Beyond a Profound and Pervasive
Impact
Microelectronics has entered an era of proliferation.
by James D. Meindl
Professor, Electrical and Computer Engineering
The genesis of microelectronics can be traced to the invention of the transistor in 1947. This Nobel Prize-winning breakthrough was of unmatched importance to microelectronics. It eliminated the oppressive requirements for several watts of filament power and several hundred volts of anode voltage in vacuum tubes in exchange for transistor operation in the tens of milliwatts range.
photo by Stanley Leary
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A second breakthrough, the invention of the integrated circuit in 1958, provided the capability to fully exploit the superb low-energy assets of the transistor. Although far less widely acclaimed as such, a third breakthrough of indispensable importance to modern microelectronics was the complementary metal-oxide-semiconductor, or CMOS, integrated circuit announced in 1963.
Early microelectronic integrated circuits used the so-called bipolar junction transistor invented in 1947. A salient feature of these circuits is their continuous energy consumption, regardless of whether they are operating in an active state — i.e., performing a binary switching transition, the canonical computing operation — or in a quiescent state, waiting to undergo a switching transition.
In contrast, CMOS integrated circuits use a second generic type of transistor, the so- called metal-oxide-semiconductor field effect transistor or MOSFET. It was invented in 1933, but undemonstrated until the early 1960s. In computing operations, CMOS' quintessential feature is integrated circuits that consume significant amounts of energy only during switching transitions and dissipate virtually zero energy during quiescent periods.
The benefits of this near-zero quiescent energy consumption — in terms of both reduced heat generation and battery energy drain — have sufficiently enabled CMOS technology to dominate microelectronics during the current decade. This dominance is expected to continue for the foreseeable future.
Throughout the past four decades, both the productivity and performance of microelectronics have advanced at exponential rates unmatched in technological history. The number of transistors per microchip has skyrocketed by a factor of about 100 million, while the cost of a chip has remained virtually constant. And the amount of energy consumed in a binary switching transition has been reduced by more than five decades!
Consequently, microelectronics has become the principal driver of the modern Information Revolution. And the ubiquitous microchip has had a profound and pervasive impact on our daily lives — enabling such advances as microelectronic wristwatches, hearing aids, implantable cardiac pacemakers, pocket calculators, personal computers, wireless cellular telephones, optoelectronic- fiber networks, communication satellites and the Internet.
Perhaps the single event that most emphatically describes the degree to which the microchip has changed the world and its economy was the selection of Intel's chairman and CEO, Andy Grove, as 1997 Man of the Year by Time magazine.
In the real world, exponential advances in metrics such as productivity and performance do not continue endlessly.
Consequently, the paramount question now facing the microelectronics industry is: Just how much longer can we expect these advances to persist? What lies beyond the profound and pervasive impact that microelectronics has already delivered to society?
In brief, the physical laws governing MOSFET behavior support the projection that critical device dimensions — which began at 25 micrometers in 1960 — can be scaled down from present values in the 0.25 micrometer range to the 0.025 micrometer or 25 nanometer range by the year 2020. Clearly, microelectronics is in rapid transition to nanoelectronics.
To achieve this additional decade of scaling, as in the past, numerous clever inventions will be necessary. Perhaps the most challenging collection of these must provide the intellectual basis for development of a post-optical microlithography technology capable of printing the 25 nanometer patterns necessary for manufacturing future microchip transistors and their interconnects.
Extreme ultraviolet (EUV) or soft X-ray projection lithography using reflective "optics" at 13.4 nanometer wavelength is a leading approach to meet this imposing challenge.
Assuming a successful EUV microlithography technology, the proliferation of terascale integration or trillion transistor microchips can be projected during the 2020s. Consequently, prospects are promising for microelectronics' continued exponential productivity advances. Thus, it will serve as the principal driver of the Information Revolution during the early 21st century.
To sustain an exponential rate of performance improvement, the minimal historic microchip material set of silicon, silicon dioxide and aluminum must proliferate in the future.
It will have to include such new materials as: silicon-based compound semiconductors, particularly for optoelectronics; both low- and high-permittivity insulators, such as silicon dioxide aerogels and ceramics, respectively; and copper alloy conductors.
The modern microchip manufacturing process sequence is the most complex and unforgiving volume production technology ever successfully practiced. To date, the precise material deposition, micropatterning and removal processes in microchip fabrication have been used almost exclusively to generate microelectronic products.
Imagine a wristwatch that is also a cellular telephone-computer terminal with color display and a built-in real-time language translator for point-to-point worldwide communication. The prospect is indeed fascinating and not an unrealistic future expectation for microelectronics.
But the prospects of applying microfabrication technology to the challenges of other non-electronic engineering and scientific disciplines are in many respects even more fascinating.
Imagine, for example, the notion of a self-navigating sub-sonic jet airplane — with a 12-inch wingspan. Or envision "biochips" coated with millions of DNA probes in microscopic checkerboard patterns. They are optically scanned to expedite exact medical diagnoses that would otherwise be prohibitively expensive and time-consuming!
These images epitomize the potential proliferation of microfabrication technology in non-electronic applications. Such applications could embrace virtually all engineering and scientific disciplines of interest to Georgia Tech.
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