WO2007139255A1 - Image sensor active pixel and method for sensing signal thereof - Google Patents

Image sensor active pixel and method for sensing signal thereof Download PDF

Info

Publication number
WO2007139255A1
WO2007139255A1 PCT/KR2006/004175 KR2006004175W WO2007139255A1 WO 2007139255 A1 WO2007139255 A1 WO 2007139255A1 KR 2006004175 W KR2006004175 W KR 2006004175W WO 2007139255 A1 WO2007139255 A1 WO 2007139255A1
Authority
WO
WIPO (PCT)
Prior art keywords
diffusion region
voltage
electrode
signal amplifier
image sensor
Prior art date
Application number
PCT/KR2006/004175
Other languages
French (fr)
Inventor
Jawoong Lee
Sungsu Lee
Jungsoon Shin
Original Assignee
Pixelplus Co., Ltd.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Pixelplus Co., Ltd. filed Critical Pixelplus Co., Ltd.
Publication of WO2007139255A1 publication Critical patent/WO2007139255A1/en

Links

Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/14—Devices 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
    • H01L27/144—Devices controlled by radiation
    • H01L27/146—Imager structures
    • H01L27/14601—Structural or functional details thereof
    • H01L27/14609—Pixel-elements with integrated switching, control, storage or amplification elements
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
    • H04N25/70—SSIS architectures; Circuits associated therewith
    • H04N25/76—Addressed sensors, e.g. MOS or CMOS sensors
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
    • H04N25/50—Control of the SSIS exposure
    • H04N25/57—Control of the dynamic range
    • H04N25/59—Control of the dynamic range by controlling the amount of charge storable in the pixel, e.g. modification of the charge conversion ratio of the floating node capacitance
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
    • H04N25/70—SSIS architectures; Circuits associated therewith
    • H04N25/76—Addressed sensors, e.g. MOS or CMOS sensors
    • H04N25/77—Pixel circuitry, e.g. memories, A/D converters, pixel amplifiers, shared circuits or shared components
    • H04N25/771—Pixel circuitry, e.g. memories, A/D converters, pixel amplifiers, shared circuits or shared components comprising storage means other than floating diffusion

Definitions

  • CMOS complementary metal-oxide-semiconductor
  • an image sensor 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 into electrons with a photodiode, and converts the accumulated charge into voltage signals.
  • the CMOS image sensor includes a Floating Diffusion (FD) sensing node as a charge sensing node in order to sense the signal charge amount.
  • a charge sensing unit includes a reset switch and a reset voltage source combined with the FD sensing node for resetting the FD sensing node.
  • Fig. 1 is a circuit diagram illustrating a unit pixel of a conventional image sensor.
  • the unit pixel of the CMOS image sensor comprises a photodiode I 9 a transfer gate 5, a charge sensing unit 6 and a signal amplifier 12.
  • the charge sensing unit 6 includes a FD sensing node 9, a reset switch 10 and a reset voltage source VR.
  • a capacitor 8 of Fig. 1 includes a junction capacitor and peripheral parasitic capacitors in the FD sensing node 9.
  • a signal voltage of the capacitor 8 is transmitted to an input terminal of the signal amplifier 12 through a conducting line which is ohmic- contacted to a n-type diffusion region of the FD sensing node 9.
  • Fig. 2 is a cross-sectional and circuit diagram illustrating the unit pixel of Fig. 1.
  • the unit pixel comprises a pinned photodiode PPD and n-channel MOSFETs.
  • the pinned photodiode includes a n-type diffusion region 3 formed in a p-type epitaxial layer P-EPI, a p+ region 4 formed in the n-type diffusion region 3 and a P-well 2 formed at a sidewall of the n-type diffusion region 3 and the p+ region 4.
  • the charge sensing unit 6 includes a P-well 7 formed in the p-type epitaxial layer P-EPI and the FD sensing node 9 formed in the P-well 7.
  • the photodiode PPD changes light signals into electrons to store the electrons in the n-type diffusion region 3. That is, the photodiode PPD absorbs light, generates photo-generated electrons, and accumulates them during the integration time before the transfer gate 5 is turned on.
  • a voltage of the n-type diffusion region of the FD sensing node 9 is reset into a voltage higher than the voltage of the n-type diffusion region 3 of the photodiode PPD with the reset switch 10 and the reset voltage source VR.
  • the transfer gate 5 When the transfer gate 5 is turned on, signal electrons accumulated in the n-type diffusion region 3 of the photodiode PPD are transferred into the n-type diffusion region of the FD sensing node 9 by the voltage difference between the photodiode PPD and the n-type diffusion region of the FD sensing node 9.
  • signal electrons are moved from the photodiode PPD into the FD sensing node 9 for transferring time so that the voltage of the n-type diffusion region of the FD sensing node 9 is changed.
  • the voltage change is transmitted to the input terminal of the signal amplifier 12 through the conducting line which is ohmic-contacted to the n-type diffusion region of the FD sensing node 9.
  • An output signal of the signal amplifier 12 is directly connected to a signal line of a pixel array or connected to a signal line through an addressing switch for connecting/disconnecting the output signal of the signal amplifier 12.
  • a directly connected structure without the addressing switch is used when the on/off states of the signal amplifier 12 can be controlled in the operating method of the pixel.
  • the n-type diffusion region 3 of the photodiode PPD is completely depleted.
  • the transfer gate 5 is turned off, and the photodiode PPD changes light signals into electrons to store the electrons in the n-type diffusion region 3.
  • the above-described operation of the unit pixel is repeated to read all image signals of the whole object for photography.
  • the CMOS image sensor uses low pixel driving voltage unlike a charge coupled device (CCD) image sensor. So, when electrons are transferred from the photodiode PPD into the FD sensing node 9, the voltage difference between the n-type diffusion regions 3 of the photodiode PPD and the FD sensing node 9 may not be enough for electrons to be fully moved into the FD sensing node 9. In order to transfer all electrons from the n-type diffusion region 3 of the photodiode PPD into that of the FD sensing node 9, the voltage of the n-type diffusion region of the FD sensing node 9 is required to be higher even in the low driving voltage.
  • CCD charge coupled device
  • the FD sensing node 9 is connected to the input terminal of the signal amplifier 12 through an ohmic-contacted conducting line.
  • the doping concentration of the diffusion region is required to be high.
  • dark current increases in the FD sensing node 9 due to the physical defects generated from the ohmic contact process. So, the dark current in the ohmic-contacted FD sensing node 9 can causes a severe error whenever the signal electrons are stored in the FD sensing node 9 for a long time.
  • a sensing node having a smaller dark current than that of the FD sensing node 9 with ohmic contact is required.
  • a global shuttering of the image sensor is performed to store signal electrons in the FD sensing node 9 for a long time.
  • the FD sensing node 9 is directly connected to the signal amplifier 12 with the conducting line. So, if the voltage of the input terminal of the signal amplifier 12 is externally changed, the signal charge stored in the FD sensing node 9 is also changed so that the stored information is lost. That is, in the conventional CMOS image sensor, the voltage of the input terminal of the signal amplifier 12 can not be externally changed to perform the next operation of the pixel without loss of the stored information in the FD sensing node 9.
  • Various embodiments of the present invention is directed at boosting a voltage of a n-type diffusion region of a charge sensing node even in a low pixel driving voltage to transfer all signal electrons from a n-type diffusion region of a photodiode into the n-type diffusion region of the charge sensing node and to increase the maximum charge storage capacity of the charge sensing node.
  • Various embodiments of the present invention is directed at transmitting a signal voltage of the charge sensing node to an input terminal of a signal amplifier with a coupling capacitor without forming ohmic contact to the n-type diffusion region of the charge sensing node in order to reduce a dark current of the sensing node than that of the conventional ohmic-contacted sensing node.
  • Various embodiments of the present invention is directed at coupling the signal voltage to the signal amplifier with a coupling capacitor, thereby facilitating the operation of the pixel that externally changes a voltage of the input terminal of the signal amplifier without loss of signal charge stored in the sensing node.
  • Various embodiments of the present invention is directed at making an electrode of the coupling capacitor included in the charge sensing unit serve as an optical blocking mask, thereby effectively blocking the incident light into the charge sensing node.
  • an image sensor active pixel comprises: a photodiode which includes a first diffusion region having a second conductive type formed in a first semiconductor region having a first conductive type, configured to absorb incident light and generate charged particles so as to store the particles in the first diffusion region; a capacitor combined floating diffusion (CCFD) sensing node which includes a second diffusion region having a second conductive type formed in a second semiconductor region having a first conductive type and a coupling capacitor having the second diffusion region as a first electrode and an electrode formed over the second diffusion region as a second electrode, configured to store the charged particles transferred from the first diffusion region in the second diffusion region; a transfer gate configured to transfer the charged particles stored in the first diffusion region into the second diffusion region; a reset switch, connected between a reset voltage source and the second diffusion region, configured to reset a voltage of the second diffusion region; a signal amplifier, which has an input terminal connected to the second electrode, configured to transmit a voltage signal corresponding to a voltage of the second electrode to a signal line
  • an image sensor active pixel comprises: a capacitor combined floating diffusion (CCFD) sensing node which includes a first diffusion region having a second conductive type formed in a first semiconductor region having a first conductive type and a coupling capacitor having the first diffusion region as a first electrode and an electrode formed over the first diffusion region as a second electrode, configured to store the charged particles externally transferred in the first diffusion region; a reset switch, connected between a reset voltage source and the first diffusion region, configured to reset a voltage of the first diffusion region; and a multi-functional switch, which has one terminal connected to the second electrode and the input terminal of the signal amplifier and the other terminal connected to a variable voltage source, configured to apply a voltage of the variable voltage source to the second electrode and the input terminal of the signal amplifier.
  • CCFD capacitor combined floating diffusion
  • a method for sensing a signal of an image sensor active pixel which comprises a photodiode which includes a first diffusion region having a second conductive type formed in a first semiconductor region having a first conductive type, a capacitor combined floating diffusion (CCFD) sensing node which includes a second diffusion region having a second conductive type formed in a second semiconductor region having a first conductive type and a coupling capacitor having the second diffusion region as a first electrode and an electrode formed over the second diffusion region as a second electrode, configured to store the charged particles transferred from the first diffusion region in the second diffusion region, a reset switch connected between a reset voltage source and the second diffusion region, a signal amplifier which has an input terminal connected to the second electrode, and a multifunctional switch configured to apply a voltage of the variable voltage source to the second electrode and the input terminal of the signal amplifier, comprises the steps of: applying a voltage of the variable voltage source to the second electrode with the multifunctional switch turned on so as to fix the second electrode at a first voltage;
  • a method for sensing a signal of an image sensor active pixel which comprises a photodiode which includes a first diffusion region having a second conductive type formed in a first semiconductor region having a first conductive type, a capacitor combined floating diffusion (CCFD) sensing node which includes a second diffusion region having a second conductive type formed in a second semiconductor region having a first conductive type and a coupling capacitor having the second diffusion region as a first electrode and an electrode formed over the second diffusion region as a second electrode, configured to store the charged particles transferred from the first diffusion region in the second diffusion region, a reset switch connected between a reset voltage source and the second diffusion region, a signal amplifier which has an input terminal connected to the second electrode, and a multi- functional switch configured to apply a voltage of the variable voltage source to the second electrode and the input terminal of the signal amplifier, comprises the steps of: turning off the reset switch and turning on the transfer gate to transfer the electrons stored in the first diffusion region into the second diffusion region and turning off the transfer
  • Fig. 1 is a circuit diagram illustrating a unit pixel of a conventional image sensor active pixel.
  • Fig. 2 is a cross-sectional and circuit diagram illustrating the unit pixel of Fig. 1.
  • Fig. 3 is a cross-sectional and circuit diagram illustrating an image sensor active pixel according to an embodiment of the present invention.
  • Fig. 4 is an expanded cross-sectional and circuit diagram illustrating a signal charge sensing node of Fig. 3.
  • Fig. 5 is a cross-sectional and circuit diagram illustrating an image sensor active pixel according to an embodiment of the present invention.
  • Fig. 6 is a cross-sectional and circuit diagram illustrating an image sensor active pixel according to an embodiment of the present invention.
  • Fig. 3 is a cross-sectional and circuit diagram illustrating an image sensor active pixel according to an embodiment of the present invention.
  • the image sensor active pixel includes a pinned photodiode PPD and n-channel
  • the image sensor active pixel comprises a pinned photodiode PPD, a transfer gate 44, a charge sensing unit 45 and a signal amplifier 54.
  • the charge sensing unit 45 includes a Capacitor Combined Floating Diffusion (CCFD) sensing node 46, a reset switch 52, a reset voltage source VR, a multi-functional switch 53, and a variable voltage source VC.
  • CCFD Capacitor Combined Floating Diffusion
  • Fig. 4 is an expanded cross-sectional and circuit diagram illustrating a signal charge sensing node of Fig. 3.
  • the pinned photodiode PPD includes a n-type diffusion region 42 formed in a p- type epitaxial layer P-EPI, a p+ region 43 formed in the n-type diffusion region 42, and a P-well 41 formed at a sidewall of the n-type diffusion region 42 and the p+ region 43.
  • a p-type substrate P-SUB can be used instead of the p-type epitaxial layer P-EPI.
  • a CCFD sensing node 46 includes a n-type diffusion region 49 formed in a P- well 47 or a p-type diffusion region which is formed in the p-type epitaxial layer P-EPI.
  • An insulating layer 51 is formed over the n-type diffusion region 49, and a second electrode 50 is formed over the insulating layer 51.
  • the coupling capacitor CC comprises the n-type diffusion region 49 as a first electrode, the insulating layer 51, and the electrode 50 as a second electrode.
  • the n-type diffusion region 49 stores electrons transferred from the pinned photodiode PPD as well as serves as a first electrode of the coupling capacitor CC.
  • the coupling capacitor CC is formed over the n-type diffusion region 49 with the in between insulating layer 51. So, the additional area of the pixel for forming the coupling capacitor CC can be reduced.
  • the thickness of the insulating layer 51 of the coupling capacitor CC is so thin that the second electrode 50 may serve as an optical blocking mask for effectively blocking the incident light into the n-type diffusion region 49 of the CCFD sensing node 46 if the second electrode 50 of the coupling capacitor CC is formed of an opaque material to light.
  • the impurity doping concentration of the n-type diffusion region 49 serving as a first electrode of the coupling capacitor CC may be smaller than that for ohmic contact.
  • the CCFD sensing node 46 can reduce dark current and noise generated from the sensing node in comparison with the conventional sensing node in which a conducting line is directly ohmic-contacted to the n-type diffusion region 49.
  • the n-type diffusion region 49 stores signal electrons transferred from the pinned photodiode PPD. Whenever electrons flow into or out from the n-type diffusion region 49, the voltage of the n-type diffusion region 49 is changed, and the voltage change is transmitted to another units through the coupling capacitor CC.
  • An insulating layer 51a is formed over the P-well 47.
  • the transfer gate 44 formed over the insulating layer 51a serves as a switch for connecting the n-type diffusion region 49 of the CCFD sensing node 46 to the n-type diffusion region 42 of the pinned photodiode PPD.
  • the pinned photodiode PPD changes incident light into electrons to store the electrons in the n-type diffusion region 42.
  • the transfer gate 44 transfers the electrons stored in the photodiode PPD into the CCFD sensing node 46 of the charge sensing unit 45.
  • the CCFD sensing node 46 stores the electrons transferred from the pinned photodiode PPD through the transfer gate 44 in the n-type diffusion region 49.
  • the reset switch 52 formed over the insulating layer 51b has one terminal connected to the n-type diffusion region 49 of the CCFD sensing node 46, and the other terminal connected to the reset voltage source VR.
  • the reset switch 52 discharges electrical charge stored in the n-type diffusion region 49 of the CCFD sensing node 46, and resets a voltage of the n-diffusion region 49.
  • the reset switch 52 can be formed a Field Effect Transistor (FET) or a Transfer Gate Structure.
  • the coupling capacitor CC has the first electrode formed with the n-type diffusion region 49, and the second electrode 50 connected in common to the multi-functional switch 53 and the input terminal of the signal amplifier 54.
  • the multi-functional switch 53 has one terminal connected to the second electrode 50 of the coupling capacitor CC and the input terminal of the signal amplifier 54, and the other terminal connected to the variable voltage source VC.
  • the multi- functional switch 53 can be formed of a FET.
  • the multi-functional switch 53 transmits a voltage of the variable voltage source VC to the second electrode 50 of the coupling capacitor CC and the input terminal of the signal amplifier 54.
  • the reset voltage source VR and the variable voltage source VC are located outside of the pixel, and connected to the corresponding nodes of each pixel by conducting lines. An output voltage of the CCFD sensing node 46 is transmitted through the coupling capacitor CC to the input terminal of the signal amplifier 54 connected to the second electrode 50 of the coupling capacitor CC.
  • the input terminal of the signal amplifier 54 is connected to the second electrode 50 of the coupling capacitor CC and the one terminal of the multi-functional switch 53.
  • An output terminal of the signal amplifier 54 is directly connected to a signal line of a pixel array, or is connected to the signal line through a switch for turning on/off an output signal of the signal amplifier 54.
  • a directly connected structure without the switch is used when the on/off states of the signal amplifier 54 can be controlled in the operating method of the pixel.
  • the charge sensing unit 45 of the unit pixel can be shared by the photodiode PPD or the signal amplifier 54 of the other pixel.
  • the above-described operation process of the image sensor active pixel according to the embodiment of the present invention is described in detail.
  • the pinned photodiode PPD changes light signals into electrons to store the electrons in the n-type diffusion region 42. That is, the pinned photodiode PPD absorbs light, generates electrons, and accumulates them during the charge integration time before the transfer gate 44 is turned on. While the transfer gate 44 is turned off, a voltage of the n-type diffusion region 49 of the CCFD sensing node 46 is reset into a voltage higher than the voltage of the n- type diffusion region 42 of the pinned photodiode PPD.
  • the resetting procedure is as follows.
  • the variable voltage source VC is maintained at a voltage level VCL, and the multi-functional switch 53 is turned on to fix the second electrode 50 of the coupling capacitor CC at a voltage level VCL. Thereafter, the reset switch 52 is turned on and the voltage of the n-type diffusion region 49 of the CCFD sensing node 46 is reset into reset voltage VRN.
  • the reset voltage VRN is determined by characteristics of the reset voltage source VR and the reset switch 52. Thereafter, the reset switch 52 is turned off and the variable voltage source VC is raised from a voltage level VCL to a voltage level VCH. By this act, the voltage of the n-type diffusion region 49 of the CCFD sensing node 46 rises from the reset voltage VRN to VRN + ⁇ x (VCH - VCL).
  • the constant ⁇ has positive value less than unity. That is, the voltage of the n-type diffusion region 49 of the CCFD sensing node 46 is boosted by ⁇ x (VCH - VCL) from the reset voltage VRN to VRN + ⁇ x (VCH - VCL).
  • the voltage level VCL and VCH are set to a ground voltage level and a VDD level of pixel driving voltage respectively.
  • the multi-functional switch 53 is turned off.
  • the n-type diffusion region 42 of the pinned photodiode PPD is completely depleted.
  • the transfer gate 44 is again turned off, and the pined photodiode PPD again begins to accumulate the photo-generated electrons in the n- type diffusion region 42.
  • the above-described operation of the unit pixel is repeated to read all image signals of the whole object for photography.
  • the operation of the pixel is similar to that of the conventional pixel.
  • the charge sensing unit 45 is characterized in that the voltage change of the n- type diffusion region 49 of the CCFD sensing node 46 is transmitted to the input terminal of the signal amplifier 54 through coupling capacitor CC. Although the voltage of the second electrode 50 of the coupling capacitor CC or the input terminal of the signal amplifier 54 is changed into a required value with the multi-functional switch 53 and the variable voltage source VC, the number of signal electrons stored in the n-type diffusion region 49 of the CCFD sensing node 46 is preserved.
  • the functions of the coupling capacitor CC in the charge sensing unit 45 are as follows.
  • the coupling capacitor CC boosts the voltage of the n-type diffusion region 49 of the CCFD sensing node 46 by the linked operation of the reset switch 52, the reset voltage source VR, the multi-functional switch 53 and the variable voltage source VC. Also, the coupling capacitor CC transmits the signal voltage of the CCFD sensing node 46 into the input terminal of the signal amplifier 54.
  • the multi-functional switch 53 provides a discharging path is to the floating structure of the second electrode 50 of the coupling capacitor CC and the input terminal of the signal amplifier 54 to discharge undesired charge, thereby preventing malfunction of devices.
  • the multi-functional switch 53 and the variable voltage source VC boost the voltage of the n-type diffusion region 49 of the CCFD sensing node 46 by the linked operation of the reset switch 52, the reset voltage source VR and the coupling capacitor CC.
  • the multi-functional switch 53 and the variable voltage source VC set an initial reference voltage of the input terminal of the signal amplifier 54.
  • the on/off states of the signal amplifier 54 can be controlled when the signal amplifier 54 is a source-follower.
  • the present invention has the following merits.
  • the n-type diffusion region 49 is used as the first electrode of the coupling capacitor CC so that ohmic contact is not formed to connect the CCFD sensing node 46 to the coupling capacitor CC with a conducting line.
  • the doping concentration of the n- type diffusion region 49 of the CCFD sensing node 46 can be reduced lower than that for ohmic contact. As a result, physical defects generated from the process can be reduced, and the dark current generated from the sensing node can be decreased.
  • the coupling capacitor CC is formed over the floating diffusion structure, thereby reducing the additional area of the pixel for forming the coupling capacitor CC.
  • the second electrode 50 of the coupling capacitor CC formed over the CCFD sensing node 46 with the in between thin ( ⁇ nm) oxide insulating layers 51 can be made of opaque materials to block the incident light into the sensing node.
  • the opaque electrode includes metal electrodes such as copper and aluminum, or poly suicide electrodes. That is, the second electrode 50 which covers the CCFD sensing node 46 in its very close distance serves as an optical blocking mask for effectively blocking the incident light into the CCFD sensing node 46.
  • Fig. 5 is a cross-sectional and circuit diagram illustrating an image sensor active pixel according to an embodiment of the present invention.
  • the image sensor active pixel of Fig. 5 is different from that of Fig. 3 in that the lower region of the transfer gate 44 between the pinned photodiode PPD and the P-well 47 is formed with a p-type diffusion region 60.
  • the other configurations and operations of Fig. 5 are substantially similar to those of Fig. 3.
  • the p-type region 60 which has a different doping concentration from that of the P-well 47, is formed between the pinned photodiode PPD and the P-well 46 to improve the transferring efficiency of the transfer gate 44.
  • Fig. 6 is a cross-sectional and circuit diagram illustrating an image sensor active pixel according to an embodiment of the present invention.
  • the signal amplifier 54 is composed of a source follower (SF) amplifier 70.
  • SF source follower
  • the SF amplifier 70 includes an active transistor 71 and a constant current source 72 connected through a signal line SL. Without the reset voltage source VR, one terminal of the reset switch 52 is combined with a drain of the SF transistor 71, and a pixel driving voltage source VDD is used as a reset voltage source.
  • the present invention has the following effects.
  • a voltage of a n-type diffusion region of a charge sensing node is boosted so that it is easy to transfer signal electrons from a photodiode into the charge sensing node. Also, the maximum charge amount stored in the charge sensing node is increased.
  • a signal voltage of the charge sensing node is transmitted to an input terminal of a signal amplifier through a coupling capacitor, thereby reducing a dark current of the sensing node in comparison with a conventional charge sensing node.
  • a voltage change of the charge sensing node is transmitted to the input terminal through coupling capacitor, a voltage of the input terminal of the signal amplifier is externally changed into a required value in order to perform the next pixel operation without loss of signal charge stored in the charge sensing node.
  • An electrode of the coupling capacitor serves as an optical blocking mask close to the charge sensing node, thereby effectively blocking an incident light into the charge sensing node.

Landscapes

  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Physics & Mathematics (AREA)
  • Power Engineering (AREA)
  • Electromagnetism (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Computer Hardware Design (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Solid State Image Pick-Up Elements (AREA)
  • Transforming Light Signals Into Electric Signals (AREA)

Abstract

A CMOS image sensor active pixel which comprises a multi-functional charge sensing unit and a method for sensing a signal thereof. Wherein a voltage of a n-type diffusion region of a charge sensing node is highly boosted even in a low driving voltage, and a signal voltage is coupled out with a coupling capacitor without forming ohmic contact in the n-type diffusion region of the charge sensing node.

Description

IMAGE SENSORACTIVE PIXELAND METHOD FOR SENSING SIGNAL
THEREOF
Technical Field The present invention generally relates to a Complementary Metal-Oxide-
Semiconductor (CMOS) image sensor active pixel and a method for sensing a signal thereof, and more specifically, to a technology of a structure, a function and an operating method of a multi-functional signal charge sensing unit in the CMOS image sensor active pixel.
Background of the Invention
Generally, an image sensor 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 into electrons with a photodiode, and converts the accumulated charge into voltage signals.
The CMOS image sensor includes a Floating Diffusion (FD) sensing node as a charge sensing node in order to sense the signal charge amount. A charge sensing unit includes a reset switch and a reset voltage source combined with the FD sensing node for resetting the FD sensing node.
Fig. 1 is a circuit diagram illustrating a unit pixel of a conventional image sensor.
The unit pixel of the CMOS image sensor comprises a photodiode I9 a transfer gate 5, a charge sensing unit 6 and a signal amplifier 12. The charge sensing unit 6 includes a FD sensing node 9, a reset switch 10 and a reset voltage source VR. A capacitor 8 of Fig. 1 includes a junction capacitor and peripheral parasitic capacitors in the FD sensing node 9. A signal voltage of the capacitor 8 is transmitted to an input terminal of the signal amplifier 12 through a conducting line which is ohmic- contacted to a n-type diffusion region of the FD sensing node 9.
Fig. 2 is a cross-sectional and circuit diagram illustrating the unit pixel of Fig. 1. The unit pixel comprises a pinned photodiode PPD and n-channel MOSFETs.
The pinned photodiode includes a n-type diffusion region 3 formed in a p-type epitaxial layer P-EPI, a p+ region 4 formed in the n-type diffusion region 3 and a P-well 2 formed at a sidewall of the n-type diffusion region 3 and the p+ region 4. The charge sensing unit 6 includes a P-well 7 formed in the p-type epitaxial layer P-EPI and the FD sensing node 9 formed in the P-well 7.
Hereinafter, the operation of the unit pixel of the conventional CMOS image sensor is described.
When the transfer gate 5 is turned off, the photodiode PPD changes light signals into electrons to store the electrons in the n-type diffusion region 3. That is, the photodiode PPD absorbs light, generates photo-generated electrons, and accumulates them during the integration time before the transfer gate 5 is turned on.
A voltage of the n-type diffusion region of the FD sensing node 9 is reset into a voltage higher than the voltage of the n-type diffusion region 3 of the photodiode PPD with the reset switch 10 and the reset voltage source VR. When the transfer gate 5 is turned on, signal electrons accumulated in the n-type diffusion region 3 of the photodiode PPD are transferred into the n-type diffusion region of the FD sensing node 9 by the voltage difference between the photodiode PPD and the n-type diffusion region of the FD sensing node 9. That is, signal electrons are moved from the photodiode PPD into the FD sensing node 9 for transferring time so that the voltage of the n-type diffusion region of the FD sensing node 9 is changed. The voltage change is transmitted to the input terminal of the signal amplifier 12 through the conducting line which is ohmic-contacted to the n-type diffusion region of the FD sensing node 9.
An output signal of the signal amplifier 12 is directly connected to a signal line of a pixel array or connected to a signal line through an addressing switch for connecting/disconnecting the output signal of the signal amplifier 12. A directly connected structure without the addressing switch is used when the on/off states of the signal amplifier 12 can be controlled in the operating method of the pixel.
After the electron transfer from the photodiode PPD into the FD sensing node 9, the n-type diffusion region 3 of the photodiode PPD is completely depleted. The transfer gate 5 is turned off, and the photodiode PPD changes light signals into electrons to store the electrons in the n-type diffusion region 3. The above-described operation of the unit pixel is repeated to read all image signals of the whole object for photography.
However, the conventional CMOS image sensor has four problems as follows. The CMOS image sensor uses low pixel driving voltage unlike a charge coupled device (CCD) image sensor. So, when electrons are transferred from the photodiode PPD into the FD sensing node 9, the voltage difference between the n-type diffusion regions 3 of the photodiode PPD and the FD sensing node 9 may not be enough for electrons to be fully moved into the FD sensing node 9. In order to transfer all electrons from the n-type diffusion region 3 of the photodiode PPD into that of the FD sensing node 9, the voltage of the n-type diffusion region of the FD sensing node 9 is required to be higher even in the low driving voltage.
In the conventional CMOS image sensor, the FD sensing node 9 is connected to the input terminal of the signal amplifier 12 through an ohmic-contacted conducting line. To form ohmic contact between the conducting line and the diffusion region of the FD sensing node 9, the doping concentration of the diffusion region is required to be high. However, dark current increases in the FD sensing node 9 due to the physical defects generated from the ohmic contact process. So, the dark current in the ohmic-contacted FD sensing node 9 can causes a severe error whenever the signal electrons are stored in the FD sensing node 9 for a long time. Thus, a sensing node having a smaller dark current than that of the FD sensing node 9 with ohmic contact is required.
For example, a global shuttering of the image sensor is performed to store signal electrons in the FD sensing node 9 for a long time.
In the conventional CMOS image sensor, the FD sensing node 9 is directly connected to the signal amplifier 12 with the conducting line. So, if the voltage of the input terminal of the signal amplifier 12 is externally changed, the signal charge stored in the FD sensing node 9 is also changed so that the stored information is lost. That is, in the conventional CMOS image sensor, the voltage of the input terminal of the signal amplifier 12 can not be externally changed to perform the next operation of the pixel without loss of the stored information in the FD sensing node 9.
Since an incident light into the FD sensing node 9 generates an error in the operation of the pixel, it is necessary to block the light. So, a charge sensing unit having a structure for effectively blocking an incident light into the charge sensing node is required.
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 is directed at boosting a voltage of a n-type diffusion region of a charge sensing node even in a low pixel driving voltage to transfer all signal electrons from a n-type diffusion region of a photodiode into the n-type diffusion region of the charge sensing node and to increase the maximum charge storage capacity of the charge sensing node. Various embodiments of the present invention is directed at transmitting a signal voltage of the charge sensing node to an input terminal of a signal amplifier with a coupling capacitor without forming ohmic contact to the n-type diffusion region of the charge sensing node in order to reduce a dark current of the sensing node than that of the conventional ohmic-contacted sensing node. Various embodiments of the present invention is directed at coupling the signal voltage to the signal amplifier with a coupling capacitor, thereby facilitating the operation of the pixel that externally changes a voltage of the input terminal of the signal amplifier without loss of signal charge stored in the sensing node.
Various embodiments of the present invention is directed at making an electrode of the coupling capacitor included in the charge sensing unit serve as an optical blocking mask, thereby effectively blocking the incident light into the charge sensing node.
Technical Solution
According to an embodiment of the present invention, an image sensor active pixel comprises: a photodiode which includes a first diffusion region having a second conductive type formed in a first semiconductor region having a first conductive type, configured to absorb incident light and generate charged particles so as to store the particles in the first diffusion region; a capacitor combined floating diffusion (CCFD) sensing node which includes a second diffusion region having a second conductive type formed in a second semiconductor region having a first conductive type and a coupling capacitor having the second diffusion region as a first electrode and an electrode formed over the second diffusion region as a second electrode, configured to store the charged particles transferred from the first diffusion region in the second diffusion region; a transfer gate configured to transfer the charged particles stored in the first diffusion region into the second diffusion region; a reset switch, connected between a reset voltage source and the second diffusion region, configured to reset a voltage of the second diffusion region; a signal amplifier, which has an input terminal connected to the second electrode, configured to transmit a voltage signal corresponding to a voltage of the second electrode to a signal line of a pixel array; and a multi-functional switch, which has one terminal connected to the second electrode and the input terminal of the signal amplifier and the other terminal connected to a variable voltage source, configured to apply a voltage of the variable voltage source to the second electrode and the input terminal of the signal amplifier.
According to an embodiment of the present invention, an image sensor active pixel comprises: a capacitor combined floating diffusion (CCFD) sensing node which includes a first diffusion region having a second conductive type formed in a first semiconductor region having a first conductive type and a coupling capacitor having the first diffusion region as a first electrode and an electrode formed over the first diffusion region as a second electrode, configured to store the charged particles externally transferred in the first diffusion region; a reset switch, connected between a reset voltage source and the first diffusion region, configured to reset a voltage of the first diffusion region; and a multi-functional switch, which has one terminal connected to the second electrode and the input terminal of the signal amplifier and the other terminal connected to a variable voltage source, configured to apply a voltage of the variable voltage source to the second electrode and the input terminal of the signal amplifier. According to an embodiment of the present invention, a method for sensing a signal of an image sensor active pixel, which comprises a photodiode which includes a first diffusion region having a second conductive type formed in a first semiconductor region having a first conductive type, a capacitor combined floating diffusion (CCFD) sensing node which includes a second diffusion region having a second conductive type formed in a second semiconductor region having a first conductive type and a coupling capacitor having the second diffusion region as a first electrode and an electrode formed over the second diffusion region as a second electrode, configured to store the charged particles transferred from the first diffusion region in the second diffusion region, a reset switch connected between a reset voltage source and the second diffusion region, a signal amplifier which has an input terminal connected to the second electrode, and a multifunctional switch configured to apply a voltage of the variable voltage source to the second electrode and the input terminal of the signal amplifier, comprises the steps of: applying a voltage of the variable voltage source to the second electrode with the multifunctional switch turned on so as to fix the second electrode at a first voltage; applying a voltage of the reset voltage source to the second diffusion region by turning on the reset switch so as to reset the second diffusion region and turning off the reset switch; changing a voltage of the variable voltage source to raise a voltage of the second electrode to a second voltage higher than the first voltage, thereby boosting a voltage of the second diffusion region, and setting the input terminal of the signal amplifier at the second voltage to read an output signal of the signal amplifier; turning off the multi-functional switch and turning on a transfer gate so as to transfer electrons stored in the first diffusion region into the second diffusion region, thereafter turning off the transfer gate; and sensing the amount of 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 active pixel, which comprises a photodiode which includes a first diffusion region having a second conductive type formed in a first semiconductor region having a first conductive type, a capacitor combined floating diffusion (CCFD) sensing node which includes a second diffusion region having a second conductive type formed in a second semiconductor region having a first conductive type and a coupling capacitor having the second diffusion region as a first electrode and an electrode formed over the second diffusion region as a second electrode, configured to store the charged particles transferred from the first diffusion region in the second diffusion region, a reset switch connected between a reset voltage source and the second diffusion region, a signal amplifier which has an input terminal connected to the second electrode, and a multi- functional switch configured to apply a voltage of the variable voltage source to the second electrode and the input terminal of the signal amplifier, comprises the steps of: turning off the reset switch and turning on the transfer gate to transfer the electrons stored in the first diffusion region into the second diffusion region and turning off the transfer gate; setting a voltage of the input terminal of the signal amplifier at a first voltage by the variable voltage source with the multi-functional switch turned on, and reading an output signal of the signal amplifier; turning off the multi-functional switch and discharging electrons of the second diffusion region by turning on the reset switch; and sensing the amount of change of the output voltage of the signal amplifier from the value of the read output voltage of the signal amplifier.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a circuit diagram illustrating a unit pixel of a conventional image sensor active pixel.
Fig. 2 is a cross-sectional and circuit diagram illustrating the unit pixel of Fig. 1. Fig. 3 is a cross-sectional and circuit diagram illustrating an image sensor active pixel according to an embodiment of the present invention.
Fig. 4 is an expanded cross-sectional and circuit diagram illustrating a signal charge sensing node of Fig. 3.
Fig. 5 is a cross-sectional and circuit diagram illustrating an image sensor active pixel according to an embodiment of the present invention.
Fig. 6 is a cross-sectional and circuit diagram illustrating an image sensor active pixel according to an embodiment of the present invention.
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 units.
Fig. 3 is a cross-sectional and circuit diagram illustrating an image sensor active pixel according to an embodiment of the present invention. The image sensor active pixel includes a pinned photodiode PPD and n-channel
MOS Field Effect Transistors (MOSFETs). The image sensor active pixel comprises a pinned photodiode PPD, a transfer gate 44, a charge sensing unit 45 and a signal amplifier 54.
The charge sensing unit 45 includes a Capacitor Combined Floating Diffusion (CCFD) sensing node 46, a reset switch 52, a reset voltage source VR, a multi-functional switch 53, and a variable voltage source VC.
Fig. 4 is an expanded cross-sectional and circuit diagram illustrating a signal charge sensing node of Fig. 3.
The pinned photodiode PPD includes a n-type diffusion region 42 formed in a p- type epitaxial layer P-EPI, a p+ region 43 formed in the n-type diffusion region 42, and a P-well 41 formed at a sidewall of the n-type diffusion region 42 and the p+ region 43. Although the n-type diffusion region 42 is formed in the p-type epitaxial layer P-EPI in the embodiment, a p-type substrate P-SUB can be used instead of the p-type epitaxial layer P-EPI. A CCFD sensing node 46 includes a n-type diffusion region 49 formed in a P- well 47 or a p-type diffusion region which is formed in the p-type epitaxial layer P-EPI. An insulating layer 51 is formed over the n-type diffusion region 49, and a second electrode 50 is formed over the insulating layer 51. The coupling capacitor CC comprises the n-type diffusion region 49 as a first electrode, the insulating layer 51, and the electrode 50 as a second electrode. The n-type diffusion region 49 stores electrons transferred from the pinned photodiode PPD as well as serves as a first electrode of the coupling capacitor CC.
The coupling capacitor CC is formed over the n-type diffusion region 49 with the in between insulating layer 51. So, the additional area of the pixel for forming the coupling capacitor CC can be reduced.
The thickness of the insulating layer 51 of the coupling capacitor CC is so thin that the second electrode 50 may serve as an optical blocking mask for effectively blocking the incident light into the n-type diffusion region 49 of the CCFD sensing node 46 if the second electrode 50 of the coupling capacitor CC is formed of an opaque material to light.
The impurity doping concentration of the n-type diffusion region 49 serving as a first electrode of the coupling capacitor CC may be smaller than that for ohmic contact. As a result, the CCFD sensing node 46 can reduce dark current and noise generated from the sensing node in comparison with the conventional sensing node in which a conducting line is directly ohmic-contacted to the n-type diffusion region 49. The n-type diffusion region 49 stores signal electrons transferred from the pinned photodiode PPD. Whenever electrons flow into or out from the n-type diffusion region 49, the voltage of the n-type diffusion region 49 is changed, and the voltage change is transmitted to another units through the coupling capacitor CC. An insulating layer 51a is formed over the P-well 47. The transfer gate 44 formed over the insulating layer 51a serves as a switch for connecting the n-type diffusion region 49 of the CCFD sensing node 46 to the n-type diffusion region 42 of the pinned photodiode PPD.
Hereinafter, functions and connections of each component of Figs. 3 and 4 are described in detail.
The pinned photodiode PPD changes incident light into electrons to store the electrons in the n-type diffusion region 42. The transfer gate 44transfers the electrons stored in the photodiode PPD into the CCFD sensing node 46 of the charge sensing unit 45. The CCFD sensing node 46 stores the electrons transferred from the pinned photodiode PPD through the transfer gate 44 in the n-type diffusion region 49.
An insulating layer 51b is formed over the P-well 47. The reset switch 52 formed over the insulating layer 51b has one terminal connected to the n-type diffusion region 49 of the CCFD sensing node 46, and the other terminal connected to the reset voltage source VR. The reset switch 52 discharges electrical charge stored in the n-type diffusion region 49 of the CCFD sensing node 46, and resets a voltage of the n-diffusion region 49. The reset switch 52 can be formed a Field Effect Transistor (FET) or a Transfer Gate Structure. The coupling capacitor CC has the first electrode formed with the n-type diffusion region 49, and the second electrode 50 connected in common to the multi-functional switch 53 and the input terminal of the signal amplifier 54. The multi-functional switch 53 has one terminal connected to the second electrode 50 of the coupling capacitor CC and the input terminal of the signal amplifier 54, and the other terminal connected to the variable voltage source VC. The multi- functional switch 53 can be formed of a FET. The multi-functional switch 53 transmits a voltage of the variable voltage source VC to the second electrode 50 of the coupling capacitor CC and the input terminal of the signal amplifier 54.
The reset voltage source VR and the variable voltage source VC are located outside of the pixel, and connected to the corresponding nodes of each pixel by conducting lines. An output voltage of the CCFD sensing node 46 is transmitted through the coupling capacitor CC to the input terminal of the signal amplifier 54 connected to the second electrode 50 of the coupling capacitor CC.
The input terminal of the signal amplifier 54 is connected to the second electrode 50 of the coupling capacitor CC and the one terminal of the multi-functional switch 53. An output terminal of the signal amplifier 54 is directly connected to a signal line of a pixel array, or is connected to the signal line through a switch for turning on/off an output signal of the signal amplifier 54. A directly connected structure without the switch is used when the on/off states of the signal amplifier 54 can be controlled in the operating method of the pixel.
The charge sensing unit 45 of the unit pixel can be shared by the photodiode PPD or the signal amplifier 54 of the other pixel. Hereinafter, the above-described operation process of the image sensor active pixel according to the embodiment of the present invention is described in detail.
When the transfer gate 44 is turned off, the pinned photodiode PPD changes light signals into electrons to store the electrons in the n-type diffusion region 42. That is, the pinned photodiode PPD absorbs light, generates electrons, and accumulates them during the charge integration time before the transfer gate 44 is turned on. While the transfer gate 44 is turned off, a voltage of the n-type diffusion region 49 of the CCFD sensing node 46 is reset into a voltage higher than the voltage of the n- type diffusion region 42 of the pinned photodiode PPD. The resetting procedure is as follows. The variable voltage source VC is maintained at a voltage level VCL, and the multi-functional switch 53 is turned on to fix the second electrode 50 of the coupling capacitor CC at a voltage level VCL. Thereafter, the reset switch 52 is turned on and the voltage of the n-type diffusion region 49 of the CCFD sensing node 46 is reset into reset voltage VRN. The reset voltage VRN is determined by characteristics of the reset voltage source VR and the reset switch 52. Thereafter, the reset switch 52 is turned off and the variable voltage source VC is raised from a voltage level VCL to a voltage level VCH. By this act, the voltage of the n-type diffusion region 49 of the CCFD sensing node 46 rises from the reset voltage VRN to VRN + α x (VCH - VCL). The constant α has positive value less than unity. That is, the voltage of the n-type diffusion region 49 of the CCFD sensing node 46 is boosted by α x (VCH - VCL) from the reset voltage VRN to VRN + α x (VCH - VCL).
In this embodiment, the voltage level VCL and VCH are set to a ground voltage level and a VDD level of pixel driving voltage respectively.
As a result, it is easy to transfer the signal electrons stored in the pinned photodiode PPD into the CCFD sensing node 46 because the voltage of the n-type diffusion region 49 of the CCFD sensing node 46 rises to the higher level. Also, the maximum charge amount which can be stored in the n-type diffusion region 49 is increased. After the boosting operation, the multi-functional switch 53 is turned off.
When the transfer gate 44 is turned on, signal electrons accumulated in the n- type diffusion region 42 of the pinned photodiode PPD are transferred into the n-type diffusion region 49 of the CCFD sensing node 46 by a voltage difference between the n- type diffusion region 42 of the pinned photodiode PPD and the n-type diffusion region 49 of the CCFD sensing node 46. As the signal electrons are moved from the pinned photodiode PPD into the CCFD sensing node 46, the voltage of the n-type diffusion region 49 of the CCFD sensing node 46 is changed. The voltage change of the n-type diffusion region 49 is transmitted into the input terminal of the signal amplifier 54 through the coupling capacitor CC.
At the end of the transferring, the n-type diffusion region 42 of the pinned photodiode PPD is completely depleted. The transfer gate 44 is again turned off, and the pined photodiode PPD again begins to accumulate the photo-generated electrons in the n- type diffusion region 42. The above-described operation of the unit pixel is repeated to read all image signals of the whole object for photography.
Except the operation of the charge sensing unit 45, the operation of the pixel is similar to that of the conventional pixel.
The charge sensing unit 45 is characterized in that the voltage change of the n- type diffusion region 49 of the CCFD sensing node 46 is transmitted to the input terminal of the signal amplifier 54 through coupling capacitor CC. Although the voltage of the second electrode 50 of the coupling capacitor CC or the input terminal of the signal amplifier 54 is changed into a required value with the multi-functional switch 53 and the variable voltage source VC, the number of signal electrons stored in the n-type diffusion region 49 of the CCFD sensing node 46 is preserved.
The functions of the coupling capacitor CC in the charge sensing unit 45 are as follows.
The coupling capacitor CC boosts the voltage of the n-type diffusion region 49 of the CCFD sensing node 46 by the linked operation of the reset switch 52, the reset voltage source VR, the multi-functional switch 53 and the variable voltage source VC. Also, the coupling capacitor CC transmits the signal voltage of the CCFD sensing node 46 into the input terminal of the signal amplifier 54.
Hereinafter, the functions of the multi-functional switch 53 and the variable voltage source VC in the charge sensing unit 45 of the pixel are explained. The multi-functional switch 53 provides a discharging path is to the floating structure of the second electrode 50 of the coupling capacitor CC and the input terminal of the signal amplifier 54 to discharge undesired charge, thereby preventing malfunction of devices.
The multi-functional switch 53 and the variable voltage source VC boost the voltage of the n-type diffusion region 49 of the CCFD sensing node 46 by the linked operation of the reset switch 52, the reset voltage source VR and the coupling capacitor CC.
Additionally, the multi-functional switch 53 and the variable voltage source VC set an initial reference voltage of the input terminal of the signal amplifier 54. The on/off states of the signal amplifier 54 can be controlled when the signal amplifier 54 is a source-follower.
When the charge sensing unit 45 with the CCFD sensing node 46 is used, the present invention has the following merits.
The n-type diffusion region 49 is used as the first electrode of the coupling capacitor CC so that ohmic contact is not formed to connect the CCFD sensing node 46 to the coupling capacitor CC with a conducting line. The doping concentration of the n- type diffusion region 49 of the CCFD sensing node 46 can be reduced lower than that for ohmic contact. As a result, physical defects generated from the process can be reduced, and the dark current generated from the sensing node can be decreased. The coupling capacitor CC is formed over the floating diffusion structure, thereby reducing the additional area of the pixel for forming the coupling capacitor CC.
The second electrode 50 of the coupling capacitor CC formed over the CCFD sensing node 46 with the in between thin (~nm) oxide insulating layers 51 can be made of opaque materials to block the incident light into the sensing node. The opaque electrode includes metal electrodes such as copper and aluminum, or poly suicide electrodes. That is, the second electrode 50 which covers the CCFD sensing node 46 in its very close distance serves as an optical blocking mask for effectively blocking the incident light into the CCFD sensing node 46.
Fig. 5 is a cross-sectional and circuit diagram illustrating an image sensor active pixel according to an embodiment of the present invention.
The image sensor active pixel of Fig. 5 is different from that of Fig. 3 in that the lower region of the transfer gate 44 between the pinned photodiode PPD and the P-well 47 is formed with a p-type diffusion region 60. The other configurations and operations of Fig. 5 are substantially similar to those of Fig. 3. The p-type region 60, which has a different doping concentration from that of the P-well 47, is formed between the pinned photodiode PPD and the P-well 46 to improve the transferring efficiency of the transfer gate 44.
Fig. 6 is a cross-sectional and circuit diagram illustrating an image sensor active pixel according to an embodiment of the present invention. In the unit pixel of Fig. 6, the signal amplifier 54 is composed of a source follower (SF) amplifier 70.
The SF amplifier 70 includes an active transistor 71 and a constant current source 72 connected through a signal line SL. Without the reset voltage source VR, one terminal of the reset switch 52 is combined with a drain of the SF transistor 71, and a pixel driving voltage source VDD is used as a reset voltage source. Industrial Applicability
As described above, the present invention has the following effects.
Even in a low driving voltage required in a CMOS image sensor active pixel, a voltage of a n-type diffusion region of a charge sensing node is boosted so that it is easy to transfer signal electrons from a photodiode into the charge sensing node. Also, the maximum charge amount stored in the charge sensing node is increased.
Without ohmic contact in the n-type diffusion region of the charge sensing node, a signal voltage of the charge sensing node is transmitted to an input terminal of a signal amplifier through a coupling capacitor, thereby reducing a dark current of the sensing node in comparison with a conventional charge sensing node.
As a voltage change of the charge sensing node is transmitted to the input terminal through coupling capacitor, a voltage of the input terminal of the signal amplifier is externally changed into a required value in order to perform the next pixel operation without loss of signal charge stored in the charge sensing node.
An electrode of the coupling capacitor serves as an optical blocking mask close to the charge sensing node, thereby effectively blocking an incident light into the charge 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. An image sensor active pixel comprising: a photodiode which includes a first diffusion region having a second conductive type formed in a first semiconductor region having a first conductive type, configured to absorb incident light and to generate charged particles so as to store the particles in the first diffusion region; a capacitor combined floating diffusion (CCFD) sensing node which includes a second diffusion region having a second conductive type formed in a second semiconductor region having a first conductive type and a coupling capacitor having the second diffusion region as a first electrode and an electrode formed over the second diffusion region as a second electrode, configured to store the charged particles transferred from the first diffusion region in the second diffusion region; a transfer gate configured to transfer the charged particles stored in the first diffusion region into the second diffusion region; a reset switch which is connected between a reset voltage source and the second diffusion region, configured to reset a voltage of the second diffusion region; a signal amplifier which has an input terminal connected to the second electrode, configured to transmit a voltage signal corresponding to a voltage of the second electrode to a signal line of a pixel array; and a multi-functional switch which has one terminal connected to the second electrode and the input terminal of the signal amplifier and the other terminal connected to a variable voltage source, configured to apply a voltage of the variable voltage source to the second electrode and the input terminal of the signal amplifier.
2. The image sensor active pixel according to claim 1, wherein the first conductive type has an opposite polarity to that of the second conductive type.
3. The image sensor active pixel according to claim 1, wherein the first semiconductor region includes one of an epitaxial layer having the first conductive type and a substrate having the first conductive type.
4. The image sensor active pixel according to claim 1, wherein the second semiconductor region is a diffusion region having the first conductive type formed in the first semiconductor region.
5. The image sensor active pixel according to claim 1, wherein the photodiode is a pinned photodiode further comprising a diffusion region having the first conductive type formed in the first diffusion region.
6. The image sensor active pixel according to claim 1, wherein the coupling capacitor includes an insulating layer formed over the first electrode and a second electrode formed over the insulating layer.
7. The image sensor active pixel according to claim 1, wherein the doping concentration of the second diffusion region is set lower than that for ohmic contact.
8. The image sensor active pixel according to claim 1, wherein the multifunctional switch includes a FET.
9. The image sensor active pixel according to claim 1, wherein the reset switch includes one of a FET and a transfer gate structure.
10. The image sensor active pixel according to claim 1, wherein the multi- functional switch forms a discharging path in order to prevent the second electrode of the coupling capacitor and the input terminal of the signal amplifier from being electrically a floating structure.
11. The image sensor active pixel according to claim 1, wherein the multi- functional switch sets voltages of the second electrode of the coupling capacitor and the input terminal of the signal amplifier to be at predetermined levels.
12. The image sensor active pixel according to claim 1, wherein the signal amplifier further comprises a switch connected between an output terminal of the signal amplifier and the signal line of the pixel array.
13. The image sensor active pixel according to claim 1, wherein the signal amplifier is a source follower amplifier.
14. The image sensor active pixel according to claim 1 or 13, wherein a driving voltage source of the signal amplifier is used as the reset voltage source.
15. The image sensor active pixel according to claim 1, wherein the signal amplifier is turned on/off by the multi-functional switch.
16. The image sensor active pixel according to claim 1, wherein two or more pixels share at least one of the CCFD sensing node, the reset switch, the multifunctional switch and the signal amplifier.
17. The image sensor active pixel according to claim 1, wherein the second electrode formed of opaque materials serves as an optical blocking mask for blocking an incident light into the second diffusion region.
18. An image sensor active pixel comprising: a capacitor combined floating diffusion (CCFD) sensing node which includes a first diffusion region having a second conductive type formed in a first semiconductor region having a first conductive type and a coupling capacitor having the first diffusion region as a first electrode and an electrode formed over the first diffusion region as a second electrode, configured to store the charged particles externally transferred in the first diffusion region; a reset switch, connected between a reset voltage source and the first diffusion region, configured to reset a voltage of the first diffusion region; and a multi-functional switch, which has one terminal connected to the second electrode and the input terminal of the signal amplifier and the other terminal connected to a variable voltage source, configured to apply a voltage of the variable voltage source to the second electrode and the input terminal of the signal amplifier.
19. The image sensor active pixel according to claim 18, wherein the first conductive type has an opposite polarity to that of the second conductive type.
20. A method for sensing a signal of an image sensor active pixel, which comprises a photodiode which includes a first diffusion region having a second conductive type formed in a first semiconductor region having a first conductive type, a capacitor combined floating diffusion (CCFD) sensing node which includes a second diffusion region having a second conductive type formed in a second semiconductor region having a first conductive type and a coupling capacitor having the second diffusion region as a first electrode and an electrode formed over the second diffusion region as a second electrode, configured to store the charged particles transferred from the first diffusion region in the second diffusion region, a reset switch connected between a reset voltage source and the second diffusion region, a signal amplifier which has an input terminal connected to the second electrode, and a multi-functional switch configured to apply a voltage of the variable voltage source to the second electrode and the input terminal of the signal amplifier, the method comprising the steps of: applying a voltage of the variable voltage source to the second electrode with the multi-functional switch turned on so as to fix the second electrode at a first voltage; applying a voltage of the reset voltage source to the second diffusion region by turning on the reset switch so as to reset the second diffusion region and turning off the reset switch; changing a voltage of the variable voltage source to raise a voltage of the second electrode to a second voltage higher than the first voltage, thereby boosting a voltage of the second diffusion region, and setting the input terminal of the signal amplifier at the second voltage to read an output signal of the signal amplifier; turning off the multi-functional switch and turning on a transfer gate so as to transfer electrons stored in the first diffusion region into the second diffusion region, thereafter turning off the transfer gate; and sensing the amount of change of the output voltage of the signal amplifier.
21. The method according to claim 20, wherein a voltage of the second diffusion region is boosted by αx(second voltage - first voltage) (0 < α < 1).
22. The method according to claim 20, wherein the first voltage is at a ground voltage level and the second voltage is at a pixel driving voltage level.
23. A method for sensing a signal of an image sensor active pixel, which comprises a photodiode which includes a first diffusion region having a second conductive type formed in a first semiconductor region having a first conductive type, a capacitor combined floating diffusion (CCFD) sensing node which includes a second diffusion region having a second conductive type formed in a second semiconductor region having a first conductive type and a coupling capacitor having the second diffusion region as a first electrode and an electrode formed over the second diffusion region as a second electrode, configured to store the charged particles transferred from the first diffusion region in the second diffusion region, a reset switch connected between a reset voltage source and the second diffusion region, a signal amplifier which has an input terminal connected to the second electrode, and a multi-functional switch configured to apply a voltage of the variable voltage source to the second electrode and the input terminal of the signal amplifier, the method comprising the steps of: turning off the reset switch and turning on the transfer gate to transfer the electrons stored in the first diffusion region into the second diffusion region and thereafter turning off the transfer gate; setting a voltage of the input terminal of the signal amplifier at a first voltage by the variable voltage source with the multi-functional switch turned on, and reading an output signal of the signal amplifier; turning off the multi-functional switch and discharging electrons of the second diffusion region by turning on the reset switch; and sensing the amount of change of the output voltage of the signal amplifier from the value of the read output voltage of the signal amplifier.
24. The method according to claim 23, wherein the first voltage is set to be higher than an input threshold voltage of the signal amplifier.
PCT/KR2006/004175 2006-05-25 2006-10-16 Image sensor active pixel and method for sensing signal thereof WO2007139255A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
KR10-2006-0047082 2006-05-25
KR1020060047082A KR100790586B1 (en) 2006-05-25 2006-05-25 CMOS image sensor active pixel and method for sensing signal thereof

Publications (1)

Publication Number Publication Date
WO2007139255A1 true WO2007139255A1 (en) 2007-12-06

Family

ID=38778762

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/KR2006/004175 WO2007139255A1 (en) 2006-05-25 2006-10-16 Image sensor active pixel and method for sensing signal thereof

Country Status (2)

Country Link
KR (1) KR100790586B1 (en)
WO (1) WO2007139255A1 (en)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2012124639A1 (en) 2011-03-11 2012-09-20 株式会社カネカ Modified aminotransferase, gene thereof, and method for producing optically active amino compound using same
WO2014167794A1 (en) * 2013-04-08 2014-10-16 Sony Corporation Solid-state image pickup device, driving method thereof, and electronic apparatus
CN104508829A (en) * 2012-07-24 2015-04-08 高通Mems科技公司 Multi-gate thin-film transistor
CN109166874A (en) * 2018-09-11 2019-01-08 德淮半导体有限公司 Back side illumination image sensor and forming method
JP2020167263A (en) * 2019-03-29 2020-10-08 ラピスセミコンダクタ株式会社 Semiconductor device and manufacturing method therefor

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR101930755B1 (en) 2012-03-21 2018-12-19 삼성전자주식회사 Method of driving an image sensor
KR102154184B1 (en) * 2014-03-10 2020-09-09 삼성전자 주식회사 Image sensor and method for manufacturing the same
KR102234041B1 (en) 2014-06-18 2021-04-01 삼성전자주식회사 Image sensor and image processing system including the same
US10236400B2 (en) 2016-02-01 2019-03-19 Heptagon Micro Optics Pte. Ltd. Quantum dot film based demodulation structures

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6493030B1 (en) * 1998-04-08 2002-12-10 Pictos Technologies, Inc. Low-noise active pixel sensor for imaging arrays with global reset
US6570144B1 (en) * 2000-03-02 2003-05-27 Hynix Semiconductor, Inc. Active pixel circuit in CMOS image sensor
US20050285215A1 (en) * 2004-06-28 2005-12-29 Lee Jun T Image sensor integrated circuit devices including a photo absorption layer and methods of forming the same

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH05167936A (en) 1991-12-13 1993-07-02 Sony Corp Solid state image pickup device
US6218691B1 (en) 1998-06-30 2001-04-17 Hyundai Electronics Industries Co., Ltd. Image sensor with improved dynamic range by applying negative voltage to unit pixel
EP1231641A1 (en) 2001-02-09 2002-08-14 C.S.E.M. Centre Suisse D'electronique Et De Microtechnique Sa Active pixel with analog storage for an opto-electronic image sensor
US7115923B2 (en) 2003-08-22 2006-10-03 Micron Technology, Inc. Imaging with gate controlled charge storage
US7115855B2 (en) * 2003-09-05 2006-10-03 Micron Technology, Inc. Image sensor having pinned floating diffusion diode

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6493030B1 (en) * 1998-04-08 2002-12-10 Pictos Technologies, Inc. Low-noise active pixel sensor for imaging arrays with global reset
US6570144B1 (en) * 2000-03-02 2003-05-27 Hynix Semiconductor, Inc. Active pixel circuit in CMOS image sensor
US20050285215A1 (en) * 2004-06-28 2005-12-29 Lee Jun T Image sensor integrated circuit devices including a photo absorption layer and methods of forming the same

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2012124639A1 (en) 2011-03-11 2012-09-20 株式会社カネカ Modified aminotransferase, gene thereof, and method for producing optically active amino compound using same
CN104508829A (en) * 2012-07-24 2015-04-08 高通Mems科技公司 Multi-gate thin-film transistor
US9105728B2 (en) 2012-07-24 2015-08-11 Qualcomm Mems Technologies, Inc. Multi-gate thin-film transistor
CN104508829B (en) * 2012-07-24 2016-10-26 高通Mems科技公司 Multi-grid electrode film transistor
WO2014167794A1 (en) * 2013-04-08 2014-10-16 Sony Corporation Solid-state image pickup device, driving method thereof, and electronic apparatus
CN105191290A (en) * 2013-04-08 2015-12-23 索尼公司 Solid-state image pickup device, driving method thereof, and electronic apparatus
US9769406B2 (en) 2013-04-08 2017-09-19 Sony Corporation Solid-state image pickup device, driving method thereof, and electronic apparatus
TWI628957B (en) * 2013-04-08 2018-07-01 新力股份有限公司 Solid-state image pickup device, driving method thereof, and electronic apparatus
CN105191290B (en) * 2013-04-08 2019-04-05 索尼公司 Solid-state imaging device and its driving method and electronic device
CN109166874A (en) * 2018-09-11 2019-01-08 德淮半导体有限公司 Back side illumination image sensor and forming method
JP2020167263A (en) * 2019-03-29 2020-10-08 ラピスセミコンダクタ株式会社 Semiconductor device and manufacturing method therefor
JP7396806B2 (en) 2019-03-29 2023-12-12 ラピスセミコンダクタ株式会社 Semiconductor device and semiconductor device manufacturing method

Also Published As

Publication number Publication date
KR100790586B1 (en) 2008-01-02
KR20070113608A (en) 2007-11-29

Similar Documents

Publication Publication Date Title
WO2007139255A1 (en) Image sensor active pixel and method for sensing signal thereof
US7973346B2 (en) Image sensor with self-boosting transfer transistor gate and methods of operating and fabricating the same
KR100381026B1 (en) CMOS Image sensor capable of increasing punch through voltage and charge integration of photodiode and method for forming the same
US7166879B2 (en) Photogate for use in an imaging device
US9117724B2 (en) Solid-state image sensing device
JP4472236B2 (en) CMOS image sensor
JP2012147169A (en) Solid state image pickup device
KR20050039083A (en) Complementary metal oxide semiconductor image sensor and method for fabricating thereof
US11038419B2 (en) Charge pump device and image sensor including the same
KR20020061502A (en) Solid-state image sensor provided with divided photoelectric conversion part
WO2007139254A1 (en) Image sensor and method for sensing signal thereof
KR100298199B1 (en) A unit pixel of a CMOS image sensor having a PIN diode
US8607424B1 (en) Reverse MIM capacitor
KR100303773B1 (en) A unit pixel of a CMOS image sensor having a p &amp;lt; th &amp;gt;
WO2007139256A1 (en) Image sensor pixel having pinned photodiode with coupling capacitor and method for sensing a signal thereof
WO2007139257A1 (en) Active pixel having pinned photodiode with coupling capacitor and method for sensing a signal thereof
KR100532286B1 (en) Cmos image sensor with new unit pixel
US20080191250A1 (en) Transistor Having Coupling-Preventing Electrode Layer, Fabricating Method Thereof, and Image Sensor Having the Same
KR20030084492A (en) Cmos image sensor with wide dynamic range
KR100830328B1 (en) CMOS Image sensor and method for fabricaing the same
KR100298198B1 (en) A unit pixel of a CMOS image sensor having a Schottky diode
US8258559B2 (en) Image sensor photodiode arrangement
KR100460760B1 (en) Unit Pixel with improved fill factor and dark signal property in cmos image sensor
KR100776152B1 (en) Cmos image sensor and the method of manufacturing thereof
US7993952B2 (en) Charge transfer device

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 06799253

Country of ref document: EP

Kind code of ref document: A1

NENP Non-entry into the national phase

Ref country code: DE

32PN Ep: public notification in the ep bulletin as address of the adressee cannot be established

Free format text: NOTING OF LOSS OF RIGHTS PURSUANT TO RULE 112(1)EPC, EPO FORM 1205A SENT ON 10/03/09

122 Ep: pct application non-entry in european phase

Ref document number: 06799253

Country of ref document: EP

Kind code of ref document: A1