Micropoint type cold cathode

Details Micropoint type cold cathode Micropoint type cold cathode

1998-07-09

2001-07-10

Patel, Ashok (Department: 2879)

Electric lamp and discharge devices

Discharge devices having a multipointed or serrated edge...

C313S336000, C313S351000, C313S495000, C313S308000

Reexamination Certificate

active

06259190

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention concerns a micropoint type cold cathode.
In particular, the invention applies to mass spectrometers in which the heated electrical filament emitting electrons is replaced by a micropoint type cold cathode. Cold cathodes of this type are electron emitting devices manufactured using semiconductor processes.
2. Description of the Prior Art
Unfortunately cold cathodes of the above type offer poor performance, only around 10% of the points of an array of micropoints emitting electrons. This is due to the non-homogeneous nature of the array of points which is caused, among other things, by manufacturing tolerances.
Because the points are non-homogeneous, the electric field at the end of a point varies greatly from one point to another. Electron emission as a function of the electric field at the end of the point obeys an exponential law. The resulting non-homogeneous emission is disadvantageous and the disadvantage is increased for operation at “high pressure”, for example at a pressure equal to or greater than 10
−4
mbar. If one point emits more electrons than its neighbors it is more sensitive to the phenomena of positive ion return and arcing which damage the points.
An aim of the present invention is therefore to propose a micropoint type cold cathode which improves the homogeneity of electron emission from the micropoints.
SUMMARY OF THE INVENTION
The invention therefore consists of a micropoint type cold cathode comprising a substrate including an array of micropoints and a plate disposed parallel to the substrate carrying the points, the plate including a hole facing each point and thereby constituting a grid, an insulator filling the space between the substrate and the grid except at the location of the points, wherein the nominal distance between the summit of a point and the face of the grid farthest from the substrate is zero, the nominal radius of curvature at the summit of each point is 25 nm and the nominal radius of the holes in the grid is 1.3 &mgr;m.
Experiments show that some parameters are very important in the geometry of a cold cathode, in particular the following parameters: the distance
d
between the summit of a point and the face of the grid farthest from the substrate, the radius of curvature RT at the summit of the point and the radius R
GH
Of the holes in the grid facing each point.
A nominal value has been found for these three parameters for which the total drift of the field value at the ends of the points relative to the three parameters
d
, R
T
and R
GH
is minimal and therefore corresponds to a value of the field at the end of the points having minimal dispersion.
These conditions yield an optimized array, i.e. an array for which the electric field at the end of the points varies only slightly, within the manufacturing tolerances, around the nominal value of these parameters. These nominal values are as follows: d=0, R
T
=25 nm and R
GH
=1.3 &mgr;m.
The result is that an array is obtained having a high number of points that emit in the same fashion, three or four times greater than in a non-optimized array.


REFERENCES:
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Patent Abstracts of Japan. vol. 095; No. 004, May 31, 1995 corresponding to JP 07 029484 A (Futaba Corp) Jan. 31, 1995.
C. A. Spindt et al. “Physical Properties of Thin-Film Field Emission Cathodes with Molybdenum Cones”, Dec. 1, 1976, Journal of Applied Physics, vol. 47, Nr. 12, pp. 5248-5263 XP000560520.

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