JPH04354379A - Photocoupler - Google Patents

Abstract

PURPOSE:To provide a photocoupler which has a photosensitive element wherein a shield countermeasure by a polysilicon layer is taken in a photosensitive part of a photosensitive IC and eliminates detrimental effect of the polysilicon layer formed as a CMRR countermeasure thereof. CONSTITUTION:To form a base region (anode) 17 of a photodiode to a lattice shape. It is possible to reduce a parasitic capacity formed between a base region 17 and a polysilicon layer 14, to reduce a junction capacity of a photodiode, to prevent deterioration of frequency characteristics of an amplifier of a photosensitive IC and to prevent deterioration of switching speed of a photocoupler influenced by the polysilicon layer 14 formed as a CMRR countermeasure.

Description

[Detailed description of the invention]

0001

FIELD OF INDUSTRIAL APPLICATION The present invention relates to a photocoupler (optical coupling device) consisting of a light emitting element and a light receiving IC, and more particularly to a photocoupler (optical coupling device) comprising a light emitting element and a light receiving IC, and more particularly to a photo coupler having a light receiving element in which the light receiving part of the light receiving IC is shielded with a polysilicon layer. Regarding coupler.

0002

[Prior Art] Conventionally, photocouplers have a structure in which a light-emitting element and a light-receiving element face each other, and usually two circuits with different potentials are electrically isolated and a signal is optically isolated. It has the function of transmitting information through and,
If this photocoupler is viewed from the standpoint of an electronic component, it can be regarded as a capacitor with electrodes on the light emitting side and the light receiving side. If the coupling capacitance between this input and output is C, and if there is also a steep noise of dv/dt, then for example, even if the LED on the light emitting side is not lit, the coupling capacitance C
A displacement current of C·dv/dt is generated due to the steep noise dv/dt, and this displacement current flows to the light receiving side and is amplified by the ampoule in the light receiving IC, causing a problem of output malfunction.

[0003] As a countermeasure, conventionally, a transparent and conductive polysilicon layer is formed on the light receiving part of the light receiving IC, and the potential is set to ground, so that the displacement current C・dv/dt is released to the ground. Prevents output malfunction. For example, an optically coupled semiconductor device has been proposed in which the surface of a semiconductor light-receiving element in the optically coupled semiconductor device is coated with a polysilicon layer (see Japanese Patent Laid-Open No. 125674/1983).

Conventional optical coupling device (photocoupler) of this type
will be explained based on FIG. FIG. 4 is a cross-sectional view of a conventional photodiode section, in which a polysilicon layer 44 is formed on the top of a base region 47 (photodiode anode, p+) via a SiO2 film 46. It is of a formed structure. In addition, in FIG. 4, 41 is a passivation film,
42 is a double layer aluminum for light shielding (GND potential), 43 is an interlayer film, 45 is a single layer aluminum for wiring, and 48 is an epitaxial region (cathode of photodiode, n-).

[0005]

[Problem to be solved by the invention] The conventional optical coupling device is
As mentioned above, the polysilicon layer 44 is formed on the top of the base region 47 (photodiode anode, p+) via the SiO2 film 46, and the polysilicon layer 44 is connected to the ground potential. In shielding the photodiode section (CMRR countermeasure) by doing this, there is a drawback that a parasitic capacitance is formed between the base region 47 and the polysilicon layer 44 which is at the ground potential.

By the way, FIG. 5 is an equivalent circuit diagram of a photodetector IC in which a parasitic capacitance is formed between the amplifier input and the ground, in which 51 is a photodiode, 52 is a parasitic capacitance, and 5
3 is a pull-up resistor, 54 is a switching transistor, and 55 is a cathode-fixed reference voltage. As shown in FIG. 5, in a photodetector IC that integrates a photodiode and a signal processing circuit connected to it, the photodiode
Since the anode of the node 51 is connected to the amplifier input, the parasitic capacitance formed by the base region 47 and the polysilicon layer 44 corresponds to the parasitic capacitance 52 in FIG. 5, and the capacitance is connected to the amplifier input. This has the problem of lowering the frequency characteristics of the amplifier of the light receiving IC and causing deterioration of the switching speed.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a photocoupler that eliminates the above-mentioned drawbacks and problems, and specifically, to reduce the parasitic capacitance formed between the base region and the polysilicon layer. Another object of the present invention is to provide a photocoupler that prevents deterioration of the frequency characteristics of the amplifier of the photodetector IC and prevents deterioration of the switching speed of the photocoupler due to the influence of the polysilicon layer formed as a countermeasure against CMRR. .

[0008]

[Means for Solving the Problems] In order to achieve the above object, the present invention is characterized in that the base region of the photodiode is shaped like a lattice. That is, the present invention provides a photocoupler that is composed of a light-emitting element and a light-receiving IC, and that the light-receiving part of the light-receiving IC is composed of a base region covered with a transparent and electrically conductive polysilicon layer and an epitaxial region. , a photocoupler characterized in that the base region is formed in a lattice shape.

[0009]

[Function] The present invention is a light receiving IC with a built-in photodiode that takes CMRR measures using a polysilicon layer, and the base region (anode) of the photodiode is shaped like a lattice. This has the effect of reducing the parasitic capacitance formed between the base region (anode) and the polysilicon layer, and also reducing the junction capacitance of the photodiode. Furthermore,
In a photodetector IC, the frequency characteristic is C, which is the product of the junction capacitance Cj of the photodiode and the feedback resistance Rf of the amplifier.
The time constant of j・Rt, and furthermore, the input capacitance C of the amplifier section (
(parasitic capacitance). Therefore, in the present invention, by reducing the above-mentioned Cj and C, there is an effect that high-speed switching is possible without deteriorating the frequency characteristics of the light-receiving IC even in shielding measures using a polysilicon layer.

That is, in contrast to the above-mentioned conventional shielding measure using a polysilicon layer, the present invention forms the base region of the light receiving section (corresponding to the anode of the photodiode) in a lattice shape,
The parasitic capacitance formed between the photodiode anode and ground (amplifier input) is reduced, and the photodiode base region (anode) and epitaxial region (cathode) It is also possible to reduce the capacitance of the formed PN junction, and there is an effect that it is possible to increase the speed of a light receiving IC that is provided with a shielding measure using a polysilicon layer.

[0011]

EMBODIMENTS Next, the present invention will be explained in detail based on FIGS. 1 to 3. FIG. 1 is a sectional view of a photodiode section which is an embodiment (Example 1) of the present invention, and FIG. 2 is a sectional view of a photodiode section which is an embodiment (Example 1) of the present invention. FIG. Further, FIG. 3 is a cross-sectional view of a photodiode section which is another embodiment (Embodiment 2) of the present invention.

(Example 1) In FIG. 1, 11 is a passivation film, 12 is a double layer aluminum for light shielding (GND potential)
, 13 is an interlayer film, 14 is a polysilicon layer, 15 is a single layer of aluminum for wiring, 16 is a SiO2 film, 17 is a base region (photodiode anode, p+), 18 is an epitaxial region (photodiode anode, p+), and 18 is an epitaxial region (photodiode anode, p+). It is the cathode of the node, n-). In addition, in FIG. 2, 21 is a base region (photodiode).
22 is an epitaxial region (cathode of photodiode), and 23 is a polysilicon layer.

In this embodiment, as shown in FIG. 1, a base region 17 (
In a photodiode formed of a photodiode anode (p+) and an epitaxial region 18 (photodiode cathode, n-), the base region 17
It has a structure in which it is formed into a lattice shape. Further, as shown in FIG. 2, the structure is such that the base region 21 is formed in a lattice shape, similar to FIG. 1.

In FIG. 1, by forming the base region 17 in a lattice shape, the base region 17, Si
The capacitance formed by the O2 film 16 and the polysilicon layer 14 is
This is lower than that in the conventional structure described above (see FIG. 4). Similarly, by forming the base region 17 in a lattice shape, the junction capacitance of the photodiode, that is, the PN junction capacitance formed by the base region 17 and the epitaxial region 18 is also reduced. Note that the same applies to FIG. 2, so the explanation will be omitted.

(Embodiment 2) As shown in FIG. 3, this embodiment has a structure in which the light receiving section is circular. In addition, Figure 3
In the figure, 31 is a base region, 32 is an epitaxial region, and 33 is a polysilicon layer. By making the light-receiving part circular in this way, the light-receiving I
When the light incident on C is a Gaussian beam, the photodiode becomes efficient.

[0016]

As described in detail above, the present invention provides a photodiode formed by a base region and an epitaxial region, in which the base region is formed in a lattice shape. A significant effect is produced in that the parasitic capacitance generated between the base region and the polysilicon layer can be reduced, and furthermore, the junction capacitance of the photodiode can also be reduced. Therefore, according to the present invention, it is possible to prevent the frequency characteristics of the amplifier of the photodetector IC from deteriorating, and the switching speed of the photocoupler is not deteriorated due to the influence of the polysilicon layer formed as a countermeasure against CMRR. .

[Brief explanation of drawings]

FIG. 1 is a sectional view of a photodiode section showing one embodiment of the present invention.

FIG. 2 is a photodiode showing another embodiment of the present invention.
FIG.

FIG. 3 is a sectional view of a photodiode section showing another embodiment of the present invention.

FIG. 4 is a sectional view of a conventional photodiode section.

FIG. 5 is an equivalent circuit diagram of a light receiving IC in which a parasitic capacitance is formed between an amplifier input and ground.

[Explanation of symbols]

11 Passivation film 12 Double layer aluminum for light shielding 13 Interlayer film 14 Polysilicon layer 15 Single layer aluminum for wiring 16 SiO2 film 17 Base area 18 Epitaxial region 21 Base area 22 Epitaxial region 23 Polysilicon layer 31 Base area 32 Epitaxial region 33 Polysilicon layer 41 Passivation film 42 Double layer aluminum for light shielding 43 Interlayer film 44 Polysilicon layer 45 Single layer aluminum for wiring 46 SiO2 film 47 Base area 48 Epitaxial region 51 Photodiode 52 Parasitic capacitance 53 Pull-up resistor 54 Switching transistor 55 Cathode fixed reference voltage

Claims (1)

[Claims] 1. A photocoupler consisting of a light-emitting element and a light-receiving IC, the light-receiving part of the light-receiving IC being composed of a base region covered with a transparent and electrically transparent polysilicon layer and an epitaxial region, A photocoupler characterized in that the base region is formed in a lattice shape.