KR20070029856A - Active pixel sensor using a pmosfet-type photodetector with a transfer gate - Google Patents

Abstract

An active pixel sensor using a PMOSFET(P Metal-Oxide Semiconductor Field Effect Transistor)-type photodetector including a transfer gate is provided to improve integrated degree by being designed through the PMOSFET-type photodetector capable of adjusting a transfer voltage for supplying a bias to the transfer gate included in the photodetector, easily changing an energy band of a channel formed between a source and a drain of the photodetector, and performing a variable optical sensibility function. A PMOSFET-type photodetector(100) includes a transfer gate for generating an optical current in proportion to injected photons, supplying a bias by a transfer voltage, changing an energy band of a channel formed between a source and a drain, and changing optical sensibility. A source of a reset transistor is connected to a reference voltage terminal, and a gate of the reset transistor is connected to a reset voltage terminal. A drain of the reset transistor is connected to a source node of the PMOSFET-type photodetector(100). When the reset transistor is turned on, the potential of an integration node(110) to which a drain node and the source node of the PMOSFET-type photodetector(100) are connected is changed by the potential of the source node connected to the reference voltage terminal. A drain of a select transistor(102) is connected to a VDD terminal, and a gate of the select transistor(102) is connected to the integration node(110). When the select transistor(102) is turned on, a voltage of a source node of the select transistor(102) is changed by a voltage of the integration node(110) supplied to the gate. A source of an access transistor(103) is connected to the source node of the select transistor(102), and a gate of the access transistor(103) is connected to a row voltage terminal. When the access terminal(103) is turned on, a drain voltage of the access transistor(103) is changed by a voltage of the source node of the select transistor(102) supplied to the source.

Description

Active pixel sensor using a PMOSFET-type photodetector with a transfer gate}

FIG. 1 illustrates a unit pixel of an image sensor using a photodiode and four transistors.

2 is a circuit diagram of an active pixel sensor using a PMOSFET photodetector including a transfer gate according to the present invention.

3 is a cross-sectional view of a PMOSFET type photodetector including a transfer gate.

4 shows an energy band diagram of the photodetector when a positive bias is applied to the transfer gate in the photodetector of FIG.

FIG. 5 shows an energy band diagram of the photodetector when a negative bias is applied to the transmission gate in the photodetector of FIG. 3.

FIG. 6 shows optical characteristics (drain current characteristics) of a PMOSFET type photodetector measured using the intensity of incident light as a variable in the drain common mode.

FIG. 7 shows optical characteristics (drain current characteristics) of a PMOSFET type photodetector measured with the wavelength of incident light as a variable in the drain common mode.

8 is a measurement waveform of a charge integrated terminal and a pixel output of an active pixel sensor according to incident light.

* Description of the main parts of the drawings *

PMOSFET photodetector with 100 transfer gates

101 Reset Transistor

102 Select Transistor

103 Access Transistor

104 Bias Transistor

110 Integration Node

The present invention relates to a unit pixel of a CMOS image sensor (CIS), a PMOSFET type photodetector having a configuration including a transfer gate using a transfer voltage (V _TX ) as a bias voltage. It relates to an active pixel sensor designed using (PMOSFET-Type Photodetector).

Due to the recent expansion of the digital camera market, interest in image detection devices such as charge-coupled devices (CCDs) and CMOS image sensors (CIS) is increasing. The CCD has an advantage of having a large gain and a noise characteristic having better performance than a CIS, but has a disadvantage of having to be manufactured through a special process. On the other hand, the CIS can be driven at a low voltage and can be manufactured through a general CMOS manufacturing process. However, there is a disadvantage in that the noise characteristics are worse than the CCD, and the CIS having good noise characteristics has been studied in various angles.

The CIS includes a unit pixel including a photodiode or a photodetector that generates a photocurrent in proportion to the recognized photons, and at least one transistor that performs noise removing, amplification, and unit pixel selection. The image is recognized through each output value generated from the unit pixel by arranging in a dimension. In addition, the performance of the CIS can be improved by controlling the noise generated.

Noise generated in the CIS may be largely classified into random noise and pattern noise.

The random noise is temporarily irregular and noise that appears inconsistently in the frames constituting the image. (This is also referred to as 'real' noise.) However, the random noise can be reduced as an average value of continuous frames, and can also be measured by statistical distribution.

The pattern noise can be measured through the observation of the image, and thus also referred to as spatial noise. Also, since the pattern noise appears fixed in successive frames, it cannot be reduced by the frame average value. The pattern noise may be classified into a fixed pattern noise (FPN) and a photo-response non-uniformity (PRNU). The fixed pattern noise (FPN) is pattern noise measured in the absence of photons. In addition, variations are mainly caused by changes in the characteristics of the photodetector, the doping concentration, the degree of contamination generated during manufacture, and the characteristics (threshold voltage, gain, width, length, etc.) of the MOSFET constituting the image sensor. In addition, the PRNU (Photo-Response non-uniformity) is a pattern noise depending on the number of photons, and depends on the characteristics of the photodetector, the doping concentration, the thickness of the overlayer and the wavelength of the light (spectral response).

As mentioned above, the FPN and PRNU fluctuation factors included in the pattern noise have characteristics of a photodetector in common, and accordingly, a current issue in the related art of the image sensor is that of a photodetector. Dynamic range and light sensitivity. Since the field in which the image sensor is used is extensive, a wide dynamic range and high photosensitivity of the photodetector are essential for extracting a good image under any conditions. However, photodiodes used as photodetectors of general image sensors have a wide dynamic range but have a low light sensitivity. In addition, while the photodetector having a function of photocurrent amplification has a high light sensitivity, the dynamic range is very limited.

FIG. 1 illustrates a unit pixel of an image sensor using a photodiode and four transistors. The conventional image sensor shown in FIG. 1 has a 4-Tr structure, and has a structure substantially similar to that of the CCD type image sensor using a floating diffusion node as an output terminal. Therefore, there is a high possibility of image lagging. In the unit pixel structure illustrated in FIG. 1, four transistors are used, and noise may be generated according to the uniformity of threshold voltages of the transistors.

The operation principle of the unit pixel structure of FIG. 1 is as follows. First, when the reset transistor located in the upper left of the figure is turned on, the potential of the output floating diffusion node becomes equal to the VDD voltage. In the above state, when light is incident on a photodiode positioned at the lower left portion, an electron-hole pair (EHP) that is proportional to the light is generated. In proportion to the current (signal charge) generated by the electron-hole pair EHP, the potential of the source node of the transfer transistor located in the middle of the left side changes. Accordingly, when an electron-hole pair (EHP) generated in proportion to the incident light is accumulated and the transfer transistor is turned on, the potential of the output floating diffusion node is increased. At the same time, the bias applied to the gate of the select transistor connected to the output floating diffusion node is also changed. This eventually leads to a potential change of the source node of the select transistor. In this case, when an access transistor connected to a source node of the source node of the selection transistor is turned on, a signal is moved toward a column. After that, when the state of the reset transistor is turned ON again, the potential of the output floating diffusion node becomes equal to VDD. By repeating the above process, an output value for light input from the outside is generated.

As shown in the case of the unit pixel shown in FIG. 1, in order to realize a variable light sensitivity, a transfer transistor for adjusting an energy band of a channel through which photocurrent flows is required inside the unit pixel. As a result, the size of the unit pixel increases, resulting in a decrease in the degree of integration of the image sensor.

The present invention is to solve the problems of the prior art, a transmission gate that serves as a transfer MOSFET (Transfer MOSFET) is additionally designed to adjust the light sensitivity of the photodetector constituting a unit pixel of the CMOS image sensor An object of the present invention is to propose an active pixel sensor configured using a photodetector.

In addition, by adjusting a transfer voltage (V _TX ) for applying a bias to a transfer gate included in the photodetector, the energy band of the channel formed between the source and the drain of the photodetector can be easily changed, thereby changing The purpose of the present invention is to propose an active pixel sensor, which is designed through a PMOSFET type photodetector capable of performing a function, with an improved degree of integration.

In addition, an object of the present invention is to propose an active pixel sensor having more sensitive optical characteristics by adjusting the type, size, and application time of the transfer voltage (V _TX ) according to the environment in which the active pixel sensor is used.

In order to achieve the above object, the present invention generates a photocurrent in proportion to the photons injected, and changes an energy band of a channel formed between the source and the drain by applying a bias by a transfer voltage (V _TX ). A PMOSFET-type photodetector including a transfer gate to change the photosensitivity;

A source is connected to a reference voltage terminal, a gate is connected to a reset voltage (V _RST ), and a drain is connected to a source node of the photodetector, and in the case of ON, the drain node and the photodetector A reset transistor whose potential V _INT of the integration node to which the source node is connected is changed by the potential of the source node connected to the reference voltage V _REF ;

A select transistor, in which a drain is connected to VDD and a gate is connected to the integration node, in which the voltage of the source node is changed by the voltage V _{INT of the integration} node applied to the gate when ON. Transistor); And

A source is connected to a source node of the select transistor, a gate is connected to a row voltage terminal, and when ON, an access in which the drain voltage is changed by the voltage of the source node of the select transistor applied to the source. An active pixel sensor using a PMOSFET type photodetector comprising a transistor (Access Transistor) is proposed.

The photodetector includes a p-substrate composed of a p-type semiconductor; An n-well located in said p-substrate and composed of n-type semiconductors; A source and a drain disposed in the n-well at a predetermined distance and composed of a highly doped p ⁺ semiconductor; A silicon oxide film located on the surface of the n-well; A gate formed on the silicon oxide film formed over the gap between the source and the drain and composed of polycrystalline silicon; A highly doped n ⁺ semiconductor located within the n-well and coupled to the gate; And a transfer gate on the silicon oxide film formed on the gap between the source and the drain, spaced apart from the gate at a predetermined interval, and composed of polycrystalline silicon doped at a high concentration.

In addition, when the transmission voltage V _TX applied to the transmission gate is a positive voltage, the energy band of the channel portion of the photodetector drops to exclude the flow of photocurrent, and when the voltage is negative, the channel of the photodetector More preferably, the energy band of the portion rises to generate a photocurrent that is proportional to the number of incident photons through the gate of the photodetector, and as the number of photons incident on the photodetector increases, the transfer voltage V It is more preferable to vary the time to apply _TX ).

The drain node of the access transistor is connected to a source node of a bias transistor having a drain connected to ground and a bias voltage V _Bias applied to a gate, so that the active pixel sensor is operated by the bias voltage. It is desirable to apply the minimum current.

Hereinafter, with reference to the accompanying drawings, a preferred embodiment of the present invention will be described.

2 is a circuit diagram of an active pixel sensor using a PMOSFET photodetector including a transfer gate according to the present invention.

The active pixel sensor proposed in the present invention includes a PMOSFET-type photodetector 100, a reset transistor 101, and a select transistor including a transfer gate. Select Transistor 102 and Access Transistor 103.

3 is a cross-sectional view of a PMOSFET type photodetector including a transfer gate. 4 shows an energy band diagram of the photodetector when a positive bias is applied to the transfer gate in the photodetector of FIG. FIG. 5 shows an energy band diagram of the photodetector when a negative bias is applied to the transmission gate in the photodetector of FIG. 3. FIG. 6 shows optical characteristics (drain current characteristics) of a PMOSFET type photodetector measured using the intensity of incident light as a variable in the drain common mode. FIG. 7 shows optical characteristics (drain current characteristics) of a PMOSFET type photodetector measured with the wavelength of incident light as a variable in the drain common mode.

As shown in FIG. 3, the PMOSFET type photodetector 100 used in the design of the active pixel sensor proposed by the present invention is characterized by including a transfer gate.

The PMOSFET photodetector 100 including the transfer gate is a substrate 11 composed of a p-type semiconductor, and is located in a portion of the p-substrate 11 and is composed of an n-type semiconductor. An n-well 12, a source 13 and a drain 14 composed of a highly doped p ⁺ semiconductor in the n-well, and a silicon oxide film located on the n-well surface ( 18) located on the silicon oxide film 18 formed at the interval between the source 13 and the drain 14 and spaced apart from the gate 15 made of polycrystalline silicon, the source 13 or the drain 14 at a predetermined distance. A silicon oxide film formed on the surface of the n-well 12 between the source 13 and the drain 14, in particular comprising a highly doped n ⁺ semiconductor 16 located within the well 12 18 is a polycrystalline silicon doped with a high concentration and located a predetermined distance apart from the gate 15 It characterized in that it comprises a transfer gate 20 that are generated.

As mentioned above, the gate 15 and the transfer gate 20 are located at a predetermined distance apart from the silicon oxide film 18 formed on the n-well 12, and also between the source 13 and the drain 14. By being located in, it is located above the channel created between the source 13 and the drain 14, and is configured to affect the energy band of the channel. When the photodetector is viewed from above, the source 13, the transfer gate 20, the gate 15, and the drain 14 are shown to be overlapped or spaced apart from each other, and the drain 14 is also located. The n ⁺ semiconductor 16 positioned in the n-well 12 spaced apart from the constant distance 12 is connected to the gate 15. The silicon oxide film 18 is an insulating film that separates the gate 15 and the transfer gate 20 from the n-well 12.

The n-well 12 is an intrinsic semiconductor with a Fermi level in the forbidden band, while the gate 15 located above the n-well 12 surface with the insulator in between has a high concentration. Since the Fermi level of the gate 15 degenerates and is located in the conduction band, since it is composed of polycrystalline silicon doped with. Thus, in order to consistently adjust the Fermi level between the n-well and the gate in equibrium, the energy band is bent near the surface of the n-well 12, whereby the built-in field is Will be formed.

In addition, as shown in FIG. 3, it is preferable to form a light blocking film 17 on the photodetector 100 so that other portions except the gate 15 are not affected by light.

When the photodetector 100 is exposed to light, photons enter the photodetector through the gate. The incoming photons apply energy into the photodetector, and electrons inside the photodetector are moved by the applied energy, and the n-wells 12 and p near the channel between the source 13 and the drain 14 are moved. Electron-Hole Pair (EHP) is generated in the depletion layer between the substrates 11.

Electron-hole pairs (EHP) generated near the channel are separated into electrons and holes by a built-in field generated by the energy band difference between the gate 15 and the n-well 12, The separated holes move towards the channel, and the separated electrons move toward the bottom of the n-well 12 with the neutral portion of the n-well 12. Holes entering the channel drift toward the drain 14 having a low potential due to the voltage difference between the source 13 and the drain 14. However, since the electrons moving to the bottom of the n-well 12 stay near the channel for a relatively long time compared to the hole, an effect that accumulates near the channel occurs.

In addition, electron-hole pairs generated in the depletion layer formed between the bottom of the n-well 12 and the p-substrate 11 are separated into electrons and holes, but by electrons accumulated in the n-well 12. A diffusion effect occurs, and the separated electron-hole pairs are separated in the vertical direction.

Preferably, almost all of the electron-hole pairs (EHPs) are generated near the channel.

The electrons accumulated in the n-well 12 through the above process lowers the barrier for holes between the source 13 and the channel, and as the barrier is lowered as described above, additionally from the source 13 Holes drift to the drain 14 side. That is, an additional channel current is generated in addition to the photo current generated by the photons incident into the device through the gate 15. Amplification is achieved through the additional channel current.

In addition, the PMOSFET type photodetector 100 is characterized in that it comprises a transfer gate that can change the energy band of the channel formed between the source 13 and the drain (14). As described above, when the energy band of the channel is changed by the bias applied to the transmission gate 20, it is possible to easily control the flow of the additional channel current, according to the brightness of the light perceived by the photodetector 100 Since the flow of the current can be easily controlled, an effect of easily controlling the noise generated as the brightness of the light changes is generated.

As shown in FIG. 4, when a positive bias is applied to the transfer gate 20, the energy band is bent downward since the source 13 and the drain 14 are p ⁺ -type semiconductors. Accordingly, the additional drain 14 current generated at the source 13 is blocked by the energy band deformed by the positive bias applied to the transfer gate 20 so as not to flow to the drain 14 side.

In addition, as shown in FIG. 5, when a negative bias is applied to the transfer gate 20, the energy band of the portion of the transfer gate 20 is bent upward according to the PMOSFET type of operation. Accordingly, unlike in the case where a positive bias is applied to the transfer gate 20 (FIG. 2), the additional drain 14 current generated in the source 13 flows well.

As described above, the optical characteristics of the photodetector can be known by looking at the change of I _DS according to the intensity of incident light under the same V _DS condition. This is because the incident light serves as a gate bias of the PMOSFET in the drain common mode. Since the incident light plays a role of gate bias, it is derived from the amount of electron-hole pairs (EHP) and the amount of electron-hole pairs (EHP) generated at two junctions inside the photodetector, depending on the intensity of the incident light. The amount of electrons and the amount of electrons change the additional drain current.

6 illustrates a case in which a negative bias is applied to the transfer gate 20, and a diagram below illustrates a case in which a positive bias is applied to the transfer gate 20. The optical characteristics of the photodetector at 0.5 GHz, 1.0 GHz, 1.5 GHz and 2.0 GHz are shown, respectively.

In the case where a negative bias is applied to the transfer gate 20, the larger the intensity of the incident light, the larger the size of the I _DS under the same V _DS condition (upper FIG. 6), but a positive bias to the transfer gate 20. It can be seen that I _DS does not increase even if the intensity of incident light is increased (lower FIG. 6). When a positive bias is applied to the transfer gate 20, the energy of the portion of the transfer gate 20 is increased. This is because the _IDS does not change even if the intensity of the incident light increases because the band rises and no current flows inside the photodetector.

FIG. 7 shows optical characteristics (drain current characteristics) of a PMOSFET type photodetector measured with the wavelength of incident light as a variable in the drain common mode. The wavelength used for the measurement is red (Red, 632.8 nm), green (Green, 533 nm), and blue (Blue, 473 nm). As shown in FIG. 7, responses of different photocurrents in the three wavelength bands can be confirmed.

As shown in FIG. 2, in the active pixel sensor proposed in the present invention, a photodetector and a reset transistor are positioned on the left side, and a select transistor and an access transistor are positioned on the right side.

The photodetector 100 is positioned between VDD and the reset transistor 101, the drain is connected to VDD and the source is connected to the drain of the reset transistor 101, and the gate is positioned to allow light to enter. . In addition, the transfer gate is connected to a transfer voltage terminal to be biased by a transfer voltage (V _TX ). As described above, the photodetector has a variable light sensitivity according to the type of bias applied to the transfer gate and the application time. The active pixel sensor using the photodetector including the transfer gate is illustrated in FIG. 1. Unlike the unit pixel of the conventional 4-Tr structure, there is an advantage that does not need to configure a transfer transistor (Transfer Transistor).

The reset transistor 101 has a source connected to a reference voltage terminal, a drain connected to a source of the photodetector 100, and a gate connected to a reset voltage terminal.

In particular, the node to which the drain of the reset transistor 101 and the source of the photodetector 100 are connected is referred to as an integration node 110, and this part becomes a reference value by a reset voltage. The potential is raised by the photocurrent generated in proportion to the photons incident by the photodetector 100. When the active pixel sensor proposed by the present invention is compared with the conventional 4-Tr structure unit pixel shown in FIG. 1, the potential is increased by the photocurrent caused by the electron-hole pair (EHP) generated by the incident photons. The output floating diffusion node and the integration node 110 may perform a similar role.

The reset transistor 101 is turned on or off by a reset voltage (V _RST ) which becomes a bias voltage of the gate. A transistor must have a bias voltage greater than or equal to a threshold voltage to form a channel inside the transistor so that a current flows. The state in which the current flows is called an ON state. When the state of the reset transistor 101 is turned on by the reset voltage V _RST , the potential of the drain node of the reset transistor 101 becomes equal to the potential of the source node. Since the potential of the source node of the reset transistor 101 is a reference voltage (V _REF ), when the reset transistor 101 is in an ON state, the potential of the drain node of the reset transistor 101 is a reference voltage ( V _REF ).

The select transistor 102 is connected to a source at VDD, a drain to a drain node of an access transistor, and a gate to an integration node 110. Accordingly, when the potential of the integration node 110 rises, the gate potential of the select transistor 102 also rises, so that the potential of the source node of the access transistor 103 connected to the drain also rises. Done.

As described above, the access transistor 103 has a source connected to a drain node of the select transistor 102 and a gate connected to a row voltage terminal. The access transistor 103 is turned on or off by a row voltage (V _ROW ), which is a bias voltage of a gate. When the access transistor 103 is turned on, the potential of the source and the drain of the source is turned on. Is equal to, the potential of the source node of the select transistor 102 becomes the potential of the drain node of the access transistor 103. The output value of the active pixel sensor is obtained by connecting to the drain node of the access transistor 103.

Finally, as shown in the lower part of FIG. 2, the active pixel sensor is connected to a bias transistor, more specifically, the source of the bias transistor is connected to the drain node of the access transistor 103, The drain is connected to GND and the gate is connected to the bias voltage terminal. The bias transistor is turned on or off by a bias voltage (V _Bias ), which is a bias voltage of the gate. When the bias transistor is turned on, a minimum current required for the active pixel sensor flows.

8 is a measurement waveform of a charge integrated terminal and a pixel output of an active pixel sensor according to incident light. 8 illustrates the change of the voltage and output value of the integration node 110 according to the change of the reset voltage, the transfer voltage, and the column selection voltage using the time axis (horizontal axis) and the voltage axis (vertical axis). The light source used in the experiment was a halogen lamp (light power = 1.5 kW).

When the reset voltage V _RST becomes 3.0 V, the reset transistor 101 using the reset voltage V _RST as the bias voltage of the gate is turned on, and the potential of the drain node is equal to the potential V _REF of the source node. Will be the same (0.0000sec)

When the reset transistor 101 is substantially the same as the OFF state, the column select voltage V _ROW becomes 3V and the access transistor 103 is turned ON. The transmission voltage V _TX is still 3V, and the bias applied to the transmission gate is a positive bias. Thus, the energy band of the channel formed in the photodetector 100 is lowered so that the photocurrent does not flow freely. At this time, the potential V _INT of the integration node 110 is not identified because the wavelength of the incident light source is divided, and it can be confirmed that the voltage falls (about 0.000125sec).

Thereafter, when the transmission voltage V _TX becomes 0V and the bias applied to the transmission gate becomes a negative bias, the energy band of the channel formed in the photodetector 100 rises so that a photocurrent flows freely. The potential V _INT of the integration node 110 gradually increases due to the photocurrent generated by the detector 100, and the response to each wavelength band can be confirmed. The select transistor 102 using the potential of the integration node 110 as the bias voltage of the gate is turned on so that the potential of the source node changes due to the potential change of the integration node 110. The potential of the source node of the access transistor 103 connected with the source node of the transistor 102 also changes. Accordingly, in the access transistor 103 which is already turned on by the column selection voltage (V _ROW = 3V), the drain node changes together with the potential change of the source node, and is recognized by the drain node of the access transistor 103. The output value (V _OUT ) is also changed. The output value V _OUT may identify the response to each wavelength band as the potential V _INT of the integration node 110 changes. (Approximately 0.0005sec)

In addition, the potential V _INT of the integration node 110 continues to rise until the transmission voltage V _TX rises. This phenomenon is due to the parasitic capacitor nature generated by the transistors located between the ground node (GND) at the integration node 110. This is because the parasitic capacitor property allows electron-hole pairs (EHP) generated by photons incident on the gate of the photodetector 100 to be continuously charged. Accordingly, in the active pixel sensor proposed in the present invention, compared with the conventional 4-Tr unit pixel structure shown in FIG. 1, the parasitic capacitor property plays a role of a capacitor connected in parallel with the photodiode.

Thereafter, when the transmission voltage V _TX becomes 3V, the potential V _INT of the integration node 110 starts to fall, and the potential V _INT of the integration node 110 becomes a reset voltage. Since (V _RST ) becomes 3V and the reset transistor 101 is turned on, the voltage continues to fall until it is changed by the reference voltage V _REF . When the column select voltage V _ROW becomes 0 V when the transfer voltage V _TX is substantially equal to 3 V, the access transistor 103 is turned OFF, and thus the output value is set to the reference value (when a dark current flows). Potential value) (about 0.0010 sec).

Accordingly, the active pixel sensor using the PMOSFET type photodetector including the transfer gate proposed in the present invention uses the transfer gate of the photodetector 100 using the transfer voltage V _TX as a bias voltage. It can be seen that the energy current of the channel generated at 100 is changed to control the photocurrent generated by the photons. It can also be seen that it exhibits sensitive optical properties that can yield an output value proportional to the wavelength. Accordingly, the present invention can implement a 3-Tr active pixel sensor having a transmission gate.

The present invention relates to energy of a channel formed between a source and a drain of a photodetector in an active pixel sensor constituting a CMOS image sensor (CIS) using a transfer voltage (V _TX ) as a bias voltage for variable light sensitivity. By including a PMOSFET-type photodetector having a configuration including a transfer gate for adjusting a band, it is not necessary to configure an additional MOSFET configured for variable light sensitivity, thereby maintaining sensitive optical characteristics. There is an advantage that the degree of integration can be improved.

In addition, by controlling the type, size and application time of the transmission voltage (V _TX ) according to the brightness of the light perceived by the photodetector, there is an advantage that can control the noise due to the brightness of the light, especially sensitive optical characteristics Since it has, there is an advantage that can control the noise by the dark current (Dark current).

Claims (5)

A photo gate is generated in proportion to the photons to be injected, and the transfer gate changes the photosensitivity by changing an energy band of a channel formed between the source and the drain by applying a bias by a transfer voltage (V _TX ). A PMOSFET-type photodetector comprising: a PMOSFET-type photodetector; A source is connected to a reference voltage terminal, a gate is connected to a reset voltage (V _RST ), and a drain is connected to a source node of the photodetector, and in the case of ON, the drain node and the photodetector A reset transistor whose potential V _INT of the integration node to which the source node is connected is changed by the potential of the source node connected to the reference voltage V _REF ; A select transistor, in which a drain is connected to VDD and a gate is connected to the integration node, in which the voltage of the source node is changed by the voltage V _{INT of the integration} node applied to the gate when ON. Transistor); And A source is connected to a source node of the select transistor, a gate is connected to a row voltage terminal, and when ON, an access in which the drain voltage is changed by the voltage of the source node of the select transistor applied to the source. Transistors; Active pixel sensor using a PMOSFET-type photodetector comprising a. The method of claim 1, The photodetector, a p-substrate composed of a p-type semiconductor; An n-well located in said p-substrate and composed of n-type semiconductors; A source and a drain disposed in the n-well at a predetermined distance and composed of a highly doped p ⁺ semiconductor; A silicon oxide film located on the surface of the n-well; A gate formed on the silicon oxide film formed over the gap between the source and the drain and composed of polycrystalline silicon; A highly doped n ⁺ semiconductor located within the n-well and coupled to the gate; And Using a PMOSFET photodetector, comprising: a transfer gate formed of polycrystalline silicon doped at a high concentration on a silicon oxide film formed over the gap between the source and the drain and spaced apart from the gate. Active pixel sensor. The method of claim 2, When the transmission voltage V _TX applied to the transmission gate is a positive voltage, the energy band of the channel portion of the photodetector is lowered to exclude the flow of the photocurrent, and when the voltage is negative, the channel portion of the photodetector The energy band of the active pixel sensor using a PMOSFET-type photodetector, characterized in that the rising of, the photocurrent in proportion to the number of incident photons through the gate of the photodetector. The method of claim 2, The active pixel sensor using the PMOSFET type photodetector, characterized in that the time for applying the transfer voltage (V _TX ) to the transfer gate is different as the number of photons incident on the photodetector increases. The method of claim 1, The drain node of the access transistor is connected to a source node of a bias transistor having a drain connected to ground and a bias voltage V _Bias applied to a gate, so that the active pixel sensor is operated by the bias voltage. An active pixel sensor using a PMOSFET type photodetector characterized in that the minimum current is applied.

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