Biomedical Engineering Reference
In-Depth Information
(
A
)
(
B
)
Organic cantiFET: Transfer characteristics
Organic cantiFET: Output characteristics
V
gS
= -40V
10
-9
8.0
×
1.2
×
10
-4
I
DS
10
-8
1/2
I
DS
10
-9
6.0
×
V
gS
= -30V
10
-9
10
-5
8.0
×
10
-9
4.0
×
V
gS
= -20V
10
-10
10
-5
4.0
×
10
-9
2.0
×
V
gS
= -10V
V
gS
= -0V
10
-11
0.0
0.0
-40
-30 -20
Gate voltage [V]
-10
0
-40
-30
-20
-10
0
Drain voltage [V]
Figure 9.13
I-V characteristics of organic CantiFETs at er silicon nitride encapsulation.
(A) Transfer characteristics (B) Output characteristics [28].
subjected to dif erent levels of compressive strain using calibrated micro-
manipulators and the I-V characteristics of the device was recorded at er
each level of strain, ε. It was observed that these organic CantiFET devices
exhibit a good strain sensitive behavior with the drain current increasing
with compressive strain [28]. h e percentage change in drain current, i eld
ef ect mobility and threshold voltage were plotted as a function of change in
the strain for the bias condition of V
GS
= V
DS
= -40 V (Figure
9.14). From this
it can be observed that the transistor parameter that is strongly inl uenced
by the strain is the i eld ef ect mobility and not the threshold voltage. h is
agrees well with the present understanding of hopping transport in penta-
cene. h e compressive strain is expected to reduce the hole hopping energy
barrier due to the decrease in hopping distance [41]. h e devices exhibited
very high strain sensitivity (ΔI/I per unit strain) of the order of 10
3
.h e sur-
face stress sensitivity for organic CantiFET devices (ΔI/I in ppm per unit
surface stress in mN/m) extracted from the electromechanical characteriza-
tion was 401 ppm [mN/m]
-1
.
h e minimum detectable surface stress for CantiFET sensors were predicted
by measuring the noise levels in these devices. A battery operated low noise
trans-impedance preamplii er (Stanford Research 570) with gain varying from
10
-3
to 10
-12
A/V was used to provide the gate bias to the CantiFETs probed
inside a shielded probe station. h e output or the drain terminal was connected
to another SR570 in order to provide drain bias and to measure and amplify
noise levels in the drain current. A spectrum analyzer (SR 750) was used to
record the noise power spectrum in frequencies ranging from 1Hz to a few kHz.
h e noise current level calculated for 1/f noise frequency range was 1.46 pA.
h e performance of CantiFET was compared with other relevant nano-
mechanical sensors such as SU-8 microcantilevers with integrated gold as
