Organic field effect transistors (PDF) - LTI

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2 Νοε 2013 (πριν από 3 χρόνια και 9 μήνες)

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∙ Organic transistors
Material taken from:
H. Sirringhaus (PlasticLogic)
A. Dodabalapur (U of Texas, Austin)
...why bother..the very first transistor in 1947 was mainly organic!
polystyrene
Transistor history
The MOS-capacitor
The MOS-capacitor
a) Accumulation:holes are accumulated near the interface
b) depletion of holes away from interface
c) moderate inversion,change fromp-type to n-type
-a positive bias induces an n-type inversion layer near the interfaces and
creates a conducting channel between the two n
+
-doped contact regions
The standard MOS-FET
The standard MOS-FET
a) moderate V
D
: channel reaches fromS to D,
transconductance is proportional to drain voltage
b) high V
D
: channel is pinched off, saturation of current
The standard MOS-FET: IV-characteristics
Organic transistors are thin film transistors:
No depletion region, they are off
due to the low conductivity of the thin film material
- they operate in the accumulation instead of inversion regime
- contacts are directly to the channel and should be Ohmic
Organic transistors as thin film transistors
Thin Film Transistor structures suitable for use with organic
materials.
(a) is a bottom contact device,
(b) is a top contact device and
(c) is generally known as a top gate structure. The metallic contacts in
(c) can be either below the polymer (as shown) or on top of the
polymer.
SiO
2
Polymer
-mobility µ can be
extracted from data!
 
 
2
2
d i g T d
d i g T
W
I µC V V V
L
W
I µC V V
L
 
 
 
 
2
2
d i g T d
d i g T
W
I µC V V V
L
W
I µC V V
L
 
 
-switching speed for e.g. charging a capacitor is
dtermined by the current and thus by the mobility
-polymer electronics research is a race for small
channel length and high mobilities
- the other important parameter for
applications is the on/off ratio (world
records are >10
8
).
-different materials than for light emitting devices
are investigated because we do not need light
Challenges for organic FET researchers
surface
energy
patterning
conducting
polymer
is inkjet
printed
to form S
and D
semicon-
ducting
polymer
is inkjet
printed
spincoating
of dieletric
layer
spin
coating of
gate
electrode
RF-ID-tag:
-reader: produces RF-electromagnetic field
-transponder: absorbs energy and rectifies
-produces DC-voltage for operation
-tag contains code generator
-only kbit/s are needed
-rf-signal is sent back to reader
-disposable electronics (rf-ID tags), smart cards
-price has to be lower than 0.02 $ per tag
- market: 2 bn $ in 2006 (Frost & Sullivan)
Appl. Phys.Lett. 73, 108 (1998)
-via holes (between different
-transistors) created
with a needle
- gives mechanical programmability
Organic field effect transistors
...that is really plastic electronics!
f=45 kHz
ring oscillator by Philips
-in 2002: 64-bit code, 48 programmable bits
700 transistors, 2.5 µm design rules, 3.2x2 mm
2
Transistor Chemical Sensors
V
g
=-50V
V
g
=0V
Odor
insulator
semiconductor
drain
source
gate
-50
-25
0
I
d,on
(

A)
20
10
0
time (sec)
-60
-30
I
d,off
(nA)
Semiconductor/Odor

Odors in end - groups
perturb core,change

.

Immobile charges will
shift V
T
.

Grain boundaries
dominate transport.

Odors in grain
boundaries will change

.
Water - based sensing: Biosensing
Si (G)
coating
semiconductor
insulator
S
D
D
pipette
water
S D
1mm
W
L
pipette
a
b
Next and last lecture:
11 Feb 2004 !