Limits on silicon nanoelectronics for terascale integration.

Throughout the past four decades, silicon semiconductor technology has advanced at exponential rates in both performance and productivity. Concerns have been raised, however, that the limits of silicon technology may soon be reached. Analysis of fundamental, material, device, circuit, and system limits reveals that silicon technology has an enormous remaining potential to achieve terascale integration (TSI) of more than 1 trillion transistors per chip. Such massive-scale integration is feasible assuming the development and economical mass production of double-gate metal-oxide-semiconductor field effect transistors with gate oxide thickness of about 1 nanometer, silicon channel thickness of about 3 nanometers, and channel length of about 10 nanometers. The development of interconnecting wires for these transistors presents a major challenge to the achievement of nanoelectronics for TSI.

New methods for whole blood oximetry.

New techniques for determining the hematocrit (Hct) and oxygen saturation (SO2) of whole blood from backscattered light measurements are described. First, theoretical and experimental results are presented which show that the empirical linear relationship between SO2 and the infrared-red backscattered light intensity ratio on which previous instruments have been based is an inadequate description primarily because it does not account for the strong effects of Hct and transducer geometry. Then it is shown that the ratio of backscattered intensities from two appropriately positioned infrared sources can be plotted against the infrared-red intensity ratio to produce a family of calibration curves from which SO2 and Hct can be independently determined. Finally, a practical implementation of an oximetry system which employs a microelectronic catheter-tip optical sensor and a microprocessor-based signal processor is proposed.

Inhibition of thrombus formation on intravascular sensors by electrical polarization.

Implantable biomedical sensors built on a silicon substrate capped with glass are currently being developed for intravascular applications. Electrical techniques for inhibiting thrombus formation on the surface of a proposed optical sensor in direct contact with blood have been investigated. Glass-on-silicon specimens (4 X 1.2 X 0.4 mm3) were coated with indium-tin oxide, a transparent conductor, and implanted in the vena cava and iliac veins of three dogs for 10, 20, or 33 days. The equilibrium surface-blood interface potentials of the specimens were modified by implanted current sources which supplied either direct current (8-15 microA) or 100 KHz alternating current (5 microA, root mean square). Light-microscopic and scanning electron-microscopic analyses showed each of the DC-polarized specimens to be free of thrombus, in contrast to nonpolarized (control) specimens on which varying amounts of adsorbed protein and thrombus deposits were found. Like the control specimens, the AC-polarized specimens formed thrombus, but the appearance of the deposits differed. These findings support the view that the polarity, magnitude and time dependence of the potential across conducting surface-blood interface significantly influence thrombogenicity. Further work is necessary to determine the roles of electrochemical and electrostatic factors in preventing thrombus formation on foreign materials.

Microelectronics and computers in medicine.

Microelectronics and computers are in use in virtually every aspect of modern medicine. Computers are used widely in medical research, where an important need is for better microelectronic sensors for data acquisition. In medical practice, data collection from patients as well as subsequent storage, retrieval, and manipulation of data are enhanced by the computer. In medical decision-making computers improve accuracy, increase cost-efficiency, and advance understanding of the structure of medical knowledge and of the decision-making process itself. Powerful new noninvasive diagnostic instruments including x-ray tomographic scanners and ultrasonic imaging systems are based on computers. The efficiency and scope of clinical laboratory procedures and advanced analytical instruments are greatly increased by computerization, and careful application of computers has improved the interpretation of diagnostic tests, such as the electrocardiogram, and monitoring of critically ill patients. The powerful sensory, computational, memory, and display capabilities of microcomputer systems and their compact size offer new opportunities to relieve functional deficiencies associated with loss of limbs, paralysis, speech impediments, deafness, and blindness.

Small-organ dynamic imaging system.

Dynamic ultrasonic imaging of superficial body organs adds a new dimension to clinical sonographic examinations in that it enables the real-time evaluation of tissue motion and vascular pulsations. A high-frequency (7.2 MHz) linear-array system has been newly developed that generates simultaneous A- and B-mode displays at 60 frames/sec. The instrument produces real-time scan-converted images in standard television format for direct viewing on television (TV) monitors or clinical recording through videotape equipment. Clinical application of this dynamic imaging system has increased the diagnostic capabilities of ultrasound in ophthalmology, radiology, and pediatrics.

Biomedical implantable microelectronics.

Innovative applications of microelectronics in new biomedical implantable instruments offer a singular opportunity for advances in medical research and practice because of two salient factors: (i) beyond all other types of biomedical instruments, implants exploit fully the inherent technical advantages--complex functional capability, high reliability, lower power drain, small size and weight-of microelectronics, and (ii) implants bring microelectronics into intimate association with biological systems. The combination of these two factors enables otherwise impossible new experiments to be conducted and new paostheses developed that will improve the quality of human life.

Integrated circuit implantable systems.

A series of totally implantable telemetry systems have been developed to chronically determine such parameters as blood flow, pressure, biopotentials and temperature. This instrumentation is currently used in medical research involving laboratory animals. Custom integrated circuits are used to realize the signal processing complexity needed for accurate and stable measurements within the size and power constraints of an implantable electronics system.

Totally implantable directional Doppler flowmeters.

Two totally implantable Doppler blood flowmeters have been developed for the chronic measurement of deep-body flows; made possibly by two custom-integrated circuits. The CW and pulsed Doppler instruments are small (less than 2.5 cm3), use little power (less than 30 mW), and have excellent baseline stability. The pulsed Doppler flowmeter is applied principally when velocity-profile information or a nonencircling transducer assembly is required but where minimal restraint of the animal for inductive telemetry is permissible. Using a circumferential cuff, the CW Doppler flowmeter monitors Doppler data over a at least a 3-meter range by means of RF telemetry and produces a single velocity estimate. These instruments compliment each other and other telemetry systems by proving the researcher with alternatives for the long-term measurement of deep-body flow without percutaneous leads.

Totally implantable dimension telemetry.

A totally implantable dimension telemetry system has been developed to instrument animals for chronic physiological research. Implantable signal processing electronics allow free-roaming animals with no percutaneous leads while retaining the long-term redproducibility of fixed implanted transducers. Two low-powered, custom-integrated circuits have been developed and assembled into an implantable package capable of measuring one dimension channel. The system has been operated in the amplitude modes of through-transmission and reflection as well as in a new Doppler-power configuration and aimed at determining interfaces between blood and surrounding structures. In a addition to single channel systems, these ICs are key elements in multimode, multidimensional implants capable of more accurate characterization of deep body structures.

An integrated circuit approach to totally implantable telemetry systems.

A series of totally implantable telemetry systems has been developed to determine such key physiological parameters as blood flow, pressure, dimensions, temperature, and bioelectrical activity in chronic research animals. Custom integrated circuits provide the signal-processing complexity and performance required to sufficiently instrument the animals for an accurate prediction of human responses. Additional implant and transducer technologies are necessary to complete the instrument package. Although the costs of these technologies are high, they are more than offset by the unique information obtained and overall reduction in the expenses of medical research because fewer animals can be studied over longer periods. A number of the IC-based implants are in use in several physiology and experimental drug studies where adequate reliability and performance could not be achieved by alternate approaches.