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High frequency
printed polymer transistors
Center for Nano Science and Technology@PoliMi Istituto Italiano di Tecnologia, Milan, Italy
Mario Caironi
“ORGANIC ELECTRONICS - Principles, devices and applications”
Politecnico di Milano, 26 November 2015
Wang et al., TLIST, 2013 Sony
Why improving «speed»
Someya et al.
2
Transconductance
Gate Voltage
Dra
in C
urr
ent
Vgs
Ids
Id
+
+ id
3
If vgs<< VGS ' (saturation regime)
GS GS
Dm OX od
GS v V
di Wg C V
dv L
id = gmvgs
𝐼𝑑 =1
2𝜇𝐶′
𝑂𝑋
𝑊
𝐿(𝑉𝐺𝑆 − 𝑉𝑇)2=
1
2𝜇𝐶′
𝑂𝑋
𝑊
𝐿𝑉𝑜𝑑
2
Transconductance vs. f
Gate Voltage
Dra
in C
urr
ent
Vgs
Ids
Id +
+ id
Frequency AC
Dra
in C
urr
ent
Am
plit
ud
e
id = gmvgs
4
Transit time 5
Carrier velocity
V
Carrier transit time
Frequency AC
Dra
in C
urr
ent
Am
plit
ud
e
id = gmvgs
Cut-off Frequency
fcut-off
L = 10 µm µ = 1 cm2/Vs fcut-off ≈ 400 kHz @10V ≈ 2 MHz @50V
𝑣 = 𝜇𝐸 = 𝜇𝑉
𝐿
102
103
104
105
106
107
10-5
10-4
10-3
10-2
10-1
T/R_T10L05S
T/R_T10L10S
T/R_T10L20S
T/R_T10L40S
T/R_T10L80S
T/R
Frequency
- +
L (μm) Fsat (Hz)
5 2M
10 600k
20 200k
40 40k
80 10k
L (μm) 5 10 20 40 80
Gm 2.7 1.31 0.76 0.36 0.21
Measurement of fcut-off 6
[μA/V]
80 µm
40 µm 20 µm 10 µm
5 µm
Effect of Capacitances
icgd
icgs
Cgs,o Cgd,o
2πfCgdvgs
Measured i’d
id’= id-icgd=gmvgs-j2πfCgdvgs
id
i’d
7
Frequency of Transition fT 8
M. Caironi et al., Semicond. Sci. Technol. 26 (2011) 034006
icgd
icgs
id
i’d icg
2πfCgdvgs
2πfCgvgs
fT
Frequency of Transition fT 9
M. Caironi et al., Semicond. Sci. Technol. 26 (2011) 034006 F. Ante et al., Small 8 (2012) 73
Ideal (no overlap):
Real (overlap):
Lov
fT for all printed OFET
L= 46 µm, W = 1180 µm, dielectric thickness = 700 nm, Vg = Vd = 40 V
Cgs = 2.3 pF - Cgd = 3.8 pF
S. Mandal et al., Organic Electronics 20 (2015) 132-141
Challenges towards printed high-speed circuits
(4) Small Overlap Cap. [Cov]
(2) Short Channel Length [L2]
(1) High Mobility (μ]
N
N
OO
O O
C10H21
C8H17
C10H21
C8H17
*
S
S *
- Organic
- Metal Oxide
- Carbon-based
- Printable Si
Self Aligned Printing
Nano-imprinting
EHD Jet printing
50~200 nm
(3) Small Contact Resistance. [Rc]
SH
FF
F
SH
HH
H
SH
CN
Au
-
+
SH
FF
F
SH
HH
H
SH
CN
SH
FF
F
SH
HH
H
SH
CN
Au
-
+
0 -1 -2 -3 -4 -5
0.0
0.1
0.2
0.3
-2 V
-3 V
-4 V
-ID [A
]
VD [V]
VG=-5 V
SAM
(5) High-Capacitance Dielectrics [Ci]
Lov
High fT
K.-J. Baeg, M. Caironi, Y.-Y. Noh, Adv. Mater. 2013, DOI: 10.1002/adma201205361
11
Organic Semiconductors Mobility
Mario Caironi
7 October 2013
H. Klauk, Chem. Soc. Rev. 39 (2010) 2643
2013
4 cm2/Vs
10 cm2/Vs
12
Effect of Pre-aggregation 13
200µm
200µm
mesitylene toluene
DCB
CN:CF
THF
Teb: 164.7 °CDielectric constant; 2.4Dipole moment: 0.047 D
Teb: 111 °CDielectric constant: 2.38Dipole moment: 0.31 D
Teb: 181 °Cdielectric constant: 9.93 Dipole moment: 2.14 D
CN: Teb: 259 °CDielectric constant: 5Dipole moment: 1.55 D
Teb: 66 °Cdielectric constant: 7.58 Dipole moment: 1.75 D
CF: Teb: 61.2 °CDielectric constant: 4.8Dipole moment: 1.04 D
bad solvent
good solvent
mesitylene toluene
DCB
CN:CF
THF
Teb: 164.7 °CDielectric constant; 2.4Dipole moment: 0.047 D
Teb: 111 °CDielectric constant: 2.38Dipole moment: 0.31 D
Teb: 181 °Cdielectric constant: 9.93 Dipole moment: 2.14 D
CN: Teb: 259 °CDielectric constant: 5Dipole moment: 1.55 D
Teb: 66 °Cdielectric constant: 7.58 Dipole moment: 1.75 D
CF: Teb: 61.2 °CDielectric constant: 4.8Dipole moment: 1.04 D
bad solvent
good solvent
mesitylene toluene
DCB
CN:CF
THF
Teb: 164.7 °CDielectric constant; 2.4Dipole moment: 0.047 D
Teb: 111 °CDielectric constant: 2.38Dipole moment: 0.31 D
Teb: 181 °Cdielectric constant: 9.93 Dipole moment: 2.14 D
CN: Teb: 259 °CDielectric constant: 5Dipole moment: 1.55 D
Teb: 66 °Cdielectric constant: 7.58 Dipole moment: 1.75 D
CF: Teb: 61.2 °CDielectric constant: 4.8Dipole moment: 1.04 D
bad solvent
good solvent
Deg
ree o
f p
re-a
gg
reg
ati
on
in
so
luti
on
A. Luzio et al. Scientific Reports 3 (2013) 3425
Film formation (spin-coating) 14
1 m
0.1 g/l
2.5 – 3.0 nm
Film formation (spin-coating) 15
0.5 g/l
1 m
0.0 0.2 0.4 0.6 0.8 1.0
012345 0.5 g/l
X (m)
Y (n
m)
0.0 0.2 0.4 0.6 0.8 1.0
012345 0.8 g/l
X (m)
Y (n
m)
Film formation (spin-coating) 16
0.8 g/l
1 m
0.0 0.2 0.4 0.6 0.8 1.00123456
Y (n
m)
X (m)
1 g/l
Film formation (spin-coating) 17
1.0 g/l
1 m
Bucella et al., Nature Communications, 6 (2015) 8394
mesitylene toluene DCB CN:CF
0.01
0.1
1
saturation @Vg=50 V
linear
[cm
2V
-1s
-1]
-10 0 10 20 30 40 5010
-7
10-6
10-5
10-4
10-3
10-2
10-1
100
101
µ sat
µ lin
[ c
m2V
-1s
-1 ]
Vg [ V ]
toluene
DCB
CN:CF
OFETs characterization 18
A. Luzio et al. Scientific Reports 3 (2013) 3425
200µm
200µm
Macro-aligned nano-fibrils 19
1 m 1 m
Solvent: mesitylene Coating Speed: 3 min/min
0.5 g/l 5 g/l
Sub-monolayer 2.4 - 2.5 nm
Thin film 10 nm
Macro-aligned nano-fibrils 20
1 m
sou
rce
dra
in
sou
rce
dra
in
MHz Fast-coated OFETs 21
Non optimized architecture for
frequency operation!
L = 5 m
Bucella et al., Nature Communications, 6 (2015) 8394
@40V
Printing
Techniques Viscosity [Pas]
Thickness
[µm]
Feature
Size [µm]
Throughput
[m2/s]
Registration
[µm] Features
Flexography 0.05-0.5 0.04-2.5 80 3-30 <200 Inexpensive plate pattern, high throughput,
thick layer / low viscosity ink
Gravure 0.01-0.2 < 0.1–8 75 3-60 >20 Fast printing, high resolution, relatively high
plate cost, low dot gain
Offset 5-100 0.5–2 10–50 3–30 >10 High quality, high throughput,
need for ink additives
Screen 0.5-50 0.015-
100 20–100 2–3 >25
Robust, simple, thick layer, large feature size,
high ink viscosity, slow speed
Inkjet 0.001-0.04 0.01-20 20–50 0.01–0.5 5–20 Non-contact, small ink quantities, digital
printing, low viscosity ink, slow speed
Printing Techniques Patterning Resolution
22
Ink-jet printing of narrow linewidths
Adv. Mater. 20 (2008) 343
40 μm linewidth 5 μm linewidth
Adv. Funct. Mater. 18 (2008) 1031
Nanotechnology 18 (2007) 345202
1-2 μm linewidth
Nat. Mater. 6 (2007) 782
High resolution e-jet
1 μm linewidth
23
PEDOT:PSS PEDOT:PSS
L: critical feature is “self-defined”
Self-Aligned Printing (SAP)
50m50m
1st
2nd
C.W. Sele et al., Adv. Mat. 17 (2005) 997
24
Single-droplet Contacts 25
1st
2
nd
1st Electrode
2nd Electrode
1
2
2nd Electrode
1st Electrode
37 μm
Single droplet
Drying Time of Ink is a Critical Factor
60 s 240 s 300 s
310 s 320 s
340 s
330 s
sintered
(a) (b) (c)
(d) (e) (f)
(g) (h)
50 μm
Extra force exerted by evaporation of the solvent Reliable dewetting, tolerant to surface defects Process window >> 10 μm
26
27
● 100% yield possible ● Very low leakage, < 2 pA at 10 V ● Breakdown voltage > 2 MVcm-1
Caironi et al., ACS Nano 4 (2010) 1452
leakage
High Yield Electrodes Array
Fully Solution Processed SAP-FET
Au source
Au drain
Ag gate
500μm
Caironi et al., A
CS
Nano 4
(2010)
1452
28
100X objective
Power = 2 mW
λ = 515nm
250 fs, 500 kHz
Direct-writing of submicron channels 29
Ag
Ag-inks
1
2
745 nm
S. Bucella et al., Organic Electronics, 14 (2013) 2249
Effect of Contact Resistance 30
Rule of Thumb for µapp
Natali, Caironi, Adv. Mater. 24 (2012) 1357
31
𝐼𝑟𝑒𝑎𝑙 = 𝐼0
𝑅𝐶ℎ
𝑅𝐶ℎ + 𝑅𝐶
𝐿𝑀𝐼𝑁 → 𝑅𝐶 = 𝑅𝐶ℎ
Laser-ablated Semi-transparent electrodes 32
λ = 1030 nm 50X, 20 mW
1.5 µm
PEDOT:PSS
Gate
Source Drain
0 5 10 15 200
1
2
3
4
5
6
7V
G ( V )
0
5
10
15
20
I DS (
µA
)
VDS
( V ) 0 5 10 15 20
0.0
0.1
0.2
0.3
0.4
0.5 VG ( V )
0
5
10
15
20
I DS (
µA
)
VDS
( V )
PEI μsat ~ 10-2 cm2/Vs μsat ~ 0.1-0.2 cm2/Vs
Geometry • W = 60 μm
• L = 1.5 μm Y. Zhou et al, Science 336 (2012) 327
Doping as a way to control injection and
uni-/ambi-polar transport
CsF F4TCNQ
33
Effect of Doping 34
High Supply Voltage 35
~ 500 nm
Low-k polymer dielectrics εr = 2 - 3
𝐶′𝑂𝑋 =
𝜀
𝑑≈ 5
𝑛𝐹
𝑐𝑚2
Forcing the use of gate voltages ≥ 40 V
Low Voltage OFETs with Hybrid Nanodielectrics 36
30 nm
10 nm
D
G
S
Al2O3
substrate
PMMAsemiconductor
A. Luzio, et al. Adv. Funct. Mater. 24 (2014) 1790
Printable dielectrics
Issue with downscaling 38
' (saturation regime)
GS GS
Dm OX od
GS v V
di Wg C V
dv L
𝑔𝑚 ∝ 𝐶′𝑂𝑋
𝑉𝑜𝑑 = 𝑐𝑜𝑛𝑠𝑡
𝐶𝑂𝑉 = 𝐶′𝑂𝑋
𝑥𝑂𝑉𝑊 ∝ 𝐶′𝑂𝑋
2πfCgvgs
fT
How to reduce Overlap Capacitance:
1. Split Gate
Jun Takeya et al., Adv. Mater. 2014 DOI: 10.1002/adma.201304976
RC !!
39
Split gate via lithograpyhy
Jun Takeya et al., Adv. Mater. 2014 DOI: 10.1002/adma.201304976
40
How to reduce Overlap Capacitance:
2. Self-Aligned Gate
Y.Y.Noh et al, Nat. Nanotechnol. 2 (2007) 784-789
41
fT of solution processed OFETs 42
Y.Y.Noh et al, Nat. Nanotechnol. 2 (2007) 784
Self-Aligned Printed 100 - 500 nm gaps
OFET fT: record values
SCALABLE PRINTING and DIRECT-WRITING
Our work
43
f T [MHz]
L [m] x OV [m] 1 cm2/Vs 5 cm2/Vs 10 cm2/Vs
2 2 9.58 47.9 95.8
1 2 22.8 114 228
1 1 38.3 192 383
0.5 1 91.3 457 913
0.5 0.5 153 767 1533
Perspective? Polymers
1985 1990 1995 2000 2005 2010 201510
-6
10-5
10-4
10-3
10-2
10-1
100
101
102
Best
Rep
ort
ed
Mo
bil
ity [
cm
2/V
s]
Year
Polymer Semiconductors
P-type (holes)
N-type (electrons)6 cm2/Vs
25 cm2/Vs
44
March 2015
Thank you for
your kind
attention
45
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