Printed Flexible Organic Transistors with Tunable Aspect Ratios

Abstract

film transistor show device performance reaching that of amorphous Si and solution-processed metal oxides. This high performance makes SOCs p-type OTFTs a strong candidate for several future complementary metal-oxide semiconductor applications. [13][14][15] Modulation of scale ratio of devices in a large array is one of the important parameters that governs circuit design. While most printing techniques can provide faster fabrication processes, the rapid on-demand modulation of W/L scale ratio in large array of devices remains as a challenge and a topic to investigate; especially for the myriad of specified circuit designs and application requirements. For instance, the tuning of the gain in each stage of an amplifier [16][17][18] or logic circuits [5] requires the modulation of OTFT W/L ratio. These configuration changes can be challenging, costly, and time consuming for common electrode printing techniques, such as screen printing and gravure printing. [19][20][21][22] These conventional mask-based approaches utilize a fixed pattern transfer that requires a full re-design for every new device structure. [21,23,24] Inkjet printing on the other hand is a nonimpact digital prototyping method that provides instant change of patterns. [25,26] This elimination of mask can reduce the processing costs especially for larger-scale production. [27] However, throughput of inkjet printing can become a limiting factor, especially when depositing over large area. [28] Interdigitated source and drain structure have been used in previous reports as a method to modify W/L ratio for a specific circuit design. [17,[29][30][31] The channel width (W) is modulated by changing the finger count. Meanwhile, channel length (L) is the smallest space between source and drain electrodes, and the resolution is associated to the printing technique. Low switching speed is one of the drawbacks of printed OTFTs compared to conventional Si technology, which can result from a number of factors such as mobility, dielectric layer thickness, and channel length. Achieving channel lengths smaller than 10 µm while maintaining high device yield is very challenging with printing techniques, especially for low-viscosity inks. The solution found to overcome this challenge is to utilize a combination of patterning techniques including the combination of conventional photolithography and direct-write printing techniques. [32] In parallel, there has been an interest to develop methods to decrease the source and drain electrode geometry and channel length using many printing methods. Interdigitated source and drain (SD) electrodes are typically used in electronics to increase channel width while maintaining small channel lengths, resulting in higher W/L ratios. There are few reports on printed interdigitated A fabrication technique that allows aspect ratio modulation in a large array of organic thin film transistors (OTFTs) is demonstrated. In this design, discrete interdigitated source and drain electrodes can be individually selected to create a range of aspe...

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