FIREBIRD: Fully Integrated Bidirectional Infrared Displays

The recent development of the Apple iPhone, Microsoft's multi-user touch table and other similar devices has shown that there is a real demand for electronic devices that do not rely on keyboards or mice to allow interaction, but which work by directly touching a display. There is also a drive towards greater energy efficiency, particularly in mobile devices, and in this regard, displays based on organic light emitting diode (OLED) technology have a clear advantage over the incumbant liquid crystal display (LCD) technology.The FIREBIRD project aims to integrate a multi-touch surface diretly with an OLED display. The multi-touch surface will be realised by optical means. Infrared OLED emitters will be arranged in a matrix over the display and coupled with an array of organic photodetectors (OPDs). Objects in close proximity to the display surface will reflect the infrared light from the emitters back onto the sensors to allow detection. A key advantage of this technology is that it can also be used to recognise patterned surfaces, and so could also be used for document scanning, for example.Three key elements are required to enable the development of the FIREBIRD multi-touch display: the OLED emitters and OPD sensors, an active matrix backplane for driving the emitters and sensors and a controller with software. The main role of Cambridge University Engineering Department (CUED) within this project will be to develop the backplane technology and to collaborate with the other partners in system integration. In order to drive the various devices that will be locted at each display pixel (display element, infrared emitter and sensor) the backplane electronics will need to have good peformance characteristics. Hydrogenated amorphous silicon (a-Si:H) has been dominant as the material of choice for large area electronics (including active matrix liquid crystal displays). However, it suffers from poor device stability and poor electron mobility. Zinc oxide is an optically transparent semiconducting material that can be alloyed with other materials to give excellent electonic properties. Indeed, thin film transistor (TFT) devices based on reactive magnetron sputtered amorphous indium zinc oxide (a-IZO) have been demonstrated at CUED with field effect mobilities ~10 cm^2/(V.s) - an order of magnitude improvement over a-Si:H. This has been enabled by a project on ZnO TFTs (HiPZOT) that has been funded through the EPSRC-funded 'Cambridge Integrated knowledge Centre for Advanced Manufacturing Technologies for Photonics and Electronics' (CIKC) in collaboration with UK-based Plasma Quest Ltd. (PQL). In this project, the platform ZnO technology that has been developed through the HiPZOT project will be applied to this new application area. This will require careful device development to ensure that the requirements of the multi-touch display backplane area realised. In particular, fully transparent TFTs can be produced using the ZnO technology, which would have particular advantages for integration with the display element. However, it is recognised that the ZnO technology is at a relatively early stae of development, and therefore a-Si:H will also be developed to ensure the success of the project, although this will lead to reduced performance of the final device and would not permit the fabrication of fully-transparent devices.