are given for the metal/oxide/metal thin-film capacitor. A new "printing" technique especially suited for the fabrication of film capacitors in printed microminiaturized electronic circuits is described for the forming of the dielectric oxide layer.

Titanium Printed Capacitors for Microminiaturization

A study of the oxidation of sputtered tantalum films was carried out to help explain the changes in electrical resistance of such films when heated in air at 100°C. A microbalance was used to obtain the oxidation data over a range of temperatures from 100-600°C in pure oxygen at a pressure of 7.6 cm of Hg. The electrical resistance of films was measured over a temperature range up to 200°C. Some results were also obtained when heating was carried out in a vacuum of 10--6mm of Hg. From a consideration of the oxidation data and the electrical resistance data, it appears that oxidative effects based on a simple model of oxide film formation do not play a major role in affecting the stability of the electrical resistance of the films under the test conditions. Oxidative effects at grain boundaries may have more of an influence. However, structural changes, not yet characterized, may be equally important in accounting for the resistance changes.

The Oxidation of Sputtered Tantalum Films and Its Relationship to the Stability of the Electrical Resistance of These Films

In the two decades since the concept of ceramic based "printed circuits" was first suggested for an Army Ordnance application, substantial changes have taken place in the techniques of electronic circuit construction in the United States. Today, such ceramic circuits, in simple and complex networks, are complemented by printed wiring assemblies in several variations. Both technologies, now well established and in mass use on production lines, represent the current plateaus in miniature circuit construction for general commercial and military usage. Other construction philosophies and technologies are now shaping in the country's industrial and military laboratories, all aimed at new orders of size reduction of electronic equipments. In the several microelectronic techniques under development, the elemental electronic part appears destined to lose its logistic identity completely, and yield its classical position as a building block to black boxes called "circuit functions." The paper provides a summary review of the evolution of current ceramic printed circuits and printed wiring practices and, in the light of today's microelectronic activities, frames the trend in equipment design in the years ahead.

Printed Circuits and Microelectronics

From 1952 to 1958, Jay Lathrop worked on a project at the National Bureau of Standards (later the US Army Diamond Ordnance Fuze Laboratory) to develop microminiaturized, transistorized hybrid integrated circuits for radio proximity fuzes. In this article, Lathrop describes his experiences during this project, the development of photolithography, and how photolithography became critical in the first efforts to produce semiconductor ICs.

The Diamond Ordnance Fuze Laboratory's Photolithographic Approach to Microcircuits

The contribution of solid-state electronic devices to microsystems electronics is important, but there is considerable confusion in this field at the present time. By dividing the field of solidstate devices into four categories into which may be placed all device approaches to microsystems electronics (and, incidentally, solid-state components in general) we may more easily assess the merit of each new contribution by comparison with existing components. These four categories are basic, complex, integrated, and array. The construction details and operating principles, as well as the electrical characteristics, of a new device must be specified in order for it to be properly categorized. Some new examples of complex and integrated devices are presented to emphasize their differences.

A Categorization of the Solid-State Device Aspects of Microsystems Electronics

A program on microelectronics (electronic microminiaturization) has been underway for the past two years at the Diamond Ordnance Fuze Laboratories (DOFL). Fourteen-component-part, transistorized binary counters were fabricated on 1/2-inch squares of steatite ceramic, 1/50 inch in thickness; and 5-part NOR's, on 1/2-inch squares of the same thickness. The techniques that have proved most useful in the program have been 1) photolithographic procedures for the accurate placement at microscopic dimensions of physical masks and electrical insulation, 2) thin film deposition using vacuum, chemical, and screening methods, 3) the use of a conductive adhesive which yields high strength and low resistivity connections, and 4) ultrasonic drilling and air abrasion enabling substrates and devices to be formed to desired sizes and shapes. Concurrent with the physical fabrication, studies were made of detailed circuit design and system applications. Future work will include 1) refinement of the present techniques to achieve inexpensive, reliable circuit wafers capable of mass production by industry, and 2) development of advanced methods more fully utilizing thin film deposition and diffusion techniques.

J. R. Nall

Papers

The DOFLM Microelectronics Program