Electric lamp and discharge devices – Cathode ray tube – Ray generating or control
Reexamination Certificate
1999-03-04
2001-05-22
Day, Michael H. (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Ray generating or control
C313S447000
Reexamination Certificate
active
06236154
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an electron tube provided with a cathode structure for emitting electrons, which is arranged on a support.
The electron tube can be used as a display tube or a camera tube but may also be embodied so as to be used for electrolithographic applications or electron microscopy.
An electron tube of the above-mentioned type is shown in U.S. Pat. No. 5,444,328. In a so-called “cold cathode”, a pn junction is operated in reverse bias in such a manner that avalanche multiplication of charge carriers occurs. In this process, electrons may receive sufficient energy to exceed the work function potential. The emission of the electrons is further enhanced by the presence of a work function potential-reducing material, in particular cesium.
The use of cesium as the work function potential-reducing material often causes problems. For example, cesium is sensitive to the presence (in the operating environment) of oxidizing gases (such as water vapor, oxygen, CO
2
). In addition, cesium has a high vapor pressure so that it vaporizes readily. Dissipation of the cathode causes the cesium to be lost as a result of an increase in temperature. In addition, ESD (Electron Stimulated Desorption) occurs; the electrons emitted by the cathode induce desorption of the cesium, in particular from slightly oxidized surfaces. This loss of cesium causes the electron-emission coefficient of the cathode to decrease during its life-time, resulting in a substantial reduction of said life-time.
OBJECT AND SUMMARY OF THE INVENTION
The invention aims, inter alia, at solving one or more of the above problems.
To achieve this, an electron tube in accordance with the invention is characterized in that a cesium source is situated in a space between the support and a grid electrode, which cesium source comprises an alloy of one or more of the combinations cesium-gold, cesium-antimony or cesium-gold-antimony.
Preferably, the cesium source is situated in the space between the support and the grid electrode opposite said support.
The source is obtained by providing (in the vicinity of the cathode structure) for example a layer of gold or antimony. The gold-cesium (antimony-cesium) alloy is obtained during the manufacture of the electron tube, in that a primary cesium source, for example a cesium-chromate dispenser, provides the cathode structure with the necessary cesium. The cesium atomized by this source also deposits elsewhere and combines with the gold (antimony) to form a cesium-gold-compound (antimony-gold-compound). The cesium delivery by the source thus obtained takes place by evaporation; if this occurs at a temperature which is substantially equal to that of the cathode, sufficient dispensation takes place. In this case, the cesium source does not have to be provided with heating means.
The supply of cesium by means of the cesium-chromate dispenser preferably takes place only in the production stage because it requires a high heating temperature involving high currents which, for use during the service life, lead to an unacceptable energy consumption for the consumer.
To obtain an accurate delivery of cesium, preferably, the cesium source is provided as a thin layer on the side of a grid electrode facing the cathode structure, which grid electrode is situated opposite the support.
To ensure the cesium supply for a sufficiently long period of time, the thickness of the layer ranges between 0.1 &mgr;m and 10 &mgr;m. The cesium source has a maximum diameter of 10 mm, and preferably 2 mm, to bring about an accurate delivery and efficient absorption of the cesium in the source.
Accelerated delivery of cesium also takes place in the case of excessive heating. Thus, to regulate the delivery, if necessary, the compound or alloy is at least partly surrounded by a layer which is practically impenetrable to cesium, such as platinum.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.
REFERENCES:
patent: 4460831 (1984-07-01), Oettinger et al.
patent: 4874987 (1989-10-01), Van Der Eijk et al.
patent: 4970392 (1990-11-01), Oettinger et al.
patent: 5444328 (1995-08-01), Van Zutphen
patent: 5898269 (1999-04-01), Baum et al.
patent: 5932966 (1999-08-01), Schneider et al.
Gehring Frederik C
Kroon Ron
Van Zutphen Tom
Day Michael H.
U.S. Philips Corporation
LandOfFree
Electron tube with a cesium source does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electron tube with a cesium source, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electron tube with a cesium source will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2459126