KR20030058278A - Unit pixel layout in CMOS image sensor - Google Patents

Abstract

PURPOSE: A unit pixel layout of a CMOS image sensor is provided to be capable of maximizing charge transfer efficiency and data conversion gain and improving sensitivity of vertical and horizontal directions. CONSTITUTION: A unit pixel is provided with a photodiode(301) having an octangular shape. A gate(302) of a transfer transistor is formed to connect one side of the octangular shape. Metal interconnections are formed on the photodiode, wherein the virtual inner region of the metal interconnection has an octangular shape. A color filter and a microlens are sequentially stacked on the photodiode(301). At this time, the color filter and the microlens have a rhombic shape, wherein the length of vertical and horizontal directions is longer than that of one side of the rhombic shape.

Description

Unit pixel layout in CMOS image sensor

The present invention relates to a CMOS image sensor integrated using complementary metal oxide semiconductor (CMOS) technology, and more particularly, to a layout of a structure suitable for improving image quality by maximizing photoelectric transfer efficiency and data conversion gain. CMOS image sensor unit pixel with

CMOS image sensor is not only a growth in the conventional image sensor market mainly focused on analog or digital TV or video, but also digital electric still camera according to the development of computer industry and communication industry. Demand is expected to grow in proportion to the growth of PC cameras, digital camcorders, and personal communication systems (PCS), as well as video game devices, security cameras, and medical micros. Demand is also expected to increase in the fields of micro cameras and HDTVs.

1 is a unit pixel circuit diagram of a conventional CMOS image sensor.

As shown in FIG. 1, a unit pixel includes one photodiode 110 and four NMOS transistors 120, 130, 140, and 150. The four NMOS transistors are a transfer transistor 120 for transporting the photocharges collected from the photodiode 110 to the floating node 160, and the potential of the node is set to discharge a charge to a desired value to discharge the charge to the floating node 160. A reset transistor 130 for resetting, a drive transistor 140 serving as a source follower buffer amplifier, and a select transistor 150 enabling addressing as a switching role. It consists of. Unexplained reference numeral 170 denotes a load transistor.

2 shows a unit pixel layout according to the prior art.

2A shows a relationship between an isolation defining an active region in which a photodiode and a diffusion region is to be formed, and a polysilicon line constituting a gate of each transistor.

Referring to FIG. 2A, the photodiode region 201 has a square shape, and the gate polysilicon 202 of the transfer transistor is in contact with one side of the photodiode.

The floating diffusion region 203 is laid out by contacting the other side of the gate polysilicon 202 of the transfer transistor by bending 90 degrees from the y (+) axis direction to the x (-) axis direction, and of the gate polysilicon 204 of the reset transistor. It comes in contact with one side.

The other side of the gate polysilicon 204 of the reset transistor is formed in contact with the drain diffusion region 205, the drain diffusion region 205 is formed by bending 90 degrees in the y (-) axis direction in the x (-) axis direction, and then drive One side of the gate polysilicon 206 of the transistor is in contact.

Subsequently, the gate polysilicon 208 of the select transistor is formed in the same direction, between the other side of the gate polysilicon 206 of the drive transistor and the gate polysilicon 208 of the select transistor, and the gate polysilicon 208 of the select transistor. Source / drain diffusion regions 207 and 209 are formed on the other side.

As described above, in the conventional CMOS image sensor unit pixel, since the photodiode region 201 that the light is incident to form the photocharge is square, the photoelectric charge transfer efficiency is lowered.

That is, the photoelectric charges collected in the photodiode are transferred to the floating diffusion region as the transfer transistor is turned on. At this time, the photoelectric charges are weakly caught at the corners of the square photodiode, and thus the photocharges are not properly transferred to the floating diffusion. This causes a problem of deterioration of image quality. This is called an image lag.

In addition, in the conventional CMOS image sensor unit pixel laid out as shown in FIG. 2A, the floating diffusion region 203 has a large capacitance, which causes a problem in that data conversion efficiency is lowered.

That is, the change in voltage that a single photocharge can produce is called data conversion gain, and the change in voltage is represented by Equation 1 below. In the conventional unit pixel layout, the floating diffusion region 203 is defined as y ( It can only be formed in a large area while being laid out at 90 degrees in the x (-) axis direction in the +) axis direction, so that it has a large capacitance, and the resulting voltage change is small, resulting in a problem of deterioration in image quality.

ΔV = ΔQ / C _f (capacitance)

In addition, the conventional CMOS image sensor unit pixel laid out as shown in FIG. 2A includes a gate polysilicon 204 of a reset transistor, a gate polysilicon 206 of a drive transistor, a gate polysilicon 208 of a select transistor, and the like. Since the layout is proximate to the area 201, noise occurs in the photodiode when reading data, which is one factor that degrades the image quality.

In addition, the conventional CMOS image sensor unit pixel laid out as shown in FIG. 2A has a problem in that the active region has a shape of “??”, which causes a lot of constraints in the process, and thus the manufacturing yield is reduced.

2b shows the relationship between the photodiode and the metallization.

Referring to FIG. 2B, the first metal wire 221 and the second metal wire 222 pass around the photodiode 201, and are formed in planarity by the first and second metal wires 221 and 222. The virtual inner region 223 is also a substantially square shape, which is the same shape as the photodiode on the photodiode, and has a length equal to the length of any side in the vertical and horizontal directions passing through the center point. This is a configuration in contrast to the present invention will be described in more detail in the following description of the present invention.

2C shows the relationship between the photodiode, the color filter and the microlens.

Referring to FIG. 2C, a color filter 241 and a microlens 242 are stacked on the photodiode 201, and the color filter 241 and the microlens 242 have a substantially square shape that is the same shape as the photodiode. The length is in the vertical and horizontal direction passing through the center point is to have the same size as the length of any side. This will also be described in more detail in the following description of the invention as a configuration in contrast to the present invention.

SUMMARY OF THE INVENTION An object of the present invention is to provide a unit pixel of a CMOS image sensor which is arranged to maximize the photocharge transfer efficiency and data conversion efficiency and to minimize the noise of the photodiode during data reading to improve the image quality of the sensor.

It is another object of the present invention to provide a unit pixel of a CMOS image sensor that is suitable for simplifying the layout of the active region, thereby simplifying the manufacturing process and improving yield.

It is still another object of the present invention to provide a unit pixel of a CMOS image sensor which is arranged to improve the image quality of the sensor by increasing sensitivity in the vertical and horizontal directions, which are sensitive parts of the human eye.

1 is a unit pixel circuit diagram of a conventional CMOS image sensor;

2a to 2c is a CMOS image sensor unit pixel layout according to the prior art,

3A to 3C illustrate a CMOS image sensor unit pixel layout according to a preferred embodiment of the present invention;

Explanation of reference numerals for the main parts of the drawing

301: photodiode 302: gate of the transfer transistor

303: floating diffusion 321, 322: first and second metal wiring

341: color filter 342: microlens

In the present invention for achieving the above object, in the unit pixel of the CMOS image sensor having a photodiode for generating a photocharge and a transfer transistor for transferring the photocharge generated in the photodiode to the floating diffusion, the photodiode Has an octagonal shape, and the gate of the transfer transistor is formed in contact with one side of the octagonal photodiode.

In addition, the present invention relates to a unit pixel of a CMOS image sensor including a photodiode, a metal wiring, a color filter, and a microlens, wherein the photodiode has an octagonal shape, and the metal wiring has a virtual internal region formed in a plane. It has an octagonal shape on the photodiode, and the color filter and the microlens are formed by stacking on the photodiode and having a planar shape whose length in the vertical and horizontal directions passing through the center point is larger than the length of one side. It is characterized by that.

In addition, the unit pixel of the CMOS image sensor of the present invention, the photodiode having an octagonal shape in a plane; A gate of a transfer transistor formed in contact with one side of an octagonal shape of the photodiode; A metal interconnection formed such that an imaginary inner region has an octagonal shape on the photodiode; And a color filter and a microlens formed by being stacked on the photodiode and having a rhombic shape whose length in the vertical and horizontal directions through which the planar shape passes through the center point is larger than the length of any side. .

Hereinafter, the most preferred embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the technical idea of the present invention.

3 is a unit pixel layout of a CMOS image sensor according to an exemplary embodiment of the present invention.

FIG. 3A shows the relationship between the isolation and the polysilicon line, FIG. 3B shows the relationship between the photodiode and the metallization, and FIG. 3C shows the relationship between the photodiode region, color filter and microlens.

Referring to FIG. 3A, unlike the conventional art, the photodiode region 301 has an octagonal shape, and active regions (including floating diffusion and drain diffusion) of the transistors constituting the unit pixels 303, 305, 307, It should be noted that 309 is formed to extend linearly in one direction from the photodiode region.

In addition, the gate polysilicon 302 of the transfer transistor is formed in contact with one surface of the octagonal photodiode region 301, and is gradually spaced apart from the photodiode, and the gate polysilicon 304 of the reset transistor is formed on the active region. The gate polysilicon 306 of the drive transistor and the gate polysilicon 308 of the select transistor are formed.

The floating diffusion region 303 is formed in an active region between the gate polysilicon 302 of the transfer transistor and the gate polysilicon 304 of the reset transistor, and is laid out in a square shape without bending.

The effect of the CMOS image sensor unit pixel having the structure of FIG. 3A will be described.

First, since the photodiode has an octagonal shape and the gate of the transfer transistor is formed in contact with one surface thereof, the photodiode is formed symmetrically with respect to the gate of the transfer transistor as compared with the prior art (FIG. 2). The electric field spreads widely in and forms satisfactorily.

Therefore, the photocharge generated in the photodiode is transferred to the floating diffusion smoothly with almost no dead zone, that is, the photoelectric charge transfer efficiency is maximized to improve the sensor image quality.

In addition, in the unit pixel structure of the present invention, since the active region is formed to extend only in one direction, the floating diffusion region 303 has a small outer area, thereby reducing capacitance. This can be maximized by increasing the voltage change as can be seen in Equation 1 above. After all, the picture quality can be improved.

In addition, since the gate of the reset transistor, the gate of the drive transistor, and the gate of the select transistor are formed to be spaced apart from the photodiode as much as possible, it is possible to minimize noise when reading data, thereby improving image quality.

In addition, since the active region is formed to extend only in one direction, the gain of the mask and the etching process is increased, thereby facilitating the manufacturing process, and thus, improving the manufacturing yield.

3B shows a relationship between the photodiode 301, the first metal wiring 321, and the second metal wiring 322, which are formed in a planar manner by the first and second metal wirings 321 and 322. The virtual inner region 323 is also octagonal on the photodiode.

3C shows the relationship between the photodiode 301, the color filter 341 and the microlens 342. The photodiode has an octagonal shape, and the color filter 341 and the microlens 342 are It should be noted that the laminate is formed on the photodiode and its planar shape is rhombic. That is, the length in the vertical and horizontal directions through the center point is greater than the length of either side. It is about twice as long. On the other hand, since the human eye is sensitive to the vertical and horizontal directions, the better the sensitivity in the vertical and horizontal directions, the better the sensitivity. Therefore, as shown in FIG. 3B, when the color filter 321 and the microlens 322 are formed large in the vertical and horizontal directions, the photocharges can be collected more in the enlarged vertical and horizontal directions, thereby providing better image quality to humans. It is.

The present invention described above is not limited to the above-described embodiments and the accompanying drawings, and various substitutions, modifications, and changes are possible in the art without departing from the technical spirit of the present invention. It will be clear to those of ordinary knowledge.

The present invention made as described above maximizes photoelectric charge transfer efficiency and data conversion efficiency, minimizes noise of photodiode when reading data, improves image quality of sensor, and simplifies manufacturing process and improves yield by simplifying layout of active area. Will bring the effect.

Claims (10)

In a unit pixel of a CMOS image sensor having a photodiode for generating a photocharge, And the photodiode has an octagonal shape, and extends linearly from one side of the octagonal photodiode to form an active region of each device. The method of claim 1, The unit pixel of the CMOS image sensor, characterized in that the transfer transistor for transferring the photocharge generated in the photodiode to the floating diffusion formed in contact with one side of the octagonal photodiode. The method of claim 2, The floating diffusion unit pixel of the CMOS image sensor, characterized in that the layout in a square. The method of claim 2, And a plurality of gates of a reset transistor, a drive transistor, and a select transistor are formed on the active area and gradually spaced apart from the photodiode. In a unit pixel of a CMOS image sensor having a photodiode, a metal wiring, a color filter, and a microlens, The photodiode has an octagonal shape, and a virtual inner region in which a metal wiring is formed in a planar shape has an octagonal shape on the photodiode, and the color filter and the microlens are formed by being stacked on the photodiode. A unit pixel of a CMOS image sensor, characterized in that the planar shape is a rhombus having a length in the vertical and horizontal directions passing through the center point is larger than the length of any one side. The method of claim 5, The metal wiring unit pixel of the CMOS image sensor, characterized in that consisting of two layers of wiring. In the unit pixel of the CMOS image sensor, A photodiode having a planar octagonal shape; A gate of a transfer transistor formed in contact with one side of an octagonal shape of the photodiode; A metal interconnection formed such that an imaginary inner region has an octagonal shape on the photodiode; And CMOS, characterized in that it comprises a color filter and a microlens formed stacked on top of the photodiode, the planar shape of which has a rhombic shape whose length in the vertical and horizontal directions passing through the center point is larger than the length of any side. Unit pixel of the image sensor. The method of claim 7, wherein The unit pixel of the CMOS image sensor, characterized in that the active region of each device constituting the unit pixel is extended linearly in one direction from the photodiode. The method of claim 8, And a floating diffusion formed in a square in the active area in contact with the gate of the transfer transistor. The method of claim 8, And a plurality of gates of a reset transistor, a drive transistor, and a select transistor are formed on the active area and gradually spaced apart from the photodiode.