High-density photosensor and contactless imaging array having wide dynamic range
First Claim
1. A bipolar phototransistor pixel element disposed on a piece of semiconductor material of a first conductivity type comprising:
- a collector comprising a region of semiconductor material;
a base comprising a doped region of a second conductivity type disposed within said collector region;
a polysilicon region doped to said first conductivity type and disposed over a portion of said base to comprise an epitaxial emitter for the phototransistor and a sense node for said pixel element; and
an insulating layer disposed over said polysilicon region and over the portion of said base not covered by said polysilicon region; and
a layer of conductive material disposed over said insulating layer and thereby capacitively coupled to said base to form a select node for said pixel element.
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Accused Products
Abstract
A photosensing pixel element comprises a bipolar phototransistor used as both an integrating photosensor and a select device. The phototransistor is a vertical structure, having as its collector a first doped region of a first conductivity type disposed in a semiconductor substrate or well structure. The base terminal of the bipolar phototransistor comprises a doped region of a second conductivity type disposed within the first doped region and is utilized as the select node for the pixel. Conventional field oxide regions may be employed to isolate the base regions of adjoining phototransistors. A polysilicon line doped to the first conductivity type is disposed over the surface of the semiconductor substrate and is insulated therefrom except in regions where it is in contact with the doped region of a second conductivity type to form an epitaxial emitter for the phototransistor. The polysilicon line also forms the emitter contact for the phototransistor. A plurality of integrating photosensors may be placed in an array of rows and columns, wherein the bases of all bipolar phototransistors in a row are capacitively coupled together to a common row-select line, and the emitters of all bipolar phototransistors in a column are integral with a column sense line. The input of a sense amplifier is connected to the sense line of each column of integrating photosensors. An integrating sense amplifier according to the present invention includes an amplifying element having an inverting input connected to the sense line. A capacitor, preferably a varactor, is also connected between the inverting input and output of the amplifying element. An exponential feedback element may be provided in the sense amplifiers for signal compression at high light levels. The outputs of the sense amplifiers are connected to sample/hold circuits. The rows of the array are selected one at a time and the outputs of the sample/hold circuits for each row are scanned out of the array while the pixel data for the next row are sampled.
178 Citations
19 Claims
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1. A bipolar phototransistor pixel element disposed on a piece of semiconductor material of a first conductivity type comprising:
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a collector comprising a region of semiconductor material; a base comprising a doped region of a second conductivity type disposed within said collector region; a polysilicon region doped to said first conductivity type and disposed over a portion of said base to comprise an epitaxial emitter for the phototransistor and a sense node for said pixel element; and an insulating layer disposed over said polysilicon region and over the portion of said base not covered by said polysilicon region; and a layer of conductive material disposed over said insulating layer and thereby capacitively coupled to said base to form a select node for said pixel element. - View Dependent Claims (2)
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3. A bipolar phototransistor pixel element disposed on a piece of n-type semiconductor material comprising:
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a collector comprising a region of said semiconductor material; a base comprising a p-type doped region disposed within said collector region; an n-type doped polysilicon region disposed over a portion of said base to comprise an epitaxial emitter for the phototransistor and a sense node for said pixel element; and an insulating layer disposed over said polysilicon region and over the portion of said base not covered by said polysilicon region; and a layer of conductive material disposed over said insulating layer and thereby capacitively coupled to said base to form a select node for said pixel element. - View Dependent Claims (4)
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5. An integrating imaging array disposed on a single piece of semiconductor substrate material, including:
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a plurality of integrating photosensors arranged in an array of at least one row and at least one column, each of said photosensors comprising a bipolar phototransistor having a collector connected to a fixed voltage source, a base connected to one end of a capacitor, the other end of said capacitor connected to a select node, and an emitter; a plurality of row lines, each one of said row lines associated with a different row in said array, each of said row lines connected to the select nodes of all of the integrating photosensors associated with its row; and a plurality of sense lines, each one of said sense lines associated with a different column in said array and comprising a doped polysilicon line, regions of said doped polysilicon line in contact with the base regions of all of said phototransistors in its column to form said emitters thereof. - View Dependent Claims (6, 7, 8, 9, 10, 11)
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12. An integrating imaging array disposed on a single piece of semiconductor material of a first conductivity type, including:
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a plurality of integrating photosensors on said piece of semiconductor material, said plurality of integrating photosensors arranged in a matrix including at least one row and at least one column, each of said integrating photosensors comprising a bipolar phototransistor having a collector comprising a collector region of said semiconductor material, a base region formed from a region of a second conductivity type disposed in said collector region of said semiconductor material, the base regions of adjacent ones of said integrating photosensors electrically isolated from one another, said piece of semiconductor material connected to a voltage source; a plurality of polysilicon sense lines doped to said first conductivity type, a different one of said sense lines associated with each of said columns in said array, each of said polysilicon sense lines oriented such that it is in contact with a portion of the base regions of all the bipolar phototransistors associated with its column so as to comprise epitaxial emitters thereof; a capacitor dielectric layer formed over said polysilicon sense lines and the portions of the base regions of all of said phototransistors not covered by said sense lines; a plurality of row lines disposed over and insulated from said polysilicon sense lines, each of said row lines oriented in a direction substantially orthogonal to said polysilicon sense lines, a different one of said row lines associated with each row in said array, each of said row lines comprising a conductive strip disposed over said capacitor dielectric layer and capacitively coupled to said portions of said base regions not covered by said sense lines in the phototransistors in the one of said rows with which it is associated. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19)
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Specification