JPS6025859B2 - cold electron emitting cathode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A cold electron emitting cathode can be obtained by activating the surface of a P-type layer in a PN junction semiconductor with cesium and oxygen to give it negative electron affinity.

For example, when such an electron-emitting cathode is used as a source of a scanning electron beam for an image pickup tube, an insulating layer is inserted between the P-type layer and the N-type layer or between the N-type layer and the N-type substrate. Then, microscopic electron passage holes are provided in the insulating layer. However, when such a hole is provided, electrons are concentrated in the hole from a wide range in the N-type semiconductor substrate, so that the electron density in the green portion of the hole becomes high. In addition, since electron emission holes are formed in the electrode provided on the surface of the P-type layer so as to face the holes, electrons injected into the center of the P-type layer are emitted toward the edges of the electrode. The electrons move in a direction parallel to the plane, and the electron density in the green part of the hole becomes even higher. Therefore, the secondary cathode has the drawback that the density of the electron flow emitted from the surface of the P-type layer into the vacuum is high at the periphery, and is hindered at the center, making it impossible to obtain a uniform density distribution. The present invention seeks to obviate the above-mentioned drawbacks. FIG. 1 is a cross-sectional view of a cold electron emitting cathode according to an embodiment of the present invention, in which an ohmic contact metal thin film 2 is provided on the back surface of an N-type silicon semiconductor substrate 1, and a circular part is left in the center on the surface. A P-type semiconductor layer 4 having a circular hole 3 is formed by diffusing appropriate impurities into the portion. An N-type silicon semiconductor layer 5 is formed on the surface of such a semiconductor.
is epitaxially grown, and then N-type impurities are implanted into the portion facing the hole 3 by ion implantation. Second
The curve Q in Figure a shows the density distribution of impurities implanted by this ion implantation method, and the distance from the point C on an arbitrary straight line passing through the center point C of the hole 3 is expressed as In addition, the position of the green part of hole 3 is set as ±, and the density of the implanted impurity Q is plotted on the vertical axis. That is, the density of the N-type impurity is made high in the center of the hole 3 and becomes lower toward the periphery. Further, a P-type epitaxial semiconductor layer 6 is further grown on the above-mentioned N-type epitaxial semiconductor layer 5, and an ohmic contact metal thin film 8 having holes 7 opposite to the holes 3 is coated on the surface of the P-type epitaxial semiconductor layer 6. It's worn. Such a semiconductor device is housed in a vacuum container, and an anode 9 is placed in the hole 7.
are arranged opposite to each other, and cesium and oxygen are adsorbed and activated on the surface of the P-type layer 6 exposed through the hole 7, thereby forming an electron emitting surface having a negative electron affinity. A power source 10 is connected between the metal thin films 2 and 8 to apply a directional voltage to the PN junction formed between the N-type epitaxial semiconductor layer 5 and the P-type epitaxial semiconductor layer 6, and the power source 11 connects the anode to the PN junction. Appropriate eating pressure is applied to 9.
In the above device, since a forward voltage is applied to the PN junction formed by the N-type layer 5 and the P-type layer 6, the P-type epitaxial layer 6 is transferred from the N-type substrate 1 through the N-type epitaxial layer 5. Electron injection takes place.

Moreover, the P-type layer 4 acts as an insulating layer, and can also be used as an insulating film. Therefore, a wide range of N-type substrates 1
The electrons are concentrated in the hole 3, and the P-type epitaxial 6
The electrons injected into the anode 9 are captured by the anode 9, which is emitted from the surface with negative electron affinity into the vacuum as shown by the arrow in FIG. In this case, electrons flowing into the N-type layer 5 from the N-type substrate 1 are concentrated in the hole 3 from a wide range, so that the electron density at the edge portion is higher than that at the center, and the electrons are injected into the P-type layer 6. The electrons diffuse toward the surface and at the same time are pulled by the green electrode of the hole 7 and move from the center to the periphery. However, as described above, in the N-type epitaxial layer 5, the impurity concentration is high in the center and decreases toward the periphery.
The electrical resistance is lower at the periphery and higher at the periphery. Therefore, the density of the electron flow injected from the N-type layer 5 to the P-type layer 6 is high at the center of the hole 3 and low at the periphery. Therefore, the above-mentioned two effects cancel each other out, and the distribution of electron density becomes almost uniform on the surface of the P-type layer 6. Therefore, the distribution of the density i of the electron current emitted into the vacuum becomes As shown by the curve q in Figure b, it can be made almost uniform regardless of the distance x. Furthermore, if the impurity concentration distribution in the N-type layer 5 is further increased at the center as shown by the curve R in Figure 2a, the electron flow distribution becomes gradually lower toward the periphery as shown by the curve r in Figure 2b. . To give an example, when the impurity concentration of the substrate 1 is 1 and 6/base, the impurity concentration Q of the curve Q is 1 and 8/base when x is 0, and 1 and 7/base when x is ±,
At this time, the radius is ±0. Pine. Electron emission occurs at a substantially uniform density within a range of degrees. Also the second
The impurity concentration of curve R in figure a is 5 x 1 p8 when x is 0.
In this case, as shown in the curve r, the electron emission density is maximum when x is 0, and the point with half the density is ± It is about 0.7 gods. In the conventional cathode, the impurity concentration of the N-type epitaxial layer was uniform as shown by the broken line S in Figure 2a, so the emitted electron current distribution was centered at the center as shown by the broken line s in Figure 2b. This was the lowest in the region. As described above with respect to the embodiments, the cold electron emitting cathode of the present invention can obtain an electron flow with uniform density in each part or with a high density in the central part.

Therefore, when used as a source of an electron beam for scanning a brazed image tube, the diameter of the beam is effectively reduced, improving resolution and reducing afterimages.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of an embodiment of the present invention, and FIG. 2 is a diagram illustrating the action of the cathode in FIG. 1. In the figure, 1 is an N-type semiconductor substrate, 2 and 8 are metal thin films, 3 and 7 are holes, 4 is a P-type layer, 5 is an N-type epitaxial semiconductor layer, 6 is a P-type epitaxial semiconductor layer, and 9 is a P-type epitaxial semiconductor layer. It is an anode. Shio/Kameji no Kaze

Claims (1)

[Claims] 1 Insulating layer with a hole in the center and N in the hole area
type semiconductor layer is formed on an N-type semiconductor substrate, and the impurity concentration in the N-type semiconductor layer gradually increases from the edge of the hole toward the center, and electrons are emitted to the surface of the N-type semiconductor layer. A cold electron emitting cathode characterized in that a P-type semiconductor layer is provided to form a PN junction.