JPH04106985A - Photocoupler - Google Patents

Abstract

PURPOSE:To release noise due to a parasitic capacitance between a light emitting side and a photodetecting side to a ground line and to prevent an erroneous operation by shielding a phototransistor by a polysilicon film, and connecting it to a ground lead terminal. CONSTITUTION:An N-type epitaxial layer 22 is formed on a P-type substrate 21, and operated as a collector. It is formed of a P-type base layer 23 formed selectively therein, and an N-type emitter region 24 formed selectively therein. A polysilicon film 13 is formed on the surface through a passivation film 25, and electrically connected to a ground lead terminal 321 via aluminum wirings, bonding wires 33, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an optical coupling device or photocoupler in which a light emitting element and a light receiving element are coupled by light, and more particularly to a general purpose photocoupler using a phototransistor as the light receiving element.

[Conventional technology]

A photocoupler is a device that receives light from an input side, that is, a light emitting element, at an output side, that is, a light receiving element, and transmits a signal.Therefore, it is advantageous and necessary that the input side and output side are completely electrically separated. As shown in FIG. 5, in the conventional photocoupler that meets these conditions, a light emitting diode 51 and a phototransistor 52 are placed on lead terminals 53 at a predetermined distance, and the light emitting diode 51
A transparent silicone resin 5 is placed between the phototransistor 52 and the phototransistor 52.
4 is filled, thereby forming a light path from the light emitting diode to the phototransistor, and as shown in FIG. Both the diode 51 and the phototransistor 52 are first molded with a transparent epoxy resin 64 to form an optical path, and then the outer periphery thereof is molded with a black epoxy resin 55.

Further, as shown in FIG. 8, the phototransistor uses an N type epitaxial region 82 formed on an N type substrate 81 as a collector, and a P wall region 83 selectively formed in the epitaxial region. The base and the N-type region 84 selectively formed within the P-type stirrup region serve as the emitter.

Therefore, since the N-type substrate 81 is electrically connected to the collector, the lead terminal that is connected to the island portion of the lead frame on which the phototransistor is mounted becomes the collector terminal.

In this conventional photocoupler, the only sorting terminals on the light receiving side were the collector terminal, emitter terminal, and base terminal of the phototransistor.

[Invention or problem to be solved]

The conventional photocoupler described above has a structure in which a light emitting diode and a phototransistor are arranged at a predetermined distance, so as shown in FIG. 7, a parasitic capacitance 73 is created between the light emitting side and the light receiving side. Electrical noise generated and entered on the input side is transmitted to the light receiving side through this parasitic capacitance 73, and an equivalent photocurrent flows. This photocurrent is amplified by the transistor, and a collector current multiplied by hFE flows, creating a state as if an input signal had been input, causing malfunction.

Regarding this, when using a photodetector IC in which a photodetector and a subsequent signal processing circuit are monolithically formed on one chip as a photodetector, a transparent conductive film is provided on the photodetector diode, and this is connected to a grounding terminal. This shields the light-receiving part by electrically connecting it to the ground terminal, thereby allowing noise transmitted through the parasitic capacitance to escape to the ground terminal. In this case, since it is an IC, it is necessary to ground the back surface of the light receiving element, so a grounding terminal is provided. However, when a phototransistor is used as a light-receiving element, it does not have a grounding terminal, so even if a shield film is provided on the light-receiving surface, there is no path for noise to escape, resulting in the disadvantage of being affected by the parasitic capacitance. be.

[Means to solve the problem]

The photocoupler of the present invention is provided with a grounding terminal not connected to any of the collector, emitter, and base of the phototransistor on the light-receiving side, and a polysilicon film is attached to at least a part of the light-receiving surface via a passivation film. This is a measure to electrically connect the grounding lead to the grounding lead to release noise transmitted through the parasitic capacitance to the grounding line.

This does not use a conventional N-type substrate with the back surface of the phototransistor as the collector electrode, but instead uses an N-type epitaxial region formed on a P-type substrate as the collector, and selectively injects the N-type epitaxial region into the N-type epitaxial region. The phototransistor has a structure in which the P-type region formed in the P-type region is the base and the f, -N-type region selectively formed in the P-type region is the emitter. This can easily be done by forming a polysilicon film using a polysilicon film, mounting this phototransistor on an island on the extension of the grounding terminal, and electrically connecting the polysilicon film to the grounding terminal using a wire, etc. realizable.

〔Example〕

FIGS. 1, 2, and 3 show an equivalent circuit diagram of a photocoupler according to the present invention, a sectional view of the phototransistor used, and a plan view of the phototransistor after wire bonding. That is, a grounding lead terminal 321 that is not connected to any of the collector, base, and emitter of the phototransistor is provided on the light receiving side, and the phototransistor 12 is mounted on an island portion extending from the grounding lead terminal 321. Further, in this phototransistor 12, as shown in FIG. 2, an N-type epitaxial layer 22 is formed on a P-type substrate 21, and this serves as a collector. It consists of a P type base region 23 selectively formed within the collector and an N type emitter region 24 selectively formed therein. A polysilicon film 13, which is a light-transmitting conductive film, is formed on this surface via a passivation film 25.
It is electrically connected to the grounding lead terminal 321 by etc. In FIG. 2, the aluminum wiring of the phototransistor, the bonding pad, and the bonding wire are omitted.

A photocoupler with such a configuration, as shown in Figure 2,
Since the base region 23, which is the light receiving part, is shielded by the polysilicon film 13, as shown in FIG. There will be no malfunction.

FIG. 4 shows an equivalent circuit diagram of the photocoupler of the second embodiment. This example uses the Darlington phototransistor 42. In this case, the synthesized hFE is large, so it is more susceptible to the influence of noise transmitted through parasitic capacitance, and the effects of the present invention are significant.

〔Effect of the invention〕

As explained above, the present invention shields a phototransistor with a polysilicon film and connects it to a grounding lead terminal that is not connected to any of the collector, base, and emitter. Noise due to capacitance is released to the ground line, which has the effect of preventing the phototransistor from malfunctioning.

[Brief explanation of drawings]

Fig. 1 is an equivalent circuit diagram of the photocoupler according to the present invention, Fig. 2 is a structural diagram of a phototransistor used in the photocoupler according to the present invention, and Fig. 3 is a diagram of the phototransistor used in the photocoupler according to the present invention after wire bonding. FIG. FIG. 4 is an equivalent circuit diagram of a second embodiment of the photocoupler according to the present invention. 5 and 6 show structural cross-sectional views of the photocoupler. FIG. 7 is an equivalent circuit diagram of a conventional photocoupler, and FIG. 8 is a structural diagram of a phototransistor used in the conventional photocoupler. 11.51... Light emitting diode, 124252...
Phototransistor, 14.73... Parasitic capacitance, 13.
・Polysilicon film, 53 ・Lead terminal, 321・
... Grounding lead terminal, 33... Bonding wire, 21... P type substrate, 81... N type substrate, 22.82... N type epitaxial layer,
23.83... P type base, 24.34... N type emitter, 25... Passivation film, 54... Transparent silicon resin, 64... Transparent epoxy resin, 55
...Exterior epoxy resin.

Claims (1)

[Claims] 1. A light-emitting side lead terminal into which an electric signal is input, a light-emitting diode connected to the light-emitting side lead terminal and emitting light in response to the electric signal, and a corresponding electric It consists of a phototransistor that outputs a signal and a plurality of light-receiving lead terminals connected to this phototransistor, and the light-receiving lead terminals are not electrically connected to the emitter, base, and collector parts of the phototransistor. A photocoupler characterized in that it has a grounding lead terminal, and the grounding lead terminal is connected to a transparent conductor provided on a light-receiving surface of a phototransistor. 2. The phototransistor is mounted on an island portion on the extension of the grounding lead terminal, and the phototransistor has an N-type epitaxial region formed on a P-type substrate as a collector, and a transistor selected in the epitaxial region. A P-type region selectively formed in the P-type region is used as a base, an N-type region selectively formed in the P-type region is used as an emitter, and a polysilicon film is further formed on at least a part of the surface with a passivation film interposed therebetween. 2. The photocoupler according to claim 1, wherein the polysilicon film is electrically connected to the grounding lead terminal.