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Capacitance loss during the heating
Organic integrated temperature sensor
Polyvinylpyrrolidone (PVPy) based organic thin film transistor
-‐2 .0 -‐1.5 -‐1.0 -‐0.5 0.0
-‐2.0µ
-‐1.5µ
-‐1.0µ
-‐500.0n
0.0
I DS (A
)
V D S (V )
VG s tep=0.25V
-‐2 .0 -‐1.5 -‐1.0 -‐0.5 0.010 -‐11
10 -‐10
10 -‐9
10 -‐8
10 -‐7
10 -‐6
0 .0
500.0µ
1.0m
1.5m
I DS (A)
VG (V )
Sqrt o
f IDS (A
0.5 )
Background and objectives
References
Conclusion
Characterization of spin coated PVPy thin film
Research student: Xiaochen Ren High senstivity organic temperature sensor
[1] X.C. Ren et al. Appl. Phys. Lett. 99, 043303 (2011). [2] T. Seketani et al. Adv. Mater. 22, 2228–2246 (2010). [3] J. Park et al. Mol. Cryst. Liq. Cryst. Vol. 531 (2010).
PVPy can be use as a polymer dielectric for organic thin film transistor due to its high dielectric constant and smooth surface. The PVPy based 1R1T temperature sensor shows the sensing dynamic range can be up to 10 bits. During the measurements, heating leads to the lost of capacitance in the dielectric and therefore the operating voltage increases. The high dynamic range temperature sensor provide high resolution sensing ability which is capable for artificial skin application and the simple fabrication process could be potentially used for flexible and large area devices.
Device structure, one thermisor one transistor sensor
Humidity dependent Capacitance-frequency response
after annealing
20 nm
The actual gate voltage of transistor is controlled by the resistor, the large on/off ratio of transistor brings large sensitivity of the sensor
Temperature sensor is one of the key components in artificial skin
Dynamic range of temperature sensor is low
T. Someya et al. Proc. Natl. Acad. Sci. USA 2005, 102, 12321.
Temperature dependent capacitance-frequency response
102 103 104 105 106 10712n
14n
16n
18n
20n
22n
Cap
citanc
e (F
/cm
2 )
F requency (H z )
R e la tive H umidity (R H )=30%
0min to 60minsT ime s tep=5 m ins
0 10 20 30 40 50 60
1.0
1.5
2.0
2.5
3.0
Normalized
Cp (
a.u.)
T ime (min)
R H :30% R H :50% R H :70%
Cp a t 10kH z
102 103 104 105 106 1075n
10n
15n
20n
Cap
citanc
e (F
/cm
2 )
F requency (H z )
T empera ture: 20oC to 90oC
20 30 40 50 60 70 80 90 1008n
10n
12n
14n
Cap
acita
nce (F
/cm
2 )
T empera ture (oC )
Decaying stage (Water vapor)
Stable stage (PVPy Intrinsic Cp)
RH=50%
RH=50%
Temperature sensor performance
transistor
thermistor
One thermistor One thermistor one transistor
PVPy
Pentacene
glass
Ag Ag
Ag NPs PVPy
Pentacene
glass
Ag
Ag NPs Pentacene Ag Ag
Ag
Ag
A A
30 40 50 60 70 80 9010-‐11
10 -‐10
10 -‐9
Current (A
)
T empera ture (oC )
V oltage bia s =2V
10 20 30 40 50 60 70 80 9010-‐10
10 -‐9
10 -‐8
10 -‐7
10 -‐6
Current (A
)
T empera ture (oC )
VDD= -‐6V
VR ead
= -‐2V
10 30 50 70 9010-‐10
10 -‐9
10 -‐8
10 -‐7
10 -‐6
10 -‐5
10 -‐4
Current (A
)
T empera ture (oC )
fres h device , V DD= -‐6V , V R ead= -‐2V
a fter hea ting , V DD= -‐40V , V R ead= -‐5V
a fter hea ting , V DD= -‐6V , V R ead= -‐2V
Surface morphology and dielectric property
PVPy Pentacene
glass Ag
Source Drain
T. Someya et al. IEDM 2003
Dynamic range: ≈2×2=2 bit
µ=1.3cm2/Vs
Rms=0.23 nm
100 101 102 103 104 105 106 1074
6
8
dielec
tric co
nstant
F requency (H z )
εr=7.4 at 1Hz
PVPy absorb water in the air, the moisture component in PVPy film increase the Cp due to the large dielectric constant of water
The moisture is vaporized at high temperature, Cp decrease after heating
pentacene
PVPy O
n
N
Gate
Ag NPs
Source-drain electrode
Current drop due to the capacitance loss during the heating
The drop of current is due to the capacitance loss during the heating, transistor need larger gate voltage to turn on, therefore it can be enhanced by increasing the VDD
Sensing dynamic range: 211>1300>210=10 bit !!!
VDD
VRead
The dynamic range is hinted by the serially connected diode, to obtain lower current at room temperature, transistor need to be at off state.
Ag
PVPy
Ag
εr=80.4(20℃)
Ag Nps increase the temperature dependent conductivity variation of film: Ref.1
At low temperature, VDD=-6V, Vresistor>VG of transistor, transistor state: off At high temperature, VDD=-6V, Vresistor<<VG of transistor, transistor state: on
Fresh device shows current drop when T>70℃
The heated device, when VDD is increasing from -6V to -40V, the sensing performance is recovered.
