Zyvex Labs - Molecular Nanotechnology

Molecular Nanotechnology:
A Realistic Treatment

Imagine a manufacturing technology capable of making trillions of tiny machines — each the size of a bacteria. Each machine could contain an onboard device programmed to control a set of molecular scale tools and manipulators. An individual machine could be designed to manufacture superior materials, convert solar energy to electricity, or even, ultimately, enter the body to fight disease and aging at the cellular and molecular level. Materials hundreds of times better than today’s best materials, vastly more powerful computers, precise machinery that doesn’t wear out, and a revolution in clean manufacturing are but a few of the predicted benefits of applying these new machines.

Nanotechnology is the enabling technology for this vision. Nanotechnology is almost certain to spring upon the world in the next twenty years and, with directed research and development, may happen much sooner. The benefits of developing nanotechnology are so great, and the cost to take the first step so comparatively modest, that those people who understand the issues are racing to be first to harness this technology. Twentieth-century manufacturing has progressed from the blacksmith, to the production line, to the wafer fab. Along the way, we have learned effective ways of making small numbers of highly customized objects (model shop), large numbers of simple 3D objects (mass production via special purpose stamping, casting, and molding machines), and massive numbers of complex 2D objects, such as photolithography. This pathway has led to much lower costs and a level of complexity unthinkable one hundred years ago. Humans are close to having the technology to take the next step to true molecular nanotechnology — atomically precise manufacturing using arrays of billions of molecular machines. It is an understatement to say this technology will transform the world more than the semiconductor revolution. It is just as important to say that it won’t happen during the next week — but rather in years.

Nobel Laureate Dr. Richard Smalley, testifying before Congress during a hearing on nanotechnology¹ on June 22, 1999, said: “The impact of nanotechnology on health, wealth, and lives of people will be at least the equivalent of the combined influences of microelectronics, medical imaging, computer-aided engineering, and man-made polymers developed in this century.”

Dr. Ralph Merkle, then with Xerox PARC, now with Singularity University, also testified, stating: “Nanotechnology will replace our entire manufacturing base with a new, radically more precise, radicallyess expensive, and radically more flexible way of making products.”

Dr. Eugene Wong, Assistant Director of the Engineering Directorate at National Science Foundation, told the committee: “Recent discoveries at this scale are promising to revolutionize biology, electronics, materials, and all their applications. We’re seeing inventions and discoveries that were unimaginable only a short time ago.”

The Chair of this subcommittee, Congressman Nick Smith (R-Michigan) stated: “Nanotechnology holds great promise for breakthroughs in health, manufacturing, agriculture, energy use, and national security.”

It should be noted that many firms are now embracing the word ‘nanotechnology’ in their corporate mission statements, product literature, and stated capabilities, due to the new distinction of nanotechnology as “the next thing” in the technical economy.

Our purpose in this paper is to put nanotechnology in its proper perspective and seriously avoid much of the “über-hype” that surrounds the field. As the first molecular nanotechnology company in the United States, Zyvex feels a genuine responsibility to clarify what’s required to tap into the significant promise of nanotechnology.

What is molecular nanotechnology?

The renowned physicist Dr. Richard Feynman gave a talk in 1959 entitled “There’s Plenty of Room at the Bottom,”² describing the possibility of constructing objects atom-by-atom. Feynman concluded that we haven’t done this yet only because “our hands, and our available tools are too large.” Eric Drexler analyzed potential approaches and in his 1992 book, “Nanosystems,”³ he concluded that there is no known physical reason molecular nanotechnology cannot be mastered. Dr. Ralph Merkle has an extensive web site discussing nanotechnology.⁴

Nature provides empirical proof of functioning molecular machines in the form of life. Starting with the relatively general “molecular machinery” common to all cells and the specific program for an individual contained in that cell’s DNA, one cell can build a complete organism of immense complexity.

Our challenge is to clearly understand and fabricate a broader variety of materials and products than nature provides.

The primary technological goal of molecular nanotechnology is to build one of the key enablers: the assembler.⁵ An assembler is a system capable of manufacturing materials or complex structures with atomic precision, positioning nearly every atom in the desired location. Starting with a generic feedstock (such as methanol), this general purpose machine would, in theory, manufacture any precisely defined object that could be built from stable arrangements of the feedstock atoms. Potential fabricated products would include most solid objects made today — from cars, to chairs, to computers. At the very least, new materials could be made from nanostructured ultra-strong, light, and low cost materials. It is quite likely that these new products would contain embedded computers, actuators, and power sources, so they could be programmed by their designers to have desired behaviors.

The popular picture of a molecular assembler is that of a small, robotically-controlled arm. However, a real assembler must be built as a complete system, not just a robotic arm, because the massive parallelism required for a practical manufacturing system requires at least as much development as the individual arm performing the assembly operation. Macroscopic objects are made of trillions of atoms; therefore, building something of that size requires billions of assembler components coordinating a hugely parallel manufacturing process.

Although a semiconductor manufacturing plant manufactures extremely complex 2 or 2 1/2-dimensional structures (with a severely restricted set of chemical compounds), it lacks atomic precision. On the other hand, bacteria are atomically precise, self-replicating “manufacturing plants” that manufacture substances with atomic precision. Genetic engineering can enable them to manufacture certain novel compounds with atomic precision, but bacteria cannot make arbitrary 3D structures out of arbitrary materials.

The assembler differs from both semiconductor manufacturing and bacteria because it operates on atomically-precise molecular building blocks to build precise structures of arbitrary complexity, as specified by a CAD/CAM program. Very simplistically, an assembler could be a bank of molecular-scale robotic arms with chemical binding sites on some arms and grippers to hold components being built on another set of arms — all under the control of an outboard computer instructing it how to snap together the building blocks for a desired product. The assembler’s control computer totally controls the product being built and drives the manipulators to execute the sequence of motions specified by the manufacturing software. In the morning, this assembler might make computer memory modules; in the afternoon, it might make medical manipulators; later in the evening, it might be programmed to build power storage devices.

This first assembler will most likely be a crude device — its purpose to demonstrate that molecular nanotechnology is feasible and to help build a better device. This can start the field on a Moore’s law type of improvement pathway.⁶ A related concept is the semiconductor “learning curve” where increasing volume allows manufacturing costs to decrease as the manufacturing process matures. This occurs because process variables are more carefully controlled and other economies of scale reduce the unit cost. To reach the desired type of learning curve, we must make a product of commercial value that cannot be economically made in another way.

For rapid progress, the manufacturing system must be capable of being improved by the same products it manufactures. A semiconductor manufacturing plant cannot manufacture itself; hence, the cost of a semiconductor production line increases with each generation, becoming more and more unaffordable. A well-designed nanotechnology manufacturing plant should not suffer from this problem, since it will be built using the same technology and techniques it uses to manufacture other goods.

A practical design for an assembler requires that the assembler be made out of materials it can handle. Assemblers can be manufactured as inexpensively as the products they fabricate. This capability is often called self-replication, although we prefer the term “exponential assembly,” which is less likely to be confused with living entities. Living systems carry their own instructions in DNA, while exponential assembly systems do not. Exponential assembly devices must receive instructions from a conventional computer control system. This system design is both simpler and safer than living systems.

How shall we define molecular nanotechnology?
Many people use the term “nanotechnology” to describe anything with characteristic dimensions at the nanometer scale (one billionth of a meter). For clarity, we will frequently use the phrase “molecular nanotechnology” (MNT) to more carefully describe the goal of adaptable, affordable, and molecularly precise manufacturing.

Molecular nanotechnology is defined as the use of a controlled sequence of nanopositioning to perform mechanochemistry at exactly the reaction sites desired, flexibly manufacturing atomically-precise products under software control.

Is nanoparticle manufacturing molecular nanotechnology?
Nanoparticle manufacturing is not MNT because it fails all aspects of the above definition. In a broad sense, it is nanotechnology, because it deals with nanometer-sized objects, but in that broad a sense, so is a chemical manufacturing plant, petroleum refinery, or drug manufacturing facility.

Is biochemistry molecular nanotechnology?
Biochemistry is arguably MNT, but it has limits in the product being made. One could argue that DNA can specify a virtually infinite number of proteins, but the materials properties of the resulting product cannot be tailored sufficiently to achieve the desired goals of MNT. Creating a good conductor or insulator capable of working in a vacuum at 200 degrees Celsius is easy for true MNT, but extremely unlikely with biochemistry.

Is self-assembly molecular nanotechnology?
Self-assembly is frequently postulated as a more likely way to achieve molecular nanotechnology than Drexler’s mechanical constructor arms. We believe self-assembly is likely to be of value with small building blocks, but is insufficient for building larger assemblies. Self-assembled materials almost always have grain defects, which cause weaknesses and unpredictable performance.

With templating to guide grain boundary growth, self-assembly might be able to create materials having desirable properties, but self-assembly is unlikely to create truly complex structures. Note that life processes are not pure self-assembly; there is a huge amount of templating going on, as well as uncountable numbers of existing cellular molecular machines actively following their own instructions. To appreciate the difference between pure self-assembly and directed molecular manufacturing, consider the likelihood of a dog spontaneously self-assembling from raw chemicals.

Is nanoelectronics molecular nanotechnology?
Nanoelectronics is probably the best funded nanoscale research at this time. While this is a good application area for an assembler, nanoelectronics cannot flexibly manufacture products. Indeed, it appears likely that even more expensive semiconductor fabrication plants will be necessary for nanoelectronics than what we have today. Molecular electronics promises to break this price spiral if it succeeds, and therefore seems a promising avenue for achieving nanoelectronics. However, if we had an assembler system, assembling arbitrarily complex nanoelectronics (based on today’s devices) would be a straightforward extension of the basic chemistry used in the first assembler. We believe that developing a mechanical assembly system is at least as important as trying to build nanoelectronics today.

The mechanical approach to molecular nanotechnology can be pursued either from the top-down or the bottom-up. Dr. Richard Feynman suggested a top-down approach (i.e., building successively smaller generations of machines until we get to a level at which there is no room for inaccuracy, with every atom precisely placed and accounted for). Dr. Eric Drexler proposes a bottom-up approach (i.e., using a tool such as an atomic force microscope) to precisely place molecular building blocks to build larger structures with precision. Feynman’s speculations predate the invention of the AFM by decades. Drexler made his original conjecture several years before the invention of the atomic force microscope.

Both approaches are likely to contribute valuable insights. Therefore, it is important to work on top-down projects that will have more near-term payoffs, and bottom-up projects that are essential for the full fruition of molecular nanotechnology.

One promising top-down approach involves using microelectromechanical systems (MEMS) components to create a micron scale analog of the assembler.

MEMS components are made via the semiconductor processing technology used for integrated circuits (IC), and can take advantage of the large investment made in IC fabrication equipment and techniques.

MEMS offers several advantages over alternative, more conventional-sized components or pure simulation:

• MEMS components are light enough that gravity and inertia are relatively unimportant, so surface forces dominate, just as they do at the nanometer scale.
• MEMS components can be made inexpensively — a typical fabrication run delivers structured parts costing pennies each⁷ — compared to dollars or hundreds of dollars each for similar prototype parts at the centimeter (or larger) scale.
• Many of the mechanisms useful in MNT also work in MEMS, such as electrostatic actuators, snap connectors, flex joints, and manipulator geometries. Conversely, macroscopic parts such as magnetic stepper motors or solenoids are not effective below the micron scale, so many changes are necessary for such a design as it scales down.
• Objects must be assembled at the micron and larger scale even with MNT, so system designs for parts assembly are required at this scale. MEMS offers an excellent test bed for quickly prototyping the system design.
• The components are visible under a microscope, so designs can be easily debugged by watching them operate.
• As the MEMS market develops, other companies will need to assemble systems at the micron to millimeter scale, creating an outside market for MEMS assembly devices. Today’s MEMS designers try to integrate entire systems on a monolithic chip, but that strategy is limiting if assembly is to be inexpensive and reliable.
• Complex systems can be designed and built more easily. By integrating common subcomponents and assembling 3D structures, one can postulate a cubic centimeter device with millions of moving parts,⁸ perhaps performing sensing functions, doing chemical separations or reactions, or even functioning as a catheter-guided surgical device. Building MEMS-based artificial ears, eyes, or nerve stimulators that could partially restore lost functions are exciting longer-term applications under development by others.

Of course, MEMS have some disadvantages when compared to molecular nanotechnology:

• Parts are not atomically precise, so bearing surfaces exhibit increased wear and system design is limited to poorer tolerances.
• The inflexibility of having to pre-manufacture parts means it is slower and more difficult to build prototypes.
• Chemistry is severely restricted, mostly to materials compatible with a semiconductor wafer fab line. Those materials are excellent by our current standards but poor compared to true MNT materials.
• Part attachment is not done by forming covalent bonds, so all forms of interconnect need to be designed carefully.
• While inexpensive, the parts are still higher-priced when compared with molecules.

This real-world, mechanistic approach to the development of molecular nanotechnology requires technological advances in three areas: nanomanipulation, mechanochemistry, and system design. All three areas must progress to deliver MNT. Mechanochemistry is the most fundamental technology needed, but probably the easiest to scale into production, given the other two capabilities. Nanopositioning is vital to hold reactants precisely at the right location so that a chemical bond can be formed at a desired reaction site and not a chemically identical site nearby. System design is the key to successfully implementing economically-viable MNT. A single nanopositioner, performing a single mechanochemistry operation per instruction, will take “geological time” to build a visible object. It is a fundamental requirement that we have immense numbers of manipulators and reactions operating simultaneously to achieve commercial success.

The fundamental operation that differentiates molecular nanotechnology from other precision manufacturing is mechanochemistry. With mechanochemistry, one can literally fabricate an object one molecule or atom at a time, placing new building blocks precisely where desired. “Machine-phase chemistry” is another term often used to describe this activity. Rather than performing chemical reactions in a solution exposed to heat and pressure using mechanochemistry, one might hold the two reacting molecules in precise orientations relative to one another and push them together, forcing them over their reaction barrier by mechanical energy. The chemistry of this is the equivalent to a solution heated to a temperature promoting that reaction; the difference is that, in solution, the molecules come together randomly, joining in a random manner. With mechanochemistry, the same chemistry is occurring, but due to the positional accuracy and ability to exert great forces, one can provide reaction conditions comparable to extreme temperatures and pressures, and build objects with exact structure. Mechanochemistry can also be performed in an ultra-high vacuum (UHV) where extremely reactive molecules or atoms with unterminated bonds can be brought together precisely to allow a reaction with no reaction barriers to occur at a desired location.

Research is necessary to develop suitable molecules to act as building blocks. The 2-4 Diels-Alder reaction has been proposed as a model (i.e., pushing together a diene and a dienophile with precise positional control joins the carbon atoms into a six-member ring, building a new composite molecule in the process). A useful building block must have enough “linker groups” to be joined to others at multiple sites, so the resulting “molecule” is suitably cross-linked internally. A molecule with tetrahedral or octahedral symmetry would be a good choice for this fundamental shape.

Depending on the molecule chosen, mechanochemistry can be performed in fluids (the way biochemical processes work), inert gases, clean air, or in a UHV. When using individual atoms as building blocks, part of the preparation process may result in unterminated bonds, which are highly reactive. This need not be a deterent: by controlling the environment where the chemistry occurs, one can ensure that there are no other reactive atoms around to react with the “dangling bond” before attaching it to the desired spot.

System design deals with controlling immense numbers of nanomanipulators performing mechanochemistry. A successful system controls and provides power to the manipulators, delivers raw materials to the manipulators, and moves finished subassemblies to the next stage. With a good modular system design, advances in nanomanipulation and mechanochemistry can be rapidly incorporated into the entire manufacturing process.

One promising technique is what Dr. Ralph Merkle describes as “convergent assembly.”⁹ The entire assembler system is composed of a series of stages at different scales. The largest, outermost system may have an output assembly compartment of 10 cm on a side. The back side of this compartment may be fed from four smaller boxes, each 2.5 cm on a side. Each of those, in turn, is fed from four, smaller assembly compartments. A series of such stages ultimately leads to a very large number of molecular scale manipulators (number of smallest assembly stations = 4x4x4…). Each of those manipulators might perform mechanochemistry to make a small component, then pass that component up the hierarchy to the larger stages, assembling components from those subcomponents. With convergent assembly, thirty stages can span nine orders of magnitude —from the nanometer to the meter size range.

Assemblers may do their mechanochemistry work in fluids, inert gases, a UHV, or some combination of these. A design might use fluids for material transport, passing materials through a manufactured membrane under an UHV where reactive chemistry is performed. Such a design would mimic nature’s own design for living organisms (e.g., passing materials through a lipid bilayer into or out of a controlled environment).

In addition to the geometry and engineering of the physical assembler, one must have software tools to design parts made with that assembler. Postulating a convergent assembly approach, one can envision two major components of such a computer-aided design (CAD) system: parts design and assembly sequencing.

Individual parts would be made in large numbers deep inside the molecular scale devices of the assembler system. The parts design software would need to assist the designer in performing molecular design work for that part, characterizing its properties, and generating assembly sequence commands to drive the nanomanipulator performing its mechanochemistry. Designing such parts would require knowledge of chemistry and engineering expertise. CAD software for this would encompass molecular design and simulation, mechanical 3D part design, and knowledge of the mechanochemistry being performed. Since computational chemistry requires computing resources that scale exponentially with the number of atoms, one would like to minimize the number of atoms in a part needing detailed chemical simulation.

Once a basic library of usable parts was developed, most designers could simply use that library to design larger assemblies. In an ideal case, there would be enough existing parts so the system designer would not have to make custom parts at all. CAD software would assist the designer in combining parts from a library to create the desired object. A graphics display designer might choose display modules from a catalog, build power and data distribution busses from snap-together pieces, design a custom package using existing outer finish components, and integrate communications modules to complete the design. A designer of drug delivery devices might integrate sensors, drug storage tanks, injectors, power supplies, and logic. Each of those integrated components might, in turn, be built from other subassemblies. The required CAD software should be able to use the characterization data for the parts at a high level to avoid the need for chemistry simulation of such a large system. Simulation would be at the system level, predicting performance, and verifying behavior.

A prototype of such an assembler system could be built today, using MEMS components, rather than molecularly precise components, such as low-level building blocks.

Furthermore, we expect to find commercial use in using such systems to create MEMS scale systems that cannot be assembled today. The inability to assemble MEMS-scale parts means those parts don’t get designed or they get designed as an integrated whole. This means that a large portion of the surface area is taken up with actuators that may get used once during the initial configuration. For example, some have designed stand-up mirrors (erected by actuators on the chip) that take up a considerable amount of the chip area simply to erect the mirror one time.

Given a very basic MNT capability, the first thing a company would likely make would be a better MNT capability. Such a process should quickly lead to a commercially viable nanomanufacturing capability, which could be sold or licensed to any company engaged in manufacturing.

Clearly, MNT is a technology that will dramatically change most industries. Companies successfully making products today have product know-how, customer relationships, and networks of support that we cannot, and should not, try to take away. For example, one of Zyvex’s goals is to provide the MNT assembler, partnering with our customers (as appropriate) to share our expertise, so our customers can change their own businesses with this technology. While nimble companies will adapt and new ones will form — slow-paced companies will go out of business. This process is described by economist Joseph Schumpeter as “creative destruction:” the dynamic renewal process that keeps free markets healthy and active. MNT applications extends across a broad spectrum of industries.

We expect business opportunities to follow the development of MNT in five major phases.

Business opportunities include selling nanomanipulation devices, building small simple structures (fewer than one hundred atoms), and developing the required CAD/CAM software. Systems may be manufactured conventionally in a machine shop or MEMS fabrication line.

This phase requires progress in nanomanipulation, mechanochemistry, control software, and component design.

With the Phase One capability working, one should be able to fabricate nanostructured and nanocomposite materials in volume. Nanocomposite materials are attractive because they can have performance exceeding any of the individual component materials. For example, the abalone shell, a composite of calcium carbonate plates sandwiched between organic material, is 3,000 times more fracture resistant than a single crystal of the pure mineral.¹⁰

Phase Two requires progress in system design (to make a cost-effective nanomanufacturing plant capable of manufacturing bulk quantities of materials) and materials design (to make interesting materials with the chemistries available at this stage).

Limiting oneself to simple materials means one can quickly build a large variety of materials with relatively little design time. It is much easier to specify the unit cell of a repeating material than to specify a complex object, such as a computer or automobile.

Once Phase One capabilities are demonstrated, complex designs can reasonably be initiated. It will take some time for most designers to become aware of the possibilities, commit to learning the new capabilities, and develop new design paradigms. Designing new approaches to sensing, actuation, and control will require more time to specify than the approaches to the simple materials of Phase Two. Phase Three requires advances in CAD/CAM software, object design, simulation, testing, and packaging.

By making products such as bio-implants for restoring lost hearing or vision, the potential for MNT will rapidly become apparent. Thousands of designers will invest in learning the new skills and macroscopic-sized objects (built with atomic precision) will show up in the marketplace.

We envision two major paths to the development of nanocomputers.

Path One occurs if mechanochemistry develops rapidly and the assembler becomes capable of building structures from all of the atoms used in current silicon electronics (such as silicon, germanium, nitrogen, oxygen, phosphorous, boron, arsenic, copper, and aluminum). In this optimistic scenario, existing semiconductor computer designs can simply be manufactured atom-by-atom by banks of inexpensive assemblers. Nanocomputers might then precede the Phase Three objects mentioned above, due to the huge economic incentives of inexpensive semiconductor manufacturing.

Path Two occurs if mechanochemistry cannot yet build with the variety of atoms needed; therefore, electronic computers can’t be built atom-by-atom. One could still build computers, but they would need to be designed more along the lines of Drexler’s mechanical computers (i.e., physically moving small molecules around). Due to the thousands of years of intellectual capital invested in computer designs and the requirement to develop new design rules and techniques, it is unlikely that any company would invest in designing a mechanical nanocomputer before Phase Three is demonstrated.

To be competitive with electronic computers, a nanocomputer company would have to invest considerably more effort than its electronic computer competitors. The need for such an investment would slow the advent of the nanocomputer.

Therefore, to obtain a nanocomputer, one must either improve the mechanochemistry required to handle all of the needed semiconductor materials, or spend a huge amount of time designing computers with a brand new principle of operation.

Phase Five: Making autonomous devices

The step that excites nanotechnology enthusiasts the most is that of making autonomous devices which carry their own onboard computers, power sources, actuators, and sensors. These tiny “robots” might travel the body fighting disease, or patrol our food crops recognizing and destroying pests. They might act as road surfaces, automatically repairing damage, while joining together the nation’s highway system in a vast grid of solar power generators (each device could be a solar cell and a road-building robot).

While expected to lead to a huge market, this technology is extremely advanced and, as a prerequisite, requires the first four phases. The design effort to build such autonomous devices is unprecedented and, like the nanocomputer, should not be seriously attempted until feasibility of MNT assemblers is proven.

The power source for such a device is currently a serious technological hurdle, but the biggest unknown is how one would program it. Our current techniques for programming large systems are limited. Rough estimates of the complexity of such a device, programmed with today’s techniques, are in the tens of millions of lines of code. Better programming methods are required to achieve Phase Five. Autonomous learning systems are promising, but testing the resulting device is problematic, and deterministic performance is unlikely.

Conclusion

Molecular nanotechnology is predicted to be the most powerful technology yet developed by humankind. It will lead to major changes in our civilization. However, three key breakthroughs are necessary: nanomanipulation, mechanochemistry, and system design. There is an immense amount of work to be done, but the number of people working in this field grows larger every day. With this increased effort, there is no question that we will see major steps toward the goal of creating molecular nanotechnology in the next ten years.

1. Prepared Statements for House Science Committee, Subcommittee on Basic Research, June 22, 1999, http://www.house.gov/science/106_hearing.htm
2. Feynman, Richard: “There’s Plenty of Room at the Bottom,” 1959 speech, http://www.zyvex.com/nanotech/ feynman.html
3. Drexler, K. Eric: “Nanosystems: molecular machinery, manufacturing, and computation,” Wiley Inter-science, 1992, http://www.zyvex. com/nanotech/nanosystems.html.
4. Merkle, Ralph: Nanotechnology web site: http://www.zyvex.com/nano/index.html.
5. Assembler description from Zyvex: http://www.zyvex.com/CorpInfo/New Assembler.html.
6. Moore’s “law” is a thirty year old observation by Gordon Moore of Intel that the number of transistors in an integrated circuit doubles every eighteen months as the manufacturing process improves in accuracy.
7. An advanced MEMS prototyping process run costs approximately $40,000–$90,000 depending on number of process steps and wafers run. Typical runs would cost $70,000 for two wafers, $90,000 for ten. Each four inch wafer may hold 500,000 parts of dimension 10 microns by 100 microns, resulting in a per-part cost ranging from $0.07/part for a small run, to $0.018/part for a large run. In a production setting, larger wafers would be used, and the silicon mold and masks would be reused, driving the per-wafer cost to below $1,000, producing 1,000,000 parts per wafer, for a per-part cost of $0.001. Regular arrays of transistors, packaged and delivered, currently cost less than $0.25 per million transistors.
8. Part counts, even with multimicron sized parts, becomes quite high if three dimensions are used. An early MEMS system might have sub-components that occupy an average volume of 50x50x200 microns. In a 3D cube, this would result in 2,000,000 components per cubic centimeter, where a component might be an actuator bank, electronic switch, or simple mechanical structure. More advanced MEMS parts might be 2x4x50 microns, leading to 1,250,000,000 parts per cubic cm.
9. Merkle, Ralph: “Convergent Assembly,” http://www.zyvex. com/nanotech/convergent.html.
10. Smith, Bettye, et al: “Molecular Mechanistic Origin of the Toughness of Natural Adhesives, Fibres and Composites,” Nature 399, 761–763 (1999).

Molecular Nanotechnology: A Realistic Treatment

Molecular Nanotechnology:
A Realistic Treatment