Page 315 - Microsensors, MEMS and Smart Devices - Gardner Varadhan and Awadelkarim

BIO(CHEMICAL) SENSORS 295

The data has been fitted to Equation (8.58) and appears approximately linear when kC is
much smaller than 1.
kC
AV GDS = AV T - AV max ---- (8.58)

The main advantages of PolFETs are that they can be operated at ambient temperatures
(and therefore require little power) and that they are compatible with CMOS technology.
However, the polymers do exhibit a significant humidity dependence and so their future
success, as gas (vapour) sensors, will depend on either employing hydrophobic films or
on-chip compensation for the humidity variation.
To date, the greatest commercial success of a polymeric potentiometric device has been
in the field of biosensors (Scheller et al. 1991). The device consists of an enzyme, such
as glucose oxidase, which is then attached to an electrode and senses potentiometrically,
amperometrically, or impedimetrically. Perhaps the most successful device has been a
glucose detector. The device is able to detect the level of glucose in blood by using a

Figure 8.62 (a) Schematic picture of an MISiC Schottky diode sensor with thin platinum as the
catalytic layer, (b) positioning of an MISiC sensor in the exhaust system of an automobile engine,
and (c) response of an MISiC gas sensor to exhaust gases when one cylinder is injected with excess
fuel. From Savage et al. (2000)