under which bioelectronic systems will find their way into human patients in the future and

raises questions about the ethically appropriate approach.

21.2 Sensor and Actuator Designs

Microelectronic implants can be divided into two broad groups of sensor and actuator

systems. For example, the sensory function is in the focus of glucose and other metabolite

monitors [8,19], but also in systems for physical quantities such as temperature or tensile

stress to determine the mechanical load in bone prostheses [20]. Other examples of

multisensor systems, such as developments for artificial retina or implantable ECG and

EEG systems, can also be counted in this group [21]. The second group of implantable

systems, on the other hand, has an actuator component such as stimulators for

Parkinson’s patients [22] implanted medication dosage devices such as insulin pumps

[13] or peripheral nerve stimulators [22], which are used to deliver stimulation pulses to

nerve or other tissues. A closer look at actuator systems reveals that most of them have

one or more integrated sensors that allow the determination of the time or boundary

condition at which they become active.

The dominant semiconductor technology today is CMOS technology, which is used to

process about 1 mm thin, single-crystalline silicon wafers. The progress of this technology

manifested itself on the one hand in the steady reduction of the processable structures,

which have now reached the nm range. The mass production of low-cost microchips

initiated with scaling was accompanied by an increase in wafer diameters from 4” to

300 mm, the transition from µm to nm lithography systems, the decrease in switching

times of field-effect transistors (FET) into the ns range, the increase in FET density to more

than 10⁹ cm⁻², the introduction of new materials such as Cu instead of Al conductors in

the back-end-of-line stack, or the integration of rare earth oxides as high-k dielectrics in

the transistor gate, to name just a few of the most important development steps.

Economically, CMOS technology was characterized by a steady increase in the necessary

investment costs for a state-of-the-art semiconductor factory (fab) to several $10⁹ in the

meantime. Due to enormous equipment costs, which can no longer be raised by research

institutes, a second development direction has established itself, which follows the claim

described as “More than Moore.” Frequently, earlier CMOS technology levels run also

FIGURE 21.1

General scheme for the construction of microelectronic sensor or actuator implants for use in human patients.

The interaction between tissue and microelectronic system runs through a window kept as small as possible to

protect the other components from corrosion or denaturation; the antenna must also be able to radiate into a

permeable medium.

Implantable Microelectronics

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