Page 130 - Organic Electronics in Sensors and Biotechnology

Strain and Pressure Sensors Based on OFET 107

Sensor response
0.5 6.0
Applied response
0.4
4.0
0.3
0.2 2.0
Δl/l 0 0.1 Pressure (kPa)
0.0 0.0
–0.1
–2.0
–0.2
–0.3 –4.0
0 50 100 150 200 250
Time (s)
FIGURE 3.16 I vs. time for compressive and tensile applied pressures.
d

from exposure to external agents (i.e. humidity, light, etc) as these
factors are known to cause drift and in general to negatively affect the
device performance.

3.4 Applications for Organic Field-Effect
Transistor Sensors
The possibility of obtaining low-cost physical sensors is attractive for
a number of applicative fields. Organic field-effect sensors are still in
their embryonic phase. As far as we know, no commercial application
has yet been developed. Despite this, many groups are working
toward innovative solutions that make use of this technology. Here
we will focus on two cases that seem particularly interesting: the first
is the realization of an artificial skin for robots, while the second con-
cerns e-textiles. Both deal with a common need, i.e., the conforma-
bility of the final product to a 3D shape, a robot in the first case and the
human body in the second. This requirement is fully satisfied by
devices realized on substrates that are able to adapt their shape to the
substrate, i.e., are flexible. Furthermore, large area is another desirable
characteristic. In the following, an overview of these applicative fields
is given with a special focus on requirements for future devices.

3.4.1 Artificial Sense of Touch
The skin is the largest organ of the human body. For the average
2
adult human, the skin has a surface area of 1.5 to 2.0 m , most of it
is 2 to 3 mm thick. The average square inch of skin holds 650 sweat
glands, 20 blood vessels, 60,000 melanocytes, and more than a thou-
sand nerve endings.
Skin is composed of three primary layers: the epidermis, which
provides waterproofing and serves as a barrier to infection; the der-
mis, which serves as a location for the appendages of skin; and the
hypodermis, which is called the basement membrane (see Fig. 3.17).