JP2690681B2 - Photodiode array and photoelectric encoder using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photodiode array in which a plurality of elongated photodiodes are arranged, and a photoelectric encoder using the photodiode array in a light receiving section.

[0002]

2. Description of the Related Art A photoelectric encoder is generally constructed by arranging a light source on one side and a light receiving element on the other side with respect to a main scale and an index scale which move relative to each other. The light from the light source is collimated and applied to the main scale. The amount of displacement of the scale can be measured by detecting the change in the light-dark pattern obtained as a result of the overlapping state of the transmissive and non-transmissive parts of the main scale and index scale changing due to the relative movement of both scales as an electrical signal. Yes, you can measure length and angle.

In this type of photoelectric encoder, a technique has been proposed in which an index scale and a light receiving element are integrated to reduce the size and cost (see, for example, Japanese Patent Laid-Open No. 64-57120). FIG. 5 shows the basic configuration of such a photoelectric encoder. The output light of the light source 2 composed of a light emitting diode or the like is collimated by the collimator lens 3 and irradiated on the scale 1. The scale 1 is composed of an optical grating in which light transmitting portions and non-light transmitting portions are alternately arranged in the relative movement direction. A photodiode array 4 is arranged behind the scale 1 as a light receiving element. The photodiode array 4 is formed by arranging a plurality of photodiodes at a predetermined pitch in relation to the pitch of the scale 1, which also serves as an ordinary index scale.

FIG. 6 shows a layout of the photodiode array 4. Since the array pitch of the photodiodes PD is defined as an index scale, in order to increase the light receiving area, it is necessary to form an elongated stripe pattern in the direction orthogonal to the moving direction of the scale 1 as shown in FIG. . As a specific example, as shown in FIG. 6, each photodiode PD has a width of 10 μm, a length of 1 mm, and an array pitch of 5 μm. From the photodiode array 4, in relation to the pitch of the scale 1 and the pitch of the photodiode array 4, four-phase output signals A, B,
/ A and / B can be obtained. Signals A and B are signals that are 90 ° out of phase with each other. By processing this detection signal, the moving direction and displacement amount of the scale can be detected.

[0005]

As shown in FIG. 6, when each photodiode PD of the photodiode array 4 has an extremely elongated pattern, high photoelectric conversion efficiency can be obtained when an electrode is provided at the end of the photodiode PD. Also, it becomes difficult to obtain excellent high-speed response. This is because the lateral resistance of the photodiode PD (that is, the resistance in the longitudinal direction of FIG. 6) increases. When the lateral resistance increases, it becomes impossible to promptly take out the signal current from the end portion far from the electrode without attenuating it. The decrease in the response speed of the photodiode causes the distortion of the sine wave output signal obtained from each photodiode when moving the scale, and thus leads to the deterioration of the high speed performance of the photoelectric encoder.

The present invention has been made in consideration of such circumstances, and an object thereof is to provide a photodiode array having high photoelectric conversion efficiency and excellent high-speed response. Another object of the present invention is to provide a photoelectric encoder that realizes excellent high-speed response by using a photodiode array having excellent high-speed response.

[0007]

A photodiode array according to the present invention has an elongated stripe pattern so as to form a light receiving junction between a semiconductor substrate of the first conductivity type and this substrate, and its longitudinal direction. A plurality of second-conductivity-type layers arranged in a direction orthogonal to the second-conductivity-type layers, and a plurality of second-conductivity-type layers arranged along the respective second-conductivity-type layers. And a plurality of electrode wirings contacting each other at a plurality of positions.

The photoelectric encoder according to the present invention comprises a scale on which an optical grating having a predetermined pitch is formed, a light irradiating means for irradiating the scale with parallel light, and a photodiode for detecting a light-dark pattern obtained from the scale. And a photodiode array arranged at a predetermined pitch, wherein the photodiode array has an elongated stripe pattern so as to form a light-receiving junction between the semiconductor substrate of the first conductivity type and the substrate. A plurality of second-conductivity-type layers that are arrayed with fine isolation regions in a direction orthogonal to the longitudinal direction, and a plurality of second-conductivity-type layers that are arrayed along each of the plurality of second-conductivity-type layers are respectively formed into second conductivity-type layers. It is characterized by having a plurality of electrode wirings which are in contact with each other at a plurality of positions in the longitudinal direction.

[0009]

In the photodiode array according to the present invention, the second conductive type layer of the stripe pattern which becomes the photodiode region is brought into contact with the electrode wirings arranged along the second conductive type layer at a plurality of positions. The signal current obtained at each part of the diode can be effectively and promptly taken out without being attenuated, and high photoelectric conversion efficiency and excellent high-speed response can be obtained. Further, in the photoelectric encoder according to the present invention, excellent high-speed response can be obtained by using the photodiode array excellent in high-speed response. Further, since the photoelectric conversion efficiency of each photodiode is higher than the conventional one, an output signal of the same level as the conventional one can be obtained with a light receiving area smaller than the conventional one.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. 1 is a plan view of a photodiode array according to an embodiment of the present invention, and FIGS. 2A and 2B are sectional views taken along the lines AA 'and BB' of FIG. 1, respectively. A plurality of p-type layers 12 having an elongated stripe pattern are diffused and formed on the surface of the n ⁻ -type silicon substrate 11 to form a photodiode array. The pn junction formed between each p-type layer 12 and the substrate 11 is the light-receiving junction of the photodiode. An n ⁺ type layer 13 is diffused between the p type layers 12 for element isolation. An Al electrode 19 is formed on the back surface of the substrate 1 via an n ⁺ type layer 18.

On the substrate on which the photodiode is formed, S
A plurality of Al wirings 15 are provided so as to be covered with an iO2 film 14 and connected to the p-type layer 12 of each photodiode. The Al wirings 15 are arranged along the p-type layer 12 so as to be adjacent to the p-type layer 12, and contact portions 17 that contact the p-type layer 12 at a plurality of positions in the longitudinal direction are formed. A p ⁺ type layer 16 is formed under the contact portion 17 in order to obtain a good ohmic contact in advance.

FIG. 3 is a schematic view of the plan view of FIG. 1 in which specific numerical examples are entered. The width of the elongated p-type layer 12 constituting each photodiode is 10 μm, and the width of the element isolation region between each p-type layer 12 is 5 μm. Further, the length of the p-type layer 12 is 1 mm, and the contact portions 17 of the Al wiring 15 are provided at intervals of 100 μm, for example.

With this structure, since the Al wiring 15 is connected to the p-type layer 12 at the plurality of contact portions 17, a reverse bias is applied between the Al wiring 15 and the n-side Al electrode 11 on the substrate side. When a voltage is applied, the pn junction is uniformly reverse biased across the p-type layer 12. And A
This is equivalent to the lateral resistance of the p-type layer 12 being substantially reduced by the l-wiring 15. As described above, the signal currents generated in the respective parts are taken out in parallel via the plurality of contact parts 17, and as a result, they are taken out from the Al wiring 15 effectively and promptly. Therefore, the photodiode array has high photoelectric conversion efficiency and excellent high-speed response. If the photoelectric conversion efficiency is high, it is possible to obtain a larger output signal than the conventional one with the same light receiving area as the conventional one, and it is possible to obtain an output signal of the same magnitude as the smaller conventional one.

Using the photodiode array of the above embodiment as a light receiving element, a photoelectric encoder can be constructed as shown in FIG. Although FIG. 5 shows the basic configuration, as a specific configuration, for example, the light source 2 may be arranged upward, and the concave mirror lens may be arranged as the collimating lens 3 above the light source 2. As described above, since the photodiode array of this embodiment has high photoelectric conversion efficiency and high-speed performance, the photoelectric encoder using the same has a small size and a large output, and exhibits excellent high-speed response.

The present invention is not limited to the above embodiment. For example, in the above embodiment, the p-type layer 12 of one photodiode is used.
Is continuous in the longitudinal direction, the p-type layer 12 may be divided into a plurality of pieces in the longitudinal direction as shown in FIG. Even if the photodiode is divided into a plurality of photodiodes in the horizontal direction as described above, the Al wiring 15 has a plurality of p-type layers 1 in the horizontal direction.
By disposing the contact portion 17 so as to connect the two, a photodiode array similar to that of the above-described embodiment can be obtained.
Further, in the embodiment, the photodiode using the pn ^- junction has been described, but the present invention is also effective in the case of using the pin junction or the avalanche photodiode.

[0016]

As described above, according to the present invention, by forming the electrode wiring so as to make contact with the elongated photodiode at a plurality of points, a photodiode exhibiting high photoelectric conversion efficiency and excellent high-speed response is obtained. A diode array can be obtained. Further, a high-performance photoelectric encoder can be realized by using such a photodiode array.

[Brief description of the drawings]

FIG. 1 is a plan view of a photodiode array according to an embodiment of the present invention.

FIG. 2 is a sectional view taken along the line AA ′ and the line BB ′ of FIG.

FIG. 3 is a diagram schematically showing the plan view of FIG.

FIG. 4 shows a photodiode array according to another embodiment.
It is a figure shown corresponding to.

FIG. 5 shows a configuration example of a conventional photoelectric encoder.

FIG. 6 shows a layout of the photodiode array of FIG.

[Explanation of symbols]

1 ... Scale, 2 ... Light source, 3 ... Collimating lens, 4 ...
Photodiode array, 11 ... n ^- type silicon substrate,
12 ... p-type layer, 13 ... n ⁺ type layer, 14 ... SiO2 film, 1
5 ... Al wiring, 16 ... P + type layer, 17 ... Contact portion,
18 ... N ⁺ type layer, 19 ... Al electrode.

Claims (2)

(57) [Claims] 1. A semiconductor substrate of the first conductivity type and a light receiving junction are respectively formed between the substrate and the semiconductor substrate.
A plurality of second conductivity type layers having a long and narrow stripe pattern and arranged in a direction orthogonal to the longitudinal direction of the plurality of second conductivity type layers; A photodiode array having a plurality of electrode wirings which are in contact with the two-conductivity type layer at a plurality of positions in the longitudinal direction. 2. A scale on which an optical grating having a predetermined pitch is formed, a light irradiation means for irradiating the scale with parallel light, and photodiodes for detecting a light-dark pattern obtained from the scale are arranged at a predetermined pitch. In a photoelectric encoder having a photodiode array, the photodiode array forms a light-receiving junction between the first conductivity type semiconductor substrate and this substrate,
A plurality of second conductivity type layers having a long and narrow stripe pattern and arranged in a direction orthogonal to the longitudinal direction of the plurality of second conductivity type layers; A photoelectric encoder comprising a plurality of electrode wirings which are in contact with the two-conductivity type layer at a plurality of positions in the longitudinal direction.