JPH0224386B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Technical Field> The present invention relates to an improvement in the structure of a light-receiving chip of a photocoupler, which particularly requires high-speed response.

<Prior Art> Conventionally, a photocoupler is constructed by a combination of a light emitting element and a light receiving element, and has been developed as a signal interface element in place of a pulse transformer. In addition, with the spread of microcomputers in recent years, their uses have expanded, and high-speed response, low current, and drive functions are required.

Generally, the photocurrent of the photodetector in a photocoupler is
It consists of a drift component and a diffusion component. Figure 2 shows the photocurrent response characteristics when a photodiode is used as the light receiving element. Figure a shows the drive pulse applied to the light emitting element, and figure b shows the photocurrent waveform of the light receiving element. Here, low current drive (i.e. high sensitivity)
In photocouplers that require a high-speed response, the photocurrent with a long lifetime, which is the diffusion component shown in FIG. 2b, causes a delay in response characteristics. FIG. 3 shows the structure of a conventional light receiving element (photodiode). In the figure, 1 is a P type substrate, 2 is an N type epitaxial layer, 3 is a P ⁺ isolation layer, and 4 is a transparent insulating layer. This structure does not have a means for blocking photons that generate many diffusion component photocurrents in the peripheral area of the photodiode. On the other hand, FIG. 4 shows the structure of a photodiode in which a light shielding means 5 made of metal or the like is provided around the chip against front light to cover the above-mentioned drawbacks.

However, even in the structure shown in Fig. 4, if a structure in which the photodiode is placed adjacent to the semiconductor chip edge is adopted, the photocurrent of the diffusion component is blocked in order to collect photons from the light irradiated on the side of the chip. I couldn't do it. In order to solve this problem, methods such as placing a light-shielding material such as Ag paste on the side walls of the chip can be considered.
There are factors such as an increase in material costs, an increase in manufacturing man-hours, and a decrease in yield, leading to higher costs.

<Purpose> The present invention was made in order to eliminate the above-mentioned drawbacks, and it is a method to generate photons by spreading them from the side of the chip.
We propose a structure in which the photocurrent of the diffusion component does not affect the signal detection photodiode.

<Embodiment> FIG. 1 shows the structure of a light-receiving element of an embodiment of a photocoupler according to the present invention, in which FIG. 1A shows a partial side sectional view and FIG. 1B shows a partial plan view. In the same figure, 1
is a P-type substrate, 2 is an N-type epitaxial layer, and 3 is a P-type substrate.
P ⁺ isolation layer 4 is a transparent insulating layer. Reference numeral 6 denotes an N-type epitaxial layer provided at the periphery of the chip, which is separate from the first photodiode for signal detection consisting of a PN junction between the P-type substrate 1 and the N-type epitaxial layer 2. A second photodiode is formed, which is composed of a PN junction between the P type substrate 1, the P ⁺ isolation layer 3, and the N type epitaxial layer 6. Reference numeral 7 denotes a light shielding means made of metal or the like, and the light shielding means 7 prevents diffusion components caused by light from the front.

FIG. 5 shows an equivalent circuit of the above light receiving element. As shown in the figure, a second photodiode 9 is formed separately from the first photodiode 8 for signal detection, and the anode and cathode of the second photodiode 9 are set at a substrate potential (ground).

In the light receiving element having the above structure, the photocurrent excited by the light irradiated onto the side surface of the chip does not reach the first photodiode 8 but is absorbed by the second photodiode 9. That is, the diffusion component from the side surface of the chip no longer affects the output of the first photodiode 8. In other words, by using a light shielding means 7 made of metal or the like for front light, and by using absorption means by the second photodiode 9 for side light, the photocurrent can be reduced.
It becomes possible to suppress diffusion components as much as possible.

FIG. 6 shows the structure of a photocoupler incorporating the above light receiving element. Figure a is a plan view, figure b is a side sectional view, and figure c is a front sectional view. 10 is an infrared light emitting diode chip, and 11 is a light receiving element chip, which are installed on the same plane. 11
a is a first photodiode for signal detection provided in the light receiving element chip 11; 11b is arranged between the infrared light emitting diode chip 10 and the first photodiode 11a;
This is a second photodiode for preventing mixing of diffusion components. Further, 12 is a transparent resin, and 13 is a heat sink. The light receiving element chip 11 is an element (OPIC light receiving element) in which a photodiode and a signal processing circuit such as amplification and waveform shaping are integrated into one chip. In a photocoupler having a structure in which an infrared light emitting diode chip 10 and a light receiving element chip 11 are installed on the same plane as shown in the figure, the light receiving element chip 1
The structure according to the present invention is extremely advantageous because the influence of light from one side is strong.

<Effects> According to the present invention, a photocoupler with high sensitivity and high speed response can be obtained.

[Brief explanation of drawings]

FIG. 1 shows the structure of a light-receiving element of an embodiment of the photocoupler according to the present invention, and FIG.
Figure b is a partial plan view, Figure 2 is a waveform diagram showing the photocurrent response characteristics of a conventional photocoupler, Figures 3 and 4.
The figure shows a side sectional view of a conventional light receiving element, FIG. 5 shows an equivalent circuit diagram of a light receiving element of an embodiment of a photocoupler according to the present invention, and FIG. 6 shows a structure of an embodiment of a photocoupler according to the present invention. Figure a shows a plan view, figure b shows a side sectional view, and figure c shows a front sectional view. In the figure, 1: P type substrate, 2: N type epitaxial layer, 3: P ⁺ isolation layer, 4: insulating layer,
5: Light shielding means, 6: N-type epitaxial layer, 7:
Light shielding means, 8: first photodiode, 9: second
photodiode, 10: infrared light emitting diode chip, 11: light receiving element chip.

Claims (1)

[Claims] 1 A light-emitting element chip and a light-receiving element chip are installed on the same plane, and the light-receiving element chip has a signal detection photodiode and a separate photodiode from the signal detection photodiode, and the light-receiving element chip is arranged on the side of the light-emitting element chip. A photocoupler characterized in that a photodiode separate from the signal detection photodiode is provided near the side surface of the element chip and between the signal detection photodiode and the signal detection photodiode.