KR20060114444A - Cmos image sensor - Google Patents

Abstract

A CMOS image sensor is provided to reduce the size of the area required from each pixel by reducing the number of transistor arranged in each pixels. A first transfer transistor(Tx1) is selectively connected between a first photodiode(PP1) and a floating node. A second transfer transistor(Tx2) is selectively connected between a second photodiode(PP2) and the floating node. A reset transistor(Rx) is used for resetting the potential of the floating node. A driving transistor(Dx) is used for driving a source node corresponding to the potential applied to the floating node. The reset transistor further includes a select transistor(Sx) for transferring a driving signal to the source node of the driving transistor.

Description

CMOS image sensor {CMOS IMAGE SENSOR}

1 is a circuit diagram showing one unit pixel in a CMOS image sensor.

FIG. 2 is a process cross-sectional view of four MOS transistors forming a unit cycle shown in FIG.

3 is a process plan view of four MOS transistors shown in FIG.

Figure 4 is a schematic cross-sectional view of an image sensor according to the prior art.

5 is a circuit diagram illustrating a CMOS image sensor according to a preferred embodiment of the present invention.

6 is a cross-sectional view of the floating node in the CMOS image sensor according to the present embodiment shown in FIG.

FIG. 7 is a plan view showing the reset transistor shown in FIG. 5; FIG.

Explanation of symbols on the main parts of the drawings

Tx1, Tx2: Transfer Transistor Rx: Reset Transistor

Dx: Driving Transistor Sx: Select Transistor

PD1, PD2: Photodiode

The present invention relates to a method for manufacturing a CMOS image sensor, and more particularly, to a stable manufacturing method of a color filter.

In general, an image sensor of a semiconductor device is a semiconductor device that converts an optical image into an electrical signal. Representative image sensor devices include a charge coupled device (CCD) and a CMOS image sensor.

Among them, the charge-coupled device is a device in which charge carriers are stored and transported in the capacitor while individual metal-oxide-silicon (MOS) capacitors are located very close to each other. By using CMOS technology that uses a signal processing circuit as a peripheral circuit, a MOS transistor (typically four MOS transistors) corresponding to the number of pixels is made and sequentially output using the MOS transistor.

1 is a circuit diagram showing one unit pixel in a CMOS image sensor.

Referring to FIG. 1, one unit pixel includes one photodiode 10 and four an MOS transistors 11, 12, 13, and 14. As shown in FIG. Four NMOS transistors 11, 12, 13, and 14 are a transfer MOS transistor 11 for transporting the photocharge generated in the photodiode 10 to the charge sensing node N, and a charge for the next signal detection. The reset MOS transistor 12 for discharging the charge stored in the sensing node 11, the drive MOS transistor 13 serving as a source follower 13, and the switching role can be addressed. It is composed of a select MOS transistor 14 to enable.

Four MOS transistors 11, 12, 13, and 14 and one photodiode 10 form one unit pixel, and are provided in the pixel array of the CMOS image sensor according to the number of unit pixels included in the CMOS image sensor. The number of photodiodes 10 and the number of MOS transistors for unit pixels corresponding thereto are determined.

FIG. 2 is a process cross-sectional view of four MOS transistors constituting a unit circuit shown in FIG. 1, and four MOS transistors 11, 12, 13, and 14 respectively transmit signals Tx, Rx, Dx, and Sx to gates. The light transmitted to the photodiode PD is transmitted to the output terminal.

3 is a process plan view of four MOS transistors shown in FIG.

As shown in FIG. 3, gate patterns Tx of four MOS transistors 11, 12, 13, and 14 for transferring electrons collected by light transmitted from the photodiode 10 to an output terminal. , Rx, Dx, and Sx are disposed, and active regions 101 to 104 are disposed to the left and right of the gate patterns Tx, Rx, Dx, and Sx, respectively.

In this case, the active region 101 is a sensing node that receives electrons collected by the photodiode.

Referring to the operation of one unit device briefly, electrons collected by light transmitted to the photodiode 10 are transferred to the sensing node 101 through the transfer transistor 11.

Since the sensing node 101 is connected to the gate of the driving transistor 13, the driving transistor 13 adjusts the voltage level of the active region 103 bonded to one end in accordance with the voltage applied to the sensing node 101. Driving. Subsequently, the select transistor 104 is turned on to output a voltage applied to the active region 103 through an output terminal.

4 is a cross-sectional view schematically showing an image sensor according to the prior art.

Referring to FIG. 4, a color filter array (CFA) such as blue, red, and green, which form unit pixels on the substrate 20 on which the photodiodes 10 and PD are formed, is formed. A color filter array 24 is disposed, and a flattening film called an overcoating layer (OCL) 25 is formed thereon, and an upper portion of the region overlapping with the color filter array 14; Convex microlenses 16 are formed.

Multi-layered wirings 23 are formed between the multi-layered insulating films 22, and the wirings 23 are disposed in regions not overlapping with the photodiode 10. The wirings formed of metal serve as a light blocking film. do.

In addition, a plurality of MOS transistors (region A) are formed on the substrate 20 adjacent to the photodiode 10, which is a transfer transistor, a select transistor, a reset transistor, and a drive as described above in the case of a 4Tr unit pixel. The transistor is placed.

A protective film 27 is formed on the microlens 26 to protect the microlens 26 from scratches and the like. Reference numeral 29 denotes a device isolation film.

Also, although not shown here, a macro lens is disposed on the upper portion of the micro lens to directly receive light incident from the outside and transmit the light to the micro lens.

With the recent shift from 0.5,0.35um technology to 0.18um technology, which is a finer linewidth, new aspects that were not previously seen began to appear in the CMOS image sensor. It is interpreted as a problem caused by a slight change in each pixel.

However, in order to integrate a large number of pixels in a limited area and to realize low power, the CMOS image sensor must be enhanced with a technology of 0.18um, which is a fine line width. Since the characteristics appear different for each, there are many problems in improving the characteristics.

The present invention has been proposed to solve the above-described problem, and by reducing the number of transistors arranged in each unit pixel, the transistors arranged in one pixel can be arranged larger, so that the change in operation characteristics between each pixel can be reduced. It is an object to provide a CMOS image sensor.

The present invention is a first photodiode; A second photodiode; A first transfer transistor for selectively connecting the first photodiode and the floating node; A second transfer transistor for selectively connecting the second photodiode and the floating node; A reset transistor for resetting the potential of the floating node; A CMOS image sensor having a driving transistor for driving a source terminal in response to a potential applied to the floating node is provided.

Hereinafter, the preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the technical idea of the present invention. .

5 is a circuit diagram illustrating a CMOS image sensor according to a preferred embodiment of the present invention.

Referring to FIG. 5, the CMOS image sensor according to the present exemplary embodiment does not form one pixel with four transistors which are most widely used, but two pixels share three transistors, and one unit pixel has 2.5 pixels. Is to use a transistor.

Therefore, by using the free space on the design rule generated in each unit pixel to design the elements that determine the characteristics of each pixel large, it is possible to greatly reduce the characteristic change between each pixel.

In general, the noise of the capacitor is relatively attenuated as the size increases, and according to the present invention, the capacitance at the floating node can be arranged three to four times larger than the conventional one. This is possible by sharing floating nodes.

In this way, two rows of pixels can be controlled by one row decoder.

As shown in FIG. 5, the CMOS image sensor according to the present embodiment has photodiodes PD1 and PD2 and transfer transistors Tx1 and Tx2 for each pixel, and the floating node FD and the reset transistor Rx. ) And the driving transistor Dx.

The reset transistor Rx plays an important role in flushing the floating node FD and bringing the photodiode into a fully depleted state. The reset setting value of the photodiode can be equalized between neighboring pixels.

In addition, since the driving transistor Dx is shared, the amplification gain is also the same between neighboring pixels.

6 is a cross-sectional view of the floating node in the CMOS image sensor according to the present embodiment shown in FIG.

FIG. 6 illustrates a bar in which two pixels share one floating node, and two photodiodes PD1 and PD2 are in contact with one floating node FD. Of course, each transfer transistor must be turned on to transfer the electrons collected by each photodiode PD1 and PD2 to the floating node so that electrons can be transferred from the photodiode region to the floating node.

FIG. 7 is a plan view illustrating the reset transistor illustrated in FIG. 5.

Referring to FIG. 7, the active region of the reset transistor Rx is formed in a T-shape. Two of the three actives each come in contact with a floating node connected to a transfer transistor disposed on two shared pixels. The other is to receive the power supply voltage.

The gate terminal of the reset transistor may be formed in the center portion of the T-shaped active region in common contact.

When applying the present invention, as described above, if each pixel region is fixed and the transistors arranged in each pixel as large as they are shared are designed, the change in characteristics of each transistor is reduced, so that the operation characteristics of each pixel can be kept constant. have.

In addition, by using 2.5 transistors for each pixel and minimizing each transistor as suggested in the present invention, the effective area required for each pixel is reduced, so that more pixels can be integrated in the same area, thereby increasing resolution. It becomes possible.

As described above, the present invention is not limited to the above-described embodiments and the accompanying drawings, and the present invention may be variously substituted, modified, and changed without departing from the spirit of the present invention. It will be apparent to those of ordinary skill in Esau.

According to the present invention, the number of transistors disposed in each pixel of the CMOS image sensor can be reduced to allow the design of the remaining transistors to be free, thereby reducing the characteristic change for each pixel. Therefore, the same operation is performed at each pixel to ensure uniformity of data processing as a whole.

In addition, according to the present invention, the number of transistors disposed in each pixel of the CMOS image sensor can be reduced, thereby reducing the size of the area required for each pixel, thereby integrating more pixels in the limited CMOS image sensor.

Claims (4)

A first photodiode; A second photodiode; A first transfer transistor for selectively connecting the first photodiode and the floating node; A second transfer transistor for selectively connecting the second photodiode and the floating node; A reset transistor for resetting the potential of the floating node; Driving transistor for driving a source terminal in response to the potential applied to the floating node CMOS image sensor having a. The method of claim 1, The reset transistor And a selection transistor for transmitting a signal driven to a source terminal of the driving transistor. The method of claim 1, The reset transistor And a gate disposed on the junction region of the T-zero active and the T-type active. The method of claim 3, wherein The floating node The CMOS image sensor of claim 1, wherein the CMOS sensor is arranged to be in contact with both the region where the first photodiode is disposed and the region where the second photodiode is disposed.

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