Inkjet-printed semiconductor

Most of the discussion thus far has focused on thin films produced by spin casting. However, one goal of these composite systems, and the acene blends in particular, is to improve processability during printing, especially inkjet printing. TIPS-pentacene-based OFETs fabricated by inkjet-printed semiconductor have been... 

While these polymeric materials hold promise for low-cost electronics and simplified device processing, they still suffer from lower performance than conventional inorganic semiconductors. As the development of these novel materials continues, an alternative technology incorporating patterning schemes such as inkjet printing and conventional vacuum deposited thin films, may provide the required overlap of performance with low-cost fabrication of microelectronic circuits on large-area platforms. 

The TFT fabrication process on glass substrates starts with 100 nm of Cr for the gate metal, and is followed by a PECVD 200 nm thick Si3N4 dielectric with a 30 nm thick SiC>2 surface layer. The source drain metal is Cr/Au. Each of these layers is patterned using printed wax masks and chemical etching, steps a to d in Fig. 11.8. The surface is modified with a solution deposition of a self-assembled monolayer of octyltrichlorosilane (OTS-8) before inkjet printing deposition of the semiconductor. It has been shown that the OTS-8 layer affects the structural order of PQT-12 in thin films, improving the performance of the TFT [23]. Encapsulation and possibly other subsequent layers may be needed on the TFT, but these are not discussed here. 

The special properties of nanomaterials, such as those currently used as the conductive "pigment" in conductive inkjet inks, will be exploited more and more in advanced second-generation products. New inks will be developed to print additional electronic functionalities such as resistors, capacitors, and semiconductors, thereby enabling inkjet printing of complete electronic components and devices. Inkjet s capability to layer materials and build 3D structures will be further developed for microelectronics applications. These efforts have already been initiated in universities, research institutes, and commercial entities — in the large established ink companies as well as smaller startups financed by joint VC and government funding. 

FIGURE 5.4.5 Process flow for the fabrication of polymer TFTs by inkjet printing. Steps 1 to 4 use a subtractive process for patterning of materials. The subtractive process prints an etch mask on a previously deposited film. Step 5 illustrates the additive inkjet printing process. The additive process simultaneously deposits and patterns the semiconductor material PQT-... 

Wood Vanessa, Panzer J. Matthew, Chen Jianglong, et al. Inkjet-printed quantum dot-polymer composites for full-color AC-driven displays. Adv. Mater. 21 no. 21 (2009) 2151-2155. Yamazoe Nohoru. New approaches for improving semiconductor gas sensors. Sens. Actual. B. 5 no. 1-4 (1991) 7-19. 

A serious consequence of polymer crystallization in solution is gel formation, which is a severe issue regarding, for example, inkjet printing of polymeric semiconductors because gelation dramatically shortens the lifetime of electronic inks. The gelation mechanism has been intensively studied by Nandi and coworkers, who describe the gel formation of P3HT as a two-step process [58,59]. In phase 1, single isolated chains undergo a coil-to-rod transformation, and phase 11 involves the... 

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