JPH06215405A - Photodetector for optical pickup device - Google Patents

Abstract

PURPOSE:To obtain a photodetector capable of obtaining an exact focusing error signal by shielding an unwanted light projected on the periphery of each light receiving cell for focusing control. CONSTITUTION:Bulging parts 7a, 9a are formed on prescribed draw-out patterns 7, 9 among the draw-out patterns 7-12 for deriving respective light receiving outputs obtained by every one of light receiving cells 1-6. The periphery of light receiving cells 1-4 for focusing control is shielded by these bulging parts and unwanted lights projected on the periphery of the light receiving cells 1-4 for focusing control are interrupted by the draw-out patterns 7-12 including the bulging parts 7a, 9a.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device for detecting a focus error of a light beam used for signal recording or signal reproduction on a disc signal surface by an astigmatism method. The present invention relates to a semiconductor photodetector used for detecting an error.

[0002]

2. Description of the Related Art In an optical pickup device for generating a light beam used for signal recording or signal reproduction, in general, the focus of the light beam is adjusted by driving an objective lens in the optical axis direction of the light beam. Matching to the signal side of the medium is performed. Therefore, in the optical pickup device, it is necessary to detect the focus error of the light beam, which is the error between the focus of the light beam and the signal surface of the medium.
As an optical pickup device used in an optical disc player, an astigmatism method is mainly used as a focus control method for detecting a focus error of a light beam and performing control to correct the focus error.

As is well known, the astigmatism method imparts astigmatism to a light beam, shifts the focal position in the x direction and the y direction of the light beam, and produces a light beam having the astigmatism.
Addition signals of light receiving outputs received by a photodetector having four light receiving areas divided by cross-shaped dividing lines and obtained from the respective light receiving areas arranged on respective diagonal lines of the four light receiving areas. The focus error signal corresponding to the focus error of the light beam is obtained by detecting the difference between the two. Then, by displacing the objective lens in the optical axis direction in accordance with the focus error signal, the focal point of the light beam is made to follow the signal surface of the medium to be in agreement.

By the way, the photodetector currently used is generally formed by a semiconductor element, and each light receiving cell forming each light receiving region is formed by a photodiode having a PN junction of a semiconductor. Then, in the photodetector formed by the semiconductor element, due to its structure, when the substrate of the semiconductor chip is irradiated with light even in a region other than the region where the light receiving cell is formed, a current flows to the nearest light receiving cell, The light receiving output obtained from the light receiving cell is affected.

Most of the current optical pickup devices are, for example, as shown in Japanese Utility Model Laid-Open No. 64-35518.
In order to perform tracking control that causes the light beam to follow the signal track of the medium, the three-beam method that uses a sub-beam before and after the main beam of the light beam used for signal reproduction is adopted. Light receiving cells for tracking control are formed adjacent to each other before and after sandwiching each light receiving cell for focus control.

FIG. 2 shows the arrangement of the respective light receiving cells of such a photodetector. In FIG. 2, the respective light receiving cells A to D for focus control are arranged in a cross shape divided by dividing lines. , And light receiving cells E and F for tracking control are arranged before and after that. In this case, each of the light receiving cells A
If the received light outputs obtained from ~ F are a to f respectively,
The light receiving sensitivity distributions of the respective light receiving cells in the XX 'direction and the YY' direction in FIG. 2 are as shown in FIGS. 3A and 3B, respectively.

As can be seen from FIGS. 3 (a) and 3 (b), if the light receiving cells are not formed adjacent to each other, the peripheral portion of the light receiving cell has a light receiving sensitivity even outside the light receiving cell region. In the case of the photodetector of FIG. 2, the light receiving cells A and C for focus control and the light receiving cells E and F for tracking control apparently have light receiving sensitivity as if the area of the light receiving cell is enlarged.

[0008]

By the way, the focus control is performed by (a + c) -of the light receiving outputs of the light receiving cells A to D.
By electrically adjusting the point at which the voltage level of the focus error signal obtained by performing the calculation of (b + d) becomes "0", the focus of the light beam is made to be the focus point that matches the signal surface of the medium, This is performed by determining the displacement amount and direction of the focus of the light beam according to the voltage level and polarity of the error signal. Therefore, when the light receiving cells A and C in one diagonal direction and the light receiving cells B and D in the other diagonal direction greatly differ from each other as in the photodetector in FIG. 2, the solid line in FIG. As described above, the point where the voltage level of the focus error signal becomes "0" needs to be one point of the in-focus point. As shown by the broken line in FIG. 4, the focus of the light beam is in front of (or behind) the signal surface of the medium. There is a problem in that the voltage level of the focus error signal becomes "0" at a position greatly separated from each other, and focus control is performed with that position as the focal point.

In the range w shown in FIG. 4, the focus can be controlled and the light beam can be focused on the signal surface of the medium.

[0010]

In view of the above-mentioned problems, the present invention provides a lead-out pattern for deriving each received light output obtained for each light receiving cell for focus control formed by the semiconductor chip. By forming a bulge portion in the predetermined lead-out pattern, the periphery of the light-receiving cell is covered with the above-mentioned lead-out pattern, and unnecessary light irradiated around the light-receiving cell of the semiconductor chip is shielded by the lead-out pattern. I have to.

[0011]

The present invention relates to a semiconductor chip photodetector,
Even if the light receiving cell is formed in a region other than the area where the light receiving cell is formed by irradiating the substrate with light, a current flows to the nearest light receiving cell, but the substrate is irradiated with light. Pay attention to the fact that no charge is generated unless the light receiving output is derived from each light receiving cell on the semiconductor chip. A peripheral portion of the light receiving cell in which the cell is not formed is covered by forming a bulge portion in the extraction pattern to prevent the substrate from being irradiated with light by the extraction pattern.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of the present invention and shows the light receiving surface of a photodetector composed of a semiconductor chip. In the photodetector of FIG. 1, focus control is based on the astigmatism method. Correspondingly, the tracking control corresponds to the 3-beam method.

In FIG. 1, reference numerals 1 to 4 denote light receiving cells for focus control, which are arranged in a four-divided shape of a square.
Reference numerals 5 and 6 denote tracking control light receiving cells which are arranged in front of and behind the light receiving cells 1 to 4, respectively.

On the semiconductor chip on which the above-mentioned light receiving cells 1 to 6 are formed, independent lead patterns 7-1 for deriving each light receiving output obtained for each light receiving cell 1 to 6.
2 is formed by aluminum vapor deposition. Of the lead-out patterns 7 to 12, the lead-out patterns 7 and 9 connected to the light receiving cells 1 and 3 have bulging portions 7a and 9 respectively.
a is formed. The bulging portion 7a extends so as to be close to the extraction pattern 8 immediately after the extraction pattern 7 is extracted from the light receiving cell 1, and covers one side of the periphery of the light reception cells 1 and 2 together with the extraction patterns 7 and 8. There is. On the other hand, the bulging portion 9a is bulged so as to be close to the lead-out pattern 10 immediately after the lead-out pattern 9 is pulled out from the light-receiving cell 1, and covers one side around the light-receiving cells 3 and 4 together with the lead-out patterns 9 and 10. ing.

That is, the light receiving cell 1 for focus control
No. 4 to No. 4 have the other light receiving cells arranged adjacent to each other on the periphery, or the lead patterns 7 to 10 and the bulging portions 7a and 9a on the sides where the other light receiving cells are not arranged adjacent to each other. Will be covered. Therefore, as the focus of the light beam is far away from the signal surface of the medium, the light spot irradiated on the photodetector in FIG. 1 extends outside the area of the light receiving cells 1 to 4 for focus control as shown by the broken line. However, most of the light spots irradiated to the outside of the area are the light receiving cells 5 and 6 for tracking control, and the extraction patterns 7-1.
It is blocked by 0 and the bulging portions 7a and 9a. In particular, by forming the bulging portions 7a and 9a on the extraction patterns 7 and 9, respectively, the maximum shielding area is secured between the extraction patterns 7 and 8 and between the extraction patterns 9 and 10, and focus control is performed. In the vicinity of each of the light receiving cells that affects the light receiving output obtained from each of the light receiving cells 1 to 4, shielding is performed almost all around.

Therefore, in each light receiving cell for focus control, there is almost no current flowing from the periphery thereof,
The light receiving sensitivity distribution of the light receiving output obtained from each of the light receiving cells is almost determined only by the light receiving cell region range and becomes almost uniform in each light receiving cell, and the focusing error signal obtained by calculating each of the light receiving outputs is As shown by the solid line in 4, the point where the voltage level becomes "0" is only one point at the focal point.

[0017]

As described above, according to the present invention, the bulging portion is formed in the extraction pattern so as to shield the unnecessary light radiated to the periphery of each light receiving cell for focus control. The accuracy of the light receiving output obtained from each of the light receiving cells can be increased, and an accurate focus error signal can be obtained.

[Brief description of drawings]

FIG. 1 is an arrangement view showing a light receiving surface of a photodetector formed of a semiconductor chip according to an embodiment of the present invention.

FIG. 2 is a layout diagram showing an example of an array of light receiving cells of a photodetector.

3A is a characteristic diagram showing a light receiving sensitivity distribution of each light receiving cell in the XX ′ direction of FIG. 2, and FIG. 3B is a characteristic diagram showing Y− of FIG.
FIG. 9 is a characteristic diagram showing a light receiving sensitivity distribution of each light receiving cell in the Y ′ direction.

FIG. 4 is a characteristic diagram showing a focus error signal.

[Explanation of symbols]

 1,2,3,4 Focus control light receiving cell 5,6 Tracking control light receiving cell 7,8,9,10,11,12 Lead-out pattern 7a, 9a Swelling portion

Claims (1)

[Claims] 1. A light receiving cell for converting a received light signal into an electric signal is constituted by a semiconductor chip formed by a plurality of PN junctions of a semiconductor in a predetermined arrangement, and each light receiving obtained for each light receiving cell for focus control. In the photodetector of the optical pickup device for detecting the focus error of the light beam on the signal surface of the disc by using the output, the extraction pattern for deriving each light reception output obtained for each light reception cell is the semiconductor chip. The extraction pattern covers the periphery of the focus control light-receiving cell by forming a bulge portion on the predetermined extraction pattern while forming the above-mentioned unnecessary pattern on the periphery of the focus control light-receiving cell. A photodetector for an optical pickup device, which is characterized in that it is shielded by an optical pickup device.