JPS5858819B2 - Hikariketsugo handoutaisouchi - Google Patents

Description

[Detailed Description of the Invention] The present invention includes a light-emitting element and a light-receiving element having a structure of three or more layers, which are incorporated into the same package, and an optical signal is transmitted by the light-emitting element on the input side to the light-receiving element on the output side. This invention relates to improvements in optically coupled semiconductor devices that convert signals.

Since an optically coupled semiconductor device, that is, a photocoupler has a circuit configuration that uses light as a medium, it has many features as described below.

(1) The input side and output side are completely electrically separated.

(2) Since the signal uses light as a medium, noise surge voltages and the like on the output side are not fed back to the input side.

(3) Since it is made of semiconductor, it is highly reliable and has a long life since it is solid.

etc., and it has begun to be used for various purposes as a signal transmission element between IC circuits that are susceptible to noise and power circuits that generate noise and surge voltage.

Hereinafter, for convenience of explanation, a case where the light receiving element is a phototransistor will be described.

Figure 1 shows an example of an applied circuit using such a photocoupler, in which 1 is an AC power supply, 2 is a switch, 3 is a load, 4 is a thyristor, 5 is a transistor, 6 is a phototransistor, and 7 is a light emitting diode, and the phototransistor 6 and the light emitting diode 7 form a photocoupler 8.

9 elements 11 is a resistor, 12 is a switch, 13 is a transformer,
14 is a single-phase full-wave rectifier, and 18 is a diode.

The operation of this circuit is that when the switch 2 is turned on, a DC voltage is created by the transformer 13 and the single-phase full-wave rectifier 14.
When the switch 12 is turned on, current flows through the light emitting diode 7, causing it to emit light.

Therefore, the phototransistor 6 receives this light and becomes conductive, bypassing the current flowing to the base circuit of the transistor 5.
The transistor 5 is made non-conductive, and current is passed through the resistor 10 to the gate of the thyristor 4 to turn on the thyristor 4.

As a result, current flows from the AC power supply 1 to the load 3.

On the other hand, when the switch 12 is not turned on, no current flows through the light emitting diode 7, so the phototransistor 6 is in a non-conductive state, so the transistor 5 is conductive, and no gate current flows through the thyristor 4, so the thyristor 4 is not turned on. .

In this way, current flows through the load 3 in response to the on/off of the switch 12.

However, in such a circuit example, the photocoupler 8
It has been found that the operation is not perfect, and there are problems particularly with features 1 and 2.

In other words, it has come to be premature to think that the input side and output side are electrically isolated.

In general, the light emitting element on the input side and the light receiving element on the output side are arranged to face each other with a certain distance between them, and a transparent epoxy resin or the like is sandwiched between them.

Therefore, although a capacitor using epoxy resin as a dielectric material is formed between the input and output, this capacitor obstructs complete electrical isolation, and it has been found that even the amount of capacitor equivalent to that of an IPF poses a problem.

This means that in FIG. 1, the AC side voltage is at terminal 15. 16 to terminal 1 to the signal circuit via transformer 13 and rectifier 14.
This is caused by the voltage of the AC power supply 1 being applied between 6 and 17, that is, between the input and output of the photocoupler 8.

That is, assuming that the capacitance between the input and output of the photocoupler is IPF, the impedance at 50H2 is calculated to be about 3000MΩ.

The insulation resistance of most transformers is 100MΩ or less,
This is a negligible value compared to 3000MΩ.

Therefore, the voltage of AC power supply 1 is applied to terminals 17 and 16, and even if switch 12 is not turned on, one line of terminal 17 is connected to light emitting diode 7, so voltage is applied between input and output. This means that

Due to the alternating current voltage, a charging current that is 90 degrees ahead of this voltage phase flows, and the higher the alternating voltage, the larger this current becomes.

If the ratio of the signal current due to light to this charging current is sufficiently large, there will be no problem, but if the ratio is small, it may cause malfunction.

If the capacitance between the input and output of the photocoupler is on the order of IPF, the voltage of the AC power supply 1 will not be much of a problem.

However, since this is a power circuit, other electric circuits are connected to the AC power supply 1, and the surge voltage generated when other switches or thyristors switch is always present. It won't happen.

The rise rate dv/dt of the surge voltage is very large, approximately 1000 V/μs to 100 V/μs, and it must be considered that this is also applied between the input and output of the photocoupler.

When a steep voltage is applied to the capacitor, the current that flows through it also increases, becoming about the same size as the normal signal current and flowing into the base of the phototransistor, so the current is amplified by the phototransistor's DC amplification factor. flows into the collector, the phototransistor operates, and the thyristor malfunctions.

FIG. 2 is a diagram showing the structure of a conventional phototransistor 6. As shown in FIG.

This is done by forming four layers 20 as a base layer on a wafer 19 with a NonN+ structure by selective diffusion, and then four layers 20 as a base layer.
An N layer 21 serving as an emitter is formed thereon by selective diffusion.

22 is an oxide film for surface protection, generally SiO
2 etc.

23 is an aluminum electrode.

24 is an antireflection film that prevents reflection of incident light.

The incident optical signal reaches the fourth layer 20 and the N layer 19 and contributes as a base current.

On the other hand, as mentioned above, there is a capacitor between the facing light emitting diode, and most of the capacitor current flows into the fourth layer 20, and this becomes a base current and is amplified, causing malfunction.

As described above, the higher the DC amplification factor of the phototransistor, the more problems arise when even a capacitor of the size of an IPF is coupled to a power circuit.

For this reason, the distance between the light emitting diode and the phototransistor must be increased to further reduce the value of the capacitor.
Although it is possible to reduce the facing area, it is not a good idea because the exchange efficiency will be reduced.

The present invention has been made in view of this point, and in a light-receiving element having a structure of three or more layers, the capacitance of the capacitor remains unchanged, and a light-transmitting insulating layer is provided on the base layer or gate layer, which is the light-receiving surface. By forming a light-transmitting conductive shield film on the insulating layer and connecting it to the emitter electrode or cathode electrode, the capacitor current does not flow to the base layer or gate layer and the emitter electrode or It is an object of the present invention to provide an optically coupled semiconductor device that can bypass the cathode electrode and eliminate malfunctions of the light receiving element.

FIG. 3 is a structural diagram of a phototransistor showing an embodiment of the present invention.

This is based on the idea that if all the capacitor current is allowed to flow to the emitter before it enters the P-type base layer 20, it will not act as a transistor and will not cause malfunctions. The capacitor current passes through the metal layer 25 which acts to bypass the emitter electrode 23.
It is arranged in layers.

That is, in the figure, first, four layers 20 are formed on the P-type base layer 20.
The oxide film 2 is
2. For example, cover with SiO2 or glass.

This SiO2 or glass can sufficiently transmit light.

Then, if a shield film 25 made of a metal such as gold, nickel, or aluminum or a semiconductor such as silicon is provided thereon and connected or integrated with the emitter electrode 23,
All of the capacitor current IC that flows into this shield film 25
All of the light is captured by the emitter 23 and flows to the emitter 23.

This shield film 25 can be easily made by vacuum deposition, sputtering, or wireless plating.

If the thickness of this shield film 3 is thick, it will also block light, but
If it is very thin, for example, several micrometers or less, it is possible to sufficiently transmit light.

Furthermore, it is not necessary to provide this shield film 25 over the entire surface;
The two layers 20 may be provided in a grid-like or other pattern.

Furthermore, since silicon has the property of transmitting light, it is most suitable for this shield film.

By making the shield film 25 sufficiently thin in this way, only the capacitor current can be captured without absorbing optical signals.

Although the above embodiment describes a phototransistor, the present invention is not limited thereto, and can be applied to other light receiving elements such as an optical thyristor, an optical conduction thyristor, an optical triac, an F
This can be applied to all ET etc.

Figure 4 is a structural diagram when implemented in an optical thyristor.
In this case, the shield film 25 is electrically connected to the cathode electrode K.

As described above, according to the optically coupled semiconductor device according to the present invention, a light-transmitting insulating film is formed on the base layer or gate layer that is the light-receiving surface, and the insulating layer is provided with a light-transmitting conductive film. Since a magnetic shielding film is formed and connected to the emitter electrode or cathode electrode, the current of the capacitor formed by the epoxy resin between the light emitting element and the light receiving element does not flow to the base layer or gate layer as described in 2. It can be bypassed to the emitter electrode or the cathode electrode, and malfunctions of the light receiving element can be eliminated.

Furthermore, since the optical signal current and the capacitor current can be separated well, it has the effect of increasing the amplification rate of the phototransistor and increasing the conversion efficiency of the photocoupler.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an example of a solid state relay circuit using a photocoupler, Fig. 2 is a cross-sectional view of a conventional phototransistor structure used as a light receiving element of the photocoupler, and Fig. 3 shows an embodiment of the present invention. Phototransistor structure cross section,
FIG. 4 is a structural sectional view of an optical thyristor in which the present invention is implemented. The same reference numerals in the figures indicate the same or corresponding parts. In the figure, 6 is a phototransistor, 7 is a light emitting diode, 9 is a semiconductor substrate, 22 is a light-transmitting insulating film, 25 is a shield film, and L is an optical signal.

Claims (1)

[Claims] 1. In an optically coupled semiconductor device in which a light-emitting element and a light-receiving element having a structure of three or more layers that receives light from the light-emitting element are incorporated in the same package, the light-receiving element has a base layer or a gate that is its light-receiving surface. A light-transmissive insulating layer formed on a layer, and a light-transparent conductive shield film formed on the insulating layer and connected to an emitter electrode or a cathode electrode. Combined semiconductor device.