JP2005116968A - Optical semiconductor coupling device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical semiconductor coupling device which attains driving at a low voltage. <P>SOLUTION: The device includes a light emitting device and a light receiving device to receive light from the light emitting device, and an In compound semiconductor is used for the light emitting device. Enough drive is obtained at a voltage range of 0.8 to 1.0V in which light is not emitted by conventional GaAs or GaAlAs, due to low forward voltage characteristics obtained by a low band gap. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical semiconductor coupling element, a so-called photocoupler.

As background art related to the present invention, there is provided means for detecting a load on the secondary side and switching between standby mode and normal power supply operation, and switching on and off the switching element provided on the primary side during standby mode. A switching power supply circuit that performs intermittent oscillation, stops normal oscillation during normal power supply operation, performs normal power supply operation, and can reduce power consumption in total is known (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 11-275857

In personal computer CPUs and mobile devices, there is a demand for lower voltages in electronic circuits and electronic components, but the same applies to optical semiconductor coupling elements such as photocouplers.
In particular, in the photocoupler, the input light emitting diode side is often arranged around a component that is adapted to low voltage, such as a control IC, as compared with the output light receiving element side arranged on the power system switching element side. Therefore, the photocoupler is required to have a lower voltage on the input side than on the output side.

For example, in the peripheral circuit of the photocoupler 1 of the switching power supply as shown in Figure 1, the voltage V _F for driving the light emitting diode 2 of the photocoupler 1 connected to the secondary shunt regulator 5, the output voltage Vo The amount obtained by subtracting the voltage applied to the shunt regulator 5 and other peripheral components, that is, the input resistor 6, is applied.

When the shunt regulator 5 is drawn in a general internal block diagram, FIG. 1 is as shown in FIG. 2, and the shunt regulator 5 is represented by a transistor 8, an operational amplifier 9, and a reference voltage power supply 10. When the peripheral components of the shunt regulator 5 other than the light emitting diode 2 on the input side are ignored, the output voltage Vo is expressed by Vo = V _F + V _BE + Vref.

Here, V _F represents the input drive voltage of the photocoupler 1, V _BE represents the base-emitter voltage of the transistor 8 of the shunt regulator, and Vref represents the voltage of the reference voltage power supply 10. Further, R1 and R2 constituting the dividing resistor 7 are given by Vo≈ (1 + R1 / R2) × Vref with respect to the output voltage Vo.

Therefore, when an output voltage of 3.3V or lower is required, Vref cannot be suppressed to about 1.26V or lower in principle. Therefore, since the value obtained by subtracting V _BE and Vref from Vo is calculated on the input side of photocoupler 1, that is, the driving voltage V _F of light emitting diode 2, driving of 1.0 V or less is considered when looking at other design margins. The voltage V _F will be required.

Further, in order to cause the light-emitting diode 2 to emit light in the photocoupler 1 and to sufficiently drive the phototransistor 3 on the receiving side, the light-emitting diode 2 generally requires an input current of about I _F = 5 to 20 mA. made, but conventional, mainly because photocoupler 1 used is a GaAs or GaAlAs and materials, its forward voltage V _F is 1.2～1.7V, a value higher than the desired voltage.

  When realizing a photocoupler that can be driven at a low voltage in order to realize a low output voltage in the power supply circuit as described above, the light-emitting diode 2 on the input side is required to have the light-receiving element 3 at a desired low voltage. It is possible to emit a sufficient amount of light to be driven.

  Conventionally, the light emitting diode materials such as GaAs or GaAlAs that are mainly used are the reason why the wavelength band with high light receiving efficiency and the ease of material are selected for the light receiving element made of silicon. .

However, the forward voltage V _F of the light emitting diode 2 as a driving voltage is thus determined by the size of the band gap of the physically direct transition type semiconductor. The size of the band gap for would be determined by the composition ratio of the semiconductor material, the GaAs or GaAlAs is often used conventionally not obtained desired low forward voltage V _F of less 1.0 V.

  For example, when a high forward voltage is required, a light receiving element made of silicon can receive high-energy short-wavelength light, but when a low forward voltage is required, low-energy long-wavelength light can be received. Since the light is emitted, most of the light is transmitted without being absorbed by the light receiving element made of silicon.

  The present invention has been made in view of such circumstances, and provides an optical semiconductor coupling element that uses an In compound semiconductor as a light emitting element and can be driven at a low voltage.

  The present invention provides an optical semiconductor coupling element including a light emitting element and a light receiving element that receives light from the light emitting element, and using an In compound semiconductor for the light emitting element.

  According to the present invention, since the In compound semiconductor is used for the light emitting element, the low forward voltage characteristic due to the low band gap enables sufficient driving in a voltage range of 0.8 to 1.0 V that does not emit light with conventional GaAs or GaAlAs. .

An optical semiconductor coupling element according to the present invention includes a light receiving element that receives light from a light emitting element, and uses In as a material of the light emitting element.
Further, In may be used as the material of the light receiving element. That is, in order to receive a long wavelength region (1200 to 1800 nm) emitted from the light emitting element, it is preferable to use an In compound semiconductor typified by GaInAs as a material of the light receiving element.

  In particular, a photodiode using GaInAs is used as a light-receiving element for optical fiber communication, and is used for receiving near-infrared light of 1300 nm or 1550 nm with a low attenuation factor in the fiber, and is suitable as a light-receiving element for long wavelength light.

Next, the light emitting element may be a laser diode, and the wavelength conversion material may be provided in the optical path from the light emitting element to the light receiving element. For example, if a wavelength conversion member made of a nonlinear crystal such as β-BaB2O4 or LiB3O4 is provided in the optical path between the light emitting element and the light receiving element, it passes through the wavelength conversion member due to SHG (Second Harmonic Generation). The coherent light is converted to a half wavelength.
Thus, when a GaInAsP laser diode that emits near-infrared light, for example, is used as the laser diode, a conventional silicon light receiving element used for reception in a wavelength band of 1000 nm or less can be used as it is.

  In addition, by installing the wavelength conversion member in a thin film on the light receiving region of the light receiving element, the incident angle of light with respect to the wavelength converting member is stabilized compared to the case where it is inserted between the light receiving and emitting elements, Stable characteristics can be ensured.

The light receiving element preferably has a reflective layer on the back surface. Thereby, the light receiving efficiency of the long wavelength light of the In compound semiconductor can be increased.
The light receiving element preferably has an electromagnetic noise removing member having a mesh structure in the light receiving region. As a result, the noise current due to the steep fluctuation of the electric field generated around the light receiving region is removed.

Embodiments of an optical semiconductor coupling element (hereinafter referred to as a photocoupler) of low input driving according to the present invention will be described in detail with reference to the accompanying drawings.
FIG. 3 is a cross-sectional view showing the overall configuration of a low input voltage driven photocoupler according to the present invention. The light emitting element (chip) 11 and the light receiving element (chip) 12 are mounted on lead frames 15 and 15a, respectively, and are connected to the lead frames 15 and 15a by bonding wires 17 and 17a. The light-emitting element 11 and the light-receiving element 12 covered with the protective transparent silicone resin 16 are covered with the light-transmitting resin 13 and the light-shielding resin 14, and both are electrically insulated. The light emitting element 11 converts an electrical signal into an optical signal and transmits it to the light receiving element 12. The optical signal reaching the light receiving element 12 is converted into an electrical signal.
FIG. 4 is an equivalent circuit of the photocoupler shown in FIG. 3, and the photocoupler includes a light emitting element 11, a light receiving element 12, and a transistor 19, as shown in FIG.

Example 1
FIG. 5 is a cross-sectional view of the principal part showing Embodiment 1 of the present invention. 3 shows a light emitting diode 20 in which a GaInAs active layer 20 is grown on an n-InP substrate 101 and a p-InP layer 103 and an electrode layer 104 are formed thereon as the light emitting element 11 of FIG. Yes.
In this case, the driving voltage of the light emitting diode 20 is 0.8 to 1.0V. Further, in order to receive light having a longer wavelength (1200 to 1800 nm) emitted from the light emitting diode 20, the light receiving element 12 is made of an In compound semiconductor formed on the electrode layer 23 as shown in FIG. A photodiode 21 is used. Examples of In compound semiconductors include GaInAs, GaInNAs, and GaInAsP semiconductors. In this embodiment, the photodiode 21 is formed of an In compound semiconductor, and the transistor 19 (FIG. 4) at the output stage is formed of silicon. However, they may be monolithic integrated on one chip. Alternatively, it may be configured discretely and coupled with a metal wire or the like inside the photocoupler.

Example 2
6 is a diagram corresponding to FIG. 5 showing Example 2, using a GaInAsP laser diode 20a as the light-emitting element 11 shown in FIG. 3, a photodiode 21a made of silicon as the light-receiving element 12, and β between the light-emitting and receiving elements. A wavelength conversion member 22 made of a non-linear crystal such as -BaB2O4 or LiB3O4 is inserted. The wavelength conversion member 22 is supported on the lead frame 15a by support members 22a and 22b. In the laser diode 20a, an n-InGaAsP layer 202, an InGaAsP active layer 203, a p-InGaAsP layer 204, a p-InP layer 205, and an electrode layer 206 are sequentially stacked on an n-InP substrate 201.

  The coherent light emitted from the laser diode 20a having a longer wavelength (1200 to 1800 nm) than the conventional wavelength is half the wavelength (600 to 900 nm) in the wavelength conversion member 22 by SHG (Second Harmonic Generation). Thus, the wavelength is sufficient for light reception by the photodiode 21a made of silicon.

Example 3
FIG. 7 is a view corresponding to FIG. 6 showing Example 3, in which the wavelength conversion member 22 in FIG. 6 is formed on the light receiving region on the surface of the photodiode 21a. Other configurations are the same as those in FIG. The coherent light emitted from the laser diode 20a with a longer wavelength (1200 to 1800 nm) becomes half the wavelength (600 to 900 nm) through the conversion member 22 due to SHG (Second Harmonic Generation). The light is received by the photodiode 21a.

Example 4
FIG. 8 is a diagram corresponding to FIG. 5 showing Example 4, in which the electrode layer 23 on the back surface of the photodiode 21 in FIG. 5 is replaced with a reflective layer 23a. Other configurations are the same as those in FIG. The reflective layer 23a is made of Al or Ag, and the surface in contact with the photodiode 21 is finished to be a mirror surface.
The light emitted from the light emitting diode 20 is received by the photodiode 21, and the light that has passed through the photodiode 21 is reflected again to the photodiode 21 by the reflection layer 23a, so that the light receiving efficiency of the photodiode 21 can be increased.

Example 5
FIG. 9 is a diagram corresponding to FIG. 5 illustrating the fifth embodiment. On the surface of the photodiode 21, a shield wiring 24 having an emitter potential is provided in a mesh shape. FIG. 10 is a plan view of the shield wiring 24 viewed from above the photodiode 21. FIG. Other configurations are the same as those shown in FIG. Noise current caused by a sharp fluctuation of the electric field generated around the light receiving region of the photodiode 21 is discharged out of the chip through the emitter terminal.
In the mesh-like structure of the shield wiring 24, the smaller the mesh interval, the higher the noise absorption performance, but the amount of received light decreases.
In addition, as a material of the shield wiring 24, it is desirable to use a metal or a semimetal having a high electric conductivity such as Al from the viewpoint of thinning.

It is a connection diagram which shows the peripheral circuit of the conventional photocoupler. FIG. 3 is a connection diagram illustrating the main part of FIG. 2 with an equivalent circuit. It is sectional drawing which shows the whole structure of the photocoupler by this invention. FIG. 4 is an equivalent circuit diagram of the photocoupler shown in FIG. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of an essential part of Embodiment 1 of the present invention. FIG. 6 is a cross-sectional view of a main part of Embodiment 2 of the present invention. FIG. 6 is a cross-sectional view of a main part of Embodiment 3 of the present invention. FIG. 6 is a cross-sectional view of a main part of Embodiment 4 of the present invention. FIG. 10 is a cross-sectional view of a main part of Embodiment 5 of the present invention. FIG. 10 is a top view of the main part of the embodiment of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Light receiving element 12 Light receiving element 13 Translucent resin 14 Light blocking resin 15 Lead frame 15a Lead frame 16 Transparent silicone resin 17 Bonding wire 17a Bonding wire 22 Wavelength conversion member 23 Electrode layer 23a Reflective layer 24 Shield wiring

Claims (6)

  An optical semiconductor coupling element comprising: a light emitting element; and a light receiving element for receiving light from the light emitting element, wherein an In compound semiconductor is used for the light emitting element.   2. The optical semiconductor coupling element according to claim 1, wherein an In compound semiconductor is used for the light receiving element.   2. The optical semiconductor coupling element according to claim 1, wherein the light emitting element is a laser diode, and further comprises a wavelength conversion portion material in an optical path from the light emitting element to the light receiving element.   4. The optical semiconductor coupling element according to claim 3, wherein the wavelength conversion member is installed in a light receiving region of the light receiving element.   5. The optical semiconductor coupling element according to claim 1, wherein the light receiving element includes a light receiving region on a front surface and a reflective layer on a back surface. 6. The optical semiconductor coupling element according to claim 1, wherein the light receiving element has a mesh structure member for removing electromagnetic noise formed in a light receiving region.

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