Intl:oducing ... semiconductor devices employing the p-n junction. In this brief 10-year period, have found use in TBE TUNNEL almost every conceivable type of elec­ tronic equipment and have taken their place alongside the tube as a permanent member of the active-device family. Now, before the industry ... has even begun to reach full maturity, another new electronically active device showing outstanding potential has been discovered. This new device, the tunnel diode, was first reported by L. Esaki of Japan in 1958. Although still in an early state of development, this new­ comer promises to assume an important place in the electronics field.

KEY FEATURES The most outstanding of the tunnel , diode's many features is speed of response. After only one year of devel­ opment, tunnel can "outrun" the fastest transistor, and in a few years it is expected that they will challenge the "fastest" electron tubes. Tunnel diodes require much less energy than transistors. Semiconductor surface variability, a knotty problem in obtaining good transistor production The remarkable characteristics of tunnel-diode devices and circuits indicate yields and stability on life, is almost that they will assume an important role among electronically active devices. totally without effect in tunnel diodes. The articles herein describe some of the many contributions of RCA engineers This fact, together with the small size and scientists to tunnel-diode development and indicate the future course and simple structure of the tunnel of this work. diode, promises a low-cost device having Following this introductory description by Dr. Donahue, the basic prin­ excellent reliability. In addition to these ciples of the tunnel diode are described by Dr. H. S. Sommers of the RCA advantages, tunnel diodes produce less Laboratories, who pioneered tunnel-diode work at RCA and has played a large noise than most other amplifying part in the success of the program. Following this, J. B. Schultz and H. B. Yin devices, can operate over greater of Home Instruments, Cherry Hill, discuss tunnel diodes in linear circuits, extremes of temperature, and are reflecting their considerable effort towards potential applications in radio orders-of-magnitude more resistant to and television. Then, R. H. Bergman and M. M. Kaufman of the Electronic nuclear radiation than are transistors. Data Processing Division, IEP, describe tunnel-diode applications for computer OPERATING PRINCIPLE logic and memories. They have done extensive work on the promising applica­ tions to very-high-speed computers. A. J. Wheeler, who was instrumental Although the tunnel diode uses the p-n in fabrication of the first good tunnel diodes at Somerville, junction, as do most other semiconduc­ describes that work in the next article. Finally, H. Nelson of the RCA Labora­ tor devices, its operating principle is tories and N. Ditrick of the Semiconductor and Materials Division discuss the radically different. cross the design and fabrication of tunnel diodes. Nelson developed a novel junction by "tunneling" through, rather junction fabrication technique and was responsible for the rapid progress made than "climbing over," as in a transistor at the Laboratories on the device fabrication. Ditrick played a key role in or ordinary semiconductor diode. The development of germanium tunnel diodes at Somerville. tunneling is made possible by a p-n As these articles show, the tunnel diode-first brought to the attention by junction having an extremely thin Japan's Esaki in I 958-is a newcomer that alt.h6ugh in an early stage of devel- depletion region 50 to 100 angstroms in opment, holds great promise as " the latest midget prodigy." width. Quantum mechanical tunneling, from by Dr. D. J. DONAHUE, Mgr. lasting importance was that of the vac- which the new device received its name, Advanced Development uum electron tube in 1907. For many is not new, even to semiconductor p-n Semiconductor and Materials Division years, vacuum tubes completely domi- junctions, since Zener breakdown of Somerville, N. J. nated the active-device field and pro­ junctions is a tunneling process. How­ vided the basis for the tremendous ever, Esaki was the first to report tun­ HE UNPARALLELED progress of the electronic industry which exists today. neling that increased and then decreased T electronics field has been charac­ Another event of comparable signifi­ with increasing forward bias of a p-n terized by the discovery and develop­ cance was the invention of the transis­ junction. It is this behavior which pro­ ment of the electronically active devices tor in 1948_ The past decade has wit­ duces the very interesting and useful used for amplification, oscillation, and nessed the development of a great num­ negative-resistance characteristic of tun­ switching. The first such discovery of ber of transistor types and related nel diodes (Fig. 1). This negative-resist-

2