KR20110065176A - 3 transistor image sensor - Google Patents

Abstract

PURPOSE: A three transistors-based image sensor is provided to improve the resolution of the image sensor by integrating the unit pixels of the image sensor in a minimum pixel region. CONSTITUTION: A detection transistor(DX) amplifies the electric signal of a first photo diode(PD1) or a second photo diode(PD2). A reset transistor(RX) initializes the first photo diode or the second photo diode. A transfer transistor(TX) selectively connects the first photo diode and the second photo diode with the reset transistor and the detection transistor. A select transistor(SX) selectively transfers the amplified electric signal to an output terminal(Vout).

Description

3T image sensor {3 transistor image sensor}

Embodiments relate to a 3T image sensor.

1 is an equivalent circuit diagram of a unit pixel of a 3T (transistor) image sensor.

As shown in FIG. 1, the unit pixel of the 3T image sensor (hereinafter referred to as “unit pixel”) includes three transistors RX, DX, and SX and a photodiode PD.

The photodiode PD performs a photoelectric conversion function, the detection transistor DX amplifies the electrical signal of the photodiode PD, and the select transistor SX selectively outputs the amplified signal. To (Vout). The reset transistor RX receives a voltage from the voltage terminal PVDD, transfers the voltage to the photodiode PD, and initializes the photodiode PD.

2 is a top view of a unit pixel of a 3T image sensor, FIG. 3 is a side cross-sectional view of a unit pixel of a 3T image sensor based on display line A-A 'of FIG. 2, and FIG. 4 is a line B-B of FIG. 2. The side cross-sectional view of the unit pixel of the 3T image sensor based on '.

As shown in FIG. 2, an active region a having a "c" shape is formed from the photodiode PD region, and the reset transistor RX, the detection transistor DX, and the select sequentially from the photodiode PD side. The gate of the transistor SX is formed.

Referring to FIG. 3, an isolation layer 11 is formed on a substrate 10, and a photodiode PD is formed on one side of the isolation layer 11. The gate insulating films 12, 13, and 14 are formed next to the photodiode PD, and the gates 15, 16, and 17 are formed on the gate insulating films 12, 13, and 14, respectively, to reset the reset transistor RX and the detection. The transistor DX and the select transistor SX are formed in this order.

A pinning conductive layer 18 is formed on the photodiode PD to mitigate signal noise. In addition, a first insulating layer 20 is formed on the substrate 10 including the gates 15, 16, 17 and the photodiode PD, and the gates 15, 16, 17 and the gates 15, 16, 17 are formed. A plurality of contact plugs 22 are formed on the first insulating layer 20 to be connected to the active region between the layers.

The metal layer 32 connected to the contact plug 22 is formed on the first insulating layer 20, and the second insulating layer 30 is formed thereon.

Referring to FIG. 4, the gate insulating layer 13 of the detection transistor DX extends to the photodiode PD, and some regions overlapping the photodiode PD are etched to form trenches. The trench is filled with the gate 16 of the detection transistor DX to form a buried contact. The buried contact is connected to the photodiode PD by the conductive layer 40 formed through ion implantation or ion diffusion from the gate 16.

Currently, the unit pixels of the image sensor are minimized and highly integrated for high resolution. Accordingly, the number of transistors per unit pixel must be reduced to increase the utilization efficiency of the pixel area.

However, since the structure of the conventional 3T image sensor is a structure in which the function of the transfer transistor of the 4T image sensor is excluded, there is a limit in reducing the number of transistors.

The embodiment aims to provide a 3T image sensor capable of reducing the number of transistors and enabling high integration by overcoming the limitation of the structure of the conventional 3T image sensor in which the function of the transfer transistor of the 4T image sensor is excluded.

The 3T image sensor according to the embodiment includes a first photodiode and a second photodiode; A detection transistor connected to the first photodiode and configured to amplify an electrical signal of the first photodiode or the second photodiode; A reset transistor connected to a voltage terminal to initialize the first photodiode or the second photodiode and connected to the first photodiode; A transfer transistor connected between the first photodiode and the second photodiode and selectively connecting the first photodiode and the second photodiode with the reset transistor and the detection transistor; And a select transistor for selectively transferring the amplified electric signal to an output terminal.

According to the embodiment, the following effects are obtained.

First, the number of total transistors can be significantly reduced through a separation structure (a 2 pixel shared 3T Pixel structure) in which a plurality of photodiodes constituting a unit pixel of an image sensor share a remaining transistor by a transfer transistor.

Second, as the number of transistors is significantly reduced, unit pixels of the image sensor may be integrated in a minimum pixel area, thereby realizing a high resolution of the image sensor.

Referring to the accompanying drawings, a 3T image sensor according to an embodiment will be described in detail.

Hereinafter, in describing the embodiments, detailed descriptions of related well-known functions or configurations are deemed to unnecessarily obscure the subject matter of the present invention, and thus only the essential components directly related to the technical spirit of the present invention will be referred to. .

In the description of an embodiment according to the present invention, each layer (film), region, pattern or structure may be "on" or "under" the substrate, each layer (film), region, pad or pattern. "On" and "under" include both "directly" or "indirectly" formed through another layer, as described in do. Also, the criteria for top, bottom, or bottom of each layer will be described with reference to the drawings.

5 is an equivalent circuit diagram of a unit pixel of a 3T (transistor) image sensor according to a first embodiment.

Referring to FIG. 5, the 3T image sensor according to the first embodiment shows unit pixels, and includes four transistors TX, RX, DX, and SX and two photodiodes PD1 and PD2.

The first photodiode PD1 and the second photodiode PD2 perform a photoelectric conversion function for converting light incident from the outside into an electrical signal, and the transfer transistor TX is configured to perform the first photodiode. The diode PD1 and the second photodiode PD2 are switched to selectively connect with the reset transistor RX and the detection transistor DX.

The detection transistor DX of a source follower structure amplifies an electrical signal of the first photodiode PD1 or the second photodiode PD2.

The select transistor SX selectively transfers the amplified signal to the output terminal Vout.

The reset transistor RX receives a voltage from the voltage terminal PVDD and transfers the voltage to the first photodiode PD1 or the second photodiode PD2 and transfers the photodiodes PD1 and PD2. Initialize

In this case, voltages are simultaneously applied to the gates of the reset transistor RX and the transfer transistor TX to initialize the photodiodes PD1 and PD2, and then the reset transistor RX and the transfer transistor TX. The voltage at the gate of is cut off.

When reading the electrical signals of the photodiodes PD1 and PD2, first, a voltage is applied to the gate of the reset transistor RX so that the electrical signal of the first photodiode PD1 is transferred to the detection transistor DX. Second, the voltage of the reset transistor RX is cut off and then applied again to reset the first photodiode PD1. Third, a voltage is then applied to the gate of the transformer transistor TX so that an electrical signal of the second photodiode PD2 is transferred to the detection transistor DX.

In the 3T image sensor according to the first exemplary embodiment, the separation structure 2 in which the two photodiodes PD1 and PD2 share the remaining transistors RX, DX, and SX by the transfer transistor TX is described above. pixel shared 3T Pixel structure).

That is, in the 3T image sensor according to the first embodiment, one transfer transistor TX is added while the photodiodes PD1 and PD2 corresponding to two pixels correspond to the remaining transistors RX, corresponding to one pixel. DX, SX) can be shared to significantly reduce the total number of transistors.

FIG. 6 is a top view schematically illustrating a structure of a unit pixel of a 3T image sensor according to a first embodiment, and FIG. 7 is a side cross-sectional view of a unit pixel of a 3T image sensor based on display line A-A 'of FIG. 6. 8 is a side cross-sectional view of a unit pixel of a 3T image sensor based on the display line BB ′ of FIG. 6.

Referring to FIG. 6, the second photodiode PD2 is formed under the semiconductor substrate 100, and the first photodiode PD1 spaced apart from the second photodiode PD2 by the device isolation layer 110. ) Is formed on the upper side thereof.

The active region b defined by the isolation layer 110 may include the first photodiode PD1 and the second photodiode PD2, and may move upward from the photodiode PD1 and PD2 regions. It is formed in the form of "".

The gate 122 of the transfer transistor TX is formed in a part of the active region b between the first photodiode PD1 and the second photodiode PD2 and the gate of the reset transistor RX 132 is formed in the active region b next to the first photodiode PD1.

The gate 142 of the detection transistor DX is formed in the active region b next to the gate 132 of the reset transistor RX and above the first photodiode PD1, and the first photodiode PD1) and some regions are extended to overlap.

The gate 152 of the select transistor SX is formed in the active region b next to the gate 142 of the detection transistor DX and above the first photodiode PD1.

Referring to FIG. 7, an isolation layer 110 defining an active region b is formed on the semiconductor substrate 100, and a second photodiode PD2 is formed on one side of the isolation layer 110.

The first photodiode PD1 is formed next to the second photodiode PD2 at predetermined intervals, and the semiconductor substrate 100 is disposed between the first photodiode PD1 and the second photodiode PD2. The gate insulating layer 121 and the gate 122 constituting the transfer transistor TX are formed on the substrate.

Pinning conductive layers 111 and 112 are respectively disposed on the first photodiode PD1 and the second photodiode PD2 to mitigate signal noise.

Gate insulating layers 131, 141, and 151 are formed next to the first photodiode PD1, and gates 132, 142, and 152 are formed on the gate insulating layers 131, 141, and 151, respectively. RX, the detection transistor DX, and the select transistor SX are formed in this order.

In addition, a first insulating layer 160 is formed on the semiconductor substrate 100 including the gates 132, 142, and 152 and the photodiodes PD1 and PD2, and the gates 132, 142, A plurality of contact plugs 162 connected to the active region between the 152 and the gates 132, 142, and 152 are formed on the first insulating layer 160.

A metal layer 172 connected to the contact plug 162 is formed on the first insulating layer 160, and a second insulating layer 170 is formed thereon.

Referring to FIG. 8, the gate insulating layer 141 of the detection transistor DX extends to the first photodiode PD1, and a portion of the region overlapping the first photodiode PD1 is etched to form a trench. Is formed.

The trench is filled with a material forming the gate 142 of the detection transistor DX to form a buried contact. The buried contact is connected to the first photodiode PD1 by the conductive layer 180 formed through ion implantation or ion diffusion from the gate 142.

9 is a top view schematically illustrating a structure of a 3T image sensor according to a second embodiment.

9, since the 3T image sensor according to the second embodiment has a structure basically similar to that of the first embodiment, repeated description thereof will be omitted.

The 3T image sensor according to the second embodiment is different from the first embodiment in that the gate 122 of the transfer transistor TX according to the first embodiment has the first photodiode PD1 and the second photodiode. The gate 122a of the transfer transistor TX according to the second embodiment is formed between the first photodiode PD1 and the second photodiode PD2 while the active region b is formed between the first and second photodiodes PD2. It is a point formed across the whole active area (b).

In the second embodiment, the first photodiode PD1 and the second photodiode PD2 may be separated by using a self align method of the transfer transistor TX gate 122a.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, It will be understood that various modifications and applications other than those described above are possible. For example, each component specifically shown in the embodiments of the present invention can be modified and implemented. And differences relating to such modifications and applications will have to be construed as being included in the scope of the invention defined in the appended claims.

1 is an equivalent circuit diagram of a unit pixel of a 3T (Transistor) image sensor.

2 is a top view of a unit pixel of a 3T image sensor.

3 is a side cross-sectional view of a unit pixel of a 3T image sensor based on the display line A-A 'of FIG. 2;

4 is a side cross-sectional view of a unit pixel of a 3T image sensor based on the display line BB ′ of FIG. 2.

5 is an equivalent circuit diagram of a unit pixel of the 3T image sensor according to the first embodiment;

6 is a top view schematically illustrating a structure of a unit pixel of a 3T image sensor according to a first embodiment.

FIG. 7 is a side cross-sectional view of a unit pixel of a 3T image sensor based on display line A-A 'of FIG. 6;

FIG. 8 is a side cross-sectional view of a unit pixel of a 3T image sensor based on display line B-B 'of FIG. 6;

9 is a top view schematically showing the structure of a 3T image sensor according to the second embodiment;

Claims (10)

A first photodiode and a second photodiode; A detection transistor connected to the first photodiode and configured to amplify an electrical signal of the first photodiode or the second photodiode; A reset transistor connected to a voltage terminal to initialize the first photodiode or the second photodiode and connected to the first photodiode; A transfer transistor connected between the first photodiode and the second photodiode and selectively connecting the first photodiode and the second photodiode with the reset transistor and the detection transistor; And 3T (Transistor) image sensor including a select transistor for selectively transmitting the amplified electrical signal to the output terminal. The method of claim 1, 3T, characterized in that the voltage is applied to the gate of the reset transistor and the transfer transistor at the same time to initialize the first photodiode and the second photodiode, after which the voltage of the gate of the reset transistor and the transfer transistor is disconnected. Image sensor. The method of claim 1, wherein when reading an electrical signal, A voltage is applied to a gate of the reset transistor to transfer an electrical signal of the first photodiode to the detection transistor, Interrupting the voltage of the reset transistor and applying it again to initialize the first photodiode,  Thereafter, a voltage is applied to a gate of the transfer transistor to transfer an electrical signal of the second photodiode to the detection transistor. The method of claim 1, wherein the detection transistor is 3T image sensor characterized by a source follower structure. The semiconductor substrate of claim 1, wherein the semiconductor substrate is projected from an upper surface. The second photodiode is formed below the semiconductor substrate, and the first photodiode is formed spaced apart from the upper side of the second photodiode PD1. The active region defined by the device isolation layer includes the first photodiode and the second photodiode, and is formed in a “c” shape on the upper side thereof. A gate of the transfer transistor is formed in an active region between the first photodiode and the second photodiode, A gate of the reset transistor is formed in an active region next to the first photodiode, The gate of the detection transistor is formed in an active region next to the gate of the reset transistor and above the first photodiode, and extends to overlap the first photodiode and a partial region, And the gate of the select transistor is formed in an active region next to the gate of the detection transistor and above the first photodiode. The semiconductor substrate of claim 1, wherein the semiconductor substrate is projected from the side surface of the entire active region defined by the device isolation film. The first photodiode is formed next to the second photodiode spaced by a predetermined interval, A gate insulating layer and a gate of the transfer transistor are formed on the semiconductor substrate between the first photodiode and the second photodiode, And the reset transistor, the detection transistor, the gate insulating film and the gate of the select transistor are sequentially formed on the semiconductor substrate next to the first photodiode. The method of claim 6, A first insulating layer formed on the semiconductor substrate; A plurality of contact plugs connected to the transfer transistor, the reset transistor, the detection transistor, the gate of the select transistor, and an active region therebetween and formed in the first insulating layer; And 3T image sensor comprising a metal layer connected to the contact plug, and a second insulating layer formed on the first insulating layer. The method according to claim 5 or 6, And a pinning conductive layer formed on the first photodiode and the second photodiode to respectively mitigate signal noise. The method according to claim 5 or 6, The first photodiode and the second photodiode are separated by a portion of the gate of the transfer transistor and a portion of the device isolation layer, or only by a gate of the transfer transistor across the first photodiode and the second photodiode. 3T image sensor, characterized in that spaced apart. The semiconductor substrate of claim 1, wherein the semiconductor substrate is projected from the detection transistor to the first photodiode region from the side. The gate insulating layer of the detection transistor extends to the first photodiode, a portion of which overlaps the first photodiode is etched to form a trench, And a material forming a gate of the detection transistor is embedded in the trench and comprises a conductive layer connected to the first photodiode.

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