The document discusses organic transistors, including their advantages over inorganic transistors like being lighter, more flexible, and less expensive to produce. However, organic transistors also have disadvantages like higher resistance and shorter lifetimes. The document describes the structure and characteristics of organic field effect transistors. Potential applications discussed include displays using organic light emitting diodes and RFID tags. The future of organic transistors is also briefly mentioned.

1. Seminar
VSD 539
M.Sc. [Engg.] in VLSI System Design
Module Title: Nano electronics
ORGANIC TRANSISTORS
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2. Contents
• Why Organic?
• Advantages
• Disadvantages
• Organic Field Effect Transistors
• Current-Voltage characteristics
• Applications
• Future of Organic transistors
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3. Why Organic?
• Organic electronics are lighter, more flexible, and less
expensive than their inorganic counterparts.
• They are also biodegradable (being made from carbon).
• This opens the door to many exciting and advanced new
applications that would be impossible using copper or silicon.
• However, conductive polymers have high resistance and
therefore are not good conductors of electricity.
• In many cases they also have shorter lifetimes and are much
more dependant on stable environment conditions than
inorganic electronics would be.
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4. Inorganic vs. Organic
• Organic electronics, or plastic electronics, is the branch of
electronics that deals with conductive polymers, which are
carbon based.
• Inorganic electronics, on the other hand, relies on inorganic
conductors like copper or silicon.
Silicon sample
Carbon sample
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5. Organic vs. Silicon
Organic Electronic Silicon
Cost $5 / ft2 $100 / ft2
Fabrication Cost Low Capital $1-$10 billion
Device Size 10 ft x Roll to Roll < 1m2
Material Flexible Plastic Rigid Glass or Metal
Substrate
Required Ultra Cleanroom
Conditions Ambient Processing
Multi-step
Process Continuous Direct Photolithography
Printing
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6. Advantages of Organic
• Organic electronics are lighter, more flexible
• Low-Cost Electronics
– No vacuum processing
– No lithography (printing)
– Low-cost substrates (plastic, paper, even cloth…)
– Direct integration on package (lower insertion
costs)
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7. Disadvantages of Organic
• Conductive polymers have high resistance and
therefore are not good conductors of electricity.
• Because of poor electronic behavior (lower mobility),
they have much smaller bandwidths.
• Shorter lifetimes and are much more dependant on
stable environment conditions than inorganic
electronics would be.
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8. Organic Field-Effect Transistors (OFETs)
Structure of an Organic Thin Film Transistor
conducting channel
+
source semiconductor drain
⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕
insulator ID
– – – – – – – – – – – – – – – – – –
- gate VD
VG
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By G. Horowitz

9. Current – Voltage characteristics
Transfer characteristic
10-5
10-6 ON = conduction channel open
Drain current (A)
10-7 The charge in the channel is
10-8 modulated by adjusting Vg, so that
Vd=-25 V
the device behaves as a variable
10-9
resistance.
10-10
10-11 OFF = No conduction channel
10-12
-20 0 20 40 60 80 100
Gate voltage (V)
A FET is basically a capacitor, where one plate is constituted by the gate
electrode, and the other one by the semiconductor film. When a voltage V g is
applied between source and gate, majority carriers accumulate at the insulator-
semiconductor interface, leading to the formation of a conduction channel
between source and drain.
 A potential signal Vg is transformed in a current signal Id
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10. Output characteristic
Linear regime:
For a given Vg>0, the current provided by the conduction channel increases with Vd. The
drain electrode inject the charge carriers passing through the channel, the channel let pass as
many charges the drain electrode injects.
Vg controls the doping level N in the conduction channel: large Vg → large current Id
-5 10-6 W and L= channel width and length
0V Ci= capacitance of the insulator layer
-4 10-6 -20 V Vg
μ = field-effect mobility
Drain current (A)
-40 V
-6
-3 10 -60 V
-80 V VT= threshold voltage (accounts for
-2 10-6 voltage drops of various origin across
the insulator-semiconductor interface)
-1 10-6
0 No conduction channel
W
I D = Ci µ (VG − VT )VD
-6
1 10
20 0 -20 -40 -60 -80 -100 -120
Drain voltage (V)
L
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11. Saturation regime
For a given Vg, when Vd=Vg, the electrical potential between drain and gate is zero. This
destroys the capacitor created between the doped channel and the gate : pinch off. The
channel is then interrupted close to the drain.
-6
-5 10
0V Saturation
-4 10-6 -20 V Vg
Drain current (A)
-40 V
W
-6
-3 10 -60 V
= Ci µ (VG − VT )
-80 V 2
-2 10
-6 I D , sat
-6
2L
-1 10
0
1 10-6
20 0 -20 -40 -60 -80 -100 -120
Drain voltage (V)
Output characteristic
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12. How to get the field effect mobility?
1) If Vd small, the charge is nearly constant over the channel and the drain current is :
Z=channel width
Z
Linear I D = Ci µ (VG − VT )VD
L
•The channel conductance gd can be expanded to first order:
2) A further step of the method consists of
introducing a contact series resistance
Rs, which leads to
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13. Applications
• Displays:
– (OLED) Organic Light Emitting Diodes
• RFID :
– Organic Nano-Radio Frequency Identification
Devices
• Solar cells
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14. Displays (OLED)
• One of the biggest applications of organic
transistors right now.
Organic TFTs may be used to drive LCDs and
potentially even OLEDs, allowing integration of entire
displays on plastic.
• Brighter displays
• Thinner displays
• More flexible
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15. RFID
• Passive RF Devices that talk to the outside world
… so there will be no need for scanners.
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16. RFID benefits
• Quicker Checkout
• Improved Inventory Control
• Reduced Waste
• Efficient flow of goods from
manufacturer to consumer
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17. Solar cells
• The light falls on the polymer
• Electron/hole is generated
• The electron is captured C60
• The electricity is passed by the
nanotube
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18. Future of Organic Semiconductora
• Smart Textiles
• Lab on a chip
• Portable compact screens
• Skin Cancer treatment
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19. Smart Textiles
• Integrates electronic
devices into textiles, like
clothing
• Made possible because of
low fabrication
temperatures
• Has many potential
uses, including:
• Monitoring heart-rate and
other vital signs,
• controlling embedded
devices (mp3 players),
• keep the time…
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20. Lab on a Chip
• A device that incorporates
multiple laboratory functions in
a single chip
• Organic is replacing some Si
fabrication methods:
-Lower cost
-Easier to manufacture
-More flexible
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21. Portable, Compact Screens
• Screens that can roll up into small devices
• Black and White prototype already made by Philips
(the Readius at the bottom-left)
• Color devices will be here eventually
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22. Thank You
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