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Organic transistors
 

Organic transistors

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  • Intermolecular interactions are weak - Electronic bandwidths are small Prone to disorder and localization Many organic materials are extremely sensitive to oxygen and moisture
  • Radio Frequency Identification Devices, or RFID, on Tags are used for item-level tracking of individual consumer goods. Such tags are expected to dramatically improve the automation, inventory control and checkout operations of products.
  • Using Nano devices researchers intend to replace the cumbersome UPC barcode that is found on many products and replace it with one of these tags. Scientists are currently working on this technology to apply it to mass checkout at supermarkets, but have several minor obstacles that still must be overcome. Two of these obstacles are that each individual tag must cost less than one cent, and each RFID must function in the presence of substantial amounts of metal and radio frequency absorbing fluids. Vacuum Sublimation has allowed for excellent performance using small-molecule organic materials, resulting in circuits operating at several megahertz. Each nano-device will consist of 96 bits of information, but may contain more, such as 128 bits. The operating range for low cost devices will be limited by the power delivery from the reader to each tag. This makes the lower frequencies more appealing because they are better for power coupling. Thus, 13.54MHz looks like the most attractive frequency, however researchers are also considering the frequency at the 900Mhz range also plausible.
  • Conventional solar cells are made out of silicon. Organic Solar cells are made out of photoactive polymers in which when the light shines on it the polymer goes to the excitement state. What researchers at New Jersey IT have done is that they have used Fullerene as the backbone of Carbon nanotubes to generate electricity out of solar energy. SWNT: Single Wall Nano Tube The way it works is that the light falls on to the polymer it generates an electron and a hole. The electron is captured by the bucky ball. But it can not conduct electricity but the nanotube can do the job very well. The efficiency is still not very good compare to silicon, but the advantage as we talked about is the cost! This is a very low cost fabricated device.
  • Smart Textiles: Interactive textiles or so-called smart fabric products are reaching the market for healthcare/medical, public safety, military, and sporting applications. These products will be designed to monitor the wearer's physical well being and vital signs such as heart rate, temperature, and caloric consumption, among many others. Smart fabrics are driven by technological improvements and increasing reliance on MEM’s based integrated sensors. Development of flexible displays comprised of OLED technologies will be integrated into clothing solutions, providing the ability to view information in real-time via wireless communications. Skin Cancer Treatment: team of researchers in Scotland has demonstrated in a pilot study that OLEDs may one day change the way photodynamic therapy (PDT) is used to treat skin cancer. In addition to the treatment of skin cancers, the researchers believe the technology could also be used in the cosmetic industry for anti-aging treatments or skin conditions such as acne. 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) 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
  • Technology developed in 1990 by Cambridge University in the UK • Spin off into a private company: Cambridge Display Technology (CDT) • P-OLEDs allow the solution of organic material in liquid -Production process can be spin coating or Ink Jet printing - inexpensive and easy to industrialize • Flexible supports (plastic) possible - more options than glass only • Still lag behind SM-OLEDs in picture quality • The technology has been licensed to a variety of companies including Philips, Seiko, Epson and OSRAM .

Organic transistors Organic transistors Presentation Transcript

  • Seminar VSD 539 M.Sc. [Engg.] in VLSI System Design Module Title: Nano electronicsORGANIC TRANSISTORS M. S. Ramaiah School of Advanced Studies 1
  • Contents• Why Organic?• Advantages• Disadvantages• Organic Field Effect Transistors• Current-Voltage characteristics• Applications• Future of Organic transistors M. S. Ramaiah School of Advanced Studies 2
  • 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. M. S. Ramaiah School of Advanced Studies 3
  • 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 M. S. Ramaiah School of Advanced Studies 4
  • Organic vs. Silicon Organic Electronic Silicon Cost $5 / ft2 $100 / ft2Fabrication 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 M. S. Ramaiah School of Advanced Studies 5
  • 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) M. S. Ramaiah School of Advanced Studies 6
  • 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. M. S. Ramaiah School of Advanced Studies 7
  • Organic Field-Effect Transistors (OFETs) Structure of an Organic Thin Film Transistorconducting channel +source semiconductor drain ⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕ insulator ID – – – – – – – – – – – – – – – – – – - gate VD VG M. S. Ramaiah School of Advanced Studies 8 By G. Horowitz
  • Current – Voltage characteristicsTransfer 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 gateelectrode, and the other one by the semiconductor film. When a voltage V g isapplied between source and gate, majority carriers accumulate at the insulator-semiconductor interface, leading to the formation of a conduction channelbetween source and drain.  A potential signal Vg is transformed in a current signal Id M. S. Ramaiah School of Advanced Studies 9
  • 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 mobilityDrain 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 M. S. Ramaiah School of Advanced Studies 10
  • 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 VgDrain 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 M. S. Ramaiah School of Advanced Studies 11
  • 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 M. S. Ramaiah School of Advanced Studies 12
  • Applications• Displays: – (OLED) Organic Light Emitting Diodes• RFID : – Organic Nano-Radio Frequency Identification Devices• Solar cells M. S. Ramaiah School of Advanced Studies 13
  • 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 M. S. Ramaiah School of Advanced Studies 14
  • RFID• Passive RF Devices that talk to the outside world … so there will be no need for scanners. M. S. Ramaiah School of Advanced Studies 15
  • RFID benefits• Quicker Checkout• Improved Inventory Control• Reduced Waste• Efficient flow of goods from manufacturer to consumer M. S. Ramaiah School of Advanced Studies 16
  • Solar cells • The light falls on the polymer • Electron/hole is generated • The electron is captured C60 • The electricity is passed by the nanotubeM. S. Ramaiah School of Advanced Studies 17
  • Future of Organic Semiconductora• Smart Textiles• Lab on a chip• Portable compact screens• Skin Cancer treatment M. S. Ramaiah School of Advanced Studies 18
  • 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… M. S. Ramaiah School of Advanced Studies 19
  • 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 M. S. Ramaiah School of Advanced Studies 20
  • 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 M. S. Ramaiah School of Advanced Studies 21
  • Thank YouM. S. Ramaiah School of Advanced Studies 22