Page 163 - Organic Electronics in Sensors and Biotechnology

140 Cha pte r F o u r

100

9
Z MBPA = 10 Ω
Voltage sensitivity (V/W) 1 Laser code Z LI = 10 Ω amplifier 2.0 μm
10
8
PVDF-sensor
Lock-in
Waveform

0.1 generator Computer
MBPA
Lock in V ~ 1/ω
0.01
0.01 0.1 1 10 100 1000 10,000
Frequency (Hz)

Voltage output V sense at 0.1 Hz with MBPA
0.5

–0.5
V Sensor (V) –1.5

–2.5

–3.5
–4.5
0 10 20 30 40 50 60 70 80
Time (s)
FIGURE 4.13 Top: Voltage sensitivity of a 2 μm thick capacitive PVDF-TrFE
thin-fi lm sensor with Ag top and bottom contacts and a graphite absorbing
layer on top (PVDF:TrFE = 55:45). The pyroelectric response of the thin-fi lm
sensor was measured in the low-frequency range by a high-impedance
parameter analyzer (MBPA) and at medium and higher frequencies by a lock-
in amplifi er. The inserts show an AFM micrograph of the phase signal of the
surface of the PVDF layer and the equivalent circuit diagram of the
measuring setup. Bottom: The voltage output of the PVDF sensor measured
with the MBPA at a modulation frequency of 0.1 Hz is shown.

magnitude lower. The calculated values are f = 2.6 Hz for the lock-in
co
measurement and f = 0.3 Hz for the parametric analyzer MBPA, both
co
of which are consistently reproduced in the voltage sensitivity meas-
urements. The overall voltage sensitivity at low frequencies (0.01 Hz)
is about R = 100 V/W which, normalized to the ferroelectric polymer
V