Thin-film transistor technique

As an example of the latter technique, Volkman et al. demonstrated the feasibility of using spin-cast zinc oxide nanoparticles encapsulated in 1-dodecanethiol to fabricate a functional transistor.44 The zinc oxide was deposited on a thermally grown silicon dioxide layer on a conventional silicon wafer, with thermally evaporated gold source and drain electrodes. As reported, the process requires very small particles (3nm or less) and a 400 °C forming gas anneal. A similar approach was also reported by Petrat, demonstrating n-channel thin-film transistor operation using a nanoparticle solution of zinc oxide dispersed onto a thermally grown silicon dioxide layer on a conventional... 

At this stage, a technique that would enable independent access to the channel and contact resistances is needed. Such a feature is offered by the transfer line method (TLM) [38-41, 89], a method adapted from a classical technique use to estimate contact resistance, and first developed for the amorphous silicon thin-film transistor [42]. The method consists of measuring the channel resistance for different channel lengths. The measured resistance is actually the sum of the channel and contact resistances. As long as the measurement is performed in the linear regime (small drain voltage) the channel resistance is proportional to L (see Eq. 1) and the width-normalized (Rx W) total resistance is given by ... 

M = Tb, Lu) into organic thin-film transistors by LB technique and reported their field effect mobility, which represented the first report for p-type OFETs based on bis(phthalocyaninato) rare earth complexes prepared via LB method [88], Due to the highly ordered molecular arrangement of M(Pc)[Pc(OC8Hi7)g] (M = Tb, Lu) in LB films and the appropriate HOMO energy level of these double-deckers relative to the Au source-drain electrodes, the OFETs reported in that work exhibited higher hole transfer mobility of 1.7 x 10-3 cm2 V-1 s-1 in comparison with those fabricated from monomeric phthalocyanine LB films. 

FIG. 6.1. Schematic diagram of the thin film transistor using an -6T polymer for the active layer [155]. Gold source and drain pads are fabricated using the photolithographic technique. The gate length varied between 2.5 and 150 nm and the width was 250 pm. The polymer (from 2.5 to 150 nm thick) is sublimed over the contacts. 

Kawase et al. [17] fabricated All-polymer thin film transistors by inkjet printing technique. They used these transistors as active-matrix backplane for information displays. This field has been dominated by amorphous Si TFTs and large liquid crystal displays with an amorphous Si TFT active matrix backplane have been manufactured at a reasonable cost. An organic TFT is expected to reduce the cost even more, and to be applied to flexible displays based on a plastic substrate. The TFT characteristics required for active-matrix displays are (1) sufficient drain cmrent, (2) low off current, (3) low gate leakage current through an insulator, (4) small gate overlap capacitance and (5) uniform characteristics. 

An alternative approach to the complicated photoresist systems could be the application of APD (ablative photodecomposition), where a strong absorbance at the irradiation wavelength is one of the conditions for successful ablation. A logical approach to the use of APD as a dry etching technique in microlithography is the development of polymers designed for APD. This is especially true for photolithographic applications that do not require a submicron resolution, such as thin film transistor (TFT) fabrication for liquid crystal displays (LCD) which require a resolution around 1 pm. 

Polymeric semiconductors have many attractive features for thin-film transistor (TFT) fabrication. Solution viscosity can be widely tuned (increased) by (increasing) molecular weight opening up the possibility to formulate solutions compatible with high viscosity printing techniques such as gravure... 

Polycrystalline silicon thin film transistors have also been employed for the detection of DNA hybridization [16]. A mixed self-assembled monolayer of thiolated DNA probes and mercapto-hexanol was immobilized onto the gold gate of an extended gate poly-Si TFT. A shift of the I-V characteristics on the order of 300 mV was obtained upon hybridization of the immobilized probe with a fully complementary strand. The shift is independent of electrode area, so microarrays can be constructed where a known DNA probe is immobilized on each FET. The inherent miniaturization and compatibility with microfabrication technologies make the technique highly promising for the development of low-cost portable devices. 

A common gate flexible thin-film transistor on a PEN film can be fabricated by step and flash imprint lithography [96]. It has been demonstrated that the step and flash imprint lithography is a roll-to-roll compatible and down scalable patterning technique on a flexible PEN foil for the fabrication of flexible high-quality thin film transistors. 

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