Microsystems for Bioelectronics

Concluding remarks

In this book, the thought-problem of designing a highly functional, micron-scale electronic system has

been explored in the context of possible in vivo applications in the human body. The idea of designing

this nanomorphic system, although insp ired by the continued scaling of feature sizes of transistors and

memory elements in integrated circuit technology, extends the scaling concept in at least two ways.

First, additional components of the nanomorphic cell such as energy sources, sensors and commu-

nication systems must also be scaled into micron or submicron dimensions. This property of the

nanomorphic cell has a relation to system-on-a-chip technology but with an increased emphasis on the

variety of components that must be scaled and assembled into an integrated system. A second

differentiation from classical integrated circuit technology is the physical size of the nanomorphic

system and the implied fabrication technology. In the integrated circuit case, the systems have

dimensions on the order of centimeters; much larger than the micron-scale dimensions of the nano-

morphic cell.

One of the encouraging findings in the book is the degree of support for realization of the nano-

morphic cell provided by the continued scaling of logic and memory elements. It appears that thou-

sands of logic and memory elements could be integrated into the 10 micron nanomorphic cell if scaled

device feature sizes in the far submicron regime are achieved by the industry as planned. Such devices

are projected to be available in the 2020 timeframe by the International Technology Roadmap for

Semiconductors. Moreover, it is expected that these devices will become more energy efficient in their

operation as a result of continued feature size scaling. (1) Nevertheless, there is a continuing need to

dramatically decrease device switching energy over the best scaled projections in order to reduce

demands on energy use for computation and sensing.

One clear implication of the topics addressed in this book is that the nanomorphic cell must

perform its functions at the extremes of energy efficiency. Only micro joules are likely to be available

from energy sources in the small volume of the nanomorphic cell and this energy must support all cell

functions. The examination of potential energy sources given in Chapter 2 emphasized the limits

attainable for energy per unit volume and energy per unit mass for a variety of energy sources

including the super capacitor, the fuel cel l, radio-isotope sources, and various energy-harvesting

techniques. Each of these energy sources occupies a different location in the power–energy space. In

vivo energy harvesting is an appealing idea since operation of the nanomorphic cell could be extended

for a considerable period of time. However, it appea rs that only a miniscule amount of energy could be

captured by most of the known techniques and that this would need to be converted into a form for use

by the nanomorphic cell. However, conditioning of the harvested energy would require utilization of

some of the very limited volume of the cell. The galvanic cell was chosen as a model energy source in

the book but even if all of the 10 micron cube volume is devoted to the galvanic cell, only about one

micro joule of energy could be stored. (2) The need for an adequate supply of energy to support the

necessary functions of the nanomorphic cell is a possible show-stopper and creative solutions are

needed.

Microsystems for Bioelectronics the Nanomorphic Cell

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