Transparent transistors

Norris, B. J. Anderson, J. Wager, J. F. Keszler, D. A. 2003. Spin-coated zinc oxide transparent transistors. J. Phys. D.Appl. Phys. 36 L105-L107. 

Boyd, I Moore, S. K. 2005. Transparent transistors. IEEE Spectrum March 2005 18-19. 

By 1988, a number of devices such as a MOSFET transistor had been developed by the use of poly(acetylene) (Burroughes et al. 1988), but further advances in the following decade led to field-effect transistors and, most notably, to the exploitation of electroluminescence in polymer devices, mentioned in Friend s 1994 survey but much more fully described in a later, particularly clear paper (Friend et al. 1999). The polymeric light-emitting diodes (LEDs) described here consist in essence of a polymer film between two electrodes, one of them transparent, with careful control of the interfaces between polymer and electrodes (which are coated with appropriate films). PPV is the polymer of choice. 

The TFTs are made on transparent glass substrates, onto which gate electrodes are patterned. Typically, the gate electrode is made of chromium. This substrate is introduced in a PECVD reactor, in which silane and ammonia are used for plasma deposition of SiN as the gate material. After subsequent deposition of the a-Si H active layer and the heavily doped n-type a-Si H for the contacts, the devices are taken out of the reactor. Cr contacts are evaporated on top of the structure. The transistor channel is then defined by etching away the top metal and n-type a-Si H. Special care must be taken in that the etchant used for the n-type a-Si H also etches the intrinsic a-Si H. Finally the top passivation SiN, is deposited in a separate run. This passivation layer is needed to protect the TFT during additional processing steps. 

The low-melting-point (157 °C), silver metal is mainly used in alloys to decrease the melting point. Combined with tin, lead, and bismuth to produce soldering metal for wide temperature ranges. The element is highly valuable in the electronics age as its unique properties are ideal for solar cells, optoelectronics, and microwave equipment. The arsenide is used in lasers and is also suitable for transistors. ITO (indium tin oxide) is a transparent semiconductor with wide application in displays, touchscreens, etc. In the household, indium as an additive prevents the tarnishing of silverware. Some electronic wristwatches contain indium batteries. 

Nomura, K. Ohta, H. Ueda, K. Kamiya, T. Hirano, M. Hosono, H. 2003. Thin-film transistor fabricated in single-crystalline transparent oxide semiconductor. Science 300 1269-1273. 

Wang, L. Yoon, M-H. Lu, G. Yang, Yu Facchetti, A. Marks, T. J. 2006. High-performance transparent inorganic-organic hybrid thin-film n-type transistors. Nat. Mater. 5 893-900. 

Cao, Q. et al. 2006. Highly bendable, transparent thin-film transistors that use carbon-nanotube-based conductors and semiconductors with elastomeric dielectrics. Adv. Mater. 18 304-309. 

It is interesting to note that Mauguin had discovered the TN LC cell in 1911. Commercialization of this device did not occur for some 75 years, but since then, with the development of thin-film transistor arrays, transparent... 

Polythiophenes (PTs)/CNTs composites have emerged as an intriguing system for use as photovoltaic devices and field effect transistors [57]. Swager and Bao independently reported methods for the assembling of PTs/CNTs systems and showed their great potential as transparent conductive films [58]. Another interesting application arises from the possibility to functionalize the polythiophene backbone for applications as chemical sensors [134]. 

Recently, field-effect transistors based on zinc oxide were reported [173,174], opening the opportunity to design microelectronic devices that are transparent and/or work at high temperatures [175]. More details on thin film transistors employing transparent conducting oxides are given in Chap. 2. 

Fig. 2.19. (a) Scheme of a transparent field effect transistor based on ZnO [191]. The gate electrode consists of tin-doped indium oxide (ITO) and the gate dielectric is a multilayer of AECE/TiCE (ATO). (b) Output characteristics (drain-source current as a function of the drain-source voltage) for different gate voltages. The saturation current is about 530 rA at a gate bias of 40 V. From this output characteristics a threshold voltage of 19 V and a field-effect mobility of 27 cm2 V-1 s-1 were calculated [192]... 

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