Development of a low cost custom touch screen
studenten: 1 of 2
Begeleider 1: Ahmed Gamal
Trefwoorden: touch screen, screenprinten, aerosoljet, capacitive, resistive, display
Passive displays for personal mobile devices have been progressively replaced by touchscreens since they enable the user to interact directly with what is displayed, rather than using a mouse, touchpad, keypads, or any other intermediate device. A touchscreen can be controlled by the user through simple or multi-touch gestures by touching the screen with a special stylus/pen and-or one or more fingers. The popularity of smartphones, tablets, and many types of information appliances have mainly been driving the demand and acceptance of common touchscreens but are also found in the medical field and in heavy industry, as well as for automated teller machines (ATMs), and kiosks such as museum displays or room automation.
The most straightforward way of localized sensing of touch are either resistive or capacitive. In both cases, two conductive layers are needed, separated by an insulating layer. This layer stack has to be as optically transparent as possible in order to allow the backlighting of the touch screen to be undistorted from the displays users perspective. Indium Tin Oxide or short ITO is a well established transparent conductive material for displays for a long time, but it is a rather expensive material, needs to be deposited in vacuum and needs a postdeposition patterning technique like photolithography to structure it. Lately, new materials are developed or are under development in order to tackle these material drawbacks. PEDOT and nano Ag-inks have proven to be good alternative candidates which are less costly and can be additively patterned, e.g. by printing.
Quad Industries is an industrial player in the field of printed electronics and is evaluating different lowcost techniques to make custom touch screens. Commercially available touch screens are typically rectangular and have often too high specs related to the demands of custom control panels, often only needing several randomly positioned touch areas. In order to create custom touch panel areas, Quad Ind. Wants to look further into printing of PEDOT and Ag-inks but sees limitations of standard screenprinting to deposit and pattern these materials: the deposition thickness of screenprinted structures is quite thick, which implicates reduced transparency.
A high potential candidate solution for this problem is the use of an aerosoljet printer: a device which transforms the material into airborn solid nanoparticles which are directed and focused onto the substrate. The result is a direct deposition of the material according to a software based design. The deposited features are much thinner compared to screen printing and due to the focusing much smaller. Both are advantageous for the touch screens visual quality.
Goals of the thesis
This thesis will be performed in cooperation with Quad Industries. During the thesis, the candidate will develop an aerosoljetprinting process for new transparent conductive materials like PEDOT and nanoparticle Ag-inks. The deposition of these materials from an aerosol state to a solid state on the substrate will be investigated by perfoming experiments on the new state-of-the-art aerosoljet printer in the cleanrooms of CMST. After optimalisation of the deposition process, touch screen lay-out schemes can be designed and fabricated by aerosoljet printing the conductive material layers in the cleanrooms at CMST and screenprinting and lamination of the other layers at Quad Ind. Finally the prototypes will be characterized and evaluated.
This thesis is mainly technology driven and focusses on the fabrication processes rather than on the electronics around the touch screen pad for read-out and driving the device.
Locatie: Ardoyen (clean rooms), Quad Industries and from home.