New Processing Methods for Large-Area Electronics: Dissertation

In Large-Area Electronics (LAE) there are multiple processing methods to take advantage of. Components can be produced for example by directly printing patterned layers on top of each other. Most common printing methods are gravure, flexographic, silk screen and inkjet. Electronics done only by such processes suffer from the limitations stated by the printable materials and the process equipment.

This thesis shows some critical LAE processing challenges, and introduces new ways to overcome them. The goal is to use roll-to-roll compatible methods. Some traditional processing techniques are used in a new way. Commercial and prototype materials are used in the testing. The work includes experimental results of printed thin films made with polymer or carbon nanotube semiconductors and either low- or high permittivity dielectrics.

After material selection, the transistor electrode quality and pattern resolution (dimensions) govern the electrical performance. Electrical results of low-voltage (5V) thin film transistors and circuits are reported. This work includes the experimental results of roll-to-roll (R2R) compatible thin metal film patterning methods like etching with a new printable gel etchant, and high resolution laser ablation. Furthermore, a new lamination concept is introduced. Laminating together two separate substrates allows new possible material combinations and new electrode options for both sides of the device.

Finally, these methods are combined in a demonstration device: a tactile sensor matrix is built using air-gap transistors. The transistors are constructed using R2R printed active layers including gel etched electrodes on one foil, and inkjet printed spacers and electrodes on another foil. When foils are laminated together, air-gap transistors are formed, and the flexible structure make the transistors sensitive to tactile input. The shape and sensitivity of such sensor structure is easy to modify for different applications.