TOPIC 2:
SYSTEMS

Three papers were presented in this session, one by Kwan Kwok, DARPA, one by Rich Fletcher, the Massachusetts Institute of Technology (MIT) and TagSense, Inc., and one by Chris Murphy, NRC Board on Chemical Sciences and Technology.

APPLICATIONS OF MOLECULAR ELECTRONICS TECHNOLOGY (MOLEAPPS) PROGRAM

Kwan Kwok reviewed the goals and achievements to date of the new 5-year DARPA MoleApps program, which aims to apply molecular-scale electronics technology to the development of ultradense molecular electronic computer processors (this thrust is called MoleComputing) and molecular electronic sensor systems (MoleSensing). For the purposes of the MoleApps program, molecular-scale electronics technology refers to using single molecules, small numbers of molecules, nanoparticles, nanoscale metallic and/or semiconductor wires, nanotubes, and so on as electronic components.

The goal of the MoleComputing thrust is to develop a prototype molecular (no-silicon) electronic computer processor having local molecular device densities of 1011/cm2 and a clock rate of at least 10 kHz and consuming no more than 10 W/cm2 of power. Such a processor would be equivalent in complexity to a 1971-vintage microprocessor such as the Intel 4004 but have an area 100,000 times smaller.

It would have to be compatible with molecular memory devices such as those being developed in the concurrent DARPA programs, Moltronics, for example, a team of researchers from Rice and Yale Universities, is developing a 10 μm×10 μm 16-kbit memory consisting of an ultra-high-density network of molecular wires and switches that will fit on a human cell. The manufacturing processes to produce such components in bulk do not exist yet, and such molecular memories are affected by, among other things, cosmic rays and incomplete reactions, but they will be self-repairable and fault-tolerant (able to operate with up to 10 percent defects). In 2001, researchers from Hewlett-Packard and the University of California at Los Angeles produced crossed-wire memory devices by sandwiching perpendicular layers of nanoscale wires (reminiscent of the ferrite core memory structures used in the early days of computers). The pitch (spacing between parallel wires) was 33 nm in those devices, and more recent efforts have reduced the pitch to 20 nm.

The goal of the MoleSensing thrust is to develop a prototype molecular electronic sensor system having at least 1,000 nanosensors per square micrometer (1011 per square meter) and sensitivity and discrimination equivalent to a dog’s nose. DARPA has funded research on artificial dog’s noses for a number of years, but progress has been slow. The sensor should be able to uniquely identify any of 255 different chemical and biological agents in concentrations as small as 500 parts per trillion. It should have a chemical response time of no more than 10 seconds after exposure to the sample and an electrical



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 7
Summary of the Sensing and Positioning Technology Workshop of the Committee on Nanotechnology for the Intelligence Community: Interim Report TOPIC 2: SYSTEMS Three papers were presented in this session, one by Kwan Kwok, DARPA, one by Rich Fletcher, the Massachusetts Institute of Technology (MIT) and TagSense, Inc., and one by Chris Murphy, NRC Board on Chemical Sciences and Technology. APPLICATIONS OF MOLECULAR ELECTRONICS TECHNOLOGY (MOLEAPPS) PROGRAM Kwan Kwok reviewed the goals and achievements to date of the new 5-year DARPA MoleApps program, which aims to apply molecular-scale electronics technology to the development of ultradense molecular electronic computer processors (this thrust is called MoleComputing) and molecular electronic sensor systems (MoleSensing). For the purposes of the MoleApps program, molecular-scale electronics technology refers to using single molecules, small numbers of molecules, nanoparticles, nanoscale metallic and/or semiconductor wires, nanotubes, and so on as electronic components. The goal of the MoleComputing thrust is to develop a prototype molecular (no-silicon) electronic computer processor having local molecular device densities of 1011/cm2 and a clock rate of at least 10 kHz and consuming no more than 10 W/cm2 of power. Such a processor would be equivalent in complexity to a 1971-vintage microprocessor such as the Intel 4004 but have an area 100,000 times smaller. It would have to be compatible with molecular memory devices such as those being developed in the concurrent DARPA programs, Moltronics, for example, a team of researchers from Rice and Yale Universities, is developing a 10 μm×10 μm 16-kbit memory consisting of an ultra-high-density network of molecular wires and switches that will fit on a human cell. The manufacturing processes to produce such components in bulk do not exist yet, and such molecular memories are affected by, among other things, cosmic rays and incomplete reactions, but they will be self-repairable and fault-tolerant (able to operate with up to 10 percent defects). In 2001, researchers from Hewlett-Packard and the University of California at Los Angeles produced crossed-wire memory devices by sandwiching perpendicular layers of nanoscale wires (reminiscent of the ferrite core memory structures used in the early days of computers). The pitch (spacing between parallel wires) was 33 nm in those devices, and more recent efforts have reduced the pitch to 20 nm. The goal of the MoleSensing thrust is to develop a prototype molecular electronic sensor system having at least 1,000 nanosensors per square micrometer (1011 per square meter) and sensitivity and discrimination equivalent to a dog’s nose. DARPA has funded research on artificial dog’s noses for a number of years, but progress has been slow. The sensor should be able to uniquely identify any of 255 different chemical and biological agents in concentrations as small as 500 parts per trillion. It should have a chemical response time of no more than 10 seconds after exposure to the sample and an electrical

OCR for page 7
Summary of the Sensing and Positioning Technology Workshop of the Committee on Nanotechnology for the Intelligence Community: Interim Report response time (after receptor attachment) of no more than 1 second. The active detection area should be no more than 25 nm2. The research is being conducted at the Army Research Laboratory (ARL), Naval Research Laboratory (NRL), MITRE, and Northwestern, Harvard, and Yale Universities. Kwok speculated that with the new sensing capabilities of molecular-scale sensors, one would be able to differentiate dirty radiological bombs from nuclear weapons and locate hard-to-identify terrorists, though he did not explore how this would be done operationally. Kwok noted two concept targets that might result from this effort: a personal computer with the thickness of a piece of paper with a chem/bio detector attached; and a black box detector mounted on a watch battery. RFID TECHNOLOGY: OPPORTUNITIES AND CHALLENGES Rich Fletcher reviewed the basics of RFID tags, which were invented in 1975, noting that WalMart is requiring all vendors to tag their products by 2007, with DoD and the FDA also issuing requirements for vendor RFID tags to help in management of product inventories. Credit cards are also converting to RFID technology (e.g., ExxonMobil’s smart tag system). The simplest type of RFID tags are chipless tags, which are stamped metal foils that can code on the order of 10 bits of information. At short range, where the tag and reader are in close proximity, the RFID tag looks like a resonant LC circuit, and information is encoded in the resonant frequency or the loss profile, or by modulation. At longer ranges, a chip (which may be powered by a battery) is used in the circuit to create an active tag, and information is coded in the modulated backscatter. Radio frequency is not the only available power source for these kinds of tags; tags can also be powered by light, sound, or by changes in the electric field (capacitively coupled). Chipless RFID sensors are tags that convey information not only about the object’s ID but also about its state or history—for example, has it been broken or tampered with, or is it being squeezed? Commercial examples include simple pressure and temperature sensors. A major challenge with RFID tags is providing the power to turn them on; they must be held close to the reader to be activated, although the sensing function itself does not require much power. Fletcher favors capacitively coupled tags because they do not require large activation currents—small gradients in the electric field are sufficient. Examples include (1) touch-based tags, where touch can be used to transfer information (e.g., an instrumented doorknob) and (2) tags that use the human body, both as a power source and as an antenna. An option for electronically displaying information from RFID tags is to use microencapsulated black and white ink particles that respond differently to dipole fields and can be read optically. Fletcher cited some key challenges for the future. One is reducing the cost of manufacturing and handling tiny chips, which may be 0.1 μm on a side. Fluidic self-assembly based on shaking the chips and allowing them to settle in precision-machined channels is now used. Another challenge is ensuring compatibility of different RFID systems. Options include making readers with multiple front-ends to read different tags or making more agile tags that can be read by multiple readers such as those using multifrequency power and readout. In the future, analog information from sensors may also be encoded in smart antennas. Polymer electronics with printed logic and batteries and solar cells and displays on flexible substrates are enabling a whole new range of smart tags for products. Also in the future, DNA could be tagged with gold nanoparticles attached to specific sites that could be read by irradiating with a specific frequency that would be absorbed, producing local heating that would change the local molecular conformation. In conclusion, Fletcher noted that RFID applications are already a large business that is growing very rapidly. Materials and manufacturing technologies are enabling an increasing market for wireless and cheap tags. Nanotechnology and new power sources can enable greater performance.

OCR for page 7
Summary of the Sensing and Positioning Technology Workshop of the Committee on Nanotechnology for the Intelligence Community: Interim Report REVIEW OF EXISTING AND POTENTIAL STANDOFF EXPLOSIVE DETECTION TECHNIQUES Chris Murphy described an ongoing NRC study aimed at standoff detection of explosives (e.g., those contained in a belt worn by a suicide bomber). In this case, standoff is defined as detection from at least 20 meters with a response time of 5–10 seconds. Promising technologies include x-ray backscatter, IR imaging, and terahertz imaging, but there does not appear to be a clear winner for all scenarios. A systems-level approach is needed, with fusion of data from multiple sensors, discrimination, and identification to yield a high probability of detection with a low false alarm rate. PANEL 2 DISCUSSION Discussion in this segment began with concerns being expressed about the feasibility of molecular-scale sensing devices. For example, would bacteria in the background environment interfere with the detection of biological agents? Kwok’s answer was that one is not dealing with a single 1 μm x 1 μm CMOS chip; rather, if the sensor is structured in a crossed-wire configuration with target-specific antibody sites at the nodes, one has the equivalent of an array of 1,000 such chips, and only one triggered cross point is needed for detection. Diffusion is fast across this area and one can design 255 different signatures to detect an equivalent number of agents. Another issue was raised: the significant problem with detecting small things in large volumes—for example, screening 5 liters of liquid to find one organism. Selectivity is yet another key issue, indeed a bottleneck: The transduction element must only respond to the target ligand. Kwok’s response was that DARPA’s goal is not to develop new chem/bio sensor systems per se but to push nanotechnology forward using the performance of a dog’s nose as a metric. He wants to “build a different way to look at the problem.” It was also asked whether having more nodes in sensors is necessarily better. With a large number of nodes, there could be a data processing problem that would degrade the overall signal. An important question for sensor integration is, How many nodes are enough? Rich Fletcher was asked about the limitations imposed on the covertness of RF tags by the need for antennas, and whether negative refractive index materials (and photonic band gap materials in general) might be useful in addressing this problem. What power levels are required for these materials as a function of distance? Fletcher did not answer directly but noted that while good work on negative refractive index materials is being done in academia, the work has not yet been transitioned to the commercial world. With regard to antennas, while they may be long, they can be made so thin that they are invisible to the eye. One can also use higher-frequency systems to reduce antenna size, but the higher frequencies don’t penetrate well in enclosed spaces. It was also asked why if capacitive RFID tags are so promising, Motorola had dropped its program in this area. Fletcher believes that this was a case of throwing out the baby with the bath water: Motorola determined it was losing money in the tagging area and terminated all of its programs in that area.

OCR for page 7
Summary of the Sensing and Positioning Technology Workshop of the Committee on Nanotechnology for the Intelligence Community: Interim Report This page intentionally left blank.