WO2007139253A1 - Image sensor pixel having photodiode with coupling capacitor and method for sensing a signal - Google Patents

Image sensor pixel having photodiode with coupling capacitor and method for sensing a signal Download PDF

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Publication number
WO2007139253A1
WO2007139253A1 PCT/KR2006/004173 KR2006004173W WO2007139253A1 WO 2007139253 A1 WO2007139253 A1 WO 2007139253A1 KR 2006004173 W KR2006004173 W KR 2006004173W WO 2007139253 A1 WO2007139253 A1 WO 2007139253A1
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WIPO (PCT)
Prior art keywords
diffusion region
voltage
coupling capacitor
reset
photodiode
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PCT/KR2006/004173
Other languages
French (fr)
Inventor
Jawoong Lee
Sang Wook Han
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Pixelplus Co., Ltd.
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Application filed by Pixelplus Co., Ltd. filed Critical Pixelplus Co., Ltd.
Publication of WO2007139253A1 publication Critical patent/WO2007139253A1/en

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    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L27/00Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/14Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
    • H01L27/144Devices controlled by radiation
    • H01L27/146Imager structures
    • H01L27/14601Structural or functional details thereof
    • H01L27/14609Pixel-elements with integrated switching, control, storage or amplification elements
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L27/00Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/14Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
    • H01L27/144Devices controlled by radiation
    • H01L27/146Imager structures
    • H01L27/14643Photodiode arrays; MOS imagers
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L27/00Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/14Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
    • H01L27/144Devices controlled by radiation
    • H01L27/146Imager structures
    • H01L27/14601Structural or functional details thereof
    • H01L27/14603Special geometry or disposition of pixel-elements, address-lines or gate-electrodes
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L27/00Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/14Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
    • H01L27/144Devices controlled by radiation
    • H01L27/146Imager structures
    • H01L27/14683Processes or apparatus peculiar to the manufacture or treatment of these devices or parts thereof
    • H01L27/14689MOS based technologies
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04NPICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N25/00Circuitry of solid-state image sensors [SSIS]; Control thereof
    • H04N25/70SSIS architectures; Circuits associated therewith
    • H04N25/709Circuitry for control of the power supply

Definitions

  • the present invention generally relates to a CMOS image sensor, and more specifically, to a capacitor combined photodiode including a floating layer and a coupling capacitor without an ohmic-contacted output node, and an image sensor pixel using the same.
  • an image sensor active pixel is a device configured to convert an external optical image signal into an electric image signal.
  • a CMOS image sensor is fabricated with a CMOS manufacturing technology. Each pixel of the CMOS image sensor changes light signals radiated from the corresponding part of an object for photography into electrons with a photodiode, and converts the accumulated charge into voltage signals.
  • Fig. 1 is a circuit diagram illustrating a unit pixel of a general 3-transistor CMOS image sensor.
  • the unit pixel of the CMOS image sensor comprises a photodiode (PD) 1, a reset switch (RSW) 2, a capacitor CFD 4 of a floating diffusion sensing node 3, and a signal amplifier 5.
  • the reset switch 2 resets the floating diffusion sensing node (FDSN) 3 into a reset voltage VR which is an initial value.
  • Signal electrons generated corresponding to incident light in the photodiode 1 are accumulated in the capacitor CFD 4 of the floating diffusion sensing node FDSN 3.
  • the capacitor CFD 4 includes a junction capacitor of the photodiode 1, a capacitor located at an input terminal of the signal amplifier 5, and peripheral parasitic capacitors which are connected in parallel.
  • An output signal of the signal amplifier 5 is connected to a signal line of a pixel array.
  • the ohmic-contacted floating diffusion sensing node FDSN 3 transmits the signal of the photodiode 1 to the input terminal of the signal amplifier 5.
  • the photodiode 1 Since the photodiode 1 is directly connected to the floating diffusion sensing node FDSN 3 in the 3-transistor pixel, it is impossible to embody a shared structure where structures other than the photodiode 1 are shared in two or more pixels to reduce the number of devices per pixel.
  • the share structure cannot be adopted because electrons generated from all photodiodes of the shared pixels are mixed with each other.
  • Fig. 2 is a cross-sectional and circuit diagram illustrating a general 3-transistor image sensor pixel.
  • a partially pinned photodiode part Dl and a reset switch part D2 are shown in the cross-sectional diagram, and a source follower 6 and an address switch 7 are shown in the circuit diagram.
  • the CMOS image sensor pixel comprises a partially pinned photodiode (PPPD), a reset switch (RSW), a source follower (SF) 6, an address switch (ASW) 7 and a constant current source 8.
  • PPPD partially pinned photodiode
  • RSW reset switch
  • SF source follower
  • ASW address switch
  • a signal amplifier 5 includes the source follower SF 6, the address switch ASW 7 and the constant current source 8.
  • the reset switch RSW and the address switch ASW 7 are formed of a field effect transistor (FET) respectively.
  • the reset switch RSW having a common drain with the source follower SF 6 is connected to a driving voltage VDD.
  • an additional reset voltage VR is not used but the driving voltage VDD is used as a reset voltage.
  • the partially pinned photodiode PPPD is formed of a photodiode PPD including an ohmic-contacted diffusion sensing node.
  • the partially pinned photodiode part Dl includes a n-type diffusion region 10 and a p+ diffusion region 11 which are formed in a p-type epitaxial layer (or p-type substrate) 9, and a n+ type diffusion region 12 for forming the ohimic contact sensing node in the n-type diffusion region 10.
  • the reset switch part D2 comprises a p-type well 13 formed in the p-type epitaxial layer (or p-type substrate) 9, a n+ type diffusion region 14 used as a reset- voltage-applying terminal formed in the p-type well 13, and an insulating layer and a gate electrode over a region where a channel is formed between the n+ type diffusion region 12 and the n+ type diffusion region 14.
  • a p-type well 15 is formed around the partially pinned photodiode part Dl.
  • the partially pinned photodiode PPPD has a smaller dark current generated from the silicon surface than that of the general photodiode. However, there is a large dark current generated from the n+ type diffusion region 12 for forming the ohmic-contacted diffusion sensing node and a reset noise generated by the reset switch RSW.
  • the present invention has the following objects.
  • Various embodiments of the present invention are directed at providing a photodiode and an image sensor pixel configured to reduce a dark current generated from ohmic-contacted diffusion sensing node.
  • Various embodiments of the present invention are directed at providing a photodiode and an image sensor pixel configured to reduce a reset noise.
  • Various embodiments of the present invention are directed at providing a photodiode and an image sensor pixel configured to have a shared structure without any transfer gates between the photodiode and the sensing node.
  • a photodiode comprises: an epitaxial layer having a first conductive type; a first diffusion region having a second conductive type formed in the epitaxial layer; a second diffusion region having a first conductive type and floating in the first diffusion region; and a coupling capacitor configured to transmit outside a voltage change of the first diffusion region.
  • an image sensor pixel comprises: a photodiode which comprises an epitaxial layer having first conductive type, a first diffusion region having a second conductive type formed in the epitaxial layer, a second diffusion region having a first conductive type and floating in the first diffusion region, and a coupling capacitor configured to transmit outside a voltage change of the first diffusion region; a reset switch configured to reset the first diffusion region of the photodiode with a reset voltage source; a multi-functional switch, connected between a variable voltage source and an output terminal of the coupling capacitor, configured to apply a voltage of the variable voltage source to the output terminal; and a signal amplifier configured to transmit a voltage signal corresponding to the voltage change transmitted by the coupling capacitor to a signal line of a pixel array.
  • a method for sensing a signal of an image sensor pixel which comprises: a photodiode comprising an epitaxial layer having a first conductive type, a first diffusion region having a second conductive type formed in the epitaxial layer, a second diffusion region having a first conductive type and floating in the first diffusion region, and a coupling capacitor configured to transmit outside a voltage change of the first diffusion region; a reset switch configured to reset the first diffusion region of the photodiode with a reset voltage source; a multi-functional switch, connected between a variable voltage source and an output terminal of the coupling capacitor, configured to apply a voltage of the variable voltage source to the output terminal; and a signal amplifier configured to transmit a voltage signal corresponding to the voltage change transmitted by the coupling capacitor to a signal line of a pixel array, comprises the steps of: fixing the output terminal of the coupling capacitor at a first voltage level with the variable voltage source when the multifunctional switch is turned on; resetting the first diffusion region by turning on
  • a method for sensing a signal of an image sensor pixel which comprises: a photodiode comprising an epitaxial layer having a first conductive type; a first diffusion region having a second conductive type formed in the epitaxial layer; a second diffusion region having a first conductive type and floating in the first diffusion region; and a coupling capacitor configured to transmit outside a voltage change of the first diffusion region; a reset switch configured to reset the first diffusion region of the photodiode with a reset voltage source; a multi-functional switch, connected between a variable voltage source and an output terminal of the coupling capacitor, configured to apply a voltage of the variable voltage source to the output terminal; and a signal amplifier configured to transmit a voltage signal corresponding to the voltage change transmitted by the coupling capacitor to a signal line of a pixel array, comprises the steps of: fixing the output terminal of the coupling capacitor at a first voltage level with the variable voltage source when the multifunctional switch is turned on; resetting the first diffusion region by turning on
  • Fig. 1 is a circuit diagram illustrating a general 3-transistor image sensor pixel.
  • Fig. 2 is a cross-sectional and circuit diagram illustrating a general 3-transistor image sensor pixel.
  • Fig. 3 is a diagram illustrating a capacitor combined photodiode (CCPD) according to an embodiment of the present invention.
  • CCPD capacitor combined photodiode
  • Fig. 4 is a cross-sectional diagram taken along A-A' of Fig. 3.
  • Fig. 5 is a cross-sectional diagram taken along B-B' of Fig. 3.
  • Fig. 6 is a cross-sectional diagram taken along C-C of Fig. 3.
  • Fig. 7 is a diagram illustrating the CCPD and a reset switch part D3 in an embodiment where the CCPD is connected to the reset switch part D3.
  • Fig. 8 is a cross-sectional diagram taken along D-D' of Fig. 7.
  • Fig. 9 is a cross-sectional and circuit diagram illustrating an image sensor pixel including the CCPD and the reset switch RSW of Figs. 7 and 8, a multi-functional switch 24 and a signal amplifier 25.
  • Fig. 10 is a diagram illustrating an example of Fig. 9 with the signal amplifier 25 composed of a source follower (SF) 26 and a constant current source 27.
  • SF source follower
  • Fig. 11 is a diagram illustrating an example of Fig. 10 wherein a driving voltage VDD of the source follower 26 is used in common as the reset voltage sources.
  • Fig. 3 is a diagram illustrating a capacitor combined photodiode (CCPD) according to an embodiment of the present invention.
  • the capacitor combined photodiode CCPD comprises a floating-layer photodiode region FLPD and a coupling capacitor region CC.
  • the geometrical shape of the floating-layer photodiode region FLPD and the coupling capacitor region CC can be changed.
  • Fig. 4 is a cross-sectional diagram taken along A-A' of Fig. 3
  • Fig. 5 is a cross-sectional diagram taken along B-B' of Fig. 3.
  • the floating-layer photodiode region FLPD includes a n-type diffusion region 10 and a p+ type diffusion region 11 which are formed in a p-type epitaxial layer (or p-type substrate) 9.
  • the floating layer 11 is completely floated without being contacted to the p-type epitaxial layer (or p-type substrate) 9 or a p-type well 15.
  • the p-type well 15 is formed around the periphery of the floating-layer photodiode region FLPD.
  • Fig. 6 is a cross-sectional diagram taken along C-C of Fig. 3.
  • the floating-layer photodiode region FLPD includes the n-type diffusion region
  • the coupling capacitor CC has the p+ type floating layer 11 as a first electrode, an oxide insulating layer 18 over the p+ type floating layer 11 as a dielectric layer, and a second electrode 19.
  • the coupling capacitor CC is electrically connected to the n-type diffusion region 10 of the floating-layer photodiode region FLPD through the floating layer 11 without ohmic contact, and transmits a voltage change of the n-type diffusion region 10 to the outside.
  • the coupling capacitor CC is serially connected in the circuit with a pn junction capacitor CFP formed between the floating layer 11 and the n-type diffusion region 10.
  • the voltage change of the n-type diffusion region 10 occurs by signal electrons generated by light absorption, the voltage change is transmitted to the coupling capacitor CC through the junction capacitor CFP, and to the outside through the second electrode 19 of the coupling capacitor CC. That is, when the second electrode 19 of the coupling capacitor CC is connected to the input terminal of the signal amplifier, a voltage proportional to the signal voltage change of the n-type diffusion region 16 is transmitted to the input terminal of the signal amplifier.
  • the sensing node using the coupling capacitor CC can reduce a dark current in comparison with ohmic-contacted diffusion sensing nodes because physical defects generated in the sensing nodes 3 for forming the ohmic contact can be reduced.
  • the physical defects of the sensing nodes are main cause of the dark current in the sensing nodes.
  • the p+ type floating layer 11 is floated in the n-type diffusion region 10, it is electrically connected to the outside through the coupling capacitor CC so that a reverse bias voltage can be applied between the floating layer 11 and the n-type diffusion region 10. If the doping concentration, depth and width of the n-type diffusion region 10 are adjusted, the n-type diffusion region 10 can be fully depleted by the reset operation.
  • Fig. 7 is a diagram illustrating the capacitor combined photodiode CCPD and a reset switch part D3 in an embodiment where the floating-layer photodiode region FLPD is connected to the reset switch part D3.
  • the floating-layer photodiode region FLPD includes a coupling capacitor CC region over itself, and is connected to the reset switch region D3.
  • the geometrical shape of the floating-layer photodiode region FLPD, the coupling capacitor region CC and the reset switch region D3 can be changed.
  • Fig. 8 is a cross-sectional diagram taken along D-D' of Fig. 7.
  • the FLPD includes the n-type diffusion region 10 and the p+ type diffusion region 11 which are formed in the p-type epitaxial layer (or p-type substrate) 9.
  • the coupling capacitor CC has the p+ type floating layer 11 as a first electrode, and an oxide insulating layer 18 over the p+ type floating layer 11 as a dielectric layer, and a second electrode 19.
  • the reset switch part D3 comprises a p-type well 20 formed in the p-type epitaxial layer (or p-type substrate) 9, a n+ type diffusion region 21 used as a reset- voltage-applying terminal formed in the p-type well 20, and an oxide insulating layer 22 and a gate electrode 23 over a region where a channel is formed between the n-type diffusion region 10 of the floating-layer photodiode region FLPD and the n+ type diffusion region 21.
  • Fig. 9 is a cross-sectional and circuit diagram illustrating an image sensor pixel including the capacitor combined photodiode CCPD and the reset switch RSW of Figs. 7 and 8, a multi-functional switch 24 and a signal amplifier 25.
  • the capacitor combined photodiode CCPD and the reset switch part D3 are shown in the cross-sectional diagram, and the multi-functional switch 24 and the signal amplifier 25 are shown in the circuit diagram.
  • the floating-layer photodiode FLPD absorbs light radiated from an object for photography to change the light into signal electrons.
  • the signal electrons are accumulated in the n-type diffusion region 10.
  • the coupling capacitor CC transmits a voltage change of the n-type diffusion region 10 to the input terminal of the signal amplifier 25.
  • the voltage change occurs when the signal electrons flow into or out form the n-type diffusion region 10.
  • the reset switch RSW discharges the electrical charge stored in the n-type diffusion region 10 through the n+ type diffusion region 21 connected to a reset voltage source VR, to reset the voltage of the n-type diffusion region 10 into an initial value.
  • the multi-functional switch 24 has the following functions in the operation of the above-described pixel.
  • the multi-functional switch 24 provides a discharging path to a floating structure when the input terminal of the signal amplifier 25 is floating.
  • the multi-functional switch 24 prevents the related devices such as the signal amplifier and coupling capacitor from malfunctioning and being damaged.
  • the multi-functional switch 24 sets the initial voltage of the input terminal of the signal amplifier 25 and the second electrode 19 of the coupling capacitor CC into a specific value with the variable voltage source VC.
  • the output terminal of the signal amplifier 25 is directly connected to a signal line of a pixel array, or is connected to the signal line through an addressing switch for connecting/disconnecting an output signal of the signal amplifier 25.
  • the signal amplifier 25 is required to be controlled on/off states.
  • a voltage of the variable voltage source VR is set to a first voltage VL (e.g., OV) and the multi-functional switch 24 is turned on so that a voltage of the second electrode 19 of the coupling capacitor CC is fixed at the first voltage VL.
  • the reset switch RSW is turned on to reset the n-type diffusion regions 10.
  • the voltage of the variable voltage source VC is set to a second voltage VH higher than the first voltage VL.
  • the second voltage VH is set to a sufficiently higher value (e.g., driving voltage VDD of the signal amplifier 25) in consideration of a dropping range of the signal voltage due to light.
  • the reset switch RSW and the multi-functional switch 24 are turned off to finish the reset operation of the capacitor combined photodiode CCPD.
  • the voltage of the n-type diffusion region 10 falls down and the voltage change is transmitted to the signal amplifier 25 through the junction capacitor CFP and the coupling capacitor CC. That is, the voltage of the second electrode 19 of the coupling capacitor CC and the input terminal of the signal amplifier 25 falls down form the initial value VH.
  • the change of the signal voltage of the input terminal of the signal amplifier 25 gives information on the amount of the signal electrons, that is, on the amount of the incident light into the pixel.
  • the voltage of the variable voltage source VC is set to the first voltage VL (e.g., OV), and the multi-functional switch 24 is turned on to fix the voltage of the second electrode 19 of the coupling capacitor CC at the first voltage VL.
  • the reset switch RSW is turned on to reset the n-type diffusion regions 10 of the capacitor combined photodiode CCPD.
  • the reset switch RSW is turned off to finish the reset operation of the capacitor combined photodiode CCPD.
  • the multi- functional switch 24 is kept on or turned off. Both of the ways are possible.
  • the signal electrons are accumulated in the n-type diffusion regions 10 by the incident light, and the amount of the accumulated signal electrons is read by the following operation.
  • variable voltage source VC is set to a voltage VLl larger than an input threshold voltage VT of the signal amplifier 25.
  • the multi-functional switch 24 is turned on, if it was turned off before, to set the initial value of the second electrode of the coupling capacitor CC and the input terminal of the signal amplifier 25 to the voltage
  • the multi-functional switch 24 is turned off and the reset switch RSW is turned on to remove the signal electrons from the n-type diffusion regions 10. As a result, the voltage of the n-type diffusion region 10 rises. The voltage change is transmitted to the coupling capacitor CC, and to the input terminal of the signal amplifier 25 through the second electrode 19 of the coupling capacitor CC.
  • the signal electrons accumulated in the capacitor combined photodiode CCPD are reset, the voltage of the input terminal of the signal amplifier 25 rises from the initial value VLl.
  • the amount of the signal electrons that is, the amount of the incident light can be evaluated from the voltage rise value.
  • the second operation method is roughly opposite in concept to that of a general 4-transistor pixel.
  • Fig. 10 is a diagram illustrating an example of Fig. 9 with the signal amplifier which comprises a source follower (SF) 26 and a constant current source 27.
  • SF source follower
  • Fig. 11 is a diagram illustrating an example of Fig. 10 wherein a driving voltage VDD of the source follower 26 is used in common as the reset voltage source.
  • the voltage of the variable voltage source VC is set to the first voltage VL (e.g., OV), and the multi-functional switch 24 is turned on to fix the voltage of the second electrode 19 of the coupling capacitor CC at the first voltage VL.
  • VL e.g., OV
  • the source follower active transistor 26 is automatically turned off.
  • the reset switch RSW is turned on to reset the n-type diffusion regions 10.
  • the reset switch RSW is turned off to finish the reset operation of the capacitor combined photodiode CCPD.
  • the multi- functional switch 24 is kept on or turned off. Both of the ways are possible.
  • the signal electrons are accumulated in the n-type diffusion regions 10 of the capacitor combined photodiode CCPD by the incident light signal.
  • the amount of the accumulated signal electrons is read by the following operation.
  • variable voltage source VC is set to a voltage VLl larger than an input threshold voltage VT of the source follower active transistor 26.
  • the multi-functional switch 24 is turned on, if it was turned off before, to set the initial value of the second electrode 19 of the coupling capacitor CC and a gate of the source follower active transistor 26 to the voltage VLl.
  • the multi-functional switch 24 is turned off and the reset switch RSW is turned on to remove the signal electrons from the n-type diffusion regions 10. As a result, the voltage of the n-type diffusion region 10 rises. The voltage change is transmitted to the gate of the source follower active transistor 26 through the second electrode 19 which is an output terminal of the coupling capacitor CC.
  • the voltage of the gate of the source follower active transistor 26 rises from the initial value VLl.
  • the amount of the signal electrons that is, the amount of the incident lights can be evaluated from the voltage rising value.
  • the on/off states of the source follower active transistor 26 are controlled by the voltage setting value of the gate terminal so that an addressing switch for selectively transmitting an output voltage to the signal line of the pixel array is not required.
  • the multi-functional switch 24 has the following functions in the pixel.
  • the multi-functional switch 24 provides a path for discharging net charge flowed into the electrically floating structure at the connecting node of the gate of the source follower 26 and second electrode 19 of the coupling capacitor CC.
  • the multi-functional switch 24 prevents the malfunction or damages of the coupling capacitor CC and the source follower active transistor 26.
  • the multi-functional switch 24 sets the initial voltage of the gate of the source follower active transistor 26 and the second electrode 19 of the coupling capacitor CC at a specific value with the variable voltage source VC.
  • the CMOS image sensor has the following effects.
  • the signal voltage is transmitted to the signal amplifier with the coupling capacitor instead of the ohmic-contacted diffusion sensing node in order to reduce the dark current generated from the ohmic contact.
  • the n-type diffusion regions 10 of the capacitor combined photodiode CCPD are fully depleted by the reset operation to remove a reset noise and an image lag.
  • the shared structure can be embodied by using the coupling capacitor instead of the ohmic-contacted diffusion sensing node.

Abstract

A photodiode with a floating layer and coupling capacitor, and an image sensor pixel using it. The photodiode comprises an epitaxial layer having a first conductive type; a first diffusion region having a second conductive type formed in the epitaxial layer; a second diffusion region having a first conductive type formed over the first diffusion region; and a coupling capacitor configured to transmit outside a voltage change of the first diffusion region. The active pixel comprises the photodiode described above, a reset switch, a multi-functional switch between a variable voltage source and an output terminal of the coupling capacitor, and a signal amplifier.

Description

IMAGE SENSOR PIXEL HAVING PHOTODIODE WITH COUPLING CAPACITORAND METHOD FOR SENSING A SIGNAL
Technical Field The present invention generally relates to a CMOS image sensor, and more specifically, to a capacitor combined photodiode including a floating layer and a coupling capacitor without an ohmic-contacted output node, and an image sensor pixel using the same.
Background of the Invention
Generally, an image sensor active pixel is a device configured to convert an external optical image signal into an electric image signal. Specifically, a CMOS image sensor is fabricated with a CMOS manufacturing technology. Each pixel of the CMOS image sensor changes light signals radiated from the corresponding part of an object for photography into electrons with a photodiode, and converts the accumulated charge into voltage signals.
Fig. 1 is a circuit diagram illustrating a unit pixel of a general 3-transistor CMOS image sensor.
The unit pixel of the CMOS image sensor comprises a photodiode (PD) 1, a reset switch (RSW) 2, a capacitor CFD 4 of a floating diffusion sensing node 3, and a signal amplifier 5.
Hereinafter, the operation of the unit pixel of the CMOS image sensor is described.
The reset switch 2 resets the floating diffusion sensing node (FDSN) 3 into a reset voltage VR which is an initial value. Signal electrons generated corresponding to incident light in the photodiode 1 are accumulated in the capacitor CFD 4 of the floating diffusion sensing node FDSN 3. The capacitor CFD 4 includes a junction capacitor of the photodiode 1, a capacitor located at an input terminal of the signal amplifier 5, and peripheral parasitic capacitors which are connected in parallel.
As the signal electrons are accumulated in the capacitor CFD 4, a changing signal voltage is transmitted to the input terminal of the signal amplifier 5.
An output signal of the signal amplifier 5 is connected to a signal line of a pixel array. In the general CMOS image sensor pixel of Fig. 1 , the ohmic-contacted floating diffusion sensing node FDSN 3 transmits the signal of the photodiode 1 to the input terminal of the signal amplifier 5.
While the ohmic contact is formed, physical defects are generated so that a large dark current is generated from the floating diffusion sensing node FDSN 3. Electrons of the dark current from the ohmic contact are added in the signal electrons while the photodiode 1 receives light and accumulates the signal electrons in the 3-transistor pixel structure and operation.
As a result, a noise generated around the floating diffusion sensing node FDSN 3 by the dark current severely degrades the image quality in the 3-transistor pixel structure. When the photodiode 1 is reset at the reset voltage VR with the reset switch 2, a kTC reset noise is generated. And a correlated double sampling CDS method used in a 4-transistor pixel cannot be used to remove the reset noise in the 3-transistor pixel structure.
Since the photodiode 1 is directly connected to the floating diffusion sensing node FDSN 3 in the 3-transistor pixel, it is impossible to embody a shared structure where structures other than the photodiode 1 are shared in two or more pixels to reduce the number of devices per pixel. The share structure cannot be adopted because electrons generated from all photodiodes of the shared pixels are mixed with each other.
Fig. 2 is a cross-sectional and circuit diagram illustrating a general 3-transistor image sensor pixel. A partially pinned photodiode part Dl and a reset switch part D2 are shown in the cross-sectional diagram, and a source follower 6 and an address switch 7 are shown in the circuit diagram.
The CMOS image sensor pixel comprises a partially pinned photodiode (PPPD), a reset switch (RSW), a source follower (SF) 6, an address switch (ASW) 7 and a constant current source 8.
A signal amplifier 5 includes the source follower SF 6, the address switch ASW 7 and the constant current source 8.
The reset switch RSW and the address switch ASW 7 are formed of a field effect transistor (FET) respectively. The reset switch RSW having a common drain with the source follower SF 6 is connected to a driving voltage VDD. As a result, an additional reset voltage VR is not used but the driving voltage VDD is used as a reset voltage.
The partially pinned photodiode PPPD is formed of a photodiode PPD including an ohmic-contacted diffusion sensing node. The partially pinned photodiode part Dl includes a n-type diffusion region 10 and a p+ diffusion region 11 which are formed in a p-type epitaxial layer (or p-type substrate) 9, and a n+ type diffusion region 12 for forming the ohimic contact sensing node in the n-type diffusion region 10.
The reset switch part D2 comprises a p-type well 13 formed in the p-type epitaxial layer (or p-type substrate) 9, a n+ type diffusion region 14 used as a reset- voltage-applying terminal formed in the p-type well 13, and an insulating layer and a gate electrode over a region where a channel is formed between the n+ type diffusion region 12 and the n+ type diffusion region 14.
A p-type well 15 is formed around the partially pinned photodiode part Dl.
The partially pinned photodiode PPPD has a smaller dark current generated from the silicon surface than that of the general photodiode. However, there is a large dark current generated from the n+ type diffusion region 12 for forming the ohmic-contacted diffusion sensing node and a reset noise generated by the reset switch RSW.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Technical Subject
In order to overcome the above-described shortcomings, the present invention has the following objects.
Various embodiments of the present invention are directed at providing a photodiode and an image sensor pixel configured to reduce a dark current generated from ohmic-contacted diffusion sensing node.
Various embodiments of the present invention are directed at providing a photodiode and an image sensor pixel configured to reduce a reset noise.
Various embodiments of the present invention are directed at providing a photodiode and an image sensor pixel configured to have a shared structure without any transfer gates between the photodiode and the sensing node.
Technical Solution
According to an embodiment of the present invention, a photodiode comprises: an epitaxial layer having a first conductive type; a first diffusion region having a second conductive type formed in the epitaxial layer; a second diffusion region having a first conductive type and floating in the first diffusion region; and a coupling capacitor configured to transmit outside a voltage change of the first diffusion region.
According to an embodiment of the present invention, an image sensor pixel comprises: a photodiode which comprises an epitaxial layer having first conductive type, a first diffusion region having a second conductive type formed in the epitaxial layer, a second diffusion region having a first conductive type and floating in the first diffusion region, and a coupling capacitor configured to transmit outside a voltage change of the first diffusion region; a reset switch configured to reset the first diffusion region of the photodiode with a reset voltage source; a multi-functional switch, connected between a variable voltage source and an output terminal of the coupling capacitor, configured to apply a voltage of the variable voltage source to the output terminal; and a signal amplifier configured to transmit a voltage signal corresponding to the voltage change transmitted by the coupling capacitor to a signal line of a pixel array.
According to an embodiment of the present invention, a method for sensing a signal of an image sensor pixel, which comprises: a photodiode comprising an epitaxial layer having a first conductive type, a first diffusion region having a second conductive type formed in the epitaxial layer, a second diffusion region having a first conductive type and floating in the first diffusion region, and a coupling capacitor configured to transmit outside a voltage change of the first diffusion region; a reset switch configured to reset the first diffusion region of the photodiode with a reset voltage source; a multi-functional switch, connected between a variable voltage source and an output terminal of the coupling capacitor, configured to apply a voltage of the variable voltage source to the output terminal; and a signal amplifier configured to transmit a voltage signal corresponding to the voltage change transmitted by the coupling capacitor to a signal line of a pixel array, comprises the steps of: fixing the output terminal of the coupling capacitor at a first voltage level with the variable voltage source when the multifunctional switch is turned on; resetting the first diffusion region by turning on the reset switch; setting a voltage of the input terminal of the signal amplifier at a second voltage higher than the first voltage with the variable voltage source to read a value of the output voltage of the signal amplifier; storing electrons generated by absorbing light in the first diffusion region after the reset switch and the multi-functional switch are turned off; and sensing a change of the output voltage of the signal amplifier.
According to an embodiment of the present invention, a method for sensing a signal of an image sensor pixel, which comprises: a photodiode comprising an epitaxial layer having a first conductive type; a first diffusion region having a second conductive type formed in the epitaxial layer; a second diffusion region having a first conductive type and floating in the first diffusion region; and a coupling capacitor configured to transmit outside a voltage change of the first diffusion region; a reset switch configured to reset the first diffusion region of the photodiode with a reset voltage source; a multi-functional switch, connected between a variable voltage source and an output terminal of the coupling capacitor, configured to apply a voltage of the variable voltage source to the output terminal; and a signal amplifier configured to transmit a voltage signal corresponding to the voltage change transmitted by the coupling capacitor to a signal line of a pixel array, comprises the steps of: fixing the output terminal of the coupling capacitor at a first voltage level with the variable voltage source when the multifunctional switch is turned on; resetting the first diffusion region by turning on the reset switch; storing electrons generated by absorbing light in the first diffusion region after the reset switch and the multi-functional switch are turned off; setting a voltage of the input terminal of the signal amplifier at a second voltage higher than an input threshold voltage of the signal amplifier with the variable voltage source after turning on the multi- functional switch, and reading an output signal of the signal amplifier after the multifunctional switch is turned off; removing the electrons stored in the first diffusion region by turning on the reset switch; and sensing a change of the output voltage of the signal amplifier.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a circuit diagram illustrating a general 3-transistor image sensor pixel.
Fig. 2 is a cross-sectional and circuit diagram illustrating a general 3-transistor image sensor pixel. Fig. 3 is a diagram illustrating a capacitor combined photodiode (CCPD) according to an embodiment of the present invention.
Fig. 4 is a cross-sectional diagram taken along A-A' of Fig. 3.
Fig. 5 is a cross-sectional diagram taken along B-B' of Fig. 3.
Fig. 6 is a cross-sectional diagram taken along C-C of Fig. 3. Fig. 7 is a diagram illustrating the CCPD and a reset switch part D3 in an embodiment where the CCPD is connected to the reset switch part D3.
Fig. 8 is a cross-sectional diagram taken along D-D' of Fig. 7.
Fig. 9 is a cross-sectional and circuit diagram illustrating an image sensor pixel including the CCPD and the reset switch RSW of Figs. 7 and 8, a multi-functional switch 24 and a signal amplifier 25.
Fig. 10 is a diagram illustrating an example of Fig. 9 with the signal amplifier 25 composed of a source follower (SF) 26 and a constant current source 27.
Fig. 11 is a diagram illustrating an example of Fig. 10 wherein a driving voltage VDD of the source follower 26 is used in common as the reset voltage sources. Preferred Embodiments
The present invention will be described in detail with reference to the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. Fig. 3 is a diagram illustrating a capacitor combined photodiode (CCPD) according to an embodiment of the present invention.
The capacitor combined photodiode CCPD comprises a floating-layer photodiode region FLPD and a coupling capacitor region CC. The geometrical shape of the floating-layer photodiode region FLPD and the coupling capacitor region CC can be changed.
Fig. 4 is a cross-sectional diagram taken along A-A' of Fig. 3, and Fig. 5 is a cross-sectional diagram taken along B-B' of Fig. 3.
The floating-layer photodiode region FLPD includes a n-type diffusion region 10 and a p+ type diffusion region 11 which are formed in a p-type epitaxial layer (or p-type substrate) 9. The floating layer 11 is completely floated without being contacted to the p-type epitaxial layer (or p-type substrate) 9 or a p-type well 15.
The p-type well 15 is formed around the periphery of the floating-layer photodiode region FLPD.
Fig. 6 is a cross-sectional diagram taken along C-C of Fig. 3. The floating-layer photodiode region FLPD includes the n-type diffusion region
10 and the p+ type diffusion region 11 which are formed in the p-type epitaxial layer (or p-type substrate) 9. The coupling capacitor CC has the p+ type floating layer 11 as a first electrode, an oxide insulating layer 18 over the p+ type floating layer 11 as a dielectric layer, and a second electrode 19. The coupling capacitor CC is electrically connected to the n-type diffusion region 10 of the floating-layer photodiode region FLPD through the floating layer 11 without ohmic contact, and transmits a voltage change of the n-type diffusion region 10 to the outside. The coupling capacitor CC is serially connected in the circuit with a pn junction capacitor CFP formed between the floating layer 11 and the n-type diffusion region 10.
When the voltage change of the n-type diffusion region 10 occurs by signal electrons generated by light absorption, the voltage change is transmitted to the coupling capacitor CC through the junction capacitor CFP, and to the outside through the second electrode 19 of the coupling capacitor CC. That is, when the second electrode 19 of the coupling capacitor CC is connected to the input terminal of the signal amplifier, a voltage proportional to the signal voltage change of the n-type diffusion region 16 is transmitted to the input terminal of the signal amplifier.
As a result, the sensing node using the coupling capacitor CC can reduce a dark current in comparison with ohmic-contacted diffusion sensing nodes because physical defects generated in the sensing nodes 3 for forming the ohmic contact can be reduced. The physical defects of the sensing nodes are main cause of the dark current in the sensing nodes.
Although the p+ type floating layer 11 is floated in the n-type diffusion region 10, it is electrically connected to the outside through the coupling capacitor CC so that a reverse bias voltage can be applied between the floating layer 11 and the n-type diffusion region 10. If the doping concentration, depth and width of the n-type diffusion region 10 are adjusted, the n-type diffusion region 10 can be fully depleted by the reset operation.
In this way, since the n-type diffusion region 10 is fully depleted, the pixel including the capacitor combined photodiode CCPD can reduce an image lag and a reset noise. Fig. 7 is a diagram illustrating the capacitor combined photodiode CCPD and a reset switch part D3 in an embodiment where the floating-layer photodiode region FLPD is connected to the reset switch part D3.
The floating-layer photodiode region FLPD includes a coupling capacitor CC region over itself, and is connected to the reset switch region D3.
The geometrical shape of the floating-layer photodiode region FLPD, the coupling capacitor region CC and the reset switch region D3 can be changed.
Fig. 8 is a cross-sectional diagram taken along D-D' of Fig. 7.
The FLPD includes the n-type diffusion region 10 and the p+ type diffusion region 11 which are formed in the p-type epitaxial layer (or p-type substrate) 9. The coupling capacitor CC has the p+ type floating layer 11 as a first electrode, and an oxide insulating layer 18 over the p+ type floating layer 11 as a dielectric layer, and a second electrode 19.
The reset switch part D3 comprises a p-type well 20 formed in the p-type epitaxial layer (or p-type substrate) 9, a n+ type diffusion region 21 used as a reset- voltage-applying terminal formed in the p-type well 20, and an oxide insulating layer 22 and a gate electrode 23 over a region where a channel is formed between the n-type diffusion region 10 of the floating-layer photodiode region FLPD and the n+ type diffusion region 21. Fig. 9 is a cross-sectional and circuit diagram illustrating an image sensor pixel including the capacitor combined photodiode CCPD and the reset switch RSW of Figs. 7 and 8, a multi-functional switch 24 and a signal amplifier 25. The capacitor combined photodiode CCPD and the reset switch part D3 are shown in the cross-sectional diagram, and the multi-functional switch 24 and the signal amplifier 25 are shown in the circuit diagram. The floating-layer photodiode FLPD absorbs light radiated from an object for photography to change the light into signal electrons. The signal electrons are accumulated in the n-type diffusion region 10.
The coupling capacitor CC transmits a voltage change of the n-type diffusion region 10 to the input terminal of the signal amplifier 25. The voltage change occurs when the signal electrons flow into or out form the n-type diffusion region 10.
The reset switch RSW discharges the electrical charge stored in the n-type diffusion region 10 through the n+ type diffusion region 21 connected to a reset voltage source VR, to reset the voltage of the n-type diffusion region 10 into an initial value. The multi-functional switch 24 has the following functions in the operation of the above-described pixel.
The multi-functional switch 24 provides a discharging path to a floating structure when the input terminal of the signal amplifier 25 is floating.
So, the multi-functional switch 24 prevents the related devices such as the signal amplifier and coupling capacitor from malfunctioning and being damaged.
The multi-functional switch 24 sets the initial voltage of the input terminal of the signal amplifier 25 and the second electrode 19 of the coupling capacitor CC into a specific value with the variable voltage source VC.
The output terminal of the signal amplifier 25 is directly connected to a signal line of a pixel array, or is connected to the signal line through an addressing switch for connecting/disconnecting an output signal of the signal amplifier 25. When the output terminal of the signal amplifier 25 is directly connected to the signal line of the pixel array without the addressing switch, the signal amplifier 25 is required to be controlled on/off states. There are two methods for the operation of the unit pixel of Fig. 9. In a first method, a voltage of the variable voltage source VR is set to a first voltage VL (e.g., OV) and the multi-functional switch 24 is turned on so that a voltage of the second electrode 19 of the coupling capacitor CC is fixed at the first voltage VL. The reset switch RSW is turned on to reset the n-type diffusion regions 10. The voltage of the variable voltage source VC is set to a second voltage VH higher than the first voltage VL. The second voltage VH is set to a sufficiently higher value (e.g., driving voltage VDD of the signal amplifier 25) in consideration of a dropping range of the signal voltage due to light. The reset switch RSW and the multi-functional switch 24 are turned off to finish the reset operation of the capacitor combined photodiode CCPD. As the signal electrons corresponding to incident light are accumulated in the n- type diffusion regions 10 after resetting of the capacitor combined photodiode CCPD, the voltage of the n-type diffusion region 10 falls down and the voltage change is transmitted to the signal amplifier 25 through the junction capacitor CFP and the coupling capacitor CC. That is, the voltage of the second electrode 19 of the coupling capacitor CC and the input terminal of the signal amplifier 25 falls down form the initial value VH. The change of the signal voltage of the input terminal of the signal amplifier 25 gives information on the amount of the signal electrons, that is, on the amount of the incident light into the pixel.
In a second method, the voltage of the variable voltage source VC is set to the first voltage VL (e.g., OV), and the multi-functional switch 24 is turned on to fix the voltage of the second electrode 19 of the coupling capacitor CC at the first voltage VL. The reset switch RSW is turned on to reset the n-type diffusion regions 10 of the capacitor combined photodiode CCPD. The reset switch RSW is turned off to finish the reset operation of the capacitor combined photodiode CCPD. Here, the multi- functional switch 24 is kept on or turned off. Both of the ways are possible. The signal electrons are accumulated in the n-type diffusion regions 10 by the incident light, and the amount of the accumulated signal electrons is read by the following operation.
The value of the variable voltage source VC is set to a voltage VLl larger than an input threshold voltage VT of the signal amplifier 25. The multi-functional switch 24 is turned on, if it was turned off before, to set the initial value of the second electrode of the coupling capacitor CC and the input terminal of the signal amplifier 25 to the voltage
VLl. The multi-functional switch 24 is turned off and the reset switch RSW is turned on to remove the signal electrons from the n-type diffusion regions 10. As a result, the voltage of the n-type diffusion region 10 rises. The voltage change is transmitted to the coupling capacitor CC, and to the input terminal of the signal amplifier 25 through the second electrode 19 of the coupling capacitor CC.
That is, when the signal electrons accumulated in the capacitor combined photodiode CCPD are reset, the voltage of the input terminal of the signal amplifier 25 rises from the initial value VLl. The amount of the signal electrons, that is, the amount of the incident light can be evaluated from the voltage rise value.
The second operation method is roughly opposite in concept to that of a general 4-transistor pixel.
Fig. 10 is a diagram illustrating an example of Fig. 9 with the signal amplifier which comprises a source follower (SF) 26 and a constant current source 27.
Fig. 11 is a diagram illustrating an example of Fig. 10 wherein a driving voltage VDD of the source follower 26 is used in common as the reset voltage source.
The operation of Figs. 10 and 11 is as follows.
The voltage of the variable voltage source VC is set to the first voltage VL (e.g., OV), and the multi-functional switch 24 is turned on to fix the voltage of the second electrode 19 of the coupling capacitor CC at the first voltage VL. At the time, the source follower active transistor 26 is automatically turned off. The reset switch RSW is turned on to reset the n-type diffusion regions 10. The reset switch RSW is turned off to finish the reset operation of the capacitor combined photodiode CCPD. Here, the multi- functional switch 24 is kept on or turned off. Both of the ways are possible.
The signal electrons are accumulated in the n-type diffusion regions 10 of the capacitor combined photodiode CCPD by the incident light signal. The amount of the accumulated signal electrons is read by the following operation.
The value of the variable voltage source VC is set to a voltage VLl larger than an input threshold voltage VT of the source follower active transistor 26.
The multi-functional switch 24 is turned on, if it was turned off before, to set the initial value of the second electrode 19 of the coupling capacitor CC and a gate of the source follower active transistor 26 to the voltage VLl.
The multi-functional switch 24 is turned off and the reset switch RSW is turned on to remove the signal electrons from the n-type diffusion regions 10. As a result, the voltage of the n-type diffusion region 10 rises. The voltage change is transmitted to the gate of the source follower active transistor 26 through the second electrode 19 which is an output terminal of the coupling capacitor CC.
That is, when the signal electrons accumulated in the capacitor combined photodiode CCPD are reset, the voltage of the gate of the source follower active transistor 26 rises from the initial value VLl. The amount of the signal electrons, that is, the amount of the incident lights can be evaluated from the voltage rising value.
In the above-described operation method of the pixel, the on/off states of the source follower active transistor 26 are controlled by the voltage setting value of the gate terminal so that an addressing switch for selectively transmitting an output voltage to the signal line of the pixel array is not required.
The multi-functional switch 24 has the following functions in the pixel.
The multi-functional switch 24 provides a path for discharging net charge flowed into the electrically floating structure at the connecting node of the gate of the source follower 26 and second electrode 19 of the coupling capacitor CC.
As a result, the multi-functional switch 24 prevents the malfunction or damages of the coupling capacitor CC and the source follower active transistor 26.
The multi-functional switch 24 sets the initial voltage of the gate of the source follower active transistor 26 and the second electrode 19 of the coupling capacitor CC at a specific value with the variable voltage source VC.
Industrial Applicability
As described above, the CMOS image sensor according to an embodiment of the present invention has the following effects. The signal voltage is transmitted to the signal amplifier with the coupling capacitor instead of the ohmic-contacted diffusion sensing node in order to reduce the dark current generated from the ohmic contact.
The n-type diffusion regions 10 of the capacitor combined photodiode CCPD are fully depleted by the reset operation to remove a reset noise and an image lag. The shared structure can be embodied by using the coupling capacitor instead of the ohmic-contacted diffusion sensing node.
While the invention is susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and described in detail herein. However, it should be understood that the invention is not limited to the particular forms disclosed. Rather, the invention covers all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined in the appended claims.

Claims

What is Claimed is:
1. A photodiode comprising: an epitaxial layer having a first conductive type; a first diffusion region having a second conductive type formed in the epitaxial layer; a second diffusion region having a first conductive type and floating in the first diffusion region; and a coupling capacitor configured to transmit outside a voltage change of the first diffusion region.
2. The photodiode according to claim 1, wherein the second conductive type has an opposite polarity to that of the first conductive type.
3. The photodiode according to claim 1, wherein the coupling capacitor comprises: a first electrode formed with the second diffusion region; an insulating layer formed over the second diffusion region; and a second electrode formed over the insulating layer.
4. The photodiode according to claim 3, wherein the coupling capacitor is formed over a part of the second diffusion region.
5. An image sensor pixel comprising: a photodiode which comprises an epitaxial layer having a first conductive type; a first diffusion region having a second conductive type formed in the epitaxial layer; a second diffusion region having a first conductive type and floating in the first diffusion region; and a coupling capacitor configured to transmit outside a voltage change of the first diffusion region; a reset switch configured to reset the first diffusion region of the photodiode with a reset voltage source; a multi-functional switch, connected between a variable voltage source and an output terminal of the coupling capacitor, configured to apply a voltage of the variable voltage source to the output terminal; and a signal amplifier configured to transmit a voltage signal corresponding to the voltage change transmitted by the coupling capacitor to a signal line of a pixel array.
6. The image sensor pixel according to claim 5, wherein the second conductive type has an opposite polarity to that of the first conductive type.
7. The image sensor pixel according to claim 5, wherein the coupling capacitor comprises: a first electrode formed with the second diffusion region; an insulating layer formed over the second diffusion region; and a second electrode formed over the insulating layer.
8. The image sensor pixel according to claim 5, wherein the coupling capacitor is formed over a part of the second diffusion region.
9. The image sensor pixel according to claim 5, wherein the first diffusion region is fully depleted in the reset operation.
10. The image sensor pixel according to claim 5, wherein the reset switch is connected between the first diffusion region and the reset voltage source.
11. The image sensor pixel according to claim 5, wherein the reset switch includes a Field Effect Transistor (FET) or a transfer gate structure.
12. The image sensor pixel according to claim 5, wherein the multi- functional switch forms a discharging path in order to prevent the output terminal of the coupling capacitor and the input terminal of the signal amplifier from being electrically a floating structure.
13. The image sensor pixel according to claim 5, wherein the multi- functional switch sets voltages of the output terminal of the coupling capacitor and the input terminal of the signal amplifier to be at predetermined values respectively.
14. The image sensor pixel according to claim 5, further comprising a switch configured to connect the output terminal of the signal amplifier to the signal line of the pixel array.
15. The image sensor pixel according to claim 5, wherein the signal amplifier is a source follower amplifier.
16. The image sensor pixel according to claim 5, wherein the reset voltage source is a driving voltage of the signal amplifier.
17. The image sensor pixel according to claim 5, wherein two or more pixels share the multi-functional switch and the signal amplifier.
18. A method for sensing a signal of an image sensor pixel, which comprises: a photodiode comprising an epitaxial layer having a first conductive type, a first diffusion region having a second conductive type formed in the epitaxial layer, a second diffusion region having a first conductive type and floating in the first diffusion region; and a coupling capacitor configured to transmit outside a voltage change of the first diffusion region; a reset switch configured to reset the first diffusion region of the photodiode with a reset voltage source; a multi-functional switch, connected between a variable voltage source and an output terminal of the coupling capacitor, configured to apply a voltage of the variable voltage source to the output terminal; and a signal amplifier configured to transmit a voltage signal corresponding to the voltage change transmitted by the coupling capacitor to a signal line of a pixel array, the method comprising the steps of: fixing the output terminal of the coupling capacitor at a first voltage level with the variable voltage source when the multi-functional switch is turned on; resetting the first diffusion region by turning on the reset switch; setting a voltage of the input terminal of the signal amplifier at a second voltage higher than the first voltage with the variable voltage source to read a value of the output voltage of the signal amplifier; storing electrons generated by absorbing light in the first diffusion region after the reset switch and the multi-functional switch are turned off; and sensing a change of the output voltage of the signal amplifier.
19. A method for sensing a signal of an image sensor pixel, which comprises: a photodiode comprising an epitaxial layer having a first conductive type; a first diffusion region having a second conductive type formed in the epitaxial layer; a second diffusion region having a first conductive type and floating in the first diffusion region; and a coupling capacitor configured to transmit outside a voltage change of the first diffusion region; a reset switch configured to reset the first diffusion region of the photodiode with a reset voltage source; a multi-functional switch, connected between a variable voltage source and an output terminal of the coupling capacitor, configured to apply a voltage of the variable voltage source to the output terminal; and a signal amplifier configured to transmit a voltage signal corresponding to the voltage change transmitted by the coupling capacitor to a signal line of a pixel array, the method comprising the steps of: fixing the output terminal of the coupling capacitor at a first voltage level with the variable voltage source when the multi-functional switch is turned on; resetting the first diffusion region by turning on the reset switch; storing electrons generated by absorbing light in the first diffusion region after the reset switch and the multi-functional switch are turned off; setting a voltage of the input terminal of the signal amplifier at a second voltage higher than an input threshold voltage of the signal amplifier with the variable voltage source after turning on the multi-functional switch, and reading an output signal of the signal amplifier after the multi-functional switch is turned off; removing the electrons stored in the first diffusion region by turning on the reset switch; and sensing a change of the output voltage of the signal amplifier.
20. The method according to claim 19, wherein the storing-the-electrons step is performed without turning off the multi-functional switch.
PCT/KR2006/004173 2006-05-25 2006-10-16 Image sensor pixel having photodiode with coupling capacitor and method for sensing a signal WO2007139253A1 (en)

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2001346104A (en) * 2000-06-02 2001-12-14 Nikon Corp Solid-state image pickup device and image pickup device using it
KR20030037871A (en) * 2001-11-06 2003-05-16 주식회사 하이닉스반도체 Cmos image sensor and method of manufacturing the same
KR20060090540A (en) * 2005-02-07 2006-08-11 삼성전자주식회사 Cmos image sensor and method of fabricating the same

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2001346104A (en) * 2000-06-02 2001-12-14 Nikon Corp Solid-state image pickup device and image pickup device using it
KR20030037871A (en) * 2001-11-06 2003-05-16 주식회사 하이닉스반도체 Cmos image sensor and method of manufacturing the same
KR20060090540A (en) * 2005-02-07 2006-08-11 삼성전자주식회사 Cmos image sensor and method of fabricating the same

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