Thin film transistor

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A thin film transistor ( English thin-film transistor , short TFT ) is a specific field effect insulated gate transistor (IGFET, also MISFET), can be prepared with the large-scale electronic circuits. It was developed by Paul K. Weimer in the early 1960s at RCA Laboratories.


Scheme of a thin-film transistor in the construction variant "staggered bottom-gate" (stacked with the gate below)
Basic construction variants of thin film transistors

The structure of a thin-film transistor corresponds to the scheme of the well-known metal-oxide-semiconductor field effect transistor (MOSFET), the most commonly used IGFET variant. In addition to the materials typically used, the main differences are in the subsequently applied semiconductor layer and the gate, which is often designed over a large area, that is, the source or drain and the gate are often one above the other.

With regard to the structure, thin-film transistors can be divided into “ bottom-gate ” (dt. Lower gate , also called top-contact , dt. Upper source / drain contacts ) and “ top-gate ” (dt. Upper gate , and bottom-contact , dt. underlying source / drain contacts ) called in "to the other staggered " (dt. stacked ) and " coplanar " (dt. lying in the same plane distinguished). There are four basic variants in the layer structure. The variant shown is a “ staggered bottom-gate TFT ”, ie a “stacked thin-film transistor with a gate below”. In this case, the gate ( bottom gate ) deposited first and the source / drain contacts are separated ( staggered ) by a layer stack made of dielectric and semiconductor . In the opposite variant, the “ coplanar top-gate TFT ”, the gate would have been deposited last (after the source / drain contact, the semiconductor and the dielectric ) and the semiconductor material would only be between the source and drain contact that is, the contacts are in direct contact with the dielectric.

Hydrogenated amorphous silicon (α-Si: H) is mostly used as the active semiconductor . B. can be converted into polycrystalline silicon by means of an excimer laser . Furthermore, are compound semiconductors such as cadmium selenide (CdSe) and transparent metal oxides such as zinc oxide used. Other materials, such as those used in organic field effect transistors , are the subject of current research (status: 2009).


Section through a TFT display. The thin-film transistors are labeled (9) in the lower area.

Widespread use is the orientation of liquid crystal - flat screens , where three transistors are used per pixel. This type of display is known as matrix LCD , but is also often referred to colloquially as a TFT display. Transreflective , TFT-based LCDs , which can also be used outdoors , are often used in PDAs . Similarly, thin-film transistors are also used in screens based on organic light-emitting diodes (OLED).

Web links

Commons : Thin Film Transistors  - collection of images, videos and audio files

Individual evidence

  1. ^ Paul K. Weimer: The TFT A New Thin-Film Transistor . In: Proceedings of the IRE . tape 50 , no. 6 , 1962, pp. 1462-1469 , doi : 10.1109 / JRPROC.1962.288190 .
  2. Patrick Görrn: Transparent electronics for active matrix displays . Cuvillier Verlag, 2008, ISBN 978-3-86727-758-7 , pp. 4 ( limited preview in the Google book search - Diss., Braunschweig, Techn. Univ., 2008).
  3. TP Brody: The thin film transistor - A late flowering bloom . In: IEEE Transactions on Electron Devices . tape 31 , no. 11 , 1984, pp. 1614-1628 , doi : 10.1109 / T-ED.1984.21762 .
  4. ^ David Stauth: OSU Engineers Create World's First Transparent Transistor . College of Engineering, Oregon State University: OSU News & Communication, March 24, 2003, accessed August 15, 2009.