MOS image sensor
First Claim
Patent Images
1. An image sensor circuit, comprising:
- a first photodiode, having first and second terminals;
a first metal oxide semiconductor (MOS) transistor, a drain of said MOS transistor being coupled to said first terminal of said first photodiode for collecting charge developed by light falling on said first photodiode;
a second MOS transistor, a source of said second MOS transistor being coupled to said first terminal of said first photodiode and to said drain of said first MOS transistor;
a capacitor, one terminal of said capacitor being coupled to a drain of said second transistor;
a third MOS transistor, said source of said third MOS transistor being coupled to said drain of said second transistor;
wherein said charge collected in said first MOS transistor is transferred through said second MOS transistor and converted into a voltage by said capacitor.
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Abstract
An image sensor circuit which employs a photodiode in conjunction with a charge transfer mechanism. By employing the photodiode, at least a portion of the light sensed does not pass through a layer of polysilicon, and so is not prevented from reaching the sensing area by the polysilicon. The image sensor circuit of the invention is made up of device structures readily available in standard CMOS process technologies Advantageously, image sensors embodying the invention show substantially improved quantum efficiency for short wavelength light over the prior art sensors. In addition, image sensors embodying the invention display improved dark current uniformity, thus improving yield.
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Citations
33 Claims
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1. An image sensor circuit, comprising:
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a first photodiode, having first and second terminals; a first metal oxide semiconductor (MOS) transistor, a drain of said MOS transistor being coupled to said first terminal of said first photodiode for collecting charge developed by light falling on said first photodiode; a second MOS transistor, a source of said second MOS transistor being coupled to said first terminal of said first photodiode and to said drain of said first MOS transistor; a capacitor, one terminal of said capacitor being coupled to a drain of said second transistor; a third MOS transistor, said source of said third MOS transistor being coupled to said drain of said second transistor; wherein said charge collected in said first MOS transistor is transferred through said second MOS transistor and converted into a voltage by said capacitor. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
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20. An image sensor circuit, comprising:
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a p-substrate having formed therein at least one n+ region, a junction between said p-substrate and said n+ region forming a first photodiode; an insulator layer between said p-substrate layer and a layer of polysilicon to form a first NMOS transistor, a cathode of said at least one photodiode being coupled to a drain of said NMOS transistor, said first NMOS transistor being for collecting charge developed by light falling on said first photodiode; a second NMOS transistor, a source of said second NMOS transistor being coupled to said first terminal of said first photodiode and to said drain of said first NMOS transistor; a capacitor, one terminal of said capacitor being coupled to a drain of said second transistor; a third MOS transistor, said source of said third MOS transistor being coupled to said drain of said second NMOS transistor; wherein said charge collected in said first NMOS transistor is transferred through said second NMOS transistor and converted into a voltage by said capacitor. - View Dependent Claims (24, 25)
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21. The invention as defined in 20 wherein said third MOS transistor is a NMOS transistor.
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22. The invention as defined in 20 wherein said third MOS transistor is a PMOS transistor.
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23. The invention as defined in 20 further including at least a second n+ region, a junction between said p-substrate and said second n+ region forming a second photodiode, a cathode of said second photodiode being coupled to a source of said first NMOS transistor wherein said first NMOS transistor also collects charge developed by light falling on said second photodiode.
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26. An image sensor circuit, comprising:
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a n-substrate having formed therein at least one p+ region, a junction between said n-substrate and said p+ region forming a first photodiode; an insulator layer between said n-substrate layer and a layer of polysilicon to form a first PMOS transistor, an anode of said photodiode being coupled to a drain of said PMOS transistor; a second PMOS transistor, a source of said second PMOS transistor being coupled to said first terminal of said first photodiode and to said drain of said first PMOS transistor; a capacitor, one terminal of said capacitor being coupled to a drain of said second transistor; a third MOS transistor, said source of said third MOS transistor being coupled to said drain of said second PMOS transistor; wherein said charge collected in said first PMOS transistor is transferred through said second PMOS transistor and converted into a voltage by said capacitor. - View Dependent Claims (27, 28, 29, 30, 31)
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32. A method for operating an image sensor circuit, said image sensor including
a first photodiode, having first and second terminals; -
a first metal oxide semiconductor (MOS) transistor, a drain of said MOS transistor being coupled to said first terminal of said first photodiode for collecting charge developed by light falling on said first photodiode; a second MOS transistor in a common gate configuration, a source of said second MOS transistor being coupled to said first terminal of said first photodiode and to said drain of said first MOS transistor; a capacitor, one terminal of said capacitor being coupled to a drain of said second transistor; a third MOS transistor, said source of said third MOS transistor being coupled to said drain of said second transistor; the method comprising the steps of; collecting electrons developed by light falling on said first photodiode; setting the value of a voltage across said capacitor to a first value; storing a representation of said first value; transferring said collected electrons to said capacitor; and storing a representation of the value of a second voltage across said capacitor after said transferring step. - View Dependent Claims (33)
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Specification