JPH0653377A - Diode - Google Patents

Abstract

PURPOSE:To enhance the insulation between an external lead-out wire of a diode and a semiconductor substrate by covering the side of the semiconductor substrate of the lower part of a metal foil drawn to the outside of the diode with an insulating film. CONSTITUTION:A mesa 10 is formed by performing a mesa etching in the side of a semiconductor substrate 1 of the lower part of a metal foil 6. The distance between the metal foil 6 and the semiconductor substrate 1 due to the mesa 10 is increased and thereby the insulation is enhanced. Particularly, at least the side of the semiconductor substrate 1 of the lower part of the metal foil 6 is covered with an insulating film 11. A substance in which, for example, a material in which a silicon oxide film is dissolved with a solvent is applied to the side of the semiconductor substrate 1 and materials such as insulating film, polyimide film, glass layer formed by a thermal treatment are formed in a single layer or a plurality of layers is used as the insulating film 11. Thus, since the insulating film 11 between the semiconductor substrate 1 and the metal foil 6 is formed, the insulation is enhanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used as a blocking diode or a bypass diode for protecting a solar cell in a solar cell, particularly a solar cell used as a power source for an artificial satellite or a space station operating in outer space. The present invention relates to improvement of a diode.

[0002]

2. Description of the Related Art In an artificial satellite or a space station operating in outer space, a so-called solar cell panel is used as a power source, in which a plurality of solar cells are connected and pasted on the panel. The demand for electric power is increasing with the increase in functionality and size of artificial satellites, and accordingly, there is a demand for size increase of solar cell panels. However, the launch rocket is limited in capacity and launch weight, and it is desired that the solar panel be small and lightweight at the time of launch. Diodes are connected to the solar cell panel to protect the solar cell.

Conventionally, this diode has been attached to the back of a solar cell panel or the main body of an artificial satellite, but the solar cell panel was folded when the artificial satellite was launched.
As it has been deployed in outer space, the panel itself has become thinner and smaller, and the diode itself has been developed to have the same thickness as the solar cell. This thin diode uses a semiconductor substrate as a diode substrate, and one of its electrodes has a metal attached to the back surface of the semiconductor substrate.
The other electrode has a metal foil as a terminal.

FIG. 2 is a schematic cross-sectional view of an example of a conventional thin diode. For example, a P-type semiconductor substrate 1
Is made of a silicon single crystal having a size of 2 cm × 2 cm and a thickness of 0.1 to 0.5 mm. The size of one side of the semiconductor substrate 1 may be about 1 cm to 10 cm. An N type diffusion layer 3 is formed on the surface of the semiconductor substrate 1, and a PN junction 9 is formed between the semiconductor substrate 1 and the semiconductor substrate 1 to function as a diode. The surface is covered with an oxide film 2 such as SiO ₂ . The metal foil 6 is attached to the electrode 4 of the N type diffusion layer 3 by welding or soldering and is drawn out as a terminal. A metal film is provided on the back surface of the semiconductor substrate 1 to form the electrodes 5. To improve heat dissipation in outer space, to prevent sunlight from entering the semiconductor substrate, and to reduce leakage current in the reverse direction of the diode due to photocurrent, the surface is reflected by an aluminum plate or mirror. Layer 8 is attached by adhesive 7. The semiconductor substrate 1 and the metal foil 6 are insulated by the oxide film 2 and the adhesive 7.

The metal foil 6 and the semiconductor substrate 1 need to be insulated, and if the insulation between them is broken, they will not function as a diode. Therefore, it has been considered that the semiconductor substrate 1 is subjected to mesa etching in order to strengthen the insulation to improve the insulation of the portion where the metal foil 6 is in contact with the semiconductor substrate 1.

FIG. 3 is a schematic cross-sectional view of an example thereof, in which a mesa 10 is provided on the side of the semiconductor substrate 1 below the metal foil 6 by mesa etching. The mesa 10 increases the distance between the metal foil 6 and the semiconductor substrate 1 and strengthens the insulation.

[0007]

In the case of the conventional structure, there is a possibility that dust or the like will adhere between the semiconductor substrate 1 and the metal foil 6 to make them conductive.

[0008]

In the present invention, at least the side surface of the semiconductor substrate below the metal foil is covered with an insulating film.

[0009]

Since the metal foil and the semiconductor substrate are covered with the insulating film, they are not electrically connected to each other.

[0010]

1 is a schematic sectional view of an embodiment of the present invention. The difference from the conventional example shown in FIG. 3 is that at least the side surface of the semiconductor substrate 1 below the metal foil 6 is covered with the insulating film 11. The insulating film 11 is, for example, an insulating film formed by coating a side surface of a solution of a silicon oxide film with a solvent and performing a heat treatment, or a polyimide film formed by applying a polyimide varnish and performing a heat treatment, or A glass layer or the like formed by heat-fusing powder glass by electric fusion and forming a single layer or multiple layers is used.

In FIG. 1, the mesa 10 is formed by mesa etching, but since the insulating film 11 is provided, the insulating effect of the side surface portion is enhanced without the mesa. Of course, by using the mesa 10 together, the insulation is further strengthened.

As a method for forming this insulating film with a uniform thickness, for example, a material to be applied is spin-coated on a plate having a flat surface, and the material is spread to a uniform thickness.
The semiconductor substrate of the diode can be placed on top of it and the material can be transferred to the side.

[0013]

According to the present invention, the semiconductor substrate 1 and the metal foil 6 are
Since the insulating film 11 is provided between and, the insulation is strengthened.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view of an example of a conventional diode.

FIG. 3 is a schematic cross-sectional view of another example of a conventional diode.

[Explanation of symbols]

 1 Semiconductor Substrate 2 Oxide Film 3 Diffusion Layer 4, 5 Electrode 6 Metal Foil 7 Adhesive 8 Reflective Layer 9 PN Junction 10 Mesa 11 Insulating Film

Claims (1)

[Claims] 1. A second conductive film is formed on the surface of a semiconductor substrate of the first conductivity type.
2. A diode characterized in that a conductive type diffusion layer is formed, an electrode is provided on each surface, and at least a side surface of the semiconductor substrate on the side having the external lead wire is covered with an insulating film.