s c i e n c e / t e c h n o l o g y

AN INNOVATION ENGINE FOR LUCENT In both fundamental and applied research, Bell Labs forges ahead with a new spirit and an eye on the bottom line Ron Dagani C&EN Washington

The people who helped transform the 20th century with the transistor, the solar cell, the laser, communications

satellites, long-distance TV transmission, and cellular telephony—among many oth­er bold technological innovations—are ready to take on the next century.

The next 100 years may well be shaped by newer wonders recently fashioned by the scientists and engineers of Bell Laboratories, the research and devel­opment arm of Lucent Technolo­gies. Consider, for example:

• A technology that promises the efficient delivery of high-quality speech and music over the Internet.

• An electron-beam lithogra­phy system, four generations ahead of technology currently used to manufacture computer chips, that can make transistors and integrated circuits with fea­tures just 250 atoms wide.

• Plastic transistors that are far less expensive to make than cur­rent silicon transistors and could be used in products such as flexi­ble computer screens and credit-card-sized smart cards.

• Experimental "bow-tie" micro-lasers so small that hundreds would fit on the head of a pin and emit highly directional beams of light with more than 1,000 times the power of conventional, disk-shaped micro-lasers. These high-power microlasers could increase the speed of voice, video, Internet, and other data transmission via existing fiber-optic networks or could be­come the basis of entirely new architec­tures for local-area optical networks.

This is just a sampling of the many in­novations that Bell Labs, once a part of AT&T Corp., is now making available to Lucent in what appears to be a sunny sec­

ond marriage. The calm has returned after a tumultuous period that began in 1984 with the court-ordered breakup of AT&T's Bell System monopoly, creating seven re­gional telephone companies.

During the next decade, AT&T under­went other upheavals. Fundamental re­search at Bell Labs was scaled back, and greater emphasis was placed on applied research and on meeting business objec­tives. Then, in 1996, AT&T spun off its computer business (NCR) and its systems

Chemist Glen Kowach Inspects a sample of zirconium tungstate, a ceramic that shrinks when heated, after sintering It In a high-temperature furnace.

and technology business (Lucent). Most of Bell Labs was carried off as part of Lucent, and AT&T became largely a provider of long-distance telephone, data transport, and wireless services.

Today, two years after that split, Lucent is the largest communications equipment company in the world, with 136,000 em­ployees in more than 90 countries. In fis­cal 1998, which ended Sept. 30, Lucent generated revenues of more than $30 bil­

lion, nearly 12% of which was plowed back into R&D at Bell Labs, its "innovation engine." The scientists of Bell Labs, who number 26,000 in the U.S. and 19 other countries, are reenergized, confident, and blazing new trails.

At Bell Labs' headquarters in Murray Hill, N.J., long-time members of the re­search staff still remember the day the split was announced. "It was shocking be­cause it was unexpected," says a chemist who's worked there for 23 years.

Today, research in the physical scienc­es (defined here as chemistry, physics, photonics, silicon electronics, and materi­als science) no longer predominates as it once did, but is balanced more evenly with work on mathematical and software sciences, according to James W. Mitchell. A chemist, Mitchell heads the Materials, Reliability & Ecology Research Lab where most of the chemically oriented research is done. Plans call for the software, mathe­matics, and communications sciences sec­tor to expand to more than 50% of the Bell Labs research pie, he adds.

And although fundamental re-| search still goes on at Bell Labs, % most projects are now more close-is ly tied to Lucent's business inter-^ ests in communications and net-§ working. For many researchers, | that's fulfilling because they can | see the impact of their work on Lu-ί cent's bottom line much sooner. S Lucent also seems to care more * about the research—and the re-1 searchers—at Bell Labs than AT&T

ever did. It's a closer and warmer relationship, according to the lab's employees, who speak of the emer­gence of "a new spirit," a sense that "the excitement is coming back." Indeed, says chemical engi­neer Jorge Valdes, head of the Pro­cess & Chemical Engineering Re­search Department, "Lucent is the best thing that ever happened to Bell Labs."

Lucent is a high-technology com­pany, and it recognizes that funda­mental research is necessary to

drive innovations. "If you're not doing re­search, you can't be a high-tech company 10 or 20 years down the road," says chem­ist Eisa Reichmanis, who heads the Poly­mer & Organic Materials Research Depart­ment. The commitment at Bell Labs to fundamental research is stronger now than ever, she adds. At the same time, notes physicist Cherry A. Murray, direc­tor of the Physical Research Lab, "You have to talk to people in the business

24 NOVEMBER 30, 1998 C&EN

Physicist Cherry Murray, director of the Physical Research Lab, Is the first woman In the history of Bell Labs research to reach the director level, the organization's third-highest management rank.

units to find out what they will need in the future."

Two labs, for example, are structured to support specific business units: The Silicon Electronics Research Lab, direct­ed by physicist David J. Eaglesham, is tied to the microelectronics business; the Photonics Research Lab, led by physicist Alastair M. Glass, supports Lucent's opti­cal networking business unit. Other labs, though, provide more general support to a number of business units.

Xina Quan, a chemical engineer who heads the Polymer & Chemical Engineer­ing Research Department (part of the Pho­tonics Research Lab), says there is a good relationship between the labs and the bust ness units. Because of these connections, re­searchers in some departments are used to juggling long-term projects that arc more fundamental in nature with short-term projects that may involve solving a prob­lem with a product that is not performing as well as expected in the field.

At the same time, the work environ­ment at Bell Labs has an academic flavor, but the research is much more inter- and multidisciplinary. "You don't have all the talent that's necessary in any one particu­lar shop," Mitchell points out. Most re­search projects are "a joint effort requiring expertise across a number of disciplines." In addition, he says, Bell Labs researchers have always collaborated with universities, and those ties are being strengthened.

Margaret Wright, a mathematician in

the Computing Sciences Research Center, sees Bell Labs as a special place where "magical results" hap­pen. "People arc absolutely excellent in individual areas of science, and we're encouraged to work together," she says. "It's a rare environment."

The center in which Wright works is part of Computing & Mathematical Sciences, one of the three large re­search divisions that together define the scope of work at Bell Labs. A sec­ond research division, Communica­tions Sciences, focuses on wireless communications technology, net­working, and multimedia and soft­ware systems.

The third research division, Physi­cal Sciences & Engineering, is home to most of the chemists, chemical en­gineers, physicists, electrical engi­neers, and materials scientists at Bell Labs—550 researchers in all. A large fraction of the projects in this division are materials oriented. Materials of all kinds—organic, inorganic, and com­posites—with potentially useful elec­

tronic, magnetic, optical, and mechanical properties are being studied with an eye toward future applications in communica­tions, data storage and transmission, and computing.

One of the main thrusts in materials sci­ence is the quest for organic or polymeric materials that could replace the inorganic materials that are the mainstay of today's electronic and photonic technologies. At Bell Labs, organic materials are being ex­ploited for such applications as thin-film transistors, holo­graphic storage media, and optical fibers.

Researchers who are working on the "plastic" or organic transistor do not ex­pect it will make the con­ventional silicon transistor obsolete any time soon. As a switching device, the silicon transistor appears to have a secure long-term future in high-performance or high-density devices such as computers.

But for many less de­manding applications, such as smart cards or electronic labels, organic transistors promise some striking ad­vantages. Organic devices would be easier and less ex­pensive to make than silicon devices, whose fabrication

requires high temperatures, stringently controlled environments, and precision optics. Furthermore, organic transistors of­fer mechanical flexibility, easier tunability, and good compatibility with a variety of substrates, including flexible plastics, all of which will likely open up new markets for them.

At Bell Labs, as well as other labs around the world, researchers have for years been exploring ways to make thin-film transistors using an organic semicon­ductor instead of silicon. According to chemist Howard E. Katz, the most prom­ising hole-transporting and electron-transporting alternatives to silicon are certain polythiophenes and fluorinated phthalocyanines, respectively.

Substituted polythiophenes with a very regular ordering of the monomer units have become "workhorse" semiconduc­tors because they can be applied to surfac­es from solution in a continuous manner, Katz points out. This capability allowed chemist Zhenan Bao, postdoctoral fellow Yi Feng, physicists Ananth Dodabalapur and Andrew J. Lovinger, and chemical en­gineer V. Reddy Raju to create "the first high-performance plastic transistor" in which all the essential components are printed directly onto a plastic substrate [Chem. Mater., 9, 1299 (1997)]. They used a multistep screen printing process (a low-resolution approach) to sequential­ly lay down the electrodes, the polythio-phene, and the other components. The smallest feature size achievable with this approach is 75 urn, Bao says.

Clockwise from top, chemists Zhenan Bao and Howard Katz and device physicist Ananth Dodabalapur look at test results on an organic semiconductor.

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More recently, the Bell Labs team has been exploring higher resolution meth­ods for fabricating plastic transistors. The impetus has been to reduce the feature size of the device because that will in­crease its switching speed and decrease its power consumption.

Earlier this year, chemist John A. Rog­ers, working with Bao and Raju, combined screen printing with a micromolding ap­proach developed in chemistry professor George M. Whitesides' lab at Harvard Uni­versity to produce a transistor with fea­tures as small as 1 urn [Appl. Phys. Lett., 72, 2716 (1998)]. Compared with the fast­est commercially available silicon tran­sistors, which have features as small as 0.25 pm, the organic transistor's l-um fea­tures are still relatively large. Nevertheless, says Rogers, "1 urn is about as small as you'd ever want to go with these organic systems. It gives you just about everything you want in terms of performance for the sort of applications we're interested in."

Rogers, Bao, and coworkers also are working on a high-resolution printing technique that may be more suitable for commercial production of organic micro­electronic devices. And Katz is investigat­ing spraying and casting processes using thiophene oligomers. The key point, Katz emphasizes, is that these experi­mental processes do not involve high-vacuum, high-temperature, or other steps that would interrupt a continuous printing process.

Plastic transistors won't necessarily per­form better than their inorganic counter­parts, scientists say, but they will offer at­tractive new options. For example, Doda-balapur and coworkers recendy integrated a polythiophene-based transistor with an organic light-emitting diode (LED), creat­ing "the first organic smart pixel" [Appl Phys. Lett., 73, 142 (1998)]. Such pixels could be the basis of new types of lumi­nescent displays. For example, because or­ganic transistors can be made transparent and bendable, they could be incorporated into an automobile's windshield along with the LEDs that form the display.

"Plastic electronics will extend the realm of electronics into new areas and lead to lots of new applications that we don't have at present," Dodabalapur tells C&EN.

Polymeric materials also promise to transform the realm of photonics. Scien­tists have been trying for decades to devel­op systems for storing information in three-dimensional holograms. The tradi­tional medium of study has been lithium niobate (IiNbOj), but it poses serious limita­

tions for commercial systems because of its physical properties, processibility, and cost.

With the recent advent of polymeric re­cording media, much progress has been made in high-density holographic storage in the past three years, Mitchell says. Still, he adds, "we're a long ways from having anything that's commercializable."

Undeterred by the challenges, physical chemist Mark J. Cardillo, head of the Pho­tonic Materials Research Department, and physical chemist Alex L. Harris, head of the Materials Chemistry Research Depart­ment, and their colleagues have been working on a holographic system for per­manent storage of data—the so-called WORM system (Write Once, Read Many). The system uses thick (250- to 1,000-um) photopolymer films, which are prepared by compressing an oligomer-monomer mixture between two flat pieces of glass and partially polymerizing it under illumi­nation. The remaining unreacted mono­mer is consumed during two subsequent polymerization steps, which accomplish the recording.

During recording, the interference pat­tern from two interfering laser beams (one of which carries the information) causes some of the free monomers to undergo gelation in a spatially modulated pattern. When the residual unreacted monomers are allowed to diffuse to other sites and then are locked into place by polymeriza­tion, an irreversible refractive index grat­ing is created that encodes the informa­tion in the polymer. A laser can then "read" the encoded information.

Earlier this month, Bell Labs research­ers reported that they had used this sys­

tem to demonstrate—for the first time, they believe—high-capacity holographic storage of digital data in photopolymer films of the thickness required for high storage densities [Opt. Lett., 23, 7910 (1998)]. The team included physical chemists Lisa Dhar, William L. Wilson, and Harris; organic chemist Marcia Schilling; electrical engineer Kevin Curtis; and other coworkers. The recording film they used was prepared from a mixture of a difunc-tional acrylate oligomer, the monomers ./V-vinylcarbazole and isobornyl acrylate, and a photoinitiator.

They were able to achieve high stor­age density by recording multiple pages of digital data (480 kilobits per page) in the same small volume of material. In this process, known as multiplexing, the holographic structure of each page is in­termixed with that of the other pages. The pages were then retrieved with low bit-error rates.

In other experiments, Curtis, Dhar, and coworkers achieved a storage density equivalent to 5 gigabytes of data on a 5V4-inch disc—about the same amount of in­formation that can now be stored on the 5V4-inch DVD (digital versatile disc). "Our goal is to store 100 to 200 GB on a 5%-inch disc," Harris says. That's the storage capacity that would be commercially inter­esting. To achieve this, they will have to move to new materials and new designs for the optics system. In their latest results, which will be revealed this week at the Materials Research Society meeting in Bos­ton, a new family of materials has allowed them to store the equivalent of about 50 GB on a 5^-inch disc.

i I

From left, ceramic scientist David Johnson, chemist James Mitchell, and chemical engineer Jorge Valdes take a break on the roof of Bell Labs' Murray Hill, N.J., headquarters.

26 NOVEMBER 30, 1998 C&EN

I

Chemical engineer XIna Quan's department Is working to develop plastic optical fibers.

The use of such photopolymer mate­rials offers several important advantages over lithium niobate: They are much more sensitive to light than the inorgan­ic material and can be designed to give larger refractive index contrasts, allow­ing faster writing and reading of data. In addition, photopolymers are inexpensive and can be shaped and processed more easily than inorganic crystals. And writ­ing a hologram in lithium niobate tends to erase any previously recorded holo­gram in the multiplexing process, mak­ing the crystal unsuitable for permanent data storage, Harris points out.

Because of some of these same advan­tages, polymers also are being looked at as possible replacements for fused silica (S1O2) glass used in optical fibers. The in­formation-carrying capacity of fiber optics is so great, according to Glass of the Pho­tonics Research Lab, that all of today's In­ternet traffic could be accommodated on a single optical fiber. The technology has enormous potential but its use has been limited because of the high cost of some of the optical components. The biggest challenge, Glass noted at a recent confer­ence, is cutting the cost so that homes and offices can be "wired" with optical fiber the way they are wired today with con­ventional telephone or cable TV lines.

Chemical engineer Quan and her co­workers are studying amorphous fluorinat-ed polymers as possible replacements for silica in the short lengths of optical fibers (up to 1 km) that would go into homes. They are focusing on fluorinated polymers because replacing carbon-hydrogen bonds with carbon-fluorine bonds eliminates much of the absorption losses. Quan's

dream, she tells C&EN, is to go one day to Home Depot and find plastic optical fiber for sale. Before that can happen, though, researchers will have to find polymer blends that offer the right properties and are compatible with a continuous manu­facturing process, rather than the fiber-drawing process currently used to make optical fiber.

Not only would plastic fiber be less ex­pensive to install than silica, it would also be more flexible, Quan notes. And one could make thicker fibers, which would make their interconnection easier and less expensive.

It will probably be a while before plas­tic optical fiber is manufactured in quanti­ties large enough to make producers of sil­ica fiber take notice. After all, it's estimat­ed that silica optical fiber is produced worldwide at the rate of about 2,000 miles of fiber each hour, according to David W. Johnson Jr., who heads the Ceramics & Metallurgy Research Department.

The technology for manufacturing opti­cal fiber is well established. Basically, it involves preparing a glass "preform"— a cylinder of high-purity glass (the core) surrounded by a "cladding" and an "over-cladding" layer of glass, each of which can have a slightly different chemical composi­tion. This preform is then heated and drawn out to produce the optical fiber. In this fiber, the cladding serves to keep the light confined inside the glass core, which is where it actually travels. The overclad-ding provides about 90% of the fiber's mass, making the fiber easier to handle.

The preform is prepared using a va­por deposition technique. As an alterna­tive, several groups have explored the

potential of the well-known sol-gel pro­cess to produce the preform at signifi­cantly lower cost. And earlier this year, Johnson, materials scientist John B. Mac-Chesney, and their Bell Labs coworkers described a sol-gel process that may be­come a less expensive commercial pro­cess for producing the overcladding, which is not the most important part op­tically but is quite expensive to make [/. Non-Cryst. Solids, 226, 232 (1998)].

In the Bell Labs process, colloidal sili­ca particles, so-called fumed silica, are dispersed in water at high pH by rapid mixing. Particles of zirconia and other contaminants, which would lead to flaws and fiber breakage» are removed by cen-trifugation. An ester, typically methyl for­mate, is added to the milky sol, which is then pumped into the cavity of a tubular mold. The gradual hydrolysis of the ester causes chemical changes that destabilize the sol and lead to the formation of a gel within a few minutes.

The gel body is removed and carefully dried for about six days. Then it is subject­ed to a series of heat treatments to further purify the glass. Finally, the material is sin­tered, which yields a hard, transparent tube about 115 cm long. "No one has been as successful as us in making such large bodies of optical-fiberquality silica glass" by the sol-gel route, Johnson points out.

The inner part of the preform— prepared by vapor deposition—is insert­ed into this sol-gel-derived overcladding tube, which is then heated on a glass-working lathe to shrink it down so it bonds to the inner rod, producing a thicker solid rod. The optical fibers pro­duced by drawing out this hybrid pre­form are "virtually indistinguishable" from conventionally produced fibers in their strength and optical properties, Johnson says. He believes this process could replace the process now used to make the outer part of the preform.

Another inorganic material that has be­come the focus of investigation in John­son's department is zirconium tungstate (ZrVi Og), an astonishing ceramic that shrinks—rather than expands—when heated. Scientists have known about this material's "negative thermal expansion" (ΝΤΕ) for 30 years. But their interest has perked up in the past few years because of new revelations about ZrW208's behav­ior. Specifically, the magnitude of the con­traction was found to be relatively large and to occur over a very wide tempera­ture range, from 0.3 Κ up to the material's decomposition temperature of about 1,050 Κ (777 °Q. Furthermore, the shrink-

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age occurs uniformly along all three di­mensions at lower temperatures, so the crystals remain cubic (C&EN, April 8, 1996, page 9). Previously discovered ΝΤΕ materials were less impressive because they either shrink less, shrink over only a narrow temperature range, or shrink in only one or two directions.

One immediately apparent applica­tion for zirconium tungstate and a related material, hafnium tungstate, is that they might be used in composites to compen­sate for the expansion of other materials, Johnson points out. The result might be a zero-expansion material or a material that undergoes a precisely engineered change in its dimensions during heating or cooling. Such composites might be used in components for next-generation fiber-optic systems for optical network­ing, for example.

Lucent is currently evaluating a zirconi­um tungstate composite developed by Bell Labs ceramic engineer Deb-ra A. Fleming and chemist Glen R. Kowach as a potential packaging material for a refractive index grat­ing used in glass optical fiber. The material's unique shrinkage proper­ties would compensate exactly for variations in the refractive index and dimensions of the glass fiber as the temperature changes, Bell Labs scientists explain. Otherwise, the wrong wavelength would be re­flected by the grating.

The origin of the negative ther­mal expansion phenomenon at the atomic level is of keen interest to scientists. They believe that the material's Zr-O-W linkages flex like el­bow joints when heated. This pulls the metal atoms closer together, causing the structure to contract.

Researchers at Bell Labs and at Johns Hopkins University have studied the vibra­tional modes of this process using neutron scattering. Earlier this month, they pub­lished their findings, which were obtained in part using large single crystals of ZrW208 grown by Kowach [Nature, 396, 147 (1998)]. The groups results indicate that the atomic vibrational modes occur at unusually low frequencies. This provides important information that eventually might be exploited to make other ΝΤΕ materials more easily and economically, says team member Arthur P. Ramirez, a physicist at Bell Labs.

The element zirconium also pops up in other Bell Labs research that is aimed at finding new materials with a high di­electric constant. The dielectric constant

is a measure of how much charge sepa­ration a material can accommodate.

Microelectronics researchers have been driven to create smaller components with enhanced performance. One prob­lem area involves capacitive components, which form the basis of many memory de­vices. The dielectric insulators used in these components are amorphous silicon dioxide (S1O2) and silicon nitride (S13N4), which have dielectric constants of 4 and 7, respectively. Such low dielectric con­stants limit how small a practical device can be made—a limit that is now being approached. Thus, researchers are moti­vated to find materials with significantly higher dielectric constants so that the march toward miniaturization can proceed.

The best alternative materials currently being considered for integrated-circuit ca­pacitors are barium-strontium titanates, (Ba,Sr)Ti03, which boast dielectric con-

Lynn Schneemeyer (left), Robert Fleming (right rear), and Bruce van Dover use a combinatorial approach to develop thln-fllm dielectrics.

stants in the range of 200 to 800. But mak­ing films of these materials requires a high deposition temperature (typically over 650 °Q.

Using a combinatorial chemistry ap­proach, Bell Labs chemist Lynn F. Schneemeyer and physicists R. Bruce van Dover and Robert M. Fleming recently found a family of amorphous zirconium-tin-titanium oxides that can be deposited as thin-film dielectrics by sputtering at 200 °C [Nature, 392, 162 (1998); C&EN, March 16, page 9; IEEE Electron Device Lett., 19, 329 (1998)]. This would make the oxide's deposition more compatible with current fabrication technology for silicon integrated circuits. The dielectric constants of the Zr-Sn-Ti-O materials are 50 to 70—still a major improvement over current dielectric materials.

For other device applications, scien­tists are going in the opposite direction: searching for materials with a dielectric

constant lower than Si02's but higher than air's value of 1. Such materials not only are necessary for high-speed chips but also reduce cross talk (electrical in­terference) between closely spaced met­al lines, making smaller chips more effi­cient. At Bell Labs, scientists are looking for suitable low-dielectric-constant mate­rials among porous forms of silica, fluori-nated polymers, and organic-inorganic composites.

Also of interest to Bell Labs research­ers are a wide variety of other materials, including lead-free solders, piezoelectric materials, lithographic chemicals, mag­netic materials, and superconductors.

Some of their investigations into these and other materials will undoubtedly lead to technological advances and com­mercial products. Other investigations may lead not to an immediate practical benefit but to a Nobel Prize, as happened

recendy when Bell Labs physicist ο Horst L. Stormer and two former § Bell Labs physicists—Robert B. % Laughlin and Daniel C. Tsui—were I awarded the 1998 Nobel Prize in S Physics (C&EN, Oct. 19, page 14). I That prize brought to 11 the total °- number of Nobel Laureates (all in

physics) who did their prize-winning work at Bell Labs.

A further indication of Bell Labs' stature in the world of physical sci­ences research is the degree to which the lab's published papers are cited in the scientific literature. According to the November/ December 1997 issue of Science Watch, a publication of Philadel­

phia's Institute for Scientific Information, Bell Labs received by far the most citations (18,840) of any research organization in the 1990-97 period.

As Bell Labs gets ready to celebrate its 75th anniversary in 2000, an obvious question to ask is: Can Bell Labs under Lucent continue this splendid record?

When Francis J. Di Salvo was asked this question, he fired back: "I hope so," add­ing with a laugh, "I don't have a crystal ball." Di Salvo, a materials chemistry pro­fessor at Cornell University, worked at Bell Labs from 1971 to 1986 and still maintains close ties to the facility. "Bell Labs went through some hard times" during the AT&T breakup, he says, "but I think they've recovered largely." Although it has changed, it's still an "exceptional" place, he opines, and "they still take only the top people."

That would seem to bode well for its future.^

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