1. Field of the Invention
This invention relates generally to field emission devices, and more particularly, to field emission devices with at least one internal structure that includes fiducials to optically align the faceplate and the backplate, and at least one internal structure that fixes and constrains the faceplate and backplate to align a plurality of phosphor pixels with corresponding field emitters.
2. Description of the Related Art
This application cross-references U.S. patent application Ser. Nos. 08/343,803, now allowed, and 08/343,074, now allowed, both assigned to the same assignee. Field emission devices include a faceplate, a backplate and connecting walls around the periphery of the faceplate and backplate, forming a sealed vacuum envelope. Generally in field emission devices, the envelope is held at vacuum pressure, which in the case of CRT displays is about 1.times.10.sup.-7 torr or less. The interior surface of the faceplate is coated with light emissive elements, such as phosphor or phosphor patterns, which define an active region of the display. Cathodes, (field emitters) located adjacent to the backplate, are excited to release electrons which are accelerated toward the phosphor on the faceplate, striking the phosphor, and causing the phosphor to emit light seen by the viewer at the exterior of the faceplate. Emitted electrons for each of the sets of the cathodes are intended to strike only certain targeted phosphors. There is generally a one-to-one correspondence between each emitter and a phosphor.
Flat panel displays are used in applications where the form-factor of a flat display is required. These applications are typically where there are weight constraints and the space available for installation is limited, such as in aircraft or portable computers.
A certain level of color purity and contrast are needed in field emission devices. Contrast is the difference between dark and bright areas. The higher the contrast, the better. The parameters of resolution, color-purity and contrast in a flat cathodeluminescent display depend on the precise communication of a selected electron emitter with its corresponding phosphor pixels. Additionally, high picture brightness (lumens) requires either high power consumption or high phosphor efficiency (lumens/watt).
High power consumption in many applications is not desirable. Efficiency for many phosphors increases as the operating anode voltage increases; and the required operating brightness can be achieved with lower power consumption at high voltage, as illustrated in FIG. 1. In order to satisfactorily operate at high anode voltages, e.g., 4 kV or higher, the backplate containing the emitter array must be spatially separated from the faceplate, containing the phosphor pixels, by a distance sufficient to prevent unwanted electrical events between the two. This distance, depending on the quality of the vacuum and the topography of the substrates, is typically greater than about 2 mm.
With the constraints of faceplate and backplate glass area and thickness, the vacuum envelope is unable to withstand 1 atmosphere or greater external pressure without inclusion of the spacer walls. If the spacer walls are not included then the faceplate and backplate can collapse. In rectangular displays, having greater than approximately a 1 inch diagonal, the faceplate and backplate are particularly susceptible to this type of mechanical failure due to their high aspect ratio, which is defined as the larger dimension of the display divided by the thickness of the faceplate or backplate. The use of spacer walls in the interior of the field emission device substantially eliminates this mechanical failure.
The use of spacer walls has been reported in U.S. Pat. Nos. 4,900,981; 5,170,100; EPO 464 938 A1; EPO 436 997 A1; EPO 580 244 A1; and EPO 496 450 A1.
The faceplates and backplates for the desired flat, light portable display are typically about 1 mm thick. To avoid seeing the spacer walls at the exterior of the faceplate, the spacer walls should be hidden behind a suitable structure such as a black matrix.
Additionally, flat panel displays to date and standard CRT's have high-temperature assembly requirements, including but not limited to plasma addressed liquid crystal (PALC), and the like, where the alignment during assembly consists of external, mechanical alignment of the faceplate and the backplate so that the correspondence of the phosphor pixels and the associated cathode emitters are initially within tolerance. These external fixturing devices travel with the field emission display through the required high temperature bonding and sealing processes. External fixturing devices have difficulties in maintaining a high precision of alignment because of differences in the coefficient of thermal expansion between the field emission display and the fixturing. Resulting misalignment gives a loss of color purity and resolution in the field emission display. Another disadvantage of external tooling is the cost of individual fixture tooling for each field emission display during the sealing and thermal processing of the displays.
It would be desirable to provide a field emission display which does not use external fixturing devices in the high temperature bonding and sealing processes. There is a need for a field emission display that includes fiducials to optically align the faceplate and the backplate, and at least one internal structure that fixes and constrains the faceplate and the backplate in order to align a plurality of phosphor pixels with corresponding field emitters.