RESEARCH GE Unveils Tunnel Diode Practical a p p l i c a t i o n of q u a n t u m - m e c h a n i c a l tunneling m a y l e a d t o b i g changes in electronics VJTKXERAL.
Electric
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"most important advance in semicon ductor devices since the transistor." The company's applications research ers see it as a boon '>mmunications, computers, nucle;» trol, satellites, and space vehicic-a. And OE's vice president and research director says it "could lead to revolutionary changes in the electronics industry." First an nounced last year by Japanese re searcher Leo Esaki, "it" is the tunnel diode (C&EX, July 27, page 1 7 ) . G E will soon have its experimental model available—probably in late September
or early October—for industry on a sample basis. While similar in function to transis tors, rectifiers, ordinal)' diodes, a n d other semiconductors, the tunnel diode operates by a radically different prin ciple. Its n a m e stems from t h e quan tum-mechanical tunnel effect, which explains the w a y electrical charges move through t h e device. In the tran sistor, for example, electrons start from the emitter and diffuse across the base region to the collector. Not so in t h e tunnel diode, G E explains. Here, elec trons can disappear from one side of a
NEW DEVICE. A tunnel diode is used in this vest-pocket transmitter, which has a range of a b o u t 1 / 2 mile. G u y Suits ( r i g h t ) , General Electric vice presi dent a n d director of research, speaks into t h e microphone; Jerome J. T i e m a n n holds the transmitter. An F M receiver (foreground) picks u p t h e signal 38
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potential barrier (junction region of the diode) a n d show up instantaneously on t h e other side, even t h o u g h they do not h a v e e n o u g h energy to surmount the harrier. H e n c e , tliey a p p e a r to "tun nel" underneath the barrier. Electrons in the tunnel diode travel at t h e speed of light, as contrasted to t h e relatively slow motion of electrons irk. conven tional semiconductors. GE points to these key properties of t h e tunnel diode from the electronic circuit point of view : • Extreme speed a n d insensitivity to temperature changes. • Modest power supply needs. • Operation in a variety of critical environments. • Low noise level. • Simple, light weight, small size. ► Communications. T h e tunnel di o d e is especially suited for communica tions, i n everything from broadcast re ceivers to high f recjiiency satellite trans mitters. But equally important, says G E , will be its application in high speed digital computers. T h e tunnel diode switches on o r off in a fraction of a millimicrosecond—at least 100 times faster than today's transistors. And i t can b e made to use only one h u n d r e d t h as m u c h power. T h e tunnel diode gives ci low voltage out put, a n inconvenience in some applica tions because the output must b e boosted before it is useful. But, G E points out, this is really a blessing in disguise since low voltage means the diodes do not generate m u c h heat. Thus, tunnel diodes may b e able to help t h e computer engineer plagued with t h e problem of heat dissipation. The tunnel diode works well at liq uid helium temperature—4.2° K. Raise the temperature to t h e freezing point of water, or even to 600° F . , and it remains unaffected. G E calls this temperature range u n p r e c e d e n t e d in electronic devices. G a m m a rays or high levels of fast neutron irradiation don't b o t h e r t h e diode either. This fea ture o p e n s the way for use in nuclear controls, G E points out. GE does not view t h e tunnel diode primarily as a replacement for transis tors o r other circuit components. I t may d o this in some instances, says G E , b u t i t s over-all vaKie will b e to im prove the worth of other components b y working w i t h them. Sample tunnel diodes will sell for a b o u t $75, G E esti mates,, b u t eventually they will cost less than a comparable transistor, predicts t h e company. ■
