JP2001244494A - Optical tracking sensor - Google Patents

Abstract

(57) [Problem] To provide an optical tracking sensor capable of performing optical tracking and receiving light at high speed and high gain. SOLUTION: The optical tracking sensor is a sensor made of a compound semiconductor, and has a central avalanche photodiode AP.
D can be used for light reception, and the surrounding divided photodiodes PD1 to PD4 can be used for light tracking. Since these are formed on the same semiconductor substrate, if the semiconductor substrate is directed in the direction of the received light when light tracking is performed by the split photodiode, an optical signal automatically enters the avalanche photodiode APD. Since the surface shape of the avalanche photodiode APD is circular, edge breakdown is suppressed, and the light tracking photodiodes PD1 to PD4 are arranged concentrically.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical tracking sensor.

[0002]

2. Description of the Related Art A conventional optical tracking sensor is disclosed in JP-A-6-21.
No. 4010, JP-A-11-15023 and the like. The former optical tracking sensor has a CCD having a wide viewing angle and a four-division photodiode with high responsiveness individually, and the latter optical tracking sensor uses the same photodiode array arranged around the four-division photodiode. It is formed on a semiconductor substrate. In each of the optical tracking sensors, the central photoelectric conversion element is for optical tracking with priority given to responsiveness, and the peripheral photoelectric conversion elements are for optical tracking with priority given to the viewing angle. Such an optical tracking sensor can be used for a detector or an optical pickup for an earth observation satellite.

[0003]

However, in the optical tracking sensor, it is necessary to provide a separate optical signal receiving sensor for receiving the optical signal. of course,
In the latter sensor, optical reception can be performed by using all outputs of the four-division photodiode located at the center, but this configuration is insufficient for high-speed, high-gain reception. The present invention relates to an improvement of such an optical tracking sensor, and an object of the present invention is to provide an optical tracking sensor that performs optical tracking and can receive light at high speed and high gain.

[0004]

In order to solve the above-mentioned problems, an optical tracking sensor according to the present invention is provided by forming a divided photodiode comprising a plurality of photodiodes disposed around a single photodiode on a semiconductor substrate. In this optical tracking sensor, the surface shape of a single photodiode is circular, there are three or more photodiodes constituting a plurality of photodiodes, and the photodiodes are arranged concentrically.

According to the optical tracking sensor of the present invention, a single photodiode can be used for optical reception, and the surrounding divided photodiodes can be used for optical tracking, but these are formed on the same semiconductor substrate. Therefore, when the semiconductor substrate is directed in the direction of the received light when the optical tracking is performed by the split type photodiode, an optical signal is automatically incident on a single photodiode.

When edge breakdown occurs in such a single photodiode, it becomes difficult to receive an optical signal. Therefore, in the optical tracking sensor of the present invention,
The surface shape of a single photodiode is circular, and edge breakdown is suppressed.

Further, since the plane is defined by three points, the number of light-tracking photodiodes is three or more, and a circular photodiode for receiving an optical signal is located at the center of gravity of the plurality of light-tracking photodiodes. The plurality of light-tracking photodiodes are arranged concentrically with respect to the circular photodiode so that the plurality of light-tracking photodiodes are adjacent thereto. In the optical tracking sensor of the present invention, since the circular photodiode and the optical tracking photodiode are arranged as described above, in order to direct the circular photodiode in the receiving light incident direction, the output of each optical tracking photodiode is made equal. What is necessary is just to change the direction of a semiconductor substrate.

The number of light-tracking photodiodes is an even number of 3 or more, that is, four, and if the area of each light-tracking photodiode is substantially equal, the subtraction value between the adjacent light-tracking photodiode outputs is minimized. Such a servo control can be performed at high speed because the sensor may be rotated so that When the optical tracking sensor is used in the outer space, it is preferable that the semiconductor substrate be made of a compound semiconductor so that a malfunction due to the incidence of radiation such as cosmic rays can be suppressed and the response speed is increased.

Further, in order to perform a high-speed and high-gain operation, it is preferable that the single photodiode is an avalanche photodiode. In the present invention, the single photodiode has a circular surface shape. Therefore, the edge breakdown is suppressed in this case as well.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical tracking sensor according to an embodiment will be described below. The same elements will be denoted by the same reference symbols, without redundant description.

FIG. 1 is a plan view of the optical tracking sensor according to the first embodiment. In FIG. 1, the illustration of the insulating layer ILT shown in FIG. 2 is omitted. The optical tracking sensor is a sensor made of a compound semiconductor. More specifically, the semiconductor substrate constituting the optical tracking sensor is made of a compound semiconductor.
As this compound semiconductor material, GaAs, InGaAs
s, InAs, InSb, AlGaAs, InP and the like. By selecting a material to be used, optical communication of a desired wavelength becomes possible, and according to the material characteristics,
Characteristic sensors such as those that can suppress malfunction due to the incidence of radiation such as cosmic rays and those that have extremely high response speed can be obtained.

In this optical tracking sensor, a single photodiode (light receiving element) A for receiving an optical signal is provided at the center of the substrate.
A PD is arranged, and a plurality of photodiodes (light receiving elements) PD1, PD2, PD provided around the PD for light tracking.
3, PD4 is arranged.

That is, this optical tracking sensor is an optical tracking sensor in which a divided photodiode composed of a plurality of photodiodes PD1, PD2, PD3, and PD4 arranged around a single photodiode APD is formed on a semiconductor substrate. The surface shape of a single photodiode APD is circular, and a plurality of photodiodes PD1, PD2, P
There are three or more photodiodes constituting D3 and PD4, and they are arranged concentrically.

In other words, a plurality of photodiodes PD
Each of PD1, PD2, PD3 and PD4 is arranged at a position equidistant from the center of the circular photodiode APD.

According to this optical tracking sensor, a single photodiode APD can be used for light reception, and the surrounding divided photodiodes PD1, PD2, PD3, PD
4 can be used for optical tracking, but since they are formed on the same semiconductor substrate, the semiconductor substrate is oriented in the direction of the received light when the optical tracking is performed by the divided photodiodes PD1, PD2, PD3, and PD4. When turned on, an optical signal automatically enters a single photodiode APD.

In such a photodiode, if an edge breakdown occurs, it becomes difficult to receive an optical signal. However, in the present optical tracking sensor, the surface shape of a single photodiode APD is made circular to suppress the edge breakdown. There are things. That is, since the single photodiode APD is formed of an avalanche photodiode and has a circular surface shape, edge breakdown is suppressed.

Since the plane is defined by three points, the number of light-tracking photodiodes is preferably three or more. In this example, a plurality of light-tracking photodiodes PD1, PD2, PD3, and PD4 are used. The plurality of light-tracking photodiodes PD1, PD2, PD3, and PD4 are positioned so that the center of the circular photodiode APD for receiving an optical signal is located at the center of gravity, and the plurality of light-tracking photodiodes PD1, PD2, PD3, and PD4 are adjacent to the circular photodiode APD. PD
2, PD3 and PD4 are arranged concentrically with respect to the circular photodiode APD.

In the light tracking sensor, the circular photodiode APD and the light tracking photodiode P
Since D1, PD2, PD3, and PD4 are arranged,
In order to direct the circular photodiode APD in the receiving light incident direction, each of the light tracking photodiodes PD1, PD2, P
The direction of the semiconductor substrate may be changed so that the outputs of D3 and PD4 become equal.

The number of light-tracking photodiodes may be three or more. In this embodiment, the number of light-tracking photodiodes is an even number of three or more, that is, four.
Since the areas of PD1, PD2, PD3, and PD4 are substantially equal, light tracking control is simple.

More specifically, the substrate is rotated about these boundaries as a rotation axis so that the photodiode output located in the quadrant adjacent to the specific photodiode matches the specific photodiode output.

That is, when the output of the adjacent photodiode is smaller than the specific photodiode output, the substrate is rotated in one direction about the rotation axis, and when the output difference is large, the substrate is rotated in the opposite direction. When it becomes smaller, it is further rotated in the same direction, and when it becomes equal, it is stopped, and this control (servo control for light tracking) is performed by the adjacent light tracking photodiodes PD1, PD
Light tracking can be easily performed by performing all of 2, PD3 and PD4.

In this case, the light tracking photodiode PD
1, a single photodiode APD can be directed in the direction of incidence of the received light based on the outputs of PD1, PD2, PD3 and PD4, and the operation required for this control is only the subtraction of each output. Can be done.

Each light tracking photodiode PD1,
The surface shapes of PD2, PD3, and PD4 are fan-shaped. Detail
Then, the surface shape of the light tracking photodiode PD1 becomes
An arc adjacent to a part of the circumference of the circular photodiode APD
(Inner arc) and circles with larger diameters
Connect both ends of the arc (outer arc) that is part of the circumference
And the diameter of each circle is r_small, R_big
Then, the length of the arc inside the photodiode PD1 =
(About) 0.5πr_small, Outer arc length = (approximately) 0.
5πr_big(Π is the pi). The length of each arc
Has a boundary area between the photodiodes,
These values (0.5πr_big, 0.5πr_{s mall})than
Slightly shorter. Other photodiode PD2 for light tracking, PD
3. The surface shape of PD4 is the same as photodiode PD1
It is.

The light-tracking photodiodes PD1, P
D2, PD3, PD4 and photodiode APD for optical reception
An annular guard ring 1g is provided at the boundary between the two. In this example, the length r _big = 495 μm from the center of the photodiode APD to the outer arc, and the length r _small = 70 μ m from the center of the photodiode APD to the inner arc.
m, the width c of the guard ring 1 g was set to 10 μm, the diameter d of the photodiode APD was set to 50 μm, and the gap b between the divided photodiodes was set to 10 μm.

The light carrying the optical signal becomes a spot light on the light receiving surface. When the spot light is on the light tracking sensor, the present sensor functions as follows. The two orthogonal coordinate systems that define the light receiving surface of the optical tracking sensor are defined as an X axis and a Y axis. That is, the light receiving surface has the X axis and Y
Axes, which are orthogonal. The X-axis and the Y-axis correspond to each photodiode PD in the divided photodiode.
1, located on the boundary line between PD2, PD3 and PD4.

The spot light is the photodiode P in the first quadrant.
When the light enters D1, the output of the photodiode PD1 is output from the electrode pad P1, but no output is obtained from the other photodiodes PD2, PD3, and PD4. In such a case, the photodiode PD in the adjacent quadrant
2. Until the same output is obtained from PD4, X axis and Y
By rotating the optical tracking sensor about the axis, the outputs of the four photodiodes PD1, PD2, PD3, PD4 are made equal. As described above, when the sensor is rotated, the optical signal is automatically incident on the central photodiode APD.

From this state, when the output of any of the tracking photodiodes PD1, PD2, PD3, PD4 slightly increases, the optical tracking sensor is set around the X axis and the Y axis so that the output decreases. The sensor is rotated to control the optical signal to enter the photodiode APD, and the sensor tracks the optical signal. Next, a vertical sectional configuration of the optical tracking sensor will be described.

FIG. 2 is a sectional view of the optical tracking sensor shown in FIG.
It is II arrow line sectional drawing.

In the region where the light receiving photodiode APD is formed, a buffer 1b, a light absorbing layer 1a (APDi), an n-type layer APDn, p
A mold layer APDp is sequentially formed. A p-type guard ring 1g is formed so as to surround the periphery of the n-type layer APDn and the p-type layer APDp, and the upper surface electrode eua is formed and connected to the guard ring 1g. A lower surface electrode el is formed on the back surface side of the semiconductor substrate 1s. Carriers generated by the incidence of light on the light absorption layer APDi are converted into pn junctions (n-type layer APDn and p-type layer APD
accelerated in p), avalanche amplified and the electrode eu
Output from a and el. Since the upper electrode eua is connected to the electrode pad Pa, an optical reception output is obtained from the electrode eua.

In the region where the light-tracking photodiode PD3 is formed, a buffer 1b, a light-absorbing layer 1a, and a p-type layer 1p3 are sequentially formed on a semiconductor substrate 1s, and an upper electrode eu3 is formed on the p-type layer 1p3. (See Figure 1)
A lower surface electrode el is formed on the back surface of the substrate. In this example, the light absorbing layer 1a is of a low concentration n-type,
p3 and the light absorbing layer 1a constitute a pn junction. Carriers generated by the incidence of light on the light absorption layer 1a move by an electric field in the pn junction (p-type layer 1p3 and light absorption layer 1a) in a state where a reverse bias is applied, and the electrodes eu3,
Output from el. The electrode eu3 on the upper surface side is the insulating layer I
Since it is connected to the electrode pad P3 via the wiring that runs on the LT, an optical reception output is obtained from this. A plurality of openings for forming electrodes are formed in the insulating layer ILT, and the electrodes eua, eu1, eu2, eu3, eu4, e
ui are respectively located in these openings.

In the region where the light-tracking photodiode PD4 is formed, a buffer 1b, a light-absorbing layer 1a, and a p-type layer 1p4 are sequentially formed on a semiconductor substrate 1s, and an upper electrode eu4 is formed on the p-type layer 1p4. (See Figure 1)
A lower surface electrode el is formed on the back surface of the substrate. As described above, the light absorbing layer 1a is a low concentration n-type, and the p-type layer 1p4
And the light absorption layer 1a constitute a pn junction. Light absorbing layer 1
Carriers generated by the incidence of light on a move due to the electric field in the pn junction (p-type layer 1p4 and light absorbing layer 1a) in the state where a reverse bias is applied, and the electrodes eu4, el
Output from The upper electrode eu4 is an electrode pad P4
, The optical reception output is obtained from this.

Other light-tracking photodiodes PD1,
The vertical sectional structure of PD2 is a photodiode PD for light tracking.
3 and PD4, the outputs of which are supplied to electrode pads P1, P2 via electrodes eu1, eu2 formed on the front side.
2 output.

The tracking photodiodes PD1 to PD1
4, a P-type region 1pi is formed, and the same potential as that of the lower electrode el is applied to the P-type region 1pi via the electrode pad Pi and the upper electrode eui.

The boundary between the tracking photodiodes PD1 to PD4 is n-type, and the boundary between the light receiving photodiode APD and the tracking photodiodes PD1 to PD4 is also n-type, so that the isolation between these elements is maintained. ing. This n-type isolation layer (cap layer)
The lower isolation layer 1 comprises a lower isolation layer 1nl and an upper isolation layer 1nu.
The impurity concentration of nl is set higher. In this tracking sensor, after forming two n-type layers on the light absorption layer as the above-mentioned isolation layers, the above-mentioned respective p-type regions are formed therein. For the formation, a diffusion method or an ion implantation method is used. Further, the buffer layer 1b, the light absorbing layer 1a,
The lower isolation layer 1nl and the upper isolation layer 1nu are formed by CVD, MBE or MOCVD.
And the like. The material of the semiconductor layers, the thickness and impurity concentration are as follows, an insulating layer ILT is made of SiO ₂ or SiN _X.

[0035]

[Table 1]

The light-tracking photodiodes PD1 to PD1
The surface shape of the PD 4 may be as follows.

FIG. 3 is a plan view of the optical tracking sensor according to the second embodiment, and FIG. 4 is a view showing the IV-IV of the optical tracking sensor shown in FIG.
It is arrow sectional drawing. In FIG. 3, the illustration of the insulating layer ILT shown in FIG. 4 is omitted.

The optical tracking sensor according to the present embodiment differs from the optical tracking sensor described in the first embodiment only in that the surface shapes of the photodiodes PD1 to PD4 for optical tracking are changed. Is the same as that of the first embodiment.

Each light tracking photodiode PD1, PD
2. The surface shape of PD3, PD4 is one of the rectangular corners long.
It has a shape cut out by an arc bulging inside a square. Details
In other words, the surface shape of the light tracking photodiode PD1
Is adjacent to a part of the circumference of the circular photodiode APD
An arc (inside arc) with one of the corners of a rectangle cut out
Having. In this example, this rectangle is a square,
The length of the side is r_bigbe equivalent to. Photodiode PD1
Is the same (about) 0.5π as in the above embodiment.
r_smallAnd the respective photodiodes PD1 to PD
The length of each arc of D4 is such that the boundary area between the photodiodes is
Because there is, this value (0.5πr_{smal l})than
Slightly shorter. Other photodiode PD2 for light tracking, PD
3. The surface shape of PD4 is the same as photodiode PD1
It is.

As described above, according to the optical tracking sensor described in the above embodiment,
Optical tracking and high-speed, high-gain optical reception become possible.
The sensor may be made of Si, but is preferably a compound semiconductor. The avalanche photodiode APD located at the center of the substrate may have a superlattice structure. Further, as a material of the semiconductor substrate 1s, another compound semiconductor, for example, n-type GaAs can be used. In this case, the buffer layer 1b is n-type GaAs, and the light absorbing layer 1a is n-type or intrinsic GaAs.
The lower cap layer 1nl can be an n-type GaAs, and the upper cap layer 1nu can be an n-type AlGaAs layer.
When the conductivity type of the semiconductor substrate 1s is inverted to be p-type, the conductivity types of the other layers are also inverted collectively.

[0041]

As described above, according to the optical tracking sensor of the present invention, it is possible to perform optical tracking and receive light at high speed and high gain.

[Brief description of the drawings]

FIG. 1 is a plan view of an optical tracking sensor according to a first embodiment.

FIG. 2 is a sectional view of the optical tracking sensor shown in FIG. 1 taken along the line II-II.

FIG. 3 is a plan view of an optical tracking sensor according to a second embodiment.

FIG. 4 is a sectional view taken along the line IV-IV of the optical tracking sensor shown in FIG. 3;

[Explanation of symbols]

APD: a single photodiode; PD1 to PD4: split photodiodes.

Claims (3)

[Claims] 1. An optical tracking sensor comprising a plurality of photodiodes arranged around a single photodiode formed on a semiconductor substrate.
The surface shape of the single photodiode is circular, and the photodiodes constituting the plurality of photodiodes are 3
An optical tracking sensor, comprising: at least two light concentric sensors; 2. The optical tracking sensor according to claim 1, wherein the semiconductor substrate is made of a compound semiconductor. 3. The optical tracking sensor according to claim 1, wherein the single photodiode comprises an avalanche photodiode.