Nicolaas Lambert

Modes in electron-hopping transport over insulators sustained by secondary electron emission

A general formalism for hopping electron transport over insulators sustained by secondary electron emission is presented. Steady-state electron transport takes place when the charging of the insulator, which turns out to be self-stabilizing, is such that the average secondary electron yield becomes equal to unity. The steady-state potential distribution for the electron transport is determined for various insulating geometries with the aid of Monte Carlo calculations and compared with the low-hopping approximation. The Monte Carlo results show that the steady-state potential distribution can exhibit several interesting features such as spontaneous symmetry breaking of statistical origin and the occurrence of local repulsive parts in the geometry. In several cases the numerical results, including the above two features, are found to agree well with the results of experiments.

Basics of electron transport over insulators

Abstract The basic mechanism of electron transport in vacuum through insulating structures is discussed. The transport is based on a self-regulating secondary electron emission process. A general description of the transport process is presented. Three methods to model steady-state transport are briefly reviewed. The features are discussed in the light of application in displays. Also, non-steady-state effects and the role of space charge are addressed.

Construction and physical processing of Zeus panels

Abstract The construction of a Zeus panel is discussed. This type of panel has a relatively simple self-aligned construction with a limited number of different components. Due to the low number of connections, rather robust connectors can be used. The complete physical processing cycle, very important for this type of panel, can be as short as 3 h which is shorter than the processing of a standard CRT.

Monte Carlo calculations of the electron hop transport in various parts of a Zeus display

Abstract Electron transport over insulators sustained by secondary electron emission is studied using Monte Carlo calculations. With the aid of these Monte Carlo calculations, the steady-state potential distribution and the properties of the electron trajectories in various insulating structures are determined. Each of these structures represents a part of the Zeus display and together the results show how electrons, generated by the cathode, enter the transport channels and are transported through the Zeus display until they reach the phosphor screen. In the various cases, the results according to the Monte Carlo calculations agree well with the results of experiments.

Performance of Zeus displays

Abstract It is shown that the overall performance of Zeus displays is quite good, as illustrated by photographs of operating panels displaying ‘CRT-quality’ TV pictures. Results of measurements of all relevant performance parameters are presented, as well as an analysis of these data in relation to the design and operation of the displays. Measurements of the luminance as a function of the screen current density and of the screen voltage of Zeus displays are reported. A white D65 luminance of 1000 Cd/m2 is obtained at a screen voltage of 4.5 kV and a screen current density of about 9 μA/cm2. The luminous efficacy of the phosphor screen in the panels is found to be 12 lm/W (in the absence of saturation) for white D65. The efficacy of a 17″ Zeus panel (including transport power dissipation, cathode heating power and addressing power) is about 4 lm/W. The factors determining the internal contrast and colour purity of Zeus panels are discussed. Experiments to determine the relevant contrast parameters are described as well as the results of direct measurements of the internal contrast, colour purity and colour selectivity. Internal contrast values of more than 1000 have been obtained, and a colour selectivity better than 700. The available colour gamut is close to that of CRTs. Preliminary measurements of the external contrast of 17″ panels with a black matrix and front glass with 50% optical transmission yield a contrast value of 60 at an ambient light level of 100 lux. The factors determining the picture uniformity in Zeus displays are discussed. Several panels with good uniformity have been realized. No artefacts associated with moving pictures occur, the only significant artefact is caused by charge transfer effects. The visibility of this effect can be sufficiently reduced by using suitable ‘flush’ pulses and by optimizing the geometry. The displays used for the performance measurements have a quincunx dot arrangement and dot pitches 0.5 × 0.6mm, giving PAL resolution on 28″ panels. Small experimental panels with pitches of 0.3 × 0.5 mm and 0.25 × 0.30 mm have been realized and operate satisfactorily. The viewing angle of Zeus displays is close to 180 degrees. Preliminary tests show that lifetimes well over 10,000 h are possible if the glass surfaces hit by electrons are covered with an MgO coating and if the blue phosphor is coated with a very thin calcium polyphosphate layer.

Transport and extraction in Zeus displays

Abstract In a Zeus display hopping electrons are transported through channels with extraction holes. If a sufficient transport field is applied, the electrons hop low and leakage through the holes is negligible. The electrons can be extracted from the channel by applying a positive voltage pulse to an extraction electrode. With sufficient pulse amplitude the extraction efficiency is 100 %, independent of small variations in material properties, which enables the creation of uniform images. Experiments on a model transport channel confirm the mechanisms behind transport and extraction.

Selection system of Zeus displays

Abstract Although in a Zeus display a straightforward matrix addressing system can be constructed from just vertical electron-transport channels and horizontal row extraction electrodes, there are many unique advantages in adding extra selection plates. These are, e.g. cost reduction by a trade-off between electronics complexity and panel complexity, enhancement of internal contrast and, by choosing wider channels, reduction of transport voltage and improvement of triode performance. Several implications for the system design are discussed. Some subtle effects in the physics of selection switches are explained together with design rules for the selection plate geometry that avoid the associated image artefacts.

Dynamical behavior of electron hop transport over insulating surfaces

The dynamical behavior of electron hop transport over insulators is studied. The electron hop transport is based on a self-stabilizing secondary electron emission process. It is reported that, in the steady state, the electron–current propagation is governed by a diffusion equation. Analytical calculations and Monte Carlo simulations of this type of electron propagation are presented. In particular, the effect of the backscattering process on the hop transport properties is investigated. Finally, the results are qualitatively compared with the results of experiments.

Triodes for Zeus displays

Abstract Power considerations lead to the choice of wire cathodes for the supply of current to the channels in a Zeus display panel. Each channel has its own triode, modulated by a separate G1 grid. Cathodes and other electrodes are in common use. The design of the triode is guided by the need for low modulation voltages, somewhat at the cost of mechanical tolerances and emission stability. The result is an integrated triode section that can supply 200 μA per triode, which is sufficient for a 40″ display, at 15 V modulation voltage. A dynamic control system ensures emission uniformity over all channels.

A new thin CRT

A description of the principles, the operation, the underlying physics, the technology, system aspects, and the performance of a new flat thin CRT, as invented and realized in the Philips Research Laboratories, is given. The panel operation is based on controlled electron (hop) transport in vacuum through insulating structures, enabling the use of mechanical supports inside the envelope to withstand the atmospheric pressure. The resulting flat panel has a thickness of about 1 cm for any panel size, a relatively low mass, and a reduced number of outside connections. The hop-transport process is based on a self-regulating secondary-emission process. This process involves charge deposition by electrons landing on insulating surfaces. These modify the potential distribution until a steady state is reached in which exactly one electron leaves the surface for each electron impinging on the insulator. This process is used throughout the panel to guide the electrons from the cathodes to the addressed dots at the phosphor screen. The techniques and the processes used for making the panels are described. These include a refined powder-blast process for three-dimensional structuring of thin glass plates, a wet-chemical process for realizing metal tracks on glass plates, and a low-cost process for depositing thin MgO layers. System aspects concerning the application of the flat panel in TV sets are discussed, and some of the electronic circuitry, including newly developed ICs needed for driving the panel, is described. A two-step addressing system allows the implementation of a novel multiplexing scheme, which leads to a more than three-fold reduction in the number of outside connections. Experimental 17-in, panels show good performance in terms of luminance, contrast, color purity, luminous efficacy, and viewing angle. Picture-uniformity aspects deserve further investigation, but already some good results have been obtained. The same can be said for the lifetime of the panel.