lost history of the transistor

8/12/2019 Lost History of the Transistor

1/6

+SEMICONDUCTORS

TRANSISTOR44 IEEE Spectrum | May 2004 | NA

How, 50 years ago,Texas Instruments and Bell Labs pushed

electronics into the silicon age BY MICHAEL RIORDAN

THE LOST HISTORY OF THE


2/6

he speakers words were at once laconic and electrifying.

Contrary to what my colleagues have told you about the

bleak prospects for silicon transistors, he proclaimed in

his matter-of-fact voice, I happen to have a few of them here

in my pocket.

Silicon transistors? Did he say silicon transistors?

Yesamong the few in the world at that moment. It was

10 May 1954.

A long and till-then uneventful session on silicon devices had

been winding down at the Institute of Radio Engineers (IRE)

National Conference on Airborne Electronics, in Dayton, Ohio.

There, a parade of engineers and scientists were lamenting the

sobering challenges of developing and eventually manufactur-

ing silicon transistors. Amid the torpor, scattered attendees were

stifling yawns, glancing at watches, and nodding off. But that was

before Gordon Teal of Texas Instruments Inc. made his surpris-

ing announcementand jaws dropped in disbelief.

Did you say you have silicon transistors in production?

asked a stupefied listener about 10 rows back in the audience,

which now began to perk up noticeably.

Yes, we have three types of silicon transistors in production,

Teal replied, pulling several out of his pocket to the general amaze-

ment and envy of the crowd. Then, in a bit of quaint but effec-

tive razzle-dazzle, he cranked up a record player, which began

blaring out the swinging sounds of Artie Shaws big-band hit,

Summit Ridge Drive. Amplified by germanium transistors, the

music died out instantly as Teal dunked one into a beaker of

hot oil. But when he repeated his demonstration immersing a sil-

icon transistor instead, the music played on without faltering.

As his talk ended, Teal mentioned that copies of his paper on

the subject, innocuously titled Some Recent Developments in

Silicon and Germanium Materials and Devices, were available

near the rear door. A crowd stampeded back to get them, leaving

the final speaker of the session without an audience. Minutes later,

a Raytheon engineer was overheard in the lobby shouting into a

telephone: Theyve got the silicon transistor down in Texas!

May 2004 | IEEE Spectrum | NA 45

T

IN THE BEGINNING: Gordon Teal [left] directed the development of the silicon transistor atTexasInstruments. William Shockley [middle] led the team at Bell Telephone Laboratories thatdeveloped the very first transistor, which was made of germanium. TIs silicon device with itsthree long leads became famous, making the Texas upstart the sole supplier of silicon transistorsfor several years in the 1950s. Morris Tanenbaum [right] at Bell Labs actually made the first

silicon transistor, but he felt it didnt look attractive from a manufacturing point of view.


3/646 IEEE Spectrum | May 2004 | NA

At the time, the silicon transistor seemed to be one of the first

major breakthroughs in transistor development not to occur at Bell

Telephone Laboratories in Murray Hill, N.J., where physicists John

Bardeen and Walter Brattain had invented the transistor in December

1947. Their device featured two closely spaced metal points jabbed

delicately into a germanium surfacehence its name, the point-

contact transistor. They called one point the emitter and the other

point the collector, while a third contact, known as the base,

was applied to the back side of the germanium sliver. A positive elec-

trical bias on the emitter enhanced the conductivity of the germa-

nium just beneath the collector point, amplifying the output currentthat flowed to it from the base.

Bell Labs achieved a long string of firsts

in the years following that momentous

invention, which it announced six months

later at a 30 June 1948 press conference in

New York City. Among its major advances

was the so-called junction transistor, first

conceived the previous January by William

Shockley, who led the group that included

Bardeen and Brattain. He figured that much

better transistor performance and reliabil-

ity could be realized by eliminating the frag-

ile point contacts and instead forming theemitter, base, and collector as a single semi-

conductor sandwich with three different layers [see sidebar,

Transistors 101: The Junction Transistor]. Current flowing from

emitter to collector in Shockleys device could be modulated by an

input signal on the base.

Teal (then working at Bell Labs) and his fellow physical chemist

Morgan Sparks successfully fabricated the first working junc-

tion transistor from a germanium crystal in April 1950. Butpartly

because the frequency response of early junction transistors was

inferior to that of point-contact devicesBell Labs held off

announcing this achievement for over a year, until 4 July 1951. Five

years later, Bardeen, Brattain, and Shockley shared the Nobel Prize

for inventing this revolutionary solid-state amplifier.

Their brilliant pioneering work has overshadowed much of the

subsequent development years of the transistor, including the

crucial change from germanium to silicon in the mid-1950s. That

shift in semiconductor material proved essential to the devices

glorious future as the fundamental building block of virtually all

of todays integrated circuits. For germanium, to put it simply, was

just not up to the task.

The material does have advantages: it is far less reactive than

silicon and much easier to work with because of its lower melting

temperature. And current carrierselectrons and holesflow through

germanium more rapidly than through silicon, which leads to higher

frequency response. But germanium also has serious limitations. For

example, it has a low band gap (0.67 electron volts versus 1.12 eV for

silicon), the energy required to knock electrons out of atoms into the

conduction band. So transistors made of this silvery element have

much higher leakage currents: as the temperature increases, their del-

icately balanced junctions become literally drowned in a swarming

sea of free electrons. Above about 75 C, germanium transistors quit

working altogether. These limitations proved bothersome to radio

manufacturers and especially the armed services, which needed sta-

ble, reliable equipment that would perform in extreme conditions.

Nowhere were these concerns appreciated more than at Bell Labs,

which led the way into silicon semiconductor research during the

early 1950s. Working in its chemical physics department with tech-

nician Ernie Buehler, Teal grew single crystals of silicon and dopedthem with tiny impurities to make solid-state diodes in

February 1951, publishing the results a year later. He added specific

impurity atoms to the molten silicon to alter the electrical prop-

erties of crystals drawn from it. Elements from the fifth column

of the periodic tablearsenic or antimony, for examplecreate an

excess of electrons in the tetrahedral crystal structure, yielding

n-type silicon. Elements from the third column, such as boron or

gallium, create a deficit of electrons (usually regarded as an excess

of holes), yielding p-type silicon. By adding first one kind of impu-

rity and then the other to the molten silicon from which they slowly

withdrew the crystal, Teal and Buehler formed transition regions

called pnjunctions between the two types of silicon. Small bars cutacross these junctions act as diodes when

a potential is applied across them through

electrical contacts on the two ends.

Meanwhile, Calvin Fuller was beginning

experiments in an adjacent lab on diffus-

ing impurity atoms from hot gases into the

germanium or silicon surfaceone of the

major technology milestones on the road to

the integrated circuit. By December 1953

Fuller was so successful that Shockley

started building a new research team to

attempt to fabricate silicon transistors using

the technique. And early in 1954, Fuller andGerald Pearson formed pnjunctions by dif-

fusing a thin layer of boron atoms into a wafer of n-type silicon, mak-

ing a hole-rich p-layer on its surface. These large-area diodes gen-

erated substantial current when sunlight fell on them. On 25 April,

Bell Labs trumpeted this achievement as the solar battery, the

first photovoltaic cell operating at efficiencies near 10 percent.

+ + +

By then TI had made its first silicon transistorunder Teals

general direction. Back at Bell Labs, he had become homesick for his

native Texas, where he had grown up a devout Baptist in South Dallas

and pursued his undergraduate studies in mathematics and chem-

istry at Baylor University, in Waco. Restless in Murray Hill, N.J., and

looking for more responsibility, Teal responded to an ad in The

New York Times for a research director at TI. He met with TI vice

president Pat Haggerty, who offered him the position. He began there

on 1 January 1953, bringing with him his vast expertise in growing

and doping semiconductor crystals.

Under Haggertys leadership, TI was moving aggressively into

military electronics, then burgeoning with the Cold War in full

swing. The Dallas company had been founded during the 1930s as

Geophysical Services Inc., developing and producing reflection

seismographs for the oil industry. During World War II, it snagged

a U.S. Navy contract to supply airborne submarine-detection

equipment; afterward it continued to expand its activities in mil-

itary electronics, reorganizing itself as Texas Instruments Inc. in

1951. By the time Teal arrived, the firm had almost 1800 employ-

ees and was generating about US $25 million in annual sales.

The company was also beginning to manufacture what were called

grown-junction germanium transistors under the direction of engi-

neer Mark Shepherd. He had attended a 1951 Bell Labs symposium on

transistor technology with Haggerty, where he listened to a Teal work-

shop on growing semiconductor crystals. In early 1952, after much

wheedling and cajoling by Haggerty, TI purchased a patent license

to produce transistors from Western Electric Co., AT&Ts manu-

facturing arm, for $25 000. By the end of that year, it was already man-

ufacturing and selling them under Shepherds leadership.Early the next year, Teal was back in Dallas organizing TIs

Theyve gotthe silicontransistor

down in Texas!


4/6

To understand how a transistor works, first consider the lowlydiode. It is a simple union of the two most fundamental kinds ofsemiconductor, known as n-type andp-type. Both conductcurrent, but the n-type does it with electrons, while thep-typedepends on electron deficiencies, better known as holes.Joining these two types of semiconductors forms what isknown as apnjunction at their boundary. This is the core of a

semiconductor diode, which conducts current in one direction.Connect a batterys positive terminal to the n-type material

[figure A, top] and electrons are attracted to that terminal, whileholes in thep-type material move toward the negative terminal. Inother words, charge carriers stream away from the junction,expanding a barren volume, aptly called the depletion region. Thediode is said to be reverse-biased, and hardly any current flows.

Now reverse the battery connections [figure A, bottom].Electrons in the n-type material move toward the junction and areconstantly replenished by the battery. Meanwhile, holes in the

p-type material stream toward the junction, repelled by the posi-tive battery terminal. The depletion region shrinks tremendouslyas holes and electrons combine at the junction, neutralizing one

another, as more stream in on either side from the battery. Thediode is said to be forward-biased; current flows easily. Thus, adiode can control the direction of current, but not how large it is.

A transistor, on the other hand, can control how much currentgoes through it and also act as an amplifier. The simplest transis-tor has three parts: an emitter, a base, and a collector. Think ofthe transistor as a sandwich of twopnjunctions back to back[figure B] in either npnorpnporder; they operate similarly.

In an npn transistor, for example, the n-type emitter hasmany extra electrons, the relatively thinp-type base has a smallnumber of holes, and the n-type collector has a moderate num-ber of electrons. (Junction transistors are also known as bipolardevices because, in the emitter, holes and electrons flow inopposite directions.) A transistor amplifier takes a small, varyingvoltagean input signalbetween the base and the emitter, anduses it to control a larger current flowing from the emitter to thecollector. Thats the output. The key agents in this amplificationare the depletion regions. With twopnjunctions in the device,there are two depletion regions: one between the emitter and thebase, the other between the base and the collector.

First, the emitter-base diode is forward-biased by a voltagesource [left in figure B]. Electrons flow from the emitter into thebase. The base-collector diode, on the other hand, is reverse-biased, so that holes will not flow into the base, which wouldintercept any electrons coming across from the emitter andtherefore block current from flowing through the device.

With this setup, the current through the transistor, from emit-ter to collector, is controlled by the depletion region around theemitter-base junction. When it is thick, the current is choked off;when it is thin, lots of current flows through the device. But holdonwhen it is thin, and electrons shoot across the emitter-base

junction, arent they blocked by the fat depletion region aroundthe base-collector junction? Nothe base is narrow, so themomentum of the electrons pouring in from the emitter bringsthem close to that junction. From there, the positive voltage at the

junction then sweeps most of the electrons into the collector.Only a few are lost in the base as they move into the vacant holes.

The transistor is designed so that the flow of electrons from

emitter to collector is very sensitive to the current into the base.This is done by making the base very thin (so electrons dont

have far to go before reaching the collector) and using low dop-ing (electrons cannot easily find vacant holes to fill). The voltageacross the base-emitter junction provides the electric field thatdrives electrons from the base into the collector.

With the emitter-base junction forward-biased, a varying volt-age put on top of itan input signalvaries the depletion region,which in turn varies a relatively large current flowing through the

device. Add a load resistor in the collector circuit, and that smallvarying input produces a much larger varying collector voltage:the transistor amplifies the signal at the base. Depending on thecircuit, the result will be current, voltage, or power amplification.

Although bipolar junction transistors have been surpassedfor many applications by various forms of field-effect transistors,bipolars remain popular for applications involving high-frequency signals. Theyre found in countless modern electronicdevices, including broadband Internet modems, set-topboxes, DVD players, and CD-ROMs. Alfred Rosenblatt

TRANSISTORS 101: THE JUNCTION TRANSISTOR

May 2004 | IEEE Spectrum | NA 47

FIGURE A

FIGURE B

n materialp material

Wide depletion region

n material

p material

Narrow depletion region

Very low current flow

Electrons

Holes

-+

+-

Reverse-biasedpnjunction

Forward-biasedpnjunction

n material

p material

n material

Collector

Base

Emitter

C

E

B

C

E

B

+

+

+

-

-

-

lB

lE

lE

l

l

V

V

V

V1

Electronflow

Holeflow

Electronflow

Holeflow


5/648 IEEE Spectrum | May 2004 | NA

research department. Haggerty had hired him to build a team of

scientists and engineers that could generate enough ideas and tech-

nologies to keep the firm poised at the leading edge of the explod-

ing semiconductor industry. Teal was up to the challenge. He was

introverted and difficult to work with, but also smart and stubborn.

These qualities had served him well at Bell Labs, where he pur-

sued his crystal-growing research in the late 1940s, working doggedly

after hours with almost no support from management. Perhaps

most important, this pioneering research had made him a minor

celebrity in the fledgling industry, which would prove crucial in hir-

ing bright young people for a group he had to create from scratch.We could never have attracted the stable of people that we did

without him, Shepherd admitted in a 1993 interview. And we got

some really outstanding scientists in those days.

Among his new hires was Willis Adcock, like Teal a physical

chemist with a Ph.D. from Brown University, in Providence, R.I. He

had been working for a natural gas company

in Oklahoma and joined TI early in 1953.

Adcock began leading a small research group

focused on the task of fabricating grown-

junction silicon single-crystal and small-

signal transistors that would meet military

environmental conditions, according to Teal,

who viewed this as the principal short-termgoal for his new research department.

It was no easy task at the time. Because

of a high melting temperature of 1415 C

and its great reactivity, the molten silicon

from which crystals are drawn interacts

with just about any crucible that can con-

tain it. Even fused quartz slowly reacts

with the melt, contaminating it with oxy-

gen and other impurities that subse-

quently find their way into the silicon crystal, degrading its elec-

trical performance. And most of the silicon samples then

available from suppliers came with substantial impurities.

Unlike germanium, which could be purified using zone-refining

techniques so that impurities could be reduced to about one part

per billion, the purest silicon available in those days had much higher

levels. And while silicon pnjunctions had been fabricated for more

than a decade, ever since Russell Ohl first achieved this feat at

Bell Labs in 1940, making a successful npn or pnpjunction transis-

tor from this semiconductor material was far more difficult. [See

The Origins of the pnJunction,IEEE Spectrum, June 1997.] The

main problem was the extinction of so-called minority carriers

(electrons in p-type or holes in n-type layers) due to impurities in

the base layer. Electrons will easily recombine with holes at any

impurity centers within the base. Consequently, too few of these

minority carriers could survive while crossing this daunting bridge

between emitter and collector to achieve sufficient current gain, or

amplification, in silicon. The only solution to this problem, other

than struggling to purify the silicon, was to make the base layer

extremely thin so that the minority carriers would have some chance

of making it from one side to the other.Adcock, Teal, and their team wrestled with these problems for

over a year. Then, in April 1954, using a special, high-purity silicon

purchased from DuPont at $500 a pound, they managed to grow a

suitable npn structure with an emitter region carefully doped to

enhance current gain and a p-type base layer about 1-mil (25 micro-

meters) thick. Cutting a half-inch (1.27-centi-

meter) bar from this crystal and attaching

electrical contacts on the morning of

14 April, Adcocks group prepared to test

it. Soon Haggerty got an excited call from

Teal urging him to come see a demonstra-

tion. A few minutes later, I was observing

transistor action in that first grown-junctiontransistor, Haggerty recalled at TIs

25th-anniversary celebrations in 1979. It was

a defining moment for the budding semi-

conductor company. Realizing that another

company might well achieve the same break-

through, Teal hurriedly wrote a paper for

presentation at the Dayton conference. And

held his breath after Bell Labs announced

the silicon solar battery later that month.

+ + +

Another company, in fact, had already fabricated a working sili-

con transistor a few months earlier. In January 1954, Morris

Tanenbaum made one while working as a member of Shockleys

research group at Bell Labs. But the worlds dominant semi-

conductor company kept this achievement under wraps, while the

Texas upstart rushed to announce it.

Tanenbaum had come to Bell Labs in June 1952 after earning degrees

Smart, stub-

born, and intro-verted, GordonTeal was up tothe challenge

TRANSISTOR FIRSTS: Bell Labs junction transistor, of germanium, was fabricated in 1950 [left]. Texas Instruments commercial silicon transistor came four years later.


6/6May 2004 | IEEE Spectrum | NA 49

in chemistry and physical chemistry at Johns Hopkins University,

in Baltimore, and Princeton University, in New Jersey. He started outin the chemical physics department, growing large single crystals of

various semiconductors and testing their properties. In late 1953

Shockley invited him to join the team being formed to push toward

silicon transistors. Tanenbaum continued working with Buehler, Teals

former technician, whom he describes as a master craftsman in

building apparatus and growing semiconductor crystals.

Buehler was working on a technique known as rate growing. The

rate at which impurity atoms (such as gallium and antimony) are

incorporated from the melt into the crystal depends to a great extent

on the crystals growth rateon how rapidly it is being pulled from

the melt. Both impurities are present in the melt simultaneously,

but the rate at which either one crystallizes out depends on the

pulling speed. This process enabled the team to make much nar-

rower base layers, just 13 to 25 micrometers (m) thick, which proved

to be crucial in limiting the extinction of minority carriers.

Tanenbaum cut a half-inch bar from one high-purity silicon crys-

tal that Buehler had grown using special samples from DuPont; then

he attached an aluminum lead to the narrow base layer and carefully

reheated the silicon to restore the layers p-type behavior. On

26 January 1954, according to his logbook, he achieved sufficiently

high electron current and hence amplification in annpn silicon tran-

sistor. I believe these were the first silicon transistors ever fabri-

cated, says Tanenbaum, savoring the moment in an interview nearly

half a century later.

When we made these first [silicon] transistors, he contin-

ues, we thought about patenting the process but determined

for two reasons that it wasnt worth the effort. For one, others

had developed and used similar techniques. And he really did not

like the rate-growing process, which had already been patented

by General Electric Co. It just wasnt controllable, he adds. From

a manufacturing point of view, it just didnt look attractive.

At the time, Shockleys group was concentrating on adapting

the new diffusion process pioneered by Fuller to the fabrication

of germanium and silicon transistors. Diffusion seemed much

more promisingas indeed it proved to bebecause it was sub-

stantially more controllable and could yield much narrower base

layers, just micrometers thick, and hence transistors that work at

higher frequencies. In July 1954 Charles Lee made a successful ger-manium transistor at Bell Labs using diffusion techniques, oper-

ating it at up to 500 megahertz. Tanenbaum spearheaded the effort

to duplicate this device in silicon, succeeding on 17 March 1955,

with an npn transistor that worked at up to 120 MHz.

Thus, there was little enthusiasm for the rate-grown silicon

transistors that he had developed, and Bell Labs made no effort to

publicize the achievement. Tanenbaum presented his results at the

IRE Solid-State Device Research Conference in June 1954. During

the question-and-answer session afterward, he recalls, Teal men-

tioned similar work that had been done at TIbut was cagey about

specifics. Later that year Tanenbaum submitted a paper about his

research on rate-grown silicon transistors to theJournal of AppliedPhysics, where it was finally published in June 1955.

By then the semiconductor industry was on the verge of yet

another fundamental shift. At the 1955 Solid-State Device Research

Conference held that same month, few people mentioned rate-

grown transistors. Everyone there was talking excitedly about the

newest breakthrough: diffusion. And Shockley was getting ready to

leave Bell Labs to start his own semiconductor company focused

on silicon transistors.

+ + +

It is hardly surprising that the silicon transistor was invented

twice, in two seemingly independent achievements just months apart.By 1954 the crucial underlying technologies of silicon purification and

crystal growth were at a point where the silicon transistor was per-

haps inevitable, given the market demandswhich were quite dif-

ferent for the two companies. TI was focused on military markets for

transistors as replacements for the bulkier and far more fragile vac-

uum tubes. The U.S. armed services, among its biggest customers,

were willing to pay a big premium for transistors that performed uni-

formly and flawlessly over a wide range of conditions. Bell Labs largest

customer was AT&Ts Bell Telephone System, which needed rugged,

long-lived semiconductor switches that were truly off when they

were supposed to be off. Because of high leakage currents, espe-

cially at elevated temperatures, germanium transistors simply could

not satisfy either of these important customers.

It is also obvious that the two achievements had common tech-

nological roots reaching back to the pioneering crystal-growth

research of Teal and Buehler at Bell Labs from 1949 to 1952. Teal

brought this expertise with him to TI, although perhaps not the

rate-growing techniques developed a bit later by Buehler. The two

groups both benefited from the fact that DuPont saw a growing

market for high-purity, semiconductor-grade silicon and was

beginning to supply small samples of the stuff in 1954. In both

cases, the road to the silicon transistor had to cross a narrow, high-

purity bridge made of the element.

Amidst all else that was happening at Bell Labs in the early 1950s,

the first silicon transistor may not have seemed important enough

to merit the same public attention given earlier transistors and the

solar cell. At the time, the managers were likely looking ahead eagerly

to what they considered the real breakthrough: transistors fabricated

using diffusion that operated at over 100 MHz. And overconfidence

may have played a role, too. Bell Labs had habitually kept mum for

months after its earlier breakthroughs, thereby permitting its sci-

entists and engineers to work out most of the patentable ramifica-

tions before going public.

Whatever the case, the delay allowed fledgling Texas Instruments

to leap forward and claim victory in this race. And it stood alone as

the first company to manufacture silicon transistors in volume. Thanks

to its foresight and aggressiveness, TI had the silicon transistor mar-

ket essentially to itself for the next few yearsand started down theroad to becoming the international giant we know today.

SILICON PRECURSOR: Gordon Teal (then at Bell Labs) [left] and fellow physical chemist MorganSparks successfully fabricated the first working junction transistor from a germanium crystal.

lost history of the transistor

Documents