Image sensor method and apparatus having addressable pixels and non-destructive readout
First Claim
1. A pixel element for sensing light impinging on the pixel element and providing a non-destructive readout representative of the amount of impinging light, comprising:
- a substrate capable of forming localized depletion regions in the presence of an applied voltage at the regions;
an insulating layer formed on said substrate;
a collection capacitor electrode in contact with said insulating layer and being electrically isolated from said substrate by said insulating layer, wherein said insulating layer and collection capacitor electrode are transparent to light;
a transfer electrode located adjacent said collection capacitor electrode and being electrically isolated from said substrate by said insulating layer;
a readout capacitor electrode located adjacent said transfer electrode and in contact with said insulating layer, said readout capacitor electrode being spaced from said collection capacitor electrode and being electrically isolated from said substrate by said insulating layer; and
a readout transistor having an insulated gate connected to said readout capacitor electrode, with said transistor providing an output signal that is indicative of the quantity of charge stored in said substrate under said readout capacitor electrode, whereby said readout transistor provides a non-destructive readout of the stored charge.
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Abstract
An image sensor having an array of pixel elements constructed using a two level polysilicon CMOS process that provides individual addressability and a non-destructive readout of the pixels. The pixel elements each includes a substrate, an insulating layer formed on the substrate, a collection capacitor electrode, a transfer electrode, a readout capacitor electrode, and a readout transistor. The transfer electrode is located between the collection and readout capacitor electrodes and all three electrodes are electrically isolated from the substrate and each other by the insulating layer. The collection capacitor electrode and insulating layer are transparent so that incident light can pass through these elements and be absorbed by the substrate. A bias voltage is applied to the collection electrode to form a depletion region in the substrate where photoelectrically generated charge is collected. The charge is then transferred to a second depletion region underneath the readout capacitor electrode by applying a bias voltage to the transfer electrode. The readout transistor has an insulated gate connected to the readout capacitor electrode, so that it can generate a pixel data output signal indicative of the charge that is now stored under the readout capacitor electrode. This reading out of the pixel data is therefore non-destructive, allowing the pixel to be read multiple times without loss of information. An image sensor so constructed can be used in conjunction with on-chip image processing circuits for performing such tasks as edge detection and other algorithms that involve convolutions or other combinations of pixel data.
18 Citations
34 Claims
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1. A pixel element for sensing light impinging on the pixel element and providing a non-destructive readout representative of the amount of impinging light, comprising:
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a substrate capable of forming localized depletion regions in the presence of an applied voltage at the regions;
an insulating layer formed on said substrate;
a collection capacitor electrode in contact with said insulating layer and being electrically isolated from said substrate by said insulating layer, wherein said insulating layer and collection capacitor electrode are transparent to light;
a transfer electrode located adjacent said collection capacitor electrode and being electrically isolated from said substrate by said insulating layer;
a readout capacitor electrode located adjacent said transfer electrode and in contact with said insulating layer, said readout capacitor electrode being spaced from said collection capacitor electrode and being electrically isolated from said substrate by said insulating layer; and
a readout transistor having an insulated gate connected to said readout capacitor electrode, with said transistor providing an output signal that is indicative of the quantity of charge stored in said substrate under said readout capacitor electrode, whereby said readout transistor provides a non-destructive readout of the stored charge. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. A pixel element for sensing light impinging on the pixel element and providing a non-destructive readout representative of the amount of impinging light, comprising:
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a silicon-based substrate capable of forming localized depletion regions in the presence of an applied voltage at the regions;
a transparent insulating layer formed on said substrate;
a first polycrystalline silicon electrode formed as a collection electrode that is transparent to light and that is located within said insulating layer such that it is electrically isolated from said substrate by said insulating layer, said collection electrode being spaced from said substrate such that a first depletion region can be formed in said substrate in response to a bias voltage being applied to said collection electrode, wherein light impinging upon said pixel element at said collection electrode is transmitted through said insulating layer and collection electrode and into said substrate where the impinging light forms electron-hole pairs with the electrons being collected in the substrate near the collection electrode;
a second polycrystalline silicon electrode formed as a transfer electrode located laterally adjacent said collection electrode, said transfer electrode being spaced from said substrate by said insulating layer such that a second depletion region can be formed in said substrate in response to a bias voltage being applied to said transfer electrode;
a third polycrystalline silicon electrode formed as a readout electrode that is located within said insulating layer such that it is electrically isolated by said insulating layer from said substrate and said collection and transfer electrodes, said readout electrode being spaced from said substrate such that it provides a readout of charge stored in said substrate under said readout electrode, wherein said second depletion region under said transfer electrode overlaps said first depletion region and permits charged stored in said first depletion region to be transferred to a location in said substrate underneath said readout electrode;
a readout transistor having an insulated gate connected to said readout electrode, with said transistor providing an output signal that is indicative of the quantity of charge stored in said substrate under said readout electrode, whereby said readout transistor provides a non-destructive readout of the stored charge;
an output transistor having an input connected to said output of said readout transistor, a gate connected to receive a pixel select signal, and an output, with said output transistor being operable to provide said output signal to its output in response to receiving the pixel select signal on its gate;
a dump electrode adjacent one of said first, second, and third electrodes; and
a supply connecting region in said substrate located adjacent said dump electrode and spaced from said one electrode, wherein, when a bias voltage is applied to said dump electrode with said supply connecting region being connected to a supply voltage, charge stored in said substrate underneath said readout electrode is transferred to said supply connecting region to thereby reset said pixel element. - View Dependent Claims (17, 18)
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19. A memory element for storing data and providing a non-destructive analog readout of the data, comprising:
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a substrate capable of forming localized depletion regions in the presence of an applied voltage at the regions;
an insulating layer formed on said substrate;
a collection capacitor electrode in contact with said insulating layer and being electrically isolated from said substrate by said insulating layer, said collection capacitor electrode being spaced from said substrate such that a first depletion region can be formed in said substrate in response to a bias voltage being applied to said collection capacitor electrode, whereby said substrate can store charge supplied to or generated in said first depletion region;
a transfer electrode located adjacent said collection capacitor electrode and being spaced from said substrate such that a second depletion region can be formed in said substrate in response to a bias voltage being applied to said transfer electrode;
a readout capacitor electrode located adjacent said transfer electrode and in contact with said insulating layer, said readout capacitor electrode being spaced from said substrate such that it provides a readout of charge stored in said substrate under said readout capacitor electrode, wherein said second depletion region under said transfer electrode overlaps said first depletion region and permits charged stored in said first depletion region to be transferred to a location in said substrate underneath said readout capacitor electrode;
a readout transistor having an insulated gate connected to said readout capacitor electrode, with said transistor providing an output signal that is indicative of the quantity of charge stored in said substrate under said readout capacitor electrode, whereby data can be temporarily stored in said first depletion region as stored charge which can then be transferred using said second depletion region to a location underneath said readout capacitor electrode and then used by said readout transistor to provide a non-destructive analog readout of the data. - View Dependent Claims (20, 21, 22, 23, 24, 25, 26, 27, 28, 29)
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30. A method of providing a non-destructive readout of analog data that is representative of the amount of incident light impinging upon a pixel element, comprising the steps of:
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measuring incident light using a photocapacitor that stores charge indicative of the amount of light incident on the photocapacitor;
transferring the stored charge to a second capacitor that is not sensitive to the incident light; and
providing the charge stored on the second capacitor to an insulated gate of a transistor that is connected to supply an output signal indicative of the voltage on its insulated gate. - View Dependent Claims (31, 32, 33, 34)
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Specification