Gate SiO 2 Pentacene
S D
PMMA/PVP
Fig. 4-4 Schematic structure of PVP-OTFTs and PMMA-OTFTs
Wavelength ( nm )
400 500 600 700 800
0 5 10 15 20 25
White Intensity ( uW/cm2 *sr*nm )
0 20 40 60 80 100 120
Blue 0
1 2 3 4 5 6
Red
0 10 20 30 40 50
Green
Fig. 4-5 Wavelength spectrum of light sources (Red, Green, Blue and White).
Fig. 4-6 Water contact angle of PVP and PMMA dielectric surfaces.
Wavenumber (cm-1)
2500 2750
3000 3250
3500 3750
4000
Absorbance (a.u.)
0.0 0.2 0.4 0.6 0.8
PVP PMMA OH groups
Wavenumber (cm-1)
2500 2750
3000 3250
3500 3750
4000
Absorbance (a.u.)
0.0 0.2 0.4 0.6 0.8
PVP PMMA OH groups
Fig. 4-7 FTIR spectra of PVP and PMMA film.
Gate Bias ( V )
Fig. 4-8 The linear-region initial transfer characteristic of PVP-OTFT and PMMA-OTFT. The gate bias is swept from positive bias to negative bias. The threshold voltage (Vth) is extracted by using the linear region equation.
2θ ( deg )
5 10 15 20
XRD Intensity ( a.u. )
Pentacene on PVP Pentacene on PMMA
Fig. 4-9 X-ray diffraction (XRD) pattern of pentacene deposited on PVP and PMMA dielectrics. The thickness of pentacene films deposited on PVP and PMMA dielectric are 100nm.
Fig. 4-10 Atomic force microscope (AFM) image of (a) PMMA and (b) PVP dielectric surfaces before depositing pentacene.
PMMA PVP
(a) (b)
PMMA PVP
PMMA
PMMA PVP PVP
(a) (b)
Fig. 4-11 Atomic force microscope (AFＭ) image of pentacene thin film surfaces deposited on (a) PMMA and (b) PVP dielectrics.
Gate Bias ( V )
Fig. 4-12 The linear-region transfer characteristic of PVP-OTFT swept form 15 V to -25 V and back to 15 V in ambient air and under dark while drain bias is
In air and under dark
PMMA
In air and under dark
PMMA
VD = -5 V
Fig. 4-13 The linear-region transfer characteristic of PMMA-OTFT swept form 10 V to -25 V and back to 10 V in ambient air and under dark while drain bias is kept at -5 V.
Gate Bias ( V )
Light Intenstiy = 16.9 mW/cm2
In air and under illuminaiton
PVP
Light Intenstiy = 16.9 mW/cm2
In air and under illuminaiton
PVP
VD = -5 V
Fig. 4-14 The linear-region transfer characteristic of PVP-OTFT swept form 15 V to -25 V and back to 15 V in ambient air and under illumination while drain bias and light intenstiy are kept at -5 V and 16.9 mW/cm2.
In air and under illuminaiton
PMMA
Light Intensity = 16.9 mW/cm2
VD = -5 V
In air and under illuminaiton
PMMA
Light Intensity = 16.9 mW/cm2
VD = -5 V
Fig. 4-15 The linear-region transfer characteristic of PMMA-OTFT swept form 10 V to -25 V and back to 10 V in ambient air and under illumination while drain bias and light intenstiy are kept at -5 V and 16.9 mW/cm2.
Wavelength ( nm )
440 480 520 560 600 640
Threshold Voltage Shift ( V )
0
Light Intensity = 0.05 mW/cm2
st
VGS
Wavelength ( nm )
440 480 520 560 600 640
Threshold Voltage Shift ( V )
0
Light Intensity = 0.05 mW/cm2
st
VGS
Fig. 4-16 Threshold voltage shift (ΔVth) of PMMA-OTFT and PVP-OTFT after bias stress under illumination with different wavelength. The bias stress conditions: VG – Vthini
= 15 V, VD = VS = 0 V and light intensity is 0.05 mW/cm2.
Wavelength ( nm )
400 450 500 550 600 650 700
Absorbance ( a.u. )
Pentacene deposited on PMMA Pentacene deposited on PVP
Fig. 4-17 The absorption spectra of pentacene thin films deposited on PVP and PMMA dielectric. The thicknesses of both pentacene thin films are 100 nm.
Gate Bias ( V )
Stress Time = 1000 sec
In air and under dark VD = - 5 V
Stress Time = 1000 sec
In air and under dark VD = - 5 V
st
VGS
Fig. 4-18 The transfer characteristics of PVP-OTFT and PMMA-OTFT before and after a 1000-second positive gate bias stress in ambient air and under dark.
The bias stress conditions: VG – Vthini
= 15 V, VD = VS = 0 V.
Stress Time ( sec )
0 200 400 600 800 1000
Threshold Voltage Shift ( V )
-1
In air and under dark
st
VGS
Stress Time ( sec )
0 200 400 600 800 1000
Threshold Voltage Shift ( V )
-1
In air and under dark
st
VGS
Fig. 4-19 Threshold voltage shift (ΔVth) of PVP-OTFT and PMMA-OTFT during positive gate bias stress in ambient air and under dark. The bias stress conditions:
VG – Vthini
= 15 V, VD = VS = 0 V.
Stress Time ( sec ) In air and under dark
st In air and under dark
st
VGS
Fig. 4-20 The field-effect mobility of both devices plotted as a function of positive bias stress time in ambient air and under dark. The bias stress condition: VG – Vthini
In air and under dark
st
In air and under dark
st
VGS
Fig. 4-21 The transfer characteristics of PVP-OTFT and PMMA-OTFT before and after a 1000-second negative bias stress in ambient air and under dark. The bias stress condition: VG – Vthini
= -15 V, VD = VS = 0 V.
Stress Time ( sec )
0 200 400 600 800 1000
Threshold Voltage Shift ( V )
-5
In air and under dark
st
VGS
Stress Time ( sec )
0 200 400 600 800 1000
Threshold Voltage Shift ( V )
-5
In air and under dark
st
VGS
Fig. 4-22 Threshold voltage shifts (ΔVth) of PVP-OTFT and PMMA-OTFT during positive gate bias stress in ambient air and under dark. The bias stress conditions: VG – Vthini In air and under dark
st In air and under dark
st
VGS
Fig. 4-23 The field-effect mobility of both devices plotted as a function of positive bias stress time in ambient air and under dark. The bias stress condition: VG – Vthini
= -15 V, VD = VS = 0 V.
Stress Time ( sec )
0 200 400 600 800 1000
Threshold Voltage Shift (V)
-1.0 Light Power = 2.95 mW/cm2
st
VGS
Stress Time ( sec )
0 200 400 600 800 1000
Threshold Voltage Shift (V)
-1.0 Light Power = 2.95 mW/cm2
st
VGS
Fig. 4-24 Threshold voltage shift (ΔVth) of PVP-OTFT and PMMA-OTFT during illumination. The light intensity is 2.95 mW/cm2.
Gate Bias ( V )
Light Power = 2.95 mW/cm2
In air VGSst
Light Power = 2.95 mW/cm2
In air VGSst
Fig. 4-25 The transfer characteristics of PVP-OTFT and PMMA-OTFT before and after a 1000-second positive bias stress under illumination. The bias stress conditions: VG – Vthini
= 15 V, VD = VS = 0 V. The light intensity is 2.95 mW/cm2.
Stress Time ( sec )
0 200 400 600 800 1000
Threshold Voltage Shift ( V )
-2
Light Power = 2.95 mW/cm2
In air
st
VGS
Stress Time ( sec )
0 200 400 600 800 1000
Threshold Voltage Shift ( V )
-2
Light Power = 2.95 mW/cm2
In air
st
VGS
Fig. 4-26 Threshold voltage shift (ΔVth) of PVP-OTFT and PMMA-OTFT during positive gate bias stress under dark and illumination. The bias stress condition:
VG – Vthini
Fig. 4-27 Energy-band diagram of OTFT from gate to drain/source when devices are under illumination with positive gate bias.
Stress Time ( sec )
0 1000 2000 3000 4000 5000
Threshold Voltage Shift ( V )
0
Light Power = 2.95 mW/cm2 In air
= 15 V, VVGSst S = VD = 0 V
Stress Time ( sec )
0 1000 2000 3000 4000 5000
Threshold Voltage Shift ( V )
0
Light Power = 2.95 mW/cm2 In air
= 15 V, VVGSst S = VD = 0 V
Fig. 4-28 Threshold voltage shift (ΔVth) of PVP-OTFT during positive gate bias stress under dark and illumination when extending stress time. The bias stress conditions: VG – Vthini
= 15 V, VD = VS = 0 V. The light intensity is 2.95 mW/cm2.
Stress Time ( sec )
0 200 400 600 800 1000
Threshold Voltage Shift ( V )
-2
Threshold Voltage Shift ( V )
-2
Fig. 4-29 Threshold voltage shifts (ΔVth) of PMMA-OTFT and PVP-OTFT under dark and in air and in vacuum. The bias stress conditions: VG – Vthini
= 15 V, VD = VS = 0 V.
Stress Time ( sec )
0 200 400 600 800 1000
Threshold Voltage Shift ( V )
-1
Threshold Voltage Shift ( V )
-1
Fig. 4-30 Threshold voltage shifts (ΔVth) of PMMA-OTFT and PVP-OTFT in vacuum under dark and illumination. The bias stress conditions: VG – Vthini
= 15
Table 4-1 Spin coating parameters of PMMA and PVP dielectric fabrication process.