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Field emission backlight

Objective

The project is expected to deliver an experimental 50mm x 50mm x 10mm field emission backlight incorporating a Ta-C emitter, with a high brightness of 20,000 cd/m2. The research work will concentrate on optimising the DLC deposition method, substrate material, nitrogen doping, and on the development of a resistance ballast layer beneath the DLC, to maximise the spatial uniformity and temporal stability while minimising the impact on efficiency. This experimental work will be complemented by theoretical device modelling to improve our understanding of the emission process, and in particular the low effective energy barrier level of typically 0.03 eV derived from Fowler-Nordheim plots. The research is expected to deliver an optimised DLC / resistive layer design, an appropriate deposition process and an improved theoretical understanding of emission mechanisms from Ta-C.

A system approach is adopted for the field emission device development, and therefore the proposed work includes phosphor, spacer and getter development, cell fabrication, electronic drive circuitry design, build and test, and optical characterisation and lifetesting of the device.
DLC has been characterised over a range of deposition parameters and doping levels. The beneficial effect of post-deposition surface treatments was also investigated. The emitter area has been increased from approximately 2cm2 to 36cm2. A theoretical model of the emission mechanism has been developed which explains many of the experimental findings. A resistive layer, capable of withstanding the later fabrication steps, has also been developed.
Due to unforeseen technical difficulties, work was concentrated on triode emission devices. Two approaches to producing triode structures have been investigated - one involving the use of a discrete grid, the other the use of photolithographic techniques. The former has produced the best demonstrator results, though with grid voltages of approximately 2kV. The processing of the latter has proven difficult to control reproducibly. However, triode action at very low grid voltages (approximately 12V) has been demonstrated over small areas. Finite element modelling and experiments have shown the feasibility of significantly reducing the grid voltage in discrete grid devices. A design for a sealed-off device has been formulated and the various processing steps, including frit sealing and guttering, proven.
A novel piezoelectric power supply technology was investigated but shown to be inappropriate for use in the FEDLIT device. An alternative approach using a planar transformer has been developed which meets voltage, efficiency and size requirements. Two versions have been built, suitable for either the discrete grid or thin film structures.
Actual deliverables were:
-Demonstrator produced of reduced technical specification;
-Theoretical model produced and report issued;
-Final project report.
This project is for research into diamond-like carbon (DLC) for use as a broad area electron emitter. There are two important reasons for pursuing this work:

- in the long term, as a first step towards a low cost, large area, field emission display
- in the medium term, to meet the need for a thin, high brightness backlight for LCDs
If successful, the work will enhance the competitiveness of European industry by providing an important technical lead in high performance, low cost field emission backlights and displays. Field emission devices are widely expected to be key technologies for the next generation of information displays.

DLC is an attractive emitter material because high electron currents can be obtained from it at low electric fields. It is a stable material, resistant to erosion and poisoning. It has the advantage over diamond that it can be deposited at room temperature, which means that low temperature glass substrates can be used. However, at present, emission from many types of DLC suffers from problems of spatial uniformity, temporal instability and repeatability. This project will concentrate on a novel form of DLC, tetrahedral amorphous carbon (Ta-C) developed at Cambridge University, using a filtered cathodic vacuum arc (FCVA) process. Ta-C is a form of DLC with a very high proportion of sp3 bonds (up to 75%) and no hydrogen. This gives a greater stability and uniformity of emission than from other forms of DLC, so Ta-C is a potentially much more promising emitter material.

Coordinator

Central Research Laboratories plc
Address
Dawley Road
UB3 1HH Hayes
United Kingdom

Participants (2)

Sextant Avionique
France
Address
Aerodrome De Villacoublay
78141 Velizy-villacoublay
THE CHANCELLOR, MASTERS AND SCHOLARS OF THE UNIVERSITY OF CAMBRIDGE
United Kingdom
Address
Trinity Lane, The Old Schools,
CB2 1TN Cambridge