Phototransistor

Abstract

To provide an innovative phototransistor sensor element which improves the withstand voltage capability of a phototransistor, reduces shielding of a base light receiving region by an emitter pad, and improves the performance of the sensor element.SOLUTION: The phototransistor includes a substrate, a light receiving region, an emitter active region, and an emitter electrode, wherein the light receiving region is disposed on the substrate. The emitter active region is disposed in a central region of the light receiving region to maximize a distance between an edge of the emitter active region and an edge of the light receiving region. The emitter electrode is electrically connected to the emitter operation region.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a phototransistor sensor element, and more particularly to a high-voltage phototransistor sensor element. [Background technology]

[0002] A phototransistor is a semiconductor device that converts optical signals into electrical signals. It is similar to a conventional bipolar junction transistor (BJT), and its base can be controlled by optical signals as well as current signals. Phototransistors are typically used for light detection and are applicable to, for example, photocouplers and photoelectric detectors.

[0003] The basic structure of a phototransistor is similar to that of a conventional bipolar junction transistor, usually an NPN or PNP structure. When light shines on the base region of a phototransistor, the photons excite electrons, creating electron-hole pairs. These electrons and holes are separated by the action of an electric field to form the base-collector current (IBC). Due to the flow of electrons in the base, the generated electrons mainly flow to the emitter, increasing the emitter-collector current (IEC). The IEC is usually larger than the IBC because most of the photo-generated electrons flow out through the emitter. This is the amplification effect of the phototransistor. The IEC and IBC are related as follows: IEC = β × IBC. β is the current amplification factor of the phototransistor, which is greater than 1 and typically ranges from tens to hundreds.

[0004] Figure 1 shows a conventional phototransistor 1 with a typical NPN structure. The emitter 10 and the emitter pad 20 above the emitter 10 of this type of phototransistor 1 are usually located at the edge of the device. However, this type of phototransistor structure has problems such as low breakdown voltage and the emitter pad blocking the base light-receiving region, and improvements are urgently needed. Summary of the Invention

[0005] The primary object of the present invention is to provide an innovative phototransistor sensor element that improves the breakdown voltage capability of the phototransistor, reduces the shielding of the base light receiving region by the emitter pad, and improves the performance of the sensor element.

[0006] To achieve the above object, the present invention provides a phototransistor including a substrate, a light-receiving region, an emitter active region, and an emitter electrode. The light-receiving region is disposed on the substrate. The emitter active region is disposed in a central region of the light-receiving region, thereby maximizing the distance between an edge of the emitter active region and an edge of the light-receiving region. The emitter electrode is electrically connected to the emitter active region.

[0007] In the phototransistor embodiment of the present invention, the distance between the edge of the emitter active area and the edge of the light receiving area is made uniform.

[0008] In an embodiment of the phototransistor of the present invention, the edges of the emitter active area are circular.

[0009] In an embodiment of the phototransistor of the present invention, the edges of the emitter active area are quadrilaterals.

[0010] In an embodiment of the phototransistor of the present invention, the emitter electrode includes a pad portion and an extension portion, the pad portion being located on the edge of the light-receiving region, and the extension portion extending from the pad portion to the emitter operating region and electrically connected to the emitter operating region.

[0011] In an embodiment of the phototransistor of the present invention, the extension has a shape that corresponds to the shape of the edge of the emitter active region.

[0012] In embodiments of the phototransistor of the present invention, the extension is in the form of a closed or open hollow ring, thereby substantially reducing the obscuration of the light receiving area below the emitter active area.

[0013] In an embodiment of the phototransistor of the present invention, the extensions are striped, thereby substantially reducing the obscuration of the light receiving area below the emitter active area.

[0014] In an embodiment of the phototransistor of the present invention, the emitter electrode further includes an outer ring portion that extends outward from the pad portion and surrounds the edge of the light-receiving area.

[0015] In an embodiment of the phototransistor of the present invention, the phototransistor further includes a base electrode, which is electrically connected to the light-receiving region and disposed at a diagonal position of the pad portion on the light-receiving region.

[0016] In an embodiment of the phototransistor of the present invention, the phototransistor further includes a base electrode, which is electrically connected to the light-receiving region and disposed near a side of the light-receiving region that is parallel to the side adjacent to the pad portion.

[0017] In phototransistor embodiments of the present invention, the substrate is the collector.

[0018] In an embodiment of the phototransistor of the present invention, the phototransistor further includes a collector electrode, which is disposed on the surface of the substrate opposite to the light-receiving region.

[0019] In an embodiment of the phototransistor of the present invention, the phototransistor further includes an anti-reflection layer disposed on the light-receiving region and a portion of the substrate.

[0020] Those skilled in the art can understand other objects of the present invention, as well as the technical means and embodiments of the present invention, by referring to the drawings and the embodiments described below. [Brief explanation of the drawings]

[0021] [Figure 1] Plan view showing a conventional phototransistor [Figure 2] 1 is a schematic diagram illustrating a phototransistor according to an embodiment of the present invention; [Figure 3]1 is a plan view illustrating several embodiments of the phototransistor of the present invention; [Figure 4] 1 is a plan view illustrating several embodiments of the phototransistor of the present invention; [Figure 5] 1 is a plan view illustrating several embodiments of the phototransistor of the present invention; [Figure 6] 1 is a plan view illustrating several embodiments of the phototransistor of the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0022] The present invention will be described below through examples. Note that the examples of the present invention are merely examples of embodiments and are not intended to limit the present invention to the environments, applications, or specific aspects described in the examples. Therefore, the explanation of the examples is intended to explain the present invention, but does not limit the present invention. Note that components not directly related to the present invention are omitted and not shown in the embodiments and drawings. The dimensional relationships between the components in the drawings are intended to facilitate understanding and do not limit the actual dimensions.

[0023] The present invention relates to a phototransistor sensor element, particularly a high-voltage phototransistor sensor element. The description will be made with reference to FIGS. 2(A) and 2(B). FIG. 2(A) is a plan view showing a phototransistor according to an embodiment of the present invention. FIG. 2(B) is a cross-sectional view of the phototransistor of FIG. 2(A) taken along the line AA'. As shown in FIG. 2(B), the phototransistor 100 has a substrate 110, a light-receiving region 120, an emitter operating region 130, a collector electrode 140, a base electrode 150, and an emitter electrode 160. In a specific embodiment, the substrate 110 has an N-type compound semiconductor layer, for example, an N-type gallium arsenide (GaAs) layer, formed by epitaxial growth. Sulfur (S) or silicon (Si) is used as an N-type dopant, and the N-type compound semiconductor layer is formed by epitaxial growth. 15 ~10 17 / cm 3The light receiving region 120 is a P-type compound semiconductor layer, such as a P-type gallium arsenide (GaAs) layer, disposed on the substrate 110, and is doped using zinc (Zn) or magnesium (Mg) as a P-type dopant, for example, at a low concentration of 10 17 ~10 19 / cm 3 The emitter operating region 130 is an N-type compound semiconductor layer located in the central region of the light receiving region 120. The emitter operating region 130 is an N-type gallium arsenide (GaAs) layer, and is doped using sulfur (S) or silicon (Si) as an N-type dopant, for example, 10 18 ~10 20 / cm 3 The doping concentration may be, but is not limited to,

[0024] In this embodiment, for example, the phototransistor 100 is an NPN-type bipolar junction transistor. The substrate 110 is the collector of the phototransistor 100. The light-receiving region 120 is the base of the phototransistor 100. The emitter active region 130 is the emitter of the phototransistor 100. When light is irradiated onto the surface of the light-receiving region 120, photons are effectively absorbed, exciting electrons and generating electron-hole pairs. The electron-hole pairs are separated by the action of an electric field to form a current. These electron-hole pairs are collected between the light-receiving region 120 and the substrate 110, forming a base-collector current (IBC). Meanwhile, the flow of electrons in the light-receiving region 120 increases the emitter-collector current (IEC) between the emitter active region 130 and the substrate 110. In another embodiment, the phototransistor 100 of the present invention can be a PNP-type bipolar junction transistor. Those skilled in the art can easily imagine other embodiments after understanding the present invention. The following will specifically describe the technical features of the present invention by taking an NPN bipolar junction transistor as an example.

[0025] To address the problem of low breakdown voltage of conventional phototransistors, a technical feature of the present invention is to adjust the emitter active area to improve the breakdown voltage capability of the phototransistor sensor element. As shown in FIG. 2B, the inventors discovered that the distance (d) between the edge of the emitter active area 130 and the edge of the light-receiving area 120 affects the breakdown voltage capability of the phototransistor. Therefore, to improve the breakdown voltage capability of the phototransistor, the present invention maximizes the distance (d) between the edge of the emitter active area 130 and the edge of the light-receiving area 120. While the emitter active area is located at the edge of the element in the prior art, the phototransistor 100 of the present invention places the emitter active area 130 in the central region of the light-receiving area 120, as shown in the figure, thereby increasing the distance between the edge of the emitter active area 130 and the edge of the light-receiving area 120.

[0026] FIG. 3 is a plan view illustrating several embodiments of the phototransistor of the present invention. FIG. 3 illustrates the emitter active region 130 of various sizes and shapes in several embodiments of the phototransistor 100 of the present invention. For example, the edges of the emitter active region may be circular, quadrilateral, or any other shape. A circular emitter active region can minimize the emitter area. On the other hand, the distance between the edge of the quadrilateral emitter active region and the edge of the light-receiving region 120 is uniform, thereby improving the breakdown voltage capability of the element. The size of the emitter active region can also be adjusted according to the characteristics of the sensor element.

[0027] As shown in FIG. 2B , the collector electrode 140 of the phototransistor 100 of the present invention is disposed on the opposite side of the substrate 110 from the light-receiving region 120 and is electrically connected to the substrate 110. The emitter electrode 160 includes an extension portion 162, a pad portion 164, and an outer ring portion 166. The pad portion 164 is disposed on the edge of the light-receiving region 120. The extension portion 162 extends from the pad portion 164 to the emitter operating region 130 and is electrically connected to the emitter operating region 130. Because the phototransistor electrode is made of a non-transparent metal material, the present invention designs the extension portion 162 extending from the pad portion 164 to above the emitter operating region 130 in a hollow ring or stripe shape to prevent the extension portion 162 above the emitter operating region 130 of the phototransistor from excessively shielding the light-receiving region 120 below the emitter operating region 130. As shown in FIG. 4, the extension 162 has a closed hollow ring shape or an open hollow ring shape. However, the extension 162 can also be designed in a stripe shape to substantially reduce shading of the light-receiving region below the emitter active region and achieve an optimal current path. Also, as shown in FIGS. 3 and 4, the extension 162 can be designed in a shape corresponding to the edge shape of the emitter active region 130. For example, the extension can be designed in a closed hollow ring shape, such as a circle or a rectangle, an open hollow ring shape, or a stripe shape. Furthermore, because the extension 162 of the emitter electrode 160 is designed in a hollow ring shape or a stripe shape, the pad portion 164 for external wiring should be located as close to the edge of the light-receiving region 120 as possible. As shown in the figure, by placing the pad portion 164 at the corner of the device, shading of the light-receiving region by the non-transparent pad can be substantially reduced. Similarly, the outer ring portion 166 of the emitter electrode 160 extends outward from the pad portion 164 and is disposed to surround the edge of the light-receiving region 120. However, the present invention also allows the emitter electrode 160 to be designed without the extension portion, without the outer ring portion, or with the pad portion 164 disposed on the emitter active region 130, as shown in Figure 5, according to different specification requirements in the actual application of the phototransistor sensor element. These are all possible embodiments of the present invention.

[0028] FIGS. 2A and 6 show several different embodiments of the base electrode 150 in the phototransistor 100 of the present invention. The base electrode 150 of the phototransistor 100 of the present invention is disposed on the light-receiving region 120 and is electrically connected to the light-receiving region 120. When the phototransistor 100 is not exposed to external light, an external IBC current is provided through the base electrode 150, thereby inducing an IEC current. The base electrode 150 of the phototransistor 100 of the present invention can be disposed at a diagonal position of the pad portion 164 as shown in FIG. 2A. Alternatively, it can be disposed near a side parallel to the side adjacent to the pad portion 164 as shown in FIG. 6. Furthermore, FIG. 6 also shows a case where the base electrode 150 is omitted in some phototransistor sensor elements, and the IBC current is generated simply by external light irradiation. This is also a possible embodiment of the present invention.

[0029] In a more preferred embodiment, an anti-reflective coating is provided on the device surface of the phototransistor 100 to improve photoelectric conversion efficiency. As shown in FIG. 2B, the anti-reflective layer 170 is provided on the light-receiving region 120 and a portion of the substrate 110, thereby reducing reflection loss when external light is irradiated onto the surface of the phototransistor and increasing the transmittance of the incident light. As more external light is irradiated into the phototransistor and absorbed by the light-receiving region 120, more electron-hole pairs are generated, thereby improving photoelectric conversion efficiency. The anti-reflective layer 170 may be made of silicon dioxide (SiO), silicon nitride (SiN), aluminum oxide (AlO), magnesium fluoride (MgF), or the like.

[0030] The above examples are intended to explain embodiments of the present invention and to explain the characteristic configurations of the present invention. The present invention is not limited to the above examples. Modifications or equivalent arrangements that can be easily made by those skilled in the art are also within the scope of the present invention. The scope of protection of the rights of the present invention is based on the claims. [Explanation of symbols]

[0031] 1 phototransistor 10 Emitters 20 Emitter Pad 100 Phototransistor 110 Substrate 120 light receiving area 130 Emitter operating region 140 Collector electrode 150 base electrode 160 Emitter electrode 162 Extension 164 Pad section 166 Outer ring part 170 Anti-reflection layer d distance AA' cross section line

Claims

1. A phototransistor, A substrate; a light receiving region disposed on the substrate; an emitter active area located in a central region of the light receiving area, thereby maximizing the distance between an edge of the emitter active area and an edge of the light receiving area; an emitter electrode electrically connected to the emitter active region.

2. 2. The phototransistor according to claim 1, wherein the distance between the edge of the emitter active region and the edge of the light receiving region is uniform.

3. 2. The phototransistor of claim 1, wherein the edge of the emitter active area is circular.

4. 2. The phototransistor of claim 1, wherein the edge of the emitter active area is a quadrilateral.

5. the emitter electrode includes a pad portion and an extension portion, the pad portion is disposed on the edge of the light receiving area; 2. The phototransistor according to claim 1, wherein the extension portion extends from the pad portion to the emitter operating region and is electrically connected to the emitter operating region.

6. 6. The phototransistor according to claim 5, wherein the extension has a shape corresponding to the shape of the edge of the emitter active region.

7. 6. The phototransistor of claim 5, wherein the extension is a closed or open hollow ring, thereby substantially reducing shading of the light receiving region below the emitter active region.

8. 6. The phototransistor of claim 5, wherein the extension is striped, thereby substantially reducing shading of the light receiving region below the emitter active region.

9. the emitter electrode further includes an outer ring portion; 6. The phototransistor according to claim 5, wherein the outer ring portion extends outward from the pad portion and surrounds the edge of the light receiving region.

10. further comprising a base electrode; 6. The phototransistor according to claim 5, wherein the base electrode is electrically connected to the light-receiving region and is disposed at a diagonal position of the pad portion on the light-receiving region.

11. further comprising a base electrode; 6. The phototransistor according to claim 5, wherein the base electrode is electrically connected to the light-receiving region and is disposed near a side of the light-receiving region that is parallel to a side adjacent to the pad portion.

12. 2. The phototransistor of claim 1, wherein the substrate is a collector.

13. further comprising a collector electrode; The phototransistor according to claim 12 , wherein the collector electrode is disposed on a surface of the substrate opposite to the light-receiving region.

14. The phototransistor of claim 12 , further comprising an anti-reflection layer disposed on the light-receiving region and a portion of the substrate.

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