阅读说明：本技术 光学模块及光学式编码器 (Optical module and optical encoder ) 是由 大原智光 堤司树 木村慎治 铃木修平 大场雄介 于 2020-02-06 设计创作，主要内容包括：本发明提供一种光学模块及光学式编码器,制造容易,且能够更可靠地遮蔽来自光源的侧面光。该光学模块具备：固定基板；传感器基板,其粘着于上述固定基板上,且形成有贯通孔；以及发光元件,其以位于上述贯通孔内的方式粘着于上述固定基板上,上述传感器基板具有受光元件和形成于上述受光元件与上述贯通孔之间且上述贯通孔的周围的假受光元件,上述受光元件和上述假受光元件由形成于上述传感器基板的表层的相同导电型的杂质扩散层构成,上述假受光元件的深度大于上述受光元件的深度。(The invention provides an optical module and an optical encoder, which are easy to manufacture and can more reliably shield side light from a light source. The optical module includes: fixing the substrate; a sensor substrate adhered to the fixed substrate and having a through hole formed therein; and a light emitting element bonded to the fixed substrate so as to be positioned in the through hole, wherein the sensor substrate includes a light receiving element and a dummy light receiving element formed between the light receiving element and the through hole and around the through hole, the light receiving element and the dummy light receiving element are formed of impurity diffusion layers of the same conductivity type formed on a surface layer of the sensor substrate, and a depth of the dummy light receiving element is larger than a depth of the light receiving element.)

1. An optical module is provided with:

fixing the substrate;

a sensor substrate adhered to the fixed substrate and having a through hole formed therein; and

a light emitting element adhered to the fixed substrate so as to be positioned in the through hole,

the sensor substrate includes a light receiving element and a dummy light receiving element formed between the light receiving element and the through hole and around the through hole,

the light receiving element and the dummy light receiving element are formed of impurity diffusion layers of the same conductivity type formed on the surface layer of the sensor substrate, and the depth of the dummy light receiving element is larger than the depth of the light receiving element.

2. The optical module of claim 1,

the sensor substrate is a semiconductor substrate,

the light receiving element and the dummy light receiving element are pn junction type photodiodes which are set to be reverse biased.

3. The optical module of claim 2,

the light emitting element is an LED.

4. The optical module of claim 3,

the fixed substrate side of the sensor substrate is a cathode, and the fixed substrate side of the light emitting element is a cathode.

5. The optical module of claim 1,

the impurity diffusion layer constituting the dummy light receiving element has a higher impurity concentration than the impurity diffusion layer constituting the light receiving element.

6. An optical module is provided with:

fixing the substrate;

a sensor substrate adhered to the fixed substrate and having a through hole formed therein; and

a light emitting element adhered to the fixed substrate so as to be positioned in the through hole,

the sensor substrate includes a light receiving element and a dummy light receiving element formed between the light receiving element and the through hole and around the through hole,

the light receiving element and the dummy light receiving element are each composed of an impurity diffusion layer of the same conductivity type formed on a surface layer of the sensor substrate, and the sensor substrate is bonded to the fixed substrate via a conductive adhesive layer including a light absorbing member.

7. An optical encoder is characterized by comprising:

the optical module of claim 1; and

a reflective scale.

8. An optical encoder is characterized by comprising:

the optical module of claim 6; and

a reflective scale.

Technical Field

The present invention relates to an optical module and an optical encoder.

Background

In order to detect the rotation amount, rotation speed, and rotation direction of the servo motor, an optical encoder is used. The optical encoder has a transmission type for detecting light transmitted through the scale and a reflection type for detecting light reflected by the scale. In particular, reflective optical encoders have been widely used in recent years because they can be made smaller and thinner.

As a reflective optical encoder, the following structure is known: a through hole is provided in the center of a sensor substrate having a Light receiving element, and a Light source such as an LED (Light-Emitting Diode) is disposed in the recess and the through hole (see, for example, patent document 1).

In this way, when the light source is disposed in the through hole of the sensor substrate, light emitted from the upper surface of the light source is reflected by the scale, and the reflected light is received by the light receiving element of the sensor substrate.

Disclosure of Invention

Problems to be solved by the invention

Since light leakage occurs not only from the top surface but also from the side surfaces of the light source such as an LED, when the light source is disposed in the through hole of the sensor substrate, light (side surface light) leaking from the side surfaces of the light source is directly incident on the sensor substrate. In addition, since the sensor substrate is formed of a semiconductor substrate, the sensor substrate receives the side light incident from the side surface. The reception of the side light causes a noise current to be generated in the sensor substrate. Patent document 1 describes that a light shielding member is provided on a side wall of a through hole of a sensor substrate by a thin metal film such as aluminum.

However, in order to provide the light shielding member with a thin metal film as described in patent document 1, a manufacturing process for forming the light shielding member needs to be added, which increases the manufacturing cost.

In addition, in order to dispose the light source in the through hole, the light source and the sensor substrate need to be fixed to the fixed substrate. The side light emitted from the side surface of the light source may be reflected at the interface between the fixed substrate and the sensor substrate, and may enter the sensor substrate from the back surface side of the sensor substrate.

The invention provides an optical module and an optical encoder, which are easy to manufacture and can more reliably shield side light from a light source.

Means for solving the problems

Disclosed is an optical module provided with: fixing the substrate; a sensor substrate adhered to the fixed substrate and having a through hole formed therein; and a light emitting element bonded to the fixed substrate so as to be positioned in the through hole, wherein the sensor substrate includes a light receiving element and a dummy light receiving element formed between the light receiving element and the through hole and around the through hole, the light receiving element and the dummy light receiving element are formed of impurity diffusion layers of the same conductivity type formed on a surface layer of the sensor substrate, and a depth of the dummy light receiving element is larger than a depth of the light receiving element.

Effects of the invention

According to the present invention, the side light from the light source can be shielded more reliably and with ease of manufacture.

Drawings

Fig. 1 is a plan view showing a schematic configuration of an optical encoder according to a first embodiment.

Fig. 2 is a longitudinal sectional view taken along line a-a in fig. 1.

Fig. 3 is a diagram showing an electrical connection relationship between the first light receiving element group and the external terminal.

Fig. 4 is a diagram showing an electrical connection relationship between the second light receiving element group and the external terminal.

Fig. 5 is a diagram showing an equivalent circuit of the entire optical module.

Fig. 6 is a schematic cross-sectional view showing a layer structure of the light-emitting element and the sensor substrate.

Fig. 7 is a schematic cross-sectional view showing the structure of an optical module according to a first modification.

Fig. 8 is a schematic cross-sectional view showing the structure of an optical module according to a second modification.

Fig. 9 is a schematic cross-sectional view showing the structure of an optical module according to a fourth modification.

In the figure:

1-optical encoder, 10-light emitting element, 11-light emitting window, 12-terminal, 13-light emitting layer, 20-sensor substrate, 20 a-through hole, 21-first light receiving element group, 21 a-light receiving element, 22-second light receiving element group, 22 a-light receiving element, 23-dummy light receiving element (first dummy light receiving element), 24, 25, 35-electrode pad, 30-fixed substrate, 31, 32-adhesive layer, 33-internal wiring, 35-electrode pad, 36-wiring, 37 a-first external terminal, 37 b-second external terminal, 37 c-third external terminal, 37 d-fourth external terminal, 37 e-fifth external terminal, 40-scale, 50, 51-bonding wire, 52-resin, 60-second dummy light receiving element, 70-through electrode.

Detailed Description

Hereinafter, specific embodiments will be described with reference to the drawings. In the drawings, the same components are denoted by the same reference numerals, and redundant description thereof may be omitted.

< first embodiment >

A reflective optical encoder according to a first embodiment of the present invention will be described below.

Fig. 1 is a plan view showing a schematic configuration of an optical encoder 1 according to a first embodiment. Fig. 2 is a longitudinal sectional view of the optical encoder 1 taken along line a-a in fig. 1. Note that one direction in the plane shown in fig. 1 is an X direction, and a direction orthogonal to the X direction is a Y direction. In addition, a direction orthogonal to the X direction and the Y direction is a Z direction.

As shown in fig. 1 and 2, the optical encoder 1 includes an optical module including a light emitting element 10, a sensor substrate 20, and a fixing substrate 30, and a scale 40.

The light emitting element 10 is, for example, an LED. The light emitting element 10 is a pn junction diode, and emits light through a light exit window 11 provided on an upper surface of an anode side (p-type side). A terminal 12 for applying a power supply voltage is formed on the upper surface of the anode side of the light emitting element 10.

The sensor substrate 20 is a semiconductor substrate having a rectangular planar shape, and a rectangular through hole 20a is formed in a substantially central portion. The light emitting element 10 is disposed in the through hole 20 a. The through-hole 20a can be formed by, for example, dry etching. The planar shape of the through hole 20a is not limited to a rectangular shape, and may be a circular shape or the like.

As shown in fig. 2, the upper surface of the light emitting element 10 is substantially flush with the upper surface of the sensor substrate 20. The light-emitting element 10 and the sensor substrate 20 are respectively bonded to the fixed substrate 30 via adhesive layers 31 and 32. The fixed substrate 30 is a rectangular insulating substrate larger than the sensor substrate 20.

The adhesive layers 31 and 32 are made of a conductive adhesive such as silver paste. The lower surface of the light-emitting element 10 on the cathode side (n-type side) is bonded to the fixing substrate 30 via an adhesive layer 31. In the present embodiment, the adhesive layer 32 that bonds the sensor substrate 20 to the fixed substrate 30 may be insulating.

An internal wiring 33 made of copper (Cu) or the like for applying a ground potential to the cathode of the light-emitting element 10 is formed on the fixed substrate 30. A part of the internal wiring 33 is exposed from the upper surface of the fixed substrate 30, and the exposed part is electrically connected to the lower surface (cathode) of the light-emitting element 10 via the adhesive layer 31. The internal wiring 33 is connected to external terminals 33a and 33b provided on the lower surface side of the fixed board 30.

The terminals 12 provided on the upper surface of the light-emitting element 10 and the electrode pads 24 provided on the upper surface of the sensor substrate 20 are connected via bonding wires 50.

The scale 40 is a reflective plate formed with a predetermined pattern on a transparent substrate such as glass by a thin metal film or the like. A part of the light emitted from the light emitting element 10 is reflected by the scale 40 and enters the sensor substrate 20. The sensor substrate 20 detects the light modulated by the scale 40.

As shown in fig. 1, the sensor substrate 20 is provided with a first light receiving element group 21 and a second light receiving element group 22. The first light receiving element group 21 is a light receiving element group for absolute detection composed of a plurality of light receiving elements 21a arranged in the X direction at a predetermined pitch. The second light receiving element group 22 is a light receiving element group for incremental detection composed of a plurality of light receiving elements 22a arranged in the X direction at a pitch different from that of the first light receiving element group 21. The light receiving elements 21a and 22a are pn junction type photodiodes, respectively, as will be described in detail later.

Further, a dummy light receiving element 23 is formed around the through hole 20a of the sensor substrate 20 so as to surround the through hole 20 a. That is, the dummy light receiving element 23 is disposed between the light emitting element 10 and the first and second light receiving elements 21 and 22. The dummy light receiving element 23 is a pn junction photodiode, and mainly receives side light that leaks from the side surface of the light emitting element 10.

A plurality of electrode pads 25 are formed on the upper surface of the sensor substrate 20 along a side parallel to the Y direction. Each of the electrode pads 25 is connected to the first light receiving element group 21, the second light receiving element group 22, the dummy light receiving element 23, and the like via a wiring layer (not shown) formed on the surface of the sensor substrate 20.

Electrode pads 35 are formed on the upper surface of the fixed substrate 30 at positions facing the electrode pads 25 of the sensor substrate 20. The electrode pad 25 and the electrode pad 35 facing the electrode pad 25 are connected via a bonding wire 51. The electrode pads 25 and 35 are formed of aluminum or the like. The electrode pads 25, the electrode pads 35, and the bonding wires 51 are sealed with a resin 52.

Each electrode pad 35 is connected to an external terminal 37 formed on the lower surface of the fixed substrate 30 via a wiring 36 made of copper or the like. The external terminals 37 are classified into a first external terminal 37a, a second external terminal 37b, a third external terminal 37c, a fourth external terminal 37d, and a fifth external terminal 37 e.

The first external terminal 37a is a detection terminal for acquiring a detection signal for absolute detection from the first light receiving element group 21. The second external terminal 37b is a detection terminal for acquiring a detection signal for incremental detection from the second light receiving element group 22. The third external terminal 37c is a ground terminal for applying a ground potential (GND) to the anode side (p-type side) of the dummy photo detector 23.

The fourth external terminal 37d is a power supply terminal for supplying a power supply Voltage (VCC) to cathode sides (n-type sides) of the light receiving elements 21a included in the first light receiving element group 21, the light receiving elements 22a included in the second light receiving element group 22, and the dummy light receiving element 23, and for reversely biasing the photodiodes constituting the light receiving elements. The fifth external terminal 37e is a power supply terminal for supplying a power supply Voltage (VCC) to the anode side of the light emitting element 10.

Fig. 3 is a diagram showing an electrical connection relationship between each light receiving element 21a included in the first light receiving element group 21 and the first external terminal 37a and the fourth external terminal 37 d. As shown in fig. 3, each of the first external terminals 37a is connected to any one of the light receiving elements 21a included in the first light receiving element group 21. The absolute position information can be detected by the detection signal obtained from the first external terminal 37 a.

Fig. 4 is a diagram showing an electrical connection relationship between each light receiving element 22a included in the second light receiving element group 22 and the second external terminal 37b and the fourth external terminal 37 d. As shown in fig. 4, each of the second external terminals 37b is connected to two light receiving elements 22a of the light receiving elements 22a included in the second light receiving element group 22. Specifically, the second external terminals 37b are connected to two light receiving elements 22a separated by a distance four times the arrangement pitch of the light receiving elements 22 a. The relative position information can be detected by the detection signal obtained from the second external terminal 37 b.

Fig. 5 is a diagram showing an equivalent circuit of the entire optical module. As shown in fig. 5, the light emitting element 10 emits light by being set to a forward bias. The light emitted from the light emitting element 10 is received by the light receiving elements 21a and 22a which are set to be reverse biased. Among the light emitted from the light emitting element 10, the side light is received and absorbed by the dummy light receiving element 23 which is set to be a reverse bias.

Fig. 6 is a schematic cross-sectional view showing the layer structure of the light-emitting element 10 and the sensor substrate 20. Fig. 6 schematically shows a cross section along the Y direction of the optical module.

As shown in fig. 6, in the present embodiment, the sensor substrate 20 is formed of an n-type semiconductor substrate (e.g., a silicon substrate). The light receiving elements 21a and 22a are formed of p-type diffusion layers formed by doping a p-type impurity into the surface layer of an n-type semiconductor substrate. The depth from the surface of each p-type diffusion layer constituting the light receiving element 21a and the light receiving element 22a is substantially the same. The depth of the p-type diffusion layer was D1.

Similarly, the dummy light receiving element 23 is composed of a p-type diffusion layer formed by doping a p-type impurity into a surface layer of an n-type semiconductor substrate. That is, the dummy light receiving element 23 is composed of an impurity diffusion layer having the same conductivity type as the light receiving elements 21a and 22 a.

The dummy light receiving element 23 is formed in an annular region surrounding the through hole 20 a. The depth D2 from the surface of the p-type diffusion layer constituting the dummy light receiving element 23 is larger than the depth D1. Namely, D2 > D1. The depth of the p-type diffusion layer can be determined by controlling the acceleration voltage at the time of ion implantation of the impurity.

The light receiving elements 21a and 22a and the dummy light receiving element 23 are reverse biased, and thereby the depletion layer DL generated in the surrounding pn junction region is expanded. The dummy light receiving element 23 has a function of absorbing carriers generated by light entering the sensor substrate 20 from the inside of the through hole 20 a.

Since the light-emitting element 10 has the light-emitting layer 13 in a layered form between the p-type layer and the n-type layer, light is emitted from the side surfaces as well as from the upper surface of the light-emitting layer 13. The amount of the side light is about several percent of the total amount of light emitted from the light emitting element 10. If such side light enters the sensor substrate 20 and reaches the depletion layer DL of the light receiving elements 21a and 22a, a noise current is generated, resulting in a reduction in S/N, but in the present embodiment, most of the side light entering the sensor substrate 20 is absorbed by the dummy light receiving element 23, and therefore generation of the noise current can be suppressed.

Further, although the side light having entered the sensor substrate 20 may be reflected on the lower surface of the sensor substrate 20 or the surface of the adhesive layer 32, in the present embodiment, the dummy light receiving elements 23 are formed to be deeper than the light receiving elements 21a and 22a, and therefore such reflected light is also absorbed by the dummy light receiving elements 23, and generation of noise current can be suppressed.

As described above, according to the present embodiment, unlike the conventional case where a light blocking member is provided on the side wall of the through hole, the side light can be blocked (absorbed) by the dummy light receiving element 23 formed in the sensor substrate 20. The dummy light-receiving element 23 is formed of an impurity diffusion layer having the same conductivity type as the light-receiving elements 21a and 22a, and therefore can be manufactured in the same manufacturing process as the light-receiving elements 21a and 22a, and the like, and there is no need to add a manufacturing process for forming the dummy light-receiving element 23. Therefore, according to the present embodiment, the manufacturing is easy, and the side light from the light source can be shielded more reliably.

The impurity concentration of the dummy light receiving element 23 may be the same as that of the light receiving elements 21a and 22a, but the impurity concentration of the dummy light receiving element 23 may be higher than that of the light receiving elements 21a and 22 a. This improves the light absorption rate of the pseudo light receiving element 23.

Various modifications of the above embodiment will be described below.

< first modification >

Fig. 7 is a schematic cross-sectional view showing the structure of an optical module according to a first modification. This modification has the same configuration as that of the first embodiment, except that the sensor substrate 20 has a different configuration.

In the sensor substrate 20 of the present modification, in addition to the dummy light-receiving element 23 (first dummy light-receiving element), a second dummy light-receiving element 60 is formed on the lower surface side of the sensor substrate 20. The second dummy light receiving element 60 is formed of an impurity diffused layer having the same conductivity type as the first dummy light receiving element 23. In the present modification, the second dummy photo detector 60 is formed of a p-type diffusion layer. The second dummy light-receiving element 60 is formed in an annular region surrounding the through-hole 20a, similarly to the first dummy light-receiving element 23.

By setting the second dummy light receiving element 60 to be reverse biased, the depletion layer DL generated around the p-type diffusion layer constituting the second dummy light receiving element 60 is expanded. By providing the second dummy light receiving element 60 in addition to the first dummy light receiving element 23 in this way, the side light entering the sensor substrate 20 from the light emitting element 10 can be shielded (absorbed) more reliably.

The second dummy light receiving element 60 may be connected to the first dummy light receiving element 23. The second dummy light receiving element 60 and the first dummy light receiving element 23 may have different impurity concentrations.

< second modification >

Fig. 8 is a schematic cross-sectional view showing the structure of an optical module according to a second modification. This modification has the same configuration as that of the first embodiment, except that the structure of the fixed substrate 30 is different. In the first embodiment, in order to reverse bias the light receiving elements 21a and 22a, a power supply Voltage (VCC) is supplied from the fourth external terminal 37d to the n-type region of the sensor substrate 20 via a wiring layer (not shown) formed on the upper surface side of the sensor substrate 20.

The fixed substrate 30 of the present modification includes a through electrode 70 for supplying a power supply voltage from the lower surface side of the sensor substrate 20 to the n-type region. The through electrode 70 is electrically connected to the lower surface side of the sensor substrate 20 via the conductive adhesive layer 32. The through electrode 70 is exposed from the lower surface of the fixed substrate 30 and functions as a power supply terminal for applying a power supply voltage.

In addition, the fixed substrate 30 of the present modification may be used to supply a power supply voltage to the second dummy photo detector 60 described in the second modification.

< third modification >

In the first embodiment, as shown in fig. 6, an n-type semiconductor substrate is used as the sensor substrate 20, but a p-type semiconductor substrate may be used instead of the n-type semiconductor substrate. In this case, the light receiving elements 21a and 22a and the dummy light receiving element 23 may be formed by an n-type diffusion layer.

When a p-type semiconductor substrate is used as the sensor substrate 20, the ground potential may be applied to the p-type region in order to reverse-bias the light receiving elements 21a and 22a and the dummy light receiving element 23. Therefore, in this case, since the fixed substrate 30 side of the sensor substrate 20 serves as an anode and the fixed substrate 30 side of the light-emitting element 10 serves as a cathode, a ground potential can be applied to the lower surface of the sensor substrate 20 and the lower surface of the light-emitting element 10 from the fixed substrate 30 via a common electrode. This makes it possible to form the adhesive layer 31 and the adhesive layer 32 as one conductive adhesive layer.

In addition, the conductivity types of the light emitting element 10 may be reversed such that the fixed substrate 30 side of the sensor substrate 20 is a cathode and the fixed substrate 30 side of the light emitting element 10 is an anode. In this case, the power supply voltage may be supplied from the fixed substrate 30 to the lower surface of the sensor substrate 20 and the lower surface of the light-emitting element 10 via the common electrode.

< fourth modification >

Fig. 9 is a schematic cross-sectional view showing the structure of an optical module according to a fourth modification. This modification has the same configuration as that of the first embodiment, except that the sensor substrate 20 has a different configuration. In the first embodiment, as shown in fig. 6, the impurity diffusion layer constituting the dummy light receiving element 23 is formed deeper than the impurity diffusion layers constituting the light receiving elements 21a and 22a, but in the present modification, both are formed to have the same depth.

In the sensor substrate 20 of the present modification, the adhesive layer 32 for adhering the sensor substrate 20 to the fixed substrate 30 is a conductive adhesive including a light-absorbing member. A light-shielding sheet having adhesiveness can be used as the adhesive layer 32 in the present modification.

By using the adhesive layer 32 as a conductive adhesive including a light-absorbing member in this way, reflected light reflected on the lower surface of the sensor substrate 20 or the surface of the adhesive layer 32 can be suppressed without deepening the dummy light-receiving elements 23.

In the above-described embodiment and modification, the LED is used as the optical element 10, but a semiconductor laser may be used.

While the preferred embodiments of the present invention have been described in detail, the present invention is not limited to the above embodiments, and various modifications and substitutions may be added to the above embodiments without departing from the scope of the present invention.